Overexpression of Frat1 correlates with malignant phenotype and advanced stage in human non-small cell lung cancer

Frat1 has been reported to be overexpressed in several human malignant tumors, including esophageal squamous, cervical, breast, and ovarian carcinoma, but the role of Frat1 in lung cancer is unknown. Our purpose is to investigate the expression of Frat1 and its correlation with clinicopathologic features and prognosis in lung cancer patients. Immunohistochemistry was performed on 137 cases of non-small cell lung cancer (NSCLC), including 78 cases with clinical follow-up, and Western blot and reverse transcription-polymerase chain reaction (RT-PCR) assays were performed to detect the protein and mRNA expression levels in 30 NSCLC and autologous matched normal tissues. In addition, lung cancer cell line A549 was transfected with Frat1-siRNA plasmids and Matrigel invasive assay was carried out to study the function of Frat1 in cancer cell invasiveness. The results showed that Frat1 was expressed in 85 (62.04%) cases of NSCLC by immunohistochemistry, while all 30 specimens of normal lung tissues were negative. Western blot and RT-PCR results for Frat1 mRNA were in agreement with immunohistochemical findings. Of interest, the expression of Frat1 was strongly correlated with tumor differentiation, TNM stage, and lymph node metastasis (P < 0.05). The Kaplan-Meier survival analysis demonstrated that the cases with Frat1 expression had significantly shorter survival than those without Frat1 (P < 0.001). In addition, down-regulation of Frat1 expression reduced the invasive ability in the A549 cell line, further supporting the idea that Frat1 may play a crucial role in carcinogenesis, tumor invasiveness and dissemination in human lung cancer.