The Role of Mitochondria in the Regulation of Hypoxia-inducible Factor 1 Expression during Hypoxia

Abstract

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor that regulates transcriptional activation of several genes responsive to the lack of oxygen, including erythropoietin, vascular endothelial growth factor, glycolytic enzymes, and glucose transporters. Because the involvement of mitochondria in the regulation of HIF-1 has been postulated, we tested the effects of mitochondrial electron transport chain deficiency on HIF-1 protein expression and DNA binding in hypoxic cells. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) inhibits electron transport chain at the level of complex I. MPTP is first converted to a pharmacologically active metabolite 1-methyl-4-phenylpyridinum (MPP؉). MPP؉ effectively inhibited both complex I activity and hypoxic accumulation of HIF-1␣ protein in dopaminergic cell lines PC12 and CATH.a. In C57BL/6 mice, a single dose of MPTP (15 mg/kg, intraperitoneal) inhibited complex I activity and HIF-1␣ protein accumulation in the striatum in response to a subsequent hypoxic challenge (8% O 2 , 4 h). In a genetic model system, 40% complex I-inhibited human-ape xenomitochondrial cybrids, hypoxic induction of HIF-1␣ was severely reduced, and HIF-1 DNA binding was diminished. However, succinate, the mitochondrial complex II substrate, restored the hypoxic response in cybrid cells, suggesting that electron transport chain activity is required for activation of HIF-1. A partial complex I deficiency and a mild reduction in intact cell oxygen consumption effectively prevented hypoxic induction of HIF-1␣ protein.Mammalian cells are able to sense decreased oxygen availability and activate adaptational responses including transcriptional activation of several hypoxia-inducible genes: erythropoietin, vascular endothelial growth factor, glycolytic enzymes, and glucose transporters. This allows increased O 2 delivery through enhanced erythropoiesis, angiogenesis and metabolic adaptations that facilitate glycolytic ATP production (reviewed in Ref. 1). Transcriptional activation of the erythropoietin gene is controlled via an enhancer element located in the 3Ј-flanking region of the gene and requires binding of a specific transcription factor termed hypoxia-inducible factor 1 (HIF-1) 1 (2). Identification and cloning of HIF-1 revealed a heterodimeric protein consisting of two subunits, HIF-1␣ and HIF-1␤ (3, 4). Both subunits belong to a family of basic helixloop-helix transcription factors containing a PER-ARNT-SIM homology domain (3, 4). HIF-1␤, previously identified as ARNT (aryl hydrocarbon receptor nuclear translocator), is a common binding partner for other members of the family (5), whereas HIF-1␣ is the subunit regulated by cellular O 2 tension (3, 6). Both subunits are required for DNA binding and transactivation of HIF-1 target genes (3). The consensus DNA binding sequence for HIF-1 is 5Ј-RCGTG-3Ј (7). Under normoxic conditions HIF-1␣ protein undergoes rapid degradation by a proteasome (8, 9). Hypoxia increases HIF-1␣ protein stability by inhibiting its degradat...

Hypoxia upregulates hypoxia inducible factor (HIF)-3α expression in lung epithelial cells: characterization and comparison with HIF-1α

“…Both molecules accumulated following exposure of normoxic cells to cobalt chloride and desferrioxamine. Previous results reported mitochondrial reactive oxygen species inhibitors such as DPI, rotenone and myxothiazol dramatically reduced hypoxia-induced HIF-1α accumulation and basal activity [21,43]. In the present study, we found that all the three radical scavengers partially abolished the basal and hypoxic induction of HIF-3α and HIF-1α protein.…”

Mitochondrial complex III regulates hypoxic activation of HIF

“…40 Initial studies implicating the electron transport chain in HIF-1a stabilization have demonstrated that certain inhibitors of the electron transport chain, including rotenone (which inhibits complex I distally), myxothiazol, and stigmatellin (which inhibit complex III) block the hypoxic stabilization of HIF-1a. [41][42][43] Genetic deletions of complex I, likewise, blocked HIF-1a stabilization. 44 Finally, cells depleted of their mitochondrial DNA by incubation with low levels of ethidium bromide (known as rho-zero cells) fail to stabilize HIF-1a in response to hypoxia.…”

A protective role for HIF-1 in response to redox manipulation and glucose deprivation: implications for tumorigenesis

“…The precise mechanism linking oxygen depletion to HIF-1 activity is an area of avid research. Perturbations of the mitochondrial respiratory chain under hypoxia have been implicated (Chandel et al, 1998(Chandel et al, , 2000Agani et al, 2000). However, this is contentious, and HIF-1 activation under hypoxia has been demonstrated in cells lacking the mitochondrial respiratory chain electron transport pathway (Srivanas et al, 2001).…”