Erythropoietin gene regulation depends on heme-dependent oxygen sensing and assembly of interacting transcription factors

287

234

Nickel and cobalt have wide industrial usage, which leads to environmental pollution by these metals and their by-products at all stages of production, recycling, and disposal (1, 2). Additionally, burning of fossil fuels pollutes the air with metalcontaining particles, up to 35% of which could be composed of nickel (3). Environmental or occupational exposure to particles containing nickel or cobalt causes various forms of lung injury including pneumonitis, asthma, and fibrosis (4). Both metals are carcinogenic in animals (5, 6), and nickel has been recognized as a human carcinogen (7). The mechanisms of their toxicity and carcinogenicity are not fully understood. An interesting feature of nickel or cobalt exposure is the induction of hypoxia-like stress, which is manifested in cells by the activation of the HIF-1 1 transcription factor and hypoxia-inducible genes (8 -10). It has been suggested that the induction of the hypoxia-like stress by these metals is based on their ability to substitute for an iron atom in an "oxygen sensor" (11). No direct evidence supporting this interesting hypothesis is available, although several studies have demonstrated that Co(II) can inhibit activity of recombinant asparaginyl (12) or prolyl (13) hydroxylase in vitro, presumably because of competition with Fe(II). The induction of hypoxia-like stress by nickel or cobalt has numerous implications. It is well established that HIFinducible genes are involved in crucial aspects of cancer biology, including angiogenesis, cell survival, glucose metabolism, and invasion (14, 15).Recently, using HIF-1␣ normal and knock-out cells, we have shown that nickel promotes soft agar growth via the HIF-1 transcription factor (16). These data indicate that HIF-1 induction may play an important role in nickel-mediated malignant transformation of cells. The HIF-1 transcription factor is a heterodimer composed of ␣ and ␤ subunits (17). The activity of HIF-1 depends on the accumulation of short lived HIF␣. Under normoxic conditions, hydroxylation of proline residues 402 and 564 in the ODD of HIF-1␣ leads to its interaction with the VHL tumor suppressor protein, a part of the ubiquitin⅐ligase complex, followed by ubiquitylation and rapid proteosomal degradation of . Under hypoxic conditions, limiting oxygen decreases hydroxylation, which prevents VHL binding and leads to the accumulation of HIF-1␣ protein. Nickel(II) or cobalt(II) exposure even in the presence of oxygen causes increased accumulation of HIF-1␣ protein and induction of HIF-1 transcriptional activity (17,21,22). The accumulation of HIF-1␣ protein observed in cells after cobalt(II) exposure resulted from the inability of HIF␣ to complex with the VHL protein (18). This inability, as we found here, is associated with inhibition of HIF-1␣ hydroxylation, manifested by both cobalt(II) and nickel(II) exposure. HIF activity can also be affected by the asparaginyl hydroxylation of the C-terminal transactivation domain, which is regulated by FIH-1 (23). Like the prolyl hydroxylase, this enzyme

Section: Discussionmentioning

confidence: 99%

“…Dimethyloxalylglycine (DMOG) was purchased from Frontier Scientific (Logan, UT). L- [1-14 C]Ascorbic acid (4.0 mCi/ mmol) was purchased from PerkinElmer Life Sciences, and L- [5][6][7][8][9][10][11][12][13][14] C]␣-ketoglutaric acid (50 mCi/mmol) was purchased from Moravek Biochemicals (Brea, CA).…”

Section: Methodsmentioning

confidence: 99%

Depletion of Intracellular Ascorbate by the Carcinogenic Metals Nickel and Cobalt Results in the Induction of Hypoxic Stress

Salnikow

Donald

Bruick

et al. 2004

287

234

“…The cooperative effects of HIF-1␣, HNF-4, and p300 appear to be similar as proposed for the EPO gene where, under hypoxia, heterodimeric HIF-1 binds to an HRE, while HNF-4 binds to a direct repeat downstream of the HRE. The binding of HNF-4 is crucial for an enhanced hypoxic response, and recruitment of the transcriptional coactivator p300 by HIF-1 and HNF-4 further enhanced the EPO expression (34,35).…”

