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ABSTRACT: Heterodimeric transcription factor hypoxia inducible factor-1 (HIF-1) functions as a master regulator of oxygen homeostasis in almost all nucleated mammalian cells. The fundamental process adapted to cellular oxygen alteration largely depends on the refined regulation on its alpha subunit, HIF-1α. Recent studies have unraveled expanding and critical roles of HIF-1α, involving in a multitude of developmental, physiological, and pathophysiological processes. This review will focus on the current knowledge of HIF-1α-targeting genes and its interacting proteins, as well as the concomitant functional relationships between them.
International journal of biochemistry and molecular biology. 01/2012; 3(2):165-78.
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ABSTRACT: Autophagy is a highly conserved, closely regulated homeostatic cellular activity that allows for the bulk degradation of long-lived proteins and cytoplasmic organelles. Its roles in cancer initiation and progression and in determining the response of tumor cells to anticancer therapy are complicated, and only limited investigation has been conducted on the potential significance of autophagy in the pathogenesis and therapeutic response of acute myeloid leukemia. Here we demonstrate that the inducible or transfected expression of the acute promyelocytic leukemia (APL)-specific PML-RARα, but not PLZF-RARα or NPM-RARα, fusion protein upregulates constitutive autophagy activation in leukemic and nonleukemic cells, as evaluated by hallmarks for autophagy including transmission electron microscopy. The significant increase in autophagic activity is also found in the leukemic cells-infiltrated bone marrow and spleen from PML-RARα-transplanted leukemic mice. The autophagy inhibitor 3-methyladenine significantly abrogates the autophagic events upregulated by PML-RARα, while the autophagic flux assay reveals that the fusion protein induces autophagy by increasing the on-rate of autophagic sequestration. Furthermore, this modulation of autophagy by PML-RARα is possibly mediated by a decreased activation of the Akt/mTOR pathway. Finally, we also show that autophagy contributes to the anti-apoptotic function of the PML-RARα protein. Given the critical role of the PML-RARα oncoprotein in APL pathogenesis, this study suggests an important role of autophagy in the development and treatment of this disease.
Autophagy 10/2011; 7(10):1132-44. · 7.45 Impact Factor
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ABSTRACT: Galectin-1 is a member of the galectin family and has a high affinity for galactose and N-acetylglucosamine moieties of glycoproteins. It mediates multiple signal transduction pathways to modulate cellular proliferation, survival, differentiation, and migration. However, the mechanisms for the regulation of its expression remain greatly elusive. We reported previously that galectin-1 is a direct target of the hypoxia-inducible factor 1 (HIF-1), a key heterodimeric transcriptional factor for the cellular response to hypoxia. Here we show that CCAAT/enhancer binding protein α (C/EBPα), a critical transcriptional factor for hematopoietic cell differentiation, can directly activate galectin-1 through binding to the -48 to -42 bp region of its promoter. Based on the physical interaction of C/EBPα and HIF-1α, the synergistic transcriptional activity of C/EBPα and HIF-1α on the promoter of the galectin-1 gene is also found by chromatin immunoprecipitation (ChIP), ChIP followed by ChIP (ChIP-reChIP), and luciferase assay. Moreover, knockdown or chemical inhibition of galectin-1 partially blocks the differentiation induced by HIF-1α or C/EBPα, which can be rescued by recombinant galectin-1. These discoveries would shed new insights on the mechanisms for galectin-1 expression regulation and HIF-1α- and C/EBPα-induced leukemic cell differentiation.
