Barbara Hoffman - Academia.edu (original) (raw)

Papers by Barbara Hoffman

Research paper thumbnail of Progression of the myeloid differentiation program is dominant to transforming growth factor-beta 1-induced apoptosis in M1 myeloid leukemic cells

Blood, 1994

Hematopoiesis is a profound example of cell homeostasis that is regulated throughout life. This p... more Hematopoiesis is a profound example of cell homeostasis that is regulated throughout life. This process requires the participation of many factors, including positive and negative regulators of growth and differentiation, that determine survival, growth stimulation, differentiation, functional activation, and programmed cell death. Understanding the effects of multiple stimuli on specific cells at the molecular and cellular level is crucial towards understanding how the population of blood cells maintains a homeostatic state. Two appropriate stimuli for analysis, both of which are found in bone marrow, are differentiation-inducing cytokines, which induce terminal differentiation associated with growth arrest, ultimately culminating in programmed cell death, and transforming growth factor-beta 1 (TGF- beta 1), which induces rapid growth arrest and apoptosis of hematopoietic cells. Previously, we have shown, using M1 myeloblastic leukemic cells as a model system, that differentiation-...

Research paper thumbnail of Deregulated c-myb disrupts interleukin-6- or leukemia inhibitory factor-induced myeloid differentiation prior to c-myc: role in leukemogenesis

Molecular and Cellular Biology, 1992

The c-myb proto-oncogene is abundantly expressed in tissues of hematopoietic origin, and changes ... more The c-myb proto-oncogene is abundantly expressed in tissues of hematopoietic origin, and changes in endogenous c-myb genes have been implicated in both human and murine hematopoietic tumors. c-myb encodes a DNA-binding protein capable of trans-activating the c-myc promoter. Suppression of both of these proto-oncogenes was shown to occur upon induction of terminal differentiation but not upon induction of growth inhibition in myeloid leukemia cells. Myeloblastic leukemia M1 cells that can be induced for terminal differentiation with the physiological hematopoietic inducers interleukin-6 and leukemia inhibitory factor were genetically manipulated to constitutively express a c-myb transgene. By using immediate-early to late genetic and morphological markers, it was shown that continuous expression of c-myb disrupts the genetic program of myeloid differentiation at a very early stage, which precedes the block previously shown to be exerted by deregulated c-myc, thereby indicating that t...

Research paper thumbnail of The proto-oncogene c-myc in hematopoietic development and leukemogenesis

Oncogene, 2002

expression during dierentiation, including C/EBPa, CTCF, BLIMP-1, and RFX1. Alterations in the ex... more expression during dierentiation, including C/EBPa, CTCF, BLIMP-1, and RFX1. Alterations in the expression and/or function of these transcription factors, or of the c-Myc and Max interacting proteins, such as MM-1 and Mxi1, can in¯uence the neoplastic process. Understanding how c-Myc controls cellular phenotypes, including the leukemic phenotype, should provide novel tools for designing drugs to promote dierentiation and/ or apoptosis of leukemic cells.

Research paper thumbnail of The proto-oncogene c-myc and apoptosis

Oncogene, 1998

Deregulated expression of c-Myc not only promotes proliferation, but also can either induce or se... more Deregulated expression of c-Myc not only promotes proliferation, but also can either induce or sensitize cells to apoptosis. Inappropriate expression of c-Myc under conditions which inhibit growth and down-regulate endogenous c-Myc expression, including serum deprivation and exposure to cytotoxic agents including the anticancer agents vinblastine, etoposide, Ara-C, and nocodazole, usually results in programmed cell death in many dierent cell types. Also, inappropriate Myc expression is associated with an apoptotic response elicited by induction of dierentiation. The proapoptotic property of c-Myc requires an intact N-terminal transactivation domain and bHLHZip domain, as well as interaction with Max, thereby implicating c-Myc target genes in this apoptotic process. Although some target genes, namely cdc25A and ODC, have been shown to participate in Myc-mediated apoptosis, no target gene has yet been identi®ed which is essential for this apoptotic response. It is possible that the response of cells inappropriately expressing c-Myc is due not only to the growth arrest signals per se, but also to signals elicited by speci®c growth inhibitors in the context of a particular biological setting. Also regulating the response of the cells is expression of other oncogenes and tumor suppressor genes, as well as paracrine and autocrine survival factors. Apoptosis associated with inappropriate Myc expression limits the tumorigenic eect of the cmyc proto-oncogene. Mechanisms which inhibit apoptosis should enhance or promote tumorigenesis.

Research paper thumbnail of p53-independent apoptosis associated with c-Myc-mediated block in myeloid cell differentiation

Oncogene, 2000

Previously we have shown that deregulated expression of c-myc in M1 myeloid leukemic cells blocke... more Previously we have shown that deregulated expression of c-myc in M1 myeloid leukemic cells blocked IL-6induced dierentiation and its associated growth arrest; however, the cells proliferated at a signi®cantly reduced rate compared to untreated cells. The basis for the increased doubling time of IL-6-treated M1myc cells was found to be due to the induction of a p53-independent apoptotic pathway. The apoptotic response was not completely penetrant; in the same population of cells both proliferation and apoptosis were continuously ongoing. Down-regulation of Bcl-2 was insucient to account for the apoptotic response, since deregulated expression of Bcl-2 delayed, but did not block, the onset of apoptosis. Furthermore, our results indicated that the IL-6-induced partial hypophosphorylation of the retinoblastoma gene product (Rb), observed in M1myc cells, was not responsible for the apoptotic response. Finally, the ®ndings in M1 cells were extended to myeloid cells derived from the bone marrow of wild type and p53-de®cient mice, where the deregulated expression of c-myc was also shown to block terminal dierentiation and induce apoptosis independent of p53. These ®ndings provide new insights into how myc participates in the neoplastic process, and how additional mutations can promote more aggressive tumors.

