Abstract
The synaptosomal-associated protein of 25 kDa (SNAP-25) is expressed in neurons and endocrine cells. It has been shown to play an important role in the release mechanism of neurotransmitters and peptide hormones, including insulin. Thus, when insulin-secreting cells are permeabilized and treated with botulinum neurotoxin E (BoNT/E), SNAP-25 is hydrolyzed, and insulin secretion is inhibited. Recently SNAP-23, a more generally expressed isoform of SNAP-25, has been described. The functional role of SNAP-23 has not been investigated to date. It is now shown that SNAP-23 is resistant to cleavage by BoNT/E. It was therefore possible to test whether transfection of HIT (transformed pancreatic B-) cells with SNAP-23 reconstitutes insulin release from BoNT/E treated cells, in which SNAP-25 is inactivated by the toxin. The results show that SNAP-23 is able to replace SNAP-25 when it is overexpressed. While these results demonstrate that SNAP-23 is a functional homologue of SNAP-25, able to function in regulated exocytosis, they indicate that SNAP-23 may be inefficient in this process. This suggests that both isoforms may have their own specific binding partners and discrete, albeit mechanistically similar, functional roles within the cell.
Highlights
SNAP-23 Is Not Cleaved by Botulinum Neurotoxin E and Can Replace synaptosomal-associated protein of 25 kDa (SNAP-25) in the Process of Insulin Secretion*
While these results demonstrate that SNAP-23 is a functional homologue of SNAP-25, able to function in regulated exocytosis, they indicate that SNAP-23 may be inefficient in this process
We show that SNAP-23 can replace SNAP-25 in the process of insulin secretion when it is overexpressed
Summary
Vol 272, No 52, Issue of December 26, pp. 33023–33027, 1997 Printed in U.S.A. SNAP-23 Is Not Cleaved by Botulinum Neurotoxin E and Can Replace SNAP-25 in the Process of Insulin Secretion*. While these results demonstrate that SNAP-23 is a functional homologue of SNAP-25, able to function in regulated exocytosis, they indicate that SNAP-23 may be inefficient in this process This suggests that both isoforms may have their own specific binding partners and discrete, albeit mechanistically similar, functional roles within the cell. Several lines of evidence have shown that SNAP-251 [6] plays an important role in the complex mechanism leading to regulated exocytosis in both neurons and endocrine cells. More recently SNAP-23, a ubiquitously expressed isoform of SNAP-25, was cloned from human cells and shown to be 59% identical and 72% similar to SNAP-25 at the amino acid level [22]. We show that SNAP-23 can replace SNAP-25 in the process of insulin secretion when it is overexpressed
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