title: Inducible pRb2/p130 expression and growth-suppressive mechanisms: evidence of a pRb2/p130, p27Kip1, and cyclin E negative feedback regulatory loop.
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.
authors.affiliation: Department of Pathology, Anatomy & Cell Biology, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Howard
authors.forename: P P
authors.initials: PP
authors.lastname: Claudio
authors.forename: A
authors.initials: A
authors.lastname: De Luca
authors.forename: P
authors.initials: P
authors.lastname: Stiegler
authors.forename: F P
authors.initials: FP
authors.lastname: Jori
authors.forename: N M
authors.initials: NM
authors.lastname: Safdar
authors.forename: M
authors.initials: M
authors.lastname: Caputi
authors.forename: K
authors.initials: K
authors.lastname: Khalili
authors.forename: A
authors.initials: A
authors.lastname: Giordano
mesh_terms: D000818:Animals; D042846:CDC2-CDC28 Kinases; D019556:COS Cells; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D002522:Chlorocebus aethiops; D006224:Cricetinae; D019925:Cyclin A / Q000378:metabolism; D019927:Cyclin E / Q000502:physiology*; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D016147:Genes, Tumor Suppressor; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D008954:Models, Biological; D010750:Phosphoproteins / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins; D016160:Retinoblastoma Protein / Q000096:biosynthesis* / Q000502:physiology*; D056465:Retinoblastoma-Binding Protein 1; D050717:Retinoblastoma-Like Protein p130; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019925:Cyclin A; D019927:Cyclin E; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D008869:Microtubule-Associated Proteins; D010750:Phosphoproteins; D011506:Proteins; C493837:RBL2 protein, human; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050717:Retinoblastoma-Like Protein p130; D050680:Transcription Factor DP1; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases