Joon No Lee - Academia.edu (original) (raw)

Papers by Joon No Lee

Cell Communication and Signaling

Background Lysosomes are a central hub for cellular metabolism and are involved in the regulation... more Background Lysosomes are a central hub for cellular metabolism and are involved in the regulation of cell homeostasis through the degradation or recycling of unwanted or dysfunctional organelles through the autophagy pathway. Catalase, a peroxisomal enzyme, plays an important role in cellular antioxidant defense by decomposing hydrogen peroxide into water and oxygen. In accordance with pleiotropic significance, both impaired lysosomes and catalase have been linked to many age-related pathologies with a decline in lifespan. Aging is characterized by progressive accumulation of macromolecular damage and the production of high levels of reactive oxygen species. Although lysosomes degrade the most long-lived proteins and organelles via the autophagic pathway, the role of lysosomes and their effect on catalase during aging is not known. The present study investigated the role of catalase and lysosomal function in catalase-knockout (KO) mice. Methods We performed experiments on WT and cat...

Experimental & molecular medicine, Jan 6, 2018

Defects in the PEX5 gene impair the import of peroxisomal matrix proteins, leading to nonfunction... more Defects in the PEX5 gene impair the import of peroxisomal matrix proteins, leading to nonfunctional peroxisomes and other associated pathological defects such as Zellweger syndrome. Although PEX5 regulates autophagy process in a stress condition, the mechanisms controlling autophagy by PEX5 under nutrient deprivation are largely unknown. Herein, we show a novel function of PEX5 in the regulation of autophagy via Transcription Factor EB (TFEB). Under serum-starved conditions, when PEX5 is depleted, the mammalian target of rapamycin (mTORC1) inhibitor TSC2 is downregulated, which results in increased phosphorylation of the mTORC1 substrates, including 70S6K, S6K, and 4E-BP-1. mTORC1 activation further suppresses the nuclear localization of TFEB, as indicated by decreased mRNA levels of TFEB, LIPA, and LAMP1. Interestingly, peroxisomal mRNA and protein levels are also reduced by TFEB inactivation, indicating that TFEB might control peroxisome biogenesis at a transcriptional level. Conv...

International journal of molecular medicine, 2017

Fenofibrate, an activator of peroxisome proliferator-activated receptors (PPARs), has been shown ... more Fenofibrate, an activator of peroxisome proliferator-activated receptors (PPARs), has been shown to protect the kidneys and brain cells from oxidative stress; however, its role in preventing hearing loss has not been reported to date, at least to the best of our knowledge. In this study, we demonstrated the protective effects of fenofibrate against gentamicin (GM)-induced ototoxicity. We found that the auditory brainstem response threshold which was increased by GM was significantly reduced by pre-treatment with fenofibrate in rats. In cochlear explants, the disruption of hair cell layers by GM was also markedly attenuated by pre-treatment with fenofibrate. In addition, fenofibrate almost completely abolished GM-induced reactive oxygen species generation, which seemed to be mediated at least in part by the restoration of the expression of PPAR‑α‑dependent antioxidant enzymes, including catalase and superoxide dismutase (SOD)-1. Of note, fenofibrate markedly increased the expression ...

Journal of Biological Chemistry, 2008

Proteasomes mediate the regulated degradation of Insig-1, a membrane protein of the endoplasmic r... more Proteasomes mediate the regulated degradation of Insig-1, a membrane protein of the endoplasmic reticulum (ER) that plays a crucial role in lipid metabolism. We showed previously that sterols inhibit this degradation by blocking ubiquitination of Insig-1. Here we show that unsaturated fatty acids stabilize Insig-1 without affecting its ubiquitination. Instead unsaturated fatty acids inhibit extraction of ubiquitinated Insig-1 from membranes, a process known to be mediated by valosin-containing protein and necessary for ER-associated degradation. Valosin-containing protein is recruited to Insig-1 through the action of another protein, Ubxd8. Unsaturated fatty acids block the binding between Ubxd8 and Insig-1, thereby abrogating the membrane extraction of Insig-1. Unsaturated fatty acidmediated stabilization of Insig-1 enhances the ability of sterols to inhibit proteolytic activation of SREBP-1, which activates transcription of genes involved in fatty acid synthesis. The current study provides a molecular mechanism for regulation of proteasome-mediated ER protein degradation at a postubiquitination step.

