a HepG2 cells were treated with different siRNAs targeting SIRT family members. PRMT5 was immunoprecipitated, and the succinylation of PRMT5 was analysed by Western blot analysis. b HepG2 cells were treated with different concentrations of siSIRT7 Mix (siSIRT7#1, siSIRT7#2, siSIRT7#3). PRMT5 was immunoprecipitated, and the succinylation of PRMT5 was analysed by Western blot analysis. c HepG2 cells were cotransfected with plasmids containing Flag-tagged PRMT5 and HA-tagged SIRT7 or SIRT7 mutant. Flag-tagged PRMT5 was immunoprecipitated with M2 beads, and the acetylation and succinylation levels of PRMT5 were analysed by Western blot analysis. d Methylation of global proteins and H4R3 was detected by Western blot analysis in HepG2 cells transfected with or without SIRT7 plasmids using Rme2sy and H4R3me2s antibodies. e Expression of SIRT7 in normal and LIHC (liver hepatocellular carcinoma) tumour samples in TCGA database. f The mRNA levels of SIRT7 were evaluated by RT-qPCR in 35 pairs of clinical liver cancer tissues. g The protein levels of SIRT7, H4R3me2s and PRMT5 were determined by Western blot analysis in 35 pairs of clinical liver cancer tissues. h The relationship between the levels of SIRT7 expression and the levels of H4R3me2s in the above samples was analysed by ImageJ software. i A model showed that SIRT7 desuccinylates PRMT5 to enhance the methyltransferase activity of PRMT5. Statistically significant differences are indicated: ***P < 0.001; Student’s t test.