A somatic mutation of RasGRP3 decreases Na+/I- symporter expression in metastases of radioactive iodine-refractory thyroid cancer by stimulating the Akt signaling pathway.

Mutation profiles of advanced radioactive iodine (RAI)-refractory differentiated thyroid cancer have revealed the pathogenic roles of the established oncogenic mutations of BRAF and PI3KCA, but the involvement of other genes is presently unknown. In the present study, we performed whole-exome sequencing on 10 tissue samples of metastases of RAI-refractory differentiated thyroid cancers and identified a recurrent hot-spot mutation (c.1924G>T) in the RasGRP3 gene, which codes for Ras guanine nucleotide-releasing protein 3. This mutation was found to occur at a high frequency (20%) in samples of metastases of RAI-refractory differentiated thyroid cancers compared with other types of thyroid cancer. Overexpression of mutant RasGRP3 significantly promoted cell proliferation, migration, and invasiveness of 8505C and BHT101 cells compared with cells transfected with wild-type RasGRP3 or an empty vector. In addition, mutant RasGRP3 decreased the expression of sodium iodide symporter (NIS) and thyroid-stimulating hormone receptor (TSHR), reduced the iodine uptake ability, and increased Akt phosphorylation in thyroid cancer cells. Finally, we showed that LY294002, an inhibitor of PI3K/Akt signaling, attenuated the effects of mutant RasGRP3 on thyroid cancer cells. Thus, our study revealed that the c.1924G>T hot-spot mutation in RasGRP3 is a more frequent genetic alteration in metastases of RAI-refractory differentiated thyroid cancer. This mutant RasGRP3 activated the Akt pathway, promoted thyroid cancer cell proliferation and invasion, and reduced NIS expression and the iodine uptake ability.