Epigenetically elevated RAD51AP1 regulates the RAD51-UAF1 complex contributing to temozolomide resistance in EGFRvIII glioblastoma.

Epidermal growth factor receptor variant III ( EGFRvIII ) mutation is the most prevalent genetic change in glioblastoma. Abnormal DNA damage repair caused by EGFRvIII, which leads to temozolomide (TMZ) resistance, is a major cause of reduced postoperative survival in glioblastoma patients. This study aims to uncover the molecular mechanism of TMZ resistance in EGFRvIII -mutant glioblastoma. We constructed a Clustered regularly interspaced shortpalindromic repeats (CRISPR)/CRISPR-associated (Cas) system 9 library to identify synthetic lethal genes for EGFRvIII -bearing cells. Abnormal epigenetic regulation of the RAD51-associated protein 1 ( RAD51AP1 ) promoter was assessed via chromatin immunoprecipitation sequencing (ChIP-seq) and chromatin immunoprecipitation polymerase chain reaction (ChIP-PCR) analyses. In vitro and in vivo experiments were carried out to investigate the role of the RAD51AP1 gene in TMZ resistance in EGFRvIII -bearing glioblastoma. The CRISPR/Cas9 library identified RAD51AP1 , a synthetic lethal gene for EGFRvIII -bearing cells exposed to TMZ. ChIP-seq and ChIP-PCR analyses revealed that acetylated histone H3 lysine 27 (H3K27ac) and SRY-box transcription factor 9 ( SOX9 ) together induced RAD51AP1 transcription in EGFRvIII cells. High expression levels of RAD51AP1 , promoted formation of the RAD51-UAF1 complex to activate homologous recombination and inhibit TMZ-induced DNA damage. The results of this study suggest that aberrant RAD51AP1 expression is a crucial mechanism by which EGFRvIII -mutant glioblastoma resists TMZ chemotherapy, laying the groundwork for future personalized medicine.