Syntaxin-3 Binds and Regulates Both R- and L-Type Calcium Channels in Insulin-Secreting INS-1 832/13 Cells

PLoS One. 2016 Feb 5;11(2):e0147862. doi: 10.1371/journal.pone.0147862. eCollection 2016.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium Channels, L-Type / metabolism*
  • Calcium Channels, R-Type / metabolism*
  • Cell Line
  • Humans
  • Insulin-Secreting Cells / metabolism*
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Qa-SNARE Proteins / chemistry
  • Qa-SNARE Proteins / genetics
  • Qa-SNARE Proteins / metabolism*
  • Syntaxin 1 / chemistry
  • Syntaxin 1 / metabolism


  • Calcium Channels, L-Type
  • Calcium Channels, R-Type
  • Qa-SNARE Proteins
  • Syntaxin 1