Monoclonal antibody binding to a receptor on nonspecific cytotoxic cells (NCC) increases the expression of proto-oncogene kinases and protein kinase C.

Teleost nonspecific cytotoxic cells (NCC) initiate various cell triggering responses following receptor-target cell interactions. A putative receptor protein on NCC may alternatively initiate signalling processes following crosslinkage by homologous anti-receptor mab 5C6. In the present study, we demonstrated that binding to this receptor by mab 5C6 produced increased levels of expression of cytoplasmic src family proto-oncogene kinases lck, fyn and src. The phosphorylated isoforms of each kinase were approximately the same molecular weight (p60). Unlike their mammalian T-cell and natural killer (NK) cell counterparts, NCC p56lck did not autophosphorylate on tyrosine residues. This was determined by a lack of Western blot reactivity of teleost p56lck with anti-phosphotyrosine specific antibodies PT-66 or 4G10. Additional evidence for this lack of tyrosine phosphorylation was shown by experiments treating mab 5C6 activated NCC with sodium orthovanadate. This protein tyrosine phosphatase inhibitor did not affect levels of p56lck autophosphorylation. Mab 5C6 activated NCC were also examined to determine if levels of protein kinase C (PKC) expression were affected during triggering responses. Maximum increased PKC levels occurred 5-10 min following binding. The NCC receptor-activated PKC consisted of a 60,000 M(r) isoform and a 30,000 M(r) homologue equivalent to the mammalian PKC catalytic subunit. Not all kinases examined, however, were affected by mab 5C6 binding. Levels of expression of c-myc and cdc2p34 did not change following NCC activation. This is the first study of NK-like cells in cold-blooded vertebrates regarding the expression of these vital intermediary transducing kinases.(ABSTRACT TRUNCATED AT 250 WORDS)