Research paper thumbnail of Hematopoietic cells from Gadd45a- and Gadd45b-deficient mice are sensitized to genotoxic-stress-induced apoptosis

Oncogene, 2005

Gadd45a, gadd45b and gadd45g (Gadd45/MyD118/CR6) are genes that are rapidly induced by genotoxic ... more Gadd45a, gadd45b and gadd45g (Gadd45/MyD118/CR6) are genes that are rapidly induced by genotoxic stress. However, the exact function of Gadd45 proteins in the response of mammalian cells to genotoxic stress is unclear. Here, advantage was taken of gadd45a-and gadd45b-deficient mice to determine the role gadd45a and gadd45b play in the response of bone marrow (BM) cells to genotoxic stress. BM cells from gadd45a-and gadd45bdeficient mice were observed to be more sensitive to ultraviolet radiation chemotherapy (UVC), VP-16 and daunorubicin (DNR)-induced apoptosis compared to wildtype (wt) cells. The increased apoptosis in gadd45a-and gadd45b-deficient cells was evident also by enhanced activation of caspase-3 and poly-ADP-ribose polymerase cleavage and decreased expression of c-inhibitor of apoptotic protein-1, Bcl-2, Bcl-xL compared to wt cells. Reintroduction of gadd45 into gadd45-deficient BM cells restored the wt apoptotic phenotype. Both gadd45a-and gadd45b-deficient BM cells also displayed defective G2/M arrest following exposure to UVC and VP-16, but not to DNR, indicating the existence of different G2/M checkpoints that are either dependent or independent of gadd45. Taken together, these findings identify gadd45a and gadd45b as antiapoptotic genes that increase the survival of hematopoietic cells following exposure to UV radiation and certain anticancer drugs.

Research paper thumbnail of Apoptotic signaling by c-MYC

Oncogene, 2008

c-MYC has a pivotal function in growth control, differentiation and apoptosis, and its abnormal e... more c-MYC has a pivotal function in growth control, differentiation and apoptosis, and its abnormal expression is associated with many tumors. Overexpression of c-MYC sensitizes cells to apoptosis by a variety of stimuli. The decision of a cell to undergo apoptosis and how this apoptotic response is regulated by c-MYC depends on the specific cell type and the physiological status of the cell. Multiple cooperating molecular pathways of cell survival and apoptosis determine whether a cell lives or dies, and understanding how c-MYC interfaces with these pathways to influence the survival of cells is important to understand normal and abnormal development, tumor initiation and progression, and response of tumors to different treatment regimens. This article will provide an overview of the function of the tumor suppressor gene product p53 in the c-MYC-mediated apoptotic response and how c-MYC amplifies the intrinsic mitochondrial pathway and triggers and/or amplifies the death receptor pathways. Finally, a model for how deregulated c-MYC prematurely triggers the normal apoptotic response associated with terminal myeloid differentiation while also blocking the differentiation program is presented.

Research paper thumbnail of Sequence of MyD116 cDNA: a novel myeloid differentiation primary response gene induced by IL6

Nucleic Acids Research, 1990

Research paper thumbnail of Interferon regulatory factor-1 myelodysplasia and leukemia

Research paper thumbnail of Gadd45 in stress signaling

Journal of Molecular Signaling, 2008

Research paper thumbnail of Gadd45β is an inducible coactivator of transcription that facilitates rapid liver growth in mice

Journal of Clinical Investigation, 2011

Research paper thumbnail of Gadd45a stress signaling regulates sFlt-1 expression in preeclampsia

Journal of Cellular Physiology, 2009

Preeclampsia, which affects approximately 5-8% of all pregnancies and is one of the leading cause... more Preeclampsia, which affects approximately 5-8% of all pregnancies and is one of the leading causes of maternal and fetal morbidity and mortality, is a pregnancy induced complex of multiple pathological changes, including elevated blood pressure, proteinuria and edema manifested after 20 weeks gestation. There is growing evidence that placental stresses during pregnancy, notably hypoxia, and an increase in circulating soluble Flt-1 (sFlt-1) are important in the etiopathogenesis of preeclampsia. How placental stress results in elevated sFlt-1 expression is currently unknown. Here we provide novel data implicating the Gadd45a stress sensor protein as an upstream modulator of pathophysiological changes observed in preeclampsia. It is shown that Gadd45a expression and activation of its downstream effector p38 kinase are elevated in preeclamptic placentas compared to non-preeclamptic controls, and correlate with elevated sFlt-1. Furthermore, a regulatory loop is demonstrated where stress, including hypoxia, IL-6 or hypertonic stress, caused induction of Gadd45a, leading to p38 activation and ultimately increasing sFlt-1 secretion in endothelial cells. These data provide a compelling working frame to further test the role of Gadd45 stress sensors in the etiology of preeclampsia, and set the stage for considering novel therapeutic regimens, including p38 inhibitors, for treatment of preeclampsia.

