Syntaxin 4 and Synip (syntaxin 4 interacting protein) regulate insulin secretion in the pancreatic beta HC-9 cell.
Although syntaxin 1 is generally thought to function as the primary target-N-ethylmaleimide-sensitive factor attachment protein receptor required for pancreatic beta cell insulin secretion, we have observed that overexpression of a dominant-interfering syntaxin 4 mutant (syntaxin 4/DeltaTM) attenuated glucose-stimulated insulin secretion in betaHC-9 cells. Furthermore, these cells express the selective syntaxin 4-binding protein Synip (syntaxin 4 interacting protein), and Synip was specifically co-immunoprecipitated with syntaxin 4 but not syntaxin 1. Overexpression of the full-length Synip protein (Synip/wild type) inhibited VAMP2 association with syntaxin 4 and decreased glucose-stimulated insulin secretion. This did not occur with a Synip mutant (Synip/ DeltaEF) that was incapable of binding syntaxin 4. Consistent with a functional role of syntaxin 4 in this process, expression of syntaxin 4/DeltaTM also inhibited glucose-stimulated insulin secretion. Furthermore, analysis of first and second phase insulin secretion demonstrated that syntaxin 4/DeltaTM mainly suppressed the second phase of insulin secretion. In contrast, overexpression of Synip resulted in an inhibition of both the first and second phase of glucose-stimulated insulin secretion. These data demonstrate that syntaxin 4 plays a functional role on insulin release and granule fusion in beta cells and that this process is regulated by the syntaxin 4-specific binding protein Synip.
Saito
Tsugumichi
T
Department of Medicine and Molecular Science, Gunma University Graduate School of Medicine, 3-39-15, Showa-machi, Maebashi-shi, Gunma-ken, 371-8511, Japan.
Okada
Shuichi
S
Yamada
Eijiro
E
Ohshima
Kihachi
K
Shimizu
Hiroyuki
H
Shimomura
Kenju
K
Sato
Minoru
M
Pessin
Jeffrey E
JE
Mori
Masatomo
M
D000954:Antigens, Surface / Q000378:metabolism; D015152:Blotting, Northern; D015153:Blotting, Western; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D018076:DNA, Complementary / Q000378:metabolism; D005799:Genes, Dominant; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010179:Pancreas / Q000166:cytology* / Q000378:metabolism; D010477:Perfusion; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050827:Syntaxin 1; D013997:Time Factors; D014162:Transfection; D033921:Vesicular Transport Proteins; D001616:beta-Galactosidase / Q000378:metabolism
D000954:Antigens, Surface; D002352:Carrier Proteins; D018076:DNA, Complementary; D007328:Insulin; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D012333:RNA, Messenger; C494212:STX1A protein, human; C498469:STXBP4 protein, human; C494214:Stx1a protein, mouse; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D001616:beta-Galactosidase; D005947:Glucose