EFFECT OF PROTEIN-KINASE-C INHIBITORS ON INVASIVENESS OF HUMAN-MELANOMA CLONES EXPRESSING DIFFERENT LEVELS OF PROTEIN-KINASE-C ISOENZYMES

The involvement of protein kinase C (PKC) in the mechanism of chemotax is and invasiveness of human melanoma has been studied in 6 clones of 665/2 cell line characterized by a different integrin profile, differe ntiation grade and in vitro invasive ability. The levels of total prot ein kinase C activity revealed a direct correlation with the chemotact ic and invasive ability of these clones. Protein kinase C inhibitors, sphingosine and staurosporine, reduced chemotaxis and invasiveness of the highly invasive clone 2/60, while I-(5-isoquinolinylsulfonyl)-2-me thylpiperazine (H7) was ineffective. Immunofluorescence analysis revea led high levels of protein kinase C alpha in clone 2/60, while the les s invasive clone 2/21 expressed low levels of protein kinase C alpha a nd beta, but surprisingly appreciable levels of protein C gamma. Downr egulation with phorbol 12-myristate 13-acetate (TPA) did not affect in vasiveness of clone 2/60 unless the compound was present during the as say. H7 strongly increased invasiveness of clone 2/21 and was able to reverse the inhibitory effect of TPA on clone 2/60. Preliminary experi ments showed higher levels of diacylglycerol in clones with lower prot ein kinase C, suggesting a constitutive downregulation of the enzyme i n low invasive clones. Our results support a role for protein kinase C in the invasion process, but point out the complexity of the mechanis m which might involve the proteolytic fragment of the enzyme, protein kinase M. (C) 1994 Wiley-Liss, Inc.