UBXN1 promotes liver tumorigenesis by regulating mitochondrial homeostasis.

BACKGROUND: The maintenance of mitochondrial homeostasis is critical for tumor initiation and malignant progression because it increases tumor cell survival and growth. The molecular events controlling mitochondrial integrity that facilitate the development of hepatocellular carcinoma (HCC) remain unclear. Here, we report that UBX domain-containing protein 1 (UBXN1) hyperactivation is essential for mitochondrial homeostasis and liver tumorigenesis. METHODS: Oncogene-induced mouse liver tumor models were generated with the Sleeping Beauty (SB) transposon delivery system. Assessment of HCC cell growth in vivo and in vitro, including tumour formation, colony formation, TUNEL and FACS assays, was conducted to determine the effects of UBXN1 on HCC cells, as well as the involvement of the UBXN1-prohibitin (PHB) interaction in mitochondrial function. Coimmunoprecipitation (Co-IP) was used to assess the interaction between UBXN1 and PHB. Liver hepatocellular carcinoma (LIHC) datasets and HCC patient samples were used to assess the expression of UBXN1. RESULTS: UBXN1 expression is commonly upregulated in human HCCs and mouse liver tumors and is associated with poor overall survival in HCC patients. UBXN1 facilitates the growth of human HCC cells and promotes mouse liver tumorigenesis driven by the NRas/c-Myc or c-Myc/shp53 combination. UBXN1 interacts with the inner mitochondrial membrane protein PHB and sustains PHB expression. UBXN1 inhibition triggers mitochondrial damage and liver tumor cell apoptosis. CONCLUSIONS: UBXN1 interacts with PHB and promotes mitochondrial homeostasis during liver tumorigenesis.

UBXN9 inhibits the RNA exosome function to promote T cell control of liver tumorigenesis.

BACKGROUND AND AIMS: Liver tumorigenesis encompasses oncogenic activation and self-adaptation of various biological processes in premalignant hepatocytes to circumvent the pressure of cellular stress and host immune control. Ubiquitin regulatory X domain-containing proteins (UBXNs) participate in the regulation of certain signaling pathways. However, whether UBXN proteins function in the development of liver cancer remains unclear. APPROACH AND RESULTS: Here, we demonstrated that UBXN9 (Alveolar Soft Part Sarcoma Chromosomal Region Candidate Gene 1 Protein/Alveolar Soft Part Sarcoma Locus) expression was decreased in autochthonous oncogene-induced mouse liver tumors and ~47.7% of human HCCs, and associated with poor prognosis in patients with HCC. UBXN9 attenuated liver tumorigenesis induced by different oncogenic factors and tumor growth of transplanted liver tumor cells in immuno-competent mice. Mechanistically, UBXN9 significantly inhibited the function of the RNA exosome, resulting in increased expression of RLR-stimulatory RNAs and activation of the retinoic acid-inducible gene-I-IFN-Ι signaling in tumor cells, and hence potentiated T cell recruitment and immune control of tumor growth. Abrogation of the CD8 + T cell response or inhibition of tumor cell retinoic acid-inducible gene-I signaling efficiently counteracted the UBXN9-mediated suppression of liver tumor growth. CONCLUSIONS: Our results reveal a modality in which UBXN9 promotes the stimulatory RNA-induced retinoic acid-inducible gene-I-interferon signaling that induces anti-tumor T cell response in liver tumorigenesis. Targeted manipulation of the UBXN9-RNA exosome circuit may have the potential to reinstate the immune control of liver tumor growth.

AKT hyperactivation confers a Th1 phenotype in thymic Treg cells deficient in TGF-ß receptor II signaling.

