Proteins synthesis stimulated by thyrotropin in a secretory system requires Rab1b function

MARTINEZ H*; GARCÍA I. A.*; MONETTA, P.*; DUMUR , C AND ALVAREZ, CI*.

SAN MIGUEL DE TUCUMÁN

Congreso; 45TH ANNUAL MEETING - ARGENTINA SOCIETY FOR BIOCHEMISTRY AND MOLECULAR BIOLOGY RESERCH; 2009

SOCIEDAD ARGENTINA DE INVESTIGACIÓN EN BIOQUÍMICA Y BIOLOGÍA MOLECULAR

The GTPase Rab1b is essential for membrane transport from the Endoplasmic Reticulum (ER) to the Golgi complex. Although Rab1b is ubiquitously expressed, its mRNA levels are increased in some tissues with high secretory activity. Here, a thyroid rat cell line (FRTL5) was used in order to study the role of Rab1b in a secretory system. In FRTL5 cells, the thyroid-stimulating hormone (TSH or thyrotropin), stimulates synthesis and secretion of the plasma membrane protein sodium iodide symporter (NIS) as well as thyroglobulin (TG). We have previously shown (SAIB 2008) that TSH also increased the expression of Rab1b and other Golgi proteins but the role of Rab1b was not analyzed. In this work, we inhibited Rab1b activity in FRTL5 cells by overexpressing a dominant negative Rab1b mutant (Rab1b N121I) and by knocking-down endogenous Rab1b expression levels using small interfering RNA (siRNA). Our results show that there was a significant reduction of NIS and TG synthesis in Rab1b inhibited cells compared with control cells. Moreover, ER to Golgi transport was also inhibited by Brefeldin A (BFA) addition. Interestingly, BFA did not modify NIS levels induced by TSH. Taken together our results indicate that TSH mediated synthesis of NIS in FRTL5 cells requires a Rab1b activity not related to ER to Golgi transport, suggesting a differential Rab1b role in secretory tissues.