Up-regulation of hypoxia-inducible factors HIF-1α and HIF-2α under normoxic conditions in renal carcinoma cells by von Hippel-Lindau tumor suppressor gene loss of function

Abstract

Hypoxia induces transcription of a range of physiologically important genes including erythropoietin and vascular endothelial growth factor. The transcriptional activation is mediated by the hypoxia-inducible factor-1 (HIF-1), a heterodimeric member of the basic helix ± loop ± helix PAS family, composed of a and b subunits. HIF-1a shares 48 per cent identity with the recently identi®ed HIF-2a protein that is also stimulated by hypoxia. In a previous study of hemangioblastomas, the most frequent manifestation of hereditary von HippelLindau disease (VHL), we found elevated levels of vascular endothelial growth factor and HIF-2a mRNA in stromal cells of the tumors. Mutations of the VHL tumor suppressor gene are associated with a variety of tumors such as renal clear cell carcinomas (RCC). In this study, we analysed the expression of the hypoxiainducible factors HIF-1a and HIF-2a in a range of VHL wildtype and VHL de®cient RCC cell lines. In the presence of functional VHL protein, HIF-1a mRNA levels are elevated, whereas HIF-2a mRNA expression is increased only in cells lacking a functional VHL gene product. On the protein levels, however, in VHL de®cient cell lines, both HIF-a subunits are constitutively expressed, whereas re-introduction of a functional VHL gene restores the instability of HIF-1a and HIF-2a proteins under normoxic conditions. Moreover, immunohistochemical analyses of RCCs and hemangioblastomas demonstrate up-regulation of HIF-1a and HIF-2a in the tumor cells. The data presented here provide evidence for a role of the VHL protein in regulation of angiogenesis and erythropoiesis mediated by the HIF-1a and HIF-2a proteins. Oncogene (2000) 19, 5435 ± 5443.

Target gene selectivity of hypoxia-inducible factor-α in renal cancer cells is conveyed by post-DNA-binding mechanisms

“…Although this might simply reflect greater abundance of HIF-2a versus HIF-1a in RCC versus non-RCC cells (Maxwell et al, 1999;Krieg et al, 2000), or, as illustrated here, the presence of abnormal forms of HIF-1a protein in some RCC, there appeared to be a disproportion, for instance between modestly greater HIF-2a/HIF-1a protein levels in RCC4 versus Hep3B cells, and more striking differences in dependence of PHD3 on HIF-2a. This could reflect the existence of mechanisms that restrict the activity of HIF-1a or enhance the activity of HIF-2a in the RCC context.…”

“…In contrast, overexpression of HIF-1a was found to retard the growth of similar RCC-derived experimental tumours. Interestingly, clinical RCC shows an unusual bias to greater HIF-2a rather than HIF-1a expression (Krieg et al, 2000;Turner et al, 2002), and in kidneys from patients with VHL disease, greater HIF-2a expression is associated with more advanced lesions (Mandriota et al, 2002). Taken together, these findings strongly suggest that HIF-2a has pro-tumorigenic actions in RCC that are isoform specific, and not shared by HIF-1a.…”

The HIF-2α-Driven Pseudo-Hypoxic Phenotype in Tumor Aggressiveness, Differentiation, and Vascularization

“…Thus, in CCRCCs where pVHL function has been lost, the HIF-α subunits are constitutively expressed and a pseudo-hypoxic phenotype, including increased vascularization, is present. Intriguingly, there seems to be a bias towards HIF-2α expression as compared to HIF-1α expression in these VHL-deficient carcinoma cells (Maxwell et al 1999;Krieg et al 2000). The abundance of VHL-deficient RCC cell lines expressing HIF-2α but not HIF-1α (Maxwell et al 1999) is also interesting as this contrasts with normal renal epithelial cells, where HIF-2α expression is absent during ischemia (Rosenberger et al 2003).…”

Family history of von Hippel–Lindau disease was uncommon in Chinese patients: suggesting the higher frequency of de novo mutations in VHL gene in these patients

“…Through transcriptional regulation, hypoxia-inducible factor promotes glucose uptake and expression of angiogenic, growth and mitogenic factors, including vascular endothelial growth factor, platelet derived growth factor, erythropoietin and transforming growth factor a, known to be involved in tumorigenesis. [7][8][9][10] Clinical criteria for the diagnosis of VHL disease include one of the following items: (1) more than one hemangioblastoma in CNS or retina; (2) a single hemangioblastoma in CNS or retina plus a visceral complication (such as multiple renal, pancreatic or hepatic cysts, pheochromocytoma or renal cancer) with the exception of epididymal and renal cysts; (3) any one of above manifestations with a family history. 11 There is also a classification of VHL disease based on its clinical manifestations.…”