Methionine Metabolism in Human Fetal, Adult and Cancer Stem Cells

Abstract

Methionine is an essential amino acid critical in protein synthesis and methylation reactions. In this thesis, it is aimed to determine the effect of methionine on different human stem cell groups. Mesenchymal stem cells (MSC) derived from human bone marrow (BM) and umbilical cord blood (UCB), breast cancer stem cells isolated from MDA-MB-231 cell line, were treated with different doses of L-methionine in culture. Cell surface marker and cell cycle assessment were performed by flow cytometry. WST-1 was applied for the cell viability determination. Changes in gene expressions (OCT3/4, NANOG, DMNT1, DNMT3A and DNMT3B, MAT2A and MAT2B) with methionine supplementation were examined by RT-qPCR, the changes in histone methylation (H3K4me3, H3K27me3) levels were demonstrated by western blot analysis and SAM/SAH levels by ELISA. As a result of treatment with 0, 10, 25, 50 and 100 µM methionine, cell viability was determined >80% and methionine application for five hours was determined as a fixed time in future studies. In all three cell groups, the cells were mostly arrested in the G0/G1 phase for each culture condition. It was evaluated that BM-MSCs increased all investigated gene expressions in the culture medium containing 100 µM methionine, in addition to SAM/SAH levels. On the other hand, UCB-MSCs were found to increase OCT3/4, NANOG and DNMT1 gene expressions and decrease MAT2A and MAT2B expressions in culture medium containing 10 µM methionine. Moreover, an increase was observed in the He3K4me3 methylation profile. In addition, OCT3/4, NANOG, DNMT1 and MAT2B gene expressions in CSCs increased more at 50 and 100 µM starting from the addition of 25 µM methionine. An increase was determined in H3K4me3 protein expression at 50 and 100 µM methionine supplemented culture condition. This study demonstrates that methionine plays a critical role in metabolism and epigenetic regulation in different stem cell groups, and induces the maintenance of stem cells by regulating pluripotency-related gene expression and protein levels.