Research paper thumbnail of Preeclampsia-associated stresses activate Gadd45a signaling and sFlt-1 in placental explants

Journal of Cellular Physiology, 2012

Accumulating evidence suggests that placental stresses during pregnancy can play an important rol... more Accumulating evidence suggests that placental stresses during pregnancy can play an important role in the pathogenesis of preeclampsia. A common signal pathway that senses and converts placental stresses into intracellular stress response may be contributing to this pathology. Based on our previous findings, we extended our investigation to establish that Gadd45a stress signaling regulates sFlt-1 levels, particularly in placenta, when exposed to various preeclampsia-associated stresses including AT-1 receptor agonist (Angiotensin II), hypoxia, and inflammatory cytokines. Using a placental explant model, we found that Gadd45a was induced in response to all the preeclampsia stresses stated above. Although stress induced Gadd45a was associated with the activation of its downstream effectors phospho-p38 and phospho-JNK, the subsequent regulation of sFlt-1 levels occurred through either one of these effectors, but not both. These observations indicate that Gadd45a signaling may work as a hub connecting placental stresses and the pathogenesis of preeclampsia. It also provides evidence to justify testing the role of Gadd45 in the etiology of preeclampsia using in vivo mouse (i.e., Gadd45a null mice) models.

Research paper thumbnail of Distinct mechanisms are utilized to induce stress sensorgadd45bby different stress stimuli

Journal of Cellular Biochemistry, 2009

The GADD45 family of proteins consists of three small proteins, GADD45A, GADD45B, and GADD45G, im... more The GADD45 family of proteins consists of three small proteins, GADD45A, GADD45B, and GADD45G, implicated in modulating the cellular response to genotoxic/physiological stressors. Despite similarities in sequence, structure and function, each gadd45 gene is induced differentially by different stress stimuli. Studies on stress-mediated induction of the gadd45 genes have predominantly focused on gadd45a, with knowledge of gadd45b and gadd45g regulation lacking. To generate a more complete understanding of the regulation of gadd45 genes, a comprehensive analysis of stress-mediated induction of human gadd45b has been carried out using human RKO colorectal carcinoma cells as a model system. Novel data indicate that gadd45b induction in RKO cells is regulated by distinct mechanisms in a stress-specific manner. Methylmethane sulfonate (MMS), a DNA alkylating agent, induces gadd45b transcription through a cohort of both constitutive and inducible bound factors, including NFY, Sp1 and Egr1. In contrast, in a hyperosmotic environment generated with sorbitol, gadd45b mRNA is induced exclusively by mRNA stabilization. These findings indicate that the stress-mediated induction of gadd45b is largely distinct from gadd45a. Furthermore, data obtained provide a novel paradigm for stress-response gene induction, indicating that gadd45b induction by distinct stressors, in the same cell type and under the same experimental settings, is differentially regulated at the level of mRNA transcription or mRNA stability. Importantly, this study also provides the groundwork to further examine the regulation of gadd45b expression in in vivo settings using animal models and tissues obtained from normal individuals and cancer patients prior to and after chemotherapeutic intervention.

Research paper thumbnail of Regulation of gene expression by tumor promoters. II. Control of cell shape and developmental programs for macrophages and granulocytes in human myeloid leukemic cells

International Journal of Cancer, 1981

Regulation of the developmental programs for macrophages and granulocytes has been analysed, usin... more Regulation of the developmental programs for macrophages and granulocytes has been analysed, using two-dimensional gel electrophoresis of the cytoplasmic protein changes, in a human myeloid leukemic cell line (HL60) that can be induced to differentiate to macrophages by the macrophage and granulocyte-inducing (MGI) protein and the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA), and to granulocytes by dimethylsulfoxide (DMSO). Studies on the protein changes induced by the different inducers showed a similar developmental program for macrophage differentiation induced by MGI or TPA, which differed from the beginning from the granulocyte program induced by DMSO. Comparison with normal cells from human peripheral blood has shown that the develop mental programs induced in the HL60 cells are relevant 'Part I in this series is Lotem and Sachs (1979).

Research paper thumbnail of Gadd45a Suppresses Ras-Driven Mammary Tumorigenesis by Activation of c-Jun NH2-Terminal Kinase and p38 Stress Signaling Resulting in Apoptosis and Senescence

Cancer Research, 2006

The Gadd45 family of proteins is known to play a central role as cellular stress sensors that mod... more The Gadd45 family of proteins is known to play a central role as cellular stress sensors that modulate the response of mammalian cells to stress inflicted by physiologic and environmental stressors. Gadd45a was shown to be a direct target to the p53 and BRCA1 tumor suppressor genes, whose loss of function is known to play a vital role in breast carcinogenesis; however, the role of Gadd45a in the suppression of breast cancer remains unclear. To address this issue, Gadd45a-deficient mice were crossed with breast cancer prone mouse mammary tumor virus–Ras mice to generate mice that express activated Ras and differ in their Gadd45a status. Using this mouse model, we show that the loss of Gadd45a accelerates Ras-driven mammary tumor formation, exhibiting increased growth rates and a more aggressive histologic phenotype. Moreover, it is shown that accelerated Ras-driven tumor formation in the absence of Gadd45a results in both a decrease in apoptosis, which is linked to a decrease in c-Ju...

