The Mechanism Of CBX3 In The Proliferation Of Esophageal Squamous Cell Carcinoma

Background and purpose:Esophageal cancer ranks seventh in incidence and sixth in mortality worldwide.In 2018,based on global cancer database report,an estimated of 572,034 new cases and 508,585 deaths were reported due to esophageal cancer.Esophageal cancer is the fourth leading cause of cancer-related death in China.There are two main histological types of esophageal cancer — esophageal squamous cell carcinoma(ESCC)and esophageal adenocarcinoma.ESCC is the major form of esophageal cancer among Chinese patients,which accounts for ～90% of the total esophageal cancer cases.Despite significant advances in the diagnosis and treatment of esophageal cancer,the results remain unsatisfactory.Therefore,understanding the potential mechanism of esophageal cancer with emphasis of the identification of biomarkers related to esophageal cancer is needed.The protein encoded by Chromobox homolog 3(CBX3),a heterochromatin protein 1γ(HP1γ),which belongs to the HP1 family,binds DNA and is a component of heterochromatin.CBX3 is involved in various DNA related processes,such as gene transcription,DNA damage response and epigenetic regulation.It was reported that CBX3 was overexpressed in some cancer types and could be a potential biomarker.But,there is no report on the expression pattern and pathogenic role of CBX3 in the ESCC.This study aims to analyze the expression levels of CBX3 in ESCC tissues and explore the biological function and molecular mechanism of CBX3 in ESCC to pave a new way for the diagnosis and treatment of ESCC.Methods:In this study,we analyzed the expression levels of CBX3 in ESCC and normal esophageal tissues by using Gene Expression Omnibus(GEO)and The Cancer Genome Atlas(TCGA)databases.The results were further verified by real-time quantitative PCR of ESCC clinical specimens.In order to explore the biological function of CBX3 in ESCC,we chose ESCC cell lines(ECA109 and TE1)as research objects and knocked down the expression levels of CBX3 by using small interfering RNA(si RNA)in ECA109 and TE1 cells.The effect of CBX3 on cell proliferation was determined by CCK-8 and clony formation assays.Flow cytometry was used to detect the effect of CBX3 on cell cycle and cell apoptosis.In addition,we established a tumor xenografts model in nude mice to verify the effect of CBX3 on tumor growth in vivo.Western blot was used to analyze the expression levels of CDK1,Cyclin B1 and CDC20,which were related to cell cycle,so as to explore the molecular mechanism of CBX3 in ESCC.Results:The results of GEO and TCGA databases showed that CBX3 was up-regulated in ESCC tissues.To verify these findings,we performed real-time quantitative PCR to analyze CBX3 expression levels in ESCC clinical specimens and matched adjacent non-tumor tissues.The result showed that CBX3 was overexpressed in ESCC tissues.The in vitro experiments showed that ESCC cell proliferation was inhibited with cell cycle arrest at G2/M phase after CBX3 depletion,while there was no effect on cell apoptosis.The in vivo experiment showed the same result that the tumor growth was suppressed upon CBX3 knockdown.We further explored the molecular mechanism of CBX3 in ESCC cell proliferation and cell cycle,and found that the regulation of cell cycle transition by CBX3 was mediated by CDK1/Cyclin B1 complex.Conclusions:In short,our findings demonstrated that CBX3 was up-regulated in ESCC tissues and its high expression could promote the cell cycle transition and cell proliferation.The molecular mechanism of CBX3 was mediated by CDK1/Cyclin B1 complex.These findings suggest that CBX3 plays a tumor-promoting role in ESCC and it might pave the way for its application as a therapeutic target to control the progression of ESCC.