Expression And Function Of APPL1 In Gastric Cancer

BackgroundGastric cancer is the third most common malignant tumors and the third cause of cancer-related death in China. The five-year survival rate of metastatic gastric cancer patients is only 20-30%. APPL1 is expressed in a variety of tissues and cells and is an important adapter protein with multiple biological functions. APPL1 consists of multiple functional domains including BAR domain, PH domain and PTB domain. APPL1 can combine with a variety of cell membrane receptors, signal transduction proteins and nuclear factors by those domains; therefore, it can regulate multiple cellular biological activities and processes and is closely associated with a variety of diseases.ObjectivesThe purposes of the research are to clarify the correlation between APPL1 expression and clinicopathologic characteristics and prognosis of gastric cancer, to reveal the effects and mechanisms of APPL1 on gastric cancer cell proliferation, to clarify the effects of APPL1 on miRNA expression profile of gastric cancer cells.MethodsImmunohistochemistry and reverse transcription PCR were used to detect the protein and mRNA expression of APPL1 in cancerous and non-cancerous gastric tissues. The difference of APPL1 expression in cancerous and non-cancerous gastric tissues and the correlation between APPL1 expression and clinicopathologic characteristics and prognosis of gastric cancer were analyzed by statistical methods.Lentiviral vectors overexpressing or interfering with APPL1 were constructed and gastric cancer cells were infected and stably selected. The effects and molecular mechanisms of APPL1 overexpression or knockdown on gastric cancer cell proliferation, cell cycle and apoptosis were analyzed using MTT assay, BrdU incorporation assay, flow cytometry and western blot. The effect of APPL1 interference on the miRNA expression profile of gastric cancer cells was analyzed by miRNA microarray. Differential expression of miRNA molecules were identified by quantitative real-time PCR. The effects of differentially expressed miRNA on gastric cancer cell proliferation were also detected.ResultsCompared with non-cancerous gastric tissues, the expression levels of APPL1 protein and mRNA were significantly increased in gastric cancer tissues. The increased APPL1 expression was closely related to the depth of infiltration, TNM stage and lymph node metastasis, but was not related to histopathological type. It was also found that increased expression of APPL1 was a risk factor for poor prognosis in gastric cancer patients. Overexpression of APPL1 could lead to a decrease in the proportion of G1 phase and an increase in the proportion of S phase in SGC-7901 gastric cancer cells, while APPL1 interference could lead to an increase in the proportion of G1 phase and a decrease in the proportion of S phase. The underlying molecular mechanisms were that overexpressed APPL1 induced Cyclin D1 expression and inhibited p16 and p27 expression, while APPL1 interference had opposite effects. APPL1 could affect the miRNA expression profile of gastric cancer cells and a total of eight miRNA molecules were screened and identified. miR-139 was the most highly expressed and was closely associated with the effects and mechanisms of APPL1 on gastric cancer cell proliferation.ConclusionsAPPL1 expression is related to infiltration depth, TNM stage and lymph node metastasis and is a risk factor for poor prognosis in gastric cancer patients. APPL1 can affect the proliferation of gastric cancer cells by regulating the expression of cell cycle proteins. APPL1 can also affect the miRNA expression profile of gastric cancer cells and its effects on gastric cancer cell proliferation are related to miR-139.