A VAMP7/Vti1a SNARE complex distinguishes a non-conventional traffic route to the cell surface used by KChIP1 and Kv4 potassium channels.
The KChIPs (K(+) channel-interacting proteins) are EF hand-containing proteins required for the traffic of channel-forming Kv4 K(+) subunits to the plasma membrane. KChIP1 is targeted, through N-terminal myristoylation, to intracellular vesicles that appear to be trafficking intermediates from the ER (endoplasmic reticulum) to the Golgi but differ from those underlying conventional ER-Golgi traffic. To define KChIP1 vesicles and the traffic pathway followed by Kv4/KChIP1 traffic, we examined their relationship to potential SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) proteins mediating the trafficking step. To distinguish Kv4/KChIP1 from conventional constitutive traffic, we compared it to the traffic of the VSVG (vesicular-stomatitis virus G-protein). Expression of KChIP with single or triple EF hand mutations quantitatively inhibited Kv4/KChIP1 traffic to the cell surface but had no effect on VSVG traffic. KChIP1-expressing vesicles co-localized with the SNARE proteins Vti1a and VAMP7 (vesicle-associated membrane protein 7), but not with the components of two other ER-Golgi SNARE complexes. siRNA (small interfering RNA)-mediated knockdown of Vti1a or VAMP7 inhibited Kv4/KChIP1traffic to the plasma membrane in HeLa and Neuro2A cells. Vti1a and VAMP7 siRNA had no effect on VSVG traffic or that of Kv4.2 when stimulated by KChIP2, a KChIP with different intrinsic membrane targeting compared with KChIP1. The present results suggest that a SNARE complex containing VAMP7 and Vti1a defines a novel traffic pathway to the cell surface in both neuronal and non-neuronal cells.
Flowerdew
Sarah E
SE
The Physiological Laboratory, School of Biomedical Sciences, University of Liverpool, Crown Street, Liverpool, U.K.
Burgoyne
Robert D
RD
D000818:Animals; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051605:Kv Channel-Interacting Proteins / Q000235:genetics / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D009447:Neuroblastoma; D021381:Protein Transport / Q000502:physiology*; D050766:Qb-SNARE Proteins / Q000378:metabolism; D050683:R-SNARE Proteins / Q000378:metabolism; D050600:SNARE Proteins / Q000502:physiology*; D051672:Shal Potassium Channels / Q000502:physiology*; D014759:Viral Envelope Proteins / Q000378:metabolism; D020761:rab1 GTP-Binding Proteins / Q000378:metabolism
C028391:G protein, vesicular stomatitis virus; D051605:Kv Channel-Interacting Proteins; D008562:Membrane Glycoproteins; D050766:Qb-SNARE Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; D051672:Shal Potassium Channels; C121241:VAMP7 protein, human; C491419:VTI1A protein, human; D014759:Viral Envelope Proteins; D020761:rab1 GTP-Binding Proteins