BMP-4 and Retinoic Acid interaction in the inhibition of the function of the Corticotroph cell

NIETO, L.; ARZT, E.; FUERTES, M.

Buenos Aires

Simposio; Fronteras en Biociencia 2; 2016

Instituto de Investigación en Biomedicina de Buenos Aires

Cushing´s disease (CD) is a hormonal disorder caused by the presence of a tumor in the pituitary gland, which affects several body systems and impacts on quality of life. The tumor, called corticotrophinoma generates excessive production of adrenocorticotropic hormone (ACTH), promoting cortisol hypersecretion from the adrenal cortex. Cortisol is a vital hormone in regulating metabolism and response to stress, but its excess is serious and detrimental. So far the causes or risk factors for developing the type of pituitary tumors that trigger this condition were not yet identified, nor an optimized and complete, high-effectiveness treatment scheme with low side effects to combat them. Previous studies demonstrated that BMP-4 decreases the secretion of ACTH in a cellular model in vitro, whereas Retinoic Acid (RA) blocks the proliferation and growth of corticotroph tumors in an in vivo mouse model. In this work, we delve into the molecular mechanisms of both signaling pathways, in order to find a possible interaction. Murine AtT-20 corticotrophs were transfected with a luciferase reporter vector containing the promoter sequence of the Proopiomelanocortin gene (POMC). After treatment of the cells with 50-200 ng/ml BMP-4 for 24h, we observed inhibition in the reporter transcriptional activity in a dose-dependent manner. We detected by Western Blot the expression in AtT-20 cell line of retinoid receptors (RAR) β and γ, and rexinoid receptors (RXR) α, β and γ. Co-treatment with 100 nM RA for 24h potentiated the inhibitory effect of BMP-4. Co-transfection of inhibitory Smads, Smad 6 or Smad 7, reversed the inhibition on POMC. By computational analysis, we found two response elements in the rPOMC promoter, to RA and BMP-4. Using a RARE-Luc vector, we observed that co-treatment with 100 ng/ml BMP-4 for 24h, amplified the stimulatory response of 100 nM RA on the reporter. Smad 6 or Smad 7 reversed this effect. These experimental observations allow to postulate a possible future therapeutic approach, targeting the POMC transcriptional complex, in which BMP-4 would act upstream of RA.