title: Hypoxia-inducible factor 1alpha is essential for cell cycle arrest during hypoxia.
abstract: A classical cellular response to hypoxia is a cessation of growth. Hypoxia-induced growth arrest differs in different cell types but is likely an essential aspect of the response to wounding and injury. An important component of the hypoxic response is the activation of the hypoxia-inducible factor 1 (HIF-1) transcription factor. Although this transcription factor is essential for adaptation to low oxygen levels, the mechanisms through which it influences cell cycle arrest, including the degree to which it cooperates with the tumor suppressor protein p53, remain poorly understood. To determine broadly relevant aspects of HIF-1 function in primary cell growth arrest, we examined two different primary differentiated cell types which contained a deletable allele of the oxygen-sensitive component of HIF-1, the HIF-1alpha gene product. The two cell types were murine embryonic fibroblasts and splenic B lymphocytes; to determine how the function of HIF-1alpha influenced p53, we also created double-knockout (HIF-1alpha null, p53 null) strains and cells. In both cell types, loss of HIF-1alpha abolished hypoxia-induced growth arrest and did this in a p53-independent fashion. Surprisingly, in all cases, cells lacking both p53 and HIF-1alpha genes have completely lost the ability to alter the cell cycle in response to hypoxia. In addition, we have found that the loss of HIF-1alpha causes an increased progression into S phase during hypoxia, rather than a growth arrest. We show that hypoxia causes a HIF-1alpha-dependent increase in the expression of the cyclin-dependent kinase inhibitors p21 and p27; we also find that hypophosphorylation of retinoblastoma protein in hypoxia is HIF-1alpha dependent. These data demonstrate that the transcription factor HIF-1 is a major regulator of cell cycle arrest in primary cells during hypoxia.
authors.affiliation: Molecular Biology Section, Division of Biology, University of California, San Diego, La Jolla 92093, USA.
authors.forename: Nobuhito
authors.initials: N
authors.lastname: Goda
authors.forename: Heather E
authors.initials: HE
authors.lastname: Ryan
authors.forename: Bahram
authors.initials: B
authors.lastname: Khadivi
authors.forename: Wayne
authors.initials: W
authors.lastname: McNulty
authors.forename: Robert C
authors.initials: RC
authors.lastname: Rickert
authors.forename: Randall S
authors.initials: RS
authors.lastname: Johnson
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000378:metabolism; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000235:genetics; D015687:Cell Hypoxia; D002478:Cells, Cultured; D003433:Crosses, Genetic; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D020868:Gene Silencing; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D013154:Spleen / Q000166:cytology; D014157:Transcription Factors / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases