The lysine methyltransferase KMT5a and p53 regulate the expression of the key autophagy adaptor p62/SQSTM1 in glioblastoma

KMT5a, a histone lysine methyltransferase responsible for histone H4 lysine 20 monomethylation (H4K20me1), plays a critical role in the pathogenesis of various human diseases, including cancer. In glioblastoma, KMT5a is frequently overexpressed, with elevated expression levels correlating with poor clinical outcomes, and its inhibition restrains cell growth. The KMT5a-induced H4K20 methylation regulates the expression of several oncogenes and tumor suppressor genes, but its transcriptional targets in glioblastoma remain poorly understood. Through RNA-sequencing, we found that the expression of the key autophagy adaptor p62/SQSTM1 was strongly repressed by KMT5a. To investigate the regulation of p62/SQSTM1 by KMT5a, both pharmacological inhibition and genetic silencing of KMT5a were performed in U251 glioblastoma cells. Chromatin immunoprecipitation (ChIP) assays were used to confirm KMT5a binding to the p62/SQSTM1 promoter and to examine histone modification states. The role of additional methyltransferases KMT5b and KMT5c in establishing higher-order methylation (H4K20me2/3) was also assessed. The dependency on p53 status was tested using various glioblastoma cell lines with differing p53 backgrounds (U251, SW1088, and U87MG), as well as through genetic manipulation of p53 expression. This dependency was also examined in primary glioblastoma cells and glioblastoma stem cells. Inhibition or knockdown of KMT5a led to a strong upregulation of p62/SQSTM1 transcription in U251 glioblastoma cells. ChIP assays confirmed direct binding of KMT5a to the p62/SQSTM1 promoter and deposition of the repressive H4K20me1 mark, which was reversed by the demethylase PHF8. Full repression required sequential methylation by KMT5b and KMT5c, indicating a multi-step repression mechanism. Importantly, p62/SQSTM1 induction was observed only in p53-deficient cells and was suppressed by reintroduction of wild-type p53. Conversely, dominant-negative p53 expression in p53-proficient cells restored p62/SQSTM1 induction. Starvation-induced expression of p62/SQSTM1 also required both H4K20 demethylation and p53 displacement from the promoter. KMT5a acts as a key epigenetic repressor of p62/SQSTM1 in glioblastoma through a mechanism dependent on histone methylation and p53 status. Given the emerging roles of both KMT5a and p62/SQSTM1 in glioblastoma progression, these findings also suggest that KMT5a inhibition could serve as a therapeutic strategy specifically in p53-proficient glioblastomas, where p62/SQSTM1 remains repressed. p53 status may therefore serve as a predictive biomarker for the efficacy of KMT5a-targeted therapies.