EFFECT OF PROTEIN-KINASE INHIBITOR H-7 ON THE CONTRACTILITY, INTEGRITY, AND MEMBRANE ANCHORAGE OF THE MICROFILAMENT SYSTEM

Addition of protein kinase inhibitor H-7 leads to major changes in cel l structure and dynamics. In previous studies [Citi, 1992: J. Cell Bio l. 117:169-178] it was demonstrated that intercellular junctions in H- 7-treated epithelial cells become calcium independent. To elucidate th e mechanism responsible for this effect we have examined the morpholog y, dynamics, and cytoskeletal organization of various cultured cells f ollowing H-7-treatment. We show here that drug treated cells display a n enhanced protrusive activity. Focal contact-attached stress fibers a nd the associated myosin, vinculin, and talin deteriorated in such cel ls while actin, vinculin, and N-cadherin associated with cell-cell jun ctions were retained. Furthermore, we demonstrate that even before the se cytoskeletal changes become apparent, H-7 suppresses cellular contr actility. Thus, short pretreatment with H-7 leads to strong inhibition of the ATP-induced contraction of saponin permeabilized cells. Compar ison of H-7 effects with those of other kinase inhibitors revealed tha t H-7-induced changes in cell shape, protrusional activity, and actin cytoskeleton structure are very similar to those induced by selective inhibitor of myosin light chain kinase, KT5926. Specific inhibitors of protein kinase C (Ro31-8220 and GF109203X), on the other hand, did no t induce similar alterations. These results suggest that the primary e ffect of H-7 on cell morphology, motility, and junctional interactions may be attributed to the inhibition of actomyosin contraction. This e ffect may have multiple effects on cell behavior, including general re duction in cellular contractility, destruction of stress fibers, and a n increase in lamellipodial activity. It is proposed that this reducti on in tension also leads to the apparent stability of cell-cell juncti ons in low-calcium medium. (C) 1994 Wiley-Liss, Inc.