Journal of Biological Chemistry 08/2011; 286(42):36808-19. · 4.77 Impact Factor
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ABSTRACT: The expression of galectin-1, one of the most important lectins participating in the malignant tumor development, has been shown to be regulated by hypoxia, but its exact mechanism remains elusive. Here, we find that ectopically expressed hypoxia-inducible factor (HIF) 1alpha protein, an oxygen-sensitive subunit of HIF-1 that is a master factor for cellular response to hypoxia, significantly increases galectin-1 expression in both messenger RNA and protein levels in all four colorectal cancer (CRC) cell lines tested. However, hypoxia-induced galectin-1 expression cannot be seen in sentrin/SUMO-specific protease 1 homozygous-null mouse embryonic fibroblasts that fail to accumulate HIF-1alpha protein. Furthermore, silence of HIF-1alpha or HIF-1beta expression by specific short hairpin RNAs (shRNAs) antagonizes hypoxia-induced galectin-1 expression. All these results propose that galectin-1 is a direct target of transcriptional factor HIF-1. Applying luciferase reporter assay and chromatin immunoprecipitation, we identify that two hypoxia-responsive elements located at -441 to -423 bp upstream to transcriptional start site of galectin-1 gene are essential for HIF-1-mediated galectin-1 expression. Finally, the knockdown of galectin-1 by its specific shRNA can significantly reduce hypoxia-induced invasion and migration of CRC cell line, and the ectopic expression of galectin-1 can remarkably restore invasion and migration abilities of HIF-1alpha-knocked SW620 cells, proposing that galectin-1 mediates the HIF-1-induced migration and invasion of CRC cells during hypoxia. Taken together, our results shed new light for understanding mechanism for hypoxia/HIF-1-mediated migration/invasion of CRC cells.
Carcinogenesis 08/2010; 31(8):1367-75. · 5.70 Impact Factor
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ABSTRACT: Background
The precise regulation and maintenance of balance between cell proliferation, differentiation and death in metazoan are critical for tissue homeostasis. CCAAT/enhancer-binding protein alpha (C/EBPα) has been implicated as a key regulator of differentiation and proliferation in various cell types. Here we investigated the potential dynamic change and role of C/EBPα protein during apoptosis induction.
Methodology/Principal Findings
Upon onset of apoptosis induced by various kinds of inducers such as NSC606985, etoposide and others, C/EBPα expression presented a profound down-regulation in leukemic cell lines and primary cells via induction of protein degradation and inhibition of transcription, as assessed respectively by cycloheximide inhibition test, real-time quantitative RT-PCR and luciferase reporter assay. Applying chemical inhibition, forced expression of dominant negative mutant and catalytic fragment (CF) of protein kinase Cdelta (PKCδ), which was proteolytically activated during apoptosis induction tested, we showed that the active PKCδ protein contributed to the increased degradation of C/EBPα protein. Three specific proteasome inhibitors antagonized C/EBPα degradation during apoptosis induction. More importantly, ectopic expression of PKCδ-CF stimulated the ubiquitination of C/EBPα protein, while the chemical inhibition of PKCδ action significantly inhibited the enhanced ubiquitination of C/EBPα protein under NSC606985 treatment. Additionally, silencing of C/EBPα expression by small interfering RNAs enhanced, while inducible expression of C/EBPα inhibited NSC606985/etoposide-induced apoptosis in leukemic cells.
Conclusions/Significance
These observations indicate that the activation of PKCδ upon apoptosis results in the increased proteasome-dependent degradation of C/EBPα, which partially contributes to PKCδ-mediated apoptosis.
