The role of the HIF-1α transcription factor in increased cell division at physiological oxygen tensions.
HIF-1 is a transcription factor that mediates the cellular responses to low oxygen environments, mainly as a result of having an oxygen-labile subunit, HIF-1α. HIF-1α has been carefully studied in the context of severe hypoxic stresses (<1% O2), but it is also known to be present at oxygen tensions commonly found in normal tissues in vivo (∼1-13% O2), albeit at much lower levels. Its role under these physiological conditions is not fully understood. Here, we show that a transcriptionally active HIF-1α was up-regulated at 5% O2, both in normal and cancer cells, but only some of its target genes were elevated as a result. HIF-1α induction was in part dependent on the activation of the ERK1/2 MAPK signalling pathway, which we have previously shown is active at 5% O2. We also found that HIF-1α does not contribute to the protection against DNA damage that can be observed in low oxygen environments, and that there are certain DNA damaging agents, such as doxorubicin and actinomycin D, that prevent HIF-1α induction independently of p53. Moreover, absence of HIF-1α significantly reduced the growth advantage of cells cultured at 5% O2. In view of these data, we conclude that HIF-1α can be induced and activated at physiological oxygen tensions in a MAPK-dependent manner and that, although this does not lead to pro-survival responses to stress, it determines the increased cell proliferation rates that are common under these conditions.
Department of Biochemistry, University of Leicester, Leicester, United Kingdom.
Samantha
S
Carrera
Cancer Research U.K./MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
Joana
J
Senra
Department of Biochemistry, University of Leicester, Leicester, United Kingdom.
Maria Isabel
MI
Acosta
Department of Biochemistry, University of Leicester, Leicester, United Kingdom.
Mohammad
M
Althubiti
Cancer Research U.K./MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
Ester M
EM
Hammond
Karolinska Institutet, Department of Molecular Medicine and Surgery, Urology Laboratory, and Department of Urology, Karolinska University Hospital, Stockholm, Sweden.
Petra J
PJ
de Verdier
Department of Biochemistry, University of Leicester, Leicester, United Kingdom.
Salvador
S
Macip
D049109:Cell Proliferation; D004249:DNA Damage; D003609:Dactinomycin / Q000633:toxicity; D004317:Doxorubicin / Q000633:toxicity; D045325:HCT116 Cells; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D061986:MCF-7 Cells; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D015854:Up-Regulation
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016159:Tumor Suppressor Protein p53; D003609:Dactinomycin; D004317:Doxorubicin; D010100:Oxygen