Non-pump Function Of NIS In Thyroid Cancer

Background:Thyroid cancer is the fastest rising incident cancer worldwide.Over 90%of thyroid cancers are differentiated thyroid cancers?DTC?.Radioiodide(¹³¹I)is the main post-thyroidectomy treatment of DTC,although the effecy of high dose of low dose of ¹³¹I in remnant ablation remains elusive.The sodium iodide symporter?NIS?is a classical iodide pump in normal thyroid and thyroid cancer cells,typically localizing within the cell plasma membrane,whereby NIS expression is believed to ensure success in mainstay radioiodide therapy for DTC.Although radioiodide uptake is generally reduced in thyroid cancer tissue,intracellular non-membranous NIS has been reported to increase paradoxically.Similarlly,intracellular NIS has been reported to be up regulated in some non-thyroidal cancers such as breast cancer and liver cancer,suggesting that NIS may have pump-independent function.Thyroid cancer is one of the major component cancers of Cowden syndrome,a subset of which is caused by germline PTEN mutations.In this study,we aim to investigate the efficacy of low dose or high dose for thyroid remnat ablation,and explore the non-canonical tumorigenic role of NIS in thyroid cancer cells in relationship with PTEN.Methods:1.Patients presenting for radioiodine ablation in our department were included.Inclusion criteria were aged?16 years,total or near-total thyroidectomy,tumor-node-metastasis?TNM?stage of pT1-3,any N stage,and M0.All patients were randomly allocated to either the high-dose group of 3700MBq or the low-dose group of 1850MBq for remnant ablation.The response to treatment was defined as successful or unsuccessful after a six-to nine-month interval.Ablation was considered to be successful if patients fulfilled the following criteria:no tracer uptake in the thyroid bed on diagnosis whole-body scanning and a negative level of serum thyroglobulin.2.We utilized thyroid cancer cell line with stable NIS expression and PCCL3,MCF7 cell lines with endougenous NIS to test our hypothesis.We use some methods including would healing assay,immunoprecipitation,immunofluorescence,western blot,qRT-PCR etc.We utilized siRNA tranfection to knockdown PTEN and other molecular.Results:There were 327 patients enrolled between January 2013 and December 2014.Data could be analyzed for 278 cases?Mage=44 years;71.6%women?,155 in the low-dose group and 123 in the high-dose group.The rate of initial successful ablation was 84.2%in all patients,82.6%in the lowdose group,and 86.2%in the high-dose group.There was no difference between the two groups?P=0.509?.In thyroid cancer modles,we found that PTEN knockdown stabilizes NIS protein to then increase NIS protein levels,particularly intracellular NIS,via promoting NIS-LARG?leukemia associated RhoA guanine exchange factor?interaction.Increased protein levels of cytoplasmic NIS enhance RhoA activation,resulting in a pro-migration tumorigenic phenotype.Inhibition of NIS glycosylation through activation of PTEN downstream PI3K/AKT/mTOR signaling pathway contributes to mislocalization of NIS in the cytoplasm,thus facilitating its non-pump tumorigenic function through interacting with LARG,which predominantly localizes in the cytoplasm.Moreover,PTEN or downstream PI3K/AKT/mTOR signaling pathway could affect DPAGT1,one glycosylating enzyme involved in the initial step of N-linked glycosylation,to inhibit NIS glycosylation.Conclusion:1.In Chinese patients with DTC,the low dose of 1850MBq radioiodine activity is as effective as a high dose of 3700MBq for thyroid remnant ablation.2.Our results elucidate a NIS iodide-pump-independent pro-tumorigenic role in thyroid cancer through crosstalk with PTEN signaling.