The generation of CD4⁺Foxp3⁺ Treg cells in the thymus is crucial for immune homeostasis and self-tolerance. Recent studies have shown Treg-cell plasticity when Th-related transcriptional factors and cytokines are present. However, the mechanisms that maintain the stability of Treg cells are poorly understood. Here, using mice with a T-cell-specific deletion of the transforming growth factor-ß receptor 2 (Tgfbr2⁻/⁻ mice), we identify the restriction of AKT activation as a key event for the control of Treg-cell stability in Th1 inflammation. AKT regulation was evident in thymic CD4⁺Foxp3⁺ Treg cells before they egressed to peripheral tissues. CD4⁺Foxp3⁺ thymocytes from mice with the Tgfbr2 deletion expressed high levels of CXCR3 and T-bet, and produced IFN-γ and TNF-α. Thymic Tgfbr2⁻/⁻ Treg cells also showed an increase in the activation of AKT pathway. Enhanced AKT activity induced the expression of IFN-γ both in natural and inducible Treg cells. Inhibition of AKT activity markedly attenuated the expression of IFN-γ and TNF-α in thymic Tgfbr2⁻/⁻ Treg cells in vivo. In addition, mixed bone marrow transplantation showed that TGF-ß signaling maintained Treg-cell stability in an intrinsic manner. Our results demonstrate that AKT hyperactivation contributes to the conversion of Treg cells to a Th1 phenotype.

The expression of CDK1 is associated with proliferation and can be a prognostic factor in epithelial ovarian cancer.

Overexpression of cyclin-dependent kinase 1 (CDK1) has been noted to correlation with several human cancers. However, the effects of CDK1 on ovarian cancer development remain unclear. The aim of this study was to examine the effect of CDK1 and related mechanism in the proliferation and resistance to chemotherapeutic drugs of epithelial ovarian cancer (EOC). Immunohistochemical analysis was performed in 119 human ovarian cancer samples, and the data were correlated with clinicopathologic features. Furthermore, Western blot analysis was performed for CDK1 in EOC samples and cell lines to evaluate their protein levels and molecular interaction. Kaplan-Meier survival analysis showed that strong expression of CDK1 exhibited a significant correlation with poor prognosis in human EOC (P = 0.02). Meanwhile, we found that knockdown CDK1 by shCDK1 promoted the apoptosis rate and increased the sensitivity to chemotherapy drugs. Thus, CDK1 might serve as a prognostic marker, and it might be of great value for experimental therapies in EOC.

KLF9, a transcription factor induced in flutamide-caused cell apoptosis, inhibits AKT activation and suppresses tumor growth of prostate cancer cells.

BACKGROUND: Kruppel-like factors (KLFs) are involved in various biological processes; emerging studies have indicated that KLF9 plays a critical role in regulating tumorigenesis. The role of KLF9 in prostate cancer (PCa), however, has not yet been investigated. METHODS: The expression of KLF members, AKT- and apoptosis-related proteins were analyzed by Western blot or qRT-PCR. Tet-On inducible KLF9 expression was established for the evaluation of the effects of KLF9 on cell proliferation, apoptosis, and xenograft tumor growth in nude mice. Cell cycle and apoptosis were determined by flow cytometry. RESULTS: KLF9 was induced in a time-dependent manner in flutamide-caused apoptosis, and knockdown of KLF9 significantly decreased flutamide-induced growth inhibition and apoptosis in LNCaP cells. The levels of KLF9 were relatively lower in PCa cell lines, particularly in androgen-independent cell lines compared with those in nontumorous prostate epithelial cell lines. Overexpression of KLF9 dramatically suppressed cell proliferation and caused cell cycle arrest in the G2/M phase and cell apoptosis in the androgen-independent cell lines, PC3 and DU145. Intriguingly, KLF9 expression severely suppressed the activation of AKT and its downstream targets. AKT reactivation partially rescued the KLF9-mediated inhibitory effects on the proliferation of PCa cells. More importantly, we found that KLF9 overexpression efficiently inhibited the xenograft tumor growth of PCa cells. CONCLUSIONS: These data collectively showing that KLF9 substantially inhibits AKT activation and abrogates tumor growth of PCa cells, suggest the potential of either genetic or pharmacological activation of KLF9 in the therapeutic treatment of castration-resistant PCa.

Bilateral axillary node calcifications: a case report and revisiting causes.

A 48-year woman was found to have bilateral axillary nodal microcalcifications on screening mammogram; a new finding compared to the prior mammogram done about 8 years ago. Combining the new finding with the amorphous and fine morphology of the microcalcifications, deemed it suspicious. In the absence of a definite benign cause, that could be attributed to this finding, biopsy was performed. Histology from the bilateral axillary node was reported to be benign with calcifications identified within granulomas. There are only a few cases with bilateral axillary nodal microcalcifications reported in the literature till date. Most of these are from ovarian cancer or related to chrysotherapy for rheumatoid arthritis. Our case is distinct from them as this rare finding was not due to any of the known etiologies and the morphology is quite different from the known granulomatous causes. As we report this rare case, we also revisit the causes of axillary nodal microcalcifications. Familiarity with this subject can help the reporting radiologists to avert an invasive procedure like biopsy in some cases, if the cause of benignity can be confidently identified.

