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


METHODS
786-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.


RESULTS
Cell 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.


CONCLUSIONS
HIF-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.
Department of Biology, Adelphi University, One South Avenue, P.O. Box 701, Garden City, NY 11530-0701 USA.
Alana
A
Doonachar
Department of Biology, Adelphi University, One South Avenue, P.O. Box 701, Garden City, NY 11530-0701 USA.
Michael D
MD
Gallo
Department of Biology, Adelphi University, One South Avenue, P.O. Box 701, Garden City, NY 11530-0701 USA.
Donald
D
Doukas
Department of Biology, Adelphi University, One South Avenue, P.O. Box 701, Garden City, NY 11530-0701 USA.
Rajiv
R
Pasricha
Department of Biology, Adelphi University, One South Avenue, P.O. Box 701, Garden City, NY 11530-0701 USA.
Igor
I
Lantsberg
Department of Biology, Adelphi University, One South Avenue, P.O. Box 701, Garden City, NY 11530-0701 USA.
Alan R
AR
Schoenfeld
Apoptosis; Glucose starvation; HIF-alpha; Serum starvation; UV-irradiation; VHL