The role of hypoxia-inducible factor-1 in three-dimensional tumor growth, apoptosis, and regulation by the insulin-signaling pathway.
The purpose of this study was to establish the effect of hypoxia-inducible factor-1 (HIF-1) directly on tumor growth, independently of angiogenesis. This was done by growing wild-type mouse hepatoma cells (HEPA-1) and their HIF-1-deficient counterpart C4 as multicellular tumor spheroids and quantifying differences in growth rates and proliferative and apoptotic indices. Insulin and insulin-like growth factor-I are key growth factors, also able to regulate hypoxia-responsive genes via HIF-1; thus, the effects of insulin on this model were also investigated. Two-dimensional growth was serum dependent and no difference was seen between wild-type HEPA-1 and C4 cell growth profiles, but major differences were seen in three-dimensional growth. HIF-1 supported spheroid growth under hypoxia as the HEPA-1 spheroids grew faster than the C4. Surprisingly, the HIF-1-deficient cells had a higher proliferation rate in three-dimensional growth (C4 mean S-phase index, 13.6%; HEPA-1 mean S-phase index, 9%; P = 0.009) that was associated with an inhibition of apoptosis. However, the apoptosis rate was much greater in these spheroids (C4 mean apoptotic index, 6.4; HEPA-1 mean apoptotic index, 0.78%; P = 0.0006). Addition of insulin increased proliferation and apoptosis in both HEPA-1 and C4 spheroids, demonstrating an HIF-1-independent effect of insulin signaling in three-dimensional growth. These results indicate that the enhancing effect of HIF-1 in three-dimensional tumor growth is a balance of both reduced proliferation and enhanced survival, the latter being proportionally greater.
Leek
Russell D
RD
Growth Factor Group, Cancer Research UK Molecular Oncology Laboratories, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom.
Stratford
Ian
I
Harris
Adrian L
AL
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007328:Insulin / Q000494:pharmacology*; D008114:Liver Neoplasms, Experimental / Q000473:pathology*; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D009687:Nuclear Proteins / Q000187:drug effects / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D016196:S Phase / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D018874:Spheroids, Cellular; D014157:Transcription Factors / Q000187:drug effects / Q000502:physiology*
D002867:Chromones; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C497443:Hif1a protein, mouse; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007328:Insulin; D009025:Morpholines; D009687:Nuclear Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D014157:Transcription Factors; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one