Protein kinase C-mediated translocation of secretory vesicles to plasma membrane and enhancement of neurotransmitter release from PC12 cells

In order to elucidate the molecular mechanism of phorbol ester-induced potentiation of neurotransmitter release, changes in the subcellular distribution of secretory vesicles were studied in PC12 cells. Dopamine (DA) and acetylcholine containing vesicles were selectively labelled by expressing green fluorescent protein-conjugated vesicular monoamine transporter and vesicular acetylcholine transporter, respectively. In the resting state, these vesicles were distributed throughout the cytoplasm. Phorbol-12-myristate-13-acetate (PMA), but not the inactive analogue 4alpha-PMA, induced a redistribution of both types of secretory vesicles near the plasma membrane, and this change was abolished by a protein kinase C (PKC) inhibitor, bisindolylmaleimide I (BIS). PMA also induced a marked enhancement of depolarization-induced DA release and phosphorylation of SNAP-25 at Ser(187) . BIS completely inhibited PMA-induced SNAP-25 phosphorylation but suppressed PMA-induced enhancement of DA release only partially. These results suggest that PMA enhances neurotransmitter release from PC12 cells by both PKC-dependent and PKC-independent mechanisms, and PKC enhances neurotransmitter release by recruiting secretory vesicles to the plasma membrane.