SNAP-23 Is Not Cleaved by Botulinum Neurotoxin E and Can Replace SNAP-25 in the Process of Insulin Secretion

doi:10.1074/jbc.272.52.33023

SNAP-23 Is Not Cleaved by Botulinum Neurotoxin E and Can Replace SNAP-25 in the Process of Insulin Secretion*

From the ^‡Laboratoires de Recherche Louis Jeantet, Centre Médical Universitaire, 1 rue Michel Servet, 1211 Geneva 4, Switzerland, the ^¶Institut für Biochemie, Medizinische Hochschule Hannover, OE 4310, 30623 Hannover, Germany, the ^**Experimental Immunology Branch, NCI, National Institutes of Health, Bethesda, Maryland 20892, the ^‡Division of Cell Biology, the Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada, and the ^§§Institut de Biologie Cellulaire et de Morphologie, 9 rue du Bugnon, 1005 Lausanne, Switzerland

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.

Footnotes

↵* This work was supported by Swiss National Science Foundation Grants MHV-32-45000.95 (to K. S.) and 31–40839.94 (to P. A. H.) and Juvenile Diabetes Foundation International Grants 196100 (to R. R.) and 195035 (to P. A. H.).
↵§ To whom correspondence should be addressed. Tel.: 41-22-7025537; Fax: 41-22-3473334; E-mail: karin.sadoul{at}medecine.unige.ch.
↵‖ Present address: Labor Dr. Rai, Dr. Röck, Dr. Weller, Lange Straße 65, 76530 Baden-Baden, Germany.
↵1 The abbreviations used are: SNAP-25, synaptosomal-associated protein of 25 kDa; VAMP, vesicle-associated membrane protein; SNAP, soluble NSF attachment protein; NSF, N-ethyl-maleimide sensitive fusion protein; SNARE, SNAP receptor; SLO, streptolysin-O; ELISA, enzyme-linked immunosorbent assay; PAGE, polyacrylamide gel electrophoresis; BoNT, botulinum neurotoxin; DPBS, Dulbecco’s phosphate-buffered saline.
↵2 T. Binz, T. Hayashi, S. Yamasaki, and H. Niemann, manuscript in preparation.
- Received September 26, 1997.