Cell cycle-dependent localization of the CDK3-cyclin E complex in Cajal (coiled) bodies

We have found that CDK2 and cyclin E, but not cyclin A, accumulates within Cajal bodies (CBs) in a cell cycle-dependent fashion. In the absence of cyc lin E, CDK2 is not enriched in the CB compartment, suggesting that the tran slocation of CDK2 to CBs is dependent on cyclin E. CDK2 and cyclin E could be recruited to CBs as a functional complex or CBs may serve as 'docking st ations' for CDK2-cyclin E activation by CAKs during the G(1)/S transition. Notably, CDK7-cyclin H-Mat1 complexes are known to accumulate in CBs. Treat ment of cells with inhibitors of either CDKs (olomoucine, 200 mu M) or RNA polymerase I (actinomycin D, 0.05 mu g/ml), results in a striking reorganiz ation of CDK2Z and p80 coilin to the nucleolar periphery. Furthermore, we d emonstrate that p80 coilin can be phosphorylated by purified CDK2-cyclin E complexes in vitro. Thus coilin and other CB proteins appear to be downstre am targets of CDK2-cyclin E complex-mediated signaling pathways regulating cell cycle progression and controlling aspects of CB function. Possible rol es for CDK2 and cyclin E in the well-documented association of CBs, histone gene clusters and RNA 3 ' end processing factors are discussed.