Fages C, Kaksonen M, Kinnunen T, Punnonen E L, Rauvala H
Laboratory of Molecular Neurobiology, Institute of Biotechnology, the Division of Biochemistry, Department of Biosciences, and Electron Microscopy Unit, Institute of Biotechnology, FIN-00014 University of Helsinki, Finland.
J Cell Sci. 1998 Oct;111 ( Pt 20):3073-80. doi: 10.1242/jcs.111.20.3073.
Localization of mRNAs is currently thought to be partially responsible for molecular sorting to specific compartments within the cell. In mammalian cells the best-studied example is the beta-actin mRNA that is localized to the cell processes, and its localization is necessary in migratory responses of cells. It is reasonable to assume that mRNA localization within cells is coupled to transmembrane signalling due to extracellular factors, but little is known about such putative mechanisms. We show here that HB-GAM, an extracellular matrix-associated factor that enhances migratory responses in cells, is able to localize beta-actin mRNA when locally applied to cells via microbeads. The HB-GAM-induced mRNA localization is specifically inhibited by low concentrations of heparin and by heparitinase treatment of cells, showing that cell-surface heparin-type glycans are required for the effect. The finding that soluble N-syndecan is also inhibitory suggests that the transmembrane proteoglycan N-syndecan, previously identified as an HB-GAM receptor, is involved in the mRNA-localizing effect of HB-GAM. Inhibition of the mRNA localization by the src-kinase inhibitor PP1 is compatible with an N-syndecan-mediated effect since the receptor function of N-syndecan has been recently found to depend on the src-kinase signalling pathway. The mRNA-localizing activity of N-syndecan is also suggested by the finding that affinity-purified anti-N-syndecan antibodies coated on microbeads are able to localize beta-actin mRNA.
目前认为，mRNA的定位在一定程度上负责细胞内特定区域的分子分选。在哺乳动物细胞中，研究得最透彻的例子是定位于细胞突起的β-肌动蛋白mRNA，其定位对于细胞的迁移反应是必需的。有理由推测，由于细胞外因子的作用，细胞内mRNA的定位与跨膜信号传导相关，但对于这种假定的机制知之甚少。我们在此表明，HB-GAM是一种与细胞外基质相关的因子，可增强细胞的迁移反应，当通过微珠局部应用于细胞时，它能够使β-肌动蛋白mRNA定位。低浓度肝素和对细胞进行硫酸乙酰肝素酶处理可特异性抑制HB-GAM诱导的mRNA定位，表明细胞表面的肝素型聚糖是产生这种效应所必需的。可溶性N-聚糖蛋白也具有抑制作用这一发现表明，先前被鉴定为HB-GAM受体的跨膜蛋白聚糖N-聚糖蛋白参与了HB-GAM的mRNA定位效应。src激酶抑制剂PP1对mRNA定位的抑制作用与N-聚糖蛋白介导的效应相符，因为最近发现N-聚糖蛋白的受体功能依赖于src激酶信号通路。包被在微珠上的亲和纯化抗N-聚糖蛋白抗体能够使β-肌动蛋白mRNA定位这一发现也提示了N-聚糖蛋白的mRNA定位活性。
