Recombinant scinderin enhances exocytosis, an effect blocked by two scinderin-derived actin-binding peptides and PIP2

The cortical F-actin cytoskeleton represents a negative control for secretion, and it must be locally disassembled to allow chromaffin vesicle exocytosis. Recombinant scinderin (a Ca2+-dependent F-actin-severing protein) potentiated Ca2+-evoked F-actin disassembly and exocytosis in permeabilized chromaffin cells, an effect blocked by peptides Sc-ABP(1) and Sc-ABP(2) (with sequences corresponding to two actin-binding sites of scinderin), exogenous gamma-actin, or phosphatidylinositol 4,5-bisphosphate (PIP2) PIP2 effect was blocked by peptide Sc-PIP2BP (with sequence corresponding to a PIP2-binding site of scinderin). Truncated scinderin(254-715) (lacking actin-severing domains) did not potentiate exocytosis. Sc-ABP(1), Sc-ABP(2), and gamma-actin also inhibited exocytosis in the absence of recombinant scinderin, suggesting an inhibition of endogenous scinderin. Results suggest that scinderin-evoked cortical F-actin disassembly is required for secretion and that scinderin is an important component of the exocytotic machinery.