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Functional Differences of Very-Low-Density Lipoprotein Receptor Splice Variants in Regulating Wnt Signaling

机译:低密度脂蛋白受体剪接变异体在调节Wnt信号传导中的功能差异

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The very-low-density lipoprotein receptor (VLDLR) negatively regulates Wnt signaling. VLDLR has two major alternative splice variants, VLDLRI and VLDLRII, but their biological significance and distinction are unknown. Here we found that most tissues expressed both VLDLRI and VLDLRII, while the retina expressed only VLDLRII. The shed soluble VLDLR extracellular domain (sVLDLR-N) was detected in the conditioned medium of retinal pigment epithelial cells, interphotoreceptor matrix, and mouse plasma, indicating that ectodomain shedding of VLDLR occurs endogenously. VLDLRII displayed a higher ectodomain shedding rate and a more potent inhibitory effect on Wnt signaling than VLDLRI in vitro and in vivo. O-glycosylation, which is present in VLDLRI but not VLDLRII, determined the differential ectodomain shedding rates. Moreover, the release of sVLDLR-N was inhibited by a metalloproteinase inhibitor, TAPI-1, while it was promoted by phorbol 12-myristate 13-acetate (PMA). In addition, sVLDLR-N shedding was suppressed under hypoxia. Further, plasma levels of sVLDLR-N were reduced in both type 1 and type 2 diabetic mouse models. We concluded that VLDLRI and VLDLRII had differential roles in regulating Wnt signaling and that decreased plasma levels of sVLDLR-N may contribute to Wnt signaling activation in diabetic complications. Our study reveals a novel mechanism for intercellular regulation of Wnt signaling through VLDLR ectodomain shedding.
机译:低密度脂蛋白受体(VLDLR)负调控Wnt信号。 VLDLR有两个主要的替代剪接变体,VLDLRI和VLDLRII,但其生物学意义和区别尚不清楚。在这里,我们发现大多数组织都表达VLDLRI和VLDLRII,而视网膜仅表达VLDLRII。在视网膜色素上皮细胞,感光体基质和小鼠血浆的条件培养基中检测到脱落的可溶性VLDLR细胞外域(sVLDLR-N),表明VLDLR的胞外域脱落是内源性的。与VLDLRI的体外体内相比,VLDLRII具有更高的胞外域脱落速率和对Wnt信号的更强抑制作用。 VLDLRI中存在但OLDLRII中不存在的O-糖基化决定了不同的胞外域脱落速率。此外,金属蛋白酶抑制剂TAPI-1抑制sVLDLR-N的释放,而佛波醇12-肉豆蔻酸酯13-乙酸酯(PMA)则促进sVLDLR-N的释放。另外,在低氧条件下,sVLDLR-N脱落受到抑制。此外,在1型和2型糖尿病小鼠模型中sVLDLR-N的血浆水平均降低。我们得出的结论是,VLDLRI和VLDLRII在调节Wnt信号传导方面具有不同的作用,而降低的sVLDLR-N血浆水平可能有助于糖尿病并发症中Wnt信号的激活。我们的研究揭示了一种通过VLDLR胞外域脱落对Wnt信号进行细胞间调节的新机制。

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