Decreased growth of Vhl-/- fibrosarcomas is associated with elevated levels of cyclin kinase inhibitors p21 and p27.
Inactivating mutations within the von Hippel-Lindau (VHL) tumor suppressor gene predispose patients to develop a variety of highly vascularized tumors. pVHL targets alpha subunits of the heterodimeric transcription factor hypoxia-inducible factor (HIF), a critical regulator of energy metabolism, angiogenesis, hematopoiesis, and oxygen (O(2)) delivery, for ubiquitin-mediated degradation in an O(2)-dependent manner. To investigate the role of Vhl in cellular proliferation and tumorigenesis, we utilized mouse embryonic fibroblasts (MEFs), a common tool for analyzing cell cycle regulation, and generated Vhl(-)(/)(-) MEF-derived fibrosarcomas. Surprisingly, growth of both Vhl(-)(/)(-) MEFs and fibrosarcomas was impaired, although tumor vascularity was increased. Decreased proliferation of Vhl(-)(/)(-) MEFs was correlated with an overexpression of cyclin kinase inhibitors (CKIs) p21 and p27. The transcription of p21 and p27 is inhibited by c-Myc; therefore, the induction of CKIs was attributed to the ability of HIF to antagonize c-Myc activity. Indeed, p21 mRNA levels were elevated under normoxia in Vhl(-)(/)(-) MEFs, while c-Myc transcriptional activity was markedly reduced. Gene silencing of HIF-1alpha by small interfering RNA reduced p21 and p27 protein and mRNA levels in Vhl(-)(/)(-) MEFs. The induction of p21 and p27, mediated by constitutive activation of the HIF pathway, provides a mechanism for the decreased proliferation rates of Vhl(-)(/)(-) MEFs and fibrosarcomas. These results demonstrate that a loss of pVHL can induce growth arrest in certain cells types, which suggests that additional genetic mutations are necessary for VHL-associated tumorigenesis.
Mack
Fiona A
FA
University of Pennsylvania School of Medicine, Abramson Family Cancer Research Institute, Philadelphia, PA 19104, USA.
Patel
Jagruti H
JH
Biju
Mangatt P
MP
Haase
Volker H
VH
Simon
M Celeste
MC
D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004622:Embryo, Mammalian / Q000166:cytology; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005354:Fibrosarcoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D020868:Gene Silencing; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D008817:Mice, Mutant Strains; D009154:Mutation; D016271:Proto-Oncogene Proteins c-myc / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000502:physiology*; D051794:Von Hippel-Lindau Tumor Suppressor Protein
C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C489428:Myc protein, mouse; D016271:Proto-Oncogene Proteins c-myc; D034741:RNA, Small Interfering; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D044767:Ubiquitin-Protein Ligases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; C494469:VHL protein, mouse