Miettinen H M, Jalkanen M
Centre for Biotechnology, Turku, Finland.
J Cell Sci. 1994 Jun;107 ( Pt 6):1571-81. doi: 10.1242/jcs.107.6.1571.
Cell surface heparan sulfate proteoglycans such as syndecan-1 bind various extracellular matrix proteins and have been suggested to interact with the cytoskeleton. Such interactions are thought to be important for stabilizing cell morphology. Syndecan-1 resists extraction with Triton X-100. This insolubility was reported not to be affected by removal of the glycosaminoglycan chains, suggesting that the insolubility is not due to binding to the extracellular matrix, but rather to an association with the actin cytoskeleton (Rapraeger, A., Jalkanen, M. and Bernfield, M. (1986) J. Cell Biol. 103, 2683-2696). To examine further the interaction of syndecan-1 with the Triton X-100-insoluble residue, we expressed wild-type mouse syndecan-1 and a cytoplasmic deletion mutant (tail-less) in Chinese hamster ovary cells. We observed that both the wild-type and the tail-less syndecan-1 were partly insoluble in Triton X-100. The insolubility was not affected by increasing temperature (37 degrees C or 50 degrees C) or by cytochalasin D. Removal of the glycosaminoglycan chains from the ectodomain, however, resulted in complete Triton X-100 solubility, unlike previous reports. Syndecan-1 could also be released into the Triton X-100-soluble fraction by addition of heparin or heparan sulfate to the extraction medium. We conclude that the cytoplasmic domain of syndecan-1 is not responsible for Triton X-100 insolubility. Instead, our results indicate that Triton X-100 insolubility is caused by an interaction of syndecan-1 molecules with other cellular and/or extracellular molecules mediated by the heparan sulfate chains.
细胞表面的硫酸乙酰肝素蛋白聚糖，如syndecan-1，可结合多种细胞外基质蛋白，并被认为能与细胞骨架相互作用。这种相互作用被认为对稳定细胞形态很重要。Syndecan-1能抵抗Triton X-100的提取。据报道，去除糖胺聚糖链不会影响这种不溶性，这表明这种不溶性不是由于与细胞外基质的结合，而是与肌动蛋白细胞骨架的关联（Rapraeger, A., Jalkanen, M.和Bernfield, M. (1986) J. Cell Biol. 103, 2683 - 2696）。为了进一步研究syndecan-1与Triton X-100不溶性残渣的相互作用，我们在中国仓鼠卵巢细胞中表达了野生型小鼠syndecan-1和一个细胞质缺失突变体（无尾）。我们观察到野生型和无尾的syndecan-1都部分不溶于Triton X-100。温度升高（37摄氏度或50摄氏度）或细胞松弛素D都不会影响这种不溶性。然而，与之前的报道不同，从胞外域去除糖胺聚糖链会导致其完全溶于Triton X-100。通过在提取介质中添加肝素或硫酸乙酰肝素，syndecan-1也可以释放到Triton X-100可溶部分中。我们得出结论，syndecan-1的细胞质结构域不是导致其不溶于Triton X-100的原因。相反，我们的结果表明，Triton X-100不溶性是由syndecan-1分子与其他细胞内和/或细胞外分子通过硫酸乙酰肝素链介导的相互作用引起的。
