Resistance to caspase-dependent, hypoxia-induced apoptosis is not hypoxia-inducible factor-1 alpha mediated in prostate carcinoma cells.
BACKGROUND
Hypoxia occurs in association with cancer development, the result being a more aggressive and metastatic cancer phenotype. Hypoxia, which activates hypoxia-inducible factor-1 alpha (HIF-1alpha), is associated with a number of cellular changes including increased apoptotic resistance. The authors hypothesized that HIF-1alpha is central to the cell's ability to resist apoptosis induced during the hypoxia selection process.


METHODS
PWR-1E, LNCaP, LNCaP-HOF, PC-3, and DU-145 cells were cultured in normoxic and hypoxic conditions. Apoptosis was assessed by propidium iodide DNA staining. Cleavage of specific substrates was used to assess caspase activity and Western blotting was used to assess mitochondrial release of cytochrome c and second mitochondria-derived activator caspase (SMAC)/Diablo. A dominant negative HIF-1alpha construct was transfected into the PC-3 and LNCaP cells to block HIF-1alpha activity.


RESULTS
PC-3 and DU-145 were resistant to apoptosis induced by exposure to hypoxia, but the PWR-1E and LNCaP cells were susceptible. This induction of apoptosis in the LNCaP cells was caspase dependent but independent of cytochrome c release. Blocking the activity of HIF-1alpha had no effect on increased apoptotic susceptibility in the PC-3 cells. LNCaP-HOF cells, which were resistant to hypoxia-induced apoptosis, showed no increase in HIF-1alpha expression or activity.


CONCLUSIONS
Apoptotic resistance is already established in cells that survive a hypoxic insult and whereas increased HIF-1alpha activity may be essential for the development of a more aggressive cancer phenotype, it may not be responsible for the initial selection of an apoptotic resistance phenotype.
Coffey
Ronan N T
RN
Department of Surgery, Mater Misericordiae University Hospital, Conway Institute of Biomedical and Biomolecular Research, University College Dublin, Ireland.
Morrissey
Colm
C
Taylor
Cormac T
CT
Fitzpatrick
John M
JM
Watson
R William G
RW
D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000494:pharmacology; D020169:Caspases / Q000494:pharmacology*; D015687:Cell Hypoxia / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D045304:Cytochromes c; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D024101:Mitochondrial Proteins / Q000494:pharmacology; D011471:Prostatic Neoplasms; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C412403:DIABLO protein, human; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D014157:Transcription Factors; D045304:Cytochromes c; D020169:Caspases