Fig 2: SIRT5 activates TKT by mediating its demalonylation.a, b Immunofluorescent staining results for FLAG-SIRT5 WT/H158Y (in green) and TKT (in red). Yellow in the merged magnified images indicates co-localization. Scale bar, 5 µm (a). Fluorescence intensity of FLAG-SIRT5 WT/H158Y (green line) and TKT (red line) traced along the white line in HCT116 and LoVo cells using the line profiling function of ImageJ (b). This figure represents three independent experimental replicates with similar results. c Endogenous SIRT5 was immunoprecipitated with the anti-SIRT5 antibody, followed by Western blotting using an anti-TKT antibody in HCT116 and LoVo cells. The control comprised immunoprecipitation with IgG. d The interaction between FLAG-SIRT5 WT/H158Y and TKT in HCT116 and LoVo cells. e Malonylation (MalK) levels of exogenous TKT in HCT116 and LoVo cells expressing the control vector, SIRT5 WT, or SIRT5 H158Y. f The MalK levels of exogenous TKT in SIRT5-deficient HCT116 and LoVo cells were determined by Western blotting. g, h HA-tagged TKT proteins were purified using immunoprecipitation and incubated with different concentrations of malonyl-CoA (0, 1, and 2 mM) at 37 °C for 60 min. TKT activity was determined. Representative images (g) and quantification (h) of TKT activity. (n = 3 biologically independent experiments). i K281 of TKT is evolutionarily conserved across species. These sequences of TKT from humans to Gallus gallus were aligned. j HA-tagged TKT WT/K281R/K282R/K283R mutants were transfected into HCT116 cells, followed by treatment with SIRT5 siRNAs. TKT was immunoprecipitated and MalK levels were determined. k HCT116 cells expressing HA-tagged TKT WT/K281R mutant were treated with or without SIRT5 siRNAs. TKT activity was measured and normalized against protein levels. (n = 3 biologically independent experiments). Values in (h and k) represent the mean ± SD. P values were calculated using one-way ANOVA with Tukey’s multiple comparisons test. ns, not significant. Source data are provided as a Source Data file.

Fig 3: Validation of the correlation between succinylation regulators and m6A regulators at protein level. (A) The expression pattern of CPT1A, KAT2A, SIRT5, SIRT7, LRPPRC, and EIF3B between ccRCC tissues and corresponding normal tissues by immunohistochemistry. Error bars show standard error of the mean, and the middle bar represents the median expression level of each molecule. (B) The correlation analysis between CPT1A and LRPPRC, SIRT5 and EIF3B, CPT1A and EIF3B, SIRT5 and LRPPRC according to immunohistochemistry scores in 42 ccRCC tissues. (C) In ACHN cells, the expression of LRPPRC and EIF3B were detected by western blotting after transient knockdown of CPT1A and SIRT5, respectively.

Fig 4: Succinylation regulators might impact the expression of some m6A regulators. (A) The bubble diagram displayed of all RNA related GO pathways enriched by up-regulated genes in cluster 2 compared to cluster 3. (B) The circle chart showed top 5 KEGG pathways enriched by up-regulated genes in cluster 2 compared to cluster 3. (C) A brief summary of 32 m6A regulators reported by high-quality articles. (D) The expression patterns of CPT1A, SIRT5, and 5 m6A regulators at protein level between ccRCC and normal tissues (Wilcoxon test), *P < 0.05, ****P < 0.0001. (E) The Spearman correlation analysis between the expression of CPT1A and 5 m6A regulators at protein level. (F) The Spearman correlation analysis between the protein expression of SIRT5 and 5 m6A regulators at protein level. GO, Gene Ontology; KEGG, Kyoto Encyclopedia of Genes and Genomes.

Fig 5: Oncogenic role of SIRT5 and GLUD1 is vital for the tumorigenesis capacity of SIRT5 in vivo. a HCT116 cells stably expressing the control vector, SIRT5 WT, or SIRT5 H158Y were injected subcutaneously into nude mice (n = 9 for each group). Tumor volumes were measured at the indicated time points and the mean tumor volumes were calculated. Data are presented as the mean ± SD. b–d At the end of experiment, tumors from three groups were dissected, photographed (b, c), and weighed (d). Data are presented as the mean ± SD. e, f GLUD1 enzyme activities in tumor lysates derived from xenografts were measured (e). Data are presented as the mean ± SD. GLUD1 protein level and the overexpression of SIRT5 in the xenografts were confirmed by immunoblotting (f). g–i SIRT5-overexpressing LoVo cells infected with viruses expressing non-target control (NTC) short hairpin RNA (shRNA) or GLUD1 shRNA were injected subcutaneously into nude mice (n = 6 for each group). Tumor growth curves were constructed (g). Statistical analysis of tumor weight. Each dot represents the tumor mass from one mouse (h). Digital photograph of the dissected tumors (i). Data are presented as the mean ± SD. All P values were calculated by ANOVA with Tukey’s test. **P < 0.01, ***P < 0.001, N.S. = not significant for the indicated comparison. j Schematic model showing the suggested role of SIRT5 in the regulation of glutamine metabolism in CRC. SIRT5 directly interacts with GLUD1, which functions as a critical enzyme responsible for the formation of a-KG from glutamate. This interaction results in the deglutarylation and activation of GLUD1, leading to direct glutamine flux into the mitochondrial TCA cycle, thus promoting oxidative carboxylation of glutamine. The enhanced glutaminolysis supports CRC cell proliferation