Background Fatty acids (FA) derived from adipose tissue and liver serve as the main fuel in therm... more Background Fatty acids (FA) derived from adipose tissue and liver serve as the main fuel in thermogenesis of brown adipose tissue (BAT). Catalase, a peroxisomal enzyme, plays an important role in maintaining intracellular redox homeostasis by decomposing hydrogen peroxide to either water or oxygen that oxidize and provide fuel for cellular metabolism. Although the antioxidant enzymatic activity of catalase is well known, its role in the metabolism and maintenance of energy homeostasis has not yet been revealed. The present study investigated the role of catalase in lipid metabolism and thermogenesis during nutrient deprivation in catalase-knockout (KO) mice. Results We found that hepatic triglyceride accumulation in KO mice decreased during sustained fasting due to lipolysis through reactive oxygen species (ROS) generation in adipocytes. Furthermore, the free FA released from lipolysis were shuttled to BAT through the activation of CD36 and catabolized by lipoprotein lipase in KO mi...

Journal of Biological Chemistry, 1999

Journal of Biochemistry and Molecular Biology, 1997

A novel assay method is described for rapid quantitation of reaction rate of sterol -reductase (-... more A novel assay method is described for rapid quantitation of reaction rate of sterol -reductase (-SR) which catalyzes reduction of the -double bond of sterols. Of six different organ tissues-liver, small intestine, brain, lung, kidney, and testis-. -SR activity was detected only in liver (2.30 nmol/min/mg protein) and testis (0.11 nmol/min/mg protein). Using a newly developed method which employs diet-induced enzyme proteins and ergosterol as substrate, we assessed both kinetics (, ) and inhibition of the rat hepatic -SR against well-studied cholesterol lowering agents such as triparanol (). 3--[2-(diethylamino)ethoxy]androst-5-en-17-one (U18666A) (), and trans-1.4-bis(2-chlorobenzylaminomethyl)cyclohexane dihydrochloride (AY-9944) (). Of the three well-known AY-9944-sensitive cholesterogenic enzymes (i.e., -SR, sterol -isomerase, and sterol -reductase). -SR was found to be the most sensitive enzyme with a noncompetitive inhibition of this compound (). Substrate specificity studies o...

Background: Lysosomes are a central hub for cellular metabolism and are involved in the regulatio... more Background: Lysosomes are a central hub for cellular metabolism and are involved in the regulation of cell homeostasis through the degradation or recycling of unwanted or dysfunctional organelles through the autophagy pathway. Catalase, a peroxisomal enzyme, plays an important role in cellular antioxidant defense by decomposing hydrogen peroxide into water and oxygen. In accordance with pleiotropic significance, both impaired lysosomes and catalase have been linked to many age-related pathologies with a decline in lifespan. Aging is characterized by progressive accumulation of macromolecular damage and the production of high levels of reactive oxygen species (ROS). Although lysosomes degrade the most long-lived proteins and organelles via the autophagic pathway, the role of lysosomes and their effect on peroxisomes during aging is not known. The present study investigated the role of catalase and lysosomal function in catalase-knockout (KO) mice.Results: We found that catalase-defic...

BioFactors, 2021

Peroxisomes are dynamic organelles that participate in a diverse array of cellular processes, inc... more Peroxisomes are dynamic organelles that participate in a diverse array of cellular processes, including β‐oxidation, which produces a considerable amount of reactive oxygen species (ROS). Although we showed that catalase depletion induces ROS‐mediated pexophagy in cells, the effect of catalase deficiency during conditions that favor ROS generation remains elusive in mice. In this study, we reported that prolonged fasting in catalase‐knockout (KO) mice drastically increased ROS production, which induced liver‐specific pexophagy, an autophagic degradation of peroxisomes. In addition, increased ROS generation induced the production of pro‐inflammatory cytokines in the liver tissues of catalase‐KO mice. Furthermore, there was a significant increase in the levels of aspartate transaminase and alanine transaminase as well as apparent cell death in the liver of catalase‐KO mice during prolonged fasting. However, an intra‐peritoneal injection of the antioxidant N‐acetyl‐l‐cysteine (NAC) and autophagy inhibitor chloroquine inhibited the inflammatory response, liver damage, and pexophagy in the liver of catalase‐KO mice during prolonged fasting. Consistently, genetic ablation of autophagy, Atg5 led to suppression of pexophagy during catalase inhibition by 3‐aminotriazole (3AT). Moreover, treatment with chloroquine also ameliorated the inflammatory response and cell death in embryonic fibroblast cells from catalase‐KO mice. Taken together, our data suggest that ROS‐mediated liver‐specific pexophagy observed during prolonged fasting in catalase‐KO mice may be responsible for the process associated with hepatic cell death.

