Tomosyn is expressed in beta-cells and negatively regulates insulin exocytosis.
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 beta-cells. Western blotting revealed a 130-kDa protein corresponding to tomosyn in insulin-secreting beta-cell lines. RT-PCR amplification showed that b-, m-, and s-tomosyn isoform mRNAs are expressed in beta-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 beta-cells significantly decreased exocytosis, whereas inhibition of tomosyn expression by small interfering RNA increased exocytosis. Hence, in the pancreatic beta-cell, tomosyn negatively regulates insulin exocytosis.
Zhang
Wei
W
Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
Lilja
Lena
L
Mandic
Slavena A
SA
Gromada
Jesper
J
Smidt
Kamille
K
Janson
Juliette
J
Takai
Yoshimi
Y
Bark
Christina
C
Berggren
Per-Olof
PO
Meister
Björn
B
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D005089:Exocytosis; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D051379:Mice; D008820:Mice, Obese; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D050683:R-SNARE Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D050827:Syntaxin 1 / Q000032:analysis
D007328:Insulin; D009419:Nerve Tissue Proteins; D050683:R-SNARE Proteins; D012333:RNA, Messenger; C484769:Stxbp5 protein, rat; D050827:Syntaxin 1; C112618:tomosyn protein, mouse; D005576:Colforsin; D005947:Glucose; D002118:Calcium