Research paper thumbnail of Gadd45 in the response of hematopoietic cells to genotoxic stress

Blood Cells, Molecules, and Diseases, 2007

Gadd45 genes have been implicated in stress signaling in response to physiological or environment... more Gadd45 genes have been implicated in stress signaling in response to physiological or environmental stressors, which results in either cell cycle arrest, DNA repair, cell survival and senescence, or apoptosis. Evidence accumulated implies that Gadd45 proteins function as stress sensors is mediated by a complex interplay of physical interactions with other cellular proteins that are implicated in cell cycle regulation and the response of cells to stress. These include PCNA, p21, cdc2/cyclinB1, and the p38 and JNK stress response kinases. Recently we have taken advantage of gadd45a and gadd45b deficient mice to determine the role gadd45a and gadd45b play in the response of bone marrow (BM) cells to genotoxic stress. Myeloid enriched BM cells from gadd45a and gadd45b deficient mice were observed to be more sensitive to ultraviolet radiation (UVC), VP-16 and daunorubicin (DNR) induced apoptosis compared to wild-type (wt) cells. The increased apoptosis in gadd45a and gadd45b deficient cells was evident also by enhanced activation of caspase-3 and PARP cleavage and decreased expression of cIAP-1, Bcl-2, Bcl-xL compared to wt cells. Reintroduction of gadd45 into gadd45 deficient BM cells restored the wt apoptotic phenotype. Both gadd45a and gadd45b deficient BM cells also displayed defective G2/M arrest following exposure to UVC and VP-16, but not to DNR, indicating the existence of different G2/M checkpoints that are either dependent or independent of gadd45. Additional work conducted in this laboratory has shown that in hematopoietic cells exposed to UV radiation gaddd45a and gadd45b cooperate to promote cell survival via two distinct signaling pathways involving activation of the Gadd45a-p38-NF-kB mediated survival pathway and Gadd45b mediated inhibition of the stress response MKK4-JNK pathway (59). These data reveal novel mechanisms that mediate the pro-survival functions of gadd45a and gadd45b in hematopoietic cells following UV irradiation. Taken together, these findings identify gadd45a and gadd45b as anti-apoptotic genes that increase the survival of hematopoietic cells following exposure to UV radiation and certain anticancer drugs. This knowledge should contribute to a greater understanding of the genetic events involved in the pathogenesis of different leukaemias and response of normal and malignant hematopoietic cells to chemo and radiation therapy. These observations set the stage to evaluate, in clinically relevant settings, the impact that the status of gadd45a and gadd45b might have on the efficacy of DNR or VP-16 in killing leukemic cells.

Research paper thumbnail of Egr-1 abrogates the block imparted by c-Myc on terminal M1 myeloid differentiation

Blood, 2005

Both deregulated growth and blocks in differentiation cooperate in the multistage process of leuk... more Both deregulated growth and blocks in differentiation cooperate in the multistage process of leukemogenesis. Thus, understanding functional interactions between genes that regulate normal blood cell development, including cell growth and differentiation, and how their altered expression contributes to leukemia, is important for rational drug design. Previously, we have shown that the zinc finger transcription factor Egr-1 plays a role in monocytic differentiation. Ectopic expression of Egr-1 in M1 myeloblastic leukemia cells was observed to activate the macrophage differentiation program in the absence of the differentiation inducer interleukin 6 (IL-6) and to promote terminal differentiation in its presence. In addition, we have shown that deregulated expression of the proto-oncogene c-myc blocks the myeloid terminal differentiation program. Here we show that restoring expression of Egr-1 in M1 cells that express deregulated c-Myc abrogates the c-Myc block in terminal differentiati...

Research paper thumbnail of Activation of the Jak3 pathway is associated with granulocytic differentiation of myeloid precursor cells

Blood, 2002

Jak3, a member of the Janus kinase family of cytoplasmic tyrosine kinases, is expressed at low le... more Jak3, a member of the Janus kinase family of cytoplasmic tyrosine kinases, is expressed at low levels in immature hematopoietic cells and its expression is dramatically up-regulated during the terminal differentiation of these cells. To better understand the role of Jak3 in myeloid cell development, we have investigated the role of Jak3 in myeloid cell differentiation using the 32Dcl3 cell system. Our studies show that Jak3 is a primary response gene for granulocyte colony-stimulating factor (G-CSF) and the accumulation of tyrosine phosphorylated Jak3 correlated with cell growth inhibition and terminal granulocytic differentiation in response to G-CSF. Ectopic overexpression of Jak3 in 32Dcl3 cells resulted in an acceleration of the G-CSF–induced differentiation program that was preceded by G1 cell cycle arrest, which was associated with the up-regulation of the cyclin-dependent kinase inhibitor p27Kip1 and down-regulation of Cdk2, Cdk4, Cdk6, and Cyclin E. In addition, ectopic over...

Research paper thumbnail of Transcriptional regulation of myeloid differentiation primary response (MyD) genes during myeloid differentiation is mediated by nuclear factor Y

Blood, 2002

To understand the molecular mechanism by which interleukin-6 (IL-6) regulates myeloid differentia... more To understand the molecular mechanism by which interleukin-6 (IL-6) regulates myeloid differentiation primary response (MyD) genes at the onset of M1 myeloid differentiation, we used JunB as a representative MyD gene to isolate and characterize IL-6 responsive elements. An IL-6 responsive element was localized between −65 and −52 of the JunB promoter (−65/−52 IL-6RE). By using antibody and oligonucleotide competition assays in electrophoretic mobility shift assay experiments, we have shown that the heterotrimeric transcription nuclear factor Y (NF-Y) complex binds to this element. A dominant-negative form of NF-YA, ectopically expressed in M1 cells, blocked NF-Y binding to the −65/−52 IL-6RE and reduced induction of JunB by IL-6. Furthermore, inhibition of NF-Y binding also reduced MyD gene induction by IL-6 and dampened the IL-6–induced M1 differentiation program. These findings are consistent with the observation that most MyD genes contain intact NF-Y binding motifs in their prom...

