title: Distinct expression patterns and transforming properties of multiple isoforms of Ost, an exchange factor for RhoA and Cdc42.
abstract: A search for transforming genes expressed in brain led to the identification of a novel isoform of Ost, an exchange factor for RhoA and Cdc42. In addition to the Dbl-homology (DH) and pleckstrin-homology (PH) domains identified in the original Ost, this isoform contained a SH3 domain and a novel HIV-Tat related (TR) domain. The presence or absence of these domains in Ost defined multiple isoforms of the protein. RT - PCR and in situ hybridization analysis revealed that these isoforms were generated by tissue-specific and developmentally restricted alternative splicing events. Whereas deletion of the N-terminus activated the transforming properties of Ost, the presence of the SH3 domain reduced the transforming activity of the protein. This inhibition was relieved by the presence of a TR domain, which contained a potential SH3 ligand sequence. The transforming activity of all Ost isoforms was inhibited by dominant negative forms of the Rho family proteins. Expression of Ost isoforms potently induced the formation of actin stress fibers and filopodia as well as JNK activity and AP1- and SRF-regulated transcriptional pathways. Ost transfectants also displayed elevated levels of cyclins A and D1, suggesting that the de-regulation of these cyclins is linked to Ost-mediated transformation.
authors.affiliation: Laboratory of Cellular and Molecular Biology, National Cancer Institute, Building 37 Room 1E24, 37 Convent Dr. MSC 4255, Bethesda, Maryland 20892, USA.
authors.forename: M V
authors.initials: MV
authors.lastname: Lorenzi
authors.forename: P
authors.initials: P
authors.lastname: Castagnino
authors.forename: Q
authors.initials: Q
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Hori
authors.forename: T
authors.initials: T
authors.lastname: Miki
mesh_terms: D016475:3T3 Cells; D000367:Age Factors; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D003001:Cloning, Molecular; D003599:Cytoskeleton; D004268:DNA-Binding Proteins / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D051379:Mice; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011554:Pseudopodia; D051381:Rats; D017386:Sequence Homology, Amino Acid; D026362:Serum Response Factor; D015398:Signal Transduction; D014018:Tissue Distribution; D018808:Transcription Factor AP-1 / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein; D018909:src Homology Domains
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D020662:Guanine Nucleotide Exchange Factors; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D020033:Protein Isoforms; D011506:Proteins; D026362:Serum Response Factor; D018808:Transcription Factor AP-1; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein