CBX7 Is A Glioma Prognostic Marker And Induces G1/S Arrest Via The Silencing Of CCNE1

Research background:Chromobox homolog 7(CBX7)cooperates with other polycomb group(PcG)proteins to maintain target genes in a silenced state.However,the precise role of CBX7 in tumor progression is still controversial.We found that the expression of CBX7 in four public databases was significantly lower in high grade glioma(HGG).The reduced expression of CBX7 correlated with poor outcome in HGG patients.Both KEGG and GO analyses indicated that genes that were negatively correlated to CBX7 were strongly associated with the cell cycle pathway.We observed that decreased CBX7 protein levels enhanced glioma cells proliferation,migration and invasion.Then,we verified that CBX7 overexpression arrested cells in the G0/G1 phase.Moreover,we demonstrated that the underlying mechanism involved in CBX7 induced repression of CCNE1 promoter requiring the recruitment of histone deacetylase 2(HADC2).Finally,in vivo bioluminescence imaging and survival times of nude mice revealed that CBX7 behaved as a tumor suppressor in gliomas.In summary,our results validate the assumption that CBX7 is a tumor suppressor of gliomas.Moreover,CBX7 is a potential and novel prognostic biomarker in glioma patients.We also clarified that CBX7 silences CCNE1 via the combination of CCNE1 promoter and the recruitment of HDAC2.Methods:1.Four public databases(TCGA,CGGA,REMBRANDT,and GSE16011)and twenty patients-derived glioma tissuses were used to test the relationship of CBX7 transcription level to clinical progression and to glioma histologic grades.We performed a Pearson correlation analysis to discover genes that were associated with CBX7 in CGGA,Rembrandt and GSE16011 datasets(R>0.4).To clarify the associations between these genes and specific GO functional categories,DAVID Web tool and KEGG pathway analysis were used.2.We constructed siRNAs targeting CBX7 and a lentivirus vector expressing CBX7.We then assessed the CBX7 protein levels in four GBM cell lines.To explore the biological function of CBX7 in glioma cells,EdU,CCK8,wound-healing and transwell assays were performed to study the influence of CBX7 on cell proliferation,migration and invasion.3.Flow cytometry analysis was used to test the influence of CBX7 to cell cycle.Chromatin Immunoprecipitation(ChIP)assays was conducted to test whether the CBX7 could bind to the CCNE1 promoter in glioma cells.Co-immunoprecipitation(coIP)assay was performed to test the interaction between CBX7 and HDAC2.4.An orthotopic mouse model using U87 cells was performed to further determine the role of CBX7 in gliomagenesis and intracranial tumor volume was measured weekly via in vivo optical imaging systemResults:1.Decreased CBX7 expression correlates with glioma grade and its overexpression confers a better prognosis in HGG patients.2.CBX7 associated genes are mainly enriched in cell division cycle pathways.3.Regulation of CBX7 expression influences the malignant behavior of GBM cells.4.CBX7 binds and silences CCNE1 promoter mediated by the recruitment of HDAC2 and leads to G1/S arrest.5.Overexpression of CBX7 in U87 cells impairs orthotopic tumor growth in vivo.Conclusions:1.CBX7 is a potential and novel prognostic biomarker in glioma patients.2.CBX7 is a tumor suppressor of gliomas ans silences CCNE1 via the combination of CCNE1 promoter and the recruitment of HDAC2.