UC San Diego

Cancer cells can reprogram their metabolism through altering metabolic enzymes to support increased lipid synthesis, cell proliferation, glycolysis, and tricarboxylic acid (TCA) cycling. Two important cytosolic enzymes that play a role in driving these processes include isocitrate dehydrogenase 1 (IDH1) and malate dehydrogenase 1 (MDH1), though details of their regulation and their role in cancer is still under exploration. IDH1 catalyzes the reversible conversion of isocitrate to α-ketoglutarate (αKG) via NADP+-dependent oxidation in the cytosol and in peroxisomes of cells. Mutations primarily at residue R132 have been identified in low grade gliomas and secondary glioblastomas, causing the neomorphic production of D-2-dehydroxyglutarate (D2HG) from αKG coupled to NADPH oxidation. Little is currently known about how human IDH1 activity is regulated, though recent proteomics data identified lysine acetylation sites in WT IDH1. We created lysine to glutamine (K-to-Q) acetylation mimics (Lys81, Lys224, Lys321) in WT and R132H IDH1, and found that acetylation inhibits WT IDH1 and variably regulates R132H IDH1 catalysis. A second metabolic dehydrogenase implicated in cancer is MDH1, an enzyme critical for replenishing cytosolic metabolites and for driving glycolysis through the production of NAD+ and malate from NADH and oxaloacetate (OAA), respectively. MDH1 has been reported to be amplified in squamous cell non-small cell lung cancer (NSCLC), which has high glycolytic activity. Elucidation of the role of MDH1 in altering cellular metabolism to drive tumorigenic progression has yet to be determined. Thus, we evaluated the metabolomic features in our MDH1 models and determined that loss of MDH1 led to decreased proliferation, TCA cycling, lactate secretion, and lipogenesis. We also found that amplification of MDH1 caused increased expression of malic enzyme 1 (ME1) in MDH1 amplified cell lines.