Cloning from insulinoma cells of synapsin I associated with insulin secretory granules.
Synapsin I is a synaptic vesicle-associated protein involved in neurotransmitter release. The functions of this protein are apparently regulated by Ca2+/calmodulin-dependent protein kinase II (CaM kinase II). We reported evidence for CaM kinase II and a synapsin I-like protein present in mouse insulinoma MIN6 cells (Matsumoto, K., Fukunaga, K., Miyazaki, J., Shichiri, M., and Miyamoto, E. (1995) Endocrinology 136, 3784-3793). Phosphorylation of the synapsin I-like protein in these cells correlated with the activation of CaM kinase II and insulin secretion. In the present study, we screened the MIN6 cDNA library with the full-length cDNA probe of rat brain synapsin Ia and obtained seven positive clones; the largest one was then sequenced. The largest open reading frame deduced from the cDNA sequence of 3695 base pairs encoded a polypeptide of 670 amino acids, which exhibited significant sequence similarity to rat synapsin Ib. The cDNA contained the same sequence as the first exon of the mouse synapsin I gene. These results indicate that synapsin Ib is present in MIN6 cells. Synapsin I was expressed in normal rat islets, as determined by reverse transcriptase-polymerase chain reaction analysis. Immunoblot analysis after subcellular fractionation of MIN6 cells demonstrated that synapsin Ib and delta subunit of CaM kinase II co-localized with insulin secretory granules. By analogy concerning regulation of neurotransmitter release, our results suggest that phosphorylation of synapsin I by CaM kinase II may induce the release of insulin from islet cells.
Matsumoto
K
K
Department of Pharmacology, Kumamoto University School of Medicine, Kumamoto 860-0811, Japan.
Ebihara
K
K
Yamamoto
H
H
Tabuchi
H
H
Fukunaga
K
K
Yasunami
M
M
Ohkubo
H
H
Shichiri
M
M
Miyamoto
E
E
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D003001:Cloning, Molecular; D003594:Cytoplasmic Granules / Q000201:enzymology / Q000378:metabolism*; D018076:DNA, Complementary; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008969:Molecular Sequence Data; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D016704:Synapsins / Q000235:genetics*
D018076:DNA, Complementary; D007328:Insulin; D016704:Synapsins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases