Rab1b GTPase is essential for protein transport between the endoplasmic reticulum (ER) and the Golgi complex. Rab1b is ubiquitously expressed and in some tissues with high secretory activity (like thyroid, placenta and bronchial epithelial cells) Rab1b mRNA levels are significantly augmented. The impact of Rab1b increase in secretory tissues has not been analyzed. In this work we aim to analyze the role of high Rab1b levels in a thyroid secretory cell line (FRTL-5). In these 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). GFP-Rab1bwt construct was transfected in FRTL5 cells incubated with and without TSH and NIS expression was analyzed by immunofluorescence and flow cytometry. Our esults show that Rab1b overexpression increase NIS protein levels even in absence of TSH. This data suggest that Rab1b modulates NIS expr e s s ion in abs enc e of TSH s t imul a t ion.

Finally, we analyze the impact of Rab1b level changes on regulation of NIS promoter activity by using luciferase reporter assays in FRTL5 cells. Our study indicates that Rab1b modulates NIS expression, suggesting a new Rab1b role in secretory tissues