Role And Molecular Mechanism Of MUC1-C In Biological Behavior Of Esophageal Squamous Cell Carcinoma

Background:Esophageal cancer is one of the tumors with high morbidity and mortality worldwide.It is divided into adenocarcinoma and squamous cell carcinoma.In developing countries,squamous cell carcinoma is the predominant type of cancer,and adenocarcinoma is more common in developed countries.Both types of esophageal cancer have the characteristics of malignant growth,early invasion and metastasis,which are the main cause of poor prognosis.The treatment of esophageal cancer is combined surgery with radiotherapy and chemotherapy,but the long-term survival rate is not satisfactory.In recent years,molecular targeted therapy has become a new direction and hot spot in the diagnosis and treatment of cancer.Some curative effects have been achieved in the treatment of esophageal cancer with EGFR mutation.The search for more effective target genes and elucidation of mechanism are attracting much attention.MUC1 is a transmembrane mucin that is expressed at the apical surfaces of normal epithelia,and overexpressed in diverse human carcinomas.MUC1 consists of an extracellular MUC1 N-terminal subunit(MUC1-N)and transmembrane MUC1 C-terminal transmembrane subunit(MUC1-C).These two subunits form a stable heterodimeric complex at the cell membrane.The overexpression of MUC1 was positively correlated with mucus secretion,proliferation,invasion,metastasis and poor prognosis of tumors.Our previous studies have confirmed that MUC1 is also overexpressed in esophageal squamous cell carcinoma.In recent years,researchers have focused on MUC1-C,that it plays a major role in the heterodimers.MUC1-C is phosphorylated by diverse kinases and interacts with various effectors that have been linked to transformation.Incorporation of MUC1-C into the outer mito chondrial membrane also inhibits stress-induced loss of the mitochondrial transmembrane potential.Overexpression of MUC1 in human cancers blocks the induction of apoptosis and necrosis in response to DNA damaging agents,reactive oxygen species and hypoxia.The MUC1-C cytoplasmic domain contains a CQC motif that is necessary for MUC1-C homodimerization and function.Therefore,GO-203,cellular penetrating peptides,have been developed to target the MUC1-C CQC motif,blocking the activation of various MUC1-C mediated pathwaysProtein translation is a tightly regulated process that is regulated by translation initiation.This initiation step is controlled by the initiation factors(eIF4F)complex at the ribosomal recruitment.The elF4F complex is formed by the binding of elF4E to the 5' cap of mRNAs and recruitment of eIF4G and eIF4A.The PI3K-AKT signaling pathway is a major regulator of protein translation which is upstream to the mammalian target of rapamycin complex 1(mTORC1).mTORC1 activates 40s ribosomal protein S6 kinases(S6Ks)which contribute to cap-dependent translation that,in turn,enhance the eIF4A RNA helicase activity.S6Kinduces degradation of the tumor suppressor programmed cell death protein 4(PDCD4),which is an eIF4A inhibitor[30].eIF4A initiates translation by unwinding highly structured 5'untranslated regions(UTRs)in mRNAs.In this way,tumor cells can regulate translation in response to growth signals through mTORC1-induced activation of the eIF4A RNA helicase function.Although a number of basic studies have partly revealed the mechanism of MUC1-C in tumor,there is no relevant report on its role in the growth and metastasis of esophageal squamous cell carcinoma(ESCC).Part ?Expression of MUC1-C in ESCC and its correlation with biology Objective:To explore the expression of MUC1-C in ESCC tissue sample,declare their relationship with biology,and investigate the correlation of MUC1-C and MYC in ESCC.Methods:The expression of MUC1-C and MYC in the ESCC samples and cell lines was detected by immunohistochemistry,immunofluorescence and western blot.MYC mRNA level was determined by using qRT-PCR.In addition,Cell Counting Kit-8,clonogenic assay,transwell assay were utilized to determine the role of MUC1-C in proliferation,invasion and migration of ESCC cells.Results:The level of MUC1-C in nuclear and MYC in whole cells in the ESCC tissue is significantly higher than that in the noncancerous tissue.Treatment of MUC1-C-overexpressing ESCC cells with GO-201 was associated with downregulation of MYC expression and induction of apoptosis.Besides,all assays have shown that inhibiting MUC1-C targeting to the nucleus by the GO-201 significantly decreased the abilities of proliferation,invasion and migration in ESCC cells.Conclusion:Our findings suggest that MUC1-C targeting to the nucleus plays an important role in suppressing the malignant growth of ESCC.Part ?Effect and molecular mechanism of MUC1-C in metabolism of ESCCObjective:To explore the molecular mechanism of MUC1-C in ESCC.Methods:The expression of MUC1-C and TIGAR in ESCC samples and cell lines was detected by immunohistochemistry and western blot.TIGAR mRNA level was determined by qRT-PCR.Western blot was used to examine phosphorylation of AKT pathway protein,and to detect changes of TIGAR after using pathway inhibitor.Changes of ROS and apoptosis were detected by flow cytometry,GSH and mitochondrial membrane potential were also examed.Results:TIGAR was overexpressed and correlative with MUC1-C positively in ESCC tissue.Targeting MUC1-C inhibits AKT-mTORC-S6K1 signaling and blocks TIGAR translation.We found that the inhibitory effect of GO-203 on TIGAR was mediated by inhibition of AKT-mTOR-S6K1 pathway.The results also demonstrated that the suppressive effect of GO-203 on TIGAR is related to the decrease of glutathione level,the increase of reactive oxygen species and the loss of mitochondrial transmembrane membrane potential.In xenograft tissues,GO-203 inhibited growth of ESCC cells and lead to the low expression of MUC1-C and TIGAR.Conclusion:MUC1-C regulates ESCC metabolism by AKT-mTOR-S6K1 pathway and induces TIGAR translation,wich indicated that MUC1-C is a potential target for the treatment of ESCC.