Abstract
BACKGROUND: The E3 ubiquitin ligase neural precursor cell expressed developmentally downregulated 4-1 (NEDD4-1) negatively regulates phosphatase and tensin homolog deleted on chromosome 10 (PTEN) protein levels through polyubiquitination and proteolysis, but its significance in lung cancer is still unclear. This study investigated the expression and the role of NEDD4-1 in tumor development and chemosensitivity of lung adenocarcinoma (ADC). METHODS: We retrospectively investigated the expression and significance of NEDD4-1, PTEN, and p-Akt proteins in 135 paired ADC and adjacent noncancerous tissue specimens using immunohistochemistry. Furthermore, we evaluated the relationship between NEDD4-1 expression and clinicopathologic characteristics and prognosis. The effects of small interfering RNA against NEDD4-1 on proliferation and chemosensitivity were examined in A549 cells in vitro using 3- (4,5-dimethylthiazol-2-yl) -5-(3-carboxymethoxyphenyl) -2-(4-sulfophenyl)- 2H-tetrazolium method. The ability of migration and invasion of A549 cells was tested by transwell assay. Moreover, reverse-transcription quantitative polymerase chain reaction and Western blotting analyses were used to determine the expression of NEDD4-1, PTEN, phosphoinositide 3-kinase (PI3K)/Akt activity, and its downstream target proteins. RESULTS: NEDD4-1 protein was significantly upregulated in lung ADC tissues, whereas it was weak or negative in normal lung epithelial cells. The expression of NEDD4-1 in ADC (78.5%, 106/135) was significantly much higher than that in adjacent normal lung tissue (13.3%, 29/135, P < 0.01), and it was associated with lymph node metastasis, tumor-node-metastasis (TNM) stage, and chemotherapy resistance. PTEN expression was downregulated in lung ADC (60.7% vs. 100.0% in noncancerous specimens, P = 0.007), and was negatively correlated with lymph node metastasis, histological variants, clinical stage, chemoresistance. In addition, expression of p-Akt in ADC tissues (71.1% 96/135) was much higher than that in adjacent lung epithelial cells (6.7%, 9/135, P < 0.01). Kaplan-Meier and multivariate analysis demonstrated that expressions of NEDD4-1 and PTEN were both independent risk factors for survival in patients with lung ADC. NEDD4-1 knockdown in vivo decreased proliferation, migration, and invasion and improved chemosensitivity to cisplatin and paclitaxel in A549 cells. NEDD4-1 knockdown also significantly enhanced PTEN expression and inhibited p-Akt activity and downstream target proteins. CONCLUSIONS: NEDD4-1 upregulation may contribute to the progression of lung ADC. NEDD4-1 may regulate the proliferation, invasion, migration, and chemoresistance of lung ADC cells through the PI3K/Akt pathway, suggesting that it may be regarded as a therapeutic target for the treatment of lung ADC.