1. Inducible pRb2/p130 expression and growth-suppressive mechanisms: evidence of a pRb2/p130, p27Kip1, and cyclin E negative feedback regulatory loop
- Author
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Howard, Cm, Claudio, Pp, Luca, A., Stiegler, P., Jori, Fp, Safdar, Nm, Caputi, M., Khalili, K., Antonio Giordano, Howard, Cm, Claudio, Pp, DE LUCA, Antonio, Stiegler, P, Jori, Fp, Safdar, Nm, Caputi, M, Khalili, K, and Giordano, A.
- Subjects
Down-Regulation ,Cell Cycle Proteins ,Cyclin A ,Protein Serine-Threonine Kinases ,Models, Biological ,Retinoblastoma Protein ,Cricetinae ,Chlorocebus aethiops ,Cyclin E ,CDC2-CDC28 Kinases ,Tumor Cells, Cultured ,Animals ,Humans ,Genes, Tumor Suppressor ,Retinoblastoma-Like Protein p130 ,Tumor Suppressor Proteins ,Cyclin-Dependent Kinase 2 ,Proteins ,Phosphoproteins ,Cyclin-Dependent Kinases ,E2F Transcription Factors ,DNA-Binding Proteins ,COS Cells ,Carrier Proteins ,Microtubule-Associated Proteins ,Transcription Factor DP1 ,Cyclin-Dependent Kinase Inhibitor p27 ,E2F1 Transcription Factor ,Retinoblastoma-Binding Protein 1 ,Transcription Factors - Abstract
The retinoblastoma family of proteins, pRb/p105, p107, and pRb2/ p130, cooperate to regulate cell cycle progression through the G1 phase of the cell cycle. Each of the family members realize their common goal of G1-S checkpoint regulation through overlapping and unique growth regulatory pathways. We took advantage of a tetracycline-regulated gene expression system to control the expression of RB2/p130 in JC virus-induced hamster brain tumor cells to study in vivo the molecular mechanisms used by pRb2/p130 to elicit its growth-suppressive function. We have previously used this system to demonstrate that induction of pRb/ p130 expression suppresses tumor growth in vivo by overcoming neoplastic transformation mediated by the large T-antigen oncoprotein of JCV (JCV TAg). Here we found that induction of pRb2/p130 in vivo specifically inhibits cyclin A- and cyclin E-associated kinase activity and by doing so induces p27Kip1 levels presumably by inhibiting p27Kip1-targeted proteolysis by cyclin E-Cdk2 phosphorylation of p27Kip1. RB2/p130 induction also decreased cyclin A and the transcription factor E2F-1 while increasing cyclin E at both the transcriptional and protein levels of expression. The growth inhibitory activity of pRb2/p130 also correlated with its E2F-binding capacity. Furthermore, p27Kip1 and pRb2/p130 were found to be targets of the JCV TAg oncoprotein and to interact in vivo with each other independently from the presence of TAg. Interestingly, pRb2/p130 expression negatively modulated the binding of p27Kip1 to JCV TAg. These data suggest that pRb2/p130 and p27Kip1 may cooperate in regulating cellular proliferation, and both may be involved in a negative feedback regulatory loop with cyclin E.
- Published
- 2000