Research paper thumbnail of Progression of the myeloid differentiation program is dominant to transforming growth factor-beta 1-induced apoptosis in M1 myeloid leukemic cells

Blood, 1994

Hematopoiesis is a profound example of cell homeostasis that is regulated throughout life. This p... more Hematopoiesis is a profound example of cell homeostasis that is regulated throughout life. This process requires the participation of many factors, including positive and negative regulators of growth and differentiation, that determine survival, growth stimulation, differentiation, functional activation, and programmed cell death. Understanding the effects of multiple stimuli on specific cells at the molecular and cellular level is crucial towards understanding how the population of blood cells maintains a homeostatic state. Two appropriate stimuli for analysis, both of which are found in bone marrow, are differentiation-inducing cytokines, which induce terminal differentiation associated with growth arrest, ultimately culminating in programmed cell death, and transforming growth factor-beta 1 (TGF- beta 1), which induces rapid growth arrest and apoptosis of hematopoietic cells. Previously, we have shown, using M1 myeloblastic leukemic cells as a model system, that differentiation-...

Research paper thumbnail of Deregulated c-myb disrupts interleukin-6- or leukemia inhibitory factor-induced myeloid differentiation prior to c-myc: role in leukemogenesis

Molecular and Cellular Biology, 1992

The c-myb proto-oncogene is abundantly expressed in tissues of hematopoietic origin, and changes ... more The c-myb proto-oncogene is abundantly expressed in tissues of hematopoietic origin, and changes in endogenous c-myb genes have been implicated in both human and murine hematopoietic tumors. c-myb encodes a DNA-binding protein capable of trans-activating the c-myc promoter. Suppression of both of these proto-oncogenes was shown to occur upon induction of terminal differentiation but not upon induction of growth inhibition in myeloid leukemia cells. Myeloblastic leukemia M1 cells that can be induced for terminal differentiation with the physiological hematopoietic inducers interleukin-6 and leukemia inhibitory factor were genetically manipulated to constitutively express a c-myb transgene. By using immediate-early to late genetic and morphological markers, it was shown that continuous expression of c-myb disrupts the genetic program of myeloid differentiation at a very early stage, which precedes the block previously shown to be exerted by deregulated c-myc, thereby indicating that t...

Research paper thumbnail of The proto-oncogene c-myc in hematopoietic development and leukemogenesis

Oncogene, 2002

expression during dierentiation, including C/EBPa, CTCF, BLIMP-1, and RFX1. Alterations in the ex... more expression during dierentiation, including C/EBPa, CTCF, BLIMP-1, and RFX1. Alterations in the expression and/or function of these transcription factors, or of the c-Myc and Max interacting proteins, such as MM-1 and Mxi1, can in¯uence the neoplastic process. Understanding how c-Myc controls cellular phenotypes, including the leukemic phenotype, should provide novel tools for designing drugs to promote dierentiation and/ or apoptosis of leukemic cells.

Research paper thumbnail of The proto-oncogene c-myc and apoptosis

Oncogene, 1998

Deregulated expression of c-Myc not only promotes proliferation, but also can either induce or se... more Deregulated expression of c-Myc not only promotes proliferation, but also can either induce or sensitize cells to apoptosis. Inappropriate expression of c-Myc under conditions which inhibit growth and down-regulate endogenous c-Myc expression, including serum deprivation and exposure to cytotoxic agents including the anticancer agents vinblastine, etoposide, Ara-C, and nocodazole, usually results in programmed cell death in many dierent cell types. Also, inappropriate Myc expression is associated with an apoptotic response elicited by induction of dierentiation. The proapoptotic property of c-Myc requires an intact N-terminal transactivation domain and bHLHZip domain, as well as interaction with Max, thereby implicating c-Myc target genes in this apoptotic process. Although some target genes, namely cdc25A and ODC, have been shown to participate in Myc-mediated apoptosis, no target gene has yet been identi®ed which is essential for this apoptotic response. It is possible that the response of cells inappropriately expressing c-Myc is due not only to the growth arrest signals per se, but also to signals elicited by speci®c growth inhibitors in the context of a particular biological setting. Also regulating the response of the cells is expression of other oncogenes and tumor suppressor genes, as well as paracrine and autocrine survival factors. Apoptosis associated with inappropriate Myc expression limits the tumorigenic eect of the cmyc proto-oncogene. Mechanisms which inhibit apoptosis should enhance or promote tumorigenesis.

Research paper thumbnail of p53-independent apoptosis associated with c-Myc-mediated block in myeloid cell differentiation

Oncogene, 2000

Previously we have shown that deregulated expression of c-myc in M1 myeloid leukemic cells blocke... more Previously we have shown that deregulated expression of c-myc in M1 myeloid leukemic cells blocked IL-6induced dierentiation and its associated growth arrest; however, the cells proliferated at a signi®cantly reduced rate compared to untreated cells. The basis for the increased doubling time of IL-6-treated M1myc cells was found to be due to the induction of a p53-independent apoptotic pathway. The apoptotic response was not completely penetrant; in the same population of cells both proliferation and apoptosis were continuously ongoing. Down-regulation of Bcl-2 was insucient to account for the apoptotic response, since deregulated expression of Bcl-2 delayed, but did not block, the onset of apoptosis. Furthermore, our results indicated that the IL-6-induced partial hypophosphorylation of the retinoblastoma gene product (Rb), observed in M1myc cells, was not responsible for the apoptotic response. Finally, the ®ndings in M1 cells were extended to myeloid cells derived from the bone marrow of wild type and p53-de®cient mice, where the deregulated expression of c-myc was also shown to block terminal dierentiation and induce apoptosis independent of p53. These ®ndings provide new insights into how myc participates in the neoplastic process, and how additional mutations can promote more aggressive tumors.