Comparing the effectiveness of Chinese patent medicines containing red yeast rice on hyperlipidaemia: A network meta-analysis of randomized controlled trials.

INTRODUCTION: The purpose of this study was to evaluate the therapeutic effectiveness of Chinese patent medicines containing red yeast rice for the treatment of hyperlipidaemia. METHODS: Relevant literature published until 13 August 2021, was retrieved from six electronic databases. Randomized clinical trials of Chinese patent medicines containing red yeast rice in patients with hyperlipidaemia were included in the review. Network meta-analysis was performed using Stata 13.1 software. Methodological quality was assessed using the Cochrane risk of bias tool. The surface under the cumulative ranking (SUCRA) curve probability values were used to rank the treatments. RESULTS: This study included 47 trials involving 4824 subjects. In terms of reduced total cholesterol levels, Xuezhikang (SUCRA: 84.5%) had the highest probability of being the most effective formulation, with Simvastatin (66.4%) and Zhibitai (65.4%) ranked second and third, respectively. Xuezhikang also had the highest probability of reducing low-density lipoprotein cholesterol levels to the greatest extent (SUCRA: 82.6%) with Simvastatin (SUCRA: 74.9%) and Zhibituo (SUCRA: 52.8%) being the second and third choices, respectively. For reduced triglyceride levels, Zhibituo (SUCRA: 80.2%) exhibited the highest probability of being the most effective, with Xuezhikang (SUCRA: 63.4%) and Simvastatin (SUCRA: 57.6%) in second and third places, respectively. Finally, in terms of improving high-density lipoprotein cholesterol levels, Zhibituo (SUCRA: 90.1%) had the highest probability of being the most effective, with Simvastatin (SUCRA: 82.1%) and Xuezhikang (SUCRA: 51.1%) ranked second and third, respectively. CONCLUSIONS: Xuezhikang was found to have the highest probability of being the most effective formulation for reducing total cholesterol and low-density lipoprotein cholesterol levels, while Zhibituo had the highest probability of being the most effective for controlling triglyceride and high-density lipoprotein cholesterol levels. The studies included in the review exhibited certain limitations and, therefore, more rigorously designed studies should be performed. TRIAL REGISTRATION: INPLASY registration number: INPLASY202130017.

ETV4 potentiates nuclear YAP retention and activities to enhance the progression of hepatocellular carcinoma.

Dysregulation of the Hippo pathway that promotes cell survival, proliferation and tumorigenesis, relays on the coordinated interactions of YAP with the factors that determine YAP translocation and the related transcriptional programming. Here, we demonstrate that ETV4, a transcriptional factor participating in various protumorigenic processes, enhances YAP-mediated transactivation and hepatocellular carcinoma (HCC) progression. Mechanistically, the enhancement of YAP activities is mediated by the interaction between ETV4 and YAP, which not only increases nuclear YAP accumulation but also directly augments the YAP/TEAD4-mediated transcriptional activation in tumor cells. Functionally, the interplay of ETV4 and YAP promotes growth of liver tumor cells, and activates the genes related to myeloid cell recruitment, including CXCL1 and CXCL5, leading to an enriched presence of myeloid-derived suppressive cells and macrophages but a decreased infiltration of T cells and NK cells in transplanted tumors. More importantly, the correlations between YAP activation, the altered immune cell distribution and ETV4 expression are observed in human HCCs. Therefore, our study reveals a functional interaction between ETV4 and YAP that contributes to HCC progression, and provides mechanistic insights into the regulation of nuclear YAP retention and transactivation.

Deubiquitination of the repressor E2F6 by USP22 facilitates AKT activation and tumor growth in hepatocellular carcinoma.

