Changes in the Expression of Cyclic D1-associated Rb Kinases, Their Activity and Rb Phosphorylation Status during Rat Liver Regeneration after Partial Hepatectomy

Abstract

Background/Aims: The changes of cell cycle regulators which may trigger G0 to G1 transition during liver regeneration have been examined.

Methods: Liver tissue was removed at various times after 70% partial hepatectomy. Expression of cell-cycle regulators was monitored by Western blot analysis. Association between them was assessed by Western blot analysis after immunoprecipitation. Also, immune complex kinase assay was performed.

Results and Conclusion: In vivo, thymidine uptake indicated that S-phase began about 18 hrs after partial hepatectomy and the peak of DNA synthesis appeared after 21 to 24 hrs. Immune complex kinase assay revealed that cyclin D1-associated kinase activity was increased two to three fold after the liver resection, which may partly explain the observed increase in the hyperphosphorylated form of Rb protein. As a possible explanation of the increase of kinase activity, the increase of cyclin D1 and CDK4 protein was observed, but not in CDK2. The association of cyclin D1 with CDK4 was also increased. Expression of p21CIP1 and p27KIP1 proteins increased slightly until 24 hrs. Moreover, association of CKIs with cyclin D1 also increased.