REGULATION OF EXOCYTOSIS FROM RAT PERITONEAL MAST-CELLS BY G-PROTEIN BETA-GAMMA-SUBUNITS

We applied G protein-derived beta gamma-subunits to permeabilized mast cells to test their ability to regulate exocytotic secretion. Mast ce lls permeabilized with streptolysin-O leak soluble (cytosol) proteins over a period of 5 min and become refractory to stimulation by Ca2+ an d GTP gamma S over similar to 20-30 min, beta gamma-Subunits applied t o the permeabilized cells retard this loss of sensitivity to stimulati on (run-down) and it can be inferred that they interact with the regul atory mechanism for secretion. While alpha-subunits are without effect , beta gamma-subunits at concentrations >10(-8) M enhance the secretio n due to Ca2+ and GTP gamma S. Unlike the small GTPases Rac and Cdc42, beta gamma-subunits cannot induce secretion in the absence of an acti vating guanine nucleotide, and thus further GTP-binding proteins (like ly to be Rho-related GTPases) must, be involved. The enhancement due t o beta gamma-subunits is mediated largely through interaction with ple ckstrin homology (PN) domains. It remains manifest in the face of maxi mum activation by PMA and inhibition of PKC with the pseudosubstrate i nhibitory peptide, Soluble peptides mimicking PN domains inhibit the s ecretion due to GTP gamma S and block the enhancement due to beta gamm a-subunits. Our data suggest that beta gamma-subunits are components o f the pathway of activation of secretion due to receptor-mimetic ligan ds such as mastoparan and compound 48/80.