Differential translocation of protein kinase C epsilon during HeLa cell adhesion to a gelatin substratum

The spreading of HeLa cells, following attachment to a collagen or gelatin substratum, requires the activation of protein kinase C (PKC). Membrane-bound PKC was previously shown to be activated during cell attachment and in response to the activation of a series of lipid second messengers turned on by the ligation of beta1-integrin collagen receptors. HeLa cells express the alpha, gamma, epsilon, zeta, lambda, and iota isozymes of PKC as determined by Western blotting with specific antibodies. Only PKCepsilon redistributed from the cytosol to the membrane during cell adhesion. Most of the PKCepsilon in cells that were in suspension was in the cytosolic fraction. During cell attachment to a gelatin matrix, all of the PKCepsilon moved out of the cytosol, with most going to the membrane fraction. After the cells became fully spread, PKCepsilon began to reappear in the cytosol. Translocation of PKCepsilon was not observed during the adhesion of cells to culture dishes where cells nonspecifically attach but do not spread. The conventional PKCalpha and -gamma isozymes were translocated from the cytosol to the membrane only when phorbol ester was present at a concentration that increases the rate and extent of cell spreading. Under normal conditions, i.e. in the absence of phorbol ester, PKCepsilon appears to be the PKC isozyme responsible for the regulation of HeLa cell adhesion to the extracellular matrix.