MAT2B regulates the protein level of MAT2A to preserve RNA N6-methyladenosine.

MAT2B works together with MAT2A to synthesize S-Adenosyl methionine (SAM) as the primary methyl donor. MAT2B, despite lacking catalytic activity, exerts regulatory control over the enzymatic activity of MAT2A. In addition to the enzymatic activity regulation, we find that, in an NADP⁺-dependent manner, MAT2B binds and stabilizes MAT2A. Disruption of the cellular NADP⁺ remodels the protein level of MAT2A. The pentose phosphatase pathway regulates the level of MAT2A protein through the interaction of NADP⁺ with MAT2B. Additionally, MAT2B-MAT2A interaction regulates the mRNA m6A modification and stability. In liver tumors, the Mat2a mRNA level is elevated but the protein level is decreased by the restricted NADP⁺. Blocking the interaction between MAT2B and MAT2A by the keto diet can suppress liver tumor growth. These findings reveal that MAT2B is essential for regulating the protein levels of MAT2A and connecting SAM synthesis to mRNA m6A.