Eunus S. Ali, Ph.D. | Northwestern University Feinberg School of Medicine (original) (raw)
Papers by Eunus S. Ali, Ph.D.
Molecular Cell, 2022
Bicarbonate (HCO3−) ions maintain pH homeostasis in eukaryotic cells and serve as a carbonyl dono... more Bicarbonate (HCO3−) ions maintain pH homeostasis in eukaryotic cells and serve as a carbonyl donor to support cellular metabolism. However, whether the abundance of HCO3− is regulated or harnessed to promote cell growth is unknown. The mechanistic target of rapamycin complex 1 (mTORC1) adjusts cellular metabolism to support biomass production and cell growth. We find that mTORC1 stimulates the intracellular transport of HCO3− to promote nucleotide synthesis through the selective translational regulation of the sodium bicarbonate cotransporter SLC4A7. Downstream of mTORC1, SLC4A7 mRNA translation required the S6K-dependent phosphorylation of the translation factor eIF4B. In mTORC1-driven cells, loss of SLC4A7 resulted in reduced cell and tumor growth and decreased flux through de novo purine and pyrimidine synthesis in human cells and tumors without altering the intracellular pH. Thus, mTORC1 signaling, through the control of SLC4A7 expression, harnesses environmental bicarbonate to promote anabolic metabolism, cell biomass, and growth.
Antioxidants, 2021
TRPM2 channels admit Ca2+ and Na+ across the plasma membrane and release Ca2+ and Zn2+ from lysos... more TRPM2 channels admit Ca2+ and Na+ across the plasma membrane and release Ca2+ and Zn2+ from lysosomes. Channel activation is initiated by reactive oxygen species (ROS), leading to a subsequent increase in ADP-ribose and the binding of ADP-ribose to an allosteric site in the cytosolic NUDT9 homology domain. In many animal cell types, Ca2+ entry via TRPM2 channels mediates ROS-initiated cell injury and death. The aim of this review is to summarise the current knowledge of the roles of TRPM2 and Ca2+ in the initiation and progression of chronic liver diseases and acute liver injury. Studies to date provide evidence that TRPM2-mediated Ca2+ entry contributes to drug-induced liver toxicity, ischemia–reperfusion injury, and the progression of non-alcoholic fatty liver disease to cirrhosis, fibrosis, and hepatocellular carcinoma. Of particular current interest are the steps involved in the activation of TRPM2 in hepatocytes following an increase in ROS, the downstream pathways activated by...
American Journal of Physiology-Cell Physiology, 2021
Ca2+ signaling plays a critical role in the regulation of hepatic metabolism by hormones includin... more Ca2+ signaling plays a critical role in the regulation of hepatic metabolism by hormones including insulin. Changes in cytoplasmic Ca2+ regulate synthesis and posttranslational modification of key signaling proteins in the insulin pathways. Emerging evidence suggests that hepatocyte intracellular Ca2+ signaling is altered in lipid-loaded liver cells isolated from obese rodent models. The mechanisms of altered Ca2+-insulin and insulin-Ca2+ signaling pathways in obesity remain poorly understood. Here, we show that the kinetics of insulin-initiated intracellular (initial) Ca2+ release from endoplasmic reticulum is significantly impaired in steatotic hepatocytes from obese Alström syndrome mice. Furthermore, exenatide, a glucagon-like peptide-1 (GLP-1) analog, reversed lipid-induced inhibition of intracellular Ca2+ release kinetics in steatotic hepatocytes, without affecting the total content of intracellular Ca2+ released. Exenatide reversed the lipid-induced inhibition of intracellula...
Cancers, 2020
Hepatocellular carcinoma (HCC) is a considerable health burden worldwide and a major contributor ... more Hepatocellular carcinoma (HCC) is a considerable health burden worldwide and a major contributor to cancer-related deaths. HCC is often not noticed until at an advanced stage where treatment options are limited and current systemic drugs can usually only prolong survival for a short time. Understanding the biology and pathology of HCC is a challenge, due to the cellular and anatomic complexities of the liver. While not yet fully understood, liver cancer stem cells play a central role in the initiation and progression of HCC and in resistance to drugs. There are approximately twenty Ca2+-signaling proteins identified as potential targets for therapeutic treatment at different stages of HCC. These potential targets include inhibition of the self-renewal properties of liver cancer stem cells; HCC initiation and promotion by hepatitis B and C and non-alcoholic fatty liver disease (principally involving reduction of reactive oxygen species); and cell proliferation, tumor growth, migratio...
This year nearly 20,000 lives will be lost to Glioblastoma (GBM), a treatment-resistant primary b... more This year nearly 20,000 lives will be lost to Glioblastoma (GBM), a treatment-resistant primary brain cancer. In this study, we identified a molecular circuit driven by epigenetic regulation that regulates the expression of ciliary protein ALR13B. We also demonstrated that ARL13B subsequently interacts with purine biosynthetic enzyme IMPDH2. Removal of ARL13B enhanced TMZ-induced DNA damage by reducing de-novo purine biosynthesis and forcing GBM cells to rely on the purine salvage pathway. Furthermore, targeting can be achieved by using an FDA-approved drug, Mycophenolate Moefitil. Our results suggest a clinical evaluation of MMF in combination with TMZ treatment in glioma patients.
Tumor Biology, 2019
Glioblastoma, a universally lethal primary brain tumor, harnesses cellular plasticity to drive th... more Glioblastoma, a universally lethal primary brain tumor, harnesses cellular plasticity to drive therapeutic adaptation. Critical factors in developing this plasticity are histone modifiers such as Polycomb Repressor Complex 2 protein EZH2. In order to examine tumor cell plasticity in depth, we conducted multiple ChIP Sequencing runs and demonstrate that EZH2 binds within an enhancer region of ARL13B during temozolomide (TMZ) therapy and induces an H3K4 mono-methylation mark. Concurrently, we observed an increase in H3K27ac at the transcription start site of ARL13B as well as a lack of H3K27 tri-methylation, EZH2’s canonical histone mark. Based on this we hypothesize that EZH2 could be non-canonically regulating ARL13B to allow for cellular plasticity and ultimately drive therapeutic adaptation. Delving further into this regulation we demonstrate that knockdown of ARL13B in patient derived xenograft cells significantly increased survival of mice in an orthotopic GBM model when compared to controls (p-value Citation Format: Jack Shireman, Eunus Ali, Miranda Saathoff, Cheol Park, Issam Ben-Sahra, Atique U. Ahmed. ARL13B interacts with IMPDH2 to modulate purine synthesis and temozolomide resistance in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 81.
