Removal of sialic acid involving Klotho causes cell-surface retention of TRPV5 channel via binding to galectin-1
Removal of sialic acid involving Klotho causes cell-surface retention of TRPV5 channel via binding to galectin-1
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DOI：
10.1073/pnas.0803223105
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发表时间：
2008-07-15
影响因子：
11.1
通讯作者：
Huang, Chou-Long
中科院分区：
文献类型：
--
作者：
Cha, Seung-Kuy;Ortega, Bernardo;Huang, Chou-Long
Klotho是哺乳动物衰老抑制蛋白，与糖苷酶具有同源性。Klotho的细胞外结构域分泌到尿液和血液中，并可作为体液因子发挥作用。Klotho缺陷小鼠加速衰老和离子稳态失衡。Klotho治疗通过修饰其N-连接聚糖增加肾上皮Ca 2+通道TRPV 5的细胞表面丰度。然而，Klotho的精确糖底物和调节机制尚不清楚。在这里，我们报告说，Klotho的细胞外结构域激活质膜居民TRPV 5通过从其聚糖链中去除末端唾液酸。唾液酸的去除暴露了潜在的二糖半乳糖-N-乙酰葡糖胺，一种普遍存在的半乳糖苷结合凝集素半乳糖凝集素-1的配体。在细胞外表面与半乳糖凝集素-1晶格结合导致功能性TRPV 5在质膜上积累。在人细胞系中，通过RNA干扰敲低β-半乳糖苷α 2，6-唾液酸转移酶（ST 6 Gal-1），而不是其他唾液酸转移酶，可阻止Klotho的调节。此外，Klotho的调节在缺乏内源性ST 6 Gal-1的仓鼠细胞系中不存在，但通过重组ST 6 Gal-1的强制表达而恢复。因此，Klotho参与特异性去除α 2，6-连接的唾液酸，并通过该活性调节TRPV 5的细胞表面保留。Klotho的这种作用代表了调节细胞表面糖蛋白活性的新机制，并可能有助于Klotho维持钙平衡。
Klotho is a mammalian senescence-suppression protein that has homology with glycosidases. The extracellular domain of Klotho is secreted into urine and blood and may function as a humoral factor. Klotho-deficient mice have accelerated aging and imbalance of ion homeostasis. Klotho treatment increases cell-surface abundance of the renal epithelial Ca2+ channel TRPV5 by modifying its N-linked glycans. However, the precise sugar substrate and mechanism for regulation by Klotho is not known. Here, we report that the extracellular domain of Klotho activates plasma-membrane resident TRPV5 through removing terminal sialic acids from their glycan chains. Removal of sialic acids exposes underlying disaccharide galactose-N-acetylglucosamine, a ligand for a ubiquitous galactoside-binding lectin galectin-1. Binding to galectin-1 lattice at the extracellular surface leads to accumulation of functional TRPV5 on the plasma membrane. Knockdown of beta-galactoside alpha 2,6-sialyltransferase (ST6Gal-1) by RNA interference, but not other sialyltransferases, in a human cell line prevents the regulation by Klotho. Moreover, the regulation by Klotho is absent in a hamster cell line that lacks endogenous ST6Gal-1, but is restored by forced expression of recombinant ST6Gal-1. Thus, Klotho participates in specific removal of alpha 2,6-linked sialic acids and regulates cell surface retention of TRPV5 through this activity. This action of Klotho represents a novel mechanism for regulation of the activity of cell-surface glycoproteins and likely contributes to maintenance of calcium balance by Klotho.