All-Trans-Retinoic Acid Increases SLC26A3 (DRA) Expression In Intestinal Epithelial Cells Via HNF-1{beta} [Signal Transduction]

April 17th, 2015 by Priyamvada, S., Anbazhagan, A. N., Gujral, T., Borthakur, A., Saksena, S., Gill, R. K., Alrefai, W. A., Dudeja, P. K.

ABSTRACT ATRA is an active vitamin A derivative known to modulate a number of physiological processes, including growth and development, differentiation and gene transcription. Protective effect of ATRA in gut inflammation and diarrheal diseases has been documented. In this regard, Down Regulated in Adenoma (DRA, a key luminal membrane Cl- transporter involved in NaCl absorption) has been shown to be suppressed in intestinal inflammation. This suppression of DRA is associated with diarrheal phenotype. Therefore, current studies were undertaken to examine the effects of ATRA on DRA expression. DRA mRNA levels were significantly elevated (~4 fold) in response to ATRA with induction starting as early as 8 h of incubation. Similarly, ATRA increased DRA protein expression by ~50%. Further, DRA promoter activity was significantly increased in response to ATRA indicating transcriptional activation. ATRA effects on DRA expression appeared to be mediated via RAR-β receptor subtype, as ATRA remarkably induced RAR-β mRNA levels whereas RAR-β knockdown substantially attenuated the ability of ATRA to increase DRA expression. Results obtained from agonist (CH-55) and antagonist (LE-135) studies, further confirmed that ATRA exerts its effects through RAR-β. Further, ATRA treatment resulted in a significant increase in HNF-1β mRNA levels. The ability of ATRA to induce DRA expression was inhibited in presence of HNF-1β siRNA indicative of its involvement in ATRA induced effects on DRA expression. In conclusion, ATRA may act as an antidiarrheal agent by increasing DRA expression via RAR-β/HNF-1β-dependent pathway.