Cancers, 2019
Cancer cells exhibit a dynamic metabolic landscape and require a sufficient supply of nucleotides... more Cancer cells exhibit a dynamic metabolic landscape and require a sufficient supply of nucleotides and other macromolecules to grow and proliferate. To meet the metabolic requirements for cell growth, cancer cells must stimulate de novo nucleotide synthesis to obtain adequate nucleotide pools to support nucleic acid and protein synthesis along with energy preservation, signaling activity, glycosylation mechanisms, and cytoskeletal function. Both oncogenes and tumor suppressors have recently been identified as key molecular determinants for de novo nucleotide synthesis that contribute to the maintenance of homeostasis and the proliferation of cancer cells. Inactivation of tumor suppressors such as TP53 and LKB1 and hyperactivation of the mTOR pathway and of oncogenes such as MYC, RAS, and AKT have been shown to fuel nucleotide synthesis in tumor cells. The molecular mechanisms by which these signaling hubs influence metabolism, especially the metabolic pathways for nucleotide synthesi...
Advances in experimental medicine and biology, 2017
In steatotic hepatocytes, intracellular Ca(2+) homeostasis is substantially altered compared to n... more In steatotic hepatocytes, intracellular Ca(2+) homeostasis is substantially altered compared to normal. Decreased Ca(2+) in the endoplasmic reticulum (ER) can lead to ER stress, an important mediator of the progression of liver steatosis to nonalcoholic steatohepatitis, type 2 diabetes, and hepatocellular carcinoma. Store-operated Ca(2+) channels (SOCs) in hepatocytes are composed principally of Orai1 and STIM1 proteins. Their main role is the maintenance of adequate Ca(2+) in the lumen of the ER. In steatotic hepatocytes, store-operated Ca(2+) entry (SOCE) is substantially inhibited. This inhibition is associated with a decrease in Ca(2+) in the ER. Lipid-induced inhibition of SOCE is mediated by protein kinase C (PKC) and may involve the phosphorylation and subsequent inhibition of Orai1. Experimental inhibition of SOCE enhances lipid accumulation in normal hepatocytes incubated in the presence of exogenous fatty acids. The antidiabetic drug exendin-4 reverses the lipid-induced in...
Antiviral research, Jan 13, 2016
Human noroviruses are the leading causative agents of epidemic and sporadic viral gastroenteritis... more Human noroviruses are the leading causative agents of epidemic and sporadic viral gastroenteritis and childhood diarrhoea worldwide. Human histo-blood group antigens (HBGA) serve as receptors for norovirus capsid protein attachment and play a critical role in infection. This makes HBGA-norovirus binding a promising target for drug development. Recently solved crystal structures of norovirus bound to HBGA have provided a structural basis for identification of potential anti-norovirus drugs and subsequently performed in silico and in vitro drug screens have identified compounds that block norovirus binding and may thereby serve as structural templates for design of therapeutic norovirus inhibitors. This review explores norovirus therapeutic options based on the strategy of blocking norovirus-HBGA binding.
Cell Calcium, 2019
Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and t... more Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and the sixth in women. Non-alcoholic fatty liver disease (NAFLD) is now one of the major risk factors for HCC. NAFLD, which involves the accumulation of excess lipid in cytoplasmic lipid droplets in hepatocytes, can progress to nonalcoholic steatosis, fibrosis, and HCC. Changes in intracellular Ca 2+ constitute important signaling pathways for the regulation of lipid and carbohydrate metabolism in normal hepatocytes. Recent studies of steatotic hepatocytes have identified lipid-induced changes in intracellular Ca 2+ , and have provided evidence that altered Ca 2+ signaling exacerbates lipid accumulation and may promote HCC. The aims of this review are to summarise current knowledge of the lipid-induced changes in hepatocyte Ca 2+ homeostasis, to comment on the mechanisms involved, and discuss the pathways leading from altered Ca 2+ homeostasis to enhanced lipid accumulation and the potential promotion of HCC. In steatotic hepatocytes, lipid inhibits store-operated Ca 2+ entry and SERCA2b, and activates Ca 2+ efflux from the endoplasmic reticulum (ER) and its transfer to mitochondria. These changes are associated with changes in Ca 2+ concentrations in the ER (decreased), cytoplasmic space (increased) and mitochondria (likely increased). They lead to: inhibition of lipolysis, lipid autophagy, lipid oxidation, and lipid secretion; activation of lipogenesis; increased lipid; ER stress, generation of reactive oxygen species (ROS), activation of Ca 2+ /calmodulin-dependent kinases and activation of transcription factor Nrf2. These all can potentially mediate the transition of NAFLD to HCC. It is concluded that lipid-induced changes in hepatocyte Ca 2+ homeostasis are important in the initiation and progression of HCC. Further research is desirable to better understand the cause and effect relationships, the time courses and mechanisms involved, and the potential of Ca 2+ transporters, channels, and binding proteins as targets for pharmacological intervention.
AJP Cell Physiology, 2021
Ca ²⁺ signaling plays a critical role in the regulation of hepatic metabolism by hormones includi... more Ca ²⁺ signaling plays a critical role in the regulation of hepatic metabolism by hormones including insulin. Changes in cytoplasmic Ca ²⁺ regulate synthesis and post-translational modification of key signaling proteins in the insulin pathways. Emerging evidence suggests that hepatocyte intracellular Ca ²⁺ signaling is altered in lipid-loaded liver cells isolated from obese rodent models. The mechanisms of altered Ca ²⁺ -insulin and insulin-Ca ²⁺ signaling pathways in obesity remain poorly understood. Here we show that the kinetics of insulin-initiated intracellular (initial) Ca ²⁺ release from endoplasmic reticulum is significantly impaired in steatotic hepatocytes from obese Alström syndrome mice. Furthermore, exenatide, a GLP-1 analog, reversed lipid-induced inhibition of intracellular Ca ²⁺ release kinetics in steatotic hepatocytes, without affecting the total content of intracellular Ca ²⁺ released. Exenatide reversed the lipid-induced inhibition of intracellular Ca ²⁺ release, at least partially, via lipid reduction in hepatocytes which then restored hormone-regulated cytoplasmic Ca ²⁺ signaling and insulin sensitivity. This data provides additional evidence for the important role of Ca ²⁺ signaling pathways in obesity-associated impaired hepatic lipid homeostasis and insulin signaling. It also highlights a potential advantage of GLP-1 analogs when used to treat type 2 diabetes associated with hepatic steatosis.
