CALPAIN-INDUCED DOWN-REGULATION OF ACTIVATED PROTEIN-KINASE C-ALPHA AFFECTS LUNG EPITHELIAL-CELL MORPHOLOGY

A few minutes after mouse lung epithelial cell lines were treated with 12-O-tetradecanoylphorbol-13-acetate (TPA), the cells rounded up and pulled away from their neighbors. Several hours later, the cells flatt ened out to resume their original morphology. To begin to characterize the enzymology underlying these changes, the subcellular distribution and intracellular content of the TPA receptor, protein kinase C (PKC) , and its putative endogenous regulator, the Ca2+-dependent protease, calpain, were investigated. Of eight PKC isozymes examined in several tumorigenic and nontumorigenic cell lines, all cells contained PKC-alp ha, PKC-delta, and PKC-zeta. TPA rapidly (5 min) translocated PKC-alph a from the cytosol to the particulate fraction; PKC-alpha concentratio ns then decreased with continued TPA exposure. PKC-zeta levels and int racellular location were not affected. An inhibitor of PKC activity, G F 109203X, prevented the initial morphological change. The calpain II isozyme was also found in all cell lines, and its cellular content inc reased as a result of TPA treatment. Calpain inhibitor I did not affec t the initial shape change but prevented subsequent flattening of the cells. We therefore conclude that PKC activation is required for the T PA-induced alterations in lung cell morphology and that calpain mediat es the return to a flattened epithelial appearance.