PLoS ONE 08/2009; 4(8). · 4.09 Impact Factor
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ABSTRACT: Hypoxia-inducible factor-1 (HIF-1), consisting of oxygen-sensitive HIF-1alpha and constitutively expressed HIF-1beta subunits, is a master transcriptional activator for cellular response to hypoxia. To explore direct HIF-1 targets, here we used differential gel electrophoresis (DIGE) to compare the HIF-1-regulated proteins between leukemic U937T-cell line with and without conditional induction of HIF-1alpha protein by tetracycline-off system. Among the upregulated proteins identified, mRNA levels of annexin A1, macrophage-capping protein (CapG), S100 calcium-binding protein A4 (S100A4), S100A11, acyl-CoA-binding protein and calcyclin-binding protein also increased. The expressions of the annexin A1, CapG and S100A4 genes were significantly induced by hypoxia in five adherent cell lines tested besides U937 cells, while their expressions were blocked by the short hairpin RNA specifically against HIF-1alpha. Further luciferase reporter assay and chromatin immunoprecipitation showed that HIF-1alpha directly bound to three hypoxia-responsive elements located at intron 1 of S100A4 gene and hypoxia-responsive element at -350 to -346 of CapG gene, which are essential for HIF-1-induced expression. Additionally, the role of S100A4 expression in migration and invasion of cancer cells were also confirmed. These findings would provide new sights for understanding the molecular mechanisms underlying HIF-1 action.
Proteomics 08/2009; 9(15):3901-12. · 4.43 Impact Factor
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ABSTRACT: The precise regulation and maintenance of balance between cell proliferation, differentiation and death in metazoan are critical for tissue homeostasis. CCAAT/enhancer-binding protein alpha (C/EBPalpha) has been implicated as a key regulator of differentiation and proliferation in various cell types. Here we investigated the potential dynamic change and role of C/EBPalpha protein during apoptosis induction.
Upon onset of apoptosis induced by various kinds of inducers such as NSC606985, etoposide and others, C/EBPalpha expression presented a profound down-regulation in leukemic cell lines and primary cells via induction of protein degradation and inhibition of transcription, as assessed respectively by cycloheximide inhibition test, real-time quantitative RT-PCR and luciferase reporter assay. Applying chemical inhibition, forced expression of dominant negative mutant and catalytic fragment (CF) of protein kinase Cdelta (PKCdelta), which was proteolytically activated during apoptosis induction tested, we showed that the active PKCdelta protein contributed to the increased degradation of C/EBPalpha protein. Three specific proteasome inhibitors antagonized C/EBPalpha degradation during apoptosis induction. More importantly, ectopic expression of PKCdelta-CF stimulated the ubiquitination of C/EBPalpha protein, while the chemical inhibition of PKCdelta action significantly inhibited the enhanced ubiquitination of C/EBPalpha protein under NSC606985 treatment. Additionally, silencing of C/EBPalpha expression by small interfering RNAs enhanced, while inducible expression of C/EBPalpha inhibited NSC606985/etoposide-induced apoptosis in leukemic cells.
These observations indicate that the activation of PKCdelta upon apoptosis results in the increased proteasome-dependent degradation of C/EBPalpha, which partially contributes to PKCdelta-mediated apoptosis.
PLoS ONE 02/2009; 4(8):e6552. · 4.09 Impact Factor
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ABSTRACT: Autophagy is a highly conserved, closely-regulated homeostatic cellular activity that allows for the bulk degradation of long-lived proteins and cytoplasmic organelles. Its roles in cancer initiation and progression and in determining the response of tumor cells to anticancer therapy are complicated, and the potential significance of autophagy in the pathogenesis and therapeutic response of acute myeloid leukemia has a little investigation. Here, we demonstrate that induction of acute promyelocytic leukemia (APL)-specific PML-RARα but not PLZF-RARα/NPM-RARα fusion protein up-regulates constitutive autophagic activation in leukemic and non-leukemic cells. The significant increase of autophagic activity is also found in the leukemic cells infiltrated bone marrow, spleen and liver from PML-RARα-transgenic APL syngenic transplanted mice. The specific autophagy inhibitor 3-methyladenine significantly abrogates PML-RARα-increased autophagy, while the autophagic flux assay reveals that the fusion protein induces autophagy in the manner of on-rate increase. Furthermore, this autophagy modulation of PML-RARα is possibly mediated by decreased activation of Akt/mTOR pathway. Given the critical role of the PML-RARα oncoprotein in APL pathogenesis, this study would shed new sights for an important role of autophagy in the development and treatment of this disease.
Nature Precedings.
