Protein kinase CK2: evidence for a protein kinase CK2β subunit fraction, devoid of the catalytic CK2α subunit, in mouse brain and testicles

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Abstract
The highest CK2 activity was found in mouse testicles and brain, followed by spleen, liver, lung, kidney and heart. The activity values were directly correlated with the protein expression level of the CK2 subunits α (catalytic) and β (regulatory). The α′ subunit was only detected in brain and testicles. By contrast, Northern blot analyses of the CK2α mRNA revealed a somewhat different picture. Here, the strongest signals were obtained for brain, liver, heart and lung. In kidney, spleen and testicles mRNAs were only weakly detectable. For CK2α′ mRNA distribution strong signals were observed for lung, liver and testicles. In the case of CK2β mRNA the highest signals were found for testicles, kidney, brain and liver. The amount of CK2β mRNA in testicles was estimated to be about 6-fold higher than in brain. The strongest CK2β signals in the Western blot were found for testicles and brain. The amount of CK2β protein in brain in comparison to the other organs (except testicles) was estimated to be ca. 2–3-fold higher whereas the ratio of CK2β between testicles and brain was estimated to be 3–4-fold. Results from the immunoprecipitation experiments support the notion for the existence of free CK2β population and/or CK2β in complex with other protein(s) present in brain and testicles. In all other mouse organs investigated, i.e. heart, lung, liver, kidney and spleen, no comparable amount of free CK2β was observed. This is the first physiological evidence for the existence of a ‘free CK2β’ (or in complex with proteins other than CK2α) in normal animal tissue apart from the hitherto dogmatic association with CK2α in a tetrameric holoenzyme complex.