Protein kinase Cα negatively regulates cell spreading and motility in MDA-MB-231 human breast cancer cells downstream of epidermal growth factor receptor

Previous work has shown that phorbol esters modulate chemotaxis. Here, we demonstrate that PKC activation via phorbol 12-myristate 13-acetate (PMA) treatment of MDA-MB-231 cells inhibits EGF-induced cell spreading, the initial event of motility and chemotaxis. Of five PKC isoforms (alpha,iota,lambda,delta,and epsilon) identified in this cell line, PMA treatment only induced PKCalpha translocation from the cytosol to the membrane, an event that correlated with the development of the rounded morphology. Cell recovery was linked to PKCalpha downregulation in part via the proteasome pathway since treatment with MG101 in the presence of PMA did not lead to PKCalpha degradation and cell recovery. Co-immunoprecipitation and immunolocalization demonstrated that EGF co-localized with PKCalpha and EGFR, however, PMA did not abrogate EGFR transactivation. This work suggests that PKCalpha is the primary target of PMA acting as a transient negative regulator of cell spreading and motility in MDA-MB-231 breast cancer cells.