Abstract
BackgroundThe amino acid serine is an important substrate for biosynthesis and redox homeostasis. We investigated whether glioblastoma (GBM) cells are dependent on serine for survival under conditions of the tumour microenvironment.MethodsSerine availability in GBM cells was modulated pharmacologically, genetically and by adjusting serine and glycine concentrations in the culture medium. Cells were investigated for regulation of serine metabolism, proliferation, sensitivity to hypoxia-induced cell death and redox homeostasis.ResultsHypoxia-induced expression of phosphoglycerate dehydrogenase (PHGDH) and the mitochondrial serine hydroxymethyltransferase (SHMT2) was observed in three of five tested glioma cell lines. Nuclear factor erythroid 2-related factor (Nrf) 2 activation also induced PHGDH and SHMT2 expression in GBM cells. Low levels of endogenous PHGDH as well as PHGDH gene suppression resulted in serine dependency for cell growth. Pharmacological inhibition of PHGDH with CBR-5884 reduced proliferation and sensitised cells profoundly to hypoxia-induced cell death. This effect was accompanied by an increase in reactive oxygen species and a decrease in the NADPH/NADP+ ratio. Similarly, hypoxia-induced cell death was enhanced by PHGDH gene suppression and reduced by PHGDH overexpression.ConclusionsSerine facilitates adaptation of GBM cells to conditions of the tumour microenvironment and its metabolism could be a plausible therapeutic target.
Highlights
The amino acid serine is an important substrate for biosynthesis and redox homeostasis
We report that inhibition of synthesis pathway (SSP) activity sensitises GBM cells to hypoxia-induced cell death by increasing reactive oxygen species
LNT-229 and LN-308 cells were a kind gift from N. de Tribolet (Lausanne, Switzerland), G55 cells were a kind gift from Manfred Westphal and Kathrin Lamszus (Hamburg), LN-428 cells and LN-464 cells were a kind gift from Monika Hegi (Lausanne)
Summary
Glioblastoma (GBM) is the most common primary CNS malignancy in adults with a dismal prognosis.[1]. 1234567890();,: 1392 PHGDH is a relevant factor for tumour cell proliferation when serine supply is limited.[28] In gliomas, PHGDH expression increases with WHO grade and silencing of PHGDH leads to reduced GBM cell proliferation and invasion.[29] Lately, a novel selective small-molecule inhibitor of PHGDH, CBR-5884, has been identified.[30] Serine hydroxymethyltransferases (SHMTs) catalyse the conversion of serine to glycine and vice versa.[31] SHMT1, the cytoplasmatic isoform, does not significantly contribute to the production of glycine, whereas SHMT2, the mitochondrial isoform, is an important source of glycine in proliferating cells.[32,33] In GBM, pseudopallisading cells surrounding necrotic regions express high levels of SHMT2 and glycine decarboxylase (GLDC) In those cells, SHMT2 reduces oxygen consumption to adapt to microenvironmental conditions.[34] In this project we modulated serine availability and SSP enzymatic activity under conditions mirroring the GBM microenvironment. We report that inhibition of SSP activity sensitises GBM cells to hypoxia-induced cell death by increasing reactive oxygen species
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