Study On The Expression Of MAP4 And The Mechanism Of Promoting Migration And Invasion In Lung Adenocarcinoma

Background and objective: Up to now,lung cancer is one of the most common malignant tumors in the world,and become the leading cause of cancer death.Lung adenocarcinoma is the most common type of lung cancer.Although with the development of a variety of treatment techniques,the overall survival rate is still low.It is essential to identify new molecular markers associated with lung adenocarcinoma and the therapeutic target.Microtubule is one of the important components of the cytoskeleton.Microtubule-associated protein 4(MAP4)plays an important role in microtubule assembly and stabilization.Recent studies have found that MAP4 is a tumor related gene that promotes the invasion and metastasis of bladder cancer and esophageal squamous cell carcinoma.However,there is no study to elucidate the function and molecular mechanism of MAP4 in lung adenocarcinoma.The purpose of this study was to investigate the level of expression of MAP4 in lung adenocarcinoma(LADC)samples and to evaluate its prognostic value and the influence on cancer progression in LADC patients.Materials and methods: The expression of MAP4 in 91 lung adenocarcinoma tissues and 86 adjacent lung tissues were measured by immunohistochemistry,and the correlation with clinicopathological factors were analyzed.The difference of overall survival rate between the high expression group of MAP4 and the low expression group was compared by Kaplan-Meier survival curve and Log-rank test.The effects of different clinicopathological parameters on the overall survival rate were also analysed.The risk ratio model(Cox regression)was used to analyze the adverse factors that affect the prognosis of the lung adenocarcinoma patients.In vitro,the effect of MAP4 expression on the malignant biological behavior of lung adenocarcinoma was analyzed.Lung adenocarcinoma cell line A549 and H1299 were selected and transiently transfected with MAP4-siRNA.RT-PCR method was used to determine the interference efficiency and western blot was used to verify the expression of MAP4 protein in transfected cells.The effects of MAP4 on the migration and invasion of lung adenocarcinoma cell lines were evaluated by wound healing assays and matrigel invasion assays.The cell proliferation ability was evaluated by the CCK-8 proliferation test.Flow cytometry was used to detect the apoptosis and cell cycle in the siMAP4 group and the negative control group.Results: 51 cases had high expression of MAP4 protein(56.04%)in 91 lung adenocarcinoma patients and 20 cases were highly expressed(23.26%)in 86 adjacent lung tissues.The positive expression rate of MAP4 in lung adenocarcinoma tissues was significantly higher than that in adjacent tissues after statistical analysis(P<0.0001).The expression of MAP4 in lung adenocarcinoma correlated with differentiation,pT stage and TNM stage(P=0.03,P<0.01,P<0.01),but not related to gender,age and pN stage(P=0.75,P=0.10,P=0.06).Kaplan-Meier survival curves showed that the overall survival rates of pN stage(pN1-3),II-III stage and the high expression of MAP4 group were significantly lower than pN0,stage I and low MAP4 expression group by Log-rank test(P<0.001,P<0.001,P=0.028).However,there was no significant difference in sex,age,differentiation and pT stage(P=0.207,P=0.818,P=0.927,P=0.272).Univariate cox regression analysis showed that pN stage,TNM stage and MAP4 were adverse prognostic factors in lung adenocarcinoma(P<0.001,P<0.001,P=0.028).Multivariate analysis showed that pN stage and MAP4 were independent prognostic factors for OS(P<0.001,P=0.042).The results of Western Blot showed that the expression of MAP4 protein in the A549 and H1299 cell lines was significantly lower than that of the negative control group(P<0.001,respectively).After transfection of MAP4-siRNA,A549 and H1299 cells significantly inhibited the migration ability of lung adenocarcinoma cells at each time point in wound healing assays(P<0.001,P<0.001).siMAP4 group significantly inhibited the invasive ability of lung adenocarcinoma cell lines in matrigel invasion assays.There was a significant difference between the two groups(P<0.001;P<0.001).CCK8 proliferation test showed that there was no significant difference in cell proliferation between si MAP4 group and negative control group on the first to fifth day.The results of flow cytometry showed that there was no significant difference between MAP4 expression and apoptosis and cell cycle in lung adenocarcinoma cells.Conclusion: Our research shows that MAP4 can promote the progression of lung adenocarcinoma by affecting the migration and invasion of lung adenocarcinoma cells.Meanwhile,MAP4 is an independent prognostic marker in lung adenocarcinoma and may become a potential therapeutic target for lung adenocarcinoma.