Keratocan, a cornea-specific keratan sulfate proteoglycan, is regulated by lumican
Keratocan, a cornea-specific keratan sulfate proteoglycan, is regulated by lumican
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DOI：
10.1074/jbc.m500249200
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发表时间：
2005-07-08
影响因子：
4.8
通讯作者：
Kao, WWY
中科院分区：
文献类型：
--
作者：
Carlson, EC;Liu, CY;Kao, WWY
光蛋白聚糖是一种广泛分布于哺乳动物结缔组织的细胞外基质糖蛋白。经硫酸角质素修饰的角膜光蛋白聚糖是基质中主要的蛋白聚糖之一。光蛋白聚糖缺失的小鼠表现出胶原纤维组织改变和角膜透明度丧失。一种密切相关的蛋白质——角蛋白聚糖，携带角膜中剩余的硫酸角质素，但角蛋白聚糖缺失的小鼠表现出的角膜表型较轻。在当前的研究中，我们检测了光蛋白聚糖在野生型小鼠角膜中过表达的影响。这些小鼠在胶原组织或透明度方面没有变化，但在蛋白质和mRNA水平上角蛋白聚糖的表达增加。光蛋白聚糖缺失小鼠的角膜角蛋白聚糖表达降低。在向光蛋白聚糖缺失（Lum(-/-)）小鼠的角膜基质内注射光蛋白聚糖表达小基因后，也观察到角蛋白聚糖表达与光蛋白聚糖的这种关联。体外小干扰RNA敲低光蛋白聚糖可降低角蛋白聚糖的表达，而在体内向光蛋白聚糖缺失（Lum(-/-)）小鼠的角膜基质内共注射光蛋白聚糖表达小基因和由角蛋白聚糖启动子驱动的β -半乳糖苷酶报告基因，表明光蛋白聚糖表达可使角蛋白聚糖转录活性增加。这些观察结果表明，光蛋白聚糖在转录水平对角蛋白聚糖的表达具有一种新的调节作用。这些结果有助于解释在光蛋白聚糖缺失（Lum(-/-)）和角蛋白聚糖缺失（Kera(-/-)）小鼠中发现的角膜表现严重程度的差异。结果还表明，小分子蛋白聚糖的临界水平对胶原组织至关重要，但过量并不损害细胞外基质的形态发生。
Lumican is an extracellular matrix glycoprotein widely distributed in mammalian connective tissues. Corneal lumican modified with keratan sulfate constitutes one of the major proteoglycans of the stroma. Lumican-null mice exhibit altered collagen fibril organization and loss of corneal transparency. A closely related protein, keratocan, carries the remaining keratan sulfate of the cornea, but keratocan-null mice exhibit a less severe corneal phenotype. In the current study, we examined the effect of lumican overexpression in corneas of wild type mice. These mice showed no alteration in collagen organization or transparency but had increased keratocan expression at both protein and mRNA levels. Corneas of lumican-null mice showed decreased keratocan. This coupling of keratocan expression with lumican also was observed after intrastromal injection of a lumican expression minigene into the corneal stroma of Lum(-/-) mice. Small interfering RNA knockdown of lumican in vitro reduced keratocan expression, whereas co-injection of a lumican-expressing minigene with a beta-galactosidase reporter driven by the keratocan promoter demonstrated an increase of keratocan transcriptional activity in response to lumican expression in Lum(-/-) corneas in vivo. These observations demonstrate that lumican has a novel regulatory role in keratocan expression at the transcriptional level. Such results help provide an explanation for the differences in severity of corneal manifestation found in Lum(-/-) and Kera(-/-) mice. The results also suggest a critical level of small proteoglycans to be essential for collagen organization but that overabundance is not detrimental to extracellular matrix morphogenesis.