Department of Biomedical Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark.
J Biol Chem. 2010 May 7;285(19):14247-58. doi: 10.1074/jbc.M109.056945. Epub 2010 Feb 12.
Fibroblasts null for the transmembrane proteoglycan, syndecan-4, have an altered actin cytoskeleton, compared with matching wild-type cells. They do not organize alpha-smooth muscle actin into bundles, but will do so when full-length syndecan-4 is re-expressed. This requires the central V region of the core protein cytoplasmic domain, though not interactions with PDZ proteins. A second key requirement is multiple heparan sulfate chains. Mutant syndecan-4 with no chains, or only one chain, failed to restore the wild-type phenotype, whereas those expressing two or three were competent. However, clustering of one-chain syndecan-4 forms with antibodies overcame the block, indicating that valency of interactions with ligands is a key component of syndecan-4 function. Measurements of focal contact/adhesion size and focal adhesion kinase phosphorylation correlated with syndecan-4 status and alpha-smooth muscle actin organization, being reduced where syndecan-4 function was compromised by a lack of multiple heparan sulfate chains.
与匹配的野生型细胞相比，跨膜蛋白聚糖 syndecan-4 缺失的成纤维细胞的肌动蛋白细胞骨架发生了改变。它们不会将α-平滑肌肌动蛋白组织成束，但当全长 syndecan-4 被重新表达时，它们会这样做。这需要核心蛋白细胞质结构域的中心 V 区，但不需要与 PDZ 蛋白相互作用。第二个关键要求是多个肝素硫酸盐链。没有链或只有一条链的突变 syndecan-4 未能恢复野生型表型，而表达两条或三条链的则有能力恢复。然而，用抗体聚集一条链 syndecan-4 形式克服了这种障碍，表明与配体相互作用的价数是 syndecan-4 功能的一个关键组成部分。焦点接触/黏附大小和粘着斑激酶磷酸化的测量与 syndecan-4 状态和α-平滑肌肌动蛋白组织相关，当缺乏多个肝素硫酸盐链而损害 syndecan-4 功能时，其会减少。
