SMARCC2 Mediates The Regulation Of DKK1 By The Transcription Factor EGR1 Through Chromatin Remodeling To Reduce The Proliferative Capacity Of Lioblastoma

Background:Grade Ⅳ glioblastoma(GBM)is the most common primary brain cancer in adults.With current treatment regimens,less than 10%of patients achieve 5-year survival.Surgery supplemented with postoperative radiotherapy,chemotherapy,simultaneous adjuvant temozolomide(TMZ),tumor treatment fields(TTFs)or other treatments remain the main treatment modality for glioma.However,median survival times are short regardless of the treatment strategy,mainly due to tumor recurrence and resistance to therapy.Key factors for drug resistance include the heterogeneity of these tumors,genomic deletion of tumor suppressor genes,diffuse and permeable growth of the tumor,and the presence of the blood-brain barrier.The deletion of tumor suppressor genes plays an important role.The switch/sucrose-nonfermentable(SWI/SNF)complex is a member of the chromatin remodeling protein family.To date,29 components have been identified that are involved in the assembly of three different SWI/SNF complexes,including the classical BRG1/brm-associated factor(CBAF),polybromide-associated BAF(PBAF),and the recently reported atypical BAF(ncBAF)complex.SWI/SNF,as a typical chromatin remodeling complex,has nucleosome sliding activity and unique ejection activity,generating nucleosome deletion regions(ndr),which are important for transcriptional regulation.Thus,SWI/SNF play an important role in essential cellular processes such as gene expression,DNA repair and replication,and regulation of higher order chromatin organization.Mutations and expression deletions of SWI/SNF core proteins are found in more than 20%of different tumors,such as esophageal,lung,ovarian clear cell and endometrioid cancers,making these complexes the most common altered human cancer targets.However,little is known about these complexes in gliomas,and their potential tumor suppression mechanisms are not fully understood.In most cases,they are loss-of-function(LOF)mutations that result in the deletion of mutant subunits at the protein level.However,determining the mechanism by which SWI/SNF mutations promote cancer remains a challenge.Methods:1.To analyze the expression of SMARCC2 and its downstream target gene DKK1 in glioblastoma by bioinformatics,and the relationship between its expression and prognosis.2.Exploring the effect of core basic subunits on the SWI/SNF complex by protein immunoblotting and QRT-PCR;basic cell function experiments to validate the role of SMARCC2 and its downstream target gene DKK1 in glioblastoma cell lines.3.Exploring how SMARCC2 affects DKK1 gene expression by ATAC-seq and RNA-seq high-throughput sequencing approaches.4.Using a protein structural domain molecular docking model to simulate the docking of different structural domains of SMARCC2 protein to the genome,and further molecular experiments to verify the different functions exercised by its different structural domains in glioblastoma cell lines.5.In situ tumorigenesis assay in nude mice to further validate the role of SMARCC2 in glioblastoma in vivo.Results:In the present study,we found that SMARCC2 has a unique function in inhibiting glioblastoma progression by targeting the DKK1 signaling axis.SMARCC2 is lowly expressed in malignant gliomas(GBM)at lower levels of glioma.Knockdown of SMARCC2 promoted glioblastoma cell proliferation,while overexpression of SMARCC2 did the opposite.Mechanistically,SMARCC2 negatively regulates transcription by dynamically regulating chromatin structure and shutting down the promoter region of the target gene DKK1,which can be bound by the transcription factor EGR1.downregulation of DKK1 significantly reduces proliferation of glioblastoma cell lines by inhibiting the PI3K-AKT pathway.We also investigated the function of the S WIRM structural domain and SANT structural domain of SMARCC2 and found that the SWIRM structural domain plays a more important role in the intact chromatin remodeling function of SMARCC2.Furthermore,in vivo studies confirmed that overexpression of SMARCC2 significantly inhibited the in situ size of intracranial gliomas in nude mice.Conclusion:This study demonstrates that SMARCC2 acts as a tumor suppressor to inhibit glioblastoma proliferation by targeting the transcription of oncogene DKK1 through chromatin remodeling,suggesting SMARCC2 as a potentially attractive therapeutic target for glioblastoma.