Overexpression of alpha and beta isoforms of Ca2+/calmodulin-dependent protein kinase II in neuroblastoma cells -- H-7 promotes neurite outgrowth.

Since the alpha and beta isoforms of CaM kinase II are known to be expressed almost exclusively in the brain, we compared the effect of overexpression of the beta isoform of CaM kinase II with that of the alpha isoform. The subcellular distribution of the alpha isoform was different from that of the beta isoform, although the catalytic properties of the alpha and beta isoforms expressed in transfected cells were similar to those of brain CaM kinase II. The alpha isoform was found in the soluble fraction more than in the particulate fraction, whereas most of the beta isoform bound to subcellular structures. In the cell overexpressing alpha and beta isoforms of CaM kinase II, neurite extension was promoted when compared with the morphology of neo transfectants. Neurite outgrowth of cells overexpressing CaM kinase II was further stimulated by the treatment of 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), a selective but not absolutely specific inhibitor of protein kinase C. The morphological change was rapid and observed within 1 h followed by H-7 treatment. Morphological changes, such as the number of cells with neurites and length of neurites were greater in the beta cells than in the alpha cells. Chelerythrine, a specific inhibitor of protein kinase C, also stimulated the neurite outgrowth of these cells. Some substrates of CaM kinase II related to neurite outgrowth were detected in cells overexpressing CaM kinase II stimulated with H-7. These results suggest that CaM kinase H and protein kinase C play an important role in the control of cell change, and that the subcellular distribution of CaM kinase II is important for regulating cellular functions efficiently.