SAT-LB78 TSH Is a Negative Modulator of Hippo Transcriptional Effectors

Hippo signaling pathway regulation by hormonal signals acting through G-coupled receptors has been widely described. Modulation of processes such as tissue growth or differentiation by this pathway critically relies on the location and levels of its major effectors: the cofactors YAP/TAZ and the family TEAD of transcription factors. Despite this well-defined regulatory mechanism, little is known about the Hippo pathway in the thyroid gland. Thyrotropin (TSH), main factor for thyroid follicular cells differentiation, plays its role by interacting with its G-protein-coupled receptor (TSHR). High serum TSH levels are associated with hypothyroidism, characterized by a change in thyroid follicle morphology and inflammation of the thyroid gland. This led us to study if TSH could modulate the Hippo pathway.Rat thyroid follicular cells (PCCl3) were treated with TSH and forskolin, an adenylyl cyclase activator. By immunofluorescence and western blot, levels and subcellular location of the Hippo Pathway components were assessed in different conditions. An increase of the Hippo kinase MST1/2 and LATS1/2 was observed after TSH and forskolin treatments, corresponding to a downregulation of the transcriptional mediators of the pathway TAZ, YAP and Tead1. Especially remarkable is the translocation of YAP/TAZ from the nucleus, which involves a decrease in their activity.Next, we validated the results in an in vivo model generating hypothyroidism in 3-month-old male C57BL/6J by adding MMI (2-Mercapto-1-Methylimidazole) and perchlorate (KClO4) to their drinking water. After 2 weeks of treatment, we euthanized the animals, validated higher TSH serum levels and performed analysis of the Hippo components in the thyroid by immunohistochemistry. A reduction in the levels of the Hippo effectors TAZ, YAP and Tead1 was found in the thyroid slices from hypothyroid mice, confirming the in vitro results. In addition, evaluation of a human thyroid tissue microarray, including Hashimoto disease samples, led to a validation of the previously described TSH role.Hereby, we report a crosstalk by which TSH is increasing the kinase axis of the Hippo pathway thus decreasing the activity of its main transcriptional effectors in the nuclei. Future research of the role of these transcriptional effectors will be carry out to discern if their decrease could be associated with the morphology changes linked to hypothyroidism.