Rab1b overexpression modifies Golgi size and geneexpression

Cecilia Alvarez.  Facultad deCiencias Químicas. Universidad Nacional de Córdoba.  CIBICI-CONICET. ARGENTINA

Membrane transport from the ER to theGolgi complex requires multiple molecules located in at least three distinctmembrane entities: at specialized subdomains of the Endoplasmic reticulumcalled ERES (ER exit sites), at VTCs (Vesicular tubular clusters) and at cis-Golgi network.  The mammalian Rab1 GTPase is essential for ERto Golgi transport and, through its interactions with diverse effectorproteins, regulates the formation, tethering and fusion of transport carriersderived from the ER.  It is clear thatRab1b is acting in sequential stages at the ER-Golgi transport and we propose amodel that postulates that Rab1b is a coordinator of this step of transport. Furthermore, since Rab1 isoforms (Rab1a andRab1b) are ubiquitous and different tissues express dissimilar mRNA levels ofRab1 isoforms, we also analyzed cellular effects induced by changes of Rab1blevels. We report that an increase in Rab1b levels induces changes in Golgistructure and gene expression.  Such geneexpression changes require the activation of p38 mitogen-activated proteinkinase (MAPK) and the cAMP-responsive element-binding protein (CREB) bindingconsensus site.  The data stronglysuggest that a Rab1b increase is required to elicit a secretory response.