Abstract
The histone variant H2AZ is overexpressed in diverse cancer types where it facilitates the accessibility of transcriptional regulators to the promoters of cell cycle genes. However, the molecular basis for its dysregulation in cancer remains unknown. Here, we report that glioblastomas (GBM) and glioma stem cells (GSCs) preferentially overexpress H2AZ for their proliferation, stemness and tumorigenicity. Chromatin accessibility analysis of H2AZ2 depleted GSC revealed that E2F1 occupies the enhancer region within H2AZ2 gene promoter, thereby activating H2AZ2 transcription. Exploration of other H2AZ2 transcriptional activators using a customized “anti-H2AZ2” query signature for connectivity map analysis identified STAT3. Co-targeting E2F and STAT3 synergistically reduced the levels of H2AZ, histone 3 lysine 27 acetylation (H3K27ac) and cell cycle gene transcription, indicating that E2F1 and STAT3 synergize to activate H2AZ gene transcription in GSCs. Remarkably, an E2F/STAT3 inhibitor combination durably suppresses GSC tumorigenicity in an orthotopic GBM xenograft model. In glioma patients, high STAT3 signaling is associated with high E2F1 and H2AZ2 expression. Thus, GBM has uniquely opted the use of E2F1- and STAT3-containing “enhanceosomes” that integrate multiple signaling pathways to achieve H2AZ gene activation, supporting a translational path for the E2F/STAT3 inhibitor combination to be applied in GBM treatment.
Highlights
Despite our improved molecular understanding of glioblastomas (GBM), maximal surgical resection followed by radiotherapy and adjuvant Temozolomide treatment remains the standard-of-care for this disease
On the basis of our ChIPSeq, ATAC-Seq and RNA-Seq analyses, we propose the following model to explain how the H2AZ2 protein can regulate the transcription of H2AZ2 and other glioma stem cells (GSCs)-critical genes
When the H2AZ2 protein is expressed, its deposition at enhancer region within gene promoters confers an “open” chromatin conformation that allows the access of E2F1 and STAT3 to the promoters of H2AZ2 and other E2F and STAT3 target genes (Supplementary Fig. S6A)
Summary
Despite our improved molecular understanding of glioblastomas (GBM), maximal surgical resection followed by radiotherapy and adjuvant Temozolomide treatment remains the standard-of-care for this disease. STAT3 that is downstream of RTK/JAK signaling, can direct H2AZ a myriad of in vitro and in vivo assays, including the tumorsphere transcription in GSC is unclear Such molecular insights are assay (a readout for GSC proliferation); extreme limiting dilution important as they may offer new therapeutic opportunities assay (a readout for tumor initiating cell frequency); soft agar colony for GBM. Our transcriptional analyses reduction in the number and size of tumorspheres of multiple GSC of H2AZ led to the rational combination of E2F and STAT3 lines (Supplementary Fig. S2A, B and Fig. 2A, B), indicating reduced inhibitors as a potential anti-GSC therapy, which synergistically GSC proliferation (NB: the pan-H2AZ antibody detects both H2AZ2 reduced the levels of H2AZ, chromatin accessibility and cell cycle and H2AZ1). Extending these in vitro findings to xenotransplantation experiments, we showed that H2AZ2 depleted
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