Protein kinase C delta involvement in mammary tumor cell metastasis

Metastasis requires cytoskeletal remodeling for migration, adhesion, and ex travasation of metastatic cells. Although protein kinase C (PKC) is involve d in tumor promotion/progression and cytoskeletal remodeling, its role in m etastasis has not been defined. PKC delta levels are increased in highly me tastatic 13762NF mammary tumor cells (MTLn3) compared with less metastatic, parental cell lines. To determine whether the increase in endogenous PKC d elta is functionally related to their increased metastatic potential, we pr epared MTLn3 cells that express the inhibitory regulatory domain fragment o f PKC delta (RD delta) under the control of a tetracycline-inducible promot er. RD delta expression attenuated endogenous PKC activity, as demonstrated by decreased phosphorylation of the PKC substrate adducin in migrating cel ls. Thus, in MT cells, RD delta appears to primarily influence cytoskeleton -dependent processes rather than cell cycle progression. To determine wheth er RD delta expression influenced metastatic potential in vivo, MTLn3/RD de lta cells were either grown in the mammary fat pad or injected into the tai l vein of syngeneic rats, and effects of doxycycline-induced RDF expression on pulmonary metastases were studied. Consistent with the im vitro data, i nduction of RD delta significantly reduced the number of lung metastases wi thout affecting growth of the primary tumor. These results suggest that int erfering with endogenous PKC delta activity by expressing the inhibitory RD delta fragment inhihits cytoskeleton-regulated processes important for MTL n3 cell metastasis.