Dexamethasone Upregulates Human SLC26A3 Transporter Expression in intestinal epithelial cells
Authors: Kumar Anoop , Priyamvada Shubha , Chatterjee Ishita , Anbazhagan Arivarasu Natarajan , Singhal Megha , Borthakur Alip , Saksena Seema , Gill Ravinder , Alrefai Waddah , Dudeja Pradeep Kumar 
Published: November 2023

The predominant route of electrolyte absorption in the human ileum and colon involves coupled operation of Na+/H+ and Cl−/HCO3− exchangers. The slc26a3 gene product DRA (Down‐Regulated in Adenoma) plays a critical role in intestinal chloride absorption. Decrease in DRA function and/or expression has been implicated in diarrheal disorders associated with infection or inflammation. The strategies for upregulation of DRA, therefore, are novel approaches to treat IBD and diarrheal disorders. In this regard, dexamethasone (DEX), a corticosteroid, is known to have anti‐inflammatory and immunomodulatory properties. Single pharmacological doses of DEX have been shown to stimulate net water and electrolyte absorption. An earlier study demonstrated that DEX increased NHE3 (a key player in Na+ absorption) function and expression in kidney and intestinal epithelial cells. However, the effects of DEX on DRA expression have not been investigated. The objective of the current studies, therefore, was to examine the effect of DEX on expression of apical anion exchanger SLC26A3 and to elucidate the mechanisms involved. Human intestinal Caco‐2 cells transiently transfected with glucocorticoid receptor (GR) were used as a cellular model. Promoter activity was measured by luciferase assays normalized to β‐galactosidase activity. Protein and mRNA expression was measured by immunoblotting and real time PCR, respectively. Results showed that DEX increased DRA mRNA expression in a dose dependent manner with maximum effect at 1mM dose (~70 fold, p<0.05), only when GR was transfected into these cells. DEX, however, did not alter the expression level of another apical anion exchanger, SLC26A6, indicating the specificity of effects. The increase in DRA mRNA by DEX was blocked in the presence of the GR receptor antagonist (RU486, 500 nM) further confirming the involvement of GR. Time‐course of DEX effects showed an induction in DRA mRNA as early as 6 h and was sustained till 24h. Consistent with the mRNA levels, DEX treatment of Caco‐2 cells also increased the DRA protein expression (~3 fold, p<0.05). DEX‐induced upregulation of DRA appeared at least in part to occur via transcriptional mechanism as promoter activity of DRA construct (−1183/+114bp) was stimulated (~2.5 fold) in response to DEX. In addition, the increase in DRA mRNA was partially blocked in the presence of transcription inhibitor, actinomycin D (5 mM). Similar to in vitro results, administration of DEX (2 mg/kg body wt. ip) to mice for 48 h significantly increased colonic DRA mRNA levels (~ 2.5 fold, p<0.05). DRA protein levels were also increased by DEX in mouse colon as verified by western blotting and increased DRA immunostaining at the apical membrane. These studies demonstrate that DEX stimulates DRA expression at least in part via transcriptional mechanisms and suggest that upregulation of DRA may underlie anti‐inflammatory and pro‐absorptive effects of DEX.

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