Rab1b dynamic ate the COPII-COPI interface

MARTINEZ, H; GARCIA IA; SAMPIERI, L; ALVAREZ, C

Mendoza

Congreso; SAIB 2012; 2012

SAIB

The first step in the secretory pathway is the transport of membranes from the Endoplasmic Reticulum (ER) to the Golgi complex. Sorting and concentration of cargo takes place by the action of the COPII (coatomer protein II) complex at specialized ER domains called ER exit sites (ERES). From the ERES vesicles bud and form a compartment called VTCs (Vesicle tubular clusters) that go through a maturation process where COPII is exchanged by COPI complex. The GTPase Rab1b is required for ER-Golgi transport. We have shown that Rab1b modulates both, COPII and COPI membrane association dynamic and that Rab1b promotes COPII function and VTCs maturation.  Although it is known that Rab1b is acting in two sequential stages at the ERES, is unknown how Rab1b coordinates the COPII-COPI transition.  In this work we used confocal microscopy and performed quantitative analysis to compare COPII and GFP-Rab1b co-localization in cells with or without Brefeldin A (BFA), an inhibitor of COPI complex formation. Furthermore, by performing time lapse microscopy assay in living cells, we analyzed the dynamic of pmCherry-Rab1b and GFP-COPs after BFA wash out (BFA-WO).  Our results indicates that COPII-Rab1b co-localization was increased in cells treated with BFA and show that dynamics changes between Rab1b and COPs while anterograde transport from the ER to the Golgi is recovered.  This work provides new dynamic evidence about Rab1b at the COPII-COPI interface.