Handbook of oxidative stress and cancer: Mechanistic aspects, 2021
Reactive oxygen species (ROS) are reactive chemical and/or biochemical intermediates or fragments... more Reactive oxygen species (ROS) are reactive chemical and/or biochemical intermediates or fragments containing oxygen as peroxides, superoxide (O2●−), hydrogen peroxide (H2O2), hydroxyl radical (●OH), hydroxyl ion (−OH), singlet oxygen, and nitric oxide (NO). At optimal concentration ROS have been implicated to serve varieties of important physiological functions in different types of cells under normal physiological conditions. On the other hand, excessive amounts of ROS are one of the main determinants in the pathogenesis of different types of diseases including cancer, metabolic syndromes, cardiovascular, and neurodegeneration. The mechanism of the generation of ROS and its concentration decides the fate of cells in different types and conditions; excessive ROS can cause detrimental effects on normal cells, deregulate cellular homeostasis, and induce carcinogenic changes. In order to continue their growth and proliferation, cancer cells increase ROS production rate compared with normal cells, and to maintain their ROS homeostasis, they simultaneously increase their antioxidant capacity. It is now evident that this unique and altered redox environment of cancer cells upturns or increases their vulnerability to ROS-metabolism therapies. This chapter aims to discuss a current scenario of ROS in physiological and pathological contributions with emphasis on cellular and molecular mechanistic ways. In addition, it discusses the role of oxidative stress in initiation and progression of different types of cancers as well as current and new strategies targeting ROS for the development of therapeutic interventions of ROS-induced cancers.
Antioxidants, 2021
TRPM2 channels admit Ca2+ and Na+ across the plasma membrane and release Ca2+ and Zn2+ from lysos... more TRPM2 channels admit Ca2+ and Na+ across the plasma membrane and release Ca2+ and Zn2+ from lysosomes. Channel activation is initiated by reactive oxygen species (ROS), leading to a subsequent increase in ADP-ribose and the binding of ADP-ribose to an allosteric site in the cytosolic NUDT9 homology domain. In many animal cell types, Ca2+ entry via TRPM2 channels mediates ROS-initiated cell injury and death. The aim of this review is to summarise the current knowledge of the roles of TRPM2 and Ca2+ in the initiation and progression of chronic liver diseases and acute liver injury. Studies to date provide evidence that TRPM2-mediated Ca2+ entry contributes to drug-induced liver toxicity, ischemia–reperfusion injury, and the progression of non-alcoholic fatty liver disease to cirrhosis, fibrosis, and hepatocellular carcinoma. Of particular current interest are the steps involved in the activation of TRPM2 in hepatocytes following an increase in ROS, the downstream pathways activated by the resultant increase in intracellular Ca2+, and the chronology of these events. An apparent contradiction exists between these roles of TRPM2 and the role identified for ROS-activated TRPM2 in heart muscle and in some other cell types in promoting Ca2+-activated mitochondrial ATP synthesis and cell survival. Inhibition of TRPM2 by curcumin and other “natural” compounds offers an attractive strategy for inhibiting ROS-induced liver cell injury. In conclusion, while it has been established that ROS-initiated activation of TRPM2 contributes to both acute and chronic liver injury, considerable further research is needed to elucidate the mechanisms involved, and the conditions under which pharmacological inhibition of TRPM2 can be an effective clinical strategy to reduce ROS-initiated liver injury.
Molecular Cell, 2020
The RAS-ERK/MAPK (RAS-extracellular signal-regulated kinase/mitogen-activated protein kinase) pat... more The RAS-ERK/MAPK (RAS-extracellular signal-regulated kinase/mitogen-activated protein kinase) pathway integrates growth-promoting signals to stimulate cell growth and proliferation, at least in part, through alterations in metabolic gene expression. However, examples of direct and rapid regulation of the metabolic pathways by the RAS-ERK pathway remain elusive. We find that physiological and oncogenic ERK signaling activation leads to acute metabolic flux stimulation through the de novo purine synthesis pathway, thereby increasing building block availability for RNA and DNA synthesis, which is required for cell growth and proliferation. We demonstrate that ERK2, but not ERK1, phosphorylates the purine synthesis enzyme PFAS (phosphoribosylformylglycinamidine synthase) at T619 in cells to stimulate de novo purine synthesis. The expression of nonphosphorylatable PFAS (T619A) decreases purine synthesis, RAS-dependent cancer cell-colony formation, and tumor growth. Thus, ERK2-mediated PFAS phosphorylation facilitates the increase in nucleic acid synthesis required for anabolic cell growth and proliferation.
Cancers (Basel), 2019
Cancer cells exhibit a dynamic metabolic landscape and require a sufficient supply of nucleotides... more Cancer cells exhibit a dynamic metabolic landscape and require a sufficient supply of nucleotides and other macromolecules to grow and proliferate. To meet the metabolic requirements for cell growth, cancer cells must stimulate de novo nucleotide synthesis to obtain adequate nucleotide pools to support nucleic acid and protein synthesis along with energy preservation, signaling activity, glycosylation mechanisms, and cytoskeletal function. Both oncogenes and tumor suppressors have recently been identified as key molecular determinants for de novo nucleotide synthesis that contribute to the maintenance of homeostasis and the proliferation of cancer cells. Inactivation of tumor suppressors such as TP53 and LKB1 and hyperactivation of the mTOR pathway and of oncogenes such as MYC, RAS, and AKT have been shown to fuel nucleotide synthesis in tumor cells. The molecular mechanisms by which these signaling hubs influence metabolism, especially the metabolic pathways for nucleotide synthesis, continue to emerge. Here, we focus on the current understanding of the molecular mechanisms by which oncogenes and tumor suppressors modulate nucleotide synthesis in cancer cells and, based on these insights, discuss potential strategies to target cancer cell proliferation.
