Methionine Adenosyltransferase α1 is targeted to the mitochondrial matrix and interacts with cytochrome P450 2E1 to lower its expression

Methionine adenosyltransferase alpha1 (MATalpha1, encoded by MAT1A) is responsible for hepatic biosynthesis of S-adenosyl methionine, the principal methyl donor. MATalpha1 also act as a transcriptional cofactor by interacting and influencing the activity of several transcription factors. Mat1a knockout (KO) mice have increased levels of cytochrome P450 2E1 (CYP2E1), but the underlying mechanisms are unknown. The aims of the current study were to identify binding partners of MATalpha1 and elucidate how MATalpha1 regulates CYP2E1 expression. We identified binding partners of MATalpha1 by coimmunoprecipitation (co-IP) and mass spectrometry. Interacting proteins were confirmed using co-IP using recombinant proteins, liver lysates, and mitochondria. Alcoholic liver disease (ALD) samples were used to confirm relevance of our findings. We found that MATalpha1 negatively regulates CYP2E1 at mRNA and protein levels, with the latter being the dominant mechanism. MATalpha1 interacts with many proteins but with a predominance of mitochondrial proteins including CYP2E1. We found that MATalpha1 is present in the mitochondrial matrix of hepatocytes using immunogold electron microscopy. Mat1a KO hepatocytes had reduced mitochondrial membrane potential and higher mitochondrial reactive oxygen species, both of which were normalized when MAT1A was overexpressed. In addition, KO hepatocytes were sensitized to ethanol and tumor necrosis factor alpha-induced mitochondrial dysfunction. Interaction of MATalpha1 with CYP2E1 was direct, and this facilitated CYP2E1 methylation at R379, leading to its degradation through the proteasomal pathway. Mat1a KO livers have a reduced methylated/total CYP2E1 ratio. MATalpha1's influence on mitochondrial function is largely mediated by its effect on CYP2E1 expression. Patients with ALD have reduced MATalpha1 levels and a decrease in methylated/total CYP2E1 ratio. Conclusion: Our findings highlight a critical role of MATalpha1 in regulating mitochondrial function by suppressing CYP2E1 expression at multiple levels.