Tomosyn Is Expressed in β-Cells and Negatively Regulates Insulin Exocytosis
- Wei Zhang1,
- Lena Lilja2,
- Slavena A. Mandic2,
- Jesper Gromada34,
- Kamille Smidt3,
- Juliette Janson2,
- Yoshimi Takai5,
- Christina Bark2,
- Per-Olof Berggren2 and
- Björn Meister1
- 1Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
- 2The Rolf Luft Research Center for Diabetes and Endocrinology, Department of Molecular Medicine and Surgery, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden
- 3Department of Pharmacology, University of Aarhus, Aarhus, Denmark
- 4Lilly Research Laboratories, Hamburg, Germany
- 5Department of Molecular Biology and Biochemistry, Osaka University Medical School, Suita, Japan
- Address correspondence and reprint requests to Prof. Per-Olof Berggren, The Rolf Luft Research Center for Diabetes and Endocrinology, Department of Molecular Medicine and Surgery, Karolinska University Hospital, L3, Karolinska Institutet, SE-171 76 Stockholm, Sweden. E-mail: per-olof.berggren{at}ki.se
Abstract
Tomosyn, a syntaxin-binding protein, is capable of dissociating mammalian homolog of the Caenorhabditis elegans unc-18 gene from syntaxin and is involved in the regulation of exocytosis. We have investigated the expression, cellular localization, and functional role of tomosyn in pancreatic β-cells. Western blotting revealed a 130-kDa protein corresponding to tomosyn in insulin-secreting β-cell lines. RT-PCR amplification showed that b-, m-, and s-tomosyn isoform mRNAs are expressed in β-cell lines and rat pancreatic islets. Immunohistochemistry revealed punctate tomosyn immunoreactivity in the cytoplasm of insulin-, glucagon-, pancreatic polypeptide–, and somatostatin-containing islet cells. Syntaxin 1 coimmunoprecipitated with tomosyn in extracts of insulin-secreting cells. Overexpression of m-tomosyn in mouse β-cells significantly decreased exocytosis, whereas inhibition of tomosyn expression by small interfering RNA increased exocytosis. Hence, in the pancreatic β-cell, tomosyn negatively regulates insulin exocytosis.
- GFP, green fluorescent protein
- hGH, human growth hormone
- Munc-18, mammalian homolog of the Caenorhabditis elegans unc-18 gene
- siRNA, small interfering RNA
- SNAP-25, synaptosomal-associated protein of 25 kDa
- SNARE, soluble N-ethylmaleimide–sensitive factor attachment protein receptor
Footnotes
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J.G. holds stock in Novo Nordisk and Eli Lilly.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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- Accepted December 1, 2005.
- Received January 5, 2005.
- DIABETES
