Identification and functional characterization of Lys-trimethylation of lactate dehydrogenase A

Background: Trimethylation of histones has been extensively studied, where histone methyltransferases catalyze the transfer of methyl groups from S-adenosyl methionine. Thus far, there have been no researches on the trimethylation of non-histone proteins. The precise mechanisms by which trimethylation affects cell progress and the related protein functions remain unclear. Purpose: The objective of this study was to identify the Lys-trimethylated proteins in kidney-derived cells and tissues, as well as to better understand the mechanisms underlying Lys-trimethylation-mediated cell metabolism. Methods: The levels of Lys-trimethylation in kidney-derived cells and tissues were assayed by Western blotting. Additionally, high-resolution mass spectrometry was used to analyze kidney-derived cells and tissues, and the eukaryotic expression vectors that led to the mutations of lysine were constructed and transfected into HEK293T cells. The LDHA activity of HEK293T cells was detected under conditions of Lys-trimethylation inhibition, and the proliferation of HEK293T cells was measured using EdU and Western blotting analyses. Results: The different proteins in kidney-derived cells and tissues showed different levels of Lys-trimethylation. In particular, lactate dehydrogenase A (LDHA) was Lys-trimethylated on lysine (K5). Inhibition of the Lys-trimethylation in LDHA increased the LDH activity of HEK293T cells and upregulated their proliferation. Conclusion: We suggested that LDHA affects the metabolism and proliferation of cells via a Lys-trimethylation-mediated mechanism; Lys-trimethylation might be a potential target for therapeutic research or used as a prognostic and treatment biomarker of several diseases.