Loss-of-function mutations in the histone methyltransferase EZH2 promote chemotherapy resistance in AML.

Chemotherapy resistance is the main impediment in the treatment of acute myeloid leukaemia (AML). Despite rapid advances, the various mechanisms inducing resistance development remain to be defined in detail. Here we report that loss-of-function mutations (LOF) in the histone methyltransferase EZH2 have the potential to confer resistance against the chemotherapeutic agent cytarabine. We identify seven distinct EZH2 mutations leading to loss of H3K27 trimethylation via multiple mechanisms. Analysis of matched diagnosis and relapse samples reveal a heterogenous regulation of EZH2 and a loss of EZH2 in 50% of patients. We confirm that loss of EZH2 induces resistance against cytarabine in the cell lines HEK293T and K562 as well as in a patient-derived xenograft model. Proteomics and transcriptomics analysis reveal that resistance is conferred by upregulation of multiple direct and indirect EZH2 target genes that are involved in apoptosis evasion, augmentation of proliferation and alteration of transmembrane transporter function. Our data indicate that loss of EZH2 results in upregulation of its target genes, providing the cell with a selective growth advantage, which mediates chemotherapy resistance.

Novel PKD1 and PKD2 mutations in autosomal dominant polycystic kidney disease (ADPKD).

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic renal disorder with an incidence of 1:1000. Mutations in two genes (PKD1 and PKD2) have been identified as causative. Eighty-five percent of patients with ADPKD carry their mutation in the PKD1 gene. So far, > 500 mutations for PKD1 and > 120 mutations for PKD2, respectively, are known. METHODS: In this study, we performed mutation analysis of PKD1 and PKD2 by exon sequencing in patients during routine molecular diagnostics for ADPKD. RESULTS: In total, 60 mutations were identified in 93 patients representing a mutation detection efficiency of 64.5%. Fifty-two mutations were identified in PKD1 (86.7%) and 8 in PKD2 (13.3%). These include 41 novel mutations detected in PKD1 and 5 novel mutations in PKD2. Accordingly, our data expand the spectrum of known PKD mutations by 8% for PKD1 (41/513) and 4.2% for PKD2 (5/120). These results are in agreement with the detection ranges of 42%, 63% and 64% for definitive disease-causing mutations, and 78%, 86% and 89% for all identified variants reported in several comprehensive mutation screening reports. CONCLUSIONS: The increased number of known mutations will facilitate future studies into genotype-phenotype correlations.