title: On and off membrane dynamics of the endoplasmic reticulum-golgi tethering factor p115 in vivo.
abstract: The mechanisms regulating membrane recruitment of the p115 tethering factor in vivo are unknown. Here, we describe cycling of p115 between membranes and cytosol and document the effects of Golgi matrix proteins, Rab1, and soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs) on this process. Rapid membrane/cytosol exchange is shown by swift (t1/2 approximately 20 s) loss of Golgi-localized p115-green fluorescent protein (GFP) after repeated photobleaching of cell periphery and rapid (t1/2 approximately 13 s) fluorescence recovery after photobleaching Golgi-localized p115-GFP. p115 mutant missing the GM130/giantin binding site exhibits analogous fluorescence recovery after photobleaching (FRAP) (t1/2 approximately 13 s), suggesting that GM130 and giantin are not major determinants of p115 membrane dynamics. In contrast, p115-GFP exchanges more rapidly (t1/2 approximately 8 s) in cells expressing the inactive Rab1/N121I mutant, indicating that p115 cycling is influenced by Rab1. p115-GFP dynamics is also influenced by the assembly status of SNAREs. In cells expressing an ATPase-deficient NSF/E329Q mutant that inhibits SNARE complex disassembly, the cycling kinetics of p115-GFP are significantly slower (t1/2 approximately 21 s). In contrast, in cells incubated at reduced temperature (10 degrees C) that inhibits vesicular traffic, the cycling kinetics of p115-GFP are faster (t1/2 approximately 7 s). These data suggest that p115-binding sites on the membrane are provided by unassembled SNAREs. In agreement, biochemical studies show increased p115 recruitment to membranes in the presence of NSF and alpha-SNAP. Our data support a model in which recruitment of tethers is directly regulated by the assembly status of SNAREs.
authors.affiliation: Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35924, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Brandon
authors.forename: Tomasz
authors.initials: T
authors.lastname: Szul
authors.forename: Cecilia
authors.initials: C
authors.lastname: Alvarez
authors.forename: Robert
authors.initials: R
authors.lastname: Grabski
authors.forename: Ronald
authors.initials: R
authors.lastname: Benjamin
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Kawai
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Sztul
mesh_terms: D000818:Animals; D001324:Autoantigens; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D000077614:Golgi Matrix Proteins; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000235:genetics; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D052066:N-Ethylmaleimide-Sensitive Proteins / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D020761:rab1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001324:Autoantigens; D000077614:Golgi Matrix Proteins; C097741:Golgin subfamily A member 2; D008565:Membrane Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; C087574:macrogolgin; D049452:Green Fluorescent Proteins; C091580:vesicular transport factor p115; D052066:N-Ethylmaleimide-Sensitive Proteins; D020761:rab1 GTP-Binding Proteins