Luo Bai-Hua, Xiong Feng, Wang Jun-Pu, Li Jing-He, Zhong Ming, Liu Qin-Lai, Luo Geng-Qiu, Yang Xiao-Jing, Xiao Ni, Xie Bin, Xiao Heng, Liu Rui-Jie, Dong Chang-Sheng, Wang Kuan-Song, Wen Ji-Fang
Department of Pathology, Xiangya Hospital, Central South University, Changsha, Hunan, China; Department of Pathology, School of Basic Medical Sciences, Central South University, Changsha, Hunan, China.
Center of Furong Judicial Authentication, the Second People's Hospital, Hunan, China.
PLoS One. 2014 Jun 19;9(6):e99922. doi: 10.1371/journal.pone.0099922. eCollection 2014.
Epidermal growth factor-like domain-containing protein 7 (EGFL7) is upregulated in human epithelial tumors and so is a potential biomarker for malignancy. Indeed, previous studies have shown that high EGFL7 expression promotes infiltration and metastasis of gastric carcinoma. The epithelial-mesenchymal transition (EMT) initiates the metastatic cascade and endows cancer cells with invasive and migratory capacity; however, it is not known if EGFL7 promotes metastasis by triggering EMT. We found that EGFL7 was overexpressed in multiple human gastric cancer (GC) cell lines and that overexpression promoted cell invasion and migration as revealed by scratch wound and transwell migration assays. Conversely, shRNA-mediated EGFL7 knockdown reduced invasion and migration. Furthermore, EGFL7-overexpressing cells grew into larger tumors and were more likely to metastasize to the liver compared to underexpressing CG cells following subcutaneous injection in mice. EGFL7 overexpression protected GC cell lines against anoikis, providing a plausible mechanism for this enhanced metastatic capacity. In excised human gastric tumors, expression of EGFL7 was positively correlated with expression levels of the mesenchymal marker vimentin and the EMT-associated transcription repressor Snail, and negatively correlated with expression of the epithelial cell marker E-cadherin. In GC cell lines, EGFL7 knockdown reversed morphological signs of EMT and decreased both vimentin and Snail expression. In addition, EGFL7 overexpression promoted EGF receptor (EGFR) and protein kinase B (AKT) phospho-activation, effects markedly suppressed by the EGFR tyrosine kinase inhibitor AG1478. Moreover, AG1478 also reduced the elevated invasive and migratory capacity of GC cell lines overexpressing EGFL7. Collectively, these results strongly suggest that EGFL7 promotes metastasis by activating EMT through an EGFR-AKT-Snail signaling pathway. Disruption of EGFL7-EGFR-AKT-Snail signaling may a promising therapeutic strategy for gastric cancer.
含表皮生长因子样结构域蛋白7（EGFL7）在人类上皮性肿瘤中表达上调，因此是一种潜在的恶性肿瘤生物标志物。事实上，先前的研究表明，EGFL7高表达促进胃癌的浸润和转移。上皮-间质转化（EMT）启动转移级联反应并赋予癌细胞侵袭和迁移能力；然而，尚不清楚EGFL7是否通过触发EMT促进转移。我们发现EGFL7在多种人类胃癌（GC）细胞系中过表达，划痕伤口和Transwell迁移试验显示过表达促进细胞侵袭和迁移。相反，shRNA介导的EGFL7敲低降低了侵袭和迁移能力。此外，与皮下注射小鼠后低表达的CG细胞相比，过表达EGFL7的细胞形成更大的肿瘤，并且更有可能转移至肝脏。EGFL7过表达保护GC细胞系免受失巢凋亡，为这种增强的转移能力提供了一种合理的机制。在切除的人类胃肿瘤中，EGFL7的表达与间充质标志物波形蛋白和EMT相关转录抑制因子Snail的表达水平呈正相关，与上皮细胞标志物E-钙黏蛋白的表达呈负相关。在GC细胞系中，EGFL7敲低逆转了EMT的形态学特征，并降低了波形蛋白和Snail的表达。此外，EGFL7过表达促进表皮生长因子受体（EGFR）和蛋白激酶B（AKT）的磷酸化激活，表皮生长因子受体酪氨酸激酶抑制剂AG1478可显著抑制这些作用。此外，AG1478还降低了过表达EGFL7的GC细胞系升高的侵袭和迁移能力。总之，这些结果强烈表明EGFL7通过EGFR-AKT-Snail信号通路激活EMT促进转移。破坏EGFL7-EGFR-AKT-Snail信号通路可能是一种有前景的胃癌治疗策略。
