INTRACELLULAR SIGNALING IN ARTHROPOD BLOOD-CELLS - INVOLVEMENT OF PROTEIN-KINASE-C AND PROTEIN-TYROSINE PHOSPHORYLATION IN THE RESPONSE TO THE 76-KDA PROTEIN OR THE BETA-L,3-GLUCAN-BINDING PROTEIN IN CRAYFISH

Degranulation (regulated exocytosis) of crayfish granular blood cells and release of the prophenoloxidase activating system can be triggered by two endogenous ligands, a 76-kDa cell adhesion protein or a beta-1,3-glucan-binding protein when reacted with beta-1,3-glucan (beta GBP-L). These ligands bind a recently described membrane receptor. Degranulation triggered by these ligands was inhibited by the protein kinase C (pkC) inhibitor staurosporine or by the tyrosine kinase inhibitor herbimycin A. Incubation with the 76-kDa protein increased tyrosine phosphorylation of a granular cell protein of similar to 80 kDa. In addition, the pkC activating phorbol esters PMA or beta PDD degranulated the cells in a dose-dependent manner, whereas the control isomeric phorbol ester alpha PDD that does not activate pkC did not have any effect on the cells. Thus, we propose that binding of the 76-kDa protein or beta GBP-L to the receptor triggers cellular responses via a pathway that includes pkC activation and protein tyrosine phosphorylation.