NA+/I- SYMPORTER PLASMA MEMBRANE EXPRESSION RELIES ON A CARBOXY-TERMINAL PDZBINDING MOTIF

Buenos Aires

Congreso; XVII Latin American Thyroid Congress; 2019

Sociedad Latinoamericana de Tiroides

Introduction: Na+/I- symporter (NIS)-mediated radioiodide accumulation constitutes the molecular basis for the treatment ofdifferentiated thyroid cancer. However, thyroid tumors often exhibit reduced I- transport as a consequence of abnormalities in thetransport of the protein to the plasma membrane. Objectives: To investigate the role of the PDZ binding-motif TNL643 located at thecarboxy-terminal edge of the protein in NIS plasma membrane expression under physiological conditions. Methods: Functional in vitrostudies were performed on non-polarized or polarized MDCK-II epithelial cells stably expressing wild-type or PDZ-binding domainmutant NIS. Results: Functional studies revealed that deletion of the PDZ-binding motif reduces I- uptake in non-polarized MDCKII cells, because Δ640-643 NIS expression at the plasma membrane is significantly reduced. On Western blots, the fully glycosylatedNIS polypeptide was detected in Δ640-643 NIS-expressing cells, indicating that this mutant is retained beyond the medial-Golgi,where newly synthesized membrane proteins are sorted to different subcellular compartments. Moreover, under polarized conditions,confocal microscopy revealed that Δ640-643 NIS expression at the basolateral plasma membrane is significantly reduced due toits intracellular retention in uncharacterized vesicles. Conclusion: Although the molecular mechanisms that determine NIS plasmamembrane expression in thyroid cells remain elusive, here, we provide evidence that the carboxy-terminus edge of the protein containsa PDZ-binding motif involved in plasma membrane expression. The identification of PDZ-domain-containing NIS-interacting proteinsmay novel therapeutic interventions to increase the effectiveness of radioiodide therapy.