Transcription Factors Ets1, NF-κB, and Sp1 Are Major Determinants of the Promoter Activity of the Human Protein Kinase CK2α Gene

Abstract

CK2alpha is one of two isoforms of protein kinase CK2, a highly conserved, ubiquitous, and vital phosphotransferase whose expression is kept at constant cellular levels and whose dysregulated expression has been linked to malignant diseases. The upstream sequence of the gene coding for human CK2alpha (CSNK1A1, chromosomal location 20p13) has been examined for promoter location and transcription factor interactions using reporter gene assays (luciferase; HeLa cells), site-directed mutagenesis, electrophoretic mobility shift assays, super-shifts, UV cross-linking, Western blotting, and DNA affinity chromatography. Highest promoter activity has been found in a region comprising positions -9 to 46. Factors Sp1, Ets-1, and NF-kappaB have been identified as interaction partners and, by mutation of individual sites and simultaneous mutations of two or more sites, shown to cross-talk to each other. At least two of the factors (Sp1; NF-kappaB) were susceptible to phosphorylation by CK2 holoenzyme, a tetramer composed of two CK2alpha and two regulatory CK2beta proteins, but not by individual CK2alpha. Because the phosphorylation decreases promoter binding and repeated immunoprecipitation reveals presence of "free" CK2beta in cell extracts, it is tempting to speculate that the gene product CK2alpha might readily form CK2 holoenzyme and feed back onto gene transcription. The data represent the first promoter control analysis of a mammalian CK2alpha gene and provide a hypothesis of how the constant expression level of CK2alpha may be achieved.