A ubiquitin switch controls autocatalytic inactivation of the DNA-protein crosslink repair protease SPRTN.

Repair of covalent DNA-protein crosslinks (DPCs) by the metalloprotease SPRTN prevents genome instability, premature aging and carcinogenesis. SPRTN is specifically activated by DNA structures containing single- and double-stranded features, but degrades the protein components of DPCs promiscuously and independent of amino acid sequence. This lack of specificity is useful to target diverse protein adducts, however, it requires tight control in return, in order to prohibit uncontrolled proteolysis of chromatin proteins. Here, we discover the components and principles of a ubiquitin switch, which negatively regulates SPRTN. We demonstrate that monoubiquitylation is induced in an E3 ligase-independent manner and, in contrast to previous assumptions, does not control chromatin access of the enzyme. Data obtained in cells and in vitro reveal that monoubiquitylation induces inactivation of the enzyme by triggering autocatalytic cleavage in trans while also priming SPRTN for proteasomal degradation in cis. Finally, we show that the deubiquitylating enzyme USP7 antagonizes this negative control of SPRTN in the presence of DPCs.

USP7 promotes proliferation of papillary thyroid carcinoma cells through TBX3-mediated p57KIP2 repression.

Ubiquitin-specific protease 7 (USP7/HAUSP) is known to regulate multiple cellular phenomena, including cell cycle progression and proliferation, and is involved in binding and stabilizing specific target proteins through deubiquitylation. However, the detailed role of USP7 in papillary thyroid carcinoma (PTC) remains to be investigated. In this study, our results showed that USP7 was upregulated in PTC tissues compared with adjacent nontumour tissues. Consistently, a series of gain/loss functional assays in vivo and in vitro demonstrated the role of USP7 in promoting PTC cell proliferation. Furthermore, we showed that there was a negative correlation between USP7 and the CDK inhibitor p57KIP2 expression in PTC tissues and that USP7 facilitated PTC cell proliferation by inhibiting p57KIP2. Mechanistically, USP7 inhibited p57KIP2 expression by modulating TBX3, directly binding to TBX3, and decreasing its ubiquitination and degradation. Our findings demonstrated that USP7 played a critical oncogenic role in PTC tumorigenesis, suggesting that USP7 might act as a prognostic and therapeutic target for PTC progression.

Histone chaperone FACT represses retrotransposon MERVL and MERVL-derived cryptic promoters.

Endogenous retroviruses (ERVs) were usually silenced by various histone modifications on histone H3 variants and respective histone chaperones in embryonic stem cells (ESCs). However, it is still unknown whether chaperones of other histones could repress ERVs. Here, we show that H2A/H2B histone chaperone FACT plays a critical role in silencing ERVs and ERV-derived cryptic promoters in ESCs. Loss of FACT component Ssrp1 activated MERVL whereas the re-introduction of Ssrp1 rescued the phenotype. Additionally, Ssrp1 interacted with MERVL and suppressed cryptic transcription of MERVL-fused genes. Remarkably, Ssrp1 interacted with and recruited H2B deubiquitinase Usp7 to Ssrp1 target genes. Suppression of Usp7 caused similar phenotypes as loss of Ssrp1. Furthermore, Usp7 acted by deubiquitinating H2Bub and thereby repressed the expression of MERVL-fused genes. Taken together, our study uncovers a unique mechanism by which FACT complex silences ERVs and ERV-derived cryptic promoters in ESCs.

WD repeat-containing protein 1 maintains ß-Catenin activity to promote pancreatic cancer aggressiveness.

