Subcellular localization of protein kinase CK-2 alpha- and beta-subunits in synchronized cells from primary human fibroblasts and established cell lines.

Casein kinase 2 (CK-2) subunits were sublocalized by indirect immunofluorescence in synchronized primary human fibroblasts, human HT1080, and mouse 3T3 cells. The antibodies used were directed against the CK-2 alpha- and beta-subunits. In human primary fibroblasts and the fibrosarcoma (HT1080) both the alpha and beta-subunits were predominantly localized in the nucleus, irrespective of the stage of the cell cycle. By contrast, in murine 3T3 cells, CK-2 alpha-subunit was found in the cytoplasm whereas the beta-subunit was mostly localized in the nucleus. In parallel, CK-2 activity was measured throughout the cell cycle. Apart from the well-known differences between cell lines with their high proliferation rate and higher CK-2 activity, and the slower growing primary cell cultures with lower CK-2 activity, no significant activity changes were measured. Densitometric analysis of CK-2 alpha- vs. beta-subunits after immunoblot detection revealed a 10:1 ratio for primary human skin fibroblasts at quiescent state which is significantly more than at later stages. Such an asymmetrical subunit distribution at G0 was not observed with the established cell line 3T3 where the alpha/beta ratio was 0.7-1 throughout the cell cycle.