EXPRESSION OF SYNAPTOSOMAL-ASSOCIATED PROTEIN SNAP-25 IN ENDOCRINE ANTERIOR-PITUITARY-CELLS

A growing body of evidence indicates that the fundamental molecular me chanism of exocytosis in the secretory pathway may be structurally sim ilar in all eukaryotic cells. The synaptosomal-associated protein of 2 5 kDa (SNAP-25) is a plasma membrane protein involved in regulated exo cytosis in neurons. In order to compare exocytotic components in neuro ns and endocrine cells, we have analyzed the expression of SNAP-25 in the rat anterior pituitary. Western blotting analysis documented the p resence of SNAP-25 in anterior pituitary homogenates and cultured ante rior pituitary cells. In addition to SNAP-25, other neuronal proteins involved in exocytosis (syntaxin, VAMP/synaptobrevin and Rab3A) were a lso detected in the anterior pituitary. The specific expression of SNA P-25 mRNA in anterior pituitary cells was also corroborated by Norther n analysis. SNAP-25 immunoreactivity was located at the plasma membran e of endocrine anterior pituitary cells, Characteristically, patches o f fine punctate deposits exhibited intense SNAP-25 immunoreactivity. D ouble-labeling immunocytochemistry revealed that SNAP-25 was mainly as sociated with gonadotroph cell populations. Furthermore, we demonstrat e that in the anterior pituitary, SNAP-25 is selectively cleaved by cl ostridial neurotoxins. In conclusion, our results establish the presen ce of SNAP-25 in secretory anterior pituitary cells and suggest a pote ntial role of this protein in the secretion of adenohypophysial hormon e.