Regulation of p53 mediated transactivation by the beta-subunit of protein kinase CK2

The growth suppressor protein p53 plays a main part in cellular growth cont rol, Two of its key functions are sequence specific DNA binding and transac tivation, Functions of p53 in growth control are regulated at least in part by its interaction with protein kinases, p53 binds to protein kinase CK2, formerly known as casein kinase 2, and it is phosphorylated by this enzyme. CK2 is composed of two regulating beta-subunits and two catalytic alpha- o r alpha'-subunits and the interaction with p53 is mediated by the regulator y beta-subunit of CK2. Recently we showed that the beta-subunit could inhib it the sequence specific DNA binding activity of p53 in vitro, Based on thi s finding, we asked if a coexpression of the beta-subunit of CK2 with p53 i n mammalian cells could inhibit the DNA binding activity of p53 in a physio logical context. We found that the coexpression of the beta-subunit showed the same inhibitory effect as in the previous assays with purified proteins . Then, we investigated the effects of the coexpression of the beta-subnnit of CK2 on the transactivation and transrepression activity of p53. We foun d that transactivation of the mdm2, p21(WAF1/CIP1) and cyclin G promoter wa s inhibited in three different cell lines whereas transactivation of the ba r promoter was not affected in COS1 cells but down-regulated in MCO1 and Sa osS138V21 cells. p53 mediated transrepression of the fos promoter was not i nfluenced by coexpression of the CK2 beta-subunit, Taken together we propos e a cell type dependent fine regulation of the p53 transactivation function by the CK2 beta-subunit in vivo, which does not affect p53 mediated transr epression. (C) 1999 Federation of European Biochemical Societies.