Analysis for an ovarian cancer-derived factor which decreases the expression of alpha-smooth muscle actin in stromal cells

我们先前报道，人卵巢癌细胞株的条件性基质(CM)和恶性卵巢肿瘤液都能减少成纤维细胞中α-平滑肌肌动蛋白(α-SMA)的表达。在本研究中，我们通过Western印迹分析证实，恶性卵巢肿瘤的肿瘤液中存在抑制作用，而良性卵巢肿瘤的肿瘤液中没有这种抑制作用。抗血小板分化生长因子(PDGF)的中和抗体以剂量依赖的方式部分阻断卵巢癌液诱导的抑制作用。另一方面，加入PDGF抗体后，卵巢良性肿瘤液的作用不变。接下来，我们用ELISA法检测了人卵巢癌细胞系的CMS中是否含有PDGF。9个上皮性来源的癌细胞株均向其培养上清液中释放PDGF，1个非上皮性来源的癌细胞株不释放。虽然几乎所有的良性肿瘤的肿瘤液中都不含有PDGF，但80%的癌症组织中含有相对较高水平的PDGF。因此，卵巢癌细胞释放的PDGF被认为降低了周围间质细胞中α-SMA的表达。α-SMA是一种细胞骨架蛋白，不仅在基质成纤维细胞中表达，而且在构成血管壁的细胞中也有表达。如果α-SMA表达的降低导致肿瘤细胞侵袭间质的增强，则可能是癌基因产物PDGF具有肿瘤侵袭增强剂的作用。

We previously reported that both the conditioned mcdium (CM) of human ovarian cancer cell lines and the malignant ovarian tumor fluid reduced the expression of alpha-smooth muscle actin (alpha-SMA) in fibroblasts. ln this study, we confirmed the inhibitory effect existed in tumor fluid of malignant ovarian tumors but not that of benign ones by using a Western blot analysis. Ovarian cancer fluid-induced inhibition was partially blocked by a neutralizing antibody against platelet-devived growth factor (PDGF) in a dose-dependent fashion. On the other hand, the effect of benign ovarian tumor fluid was unchanged by adding the PDGF antibody. We next checked whether the CMs of human ovarian cancer cell lines contained PDGF or not by using an ELISA system. All of 9 epithelial originated cancer cell lines released PDGF into their culture media and one non-epithelial originated line did not. Although almost all of benign tumors did not contain PDGF in their tumor fluid, 80% of cancers contained relatively high levels of PDGF.Thus, PDGF released by ovarian cancer cells is thought to decrease the expression of alpha-SMA in surrounding stromal cells. alpha-SMA is a cytoskeletal protein expressed not only in stromal fibroblasts but also in the cells consisting in the vessel wall. If a decrease in alpha-SMA expression results in the enhancement of tumor cell invasion into stroma, it is possible that the cancer-derived PDGF,sis-oncogene product, has the role of enhancer of tumor invasion.