Folate can promote the methionine-dependent reprogramming of glioblastoma cells towards pluripotency

Abstract

Methionine dependency of tumor growth, although not well-understood, is detectable by 11 C-methionine positron emission tomography and may contribute to the aggressivity of glioblastomas (GBM) and meningiomas. Cytosolic folate cycle is required for methionine synthesis. Its dysregulation may influence cell reprogramming towards pluripotency. We evaluated methionine-dependent growth of monolayer (ML) cells and stem cell-like tumor spheres (TS) derived from 4 GBM (U251, U87, LN299, T98G) and 1 meningioma (IOMM-LEE) cell lines. Our data showed that for all cell lines studied, exogenous methionine is required for TS formation but not for ML cells proliferation. Furthermore, for GBM cell lines, regardless of the addition of folate cycle substrates (folic acid and formate), the level of 3 folate isoforms, 5-methytetrahydrofolate, 5,10-methenyltetrahydrofolate, and 10-formyltetrahydrofolate, were all downregulated in TS relative to ML cells. Unlike GBM cell lines, in IOMM-LEE cells, 5-methyltetrahydrofolate was actually more elevated in TS than ML, and only 5,10-methenyltetrahydrofolate and 10-formyltetrahydrofolate were downregulated. The functional significance of this variation in folate cycle repression was revealed by the finding that Folic Acid and 5-methyltetrahydrofolate promote the growth of U251 TS but not IOMM-LEE TS. Transcriptome-wide sequencing of U251 cells revealed that DHFR , SHMT1 , and MTHFD1 were downregulated in TS vs ML, in concordance with the low activity cytosolic folate cycle observed in U251 TS. In conclusion, we found that a repressed cytosolic folate cycle underlies the methionine dependency of GBM and meningioma cell lines and that 5-methyltetrahydrofolate is a key metabolic switch for glioblastoma TS formation. The finding that folic acid facilitates TS formation, although requiring further validation in diseased human tissues, incites to investigate whether excessive folate intake could promote cancer stem cells formation in GBM patients.

MTHFR C677T and A1298C Polymorphisms in Breast Cancer, Gliomas and Gastric Cancer: A Review

“…Furthermore, folate supplementation reduces the methylation levels in tumor suppressor genes such as PTEN, P53 and Bax while increases the methylation levels of the MGMT promoter and oncogenes such as PDGF-B [ 108 ]. However, folic acid favors glioblastoma cell line stemness via tumor sphere formation, demonstrating MTHFR upregulation and hypomethylation compared with monolayers [ 110 ]. Folate may play a dual role in gliomas by preventing tumor initiation or promoting tumor progression.…”

Dietary Approaches to Cancer Therapy

“…The mechanisms underlying this cancer-specific auxotrophy for methionine are not fully understood, but may relate to defects in the methionine salvage pathways such as loss of methylthioadenosine phosphorylase (MTAP), which is often co-deleted in cancers along with the p16/INK4a tumor suppressor gene (Bertino et al, 2011), or the low level of methionine synthase expression seen in some cancer cells (Chaturvedi et al, 2018). A dysfunctional folate cycle (Zgheib et al, 2019) or an increased demand for methionine-dependent processes can also result in an increased methionine dependency. Alternatively, activation of PI3K in cancers can downregulate the cystine transporter xCT, leading to the preferential channeling of homocysteine through the transsulfuration pathway to synthesize cysteine and so reduce its availability to produce methionine (Lien et al, 2017).…”

Glucose and Amino Acid Metabolic Dependencies Linked to Stemness and Metastasis in Different Aggressive Cancer Types

“…MTAP loss results in an increased methionine uptake. When comparing methionine deprivation effects on GBM cell lines grown under conditions that favour differentiation (monolayer in media with serum) versus the same cell lines grown in stem cell conditions (spheres with a stem cell media composition), it was observed that only when GBM cells were grown under stem cell conditions, methionine was required for neurosphere formation ( Zgheib et al, 2019 ).…”