Section: Involvement Of the Pi3k/pkb Pathway In The Regulation Of Genmentioning

confidence: 99%

The Transcription Factors HIF-1 and HNF-4 and the Coactivator p300 Are Involved in Insulin-regulated Glucokinase Gene Expression via the Phosphatidylinositol 3-Kinase/Protein Kinase B Pathway

Roth

Curth

Unterman

et al. 2004

104

Glucokinase plays a key role in the regulation of glucose utilization in liver and its expression is strongly enhanced by insulin and modulated by venous pO 2 . In primary rat hepatocytes, pO 2 modulated insulindependent glucokinase (GK) gene expression was abolished by wortmannin an inhibitor of phosphatidylinositol 3-kinase (PI3K). Transfection of vectors encoding the p110 catalytic subunit of PI3K or constitutively active proteinkinase B (PKB) stimulated GK mRNA and protein expression. The transfection of GK promoter constructs together with expression vectors for p110 or constitutively active PKB revealed that the GK promoter region ؊87/؊80 mediates the response to PI3K/PKB. Transfection experiments and gel shift assays show that this element is able to bind hypoxia-inducible factor-1 (HIF-1) in a hypoxia-and PKB-dependent manner. The ability of HIF-1␣ to activate the GK promoter was enhanced by hepatocyte nuclear factor-4␣ (HNF-4␣), acting via the sequence ؊52/؊39, and by the coactivator p300. Stimulation of the GK promoter by insulin was dependent on the intact ؊87/؊80 region and maximal stimulation was achieved when HIF-1␣, HNF-4, and p300 were cotransfected with the ؊1430 GK promoter Luc construct in primary hepatocytes. Maximal stimulation of GK promoter activity by insulin was inhibited when a p300 vector was used containing a mutation within a PKB phosphorylation site. Thus, a regulatory transcriptional complex consisting of HIF-1, HNF-4, and p300 appears to be involved in insulin-dependent GK gene activation.

“…So far, most of the studies on the effects of hypoxia on gene expression have focused on the induction of hypoxic genes and have not addressed the downregulation of aerobic genes. These studies on the induction of hypoxic genes have revealed that exposure to hypoxia can initiate a complex series of events, which begin with some sort of oxygen sensor and end with a signaling pathway that upregulates hypoxic genes (1,(5)(6)(7)(8)(9)(10).…”

mentioning

confidence: 99%

Effects of Anoxia and the Mitochondrion on Expression of Aerobic Nuclear COX Genes in Yeast

Dagsgaard

Taylor

O’Brien

et al. 2001

Eucaryotic cells contain at least two general classes of oxygen-regulated nuclear genes: aerobic genes and hypoxic genes. Hypoxic genes are induced upon exposure to anoxia while aerobic genes are down-regulated. Recently, it has been reported that induction of some hypoxic nuclear genes in mammals and yeast requires mitochondrial respiration and that cytochrome-c oxidase functions as an oxygen sensor during this process. In this study, we have examined the role of the mitochondrion and cytochrome-c oxidase in the expression of yeast aerobic nuclear COX genes. We have found that the down-regulation of these genes in anoxic cells is reflected in reduced levels of their subunit polypeptides and that cytochrome-c oxidase subunits I, II, III, Vb, VI, VII, and VIIa are present in promitochondria from anoxic cells. By using nuclear cox mutants and mitochondrial rho 0 and mit ؊ mutants, we have found that neither respiration nor cytochrome-c oxidase is required for the down-regulation of these genes in cells exposed to anoxia but that a mitochondrial genome is required for their full expression under both normoxic and anoxic conditions. This requirement for a mitochondrial genome is unrelated to the presence or absence of a functional holocytochrome-c oxidase. We have also found that the down-regulation of these genes in cells exposed to anoxia and the down-regulation that results from the absence of a mitochondrial genome are independent of one another. These findings indicate that the mitochondrial genome, acting independently of respiration and oxidative phosphorylation, affects the expression of the aerobic nuclear COX genes and suggest the existence of a signaling pathway from the mitochondrial genome to the nucleus.