Loss of PBRM1 rescues VHL dependent replication stress to promote renal carcinogenesis

Abstract

Inactivation of the VHL (Von Hippel Lindau) tumour suppressor has long been recognised as necessary for the pathogenesis of clear cell renal cancer (ccRCC); however, the molecular mechanisms underlying transformation and the requirement for additional genetic hits remain unclear. Here, we show that loss of VHL alone results in DNA replication stress and damage accumulation, effects that constrain cellular growth and transformation. By contrast, concomitant loss of the chromatin remodelling factor PBRM1 (mutated in 40% of ccRCC) rescues VHL-induced replication stress, maintaining cellular fitness and allowing proliferation. In line with these data we demonstrate that combined deletion of Vhl and Pbrm1 in the mouse kidney is sufficient for the development of fully-penetrant, multifocal carcinomas, closely mimicking human ccRCC. Our results illustrate how VHL and PBRM1 co-operate to drive renal transformation and uncover replication stress as an underlying vulnerability of all VHL mutated renal cancers that could be therapeutically exploited.

PBRM1 regulates the stress response in epithelial cells

“…A role for PBRM1 in stress response is in agreement with recent findings that PBRM1 deletion alone is not sufficient for transformation but acts to facilitate oncogenesis in cooperation with VHL deletion (Espana-Agusti et al, 2017;Gu et al, 2017;Nargund et al, 2017). PBRM1 deletion allows for an amplification of oncogenic signaling (Gao et al, 2017;Nargund et al, 2017), as well as a bypass of checkpoints induced by replication stress after VHL deletion (Espana-Agusti et al, 2017). This could be in part due to PBRM1's role in regulating the hypoxia stress response in cooperation with HIF1a, which allows for the reduction of ROS and induction of apoptosis in response to hypoxia (Kim et al, 2006).…”

“…Transcriptional profiling of human ccRCC indicate that PBRM1 mutant tumors have a hypoxic transcriptional signature (Sato et al, 2013), which is in agreement with recent reports that PBRM1 mutation amplifies the hypoxia inducible factor (HIF) transcriptional program signature induced upon von Hippel-Lindau (VHL) deletion in cell culture (Gao et al, 2017) and in a mouse model of renal cancer (Nargund et al, 2017). Recent work with kidney specific (KSP and PAX8) Cre mouse models indicate that VHL knockout or PBRM1 knockout alone is not sufficient for cancer formation but that both are required for kidney tumor formation in mice (Espana-Agusti et al, 2017;Gu et al, 2017;Nargund et al, 2017).…”

“…We next observed a significant increase in ROS levels and H 2 O 2 levels in MEFs upon PBRM1 knockdown (Fig 6B, SI5B), which was most similar to the robust increase in ROS levels Genes upregulated with shPBRM1 low glucose H2O2 no treatment D observed in shPBRM1 NMuMG cells grown under high stress conditions. This particular sensitivity of MEFs to PBRM1 knockdown is most likely due to the unique susceptibility of MEFs to oxidative stress from high oxygen content in air (Espana-Agusti et al, 2017). To support this, we found that exogenous antioxidants such as Vitamin C ( Fig 6C) or N acetyl cysteine (NAC) (SI5C) were able to reverse the viability defect induced by PBRM1 knockdown in MEFs.…”

Widespread loss of the silencing epigenetic mark H3K9me3 in astrocytes and neurons along with hippocampal-dependent cognitive impairment in C9orf72 BAC transgenic mice

“…To evaluate the pattern of nuclear distribution and intensity of H3K9me3 mark in C9BAC and control astrocytes, we used immunostaining with a widely used commercial antibody against this modification [38][39][40]. Additionally, we tested the specificity of the H3K9me3 staining in N2A cells treated with chaetocin, a pharmacological inhibitor of H3K9 methyltransferase SUV39H1/2.…”

von Hippel-Lindau Disease: an Update

“…In a mouse model, a combination of Vhl −/− and Bap1 +− deficiency in nephron progenitor cells resulted in multiple renal cysts and tumours (similar to kidneys in VHL disease) whereas Vhl −/− mice did not develop cRCC [32]. Similarly, in cellular and mouse models, loss of PBRM1/Pbrm1 in addition to VHL/Vhl was oncogenic [33][34][35]. In a seminal study, Mitchell et al [36••] reported that the most frequent cause of chromosome 3p loss in cRCC is a chromothrypsis-associated rearrangement between 3p and 5q that resulted in loss of 3p and gain of 5q.…”