Distribution of MAP kinase, S6 kinase, and casein kinase II in rat tissues: activation by insulin in spleen.

We examined the distribution of mitogen-activated protein (MAP) kinase, S6 kinase, and casein kinase II (CK-II) in the muscle, spleen, brain, and testes of Wistar rats. It was observed that spleen extracts contained the highest activity of all the kinases. Anion-exchange chromatography of spleen extracts by a MonoQ column resolved a single peak of myelin basic protein phosphotransferase activity that eluted after the usual position of the previously described p42 and p44 MAP kinases. Immunoblotting of the peak fractions with anti-MAP kinase antibody did not detect any immunoreactive bands that coincided with the activity peak, suggesting that the activity may represent a potentially novel MAP kinase. The MonoQ fractionation also resolved a single peak of phosvitin phosphotransferase activity which coincided with the intensity of two immunoreactive bands of 39 and 43 kilodaltons that were detected with antibodies against CK-II. The chromatographic behaviour and immunoblotting data indicate that the phosvitin kinase peak represented CK-II and suggested that the rat spleen CK-II had a molecular structure of alpha alpha ' beta 2. Furthermore, using an intact rat model, we showed that the potentially novel spleen MAP kinase and CK-II were markedly activated following intravenous injection of insulin. The significance of these findings remains to be determined.