HPC-1/syntaxin 1A suppresses exocytosis of PC12 cells

The membrane protein syntaxin (originally named HPC-1) is involved in vesic le trafficking and required for neurotransmitter release at nerve terminals . The presence of syntaxin on target membranes is hypothesized to confer sp ecificity to targeting and fusion via interactions with complementary vesic le-associated proteins. To elucidate the function of syntaxin 1A in exocyto sis, HPC-1/syntaxin 1A-reduced PC12h cells (PC12h/Delta syx) that were stab ly transfected with a plasmid for antisense syntaxin 1A expression were con structed. Depolarizing stimulation of PC12h/Delta syx enhanced dopamine rel ease, compared with PC12h, There was a strong inverse correlation between s yntaxin 1A protein expression and enhancement of dopamine release. Reductio n of syntaxin 1A had no effect on increase of the cytoplasmic free Ca2+ con centration by depolarized stimulation. Moreover, PC12h/Delta syx clones sim ilarly enhanced of exocytosis by native secretagogues, These results indica te that syntaxin 1A has more than one function in exocytosis.