Transcription factor Paired-Box 8 regulates Na+/I- Symporter gene expression in small-intestine absorptive enterocytes - Selected for Highligted oral session

NICOLA JUAN PABLO; MASINI - REPISO AM.

Orlando, Florida

Congreso; 15th International thyroid Congress (15th ITC); 2015

American Thyroid Association

Introduction: Iodine is an essential constituent of the thyroid hormones, the only iodine-containing molecules in vertebrates. Dietary iodide (I-) absorption in the gastrointestinal tract constitutes the first step in I- metabolism, as the diet is the only source of I- for land-dwelling vertebrates. The Na+/I- symporter (NIS), an integral plasma membrane glycoprotein located in the brush border of enterocytes, i.e. the finger-like projections that protrude from the apical membrane of absorptive enterocytes into the intestinal lumen, constitutes a central component of the I- absorption system in the small intestine.Objective: To investigate the mechanisms controlling NIS gene expression in small-intestine absorptive enterocytes.Methods: Experiments were performed in male Wistar rats and the rat small intestine-derived IEC-6 cell line. Pax8 expression was evaluated by RT-PCR, western blot and immunofluorescence. Analysis of NIS gene regulatory sequence and Pax8 transcriptional activity were evaluated using gene reporter assays.Results: Considering the key role of Pax8 controlling NIS gene expression in thyroid cells, we evaluated Pax8 expression in small-intestine absorptive enterocytes. Consistently with NIS being expressed exclusively on the brush border, we detected Pax8 expression in isolated villus-tip enterocytes. In agreement, we evidenced Pax8 expression in the nucleus of IEC-6 cells. Moreover, we observed a significant induction of the Pax8 reporter vector in IEC-6 cells, thus revealing Pax8 transcriptional activity.We further evaluated the role of Pax8 modulating the activity of NIS gene regulatory sequence. Deletion analysis of the NIS promoter revealed the requirement of the NIS upstream enhancer, i.e. NIS promoter region containing Pax8 binding sites, for NIS expression in enterocytes. Interestingly, the activity of the NIS promoter mutant missing Pax8-binding sites is significantly impaired. Consistently with the role of Pax8 controlling NIS expression in enterocytes, ChIP analysis revealed Pax8 binding to the NIS upstream enhancer.Conclusion: We report the first evidence supporting the role of the transcription factor Pax8 controlling NIS gene expression in small-intestine absorptive enterocytes.