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Diabetologia. 2002 Feb;45(2):231-41.

Syntaxin-3 and syntaxin-1A inhibit L-type calcium channel activity, insulin biosynthesis and exocytosis in beta-cell lines.

Author information

1
Department of Medicine, University of Toronto, Ontario, Canada.

Abstract

AIMS/HYPOTHESIS:

Syntaxin-1A (Syn-1A) is known to play a negative regulatory role in insulin secretion but the precise mechanisms for its action are not clear. Syn-2, -3 and -4 are also present in islet beta cells but their functions are not known. Here, we investigated the role of these syntaxins in the insulin secretory process.

METHODS:

We examined the following effects of Syn-1, -2, -3 and -4 expression in insulinoma beta-cell lines. Endogenous insulin secretion was measured by batch radioimmunoassay (RIA) and single cell patch clamp capacitance measurements. The L-type Ca(2+) channel activity was studied by patch clamp electrophysiology. Insulin gene transcription was examined by Northern blotting and measurement of insulin gene promoter activity by the co-expression of cyan fluorescent protein-labelled rat insulin promoter.

RESULTS:

Syn-1A or -3, but not Syn-2 or -4 overexpression, inhibited K(+)-induced insulin release as determined by RIA (49.7 +/- 5.5 % and 49.1 +/- 6.2 %, respectively) and electrophysiologic membrane capacitance measurements (68.0 +/- 21.0 % and 58.0 +/- 13.2 %, respectively). Overexpressed Syn-1A and -3, but not Syn-2, inhibited Ca(2+) channel current amplitude by 39.5 +/- 11.6 % and 52.7 +/- 6.0 %, respectively. Of note, overexpression of Syn-1A and -3 also reduced single cell (by confocal microscopy) and total cellular endogenous insulin content (by RIA) by 24.8 +/- 4.2 % and 31.8 +/- 3.9 %, respectively. This correlated to a reduction in endogenous insulin mRNA by 24.5 +/- 4.2 % and 25.7 +/- 4.2 %, respectively. This inhibition of insulin biosynthesis is mainly at the level of insulin gene transcription as demonstrated by an inhibition of insulin gene promoter activity (53.3 +/- 9.15 % and 39.0 +/- 6.8 %, respectively).

CONCLUSIONS/INTERPRETATION:

These results demonstrate that Syn-1A and -3 possess strong inhibitory actions on both insulin exocytosis and insulin biosynthesis whereas Syn-2 and -4 do not inhibit the insulin secretory process.

PMID:
11935155
PMCID:
PMC2970522
DOI:
10.1007/s00125-001-0718-0
[Indexed for MEDLINE]
Free PMC Article

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