Trends in Endocrinology and Metabolism, 2019
Hepatic steatosis, the first step in nonalcoholic fatty liver disease (NAFLD), can arise from var... more Hepatic steatosis, the first step in nonalcoholic fatty liver disease (NAFLD), can arise from various pathophysiological conditions. While lipid metabolism in the liver is normally balanced such that there is no excessive lipid accumulation, when this homeostasis is disrupted lipid droplets (LDs) accumulate in hepatocytes resulting in cellular toxicity. The mechanisms underlying this accumulation and the subsequent hepatocellular damage are multifactorial and poorly understood, with the result that there are no currently approved treatments for NAFLD. Impaired calcium signaling has recently been identified as a cause of increased endoplasmic reticulum (ER) stress contributing to hepatic lipid accumulation. This review highlights new findings on the role of impaired Ca2+ signaling in the development of steatosis and discusses potential new approaches to NAFLD treatment based on these new insights.
In steatotic hepatocytes intracellular Ca2+ homeostasis is substantially altered compared to norm... more In steatotic hepatocytes intracellular Ca2+ homeostasis is substantially altered compared to normal. Decreased Ca2+ in the endoplasmic reticulum (ER) can lead to ER stress, an important mediator of the progression of liver steatosis to non-alcoholic steatohepatitis, type 2 diabetes and hepatocellular carcinoma. Store-operated Ca2+ channels (SOCs) in hepatocytes are composed principally of Orai1 and STIM1 proteins. Their main role is the maintenance of adequate Ca2+ in the lumen of the ER. In steatotic hepatocytes, store-operated Ca2+ entry (SOCE) is substantially inhibited. This inhibition is associated with a decrease in Ca2+ in the ER. Lipid-induced inhibition of SOCE is mediated by protein kinase C (PKC) and may involve the phosphorylation and subsequent inhibition of Orai1. Experimental inhibition of SOCE enhances lipid accumulation in normal hepatocytes incubated in the presence of exogenous fatty acids. The anti-diabetic drug exendin-4 reverses the lipid-induced inhibition of SOCE, and decreases liver lipid with rapid onset. It is proposed that lipid-induced inhibition of SOCE in the plasma membrane and of SERCA2b in the ER membrane lead to a persistent decrease in ER Ca2+, ER stress, and the ER stress response, which in turn enhances (amplifies) lipid accumulation. A low level of persistent SOCE due to chronic ER Ca2+ depletion in steatotic hepatocytes may contribute to an elevated cytoplasmic free Ca2+ concentration leading to the activation of calcium-calmodulin kinase II (CaMKII), decreased lipid removal by autophagy, and insulin resistance. It is concluded that lipid-induced inhibition of SOCE plays an important role in the progression of liver steatosis to insulin insensitivity and hepatocellular carcinoma.
Cell Calcium, 2019
Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and t... more Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and the sixth in women. Non-alcoholic fatty liver disease (NAFLD) is now one of the major risk factors for HCC. NAFLD, which involves the accumulation of excess lipid in cytoplasmic lipid droplets in hepatocytes, can progress to non-alcoholic steatosis, fibrosis, and HCC. Changes in intracellular Ca2+ constitute important signaling pathways for the regulation of lipid and carbohydrate metabolism in normal hepatocytes. Recent studies of steatotic hepatocytes have identified lipid-induced changes in intracellular Ca2+, and have provided evidence that altered Ca2+ signaling exacerbates lipid accumulation and may promote HCC. The aims of this review are to summarise current knowledge of the lipid-induced changes in hepatocyte Ca2+ homeostasis, to comment on the mechanisms involved, and discuss the pathways leading from altered Ca2+ homeostasis to enhanced lipid accumulation and the potential promotion of HCC. In steatotic hepatocytes, lipid inhibits store-operated Ca2+ entry and SERCA2b, and activates Ca2+ efflux from the endoplasmic reticulum (ER) and its transfer to mitochondria. These changes are associated with changes in Ca2+ concentrations in the ER (decreased), cytoplasmic space (increased) and mitochondria (likely increased). They lead to: inhibition of lipolysis, lipid autophagy, lipid oxidation, and lipid secretion; activation of lipogenesis; increased lipid; ER stress, generation of reactive oxygen species (ROS), activation of Ca2+/calmodulin-dependent kinases and activation of transcription factor Nrf2. These all can potentially mediate the transition of NAFLD to HCC. It is concluded that lipid-induced changes in hepatocyte Ca2+ homeostasis are important in the initiation and progression of HCC. Further research is desirable to better understand the cause and effect relationships, the time courses and mechanisms involved, and the potential of Ca2+ transporters, channels, and binding proteins as targets for pharmacological intervention.
Biochimica et biophysica acta Molecular Cell Research, Jan 10, 2016
The release of Ca(2+) from the endoplasmic reticulum (ER) and subsequent replenishment of ER Ca(2... more The release of Ca(2+) from the endoplasmic reticulum (ER) and subsequent replenishment of ER Ca(2+) by Ca(2+) entry through store-operated Ca(2+) channels (SOCE) play critical roles in the regulation of liver metabolism by adrenaline, glucagon and other hormones. Both ER Ca(2+) release and Ca(2+) entry are severely inhibited in steatotic hepatocytes. Exendin-4, a slowly-metabolised glucagon-like peptide-1 (GLP-1) analogue, is known to reduce liver glucose output and liver lipid, but the mechanisms involved are not well understood. The aim of this study was to determine whether exendin-4 alters intracellular Ca(2+) homeostasis in steatotic hepatocytes, and to evaluate the mechanisms involved. Exendin-4 completely reversed lipid-induced inhibition of SOCE in steatotic liver cells, but did not reverse lipid-induced inhibition of ER Ca(2+) release. The action of exendin-4 on Ca(2+) entry was rapid in onset and was mimicked by GLP-1 or dibutyryl cyclic AMP. In steatotic liver cells, exen...
