Identification of the Hypoxia-Inducible Factor 1α-Responsive HGTD-P Gene as a Mediator in the Mitochondrial Apoptotic Pathway

Abstract

Hypoxia-inducible factor 1␣ (HIF-1␣) controls the cellular responses to hypoxia, activating transcription of a range of genes involved in adaptive processes such as increasing glycolysis and promoting angiogenesis. However, paradoxically, HIF-1␣ also participates in hypoxic cell death. Several gene products, such as BNip3, RTP801, and Noxa, were identified as HIF-1␣-responsive proapoptotic proteins, but the complicated hypoxic cell death pathways could not be completely explained by the few known genes. Moreover, molecules linking the proapoptotic signals of HIF-1␣ directly to mitochondrial permeability transition are missing. In this work, we report the identification of an HIF-1␣-responsive proapoptotic molecule, HGTD-P. Its expression was directly regulated by HIF-1␣ through a hypoxia-responsive element on the HGTD-P promoter region. When overexpressed, HGTD-P was localized to mitochondria and facilitated apoptotic cell death via typical mitochondrial apoptotic cascades, including permeability transition, cytochrome c release, and caspase 9 activation. In the process of permeability transition induction, the death-inducing domain of HGTD-P physically interacted with the voltage-dependent anion channel. In addition, suppression of HGTD-P expression by small interfering RNA or antisense oligonucleotides protected against hypoxic cell death. Taken together, our data indicate that HGTD-P is a new HIF-1␣-responsive proapoptotic molecule that activates mitochondrial apoptotic cascades.Hypoxia is the most common cellular stress, with important pathological implications in many disease processes, including cerebral ischemia and myocardial infarction (15). Cells in hypoxia express a variety of adaptive or death gene products to satisfy altered metabolic demands or to remove irreversibly damaged cells (4). Adaptive genes allow increased O 2 delivery to the peripheral tissues through vasodilation and angiogenesis, facilitate ATP synthesis through the glycolytic pathway, or reduce proliferative rates (12,29,30). In addition, antiapoptotic Bcl-2 family proteins prevent hypoxic cell death by stabilization of mitochondria or inhibition of caspase activation (28). However, in the case of severe hypoxic damage beyond the cell's adaptive capability, death-promoting genes are expressed, resulting in necrosis or apoptosis (4).Hypoxia-inducible factor 1␣ (HIF-1␣) is known to be a master transactivator in hypoxia, which is induced, stabilized, and translocated to the nucleus to regulate the transcription of a variety of genes involved in adaptive responses such as increased O 2 delivery and angiogenesis (5, 31). While HIF-1␣ participates largely in adaptive responses to hypoxia, paradoxically it also mediates hypoxic cell death via the interaction with p53 or modulation of its effector expression (3, 14, 17). Although several proapoptotic genes induced by HIF-1␣ have been reported (3, 17, 37), the hypoxic cell death pathway might be too complicated to be explained by the few known genes.To better understand the molecular mechanism...

Down-regulation of cobalt-induced HIF-1α expression correlates with cell proliferation and apoptosis in human gastric carcinoma cells

“…An up-regulation of the Bcl-xL expression occurred in the two cell types in correlation with the increase of the HIF-1α expression as well as a higher cell viability, while both cell types showed a down-regulation of Bcl-xL and an upregulation of Bax and cleaved-caspase-9 expression and an increase in the apoptotic index with the decrease of HIF-1α. These patterns were similar to that of the MKN-1 cells (15), supporting the correlation between the HIF-1α expression and apoptosis suggested by other reports (19,20).…”

Selective silencing of the hypoxia-inducible factor 1 target gene BNIP3 by histone deacetylation and methylation in colorectal cancer

“…We have also shown that knockdown of endogenous BNIP3 in LS174T provides significant protection from hypoxically induced cell death. Less than 100% protection from hypoxic cell death in LS174T may be attributable to incomplete knockdown of the BNIP3 protein, or the result of hypoxic induction of other functional mediators of cell death of which several have been identified including Noxa and HGTD-P (Lee et al, 2004). Nonetheless, these functional data support the notion that hypoxic upregulation of BNIP3 in CRC cells significantly contributes to cell death.…”

Motexafin Gadolinium and Zinc Induce Oxidative Stress Responses and Apoptosis in B-Cell Lymphoma Lines

“…HIF-1 is often considered to be essential for tumor growth and, indeed, its inhibition is the subject of ongoing drug development activities (44). However, under the appropriate conditions, HIF-1 activation can have negative consequences for tumor growth by induction of targets linked to apoptosis, such as BNIP3, E2IG5, PMAIP1, and DDIT4, or through metabolic alteration of cells in the low nutrient context of the tumor microenvironment (45).…”