Transcription factor paired-box 8 regulates Na+ /I- symporter gene expression in small-intestine absorptive enterocytes

NICOLA, JP; MASINI-REPISO, AM

Orlando

Congreso; 15th Internation Thyroid Congress; 2015

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 unique source of I- for land-dwellingvertebrates. The Na+/I-symporter (NIS), an integral plasma membrane glycoprotein located in the brushborder of enterocytes, i.e. the finger-like projections that protrude from the apicalmembrane of absorptive enterocytes into the intestinal lumen, constitutes a central component of the I- absorption system in the small intestine.To investigate themechanisms controlling NIS gene expression in small-intestine absorptiveenterocytes.Experiments were performed in male Wistarrats and the rat small intestine-derived IEC-6 cell line. Pax8 expression wasevaluated by RT-PCR, western blot and immunofluorescence. Analysis of NIS generegulatory sequence and Pax8 transcriptional activity were evaluated using genereporter assays.Considering the key role of Pax8 controlling NIS geneexpression in thyroid cells, we evaluated Pax8 expression in small-intestine absorptiveenterocytes. Consistently with NIS being expressed exclusively on the brushborder, we detected Pax8 expression in isolated villus-tip enterocytes. Inagreement, we evidenced Pax8 expressionin the nucleus of IEC-6 cells. Moreover, we observed a significant induction ofthe Pax8 reporter vector in IEC-6 cells, thus revealing Pax8 transcriptionalactivity.We further evaluated the role of Pax8 modulating theactivity of NIS gene regulatory sequence. Deletion analysis of the NIS promoterrevealed the requirement of the NIS upstream enhancer, i.e. NIS promoter regioncontaining Pax8 binding sites, for NIS expression in enterocytes. Interestingly, the activityof the NIS promoter mutant missing Pax8-binding sites was significantlyimpaired. Consistently with the role ofPax8 controlling NIS expression in enterocytes, ChIP analysis revealed Pax8binding to the NIS upstream enhancer.We report the first evidence supporting the role of the transcriptionfactor Pax8 controlling NIS gene expression in small-intestine absorptive enterocytes.