Transcriptional modulation of SLC26A3 (DRA) by sphingosine-1-phosphate

SLC26A3 or Downregulated in adenoma (DRA) is the major Cl-/HCO3- exchanger involved in electroneutral NaCl absorption in the mammalian intestine. Alterations in DRA function and expression have been implicated in diarrheal diseases associated with inflammation or infection. Therefore, agents that upregulate DRA activity may serve as potential antidiarrheals. In this regard, sphingosine-1-phosphate (S1P), a member of the bioactive sphingolipid family, has been shown to modulate various cellular processes including improvement of intestinal barrier function. However, the role of S1P in modulating intestinal chloride absorption by regulating DRA is not known. Therefore, the present studies were designed to examine the direct effects of S1P on apical Cl-/HCO3- exchange activity and DRA expression. S1P significantly increased Cl-/HCO3- exchange activity and also significantly increased DRA mRNA and protein expression. Increased DRA mRNA by S1P was accompanied by enhanced DRA promoter activity, indicating involvement of transcriptional mechanisms. The specific S1P receptor subtype-2 (S1PR2) antagonist JTE-013 blocked the stimulatory effects of S1P on DRA promoter activity, indicating the involvement of S1PR2. S1P-mediated increase in DRA promoter activity involved PI3K/Akt pathway. Progressive deletions of the DRA promoter indicated that the putative S1P-responsive elements are present in the -790/-398 region of the DRA promoter. Furthermore, results obtained from electrophoretic mobility shift assay showed that S1P stimulated DRA promoter activity via increased binding of Ying-Yang1 (YY1) in the S1P-responsive region. In conclusion, transcriptional modulation of DRA expression and function in response to S1P through a PI3/Akt pathway represents a novel role of S1P as a potential proabsorptive agent.