A Novel SLC5A5 Variant Reveals the Crucial Role of Kinesin Light Chain 2 in Thyroid Hormonogenesis

• Published in: The journal of clinical endocrinology and metabolism 2021-07, Vol.106 (7), p.1867-1881
• Main Authors: Martín, Mariano, Modenutti, Carlos Pablo, Gil Rosas, Mauco Lucas, Peyret, Victoria, Geysels, Romina Celeste, Bernal Barquero, Carlos Eduardo, Sobrero, Gabriela, Muñoz, Liliana, Signorino, Malvina, Testa, Graciela, Miras, Mirta Beatriz, Masini-Repiso, Ana María, Calcaterra, Nora Beatriz, Coux, Gabriela, Carrasco, Nancy, Martí, Marcelo Adrián, Nicola, Juan Pablo
• Format: Article
• Language: English
• Subjects: Animals; Clinical s; Conformation; Congenital diseases; Congenital Hypothyroidism - genetics; DNA sequencing; Endoplasmic reticulum; Genetic disorders; Genetics; Health aspects; Humans; Hypothalamic-pituitary-thyroid axis; Hypothalamus; Hypothyroidism; Infant, Newborn; International economic relations; Iodides - metabolism; Kinesin; Kinesins; Male; Medical equipment and supplies industry; Medical test kit industry; Metabolism, Inborn Errors - genetics; Microtubule-Associated Proteins - metabolism; Mutation, Missense; Nucleotide sequencing; Phenotype; Phenotypes; Physiological aspects; Pituitary; Rats; Sodium iodide symporter; Symporters - genetics; Thyrocytes; Thyroid gland; Thyroid Gland - metabolism; Thyroid hormones; Thyroid Hormones - metabolism; Tryptophan
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/clinem/dgab283

Abstract Context Iodide transport defect (ITD) (Online Mendelian Inheritance in Man No. 274400) is an uncommon cause of dyshormonogenic congenital hypothyroidism due to loss-of-function variants in the SLC5A5 gene, which encodes the sodium/iodide symporter (NIS), causing deficient iodide accumulation in thyroid follicular cells. Objective This work aims to determine the molecular basis of a patient’s ITD clinical phenotype. Methods The propositus was diagnosed with dyshormonogenic congenital hypothyroidism with minimal 99mTc-pertechnetate accumulation in a eutopic thyroid gland. The propositus SLC5A5 gene was sequenced. Functional in vitro characterization of the novel NIS variant was performed. Results Sanger sequencing revealed a novel homozygous missense p.G561E NIS variant. Mechanistically, the G561E substitution reduces iodide uptake, because targeting of G561E NIS to the plasma membrane is reduced. Biochemical analyses revealed that G561E impairs the recognition of an adjacent tryptophan-acidic motif by the kinesin-1 subunit kinesin light chain 2 (KLC2), interfering with NIS maturation beyond the endoplasmic reticulum, and reducing iodide accumulation. Structural bioinformatic analysis suggests that G561E shifts the equilibrium of the unstructured tryptophan-acidic motif toward a more structured conformation unrecognizable to KLC2. Consistently, knockdown of Klc2 causes defective NIS maturation and consequently decreases iodide accumulation in rat thyroid cells. Morpholino knockdown of klc2 reduces thyroid hormone synthesis in zebrafish larvae leading to a hypothyroid state as revealed by expression profiling of key genes related to the hypothalamic-pituitary-thyroid axis. Conclusion We report a novel NIS pathogenic variant associated with dyshormonogenic congenital hypothyroidism. Detailed molecular characterization of G561E NIS uncovered the significance of KLC2 in thyroid physiology.