RECOMBINANT SCINDERIN ENHANCES EXOCYTOSIS, AN EFFECT BLOCKED BY 2 SCINDERIN-DERIVED ACTIN-BINDING PEPTIDES AND PIP2

The cortical F-actin cytoskeleton represents a negative control for se cretion, and it must be locally disassembled to allow chromaffin vesic le exocytosis. Recombinant scinderin (a Ca2+-dependent F-actin-severin g protein) potentiated Ca2+-evoked F-actin disassembly and exocytosis in permeabilized chromaffin cells, an effect blocked by peptides Sc-AB P(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 (wi th sequence corresponding to a PIP2-binding site of scinderin). Trunca ted scinderin(254-715) (lacking actin-severing domains) did not potent iate exocytosis. Sc-ABP(1), Sc-ABP(2), and gamma-actin also inhibited exocytosis in the absence of recombinant scinderin, suggesting an inhi bition of endogenous scinderin. Results suggest that scinderin-evoked cortical F-actin disassembly is required for secretion and that scinde rin is an important component of the exocytotic machinery.