title: Syntaxin 2 splice variants exhibit differential expression patterns, biochemical properties and subcellular localizations.
abstract: The syntaxins are a large protein family implicated in the targeting and fusion of intracellular transport vesicles. A subset of proteins of this family are the four syntaxin 2 splice variants, syntaxins 2A (2), 2B (2'), 2C (2") and 2D. Each syntaxin 2 variant contains an identical, or nearly identical, amino-terminal cytoplasmic domain followed by a distinct hydrophobic (syntaxins 2A and 2B) or hydrophilic (syntaxins 2C and 2D) carboxyl-terminal domain. To investigate whether the difference among the syntaxin 2 variants is functionally important, we have examined comparatively their RNA transcript and protein expression patterns, membrane associations, protein-protein interactions and intracellular localizations. Analysis of the RNA transcript and protein expression patterns demonstrated that syntaxins 2A, 2B and 2C are broadly, but not uniformly, expressed while syntaxin 2D expression is restricted to the brain. Subcellular fractionation studies showed that syntaxins 2A and 2B behave as integral membrane proteins while syntaxin 2C is only partially associated with membranes. In vitro biochemical assays demonstrated that the syntaxin 2 variants exhibit similar yet distinct interactions with other proteins implicated in vesicular trafficking, including SNAP-25, SNAP-23, VAMP-2 and n-sec1. In a variety of nonpolarized cell types, syntaxins 2A and 2B localized to both the plasma membrane and endosomal membranes. However, in two polarized epithelial cell lines, MDCK and Caco-2, syntaxin 2A localized predominantly to the apical plasma membrane while syntaxin 2B was associated with both the apical and the basolateral membranes. These observations indicate that the distinct carboxyl-terminal domains of the syntaxin 2 variants influence their biochemical and localization properties and may therefore confer upon these variants different functional roles in the regulation of intracellular membrane trafficking.
authors.affiliation: Department of Molecular Biology, University of California, Berkeley, CA 94720, USA. bq@socrates.berkeley.edu
authors.forename: B
authors.initials: B
authors.lastname: Quiñones
authors.forename: K
authors.initials: K
authors.lastname: Riento
authors.forename: V M
authors.initials: VM
authors.lastname: Olkkonen
authors.forename: S
authors.initials: S
authors.lastname: Hardy
authors.forename: M K
authors.initials: MK
authors.lastname: Bennett
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D001921:Brain / Q000378:metabolism; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D005786:Gene Expression Regulation; D014644:Genetic Variation; D006367:HeLa Cells; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013347:Subcellular Fractions / Q000378:metabolism; D050827:Syntaxin 1; D013737:Testis / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D000954:Antigens, Surface; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D011994:Recombinant Proteins; D050827:Syntaxin 1