The 25-kDa synaptosome-associated protein (SNAP-25) binds and inhibits delayed rectifier potassium channels in secretory cells.
Delayed-rectifier K(+) channels (K(DR)) are important regulators of membrane excitability in neurons and neuroendocrine cells. Opening of these voltage-dependent K(+) channels results in membrane repolarization, leading to the closure of the Ca(2+) channels and cessation of insulin secretion in neuroendocrine islet beta cells. Using patch clamp techniques, we have demonstrated that the activity of the K(DR) channel subtype, K(V)1.1, identified by its specific blocker dendrodotoxin-K, is inhibited by SNAP-25 in insulinoma HIT-T15 beta cells. A co-precipitation study of rat brain confirmed that SNAP-25 interacts with the K(V)1.1 protein. Cleavage of SNAP-25 by expression of botulinum neurotoxin A in HIT-T15 cells relieved this SNAP-25-mediated inhibition of K(DR). This inhibitory effect of SNAP-25 is mediated by the N terminus of K(V)1.1, likely by direct interactions with K(Valpha)1.1 and/or K(V)beta subunits, as revealed by co-immunoprecipitation performed in the Xenopus oocyte expression system and in vitro binding. Taken together we have concluded that SNAP-25 mediates secretion not only through its participation in the exocytotic SNARE complex but also by regulating membrane potential and calcium entry through its interaction with K(DR) channels.
Ji
Junzhi
J
Department of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Tsuk
Sharon
S
Salapatek
Anne Marie F
AM
Huang
Xiaohang
X
Chikvashvili
Dodo
D
Pasyk
Ewa A
EA
Kang
Youhou
Y
Sheu
Laura
L
Tsushima
Robert
R
Diamant
Nicholas
N
Trimble
William S
WS
Lotan
Ilana
I
Gaisano
Herbert Y
HY
D000818:Animals; D051668:Delayed Rectifier Potassium Channels; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D011485:Protein Binding; D051381:Rats; D050825:Synaptosomal-Associated Protein 25; D014407:Tumor Cells, Cultured
D051668:Delayed Rectifier Potassium Channels; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25