Dysregulated ubiquitination of tumor-related proteins plays a critical role in tumor development and progression. The deubiquitinase USP22 is aberrantly expressed in certain types of cancer and contributes to aggressive tumor progression. However, the precise mechanism underlying the pro-tumorigenic function of USP22 in hepatocellular carcinoma (HCC) remains unclear. Here, we report that E2F6, a pocket protein-independent transcription repressor, is essential for HCC cell growth, and that its activities are controlled by USP22-mediated deubiquitination. USP22 interacts with and stabilizes E2F6, resulting in the transcriptional repression of phosphatase DUSP1. Moreover, the process involving DUSP1 repression by E2F6 strengthens AKT activation in HCC cells. Therefore, these findings provide mechanistic insights into the USP22-mediated control of oncogenic AKT signaling, emphasizing the importance of USP22-E2F6 regulation in HCC development.

The deubiquitinase USP16 functions as an oncogenic factor in K-RAS-driven lung tumorigenesis.

K-RAS mutation and molecular alterations of its surrogates function essentially in lung tumorigenesis and malignant progression. However, it remains elusive how tumor-promoting and deleterious events downstream of K-RAS signaling are coordinated in lung tumorigenesis. Here, we show that USP16, a deubiquitinase involved in various biological processes, functions as a promoter for the development of K-RAS-driven lung tumor. Usp16 deletion significantly attenuates K-rasG12D-mutation-induced lung tumorigenesis in mice. USP16 upregulation upon RAS activation averts reactive oxygen species (ROS)-induced p38 activation that would otherwise detrimentally influence the survival and proliferation of tumor cells. In addition, USP16 interacts with and deubiquitinates JAK1, and thereby promoting lung tumor growth by augmenting JAK1 signaling. Therefore, our results reveal that USP16 functions critically in the K-RAS-driven lung tumorigenesis through modulating the strength of p38 and JAK1 signaling.

USP12 downregulation orchestrates a protumourigenic microenvironment and enhances lung tumour resistance to PD-1 blockade.

Oncogenic activation of KRAS and its surrogates is essential for tumour cell proliferation and survival, as well as for the development of protumourigenic microenvironments. Here, we show that the deubiquitinase USP12 is commonly downregulated in the KrasG12D-driven mouse lung tumour and human non-small cell lung cancer owing to the activation of AKT-mTOR signalling. Downregulation of USP12 promotes lung tumour growth and fosters an immunosuppressive microenvironment with increased macrophage recruitment, hypervascularization, and reduced T cell activation. Mechanistically, USP12 downregulation creates a tumour-promoting secretome resulting from insufficient PPM1B deubiquitination that causes NF-κB hyperactivation in tumour cells. Furthermore, USP12 inhibition desensitizes mouse lung tumour cells to anti-PD-1 immunotherapy. Thus, our findings propose a critical component downstream of the oncogenic signalling pathways in the modulation of tumour-immune cell interactions and tumour response to immune checkpoint blockade therapy.

Effectiveness of tonifying-kidney and regulating-liver therapy on diminished ovarian reserve: a systematic review and Meta-analysis of randomized controlled trials.

OBJECTIVE: To evaluate the effectiveness of the Traditional Chinese Medicine tonifying-kidney and regulating-liver therapy on diminished ovarian reserve (DOR). METHODS: The literature was comprehensively searched up to August 2019 using four Chinese and three English electronic databases to extract randomized clinical trials (RCTs) comparing Traditional Chinese Medicine tonifying-kidney and regulating-liver prescriptions (combined with hormone therapy or not) with Western Medicine. Data quality evaluation was conducted using the Cochrane risk of bias tool. Meta-analysis was conducted using Revman 5.3 software with effect estimates presented as mean difference (MD), risk ratio (RR), and 95% confidence interval (CI). RESULTS: A total of nine RCTs with 512 participants were extracted and eligible for Meta-analysis. There were no significant differences between Chinese medicine and Western Medicine on basal serum follicle-stimulating hormone (FSH) level (MD 0.11, 95% CI －0.52 to 0.74, 392 participants, seven trials), anti-Müllerian hormone level (MD 0.48, 95% CI －0.62 to 1.58, 95 participants, two trials), and the FSH and luteinizing hormone ratio (MD 0.01, 95% CI －0.95 to 0.96, 115 participants, two trials). Chinese medicine was more effective at improving Traditional Chinese Medicine symptom scores (TCMSS) (MD －2.39, 95% CI －3.83 to －0.94, 160 participants, three trials), effective rate of TCMSS (RR 1.18, 95% CI 1.02 to 1.36, 160 participants, three trials), antral follicle count (AFC) (MD 0.55, 95% CI 0.05 to 1.04, 155 participants, three trials), and FSH levels at 3 months post-treatment (MD -4.77, 95% CI －6.09 to －3.45, 137 participants, two trials). CONCLUSION: Compared with Western Medicine, tonifying-kidney and regulating-liver therapy is more effective at relieving symptoms and improving AFC and FSH at 3 months post-treatment.

