title: Identification of in vivo phosphorylation sites and their functional significance in the sodium iodide symporter.
abstract: The Na+/I- symporter (NIS)-mediated iodide uptake activity is the basis for targeted radioiodide ablation of thyroid cancers. Although it has been shown that NIS protein is phosphorylated, neither the in vivo phosphorylation sites nor their functional significance has been reported. In this study, Ser-43, Thr-49, Ser-227, Thr-577, and Ser-581 were identified as in vivo NIS phosphorylation sites by mass spectrometry. Kinetic analysis of NIS mutants of the corresponding phosphorylated amino acid residue indicated that the velocity of iodide transport of NIS is modulated by the phosphorylation status of Ser-43 and Ser-581. We also found that the phosphorylation status of Thr-577 may be important for NIS protein stability and that the phosphorylation status of Ser-227 is functionally silent. Thr-49 appears to be critical for proper local structure/conformation of NIS because mutation of Thr-49 to alanine, aspartic acid, or serine results in reduced NIS activity without alterations in total or cell surface NIS protein levels. Taken together, we showed that NIS protein levels and functional activity could be modulated by phosphorylation through distinct mechanisms.
authors.affiliation: Integrated Biomedical Science Graduate Program, Department of Physiology and Cell Biology, Ohio State University, Columbus 43210, USA.
authors.forename: Douangsone D
authors.initials: DD
authors.lastname: Vadysirisack
authors.forename: Eric S-W
authors.initials: ES
authors.lastname: Chen
authors.forename: Zhaoxia
authors.initials: Z
authors.lastname: Zhang
authors.forename: Ming-Daw
authors.initials: MD
authors.lastname: Tsai
authors.forename: Geen-Dong
authors.initials: GD
authors.lastname: Chang
authors.forename: Sissy M
authors.initials: SM
authors.lastname: Jhiang
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D006801:Humans; D007454:Iodides / Q000378:metabolism*; D017136:Ion Transport / Q000502:physiology; D020125:Mutation, Missense; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D011877:Radionuclide Imaging; D051381:Rats; D027981:Symporters / Q000235:genetics / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism; D000099209:Sodium-Iodide Symporters
chemical_list: D007454:Iodides; D027981:Symporters; D000099209:Sodium-Iodide Symporters