Molecular Cell, 2022
Bicarbonate (HCO3−) ions maintain pH homeostasis in eukaryotic cells and serve as a carbonyl dono... more Bicarbonate (HCO3−) ions maintain pH homeostasis in eukaryotic cells and serve as a carbonyl donor to support cellular metabolism. However, whether the abundance of HCO3− is regulated or harnessed to promote cell growth is unknown. The mechanistic target of rapamycin complex 1 (mTORC1) adjusts cellular metabolism to support biomass production and cell growth. We find that mTORC1 stimulates the intracellular transport of HCO3− to promote nucleotide synthesis through the selective translational regulation of the sodium bicarbonate cotransporter SLC4A7. Downstream of mTORC1, SLC4A7 mRNA translation required the S6K-dependent phosphorylation of the translation factor eIF4B. In mTORC1-driven cells, loss of SLC4A7 resulted in reduced cell and tumor growth and decreased flux through de novo purine and pyrimidine synthesis in human cells and tumors without altering the intracellular pH. Thus, mTORC1 signaling, through the control of SLC4A7 expression, harnesses environmental bicarbonate to promote anabolic metabolism, cell biomass, and growth.
Antioxidants, 2021
TRPM2 channels admit Ca2+ and Na+ across the plasma membrane and release Ca2+ and Zn2+ from lysos... more TRPM2 channels admit Ca2+ and Na+ across the plasma membrane and release Ca2+ and Zn2+ from lysosomes. Channel activation is initiated by reactive oxygen species (ROS), leading to a subsequent increase in ADP-ribose and the binding of ADP-ribose to an allosteric site in the cytosolic NUDT9 homology domain. In many animal cell types, Ca2+ entry via TRPM2 channels mediates ROS-initiated cell injury and death. The aim of this review is to summarise the current knowledge of the roles of TRPM2 and Ca2+ in the initiation and progression of chronic liver diseases and acute liver injury. Studies to date provide evidence that TRPM2-mediated Ca2+ entry contributes to drug-induced liver toxicity, ischemia–reperfusion injury, and the progression of non-alcoholic fatty liver disease to cirrhosis, fibrosis, and hepatocellular carcinoma. Of particular current interest are the steps involved in the activation of TRPM2 in hepatocytes following an increase in ROS, the downstream pathways activated by...
American Journal of Physiology-Cell Physiology, 2021
Ca2+ signaling plays a critical role in the regulation of hepatic metabolism by hormones includin... more Ca2+ signaling plays a critical role in the regulation of hepatic metabolism by hormones including insulin. Changes in cytoplasmic Ca2+ regulate synthesis and posttranslational modification of key signaling proteins in the insulin pathways. Emerging evidence suggests that hepatocyte intracellular Ca2+ signaling is altered in lipid-loaded liver cells isolated from obese rodent models. The mechanisms of altered Ca2+-insulin and insulin-Ca2+ signaling pathways in obesity remain poorly understood. Here, we show that the kinetics of insulin-initiated intracellular (initial) Ca2+ release from endoplasmic reticulum is significantly impaired in steatotic hepatocytes from obese Alström syndrome mice. Furthermore, exenatide, a glucagon-like peptide-1 (GLP-1) analog, reversed lipid-induced inhibition of intracellular Ca2+ release kinetics in steatotic hepatocytes, without affecting the total content of intracellular Ca2+ released. Exenatide reversed the lipid-induced inhibition of intracellula...
Cancers, 2020
Hepatocellular carcinoma (HCC) is a considerable health burden worldwide and a major contributor ... more Hepatocellular carcinoma (HCC) is a considerable health burden worldwide and a major contributor to cancer-related deaths. HCC is often not noticed until at an advanced stage where treatment options are limited and current systemic drugs can usually only prolong survival for a short time. Understanding the biology and pathology of HCC is a challenge, due to the cellular and anatomic complexities of the liver. While not yet fully understood, liver cancer stem cells play a central role in the initiation and progression of HCC and in resistance to drugs. There are approximately twenty Ca2+-signaling proteins identified as potential targets for therapeutic treatment at different stages of HCC. These potential targets include inhibition of the self-renewal properties of liver cancer stem cells; HCC initiation and promotion by hepatitis B and C and non-alcoholic fatty liver disease (principally involving reduction of reactive oxygen species); and cell proliferation, tumor growth, migratio...
This year nearly 20,000 lives will be lost to Glioblastoma (GBM), a treatment-resistant primary b... more This year nearly 20,000 lives will be lost to Glioblastoma (GBM), a treatment-resistant primary brain cancer. In this study, we identified a molecular circuit driven by epigenetic regulation that regulates the expression of ciliary protein ALR13B. We also demonstrated that ARL13B subsequently interacts with purine biosynthetic enzyme IMPDH2. Removal of ARL13B enhanced TMZ-induced DNA damage by reducing de-novo purine biosynthesis and forcing GBM cells to rely on the purine salvage pathway. Furthermore, targeting can be achieved by using an FDA-approved drug, Mycophenolate Moefitil. Our results suggest a clinical evaluation of MMF in combination with TMZ treatment in glioma patients.
Tumor Biology, 2019
Glioblastoma, a universally lethal primary brain tumor, harnesses cellular plasticity to drive th... more Glioblastoma, a universally lethal primary brain tumor, harnesses cellular plasticity to drive therapeutic adaptation. Critical factors in developing this plasticity are histone modifiers such as Polycomb Repressor Complex 2 protein EZH2. In order to examine tumor cell plasticity in depth, we conducted multiple ChIP Sequencing runs and demonstrate that EZH2 binds within an enhancer region of ARL13B during temozolomide (TMZ) therapy and induces an H3K4 mono-methylation mark. Concurrently, we observed an increase in H3K27ac at the transcription start site of ARL13B as well as a lack of H3K27 tri-methylation, EZH2’s canonical histone mark. Based on this we hypothesize that EZH2 could be non-canonically regulating ARL13B to allow for cellular plasticity and ultimately drive therapeutic adaptation. Delving further into this regulation we demonstrate that knockdown of ARL13B in patient derived xenograft cells significantly increased survival of mice in an orthotopic GBM model when compared to controls (p-value Citation Format: Jack Shireman, Eunus Ali, Miranda Saathoff, Cheol Park, Issam Ben-Sahra, Atique U. Ahmed. ARL13B interacts with IMPDH2 to modulate purine synthesis and temozolomide resistance in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 81.
