title: G1 cyclin/cyclin-dependent kinase-coordinated phosphorylation of endogenous pocket proteins differentially regulates their interactions with E2F4 and E2F1 and gene expression.
abstract: Mitogenic stimulation leads to activation of G(1) cyclin-dependent kinases (CDKs), which phosphorylate pocket proteins and trigger progression through the G(0)/G(1) and G(1)/S transitions of the cell cycle. However, the individual role of G(1) cyclin-CDK complexes in the coordinated regulation of pocket proteins and their interaction with E2F family members is not fully understood. Here we report that individually or in concert cyclin D1-CDK and cyclin E-CDK complexes induce distinct and coordinated phosphorylation of endogenous pocket proteins, which also has distinct consequences in the regulation of pocket protein interactions with E2F4 and the expression of p107 and E2F1, both E2F-regulated genes. The up-regulation of these two proteins and the release of p130 and pRB from E2F4 complexes allows formation of E2F1 complexes not only with pRB but also with p130 and p107 as well as the formation of p107-E2F4 complexes. The formation of these complexes occurs in the presence of active cyclin D1-CDK and cyclin E-CDK complexes, indicating that whereas phosphorylation plays a role in the abrogation of certain pocket protein/E2F interactions, these same activities induce the formation of other complexes in the context of a cell expressing endogenous levels of pocket and E2F proteins. Of note, phosphorylated p130 "form 3," which does not interact with E2F4, readily interacts with E2F1. Our data also demonstrate that ectopic overexpression of either cyclin is sufficient to induce mitogen-independent growth in human T98G and Rat-1 cells, although the effects of cyclin D1 require downstream activation of cyclin E-CDK2 activity. Interestingly, in T98G cells, cyclin D1 induces cell cycle progression more potently than cyclin E. This suggests that cyclin D1 activates pathways independently of cyclin E that ensure timely progression through the cell cycle.
authors.affiliation: Fels Institute for Cancer Research and Molecular Biology and Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: Joaquim
authors.initials: J
authors.lastname: Calbó
authors.forename: Matilde
authors.initials: M
authors.lastname: Parreño
authors.forename: Elena
authors.initials: E
authors.lastname: Sotillo
authors.forename: Thomas
authors.initials: T
authors.lastname: Yong
authors.forename: Adela
authors.initials: A
authors.lastname: Mazo
authors.forename: Judit
authors.initials: J
authors.lastname: Garriga
authors.forename: Xavier
authors.initials: X
authors.lastname: Grana
mesh_terms: D000256:Adenoviridae; D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins; D002460:Cell Line; D002478:Cells, Cultured; D056746:Cyclin G; D056766:Cyclin G1; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050704:E2F4 Transcription Factor; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D016195:G2 Phase; D005786:Gene Expression Regulation; D051379:Mice; D008938:Mitosis; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection
chemical_list: C534702:CCNG1 protein, human; C534703:Ccng1 protein, mouse; C534704:Ccng1 protein, rat; D018797:Cell Cycle Proteins; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050704:E2F4 Transcription Factor; C493754:E2f1 protein, mouse; C493755:E2f1 protein, rat; C493763:E2f4 protein, mouse; D010750:Phosphoproteins; D014157:Transcription Factors; D018844:Cyclin-Dependent Kinases