Differential effects of HIF-α isoforms on apoptosis in renal carcinoma cell lines

Abstract

BackgroundGermline mutations in the von Hippel-Lindau (VHL) tumor suppressor gene predispose individuals to clear cell renal carcinomas, hemangioblastomas, and pheochromocytomas. The VHL gene product forms an ubiquitin E3 ligase complex, with regulation of hypoxia-inducible factor alpha (HIF-α) as its best known function. Lack of VHL expression has been shown previously to sensitize renal cells to apoptosis caused by certain cellular stresses. In this report, the role of HIF-α in apoptosis was investigated using two parent VHL-null renal carcinoma cell lines.Methods786-O and RCC10 renal carcinoma cell lines with manipulated levels of VHL, HIF-1α, or HIF-2α were subjected to cellular stresses and analyzed by western blotting for the abundance of apoptotic markers.ResultsCell lines expressing mutant VHL proteins that were unable to regulate HIF-α had increased levels of apoptosis when irradiated with ultraviolet (UV) light. The influences of the two major isoforms of HIF-α, HIF-1α and HIF-2α, on apoptosis, were compared by creating cell lines in which levels of each isoform were modulated via short hairpin RNA interference. In UV-irradiated cells, HIF-2α expression was determined to promote apoptosis, whereas HIF-1α was anti-apoptotic. In cells deprived of either glucose or serum, HIF-1α expression was generally anti-apoptotic, while HIF-2α expression was observed to either promote apoptosis or have less of an influence on apoptosis, depending on the cell line used.ConclusionsHIF-1α and HIF-2α exerted distinct effects in each of the conditions tested, with expression of HIF-1α largely blocking apoptosis and HIF-2α generally promoting apoptosis. These results reinforce that HIF-1α and HIF-2α have distinct biological roles and that their relative expression levels may influence some therapeutic interventions that are dependent on apoptosis.

The uremic toxin p-cresyl sulfate induces proliferation and migration of clear cell renal cell carcinoma via microRNA-21/ HIF-1α axis signals

“…Some studies indicated that HIF1α acts as a renal tumor suppressor and HIF2α as a renal tumor inducer 50,51 . However, another study showed that HIF-1α inhibits and HIF-2α induces apoptosis 52 . Nevertheless, both HIF-1α and HIF-2α induce the proliferation of ccRCC cells 7,10,25,53 .…”

“…However, mutant VHL genes are found in most ccRCC cells, including in 786-O and A498 cells 58 . A study indicated that mutant VHL does not regulate HIF-α signals 52 . Our results showed that p CS induced HIF-1α and VHL and suppressed HIF-2α expression.…”

Downregulation and pro-apoptotic effect of hypoxia-inducible factor 2 alpha in hepatocellular carcinoma

“…These results together with HIF-2α expression data suggest that HIF-2α may function as an anti-tumor molecule in HCC. In fact, the pro-apoptotic function of HIF-2α has also been found in other cancers such as glioblastoma and renal carcinoma [21,22]. …”

HIF-1 in cancer therapy: two decade long story of a transcription factor

“…HIF-2a, which has a restricted expression mainly in renal, endothelial, hepatic and lung cells, has 48% amino acid sequence similarity with HIF-1a, unlike HIF-3a [reviewed in 25]. Though both HIF-1a and HIF-2a stimulate target genes by linking to same HRE, they are functionally non-redundant [26]. HIF-1a regulates glycolytic gene expression and preferentially drives apoptotic pathways not addressed by HIF-2a, whereas HIF-2a encourages tumor growth and angiogenesis [27].…”