IDENTIFICATION OF 2 ISOFORMS OF THE VESICLE-MEMBRANE FUSION PROTEIN SNAP-23 IN HUMAN NEUTROPHILS AND HL-60 CELLS

We have identified and clotted two isoforms of SNAP-23 in human neutro phils and human promyelocytic HL-60 cells. SNAP-23A which is similar t o the recently cloned SNAP-23, and a novel isoform, termed SNAP-23B. S NAP-23B results from a deletion of 159 bp of the SNAP-23A cDNA, encodi ng a protein of approximately 17.8 kDa. SNAP-23B is identical to SNAP- 23A, but lacks fifty-three amino acid residues, from 90 to 142. This r egion of SNAP-23A has a target sequence for posttranslational fatty ac id acylation, suggesting that the two isoforms can differ in their cap acity to interact with membranes. The level of SNAP-23 mRNA is increas ed during HL-60 neutrophil differentiation. These findings demonstrate the existence of two SNAP-23 proteins in human neutrophils; and there fore, these cells have all the proteins needed to carry out the exocyt ic process. (C) 1997 Academic Press.