Departamento de Bioquímica Clínica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina.
Centro de Investigaciones en Bioquímica Clínica e Inmunología (CIBICI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Córdoba, Argentina.
FASEB J. 2021 Aug;35(8):e21681. doi: 10.1096/fj.202100303R.
The sodium/iodide symporter (NIS) expresses at the basolateral plasma membrane of the thyroid follicular cell and mediates iodide accumulation required for normal thyroid hormonogenesis. Loss-of-function NIS variants cause congenital hypothyroidism due to impaired iodide accumulation in thyroid follicular cells underscoring the significance of NIS for thyroid physiology. Here we report novel findings derived from the thorough characterization of the nonsense NIS mutant p.R636* NIS-leading to a truncated protein missing the last eight amino acids-identified in twins with congenital hypothyroidism. R636* NIS is severely mislocalized into intracellular vesicular compartments due to the lack of a conserved carboxy-terminal type 1 PDZ-binding motif. As a result, R636* NIS is barely targeted to the plasma membrane and therefore iodide transport is reduced. Deletion of the PDZ-binding motif causes NIS accumulation into late endosomes and lysosomes. Using PDZ domain arrays, we revealed that the PDZ-domain containing protein SCRIB binds to the carboxy-terminus of NIS by a PDZ-PDZ interaction. Furthermore, in CRISPR/Cas9-based SCRIB deficient cells, NIS expression at the basolateral plasma membrane is compromised, leading to NIS localization into intracellular vesicular compartments. We conclude that the PDZ-binding motif is a plasma membrane retention signal that participates in the polarized expression of NIS by selectively interacting with the PDZ-domain containing protein SCRIB, thus retaining the transporter at the basolateral plasma membrane. Our data provide insights into the molecular mechanisms that regulate NIS expression at the plasma membrane, a topic of great interest in the thyroid cancer field considering the relevance of NIS-mediated radioactive iodide therapy for differentiated thyroid carcinoma.
钠/碘同向转运体（NIS）表达在甲状腺滤泡细胞的基底外侧质膜上，介导正常甲状腺激素生成所需的碘积聚。功能丧失的 NIS 变体导致先天性甲状腺功能减退症，因为甲状腺滤泡细胞中碘积聚受损，这突显了 NIS 对甲状腺生理学的重要性。在这里，我们报告了从对双胞胎先天性甲状腺功能减退症中发现的无意义 NIS 突变 p.R636* NIS（导致缺失最后八个氨基酸的截短蛋白）的彻底表征中得出的新发现。由于缺乏保守的羧基末端 1 型 PDZ 结合基序，R636* NIS 严重错误定位到细胞内囊泡隔室。因此，R636* NIS 几乎不能靶向质膜，因此碘转运减少。PDZ 结合基序的缺失导致 NIS 积聚到晚期内体和溶酶体中。使用 PDZ 结构域数组，我们揭示了含有 PDZ 结构域的蛋白 SCRIB 通过 PDZ-PDZ 相互作用与 NIS 的羧基末端结合。此外，在基于 CRISPR/Cas9 的 SCRIB 缺陷细胞中，NIS 在基底外侧质膜上的表达受损，导致 NIS 定位到细胞内囊泡隔室。我们得出结论，PDZ 结合基序是一种质膜保留信号，通过与含有 PDZ 结构域的蛋白 SCRIB 选择性相互作用，参与 NIS 的极化表达，从而将转运体保留在质膜的基底外侧。我们的数据提供了对调节 NIS 在质膜上表达的分子机制的深入了解，考虑到 NIS 介导的放射性碘治疗对分化型甲状腺癌的相关性，这是甲状腺癌领域非常感兴趣的话题。
