Zhang X, Jiang S, Mitok KA, Li L, Attie AD, Martin TFJ. BAIAP3, a C2 domain-containing Munc13 protein, controls the fate of dense-core vesicles in neuroendocrine cells.
J Cell Biol 2017. [PMID:
28626000 PMCID:
PMC5496627 DOI:
10.1083/jcb.201702099]
[Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Zhang et al. conducted a siRNA screen of C2 domain proteins involved in regulated peptide secretion. One of the hits, a Munc13 family member BAIAP3, was characterized as endosome localized involved in post-exocytic dense-core vesicle protein recycling to the TGN. BAIAP3 knockdown inhibited dense-core vesicle maturation/stability in neuroendocrine/endocrine cells.
Dense-core vesicle (DCV) exocytosis is a SNARE (soluble N-ethylmaleimide–sensitive fusion attachment protein receptor)-dependent anterograde trafficking pathway that requires multiple proteins for regulation. Several C2 domain–containing proteins are known to regulate Ca2+-dependent DCV exocytosis in neuroendocrine cells. In this study, we identified others by screening all (∼139) human C2 domain–containing proteins by RNA interference in neuroendocrine cells. 40 genes were identified, including several encoding proteins with known roles (CAPS [calcium-dependent activator protein for secretion 1], Munc13-2, RIM1, and SYT10) and many with unknown roles. One of the latter, BAIAP3, is a secretory cell–specific Munc13-4 paralog of unknown function. BAIAP3 knockdown caused accumulation of fusion-incompetent DCVs in BON neuroendocrine cells and lysosomal degradation (crinophagy) of insulin-containing DCVs in INS-1 β cells. BAIAP3 localized to endosomes was required for Golgi trans-Golgi network 46 (TGN46) recycling, exhibited Ca2+-stimulated interactions with TGN SNAREs, and underwent Ca2+-stimulated TGN recruitment. Thus, unlike other Munc13 proteins, BAIAP3 functions indirectly in DCV exocytosis by affecting DCV maturation through its role in DCV protein recycling. Ca2+ rises that stimulate DCV exocytosis may stimulate BAIAP3-dependent retrograde trafficking to maintain DCV protein homeostasis and DCV function.
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