title: Evaluation of beta-cell replication in mice transgenic for hepatocyte growth factor and placental lactogen: comprehensive characterization of the G1/S regulatory proteins reveals unique involvement of p21cip.
abstract: We hypothesized that combined transgenic overexpression of hepatocyte growth factor (HGF) and placental lactogen in islets would lead to even greater increases in beta-cell mass and replication than either growth factor alone. This did not occur, suggesting that beta-cell replication is saturable or subject to molecular restraint. We therefore performed the first comprehensive G(1)/S cell cycle survey in islets, cataloguing the broad range of kinases, cyclins, and kinase inhibitors that control the G(1)/S transition in islets from normal, HGF, placental lactogen, and doubly transgenic mice. Many of the G(1)/S checkpoint regulators (E2Fs; pRb; p107; p130; cyclins D(1),(2),(3), A, and E; cdk-2; cdk-4; p15; p16; p18; p19; p21; p27; MDM2; p53; c-Myc; and Egr-1) are present in the murine islet. Most of these proteins were unaltered by overexpression of HGF or placental lactogen, either alone or in combination. In contrast, p21(cip) was uniquely, dramatically, and reproducibly upregulated in placental lactogen and HGF islets. p21(cip) was also present in, and upregulated in, proliferating human islets, localizing specifically in beta-cells and translocating to the nucleus on mitogenic stimulation. Homozygous p21(cip) loss releases islets from growth inhibition, markedly enhancing proliferation in response to HGF and placental lactogen.
authors.affiliation: Division of Endocrinology, BST E-1140, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15213, USA. cozari@dom.pitt.edu
authors.forename: Irene
authors.initials: I
authors.lastname: Cozar-Castellano
authors.forename: Matthew
authors.initials: M
authors.lastname: Weinstock
authors.forename: Marcia
authors.initials: M
authors.lastname: Haught
authors.forename: Silvia
authors.initials: S
authors.lastname: Velázquez-Garcia
authors.forename: Darinka
authors.initials: D
authors.lastname: Sipula
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Stewart
mesh_terms: D000818:Animals; D002455:Cell Division; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D016193:G1 Phase; D017353:Gene Deletion; D017228:Hepatocyte Growth Factor / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D010928:Placental Lactogen / Q000235:genetics / Q000378:metabolism*; D016196:S Phase; D015854:Up-Regulation
chemical_list: C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D017228:Hepatocyte Growth Factor; D010928:Placental Lactogen