title: A sec1-related vesicle-transport protein that is expressed predominantly in epithelial cells.
abstract: Sec1-related proteins are involved in docking and fusion of transport vesicles in eukaryotic cells. Here we report the cloning and molecular characterization of a Sec1-related protein expressed in the MDCK epithelial cell line. This protein represents a canine counterpart of the murine Munc-18-2/Munc-18b/muSec1 protein, displays 93% amino acid identity with these proteins, has a similar tissue mRNA expression pattern, and associates in vitro with syntaxins 1A, 2, and 3. In situ hybridization analysis of embryonic mouse tissues revealed prominent expression of the munc-18-2 mRNA in the epithelia of several tissues. Cell-fractionation studies demonstrated that the majority of Munc-18-2 is membrane associated. Most of the protein is washed off the membranes by sodium carbonate, pH 11.5. However, the protein is poorly solubilized by detergent treatment. The Munc-18-2 protein was localized, by immunofluorescence microscopy, to the plasma membrane of MDCK cells, and is apically distributed in the epithelial cells of mouse tissues. When overexpressed in COS-1 cells, the protein appeared to be largely cytosolic. However, upon expression with syntaxin 1A, it displayed a shift to the plasma membrane, where the two proteins colocalized. These results identified Munc-18-2 as a predominantly epithelial vesicle-transport protein with a polarized distribution and provided novel in vivo evidence for the association of Sec1-related proteins with members of the syntaxin family.
authors.affiliation: Department of Biochemistry, National Public Health Institute, Helsinki, Finland.
authors.forename: K
authors.initials: K
authors.lastname: Riento
authors.forename: J
authors.initials: J
authors.lastname: Jäntti
authors.forename: S
authors.initials: S
authors.lastname: Jansson
authors.forename: S
authors.initials: S
authors.lastname: Hielm
authors.forename: E
authors.initials: E
authors.lastname: Lehtonen
authors.forename: C
authors.initials: C
authors.lastname: Ehnholm
authors.forename: S
authors.initials: S
authors.lastname: Keränen
authors.forename: V M
authors.initials: VM
authors.lastname: Olkkonen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002451:Cell Compartmentation; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004285:Dogs; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D015870:Gene Expression; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008566:Membranes / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D050765:Qa-SNARE Proteins; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D050827:Syntaxin 1; D014018:Tissue Distribution; D033921:Vesicular Transport Proteins
chemical_list: D008565:Membrane Proteins; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; C494214:Stx1a protein, mouse; C497941:Stxbp2 protein, mouse; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins