Human casein kinase II. The subunit alpha protein activates transcription of the subunit beta gene.

Casein kinase II (CKII), an ubiquitous serine/threonine protein kinase in control of a variety of crucial cellular functions, is composed of catalytic subunits (alpha and alpha') and regulatory subunits (beta). The adjusted activity of CKII is determined by the actual conformational state of CKII beta and the stoichiometry of the CKII subunits. Thus, the expression control of CKII beta is of particular concern. Carrying out gel shifts and footprints with affinity-purified proteins and cellular extracts in combination with mutational analysis we find that aside NF1 and Sp1, two out of the many factors predicted to bind to the upstream promoter region of the human CKII beta gene (Voss, H., Wirkner, U., Jakobi, R., Hewitt, N. A., Schwager, C., Zimmermann, J., Ansorge, W., and Pyerin, W. (1991) J. Biol. Chem. 266, 13706-13711), CKII alpha protein is able to complex with the CKII beta gene promoter. The complex of CKII beta-DNA/CKII alpha-protein is shown to occur within the 170-239-base pair (bp) segment upstream of the first transcription start site of the gene. The DNA motif contains, in a distance of 44 bp, two GC-rich boxes, 5'-GGGGCCC and 5'-CCCCTGGGC, and represents a novel cis-acting element; the binding of the CKII alpha protein activates the CKII beta gene promoter. This is manifested by driving the expression of the indicator gene luciferase or of CKII alpha-cDNA in HeLa cells. The binding of the CKII alpha protein is inhibited due to CKII beta protein addition or by mimicking the corresponding situation in vivo by overexpression of the CKII subunits. The data suggest that cells may maintain a certain CKII subunit stoichiometry via transcriptional control; excess of nuclear CKII alpha protein could activate the CKII beta gene transcription causing CKII beta protein to increase which, in turn, could feed back to abolish the action of CKII alpha at the CKII beta gene promoter.