Cancers, 2019
Cancer cells exhibit a dynamic metabolic landscape and require a sufficient supply of nucleotides... more Cancer cells exhibit a dynamic metabolic landscape and require a sufficient supply of nucleotides and other macromolecules to grow and proliferate. To meet the metabolic requirements for cell growth, cancer cells must stimulate de novo nucleotide synthesis to obtain adequate nucleotide pools to support nucleic acid and protein synthesis along with energy preservation, signaling activity, glycosylation mechanisms, and cytoskeletal function. Both oncogenes and tumor suppressors have recently been identified as key molecular determinants for de novo nucleotide synthesis that contribute to the maintenance of homeostasis and the proliferation of cancer cells. Inactivation of tumor suppressors such as TP53 and LKB1 and hyperactivation of the mTOR pathway and of oncogenes such as MYC, RAS, and AKT have been shown to fuel nucleotide synthesis in tumor cells. The molecular mechanisms by which these signaling hubs influence metabolism, especially the metabolic pathways for nucleotide synthesi...
Advances in experimental medicine and biology, 2017
In steatotic hepatocytes, intracellular Ca(2+) homeostasis is substantially altered compared to n... more In steatotic hepatocytes, intracellular Ca(2+) homeostasis is substantially altered compared to normal. Decreased Ca(2+) in the endoplasmic reticulum (ER) can lead to ER stress, an important mediator of the progression of liver steatosis to nonalcoholic steatohepatitis, type 2 diabetes, and hepatocellular carcinoma. Store-operated Ca(2+) channels (SOCs) in hepatocytes are composed principally of Orai1 and STIM1 proteins. Their main role is the maintenance of adequate Ca(2+) in the lumen of the ER. In steatotic hepatocytes, store-operated Ca(2+) entry (SOCE) is substantially inhibited. This inhibition is associated with a decrease in Ca(2+) in the ER. Lipid-induced inhibition of SOCE is mediated by protein kinase C (PKC) and may involve the phosphorylation and subsequent inhibition of Orai1. Experimental inhibition of SOCE enhances lipid accumulation in normal hepatocytes incubated in the presence of exogenous fatty acids. The antidiabetic drug exendin-4 reverses the lipid-induced in...
Antiviral research, Jan 13, 2016
Human noroviruses are the leading causative agents of epidemic and sporadic viral gastroenteritis... more Human noroviruses are the leading causative agents of epidemic and sporadic viral gastroenteritis and childhood diarrhoea worldwide. Human histo-blood group antigens (HBGA) serve as receptors for norovirus capsid protein attachment and play a critical role in infection. This makes HBGA-norovirus binding a promising target for drug development. Recently solved crystal structures of norovirus bound to HBGA have provided a structural basis for identification of potential anti-norovirus drugs and subsequently performed in silico and in vitro drug screens have identified compounds that block norovirus binding and may thereby serve as structural templates for design of therapeutic norovirus inhibitors. This review explores norovirus therapeutic options based on the strategy of blocking norovirus-HBGA binding.
Cell Calcium, 2019
Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and t... more Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and the sixth in women. Non-alcoholic fatty liver disease (NAFLD) is now one of the major risk factors for HCC. NAFLD, which involves the accumulation of excess lipid in cytoplasmic lipid droplets in hepatocytes, can progress to nonalcoholic steatosis, fibrosis, and HCC. Changes in intracellular Ca 2+ constitute important signaling pathways for the regulation of lipid and carbohydrate metabolism in normal hepatocytes. Recent studies of steatotic hepatocytes have identified lipid-induced changes in intracellular Ca 2+ , and have provided evidence that altered Ca 2+ signaling exacerbates lipid accumulation and may promote HCC. The aims of this review are to summarise current knowledge of the lipid-induced changes in hepatocyte Ca 2+ homeostasis, to comment on the mechanisms involved, and discuss the pathways leading from altered Ca 2+ homeostasis to enhanced lipid accumulation and the potential promotion of HCC. In steatotic hepatocytes, lipid inhibits store-operated Ca 2+ entry and SERCA2b, and activates Ca 2+ efflux from the endoplasmic reticulum (ER) and its transfer to mitochondria. These changes are associated with changes in Ca 2+ concentrations in the ER (decreased), cytoplasmic space (increased) and mitochondria (likely increased). They lead to: inhibition of lipolysis, lipid autophagy, lipid oxidation, and lipid secretion; activation of lipogenesis; increased lipid; ER stress, generation of reactive oxygen species (ROS), activation of Ca 2+ /calmodulin-dependent kinases and activation of transcription factor Nrf2. These all can potentially mediate the transition of NAFLD to HCC. It is concluded that lipid-induced changes in hepatocyte Ca 2+ homeostasis are important in the initiation and progression of HCC. Further research is desirable to better understand the cause and effect relationships, the time courses and mechanisms involved, and the potential of Ca 2+ transporters, channels, and binding proteins as targets for pharmacological intervention.
AJP Cell Physiology, 2021
Ca ²⁺ signaling plays a critical role in the regulation of hepatic metabolism by hormones includi... more Ca ²⁺ signaling plays a critical role in the regulation of hepatic metabolism by hormones including insulin. Changes in cytoplasmic Ca ²⁺ regulate synthesis and post-translational modification of key signaling proteins in the insulin pathways. Emerging evidence suggests that hepatocyte intracellular Ca ²⁺ signaling is altered in lipid-loaded liver cells isolated from obese rodent models. The mechanisms of altered Ca ²⁺ -insulin and insulin-Ca ²⁺ signaling pathways in obesity remain poorly understood. Here we show that the kinetics of insulin-initiated intracellular (initial) Ca ²⁺ release from endoplasmic reticulum is significantly impaired in steatotic hepatocytes from obese Alström syndrome mice. Furthermore, exenatide, a GLP-1 analog, reversed lipid-induced inhibition of intracellular Ca ²⁺ release kinetics in steatotic hepatocytes, without affecting the total content of intracellular Ca ²⁺ released. Exenatide reversed the lipid-induced inhibition of intracellular Ca ²⁺ release, at least partially, via lipid reduction in hepatocytes which then restored hormone-regulated cytoplasmic Ca ²⁺ signaling and insulin sensitivity. This data provides additional evidence for the important role of Ca ²⁺ signaling pathways in obesity-associated impaired hepatic lipid homeostasis and insulin signaling. It also highlights a potential advantage of GLP-1 analogs when used to treat type 2 diabetes associated with hepatic steatosis.
