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Involvement of Rab3A in Vesicle Priming During Exocytosis: Interaction with Munc13‐1 and Munc18‐1
Author(s) -
Huang ChienChang,
Yang DeMing,
Lin ChungChih,
Kao LungSen
Publication year - 2011
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1111/j.1600-0854.2011.01237.x
Subject(s) - exocytosis , munc 18 , biology , microbiology and biotechnology , priming (agriculture) , vesicle , secretory vesicle , vesicle fusion , synaptic vesicle , secretion , membrane , biochemistry , botany , germination
Rab3A is a small G‐protein of the Rab family that is involved in the late steps of exocytosis. Here, we studied the role of Rab3A and its relationship with Munc13‐1 and Munc18‐1 during vesicle priming. Phorbol 12‐myristate 13‐acetate (PMA) is known to enhance the percentage of fusion‐competent vesicles and this is mediated by protein kinase C (PKC)‐independent Munc13‐1 activation and PKC‐dependent dissociation of Munc18‐1 from syntaxin 1a. Our results show that the effects of PMA varied in cells overexpressing Rab3A or mutants of Rab3A and in cells with Rab3A knockdown. When Munc13‐1 was overexpressed in Rab3A knockdown cells, secretion was completely inhibited. In cells overexpressing a Rab‐interacting molecule (RIM)‐binding deficient Munc13‐1 mutant, 128‐Munc13‐1, the effects of Rab3A on PMA‐induced secretion was abolished. The effect of PMA, which disappeared in cells overexpressing GTP‐Rab3A (Q81L), could be reversed by co‐expressing Munc18‐1 but not its mutant R39C, which is unable to bind to syntaxin 1a. In cells overexpressing Munc18‐1, manipulation of Rab3A activity had no effect on secretion. Finally, Munc18‐1 enhanced the dissociation of Rab3A, and such enhancement correlated with exocytosis. In summary, our results support the hypothesis that the Rab3A cycle is coupled with the activation of Munc13‐1 via RIM, which accounts for the regulation of secretion by Rab3A. Munc18‐1 acts downstream of Munc13‐1/RIM/Rab3A and interacts with syntaxin 1a allowing vesicle priming. Furthermore, Munc18‐1 promotes Rab3A dissociation from vesicles, which then results in fusion.