Requirement for POH1 in differentiation and maintenance of regulatory T cells.

Foxp3-expressing regulatory T (Treg) cells are essential for averting autoimmune diseases and maintaining immune homeostasis. However, the molecular mechanisms underlying the development and maintenance of Treg cells are still unclear. Here, we found that T cell-specific deletion of the gene encoding the deubiquitinase POH1 compromised the development of mature T cells, especially CD4+Foxp3+ Treg cells. Moreover, POH1 deficiency significantly attenuated the transition of CD25+ Treg cell precursors into Foxp3+ Treg cells accompanied by downregulation of interleukin 2 (IL-2)-STAT5 signaling. Deletion of POH1 in generated CD4+Foxp3+ Treg cells led to an early onset of fetal autoimmune disorders and a decrease in the pool size of peripheral Treg cells in mice, which were mostly due to decreased expansion of these cells. Thus, these results revealed that POH1 has a pivotal role in the development and maintenance of CD4+Foxp3+ Treg cells and contributes to immune tolerance.

POH1 contributes to hyperactivation of TGF-ß signaling and facilitates hepatocellular carcinoma metastasis through deubiquitinating TGF-ß receptors and caveolin-1.

BACKGROUND: Hyper-activation of TGF-ß signaling is critically involved in progression of hepatocellular carcinoma (HCC). However, the events that contribute to the dysregulation of TGF-ß pathway in HCC, especially at the post-translational level, are not well understood. METHODS: Associations of deubiquitinase POH1 with TGF-ß signaling activity and the outcomes of HCC patients were examined by data mining of online HCC datasets, immunohistochemistry analyses using human HCC specimens, spearman correlation and survival analyses. The effects of POH1 on the ubiquitination and stability of the TGF-ß receptors (TGFBR1 and TGFBR2) and the activation of downstream effectors were tested by western blotting. Primary mouse liver tissues from polyinosinic:polycytidylic acid (poly I:C)- treated Mx-Cre+, poh1f/f mice and control mice were used to detect the TGF-ß receptors. The metastatic-related capabilities of HCC cells were studied in vitro and in mice. FINDINGS: Here we show that POH1 is a critical regulator of TGF-ß signaling and promotes tumor metastasis. Integrative analyses of HCC subgroups classified with unsupervised transcriptome clustering of the TGF-ß response, metastatic potential and outcomes, reveal that POH1 expression positively correlates with activities of TGF-ß signaling in tumors and with malignant disease progression. Functionally, POH1 intensifies TGF-ß signaling delivery and, as a consequence, promotes HCC cell metastatic properties both in vitro and in vivo. The expression of the TGF-ß receptors was severely downregulated in POH1-deficient mouse hepatocytes. Mechanistically, POH1 deubiquitinates the TGF-ß receptors and CAV1, therefore negatively regulates lysosome pathway-mediated turnover of TGF-ß receptors. CONCLUSION: Our study highlights the pathological significance of aberrantly expressed POH1 in TGF-ß signaling hyperactivation and aggressive progression in HCC.

USP1 inhibition destabilizes KPNA2 and suppresses breast cancer metastasis.

Metastatic progression is the main cause of mortality in breast cancer, necessitating the determination of the molecular events driving this process for the development of new therapeutic approaches. Here, we demonstrate that hyperactivation of the deubiquitinase USP1 contributes to breast cancer metastasis. Upregulated USP1 expression in primary breast cancer specimens correlates with metastatic progression and poor prognosis in breast cancer patients. USP1 enhances the expression of a number of pro-metastatic genes in breast cancer cells, promotes cell migration and invasion in vitro, and facilitates lung metastasis of breast cancer cells. Moreover, USP1-mediated deubiquitination and stabilization of KPNA2 are revealed as the downstream events crucial for USP1-pro-metastatic function. Most importantly, pharmacological intervention of USP1 function by pimozide or ML323 significantly represses breast cancer metastasis in mice, suggesting a rationale for using USP1 inhibitors for treatment of patients with breast cancer. Taken together, our results establish USP1 as a promoter of breast cancer metastasis and provide evidence for the potential practice of USP1 targeting in the treatment of breast cancer.

