STIMULATION OF CATECHOLAMINE SECRETION FROM ADRENAL CHROMAFFIN CELLS BY 14-3-3-PROTEINS IS DUE TO REORGANIZATION OF THE CORTICAL ACTIN NETWORK

Catecholamine release from digitonin-permeabilized adrenal chromaffin cells is increased by exogenous 14-3-3 proteins. In order to determine how 14-3-3 proteins stimulate exocytosis their effect on the cortical actin network was examined, Increased amounts of beta and gamma isoforms of 14-3-3 proteins were associated with the Triton-insoluble cytoskeleton of chromaffin cells following incubation with exogenous 14-3-3 proteins. The stimulation of catecholamine release by 14-3-3 proteins was abolished by prior incubation with the actin filament stabilising drug phalloidin. Rhodamine phalloidin staining showed that the cortical actin network was disassembled and actin reorganised into intracellular foci following treatment with 14-3-3 proteins. These data suggest that 14-3-3 proteins enhance catecholamine release in permeabilized chromaffin cells by reorganisation of the cortical actin barrier to allow increased availability of secretory vesicles for exocytosis.