title: Synapsin I is expressed in epithelial cells: localization to a unique trans-Golgi compartment.
abstract: Synapsin I is abundant in neural tissues. Its phosphorylation is thought to regulate synaptic vesicle exocytosis in the pre-synaptic terminal by mediating vesicle tethering to the cytoskeleton. Using anti-synapsin antibodies, we detected an 85 kDa protein in liver cells and identified it as synapsin I. Like brain synapsin I, non-neuronal synapsin I is phosphorylated in vitro by protein kinase A and yields identical (32)P-peptide maps after limited proteolysis. We also detected synapsin I mRNA in liver by northern blot analysis. These results indicate that the expression of synapsin I is more widespread than previously thought. Immunofluorescence analysis of several non-neuronal cell lines localizes synapsin I to a vesicular compartment adjacent to trans-elements of the Golgi complex, which is also labeled with antibodies against myosin II; no sub-plasma membrane synapsin I is evident. We conclude that synapsin I is present in epithelial cells and is associated with a trans-Golgi network-derived compartment; this localization suggests that it plays a role in modulating post-TGN trafficking pathways.
authors.affiliation: Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2105, USA.
authors.forename: R
authors.initials: R
authors.lastname: Bustos
authors.forename: E R
authors.initials: ER
authors.lastname: Kolen
authors.forename: L
authors.initials: L
authors.lastname: Braiterman
authors.forename: A J
authors.initials: AJ
authors.lastname: Baines
authors.forename: F S
authors.initials: FS
authors.lastname: Gorelick
authors.forename: A L
authors.initials: AL
authors.lastname: Hubbard
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001923:Brain Chemistry; D002478:Cells, Cultured; D015638:Cytochalasin D / Q000494:pharmacology; D004847:Epithelial Cells / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D006023:Glycoproteins; D022781:Hepatocytes / Q000737:chemistry / Q000378:metabolism; D008297:Male; D008361:Mannosidases / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins; D024462:Myosin Type II / Q000378:metabolism; D015739:Nocodazole / Q000494:pharmacology; D012313:RNA / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016704:Synapsins / Q000235:genetics / Q000378:metabolism*; D022161:Transport Vesicles / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism; D021601:trans-Golgi Network / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D016704:Synapsins; C513045:Tgoln2 protein, rat; D014404:Tubulin; D015638:Cytochalasin D; D012313:RNA; D008361:Mannosidases; C038829:mannosyl-oligosaccharide 1,3 - 1,6-alpha-mannosidase; D024462:Myosin Type II; D015739:Nocodazole