Autophagy, Jan 17, 2018

The primary cilia are evolutionarily conserved microtubule-based cellular organelles that perceiv... more The primary cilia are evolutionarily conserved microtubule-based cellular organelles that perceive metabolic status and thus link the sensory system to cellular signaling pathways. Therefore, ciliogenesis is thought to be tightly linked to autophagy, which is also regulated by nutrient-sensing transcription factors, such as PPARA (peroxisome proliferator activated receptor alpha) and NR1H4/FXR (nuclear receptor subfamily 1, group H, member 4). However, the relationship between these factors and ciliogenesis has not been clearly demonstrated. Here, we present direct evidence for the involvement of macroautophagic/autophagic regulators in controlling ciliogenesis. We showed that activation of PPARA facilitated ciliogenesis independently of cellular nutritional states. Importantly, PPARA-induced ciliogenesis was mediated by controlling autophagy, since either pharmacological or genetic inactivation of autophagy significantly repressed ciliogenesis. Moreover, we showed that pharmacologi...

Biochemical and biophysical research communications, Jun 27, 2018

Peroxisomes are dynamic and multifunctional organelles involved in various cellular metabolic pro... more Peroxisomes are dynamic and multifunctional organelles involved in various cellular metabolic processes, and their numbers are tightly regulated by pexophagy, a selective degradation of peroxisomes through autophagy to maintain peroxisome homeostasis in cells. Catalase, a major peroxisome protein, plays a critical role in removing peroxisome-generated reactive oxygen species (ROS) produced by peroxisome enzymes, but the contribution of catalase to pexophagy has not been reported. Here, we investigated the role of catalase in peroxisome degradation during nutrient deprivation. Both short interfering RNA-mediated silencing of catalase and pharmacological inhibition by 3-aminotriazole (3AT) decreased the number of peroxisomes and resulted in the downregulation of peroxisomal proteins, such as PMP70 and PEX14 under serum starvation. In addition, treatment with 3AT induced NBR1-dependent autophagy and PEX5 ubiquitination in the absence of serum, which was accompanied by accumulation of R...

Toxicology and applied pharmacology, Jan 13, 2018

Cisplatin is an alkylating agent that interferes with DNA replication and kills proliferating car... more Cisplatin is an alkylating agent that interferes with DNA replication and kills proliferating carcinogenic cells. Several studies have been conducted to attenuate the side effects of cisplatin; one such side effect in cancer patients undergoing cisplatin chemotherapy is ototoxicity. However, owing to a lack of understanding of the precise mechanism underlying cisplatin-induced side effects, management of cisplatin-induced ototoxicity remains unsolved. We investigated the protective effects of fenofibrate, a PPAR-α activator, on cisplatin-induced ototoxicity. Fenofibrate prevented cisplatin-induced loss of hair cells and improved cell viability; moreover, fenofibrate significantly attenuated the threshold of auditory brainstem responses (ABR) in cisplatin-injected mice. Fenofibrate significantly increased PPAR-α, PPAR-γ, and PGC-1α expression, which consequently resulted in increased number and functional enzyme levels of peroxisomes and mitochondria, and markedly decreased phospho-p...

