title: Skp2 induction and phosphorylation is associated with the late G1 phase of proliferating rat hepatocytes.
abstract: The changes in phosphoproteins purified with the affinity peptide p9CKShs1 were analyzed from extracts of regenerating rat livers in order to define some G1 and G1/S regulations characteristic of mature hepatocytes stimulated to proliferate. We observed a 47 kDa phosphoprotein that occurred first at the end of G1 before peaking in the S phase. P47 was also found to be phosphorylated in late G1 in primary hepatocyte cultures stimulated with mitogens. P47 was still phosphorylated in extracts depleted of Cdc2, but to a lesser extent after Cdk2 depletion. This phosphoprotein was identified as Skp2. (i) P47 shared the same electrophoretic mobility than Skp2, a cell cycle protein essential for S phase entry in human fibroblasts; (ii) Skp2, like P47, started to be expressed and was highly phosphorylated during the G1/S transition of hepatocytes stimulated to proliferate in vivo and in vitro; (iii) P47 was specifically immunoprecipitated by an antibody directed against Skp2. In addition, cyclin A/Cdk2 complexes from regenerating liver clearly interacted with Skp2. This is the first demonstration that Skp2 is induced and phosphorylated in the late G1 and S phase of hepatocytes in vivo in regenerating liver as well as in vitro in mitogen-stimulated hepatocytes.
authors.affiliation: INSERM U49, Unité de Recherches Hépatologiques, Hôpital Pontchaillou, Rennes, France.
authors.forename: M
authors.initials: M
authors.lastname: Bilodeau
authors.forename: H
authors.initials: H
authors.lastname: Talarmin
authors.forename: G
authors.initials: G
authors.lastname: Ilyin
authors.forename: C
authors.initials: C
authors.lastname: Rescan
authors.forename: D
authors.initials: D
authors.lastname: Glaise
authors.forename: S
authors.initials: S
authors.lastname: Cariou
authors.forename: P
authors.initials: P
authors.lastname: Loyer
authors.forename: C
authors.initials: C
authors.lastname: Guguen-Guillouzo
authors.forename: G
authors.initials: G
authors.lastname: Baffet
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002478:Cells, Cultured; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D053487:DEAD-box RNA Helicases; D004815:Epidermal Growth Factor / Q000494:pharmacology; D016193:G1 Phase; D005786:Gene Expression Regulation; D006801:Humans; D008099:Liver / Q000166:cytology* / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D016196:S Phase
chemical_list: D016213:Cyclins; D009687:Nuclear Proteins; D010710:Phosphates; D010750:Phosphoproteins; D004815:Epidermal Growth Factor; D018844:Cyclin-Dependent Kinases; C075446:Ddx39b protein, rat; D053487:DEAD-box RNA Helicases