Research paper thumbnail of Hematopoietic cells from Gadd45a- and Gadd45b-deficient mice are sensitized to genotoxic-stress-induced apoptosis

Oncogene, 2005

Gadd45a, gadd45b and gadd45g (Gadd45/MyD118/CR6) are genes that are rapidly induced by genotoxic ... more Gadd45a, gadd45b and gadd45g (Gadd45/MyD118/CR6) are genes that are rapidly induced by genotoxic stress. However, the exact function of Gadd45 proteins in the response of mammalian cells to genotoxic stress is unclear. Here, advantage was taken of gadd45a-and gadd45b-deficient mice to determine the role gadd45a and gadd45b play in the response of bone marrow (BM) cells to genotoxic stress. BM cells from gadd45a-and gadd45bdeficient mice were observed to be more sensitive to ultraviolet radiation chemotherapy (UVC), VP-16 and daunorubicin (DNR)-induced apoptosis compared to wildtype (wt) cells. The increased apoptosis in gadd45a-and gadd45b-deficient cells was evident also by enhanced activation of caspase-3 and poly-ADP-ribose polymerase cleavage and decreased expression of c-inhibitor of apoptotic protein-1, Bcl-2, Bcl-xL compared to wt cells. Reintroduction of gadd45 into gadd45-deficient BM cells restored the wt apoptotic phenotype. Both gadd45a-and gadd45b-deficient BM cells also displayed defective G2/M arrest following exposure to UVC and VP-16, but not to DNR, indicating the existence of different G2/M checkpoints that are either dependent or independent of gadd45. Taken together, these findings identify gadd45a and gadd45b as antiapoptotic genes that increase the survival of hematopoietic cells following exposure to UV radiation and certain anticancer drugs.

Research paper thumbnail of Apoptotic signaling by c-MYC

Oncogene, 2008

c-MYC has a pivotal function in growth control, differentiation and apoptosis, and its abnormal e... more c-MYC has a pivotal function in growth control, differentiation and apoptosis, and its abnormal expression is associated with many tumors. Overexpression of c-MYC sensitizes cells to apoptosis by a variety of stimuli. The decision of a cell to undergo apoptosis and how this apoptotic response is regulated by c-MYC depends on the specific cell type and the physiological status of the cell. Multiple cooperating molecular pathways of cell survival and apoptosis determine whether a cell lives or dies, and understanding how c-MYC interfaces with these pathways to influence the survival of cells is important to understand normal and abnormal development, tumor initiation and progression, and response of tumors to different treatment regimens. This article will provide an overview of the function of the tumor suppressor gene product p53 in the c-MYC-mediated apoptotic response and how c-MYC amplifies the intrinsic mitochondrial pathway and triggers and/or amplifies the death receptor pathways. Finally, a model for how deregulated c-MYC prematurely triggers the normal apoptotic response associated with terminal myeloid differentiation while also blocking the differentiation program is presented.

Research paper thumbnail of Sequence of MyD116 cDNA: a novel myeloid differentiation primary response gene induced by IL6

Nucleic Acids Research, 1990

Research paper thumbnail of Interferon regulatory factor-1 myelodysplasia and leukemia

Research paper thumbnail of Gadd45 in stress signaling

Journal of Molecular Signaling, 2008

Research paper thumbnail of Gadd45β is an inducible coactivator of transcription that facilitates rapid liver growth in mice

Journal of Clinical Investigation, 2011

Research paper thumbnail of Gadd45a stress signaling regulates sFlt-1 expression in preeclampsia

Journal of Cellular Physiology, 2009

Preeclampsia, which affects approximately 5-8% of all pregnancies and is one of the leading cause... more Preeclampsia, which affects approximately 5-8% of all pregnancies and is one of the leading causes of maternal and fetal morbidity and mortality, is a pregnancy induced complex of multiple pathological changes, including elevated blood pressure, proteinuria and edema manifested after 20 weeks gestation. There is growing evidence that placental stresses during pregnancy, notably hypoxia, and an increase in circulating soluble Flt-1 (sFlt-1) are important in the etiopathogenesis of preeclampsia. How placental stress results in elevated sFlt-1 expression is currently unknown. Here we provide novel data implicating the Gadd45a stress sensor protein as an upstream modulator of pathophysiological changes observed in preeclampsia. It is shown that Gadd45a expression and activation of its downstream effector p38 kinase are elevated in preeclamptic placentas compared to non-preeclamptic controls, and correlate with elevated sFlt-1. Furthermore, a regulatory loop is demonstrated where stress, including hypoxia, IL-6 or hypertonic stress, caused induction of Gadd45a, leading to p38 activation and ultimately increasing sFlt-1 secretion in endothelial cells. These data provide a compelling working frame to further test the role of Gadd45 stress sensors in the etiology of preeclampsia, and set the stage for considering novel therapeutic regimens, including p38 inhibitors, for treatment of preeclampsia.

