Astrocyte morphology altered by 1-(5-isoquinolinylsulfonyl) 2-methyl piperazine (H-7) and other protein kinase inhibitors.

Studies were conducted to determine if the protein kinase C inhibitor H-7 could block the effects of phorbol-12-myristate-13-acetate (PMA) on astrocyte morphology. Contrary to expectation, H-7 alone was found to induce morphological changes very similar to those elicited by PMA. This effect was shared by two other inhibitors of protein kinase C, H-8 and staurosporine, but not by the cyclic nucleotide-dependent protein kinase inhibitor HA-1004 or the calcium/calmodulin dependent protein kinase inhibitor W-7. Although the morphological effects observed with H-7 resemble those induced by PMA, H-7 did not promote the redistribution of protein kinase C to the membrane or induce the phosphorylation of endogenous proteins like PMA. In addition, the effects of H-7 were still observed in cells depleted of protein kinase C activity which were no longer responsive to treatment with PMA. Cytoskeletal elements appear to be involved in the effect of H-7 on cell shape since this effect is blocked by treatment with colchicine. Activators of the cyclic AMP-dependent protein kinase also alter astrocyte shape, however, while H-7 did cause a slight increase in cyclic AMP levels, it was unlikely that this action is responsible for its effect on morphology. One common action of both H-7 and PMA was to decrease the 32P content of several 20,000 Da proteins. While the mechanism by which H-7 exerts its influence on astrocyte morphology remains to be clarified, be it by the inhibition of protein kinase C or some other mechanism, the results suggest that caution must be used when interpreting the effects of activators and inhibitors of this kinase.