Rab1b modulates the TSH response in thyroid cells in culture.

LUCIANA SAMPIERI; HERNÁN MARTINEZ; IRIS A. GARCÍA; CECILIA ALVAREZ

Puerto Natales

Workshop; EMBO workshop: Current advances in membrane trafficking; 2014

EMBO

Rab1b belongs to the Rab-GTPase family that regulates membrane trafficking and signal transduction systems able to control diverse cellular activities, including gene expression. Rab1b is essential for endoplasmic reticulum-Golgi transport. Although it is ubiquitiously expressed, its mRNA levels vary among different tissues, but the importance of this variability in Rab expression levels remains unclear. In this study we examined different cellular effects induced by changes in Rab1b levels. FRTL-5 thyroid cells were chosen as a secretory model. In these cells, secretory activity is induced by thyroid stimulating hormone (TSH) which stimulates the synthesis of cell specific proteins that require the secretory pathway to reach their final destination. To assess the effects of Rab1b on the secretory response in our model, we performed transient transfections with GFP-Rab1bwt or its dominant-negative mutant. In order to evaluate the consequences of Rab1b depletion, silencing of Rab1b was carried out in the same cell line. Analysis were performed comparing cells grown in basal (-TSH) or stimulated (+TSH) condition. Our results show that TSH addition increases NIS (Sodium/Iodide Symporter), as well as Rab1b and GM130. Moreover, an increase in Rab1b enhances NIS expression and NIS promoter activity, suggesting a role of Rab1b in NIS activation pathway. On the other hand, we also found that Rab1b inhibition blocked the TSH-stimulated NIS and GM130 increase.Our data strongly suggests that activation of secretion (or membrane transport) by a secretory stimulus induces an increase in Rab1b levels. Additionally, changes in Rab1b expression in FRTL5 cells modify the specific TSH response. Our results show, for the first time, that changes in Rab1b levels modulate gene promoter activity and strongly suggest that a Rab1b increase is required to elicit a secretory response.