Effective treatment of differentiated thyroid cancer relies on a multifaceted approach often including administration of 131I to ablate residual cancer cells post-surgery. The success of this treatment hinges upon adequate uptake of iodide by malignant thyroid follicular cells. In a subset of patients, dedifferentiation of the carcinoma can result in aberrant expression and trafficking of the iodide transport protein, the sodium iodide symporter (NIS), resulting in a radioiodide refractory phenotype. We recently discovered two protein interactors of NIS: ARF4 and VCP. ARF4 binds to NIS and increases its localisation at the plasma membrane (PM), whilst VCP targets NIS for proteasomal degradation. To address the mechanism by which ARF4 enhances NIS PM localisation, we sub-cloned the ARF4 cDNA into dsRed and mCherry vectors and carried out advanced microscopy, including dual-view inverted selective plane illumination microscope (diSPIM) lightsheet imaging. Preliminary data show that the rate of real-time vesicular trafficking of NIS to the plasma membrane is much more rapid than in previously reported studies, indicating that the movement of this critical symporter is unexpectedly dynamic. We are currently mapping the effect of ARF4 co-expression on the trafficking of wild type NIS, as well as VAPK mutant that we have identified, and which is unable to bind ARF4. The only known protein which binds NIS and facilitates its endocytosis is pituitarytumor transforming gene binding factor (PBF). We have therefore now developed and validated CRISPR-mediated knock outs of PBF in several cell lines, allowing us to address its impact on NIS endocytosis and function. Collectively, these cutting edge imaging studies are now increasing our understanding of the mechanisms by which NIS trafficking becomes dysregulated in thyroid cancer, and how these may be targeted to boost NIS function and reduce the iodide-refractory phenotype.
19 Nov 2018 - 21 Nov 2018