Immunoprecipitated V5-hRIDA was in vitro desuccinylated with SIRT5, and immunodecorated with the antibody against hRIDA (WB: hRIDA, SIRT5-treated). and cell proliferation. This work addressed the question of UK114/RIDA expression in human non-tumor HEK293 cell lines and in some human tumor cell lines. Here we reported that human RIDA (hRIDA) was expressed in all the analyzed cell line and subjected to lysine (K-)succinylation. In HEK293, hRIDA K-succinylation was negatively correlated to the cell proliferation rate and was under the control of SIRT5. Moreover, K-succinylation clearly altered hRIDA quantification by immunoblotting, explaining, at least in part, some discrepancies about RIDA expression reported in previous studies. We found that hRIDA was able to deaminate reactive enamine-imine intermediates and that K-succinylation drastically reduced deaminase activity. As predicted by in silico analysis, the observed reduction of deaminase activity has been related to the drastic alterations of hRIDA structure inferred by K-succinylation. The role of RU 24969 hRIDA and the importance of its K-succinylation in cell metabolism, especially in cancer biology, have been discussed. and is generated by pyridoxal phosphate (PLP)-dependent serine/threonine dehydratase and cysteine desulfhydrase RU 24969 [1,2]. 2AA forms enamine/imine tautomers. In the imine form, 2AA reacts with PLP cofactor forming a covalent adduct, thus causing the inactivation of PLP-dependent enzymes [1,2]. Beside 2AA, RIDA catalyzes the hydrolysis of other reactive imines formed by L-amino acid oxidase (LAAO) [3,4,5]. Other Rabbit Polyclonal to GAB4 functions have been attributed to RIDA, such as endoribonuclease activity, inhibitor of protein synthesis, activator of -calpain protease, even though they need to be confirmed . Several crystal structures of RIDA proteins have been determined long before the discovery of their enzymatic activity. RIDA proteins are homotrimers with a cleft harboring the active site between two adjacent monomers . UK114, a mammalian member of YigF/YER057c/UK114 proteins, is also known as liver-perchloric acid soluble protein (L-PSP), being this protein detectable in the perchloric acid-soluble protein extract from goat liver . The human homolog of UK114/RIDA is encoded by gene, whose expression is high in hepatocytes and in renal distal tubular epithelial cell and low in all the other tissues [8,9]. Contrasting results concern the intracellular localization of RIDA in eukaryotes. Rat and human RIDA has been localized in cytoplasm, peroxisomal matrix, in nucleus, and in mitochondria [8,9,10,11]. Human RIDA (hRIDA) has been described as a tumor antigen in various tumors [12,13]. However, experimental data on the tumor antigenic nature of hRIDA and on its expression are quite controversial. hRIDA was shown to be down regulated in most of hepatocellular carcinoma tissues compared with the adjacent non-tumor hepatic tissue . hRIDA expression was negatively correlated with the tumor differentiation degree . However, overexpression of exogenous RIDA did not suppress the proliferation and tumorigenicity of human hepatoma cells in nude mice . Similarly, hRIDA is expressed in differentiated renal tubules , whereas a low expression has been found in kidney tumor cells . On the contrary, data available in The Human Protein Atlas program indicate that RIDA is well expressed in liver and in kidney cancers . In cultured cell lines RIDA expression has been also correlated to cell proliferation, as it was lower in the proliferation phase than in the confluent phase . Moreover, it was reduced in rat after partial hepatectomy RU 24969 and then gradually increased during liver regeneration, achieving the level of the pre-operated liver, after 7 days from partial hepatectomy . Uniprot data (uniprot.org) report that RIDA is subjected to extensive post-translational modifications (PTM), i.e., succinylation of different lysine residues (K-succinylation). Based on all the observations reported so far and considering the small dimension of the protein (14.5 KDa), we hypothesized that the discrepancies of RIDA expression among the various experimental contexts could be explained by the different sensitivity/specificity of the antibodies used in these studies. The aim of this.