Research paper thumbnail of Preeclampsia-associated stresses activate Gadd45a signaling and sFlt-1 in placental explants

Journal of Cellular Physiology, 2012

Accumulating evidence suggests that placental stresses during pregnancy can play an important rol... more Accumulating evidence suggests that placental stresses during pregnancy can play an important role in the pathogenesis of preeclampsia. A common signal pathway that senses and converts placental stresses into intracellular stress response may be contributing to this pathology. Based on our previous findings, we extended our investigation to establish that Gadd45a stress signaling regulates sFlt-1 levels, particularly in placenta, when exposed to various preeclampsia-associated stresses including AT-1 receptor agonist (Angiotensin II), hypoxia, and inflammatory cytokines. Using a placental explant model, we found that Gadd45a was induced in response to all the preeclampsia stresses stated above. Although stress induced Gadd45a was associated with the activation of its downstream effectors phospho-p38 and phospho-JNK, the subsequent regulation of sFlt-1 levels occurred through either one of these effectors, but not both. These observations indicate that Gadd45a signaling may work as a hub connecting placental stresses and the pathogenesis of preeclampsia. It also provides evidence to justify testing the role of Gadd45 in the etiology of preeclampsia using in vivo mouse (i.e., Gadd45a null mice) models.

Research paper thumbnail of Distinct mechanisms are utilized to induce stress sensorgadd45bby different stress stimuli

Journal of Cellular Biochemistry, 2009

The GADD45 family of proteins consists of three small proteins, GADD45A, GADD45B, and GADD45G, im... more The GADD45 family of proteins consists of three small proteins, GADD45A, GADD45B, and GADD45G, implicated in modulating the cellular response to genotoxic/physiological stressors. Despite similarities in sequence, structure and function, each gadd45 gene is induced differentially by different stress stimuli. Studies on stress-mediated induction of the gadd45 genes have predominantly focused on gadd45a, with knowledge of gadd45b and gadd45g regulation lacking. To generate a more complete understanding of the regulation of gadd45 genes, a comprehensive analysis of stress-mediated induction of human gadd45b has been carried out using human RKO colorectal carcinoma cells as a model system. Novel data indicate that gadd45b induction in RKO cells is regulated by distinct mechanisms in a stress-specific manner. Methylmethane sulfonate (MMS), a DNA alkylating agent, induces gadd45b transcription through a cohort of both constitutive and inducible bound factors, including NFY, Sp1 and Egr1. In contrast, in a hyperosmotic environment generated with sorbitol, gadd45b mRNA is induced exclusively by mRNA stabilization. These findings indicate that the stress-mediated induction of gadd45b is largely distinct from gadd45a. Furthermore, data obtained provide a novel paradigm for stress-response gene induction, indicating that gadd45b induction by distinct stressors, in the same cell type and under the same experimental settings, is differentially regulated at the level of mRNA transcription or mRNA stability. Importantly, this study also provides the groundwork to further examine the regulation of gadd45b expression in in vivo settings using animal models and tissues obtained from normal individuals and cancer patients prior to and after chemotherapeutic intervention.

Research paper thumbnail of Regulation of gene expression by tumor promoters. II. Control of cell shape and developmental programs for macrophages and granulocytes in human myeloid leukemic cells

International Journal of Cancer, 1981

Regulation of the developmental programs for macrophages and granulocytes has been analysed, usin... more Regulation of the developmental programs for macrophages and granulocytes has been analysed, using two-dimensional gel electrophoresis of the cytoplasmic protein changes, in a human myeloid leukemic cell line (HL60) that can be induced to differentiate to macrophages by the macrophage and granulocyte-inducing (MGI) protein and the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA), and to granulocytes by dimethylsulfoxide (DMSO). Studies on the protein changes induced by the different inducers showed a similar developmental program for macrophage differentiation induced by MGI or TPA, which differed from the beginning from the granulocyte program induced by DMSO. Comparison with normal cells from human peripheral blood has shown that the develop mental programs induced in the HL60 cells are relevant 'Part I in this series is Lotem and Sachs (1979).

Research paper thumbnail of Gadd45a Suppresses Ras-Driven Mammary Tumorigenesis by Activation of c-Jun NH2-Terminal Kinase and p38 Stress Signaling Resulting in Apoptosis and Senescence

Cancer Research, 2006

The Gadd45 family of proteins is known to play a central role as cellular stress sensors that mod... more The Gadd45 family of proteins is known to play a central role as cellular stress sensors that modulate the response of mammalian cells to stress inflicted by physiologic and environmental stressors. Gadd45a was shown to be a direct target to the p53 and BRCA1 tumor suppressor genes, whose loss of function is known to play a vital role in breast carcinogenesis; however, the role of Gadd45a in the suppression of breast cancer remains unclear. To address this issue, Gadd45a-deficient mice were crossed with breast cancer prone mouse mammary tumor virus–Ras mice to generate mice that express activated Ras and differ in their Gadd45a status. Using this mouse model, we show that the loss of Gadd45a accelerates Ras-driven mammary tumor formation, exhibiting increased growth rates and a more aggressive histologic phenotype. Moreover, it is shown that accelerated Ras-driven tumor formation in the absence of Gadd45a results in both a decrease in apoptosis, which is linked to a decrease in c-Ju...

