CK2 kinase activity but not its binding to CK2 promoter regions is implicated in the regulation of CK2α and CK2β gene expressions

Abstract

Protein kinase CK2, a ubiquitous serine/threonine kinase in control of a variety of crucial cellular functions, is composed of catalytic a- and a0-subunits and non-catalytic b-subunits which form holoenzymes such as CK2(ab)2, CK2aa'b2, or CK2(a'b)2. In addition, there is sample evidence for the occurrence of the individual subunits beside the holoenzyme. While the CK2 subunits are well analyzed on the protein level, only little is known about the regulation of their transcription. The existence of multiple forms of CK2 subunits raised the question about a mutual regulation of their expression. Here we defined two 50-upstream regions of the CK2alpha and the CK2beta genes, respectively, as sequences with promoter activities. We found that CK2alpah and CK2alpha' stimulated the expression of the reporter constructs whereas, CK2beta was inactive. Using chromatin immunoprecipitation assays, we were unable to detect binding of endogenous CK2 subunits to these promoter sequences in vivo. However, it turned out that inhibition of the kinase activity of CK2 attenuated the promoter activity indicating that CK2alpha and CK2alpha' might regulate their gene expression indirectly by phosphorylation reactions. Thus, we have shown here (i) that under normal physiological conditions CK2 does not bind to CK2 promoter regions and (ii) that the CK2 kinase activity is implicated in the regulation of its own expression.