Glutamine deprivation link impaired metabolism to ERK pathway activation and drug resistance in liver cancer

Cancer cells use glutamine to meet the increased metabolic requirements imposed by rapid proliferation. The molecular role of glutamine to liver cancer is still largely unknown. Here we report that a subset of hepatocellular carcinoma (HCC) cell lines use extracellular glutamine to suppress signal transduction activities. Glutamine deprivation triggers phosphorylation of kinases, notably extracellular signal-regulated kinases (ERK), causing resistance to the anti-proliferative effects of kinase inhibitors (e.g. Sorafenib, Erlotinib, LY294002 and U0126). Genomics and metabolomics profiling showed that upon glutamine withdrawal, metabolism is severely impaired, with a significant accumulation of intracellular serine. Mechanistically, serine overload suppresses cell proliferation and contributes to ERK pathway activation and kinase inhibitor resistance. We found that in the impaired metabolic state, treatment with inhibitors of ERK pathway induced cell proliferation and pro-cancer metabolic reprogramming, including aerobic glycolysis, suppressed glucose contribution to intracellular serine, and a redirection of 13C-glucose-derived carbon towards the production of glutamine, glutamate, malate and aspartate. In conclusion, we show for the first time that HCC cell lines depend on glutamine to inhibit signaling networks, in part by preventing intracellular serine accumulation, and that inhibiting kinases in an impaired metabolic state induces tumourigenic phenotypes. These data offer novel insights for overcoming drug resistance in liver cancer.