MICROSOMAL LOCALIZATION OF CYCLIN-A AND CDK2 IN PROLIFERATING RAT-LIVER CELLS

The expression and intracellular localization of cyclin A and cdk2 hav e been analyzed in rat liver cells proliferatively activated in vivo b y a partial hepatectomy. Western blot analysis revealed that cyclin A started to increase during G1 (at 6 h after hepatectomy) reaching maxi mal levels during S phase (at 18 h). Cdk2 began to increase during lat e G1 (at 12 h) peaking also at 18 h. At the latter time cyclin A was m ainly localized in the microsomal fraction, although it was also prese nt in cytosol, plasma membrane and nucleus. Active cyclin/cdks complex es containing cyclin A and cdk2 were obtained by precipitation with p1 3-Sepharose after solubilization of microsomes with triton X-100. The presence of active cyclin A/cdk2 complexes in microsomes was confirmed by immunoprecipitation experiments with anti-cdk2 antibodies. These r esults suggest a putative role of cyclin A/cdk2 during S phase which w ould be related with microsomal function. (C) 1994 Academic Press, Inc .