Endocrine Abstracts

Introduction

The Sodium Iodide Symporter (NIS) is responsible for the active transport of iodide into thyroid cells. Most of differentiated thyroid carcinomas (TC) retain the functional expression of NIS, which allows the use of radioiodide (RAI) as the systemic treatment of choice for metastatic disease. Still, a significant proportion of patients with advanced thyroid cancer fail to respond to RAI therapy (refractory-TC), which makes their management very challenging. In addition to reduced NIS expression, the limited iodide uptake observed in cancer tissue is also a consequence of an impairment of plasma membrane (PM) targeting and retention of NIS. However, signaling cues potentially mediating the activation of pathway components leading to NIS functional expression at the PM, remain elusive. Using a proteomic approach, we have recently identified a set of proteins that interact with NIS selectively at the PM, potentially modulating its abundance and stability at the surface of TC cells. The G protein subunit gamma 12 (GNG12) was detected as a specific PM-interactor of NIS. This is one of twelve Gγ subunits in the human genome that can pair with Gβ subunits to form unique Gβγ complex combinations. Along with Gα, Gβγ are key regulators of G protein-coupled receptor (GPCR) signaling, having the ability to activate several signaling mediators such as kinases, GTPases or lipases.

Objective

To evaluate whether modulation of Gγ12 subunit would have an impact on NIS PM abundance.

Methods

The TPC1 thyroid cancer cell line stably expressing a full-length NIS construct containing an extracellular triple HA tag (NIS-HA-TPC1) was used to assess the PM levels of NIS upon siRNA-mediated knockdown of GNG12 expression. NIS PM levels were assessed using surface protein biotinylation assays coupled to WB detection of NIS-HA using anti-HA primary antibody. A non-radioactive iodide influx assay was used to further analyze the impact of GNG12 on NIS function by assessing the rate of iodide uptake.

Results

siRNA-mediated GNG12 depletion, although partial (∼30% reduction), was able to induce a 1.6-fold decrease in NIS cell surface levels and also impair iodide uptake efficiency, halving the influx rates in HA-NIS-TPC1 cells.

Conclusion

Our findings suggest that signaling cues that lead to the release and activation of Gβγ may act upstream of signaling pathways that enhance NIS expression in the PM. This supports the relevance of further studying the impact of modulating Gβγ-mediated signaling on NIS functional expression, as a potential approach to enhance the efficiency of iodide uptake.