mBet3p is required for homotypic COPII vesicle tethering in mammalian cells.
TRAPPI is a large complex that mediates the tethering of COPII vesicles to the Golgi (heterotypic tethering) in the yeast Saccharomyces cerevisiae. In mammalian cells, COPII vesicles derived from the transitional endoplasmic reticulum (tER) do not tether directly to the Golgi, instead, they appear to tether to each other (homotypic tethering) to form vesicular tubular clusters (VTCs). We show that mammalian Bet3p (mBet3p), which is the most highly conserved TRAPP subunit, resides on the tER and adjacent VTCs. The inactivation of mBet3p results in the accumulation of cargo in membranes that colocalize with the COPII coat. Furthermore, using an assay that reconstitutes VTC biogenesis in vitro, we demonstrate that mBet3p is required for the tethering and fusion of COPII vesicles to each other. Consistent with the proposal that mBet3p is required for VTC biogenesis, we find that ERGIC-53 (VTC marker) and Golgi architecture are disrupted in siRNA-treated mBet3p-depleted cells. These findings imply that the TRAPPI complex is essential for VTC biogenesis.
Yu
Sidney
S
Howard Hughes Medical Institute and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06519, USA.
Satoh
Ayano
A
Pypaert
Marc
M
Mullen
Karl
K
Hay
Jesse C
JC
Ferro-Novick
Susan
S
D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D022181:COP-Coated Vesicles / Q000378:metabolism*; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D021381:Protein Transport / Q000187:drug effects; D033921:Vesicular Transport Proteins / Q000378:metabolism*
D002352:Carrier Proteins; C507455:SEC31A protein, human; C521195:SEC31B protein, human; C503571:TRAPPC3 protein, human; D033921:Vesicular Transport Proteins; D020126:Brefeldin A