BACKGROUND: The molecular signature underlying pancreatic ductal adenocarcinoma (PDAC) progression may include key proteins affecting the malignant phenotypes. Here, we aimed to identify the proteins implicated in PDAC with different tumour-node-metastasis (TNM) stages. METHODS: Eight-plex isobaric tags coupled with two-dimensional liquid chromatography-tandem mass spectrometry were used to analyse the proteome of PDAC tissues with different TNM stages. A loss-of-function study was performed to evaluate the oncogenic roles of WD repeat-containing protein 1 (WDR1) in PDAC. The molecular mechanism by which WDR1 promotes PDAC progression was studied by real-time qPCR, Western blotting, proximity ligation assay and co-immunoprecipitation. RESULTS: A total of 5036 proteins were identified, and 4708 proteins were quantified with high confidence. Compared with normal pancreatic tissues, 37 proteins were changed significantly in PDAC tissues of different stages. Moreover, 64 proteins were upregulated or downregulated in a stepwise manner as the TNM stages of PDAC increased, and 10 proteins were related to tumorigenesis. The functionally uncharacterised protein, WDR1, was highly expressed in PDAC and predicted a poor prognosis. WDR1 knockdown suppressed PDAC tumour growth and metastasis in vitro and in vivo. Moreover, WDR1 knockdown repressed the activity of the Wnt/ß-Catenin pathway; ectopic expression of a stabilised form of ß-Catenin restored the suppressive effects of WDR1 knockdown. Mechanistically, WDR1 interacted with USP7 to prevent ubiquitination-mediated degradation of ß-Catenin. CONCLUSION: Our study identifies several previous functional unknown proteins implicated in the progression of PDAC, and provides new insight into the oncogenic roles of WDR1 in PDAC development.

USP7 inhibition inhibits proliferation and induces megakaryocytic differentiation in MDS cells by upregulating gelsolin.

Myelodysplastic syndrome (MDS), a largely incurable hematological malignancy, is driven by complex genetic and epigenetic alterations from an aberrant clone of hematopoietic stem/progenitor cells (HSPCs). Ubiquitin-specific protease 7 (USP7) has been demonstrated to have an important oncogenic role in the development of several cancer types, but its role in MDS is unknown. Here, we demonstrate that USP7 expression is elevated in MDS cell lines and patient samples. The USP7-selective small-molecule inhibitors P5091 and P22077 inhibited cell proliferation and induced megakaryocytic differentiation in both cell lines and primary cells. Furthermore, pharmacological inhibition of USP7 markedly suppressed the growth of MDS cell lines in xenograft mouse models. To explore the mechanisms underlying the observed phenotypic changes, we employed RNA-seq to compare the differences in genes after USP7 inhibitor treatment and found that gelsolin (GSN) expression was increased significantly after USP7 inhibitor treatment. Furthermore, knockdown of GSN attenuated the proliferation inhibition, apoptosis induction and megakaryocyte differentiation induced by USP7 inhibitors in MDS cells. Collectively, our findings identify previously unknown roles of USP7 and suggest that the USP7/GSN axis may be a potential therapeutic target in MDS.

Blockade of deubiquitinase USP7 overcomes bortezomib resistance by suppressing NF-κB signaling pathway in multiple myeloma.

The treatment of multiple myeloma (MM) with bortezomib (BTZ) is promising; however, the emergence of resistance is challenging in the clinical treatment. Thus, a novel targeted treatment or exploring the mechanism underlying BTZ resistance is an urgent requisite. The current data showed that high expression of USP7 in myeloma was a predictor of short overall survival and poor outcome. USP7 knockout significantly suppressed the colony formation, inhibited the proliferation of BTZ-resistant MM cells even in the presence of growth factors, and overcame BTZ resistance. The knockout markedly inhibited the tumor growth and prolonged the survival of mice bearing BTZ-resistant MM cells. Mechanistically, USP7 knockout remarkably increased the sensitivity to BTZ by stabilizing ΙκΒα and blocking the NF-κB pathway. Not surprisingly, when IκBα was knocked down by siRNA transfection, the MM cells restored the BTZ resistance. Importantly, usage of USP7 inhibitors also suppressed the activation of NF-κB and combination with BTZ triggered the synergistic antitumor activity in BTZ-resistant MM cells. Taken together, this study provides the rationale for clinical protocols evaluating USP7 inhibition, alone and in combination with BTZ, to overcome BTZ resistance and improve the patient outcome in MM.