Investigation of post-translational histone modifications in pheochromocytomas and paragangliomas

Pheochromocytomas and paragangliomas (PPGLs) are neuroendocrine tumours affecting a range of body sites and have the highest degree of heritability of any cancer type. SDHA, SDHB, SDHC, SDHD and SDHAF2 (collectively SDHx) code for subunits of succinate dehydrogenase, an enzyme complex in the tricarboxylic cycle that converts succinate to fumarate. Mutations in all SDHx genes play a role in PPGL pathogenesis and completely abolish succinate dehydrogenase enzymatic activity causing intracellular accumulation of oncometabolites which competitively inhibit 2-oxoglutarate-dependent oxygenases. This is a family of enzymes includes TET DNA demethylases and Jumonji C (JmjC) domain-containing histone demethylates. We and others have found that the inhibition of DNA demethylation leads to profound global DNA hypermethylation which influences expression of genes responsible for important clinical characteristics of these tumours but cannot explain the full spectrum of transcriptomic changes. We profiled histone PMTs to complement DNA methylation data and fully characterise the epigenome of these tumours.