Cyclin A expression and growth in suspension can be uncoupled from p27 deregulation and extracellular signal-regulated kinase activity in cells transformed by bovine papillomavirus type 4 E5.
As the biochemical detection of bovine papillomavirus type 4 E5 is problematic, a fusion form of E5 and the green fluorescent protein (GFP-E5) was constructed and its characteristics were examined. GFP-E5 was detected in cells by autofluorescence and immunoblotting. Like wild-type (wt) E5, GFP-E5 localized in the endomembranes and permitted anchorage-independent (AI) growth. However, unlike wt E5, cells expressing GFP-E5 became quiescent in low serum and failed to sustain expression of cyclins D1 and to inactivate retinoblastoma protein (pRb). The normal anchorage requirement for cyclin D1 and cyclin A expression was abolished in cells expressing wt E5 or GFP-E5, residual extracellular signal-regulated kinase (ERK 1/2) activity was not required to sustain cyclin D1 and cyclin A expression in suspension and deregulation of cyclin A-cyclin-dependent kinase (CDK) activity was sufficient to account for AI growth of cells expressing E5. Constitutive upregulation of the CDK inhibitor p27(KIP1), characteristic of cells expressing wt E5, was not observed in those expressing GFP-E5; therefore, p27(KIP1) deregulation is not required for E5-mediated AI growth.
Zago
Manola
M
Beatson Institute for Cancer Research, CR UK Beatson Laboratories, Glasgow, UK.
Campo
M Saveria
MS
Institute of Comparative Medicine, Glasgow University Veterinary School, Glasgow, UK.
O'Brien
Vincent
V
Beatson Institute for Cancer Research, CR UK Beatson Laboratories, Glasgow, UK.
D000818:Animals; D018797:Cell Cycle Proteins / Q000502:physiology*; D002472:Cell Transformation, Viral; D019925:Cyclin A / Q000032:analysis*; D019938:Cyclin D1 / Q000032:analysis; D050760:Cyclin-Dependent Kinase Inhibitor p27; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3 / Q000502:physiology*; D041681:NIH 3T3 Cells; D009856:Oncogene Proteins, Viral / Q000032:analysis / Q000502:physiology*; D016160:Retinoblastoma Protein / Q000378:metabolism; D013535:Suspensions; D025521:Tumor Suppressor Proteins / Q000502:physiology*
C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D019925:Cyclin A; D009856:Oncogene Proteins, Viral; D016160:Retinoblastoma Protein; D013535:Suspensions; D025521:Tumor Suppressor Proteins; C054304:oncogene protein E5, Bovine papillomavirus type 1; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3