HIF-1 alpha: a key survival factor for serum-deprived prostate cancer cells.
BACKGROUND
Hypoxia-inducible factor-1 alpha (HIF-1 alpha) is commonly overexpressed in prostate cancer (PCa) cells. As PCa cells are known to survive serum deprivation, we investigated the effect of prolonged serum deprivation on HIF-1 alpha expression, and the function of HIF-1 alpha in regulating the survival of normoxic serum-deprived PCa cells.


METHODS
HIF-1 alpha protein was assessed by immunoblots. Cell viability and proliferation were assessed by trypan blue assay and flow cytometric analysis. Transcriptional activity was assessed by luciferase reporter assay and RT-PCR. HIF-1 alpha expression was suppressed with siRNA. Activities of HIF-1 alpha-target genes were inhibited with neutralizing antibody.


RESULTS
Prolonged serum deprivation is a potent inducer of HIF-1 alpha in PC-3 and LNCaP PCa cells, despite normal oxygen conditions. In contrast, cells grown in the presence of serum did not show HIF-1 alpha protein accumulation. Moreover, HIF-1 alpha protein increase during serum deprivation correlated with increased cell survival, while suppression of HIF-1 alpha expression significantly decreased PCa cell viability. Our results further demonstrate that HIF-1 alpha protein increase is due to increased HIF-1 alpha protein synthesis. First, there was no significant increase in HIF-1 alpha mRNA. Secondly, cycloheximide, a protein synthesis inhibitor, prevented HIF-1 alpha protein increase in serum-deprived PCa cells. Moreover, the expression of HIF-1 alpha-target genes, VEGF and IGF-2, was concomitantly increased in serum-deprived PCa cells, while suppression of HIF-1 alpha expression significantly inhibited their induction. Furthermore, inhibition of IGF-2 activity resulted in a significant decline in PCa cell survival.


CONCLUSIONS
PCa cells counteract the stress of prolonged serum deprivation by upregulating HIF-1 alpha protein which increases IGF-2 expression to promote cell survival.
Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, Texas 76107, USA.
Rusha
R
Thomas
Myoung H
MH
Kim
D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology*; D000906:Antibodies / Q000494:pharmacology; D014408:Biomarkers, Tumor / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000276:immunology / Q000378:metabolism; D008297:Male; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
D000906:Antibodies; D014408:Biomarkers, Tumor; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011500:Protein Synthesis Inhibitors; D034741:RNA, Small Interfering; D042461:Vascular Endothelial Growth Factor A; D012710:Serum Albumin, Bovine; D007335:Insulin-Like Growth Factor II; D003513:Cycloheximide