Research paper thumbnail of Gadd45 in the response of hematopoietic cells to genotoxic stress

Blood Cells, Molecules, and Diseases, 2007

Gadd45 genes have been implicated in stress signaling in response to physiological or environment... more Gadd45 genes have been implicated in stress signaling in response to physiological or environmental stressors, which results in either cell cycle arrest, DNA repair, cell survival and senescence, or apoptosis. Evidence accumulated implies that Gadd45 proteins function as stress sensors is mediated by a complex interplay of physical interactions with other cellular proteins that are implicated in cell cycle regulation and the response of cells to stress. These include PCNA, p21, cdc2/cyclinB1, and the p38 and JNK stress response kinases. Recently we have taken advantage of gadd45a and gadd45b deficient mice to determine the role gadd45a and gadd45b play in the response of bone marrow (BM) cells to genotoxic stress. Myeloid enriched BM cells from gadd45a and gadd45b deficient mice were observed to be more sensitive to ultraviolet radiation (UVC), VP-16 and daunorubicin (DNR) induced apoptosis compared to wild-type (wt) cells. The increased apoptosis in gadd45a and gadd45b deficient cells was evident also by enhanced activation of caspase-3 and PARP cleavage and decreased expression of cIAP-1, Bcl-2, Bcl-xL compared to wt cells. Reintroduction of gadd45 into gadd45 deficient BM cells restored the wt apoptotic phenotype. Both gadd45a and gadd45b deficient BM cells also displayed defective G2/M arrest following exposure to UVC and VP-16, but not to DNR, indicating the existence of different G2/M checkpoints that are either dependent or independent of gadd45. Additional work conducted in this laboratory has shown that in hematopoietic cells exposed to UV radiation gaddd45a and gadd45b cooperate to promote cell survival via two distinct signaling pathways involving activation of the Gadd45a-p38-NF-kB mediated survival pathway and Gadd45b mediated inhibition of the stress response MKK4-JNK pathway (59). These data reveal novel mechanisms that mediate the pro-survival functions of gadd45a and gadd45b in hematopoietic cells following UV irradiation. Taken together, these findings identify gadd45a and gadd45b as anti-apoptotic genes that increase the survival of hematopoietic cells following exposure to UV radiation and certain anticancer drugs. This knowledge should contribute to a greater understanding of the genetic events involved in the pathogenesis of different leukaemias and response of normal and malignant hematopoietic cells to chemo and radiation therapy. These observations set the stage to evaluate, in clinically relevant settings, the impact that the status of gadd45a and gadd45b might have on the efficacy of DNR or VP-16 in killing leukemic cells.

Research paper thumbnail of Egr-1 abrogates the block imparted by c-Myc on terminal M1 myeloid differentiation

Blood, 2005

Both deregulated growth and blocks in differentiation cooperate in the multistage process of leuk... more Both deregulated growth and blocks in differentiation cooperate in the multistage process of leukemogenesis. Thus, understanding functional interactions between genes that regulate normal blood cell development, including cell growth and differentiation, and how their altered expression contributes to leukemia, is important for rational drug design. Previously, we have shown that the zinc finger transcription factor Egr-1 plays a role in monocytic differentiation. Ectopic expression of Egr-1 in M1 myeloblastic leukemia cells was observed to activate the macrophage differentiation program in the absence of the differentiation inducer interleukin 6 (IL-6) and to promote terminal differentiation in its presence. In addition, we have shown that deregulated expression of the proto-oncogene c-myc blocks the myeloid terminal differentiation program. Here we show that restoring expression of Egr-1 in M1 cells that express deregulated c-Myc abrogates the c-Myc block in terminal differentiati...

Research paper thumbnail of Activation of the Jak3 pathway is associated with granulocytic differentiation of myeloid precursor cells

Blood, 2002

Jak3, a member of the Janus kinase family of cytoplasmic tyrosine kinases, is expressed at low le... more Jak3, a member of the Janus kinase family of cytoplasmic tyrosine kinases, is expressed at low levels in immature hematopoietic cells and its expression is dramatically up-regulated during the terminal differentiation of these cells. To better understand the role of Jak3 in myeloid cell development, we have investigated the role of Jak3 in myeloid cell differentiation using the 32Dcl3 cell system. Our studies show that Jak3 is a primary response gene for granulocyte colony-stimulating factor (G-CSF) and the accumulation of tyrosine phosphorylated Jak3 correlated with cell growth inhibition and terminal granulocytic differentiation in response to G-CSF. Ectopic overexpression of Jak3 in 32Dcl3 cells resulted in an acceleration of the G-CSF–induced differentiation program that was preceded by G1 cell cycle arrest, which was associated with the up-regulation of the cyclin-dependent kinase inhibitor p27Kip1 and down-regulation of Cdk2, Cdk4, Cdk6, and Cyclin E. In addition, ectopic over...

Research paper thumbnail of Transcriptional regulation of myeloid differentiation primary response (MyD) genes during myeloid differentiation is mediated by nuclear factor Y

Blood, 2002

To understand the molecular mechanism by which interleukin-6 (IL-6) regulates myeloid differentia... more To understand the molecular mechanism by which interleukin-6 (IL-6) regulates myeloid differentiation primary response (MyD) genes at the onset of M1 myeloid differentiation, we used JunB as a representative MyD gene to isolate and characterize IL-6 responsive elements. An IL-6 responsive element was localized between −65 and −52 of the JunB promoter (−65/−52 IL-6RE). By using antibody and oligonucleotide competition assays in electrophoretic mobility shift assay experiments, we have shown that the heterotrimeric transcription nuclear factor Y (NF-Y) complex binds to this element. A dominant-negative form of NF-YA, ectopically expressed in M1 cells, blocked NF-Y binding to the −65/−52 IL-6RE and reduced induction of JunB by IL-6. Furthermore, inhibition of NF-Y binding also reduced MyD gene induction by IL-6 and dampened the IL-6–induced M1 differentiation program. These findings are consistent with the observation that most MyD genes contain intact NF-Y binding motifs in their prom...