Aberrant downstream mechanisms following depletion of KMT2C and KMT2D in Pancreatic Ductal Adenocarcinoma

Abstract

Genomic sequencing of pancreatic ductal adenocarcinoma (PDAC) tumours has highlighted the existence of wide genetic diversity alongside frequent mutations in KRAS, TP53 and SMAD4. Within this heterogeneity many components of the epigenetic machinery are mutated, including the histone H3 lysine 4 methyltransferases KMT2C and KMT2D, which are frequently subject to mutation and can identify patients with a more favorable prognosis. In this thesis low expression of KMT2C and KMT2D were shown to also define better outcome groups, with median survivals of 15.9 vs 9.2 months (p = 0.029), and 19.9 vs 11.8 months (p = 0.001) respectively. Experiments across eight human pancreatic cell lines following their depletion suggest that this improved outcome may be due to attenuated cell proliferation, with decreased progression of cells from G0/G1 observed upon KMT2D loss. Whole transcriptome analysis of PDAC cell lines following KMT2C or KMT2D knockdown identified 31 and 124 differentially expressed genes respectively, with 19 common to both. Gene set enrichment analysis revealed a significant downregulation of genes relating to cell-cycle pathways, confirmed by interrogation of the International Cancer Genome Consortium and The Cancer Genome Atlas PDAC data series. Furthermore, these experiments highlighted a potential role for NCAPD3, a subunit of the condensin II complex, as a PDAC outcome predictor across four patient gene expression series. Alongside this, Kmt2d depletion in cells derived from murine models of pancreatic cancer led to an increase in their response to the antimetabolites 5-fluorouracil and gemcitabine. Taken together, the studies herein suggest that lower levels of this methyltransferase may mediate the sensitivity of PDAC patients to particular treatments. Altogether, these data suggest a potential therapeutic benefit in targeting these methyltransferases within PDAC, especially in those patients that demonstrate higher KTM2C/D expression.