GLUL and cancer: GS expression is high in liver and brain, and we found that cancer cell lines derived from these organs (HepG2 and T16 (ref. 21)) produce N5-methylglutamine after supplementation of methylamine (Fig. 4c,d), whereas Cas9-mediated deletion of GS in HepG2 cells significantly inhibited N5-methylglutamine production (Fig. 4c).