Biochemical and biophysical research communications, Jan 13, 2018

Primary cilium is a microtubule structure that emanates from the surface of most human cells. Pri... more Primary cilium is a microtubule structure that emanates from the surface of most human cells. Primary cilia assemble during the resting stage (G phase) and disassemble with cell cycle progression. Defects associated with the control of the assembly or disassembly of the primary cilium have been implicated in various human diseases, including ciliopathy and cancer. Although studies have suggested the interplay between activation of autophagy and ciliogenesis, any direct mechanism between autophagy abatement and disassembly of primary cilium remains elusive. In this study, we found that the gradual abatement in autophagy during serum-restimulation was a dynamic process and significantly correlated with the disassembly of primary cilium in human retinal pigmented epithelial (RPE1) cells. Although autophagy activity was gradually decreased during serum-restimulation, the alteration in autophagy under the same condition prevented the disassembly of the primary cilium. Autophagy inhibitor...

Molecular & Cellular Toxicology, 2017

Cobalt is an essential metal that is required for the generation of vitamin B12. However, exposur... more Cobalt is an essential metal that is required for the generation of vitamin B12. However, exposure to excess cobalt for a prolonged period may adversely affect the human body, causing hepatotoxicity, pulmonary fibrosis, and neurotoxicity. 3-Aminotriazole (3-AT) is a catalase inhibitor that is often used to examine the cellular role of catalase. in the present study, we showed that 3-AT treatment significantly reduced cobalt (II) chloride (CoCl2)-induced cytotoxicity in Hepg2 cells by suppressing the expression and activation of apoptotic markers, caspase-3 and poly adenosine diphosphate ribose polymerase (PARP). Mechanistically, 3-AT treatment attenuated CoCl2-induced accumulation of reactive oxygen species (ROS) and expression of roS-responsive genes. Furthermore, the CoCl2-induced mitochondrial membrane potential (Δψm) shift and mitochondrial damage were attenuated by 3-AT. Taken together, these findings suggest that 3-AT alleviates CoCl2-induced cytotoxicity by reducing roS generation and protecting against mitochondrial damage.

Biochemical and biophysical research communications, Jan 30, 2016

β-lapachone (β-L) is a substrate of reduced nicotinamide adenine dinucleotide (NADH): quinone oxi... more β-lapachone (β-L) is a substrate of reduced nicotinamide adenine dinucleotide (NADH): quinone oxidoreductase 1 (NQO1). NQO1 reduces quinones to hydroquinones using NADH as an electron donor and consequently increases the intracellular NAD+/NADH ratio. The activation of NQO1 by β-L has beneficial effects on several metabolic syndromes, such as obesity, hypertension, and renal injury. However, the effect of β-L on bone metabolism remains unclear. Here, we show that β-L might be a potent inhibitor of receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. β-L inhibited osteoclast formation in a dose-dependent manner and also reduced the expression of osteoclast differentiation marker genes, such as tartrate-resistant acid phosphatase (Acp5 or TRAP), cathepsin K (CtsK), the d2 isoform of vacuolar ATPase V0 domain (Atp6v0d2), osteoclast-associated receptor (Oscar), and dendritic cell-specific transmembrane protein (Dc-stamp). β-L treatment of RANKL-induced oste...

Organogenesis, Apr 14, 2016

Very long chain fatty acids are required for sphingolipid synthesis, lipid homeostasis, myelin fo... more Very long chain fatty acids are required for sphingolipid synthesis, lipid homeostasis, myelin formation, epidermal permeability, and retinal function. Seven different enzymes are known to be involved in the elongation cycle of fatty acids, with different chain-length specificities. Elovl1 is one of those enzymes whose function has been linked mainly to the synthesis of sphingolipids and the epidermal barrier. However, the role of Elovl1 in organogenesis is not clear. In zebrafish, two Elovl1 genes, elovl1a and elovl1b, are highly expressed in the swim bladder, and elovl1b is also expressed in the kidney. We found that both elovl1 knockdown embryos contain increased levels of long chain fatty acids from carbon number 14 to 20 as compared to control embryos. Oil-Red-O staining shows that yolk lipid consumption is greatly reduced, whereas lipid droplets accumulate within the swim bladder. Notably, knockdown of either elovl1a or elovl1b affects the expression of genes involved in swim ...

