Li Ailin, Zhang Weiwei, Xia Huifang, Miao Yuan, Zhou Haijing, Zhang Xiupeng, Dong Qianze, Li Qingchang, Qiu Xueshan, Wang Enhua
Department of Radiotherapy, The First Affiliated Hospital of China Medical University, Shenyang, China.
Department of Pathology, The First Affiliated Hospital and College of Basic Medical Sciences of China Medical University, Shenyang, China.
Tumour Biol. 2016 Nov;37(11):15157-15164. doi: 10.1007/s13277-016-5411-5. Epub 2016 Sep 27.
The role of Crk-associated substrate (CAS) family members in regulating invasion and metastasis has been described in several cancers. As the fourth member of the CAS family, CASS4 is also related with positive lymph node metastasis and poor prognosis in lung cancer. However, the underlying mechanisms and downstream effectors of CASS4 in the development and progression of non-small cell lung cancer (NSCLC) remain unclear. In this study, CASS4 overexpression inhibited E-cadherin expression and enhanced invasion in NSCLC cell line transfected with CASS4 plasmid, while CASS4 depletion upregulated E-cadherin expression and inhibited invasion in NSCLC cell line transfected with CASS4 siRNA. The effect of CASS4 overexpression in facilitating invasion of NSCLC cells was reversed by restoring E-cadherin expression, which indicates that CASS4 may promote invasion by inhibiting E-cadherin expression. Subsequent immunohistochemistry results confirmed that CASS4 overexpression correlated with loss of E-cadherin expression. We next investigated the phosphorylation levels of focal adhesion kinase (FAK), p38, extracellular signal-related kinase (ERK), and AKT after CASS4 plasmid or CASS4 siRNA transfection. CASS4 facilitated AKT (Ser473) phosphorylation. Treatment with an AKT phosphorylation inhibitor reversed the increased invasive capacity and downregulation of E-cadherin protein induced by CASS4 overexpression. Taken together, the present results indicate that CASS4 may promote NSCLC invasion by activating the AKT signaling pathway, thereby inhibiting E-cadherin expression.
Crk相关底物（CAS）家族成员在调控多种癌症的侵袭和转移过程中的作用已得到阐述。作为CAS家族的第四个成员，CASS4也与肺癌的阳性淋巴结转移及不良预后相关。然而，CASS4在非小细胞肺癌（NSCLC）发生发展过程中的潜在机制及下游效应分子仍不清楚。在本研究中，CASS4过表达抑制了用CASS4质粒转染的NSCLC细胞系中E-钙黏蛋白的表达并增强了侵袭能力，而CASS4缺失则上调了用CASS4 siRNA转染的NSCLC细胞系中E-钙黏蛋白的表达并抑制了侵袭。恢复E-钙黏蛋白表达可逆转CASS4过表达促进NSCLC细胞侵袭的作用，这表明CASS4可能通过抑制E-钙黏蛋白表达来促进侵袭。随后的免疫组化结果证实，CASS4过表达与E-钙黏蛋白表达缺失相关。接下来，我们研究了转染CASS4质粒或CASS4 siRNA后黏着斑激酶（FAK）、p38、细胞外信号调节激酶（ERK）和AKT的磷酸化水平。CASS4促进了AKT（Ser473）的磷酸化。用AKT磷酸化抑制剂处理可逆转CASS4过表达诱导的侵袭能力增强和E-钙黏蛋白蛋白下调。综上所述，目前的结果表明CASS4可能通过激活AKT信号通路促进NSCLC侵袭，从而抑制E-钙黏蛋白表达。
