Role of Rab1b in COPII dynamics and function

IRIS A. GARCÍA; HERNÁN MARTINEZ; ILEANA SLAVIN; CECILIA ALVAREZ

Puerto Madryn

Congreso; SAIB 2010; 2010

SAIB

In eukariotic cells, proteins destined to be exported are translocated to the Endoplasmic Reticulum (ER) and are selectively sorted in specialized sites called "ER exit sites" (ERES). Selection and incorporation of the proteins in ERES is performed by Coat protein complex II (COPII). This coat is assembled by recruitment of Sec23/24 and Sec13/31 by Sar1 GTPase (activated by its GEF, Sec12). A further component, Sec16, acts as a platform for COPII assembly at ERES it appears to stabilize Sar1-GTP. After vesicle budding, COPII is exchanged by COPI complex, a crucial step for ER-Golgi transport. Rab1b GTPase is essential to recruit COPI. We have previously shown that Rab1b interacts with the COPII component Sec23. Furthermore, FRAP experiments co-expressing Sec13 and Rab1Q67L indicated that Rab1b activity affects Sec13 membrane association-dissociation kinetics at the ERES. Here we show that in vivo Rab1b, also interacts with Sec24 and Sec31. In agreement, immunofluorescence assays show that Rab1b colocalizes with these COPII structures. Moreover, Rab1b inhibition delays cargo sorting at the ERES. In contrast with Sec13, Sec16 dynamics is not affected by Rab1Q67L, consistent with the fact that Sec16 acts upstream of Sar1. Our data suggest that Rab1b can interact and modulate dynamic of COPII components acting downstream of Sec16.