Deep sequencing of human tumours has uncovered a previously unappreciated role for epigenetic regulators in tumorigenesis. H3K4 methyltransferase KMT2C/MLL3 is mutated in several solid malignancies, including more than 10% of breast tumours. To study the tumour suppressor role of KMT2C in breast cancer, we generated mouse models of Erbb2/Neu, Myc or PIK3CA-driven tumorigenesis, in which the Kmt2c locus is knocked out specifically in the luminal lineage of mouse mammary glands using the Cre recombinase. Kmt2c knock out mice develop tumours earlier, irrespective of the oncogene, assigning a bona fide tumour suppressor role for KMT2C in mammary tumorigenesis. Loss of Kmt2c induces extensive epigenetic and transcriptional changes, which lead to increased ERK1/2 activity, extracellular matrix re-organization, epithelial-to-mesenchymal transition and mitochondrial dysfunction, the latter associated with increased reactive oxygen species production. Loss of Kmt2c renders the Erbb2/Neu-driven tumours more responsive to lapatinib. Publicly available clinical datasets revealed an association of low Kmt2c gene expression and better long-term outcome. Collectively, our findings solidify the role of KMT2C as a tumour suppressor in breast cancer and identify dependencies that could be therapeutically amenable.

Temozolomide (TMZ) represents the cornerstone of therapy for glioblastoma (GBM). However, acquisition of resistance limits its therapeutic potential and therefore poses the need to identify new therapeutic combinations that could improve treatment outcomes. Despite the human kinome has proved to be an undisputable source of druggable targets, our knowledge remains confined to a limited fraction of it, with a multitude of under-investigated proteins yet to be characterised. Using a kinome-wide RNAi screen, we found that abrogation of pantothenate kinase 4 (PANK4) enhances the antiproliferative effects of TMZ in GBM in vitro. Further validation of our top-hit across various TMZ-resistant GBM cell models, patient-derived GBM cell lines and tissue samples, as well as in vivo studies, corroborated the potential translational significance of our findings. We showed that PANK4 expression is induced during TMZ treatment, and its expression is associated with a worse clinical outcome. Using a Tandem Mass Tag (TMT)-based quantitative proteomic approach, a comprehensive global protein dynamics analysis was undertaken to identify key response signatures upon PANK4 knockdown, in the presence or absence of TMZ. We revealed that silencing of PANK4 leads to a marked downregulation of a subset of proteins involved in cellular detoxification. More specifically, as cells undergo genotoxic stress during TMZ exposure, PANK4 depletion represents a synthetic vulnerability, focal point that can lead to critical cellular damage, accumulation of toxic metabolites, and subsequent cell death. Taken together, we unveil a previously unreported role for PANK4 in mediating therapeutic resistance to TMZ in GBM.