The Transcription Factor ELF4 Contributes To Mesenchymal Transformation In Glioblastoma

Background and Objective:Gliomas are the most common clinical malignancies of the central nervous system,accounting for nearly 80%of all malignant cases.Among them,glioblastoma multiforme(GBM)is the most common and malignant subtype of glioma in adults.Molecular targeted therapies for GBM have largely failed in clinical trials over the past decade,and the high degree of tumor heterogeneity may be the main reason.Understanding the cellular diversity and plasticity of GBM and finding the key regulatory genes that mediate this heterogeneity is critical.The mesenchymal subtype is a molecular subtype of GBM with the poorest prognosis,characterized by high infiltration of tumor-associated macrophages(TAMs).In fact,transcription factors are master regulators of specific cancer hallmarks and are closely related to the activation of mesenchymal signature.In this study,we aimed to investigate in depth the regulatory role of the transcription factor ELF4 in the GBM microenvironment and to elucidate the underlying mechanisms.Methods:The expression of ELF4 in GBM and its correlation with patient prognosis,molecular subtypes,immune infiltration,and biological processes were analyzed by bioinformatics and validated in clinical samples by immunohistochemistry and immunofluorescence.Stable ELF4-overexpressed or silenced GBM cells were established and co-cultured with macrophages in vitro or used to establish an intracranial transplantation model in nude mice.The infiltration and phenotypic changes of macrophages were detected by transwell assays,flow cytometry,and immunohistochemistry analyses.The target genes of ELF4 were identified and validated by RNA sequencing,qRT-PCR,western blotting,and dual luciferase reporter assays.On the other hand,we explored the effects of ELF4on mesenchymal transformation of GBM cells.Finally,an intracranial transplantation model of C57BL/6 mice was constructed,and the therapeutic value of targeting ELF4 for GBM was explored by detecting tumor growth and changes of immune infiltration in the tumor microenvironment through intracranial luminescence,flow cytometry and immunohistochemistry.Results:1.ELF4 is significantly elevated in GBM and is closely associated with poor patient prognosis and mesenchymal subtype,immunosuppression in GBM;2.ELF4 in GBM cells promoted macrophage infiltration and immunosuppressive phenotypes in the tumor microenvironment through transcriptional regulation of chemokine CCL2 expression;3.ELF4 in GBM cells activated the mesenchymal signature;4.ELF4 inhibited T-cell infiltration in the GBM tumor microenvironment.Conclusion:The transcription factor ELF4 is a master regulator of mesenchymal GBM.On the one hand,ELF4 exerts its chemotactic effect on TAMs through regulating the expression of CCL2 and induces its immunosuppressive phenotype.On the other hand,ELF4 activates the mesenchymal gene expression profile of GBM cells,enhancing their invasiveness and promoting angiogenesis.The two aspects synergistically promote GBM progression and immunosuppression.