ACTIVATION OF PROTEIN-KINASE-C-ALPHA ISOFORM IN MURINE MELANOMA-CELLSWITH HIGH METASTATIC POTENTIAL

Metastasis is a multistep process in which protein kinase C (PKC) appe ars to be significantly involved. We analysed the activity and express ion of classical (alpha, beta, gamma) and novel PKC epsilon isoforms i n B16-F1 and B16-BL6 melanoma cells maintained under different culture conditions in vitro. We used high and low concentrations of tyrosine and phenylalanine in different media (DMEM or RPMI 1640 respectively) that affect the metastatic potential and also the proliferative, capac ity of the cells. We also tested a weakly metastatic amelanotic B78-H1 melanoma cell line which is unaffected by the different culture condi tions. In both B16 melanoma tell lines activation of PKC alpha (withou t increased expression) occurred under growth conditions permissive of metastasis (DMEM). In contrast, the weakly metastatic amelanotic B78- H1 cell line showed a substantial inactivation of this isoform in the two different culture media, suggesting a specific involvement of PKC alpha in the metastatic process, Moreover, in B16 melanoma cells, nove l PKC epsilon was activated under culture conditions which stimulated grow th but not metastasis (RPMI 1640). In order to define the relatio nship between PKC activation and the metastatic process we also determ ined the release of cathepsin B. No correlation between PKC activity a nd cathepsin B release in either B16 melanoma cell lines could be demo nstrated.