title: E7 abolishes raf-induced arrest via mislocalization of p21(Cip1).
abstract: The cellular response to oncogenic Ras depends upon the presence or absence of cooperating mutations. In the absence of immortalizing oncogenes or genetic lesions, activation of the Ras/Raf pathway results in a p21(Cip1)-dependent cellular arrest. The human papillomavirus oncoprotein E7 transforms primary cells in cooperation with Ras and abolishes p21(Cip1)-mediated growth arrest in the presence of various antimitogenic signals. Here we have utilized a conditional Raf molecule to investigate the effects of E7 on p21(Cip1) function in the context of Raf-induced cellular arrest. E7 bypassed Raf-induced arrest and alleviated inhibition of cyclin E-CDK2 without suppressing Raf-specific synthesis of p21(Cip1) or derepressing p21(Cip1)-associated CDK2 complexes. Activation of Raf led to nuclear accumulation of p21(Cip1), and we provide evidence that this effect is mediated by inhibition of Akt, a regulator of p21(Cip1) localization. Loss of Akt activity appears to be an important event in the cellular arrest associated with Raf-induction, since maintenance of Akt activity was necessary and sufficient to bypass Raf-induced arrest. In agreement, expression of E7 sustained Akt activity and reduced nuclear accumulation of p21(Cip1), resulting in decreased association between p21(Cip1) and cyclin E-CDK2. Taken together, these data suggest that E7 inhibits p21(Cip1) function in the context of Raf signaling by altering Raf-Akt antagonism and preventing the proper subcellular localization of p21(Cip1). We propose that E7 elicits a proliferative response to Raf signaling by targeting p21(Cip1) function via a novel mechanism.
authors.affiliation: Department of Microbiology and Immunology. Department of Biochemistry and Biophysics. The Cancer Center, University of Rochester, Rochester, New York 14642, USA.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Westbrook
authors.forename: Don X
authors.initials: DX
authors.lastname: Nguyen
authors.forename: Barry R
authors.initials: BR
authors.lastname: Thrash
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: McCance
mesh_terms: D016475:3T3 Cells; D000818:Animals; D042846:CDC2-CDC28 Kinases; D002455:Cell Division; D019927:Cyclin E / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism*; D004791:Enzyme Inhibitors; D006801:Humans; D051379:Mice; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D027383:Papillomaviridae / Q000378:metabolism*; D050725:Papillomavirus E7 Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D042846:CDC2-CDC28 Kinases; D019927:Cyclin E; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases; D016213:Cyclins; D004791:Enzyme Inhibitors; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D011993:Recombinant Fusion Proteins; C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; C059731:oncogene protein E7, Human papillomavirus type 16; C494918:AKT1 protein, human; C495894:CDK2 protein, human; C495893:Cdk2 protein, mouse