Hypoxia-induced radioresistance is independent of hypoxia-inducible factor-1A in vitro.
OBJECTIVE
We sought to determine whether hypoxia-induced radioresistance is mediated by the transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha).


METHODS
We used 2 mouse embryonic fibroblast cell lines transformed with H-ras and TAg, 1 HIF-1alpha+/+ and the other HIF-1alpha-/-. Cell were exposed to either 95% air and 5% CO2 (normoxic conditions) or 0.2% O2, 94.8% N2, and 5% CO2 (hypoxic conditions) for 4 hours. Cells were then irradiated and subjected to clonogenic survival assays.


RESULTS
Whereas neither +/+ ras/TAg nor -/- ras/TAg cells expressed HIF-1alpha under normoxic conditions, hypoxia induced expression of HIF-1alpha only in +/+ ras/TAg cells, confirming the absence of HIF-1alpha in -/- ras/TAg cells. Clonogenic survival curves for +/+ ras/TAg and -/- ras/TAg cells under normoxia and hypoxia demonstrated that hypoxia increased radioresistance in both cell lines to the same degree. At 1-log cell kill, the +/+ ras/TAg and -/- ras/TAg cells had an identical oxygen enhancement ratio of 1.28 +/- 0.09 and nearly identical oxygen enhancement ratios at 2-log cell kill.


CONCLUSIONS
In our system of transformed mouse embryonic fibroblasts, hypoxia-mediated radiation resistance is independent of HIF-1alpha.
Arvold
Nils D
ND
Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA 94143-1932, USA.
Guha
Neela
N
Wang
Dongfang
D
Matli
Mary
M
Deen
Dennis F
DF
Warren
Robert S
RS
Haas-Kogan
Daphne A
DA
D000818:Animals; D015687:Cell Hypoxia / Q000502:physiology*; D002461:Cell Line, Transformed / Q000378:metabolism / Q000528:radiation effects; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D011836:Radiation Tolerance / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism*
D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D014157:Transcription Factors