Fig 1: Lysine Homocysteinylation of DNA-PKcs Increases Cell DNA Repair through Facilitating DNA-PK Complex Formation.a, b Comparison of K-Hcy levels in cells subjected to various treatments. c Structure of DNA-PK complex. K-Hcy sites in DNA-PKcs protein were highlighted in red. d Co-immunoprecipitation showing that endogenous DNA-PKcs interacts with endogenous MARS (n = 3 biological repeats). e Western blot analysis of K-Hcy levels of DNA-PKcs, DNA-PKcs (pS2056), and p53 (Ser15) in cells subjected to various treatments. f Comet assay of DNA damage levels in ccRCC tumor vs. adjacent normal tissues (n = 10). P value is derived from two-sided paired t test. g, h NNMT overexpression enhancess the interaction between endogenous DNA-PKcs and endogenous KU70 or KU80 in ACHN and 769-P cells. i In vitro DNA-PKcs activity assayed by monitoring its kinase activity in phosphorylating its substrate p53. j DNA-PKcs activity indicated by measuring ADP formation in an ADP-Glo-DNA-PK assay (n = 5 repeats per group). P values are derived from two-sided t test. Data are shown as the mean ± SD. k HTL increases the in vitro DNA-PKcs activity. l DNA-PK activity under different treatments (n = 5 repeats per group). P values are derived from two-sided t test. Data are shown as the mean ± SD. m, n DNA-PKcs KW and 3KW mutants exhibit enhanced binding affinity for KU70 and KU80 compared to wild-type DNA-PKcs. o DNA-PKcs 3KW mutant exhibits enhanced kinase activity. p, q Tumor size of cell xenografts under different treatments in normal and NAC-administered nude mice. r Model depicting NNMT-mediated DNA repair and cell proliferation in ccRCC.