Handbook of oxidative stress and cancer: Mechanistic aspects, 2021
Reactive oxygen species (ROS) are reactive chemical and/or biochemical intermediates or fragments... more Reactive oxygen species (ROS) are reactive chemical and/or biochemical intermediates or fragments containing oxygen as peroxides, superoxide (O2●−), hydrogen peroxide (H2O2), hydroxyl radical (●OH), hydroxyl ion (−OH), singlet oxygen, and nitric oxide (NO). At optimal concentration ROS have been implicated to serve varieties of important physiological functions in different types of cells under normal physiological conditions. On the other hand, excessive amounts of ROS are one of the main determinants in the pathogenesis of different types of diseases including cancer, metabolic syndromes, cardiovascular, and neurodegeneration. The mechanism of the generation of ROS and its concentration decides the fate of cells in different types and conditions; excessive ROS can cause detrimental effects on normal cells, deregulate cellular homeostasis, and induce carcinogenic changes. In order to continue their growth and proliferation, cancer cells increase ROS production rate compared with normal cells, and to maintain their ROS homeostasis, they simultaneously increase their antioxidant capacity. It is now evident that this unique and altered redox environment of cancer cells upturns or increases their vulnerability to ROS-metabolism therapies. This chapter aims to discuss a current scenario of ROS in physiological and pathological contributions with emphasis on cellular and molecular mechanistic ways. In addition, it discusses the role of oxidative stress in initiation and progression of different types of cancers as well as current and new strategies targeting ROS for the development of therapeutic interventions of ROS-induced cancers.
Antioxidants, 2021
TRPM2 channels admit Ca2+ and Na+ across the plasma membrane and release Ca2+ and Zn2+ from lysos... more TRPM2 channels admit Ca2+ and Na+ across the plasma membrane and release Ca2+ and Zn2+ from lysosomes. Channel activation is initiated by reactive oxygen species (ROS), leading to a subsequent increase in ADP-ribose and the binding of ADP-ribose to an allosteric site in the cytosolic NUDT9 homology domain. In many animal cell types, Ca2+ entry via TRPM2 channels mediates ROS-initiated cell injury and death. The aim of this review is to summarise the current knowledge of the roles of TRPM2 and Ca2+ in the initiation and progression of chronic liver diseases and acute liver injury. Studies to date provide evidence that TRPM2-mediated Ca2+ entry contributes to drug-induced liver toxicity, ischemia–reperfusion injury, and the progression of non-alcoholic fatty liver disease to cirrhosis, fibrosis, and hepatocellular carcinoma. Of particular current interest are the steps involved in the activation of TRPM2 in hepatocytes following an increase in ROS, the downstream pathways activated by the resultant increase in intracellular Ca2+, and the chronology of these events. An apparent contradiction exists between these roles of TRPM2 and the role identified for ROS-activated TRPM2 in heart muscle and in some other cell types in promoting Ca2+-activated mitochondrial ATP synthesis and cell survival. Inhibition of TRPM2 by curcumin and other “natural” compounds offers an attractive strategy for inhibiting ROS-induced liver cell injury. In conclusion, while it has been established that ROS-initiated activation of TRPM2 contributes to both acute and chronic liver injury, considerable further research is needed to elucidate the mechanisms involved, and the conditions under which pharmacological inhibition of TRPM2 can be an effective clinical strategy to reduce ROS-initiated liver injury.
Molecular Cell, 2020
The RAS-ERK/MAPK (RAS-extracellular signal-regulated kinase/mitogen-activated protein kinase) pat... more The RAS-ERK/MAPK (RAS-extracellular signal-regulated kinase/mitogen-activated protein kinase) pathway integrates growth-promoting signals to stimulate cell growth and proliferation, at least in part, through alterations in metabolic gene expression. However, examples of direct and rapid regulation of the metabolic pathways by the RAS-ERK pathway remain elusive. We find that physiological and oncogenic ERK signaling activation leads to acute metabolic flux stimulation through the de novo purine synthesis pathway, thereby increasing building block availability for RNA and DNA synthesis, which is required for cell growth and proliferation. We demonstrate that ERK2, but not ERK1, phosphorylates the purine synthesis enzyme PFAS (phosphoribosylformylglycinamidine synthase) at T619 in cells to stimulate de novo purine synthesis. The expression of nonphosphorylatable PFAS (T619A) decreases purine synthesis, RAS-dependent cancer cell-colony formation, and tumor growth. Thus, ERK2-mediated PFAS phosphorylation facilitates the increase in nucleic acid synthesis required for anabolic cell growth and proliferation.
Cancers (Basel), 2019
Cancer cells exhibit a dynamic metabolic landscape and require a sufficient supply of nucleotides... more Cancer cells exhibit a dynamic metabolic landscape and require a sufficient supply of nucleotides and other macromolecules to grow and proliferate. To meet the metabolic requirements for cell growth, cancer cells must stimulate de novo nucleotide synthesis to obtain adequate nucleotide pools to support nucleic acid and protein synthesis along with energy preservation, signaling activity, glycosylation mechanisms, and cytoskeletal function. Both oncogenes and tumor suppressors have recently been identified as key molecular determinants for de novo nucleotide synthesis that contribute to the maintenance of homeostasis and the proliferation of cancer cells. Inactivation of tumor suppressors such as TP53 and LKB1 and hyperactivation of the mTOR pathway and of oncogenes such as MYC, RAS, and AKT have been shown to fuel nucleotide synthesis in tumor cells. The molecular mechanisms by which these signaling hubs influence metabolism, especially the metabolic pathways for nucleotide synthesis, continue to emerge. Here, we focus on the current understanding of the molecular mechanisms by which oncogenes and tumor suppressors modulate nucleotide synthesis in cancer cells and, based on these insights, discuss potential strategies to target cancer cell proliferation.
