title: Syntaxin-3 Binds and Regulates Both R- and L-Type Calcium Channels in Insulin-Secreting INS-1 832/13 Cells.
abstract: Syntaxin (Syn)-1A mediates exocytosis of predocked insulin-containing secretory granules (SGs) during first-phase glucose-stimulated insulin secretion (GSIS) in part via its interaction with plasma membrane (PM)-bound L-type voltage-gated calcium channels (Cav). In contrast, Syn-3 mediates exocytosis of newcomer SGs that accounts for second-phase GSIS. We now hypothesize that the newcomer SG Syn-3 preferentially binds and modulates R-type Cav opening, which was postulated to mediate second-phase GSIS. Indeed, glucose-stimulation of pancreatic islet β-cell line INS-1 induced a predominant increase in interaction between Syn-3 and Cavα1 pore-forming subunits of R-type Cav2.3 and to lesser extent L-type Cavs, while confirming the preferential interactions between Syn-1A with L-type (Cav1.2, Cav1.3) Cavs. Consistently, direct binding studies employing heterologous HEK cells confirmed that Syn-3 preferentially binds Cav2.3, whereas Syn-1A prefers L-type Cavs. We then used siRNA knockdown (KD) of Syn-3 in INS-1 to study the endogenous modulatory actions of Syn-3 on Cav channels. Syn-3 KD enhanced Ca2+ currents by 46% attributed mostly to R- and L-type Cavs. Interestingly, while the transmembrane domain of Syn-1A is the putative functional domain modulating Cav activity, it is the cytoplasmic domain of Syn-3 that appears to modulate Cav activity. We conclude that Syn-3 may mimic Syn-1A in the ability to bind and modulate Cavs, but preferring Cav2.3 to perhaps participate in triggering fusion of newcomer insulin SGs during second-phase GSIS.
authors: Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors: Li
authors: L
authors: Xie
authors: Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors: Subhankar
authors: S
authors: Dolai
authors: Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors: Youhou
authors: Y
authors: Kang
authors: Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors: Tao
authors: T
authors: Liang
authors: Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors: Huanli
authors: H
authors: Xie
authors: Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors: Tairan
authors: T
authors: Qin
authors: Institute of Molecular Medicine, Peking University, Beijing, China.
authors: Lu
authors: L
authors: Yang
authors: Institute of Molecular Medicine, Peking University, Beijing, China.
authors: Liangyi
authors: L
authors: Chen
authors: Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors: Herbert Y
authors: HY
authors: Gaisano
mesh_terms: D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020908:Calcium Channels, R-Type / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D050765:Qa-SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050827:Syntaxin 1 / Q000737:chemistry / Q000378:metabolism
chemical_list: D020746:Calcium Channels, L-Type; D020908:Calcium Channels, R-Type; D050765:Qa-SNARE Proteins; D050827:Syntaxin 1