title: Syntaxin-6 SNARE involvement in secretory and endocytic pathways of cultured pancreatic beta-cells.
abstract: In pancreatic beta-cells, the syntaxin 6 (Syn6) soluble N-ethylmaleimide-sensitive factor attachment protein receptor is distributed in the trans-Golgi network (TGN) (with spillover into immature secretory granules) and endosomes. A possible Syn6 requirement has been suggested in secretory granule biogenesis, but the role of Syn6 in live regulated secretory cells remains unexplored. We have created an ecdysone-inducible gene expression system in the INS-1 beta-cell line and find that induced expression of a membrane-anchorless, cytosolic Syn6 (called Syn6t), but not full-length Syn6, causes a prominent defect in endosomal delivery to lysosomes, and the TGN, in these cells. The defect occurs downstream of the endosomal branchpoint involved in transferrin recycling, and upstream of the steady-state distribution of mannose 6-phosphate receptors. By contrast, neither acquisition of stimulus competence nor the ultimate size of beta-granules is affected. Biosynthetic effects of dominant-interfering Syn6 seem limited to slowed intragranular processing to insulin (achieving normal levels within 2 h) and minor perturbation of sorting of newly synthesized lysosomal proenzymes. We conclude that expression of the Syn6t mutant slows a rate-limiting step in endosomal maturation but provides only modest and potentially indirect interference with regulated and constitutive secretory pathways, and in TGN sorting of lysosomal enzymes.
authors.affiliation: Division of Endocrinology and Department of Developmental/Molecular Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: Regina
authors.initials: R
authors.lastname: Kuliawat
authors.forename: Elena
authors.initials: E
authors.lastname: Kalinina
authors.forename: Jason
authors.initials: J
authors.lastname: Bock
authors.forename: Lloyd
authors.initials: L
authors.lastname: Fricker
authors.forename: Timothy E
authors.initials: TE
authors.lastname: McGraw
authors.forename: Se Ryoung
authors.initials: SR
authors.lastname: Kim
authors.forename: Jiayu
authors.initials: J
authors.lastname: Zhong
authors.forename: Richard
authors.initials: R
authors.lastname: Scheller
authors.forename: Peter
authors.initials: P
authors.lastname: Arvan
mesh_terms: D000418:Albumins / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002401:Cathepsin B / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D005089:Exocytosis; D005799:Genes, Dominant; D007515:Islets of Langerhans / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008565:Membrane Proteins / Q000096:biosynthesis*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009154:Mutation; D011233:Precipitin Tests; D050765:Qa-SNARE Proteins; D051381:Rats; D050600:SNARE Proteins; D022142:Secretory Vesicles / Q000378:metabolism; D012672:Semliki forest virus / Q000378:metabolism; D013395:Sucrose / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014168:Transferrin / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000502:physiology*; D021601:trans-Golgi Network / Q000378:metabolism*
chemical_list: D000418:Albumins; D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D014168:Transferrin; D033921:Vesicular Transport Proteins; D013395:Sucrose; D004247:DNA; D002401:Cathepsin B