TRANSCRIPTION FACTOR PAIRED-BOX 8 REGULATES NA+/I- SYMPORTER GENE EXPRESSION IN SMALL-INTESTINE ABSORPTIVE ENTEROCYTES

Buenos Aires

Congreso; XVII Latin American Thyroid Congress; 2019

Sociedad Latinoamericana de Tiroides

Introduction: Dietary I- absorption in the gastrointestinal tract constitutes the first step in I- metabolism, as the diet is the uniquesource of I- for land-dwelling vertebrates. The Na+/I- symporter (NIS), an integral plasma membrane glycoprotein located in theapical membrane (brush border) of absorptive enterocytes, constitutes the central component of the I- absorption system in thesmall intestine. Objectives: To investigate the mechanisms regulating NIS gene expression in small-intestine absorptive enterocytes.Methods: Experiments were performed on isolated villus-tip enterocytes and small intestine-derived IEC-6 cells. Pax8 expressionwas evaluated by RT-PCR, western blot and immunofluorescence. NIS gene regulatory sequence and Pax8 transcriptional activitywere evaluated using gene reporter assays. Results: Consistently with NIS being expressed exclusively on the brush border of smallintestine, we detected Pax8 expression in isolated villus-tip enterocytes. In agreement, we evidenced Pax8 nuclear expression andits transcriptional activity in IEC-6 cells. Short-hairpin RNA-mediated Pax8 knock-down in IEC-6 cells reduces NIS expression,and consequently I- accumulation. Moreover, the activity of the NIS promoter mutant missing Pax8-binding sites was significantlyimpaired. Consistently with the role of Pax8 controlling NIS expression in enterocytes, ChIP analysis revealed Pax8 binding to the NISupstream enhancer, i.e. NIS promoter region containing Pax8 binding sites. Conclusion: Considering the key role of Pax8 controllingNIS gene expression in thyroid cells, we report the first evidence supporting the role of the transcription factor Pax8 regulating NISgene expression in small-intestine absorptive enterocytes.