Department of Medical Oncology, Second Affiliated Hospital, Medical School of Zhejiang University, Hangzhou, China.
PLoS One. 2012;7(10):e47901. doi: 10.1371/journal.pone.0047901. Epub 2012 Oct 24.
Liver metastasis is a major cause of mortality from colorectal cancer (CRC). However, mechanisms underlying this process are largely unknown. Osteopontin (OPN) is a secreted phosphorylated glycoprotein that is involved in tumor migration and metastasis. The role of OPN in cancer is currently unclear. In this study, OPN mRNA was examined in tissues from CRC, adjacent normal mucosa, and liver metastatic lesions using quantitative real-time PCR analysis. The protein expression of OPN and its receptors (integrin αv and CD44 v6) was detected by using an immunohistochemical (IHC) method. The role of OPN in liver metastasis was studied in established colon cancer Colo-205 and SW-480 cell lines transfected with sense- or antisense-OPN eukaryotic expression plasmids by flow cytometry and cell adhesion assay. Fluorescence redistribution after photobleaching (FRAP) was used to study gap functional intercellular communication (GJIC) among OPN-transfected cells. It was found that OPN was highly expressed in metastatic hepatic lesions from CRC compared to primary CRC tissue and adjacent normal mucosa. The expression of OPN mRNA in tumor tissues was significantly related with the CRC stages. OPN expression was also detected in normal hepatocytes surrounding CRC metastatic lesions. Two known receptors of OPN, integrin αv and CD44v6 proteins, were strongly expressed in hepatocytes from normal liver. CRC cells with forced OPN expression exhibited increased heterotypic adhesion with endothelial cells and weakened intercellular communication. OPN plays a significant role in CRC metastasis to liver through interaction with its receptors in hepatocytes, decreased homotypic adhesion, and enhanced heterotypic adhesion.
肝转移是结直肠癌（CRC）患者死亡的主要原因。然而，其具体机制仍不清楚。骨桥蛋白（OPN）是一种分泌型磷酸化糖蛋白，参与肿瘤的迁移和转移。目前，OPN 在癌症中的作用尚不清楚。本研究采用实时定量 PCR 分析检测 CRC 组织、癌旁正常黏膜组织和肝转移灶中 OPN mRNA 的表达，采用免疫组化（IHC）方法检测 OPN 及其受体（整合素αv 和 CD44v6）的蛋白表达。采用流式细胞术和细胞黏附实验，研究转染 sense-或 antisense-OPN 真核表达质粒的结肠癌 Colo-205 和 SW-480 细胞系中 OPN 对肝转移的作用。通过荧光漂白后再分布（FRAP）实验研究 OPN 转染细胞之间的缝隙连接细胞间通讯（GJIC）。结果发现，与原发性 CRC 组织和癌旁正常黏膜相比，CRC 肝转移灶中 OPN 高表达。肿瘤组织中 OPN mRNA 的表达与 CRC 分期显著相关。在 CRC 肝转移灶周围的正常肝细胞中也检测到 OPN 的表达。OPN 的两个已知受体，整合素αv 和 CD44v6 蛋白，在正常肝组织中的肝细胞中强烈表达。过表达 OPN 的 CRC 细胞与内皮细胞的异型黏附增加，细胞间通讯减弱。OPN 通过与肝细胞上的受体相互作用，降低同源黏附，增强异型黏附，在 CRC 肝转移中发挥重要作用。