Biochemical and biophysical research communications, Jan 22, 2015

Pexophagy is the selective degradation of peroxisomes for maintaining peroxisome homeostasis with... more Pexophagy is the selective degradation of peroxisomes for maintaining peroxisome homeostasis within cells. Peroxisome dynamics and pexophagy are important events required to maintain the quality control of peroxisomes, thereby preventing peroxisome-associated diseases. To identify novel pexophagy modulators, we developed a cell-based screening system and selected 2,2'-dipyridyl (2,2-DP) as a candidate molecule. 2,2-DP treatment induced peroxisome degradation as evidenced by an increased number of low-pH autolysosomes originating from peroxisomes and a decrease in the expression of peroxisomal proteins such as catalase, Pex14, and PMP70. The phenotype was defined as pexophagy, because 2,2-DP induced autophagy and inhibition of autophagy significantly reduced the degree of peroxisome degradation. Mechanistically, 2,2-DP-dependent pexophagy seemed to be mediated by iron chelation, since another iron chelator displayed a similar effect on pexophagy, but a copper chelator did not. No...

Proceedings of the National Academy of Sciences, 1998

Inhibitors of the last steps of cholesterol biosynthesis such as AY9944 and BM15766 severely impa... more Inhibitors of the last steps of cholesterol biosynthesis such as AY9944 and BM15766 severely impair brain development. Their molecular target is the Δ7-sterol reductase (EC 1.3.1.21 ), suspected to be defective in the Smith–Lemli–Opitz syndrome, a frequent inborn disorder of sterol metabolism. Molecular cloning of the cDNA revealed that the human enzyme is a membrane-bound protein with a predicted molecular mass of 55 kDa and six to nine putative transmembrane segments. The protein is structurally related to plant and yeast sterol reductases. In adults the ubiquitously transcribed mRNA is most abundant in adrenal gland, liver, testis, and brain. The Δ7-sterol reductase is the ultimate enzyme of cholesterol biosynthesis in vertebrates and is absent from yeast. Microsomes from Saccharomyces cerevisiae strains heterologously expressing the human cDNA remove the C 7–8 double bond in 7-dehydrocholesterol. The conversion to cholesterol depends on NADPH and is potently inhibited by AY9944 ...

Biochemical and biophysical research communications, Jan 2, 2015

Even though bortezomib, a proteasome inhibitor, is a powerful chemotherapeutic agent used to trea... more Even though bortezomib, a proteasome inhibitor, is a powerful chemotherapeutic agent used to treat multiple myeloma (MM) and other lymphoma cells, recent clinical reports suggest that the proteasome inhibitor therapy may be associated with severe bilateral hearing loss. We herein investigated the adverse effect of proteasome inhibitor on auditory hair cells. Treatment of a proteasome inhibitor destroys stereocilia bundles of hair cells resulting in the disarray of stereocilia in the organ of Corti explants. Since proteasome activity may be potentially important for biogenesis and function of the peroxisome, we tested whether proteasome activity is necessary for maintaining functional peroxisomes. Our results showed that treatment of a proteasome inhibitor significantly decreases both the number of peroxisomes and expression of peroxisomal proteins such as PMP70 and Catalase. In addition, we also found that proteasome inhibitor impairs the import pathway of PTS1-peroxisome matrix pro...

Proceedings of the National Academy of Sciences, 2006

Insig-1 and Insig-2 are closely related proteins of the endoplasmic reticulum (ER) that mediate f... more Insig-1 and Insig-2 are closely related proteins of the endoplasmic reticulum (ER) that mediate feedback control of cholesterol synthesis by sterol-dependent binding to the following two membrane proteins: the escort protein Scap, thus preventing proteolytic processing of sterol regulatory element-binding proteins; and the cholesterol biosynthetic enzyme 3-hydroxy-3-methylglutaryl CoA reductase, thus inducing the ubiquitination and ER-associated degradation of the enzyme. Here, we report that the conserved Asp-205 in Insig-1, which abuts the fourth transmembrane helix at the cytosolic side of the ER membrane, is essential for its dual function. When Asp-205 was mutated to alanine, the mutant Insig-1 lost the ability to bind to Scap and, thus, was unable to suppress the cleavage of sterol regulatory element-binding proteins. The mutant Insig-1 was ineffective also in accelerating sterol-stimulated degradation of 3-hydroxy-3-methylglutaryl CoA reductase. Alanine substitution of the co...