Trends in Endocrinology and Metabolism, 2019
Hepatic steatosis, the first step in nonalcoholic fatty liver disease (NAFLD), can arise from var... more Hepatic steatosis, the first step in nonalcoholic fatty liver disease (NAFLD), can arise from various pathophysiological conditions. While lipid metabolism in the liver is normally balanced such that there is no excessive lipid accumulation, when this homeostasis is disrupted lipid droplets (LDs) accumulate in hepatocytes resulting in cellular toxicity. The mechanisms underlying this accumulation and the subsequent hepatocellular damage are multifactorial and poorly understood, with the result that there are no currently approved treatments for NAFLD. Impaired calcium signaling has recently been identified as a cause of increased endoplasmic reticulum (ER) stress contributing to hepatic lipid accumulation. This review highlights new findings on the role of impaired Ca2+ signaling in the development of steatosis and discusses potential new approaches to NAFLD treatment based on these new insights.
In steatotic hepatocytes intracellular Ca2+ homeostasis is substantially altered compared to norm... more In steatotic hepatocytes intracellular Ca2+ homeostasis is substantially altered compared to normal. Decreased Ca2+ in the endoplasmic reticulum (ER) can lead to ER stress, an important mediator of the progression of liver steatosis to non-alcoholic steatohepatitis, type 2 diabetes and hepatocellular carcinoma. Store-operated Ca2+ channels (SOCs) in hepatocytes are composed principally of Orai1 and STIM1 proteins. Their main role is the maintenance of adequate Ca2+ in the lumen of the ER. In steatotic hepatocytes, store-operated Ca2+ entry (SOCE) is substantially inhibited. This inhibition is associated with a decrease in Ca2+ in the ER. Lipid-induced inhibition of SOCE is mediated by protein kinase C (PKC) and may involve the phosphorylation and subsequent inhibition of Orai1. Experimental inhibition of SOCE enhances lipid accumulation in normal hepatocytes incubated in the presence of exogenous fatty acids. The anti-diabetic drug exendin-4 reverses the lipid-induced inhibition of SOCE, and decreases liver lipid with rapid onset. It is proposed that lipid-induced inhibition of SOCE in the plasma membrane and of SERCA2b in the ER membrane lead to a persistent decrease in ER Ca2+, ER stress, and the ER stress response, which in turn enhances (amplifies) lipid accumulation. A low level of persistent SOCE due to chronic ER Ca2+ depletion in steatotic hepatocytes may contribute to an elevated cytoplasmic free Ca2+ concentration leading to the activation of calcium-calmodulin kinase II (CaMKII), decreased lipid removal by autophagy, and insulin resistance. It is concluded that lipid-induced inhibition of SOCE plays an important role in the progression of liver steatosis to insulin insensitivity and hepatocellular carcinoma.
Cell Calcium, 2019
Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and t... more Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and the sixth in women. Non-alcoholic fatty liver disease (NAFLD) is now one of the major risk factors for HCC. NAFLD, which involves the accumulation of excess lipid in cytoplasmic lipid droplets in hepatocytes, can progress to non-alcoholic steatosis, fibrosis, and HCC. Changes in intracellular Ca2+ constitute important signaling pathways for the regulation of lipid and carbohydrate metabolism in normal hepatocytes. Recent studies of steatotic hepatocytes have identified lipid-induced changes in intracellular Ca2+, and have provided evidence that altered Ca2+ signaling exacerbates lipid accumulation and may promote HCC. The aims of this review are to summarise current knowledge of the lipid-induced changes in hepatocyte Ca2+ homeostasis, to comment on the mechanisms involved, and discuss the pathways leading from altered Ca2+ homeostasis to enhanced lipid accumulation and the potential promotion of HCC. In steatotic hepatocytes, lipid inhibits store-operated Ca2+ entry and SERCA2b, and activates Ca2+ efflux from the endoplasmic reticulum (ER) and its transfer to mitochondria. These changes are associated with changes in Ca2+ concentrations in the ER (decreased), cytoplasmic space (increased) and mitochondria (likely increased). They lead to: inhibition of lipolysis, lipid autophagy, lipid oxidation, and lipid secretion; activation of lipogenesis; increased lipid; ER stress, generation of reactive oxygen species (ROS), activation of Ca2+/calmodulin-dependent kinases and activation of transcription factor Nrf2. These all can potentially mediate the transition of NAFLD to HCC. It is concluded that lipid-induced changes in hepatocyte Ca2+ homeostasis are important in the initiation and progression of HCC. Further research is desirable to better understand the cause and effect relationships, the time courses and mechanisms involved, and the potential of Ca2+ transporters, channels, and binding proteins as targets for pharmacological intervention.
Biochimica et biophysica acta Molecular Cell Research, Jan 10, 2016
The release of Ca(2+) from the endoplasmic reticulum (ER) and subsequent replenishment of ER Ca(2... more The release of Ca(2+) from the endoplasmic reticulum (ER) and subsequent replenishment of ER Ca(2+) by Ca(2+) entry through store-operated Ca(2+) channels (SOCE) play critical roles in the regulation of liver metabolism by adrenaline, glucagon and other hormones. Both ER Ca(2+) release and Ca(2+) entry are severely inhibited in steatotic hepatocytes. Exendin-4, a slowly-metabolised glucagon-like peptide-1 (GLP-1) analogue, is known to reduce liver glucose output and liver lipid, but the mechanisms involved are not well understood. The aim of this study was to determine whether exendin-4 alters intracellular Ca(2+) homeostasis in steatotic hepatocytes, and to evaluate the mechanisms involved. Exendin-4 completely reversed lipid-induced inhibition of SOCE in steatotic liver cells, but did not reverse lipid-induced inhibition of ER Ca(2+) release. The action of exendin-4 on Ca(2+) entry was rapid in onset and was mimicked by GLP-1 or dibutyryl cyclic AMP. In steatotic liver cells, exen...