title: GCIP, a novel human grap2 and cyclin D interacting protein, regulates E2F-mediated transcriptional activity.
abstract: Regulation of mammalian cell growth and proliferation is governed through receptor-mediated signaling networks that ultimately converge on the cell cycle machinery. Adaptor proteins play essential roles in the formation of intracellular signaling complexes, relaying extracellular signals from the plasma membrane to the nucleus of a cell. The leukocyte-specific adaptor protein Grap2 is a central linker protein in immune cell signaling and activation. Using Grap2 as bait protein, we identified a novel human protein, GCIP (Grap2 cyclin-D interacting protein). We found that GCIP bound to Grap2 in both yeast two-hybrid assays and in mammalian cells through binding to the COOH-terminal unique domain and SH3 domain (designated QC domain) of Grap2. GCIP also associated with cyclin D both in vitro and in vivo. The expression of GCIP was found in all human tissues examined with the highest level of expression in the heart, muscle, peripheral blood leukocytes, and brain. Furthermore, phosphorylation of retinoblastoma protein by cyclin D-dependent protein kinase was reduced and E2F1-mediated transcription activity was inhibited in cells transfected with GCIP. High level expression of GCIP in terminally differentiated tissues and the inhibition of E2F1 transcription activation suggest that GCIP could play an important role in controlling cell differentiation and proliferation.
authors.affiliation: Department of Medical Biochemistry and Genetics, Center for Cancer Biology and Nutrition, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030, USA.
authors.forename: C
authors.initials: C
authors.lastname: Xia
authors.forename: Z
authors.initials: Z
authors.lastname: Bao
authors.forename: F
authors.initials: F
authors.lastname: Tabassam
authors.forename: W
authors.initials: W
authors.lastname: Ma
authors.forename: M
authors.initials: M
authors.lastname: Qiu
authors.forename: S
authors.initials: S
authors.lastname: Hua
authors.forename: M
authors.initials: M
authors.lastname: Liu
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D002460:Cell Line; D003001:Cloning, Molecular; D019938:Cyclin D1 / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics*; D016160:Retinoblastoma Protein / Q000378:metabolism; D056465:Retinoblastoma-Binding Protein 1; D016415:Sequence Alignment; D015398:Signal Transduction; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C485815:CCNDBP1 protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; C409587:GRAP2 protein, human; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D019938:Cyclin D1; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases