Chambers A F, Hota C, Prince C W
London Regional Cancer Centre, Department of Oncology, University of Western Ontario, Canada.
Cancer Res. 1993 Feb 1;53(3):701-6.
We previously reported that H-ras-induced metastatic ability in murine NIH 3T3 cells is accompanied by increased expression of osteopontin (OPN). OPN is a secreted phosphoprotein that contains a GRGDS amino acid sequence, suggesting adhesive function, but the function of OPN in tumor cells remains poorly understood. Here we report that PAP2 cells (ras-transformed, metastatic NIH 3T3 cells) adhere and spread on OPN-coated substrates, while NIH 3T3 cells adhere and spread poorly on OPN. A similar pattern was seen for adhesion to laminin, while both cell lines adhered equally well to fibronectin. Adhesive interactions to OPN, laminin, and fibronectin were specific and were blocked by GRGDS (but not control GRGESP) peptides. The kinetics of adhesion to all three substrates was examined. Maximum adhesion was observed at 30-60 min, with reduced adhesion thereafter. We also purified metabolically labeled [32P]OPN secreted by PAP2 cells. Labeled OPN bound better in solution to PAP2 cells than to NIH 3T3 cells, and binding to both cell lines was blocked by GRGDS peptides, results that are consistent with the adhesion and spreading of these cells to OPN-coated substrates. Malignant PAP2 cells thus not only secrete increased levels of OPN, relative to NIH 3T3 cells, but also adhere better to this protein. While the target of OPN secreted by tumor cells is not known, our results raise the possibility that tumor cells that secrete OPN may also bind this protein and that this binding may function in autocrine-type signal transduction important to malignancy.
我们之前报道过，在鼠源NIH 3T3细胞中，H-ras诱导的转移能力伴随着骨桥蛋白（OPN）表达的增加。OPN是一种分泌型磷蛋白，含有GRGDS氨基酸序列，提示其具有黏附功能，但OPN在肿瘤细胞中的功能仍知之甚少。在此我们报道，PAP2细胞（ras转化的、具有转移能力的NIH 3T3细胞）能在包被有OPN的基质上黏附并铺展，而NIH 3T3细胞在OPN上的黏附与铺展较差。对于层粘连蛋白的黏附也观察到类似模式，而两种细胞系对纤连蛋白的黏附同样良好。与OPN、层粘连蛋白和纤连蛋白的黏附相互作用是特异性的，并被GRGDS（而非对照GRGESP）肽阻断。检测了对所有三种基质的黏附动力学。在30 - 60分钟时观察到最大黏附，此后黏附减少。我们还纯化了PAP2细胞分泌的经代谢标记的[32P]OPN。标记的OPN在溶液中与PAP2细胞的结合优于与NIH 3T3细胞的结合，并且与两种细胞系的结合均被GRGDS肽阻断，这些结果与这些细胞在包被有OPN的基质上的黏附与铺展一致。因此，恶性PAP2细胞不仅相对于NIH 3T3细胞分泌更高水平的OPN，而且对这种蛋白的黏附性更好。虽然肿瘤细胞分泌的OPN的靶点尚不清楚，但我们的结果提出了一种可能性，即分泌OPN的肿瘤细胞也可能结合这种蛋白，并且这种结合可能在对恶性肿瘤至关重要的自分泌型信号转导中发挥作用。
