The Role Of Exo70 In Colon Cancer And Its Molecular Mechanism

Exo70,a key component of the exocyst complex,plays important roles in human cancer progression beyond exocytosis.However,the expression of Exo70 and its prognostic value for patients with colon cancer has not been well investigated to date.This study was the first to systematically explore the role of Exo70 in colon cancer,to evaluate its expression in colon cancer patients from multiple independent cohorts,and then to conduct an in-depth analysis of its clinical significance in colon cancer.Since then,we have performed a series of fimctional validation studies in colon cancer cell lines and xenograft animal models,and identified that Exo70 is an oncogene in colon cancer.Meta-analysis of individual gene Exo70 expression was performed using a public microarray dataset from the Oncomine database.Meta-analysis together revealed a significant up-regulation of Exo70 mRNA in colon cancer patients.In this study,we observed that the mRNA and protein levels of Exo70 were upregUlated in 11 of 13 colon cancer tissues,compared with their normal counterparts,which was validated by immunohistochemical analysis in a tissue microarray containing 89 pairs of colon cancer tissues and the matched adjacent normal tissues.Statistical analysis revealed that Exo70 expression is positively correlated wtth tumor size,invasion depth,TNM stage and distant metastasis.Kaplan-Meier survival analysis showed that colon cancer patients with higher Exo70 expression have a poorer clinical outcome than those with lower Exo70 expression.Multivariate Cox regression analysis revealed that Exo70,age and distant metastasis were there independent prognostic factors for overall survival rate of colon cancer patients.Through gain-and loss of Exo70 in colon cancer cells,we found that Exo70 promotes invasion and migration of HCT116 cells;knockdown of Exo70 inhibits proliferation,invasion and migration,and tumor formation in RXO cells.In vitro and in vivo studies further confirm the role of Exo70 in promoting tumor progression in colon cancer.We induced EMT with TGF-? in several colon cancer cells including HCT-116,SW620 and RKO and observed the mRNA changes of Exo70 isoform 1,2(M form in breast cancers),4 and 5(E form in breast cancers).The results showed that the mRNA levels of isoform 2 and 5 were not quite changed.However,the mRNA levels of Exo70 isoform 1 and 4 were significantly raised during EMT in these colon cancer cells.Nevertheless,none of these isoforms were down-regulated during EMT,suggesting an upregulation of total Exo70 in colon cancer cell,which is quite different from the situation in the breast cancerTaken together,our results demonstrate for the first time that Exo70 is up-regulated in colon cancer,and patients with high Exo70 expression are associated with higher tumor burden,exhibiting poorer clinicopathological features and shorter overall survival.High Exo70 expression can be an important and independent negative prognostic marker for colon cancer.In addition,we investigated the functional role of altered Exo70 expression and demonstrated its role as an oncogene in promoting migration of colon cancer.Our data emphasize that Exo70 is functioned as an oncogene and that high expression of Exo70 can be used as a potential treatment target in colon cancer.