Abstract 2372: DUSP3-NPM-P53 axis: a new regulator of genomic stability of cells under genotoxic stress
Authors: Fábio L. Forti, Lilian C. Russo
Journal: Cancer Research (2020)

Abstract The dual-specificity phosphatase 3 (DUSP3) is an atypical tyrosine phosphatase that dephosphorylates residues of p-Tyrosine and p-Threonine in protein substrates. DUSP3 is overexpressed in some human tumors, where it regulates cell cycle progression and has preferably nuclear localization. DUSP3 contributes to cellular genomic stability through mechanisms that begin to be clarified here. Our group used biochemical, bioinformatics, proteomics and interactome approaches to identify and validate nuclear proteins interacting with DUSP3 under cellular conditions of genotoxic stress promoted by UV-radiation. One of these targets is the nucleophosmin (NPM) protein, which plays key roles in nucleotide excision repair (NER) pathway. Surface Plasmon Resonance analyses showed a very strong physical bimolecular interaction between NPM-DUSP3. In order to verify the involvement of this phosphatase in DNA repair, DUSP3 knockdown was carried out in MRC-5 (normal fibroblasts) or XPA (NER-deficient cell line lacking the XPA protein) cell lines. By alkaline comet assays we found DUSP3 knockdown caused delay in DNA repair even in XPA cells, which is not to repair UV-radiation induced damage. This effect was supported by immuno-slot-blot assays specifically measuring the distortions of CPD and 6,4-photoproducts (6-4-PP) caused by UV-radiation on cells genome. Once again, MRC-5 cells DUSP3 silenced exhibited delay in the repair of these lesions, whereas XPA cells were not able to repair them even after 72h of the UVC exposure, but the accumulation of CPD and 6-4-PP lesions was even higher under DUSP3 silencing. Next we verify that NPM is a substrate of DUSP3 by immunoprecipitating tyrosine-phosphorylated NPM, and which levels are increased in both cells under DUSP3 knockdown. Using phospho-specific antibodies designed against the four tyrosine residues of NPM, immunoblotings revealed that DUSP3 specifically dephosphorylates tyrosine 29, 67 and 271 residues of NPM after UV radiation altering its subnuclear localization. Furthermore immunoblotting and imunofluorescence assays revealed an unexpected increase in phospho-p53-Ser15 and p53 transcriptional activity in DUSP3 deficient cells after exposure to UV radiation, which can be correlated to nuclear NPM functions in the repair of UV-promoted DNA lesions. Even so, we observed that DUSP3 knockdown also causes an earlier nucleolus-nucleoplasm translocation of NPM after genotoxic stress that is followed by an earlier ARF translocation and co-localization of both proteins with HDM2 and p53 at nucleoplasm. This leads to disruption of HDM2-p53 interaction, to non-degradation and earlier phosphorylation of p53-Ser15. Interestingly, using cycloheximide to inhibit protein synthesis, we confirmed that the half-life of p53 and NPM is longer in the DUSP3-deficient cells. Altogether our data highlight DUSP3 unknown roles in different signaling modules regulating biological processes involved in genomic stability through an unusual target, the NPM-p53 axis. Citation Format: Fábio L. Forti, Lilian C. Russo. DUSP3-NPM-P53 axis: a new regulator of genomic stability of cells under genotoxic stress [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2372.