Acute myeloid leukemia (AML) is a genetically heterogeneous malignant disorder of the hematopoietic system, characterized by the accumulation of DNA-damaged immature myeloid precursors. Here, we find that hCINAP is involved in the repair of double-stranded DNA breaks (DSB) and that its expression correlates with AML prognosis. Following DSB, hCINAP is recruited to damage sites where it promotes SENP3-dependent deSUMOylation of NPM1. This in turn results in the dissociation of RAP80 from the damage site and CTIP-dependent DNA resection and homologous recombination. NPM1 SUMOylation is required for recruitment of DNA repair proteins at the early stage of DNA-damage response (DDR), and SUMOylated NPM1 impacts the assembly of the BRCA1 complex. Knockdown of hCINAP also sensitizes a patient-derived xenograft (PDX) mouse model to chemotherapy. In clinical AML samples, low hCINAP expression is associated with a higher overall survival rate in patients. These results provide mechanistic insight into the function of hCINAP during the DNA-damage response and its role in AML resistance to therapy.

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NEDDylation has been shown to participate in the DNA damage pathway, but the substrates of neural precursor cell expressed developmentally downregulated 8 (NEDD8) and the roles of NEDDylation involved in the DNA damage response (DDR) are largely unknown. Translesion synthesis (TLS) is a damage-tolerance mechanism, in which RAD18/RAD6-mediated monoubiquitinated proliferating cell nuclear antigen (PCNA) promotes recruitment of polymerase η (polη) to bypass lesions. Here we identify PCNA as a substrate of NEDD8, and show that E3 ligase RAD18-catalyzed PCNA NEDDylation antagonizes its ubiquitination. In addition, NEDP1 acts as the deNEDDylase of PCNA, and NEDP1 deletion enhances PCNA NEDDylation but reduces its ubiquitination. In response to H2O2 stimulation, NEDP1 disassociates from PCNA and RAD18-dependent PCNA NEDDylation increases markedly after its ubiquitination. Impairment of NEDDylation by Ubc12 knockout enhances PCNA ubiquitination and promotes PCNA-polη interaction, while up-regulation of NEDDylation by NEDD8 overexpression or NEDP1 deletion reduces the excessive accumulation of ubiquitinated PCNA, thus inhibits PCNA-polη interaction and blocks polη foci formation. Moreover, Ubc12 knockout decreases cell sensitivity to H2O2-induced oxidative stress, but NEDP1 deletion aggravates this sensitivity. Collectively, our study elucidates the important role of NEDDylation in the DDR as a modulator of PCNA monoubiquitination and polη recruitment.Electronic supplementary materialThe online version of this article (doi:10.1007/s13238-017-0455-x) contains supplementary material, which is available to authorized users.

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The DNA damage response (DDR) is essential for maintaining genome integrity. Mounting evidence reveals that protein modifications play vital roles in the DDR. Here, we show that USP38 is involved in the DDR by regulating the activity of HDAC1. In response to DNA damage, USP38 interacted with HDAC1 and specifically removed the K63-linked ubiquitin chain promoting the deacetylase activity of HDAC1. As a result, HDAC1 was able to deacetylate H3K56. USP38 deletion resulted in persistent focal accumulation of nonhomologous end joining (NHEJ) factors at DNA damage sites and impaired NHEJ efficiency, causing genome instability and sensitizing cancer cells to genotoxic insults. Knockout of USP38 rendered mice hypersensitive to irradiation and shortened survival. In addition, USP38 was expressed at low levels in certain types of cancers including renal cell carcinoma, indicating dysregulation of USP38 expression contributes to genomic instability and may lead to tumorigenesis. In summary, this study identifies a critical role of USP38 in modulating genome integrity and cancer cell resistance to genotoxic insults by deubiquitinating HDAC1 and regulating its deacetylation activity. Significance: This study demonstrates that USP38 regulates genome stability and mediates cancer cell resistance to DNAdamaging therapy, providing insight into tumorigenesis and implicating USP38 as a potential target for cancer diagnosis.