ACAA1 Inhibits The Metastasis Of Nasophayrngeal Carcinoma Via PTEN/Akt/EMT Pathway

BackgroundNasopharyngeal carcinoma (NPC) is a primary malignant tumor arising from the epithelium of nasopharynx, with a high incidence in southern China and Southeast Asia. At present, it is widely accepted that the pathogenesis of NPC is a multistep and complicated procedure, mainly caused by EBV infection,genetic susceptibility and environmental carcinogens. According to the world health organization (WHO), the histopathological classification of NPC is categorized into three types: nonkeratinizing carcinoma, keratinizing squamous cell carcinoma and basaloid squamous cell carcinoma. One of the characteristics of NPC is the early lymph node metastasis. For NPC patients without distant metastasis, radiotherapy is the main treatment. However, distant metastasis is the main reason for failure of NPC treatment at present. Therefore, to explore the mechanism of NPC metastasis and to look for a reliable target for inhibiting tumor metastasis is one of the hot spots in the transformation study of NPC. In previous study, we found an accumulation of lipid droplets (LDs) in NPC,suggesting that the fatty acid metabolism in NPC is reprogrammed and participate in the tumorigenesis and progression of NPC. However, the relationship between changes in fatty acid metabolism and cancer has not been clarified. Very limited literatures on the alteration of fatty acid metabolism and associated genes in NPC were found.ObjectiveTo screen out the abnormal expression fatty acid metabolism related genes in NPC. To further investigate their effect on the malignant biological behavior of NPC and the possible molecular mechanisms.Methods1. Screening out the differentially expressed genes related to fatty acid metabolism in NPC by analyzing the expression profiles of NPC from GEO database of NCBI.2. Analyzing the expression of ACAA1 gene in 10 types of human tumors based on the TCGA database.3. Verifying the transcription and expression of ACAA1 in nasopharyngeal carcinoma was verified by real-time RT-PCR, Western blot and immunohistochemistry assays, respectively.4. Establishing ACAA1 stably overexpressed NPC cells, and investigating the biological function of ACAA1 gene in NPC cells by performing proliferation assay, colony formation assay, wound healing and transwell assays.5. Detecting the expression of PTEN?Akt/pAkt and epithelial mesenchymal transition (EMT) related factors Snail?MMP9?MMP2 and E-cadherin by Western blot assay. Identifying whether ACAA1 gene affected nasopharyngeal carcinoma cell metastasis via the PTEN/Akt signal pathway with PTEN inhibitor, phen, acting on the NPC cells of overexpressed ACAA1.Results1. The transcription of ACAA1, involved in fatty acid metabolism, was downregulated in NPC and other 10 kinds of tumorsBy bioinformatic analysis, we found that the transcription of ACAA1 was downregulated in NPC and other 10 kinds of cancer, including head and neck squamous cell cancers, lung cancers, liver cancer and so on. We also detected the transcription and expression of ACAA1 in NPC and normal control samples by real time RT-PCR and immunohistochemistry staining assays. Our results further validate the findings from bioinformatic analysis,that ACAA1 was aberrantly downregulated in NPC.2. ACAA1 inhibits the malignant behavior of NPC cellsBy establishing the NPC cell line overexpressed ACAA1, we found that ectopic expression of ACAA1 inhibits the proliferation, colony formation,migratory and invasive capacity of NPC cells.3. ACAA1 inhibits the EMT of NPC cellsWe found the expression of Snail, MMP9 and MMP2 were downregulated in ACAA1 overexpressed NPC cells, while E-cadherin was upregulated, which indicating the role of ACAA1 in reversing EMT in NPC.4. ACAA1 suppresses the metastasis of NPC cells through PTEN/Akt/EMT pathwayWe found that overexpression of ACAA1 in NPC cells increases the expression of PTEN, and decreases the phosphorylation of Akt. In addition,PTEN inhibitor phen significantly promotes the phosphorylation of Akt and the motility of NPC cells with ACAA1 overexpressed. These results suggest that ACAA1 suppresses the motility of NPC cells via PTEN/Akt/EMT pathway.Conclusion1. ACAA1 was downregulated in NPC.2. ACAA1 inhibits the malignant phenotype of NPC cells.3. ACAA1 suppresses the metastasis of NPC cells via PTEN/Akt/EMT pathway.Overall, ACAA1 may be a candidate tumor suppressor gene in NPC.