Impact of glioma-relevant IDH1 mutation on protein methylation profiles

Abstract

Glioma-relevant mutation in the isocitrate dehydrogenase 1 (IDH1) gene is associated with better patient prognosis. It alters cellular metabolism by causing the buildup of D-2HG, an oncometabolite. D-2HG affects both DNA and histone methylation by inhibiting demethylases. As such, this study hypothesises that D-2HG accumulation causes variation in protein lysine and arginine methylation patterns. Mutant IDH1 transformed astrocytes (referred to as mIDH1) and astrocytes transformed with an empty lentiviral plasmid (referred to as empty) were the cell models used. D-2HG assay shows a 300-fold increase of D-2HG in mIDH1 than in empty astrocytes. Western blot investigation demonstrated that levels of methylated lysine, monomethylated arginine, and dimethylated arginine were hardly altered, with just a few proteins exhibiting marginal alterations in intensity in mIDH1 astrocytes. Additionally, quantitative abundance proteomics showed that these mIDH1 cells had slight differences in the writer and eraser enzyme levels implicated in methylation indicators. Using AGI-5198, a time-chase inhibition of mIDH1 was performed, showing a gradual decline in D-2HG levels over a 48-hour period. Western blot displayed a decrease in protein methylation across mIDH1 samples testing for methylated lysine, monomethyl arginine and dimethyl arginine. Quantitative abundance proteomics of 24h AGI-5198 treated mIDH1 showed a subtle shift in protein abundance, especially for protein demethylases. While lowered D-2HG levels of mIDH1 only minimally alter protein methylation within 24 hours, a longer observation period can be used in the future to acquire a more comprehensive understanding.