POH1 deubiquitinates pro-interleukin-1ß and restricts inflammasome activity.

Inflammasome activation is essential for host defence against invading pathogens, but is also involved in various forms of inflammatory diseases. The processes that control inflammasome activity are thus important for averting excessive immune responses and tissue damage. Here we show that the deubiquitinase POH1 negatively regulates the immune response triggered by inflammasome activation. POH1 deficiency in macrophages enhances mature IL-1ß production without significant alterations in inflammasome priming and ASC-caspase-1 activation. In WT macrophages, POH1 interacts with and deubiquitinates pro-IL-1ß by decreasing the K63-linked polyubiquitin chains, as well as decreases the efficacy of pro-IL-1ß cleavage. Furthermore, myeloid cell-specific deletion of POH1 aggravates lipopolysaccharide-induced systemic inflammation and alum-induced peritonitis inflammatory responses in vivo. Our study thereby reveals that POH1-mediated deubiquitination of pro-IL-1ß is an important regulatory event that restrains inflammatory responses for the maintenance of immune homeostasis.

USP16 Downregulation by Carboxyl-terminal Truncated HBx Promotes the Growth of Hepatocellular Carcinoma Cells.

Hepatitis B virus (HBV) infection is a major factor that contributes to the development of hepatocellular carcinoma (HCC). HBV X protein (HBx) has been shown to accelerate HCC progression by promoting tumour growth and metastasis. In the clinic, carboxyl-terminal truncated HBx (Ct-HBx) proteins are frequently present in HCC tumour tissues, but not in non-tumorous tissues. In this study, we analysed deubiquitinase expression profiles in cells with or without ectopic expression of the Ct-HBx proteins and observed that the expression of ubiquitin specific peptidase 16 (USP16) was substantially inhibited by Ct-HBx proteins. Liver tumour cells with forced down-regulation of USP16 exhibited increased capabilities for colony formation and tumour growth in vivo. In addition, USP16 inhibition promoted stem-like properties in tumour cells, as evidenced by their spheroid formation and chemo-responsiveness. Furthermore, ectopic expression of USP16 in tumour cells significantly abrogated the tumour promoting activities of the Ct-HBx proteins (HBxΔ35), leading to decreased tumour cell viability and tumour growth. In human HCCs, USP16 was frequently downregulated, and the decreased expression of USP16 was correlated with high tumour stages and poor differentiation status. Taken together, our study suggests that USP16 downregulation is a critical event in Ct-HBx-mediated promotion of HCC tumorigenicity and malignancy.

Association of interleukin-12 gene polymorphisms with cancer susceptibility: a meta-analysis.

OBJECTIVE: To evaluate the association between interleukin-12 (IL-12) gene polymorphism and cervical cancer susceptibility. METHODS: We comprehensively retrieved the relevant English and Chinese database to collect case-control studies on the association between the IL-12 gene polymorphism and cervical cancer susceptibility. Data were extracted independently by two researchers respectively, the summary data were analyzed using Revman 5.2 software, the association was described using odds ratios (OR) and 95% confidence intervals (95% CI). RESULTS: According to inclusion and exclusion criteria, 5 case-control studies involving 2552 cervical cancer patients and 2232 healthy controls were included. The meta-analysis results showed that 3'UTR+1188 (rs3212227) polymorphism in IL-12 gene was not associated with cervical cancer risk (C vs. A: OR=1.09, 95% CI: 0.88~1.35, P=0.45; AA+AC vs. CC: OR=0.88, 95% CI: 0.67~1.15, P=0.34; AA vs. AC+CC: OR=0.89. 95% CI: 0.56-1.42, P=0.62; CC vs. AA: OR=1.30. 95% CI: 0.79-2.12, P=0.30). CONCLUSION: The available evidence suggested that rs3212227 polymorphism in IL-12 gene may not be the risk factor to cervical cancer.

POH1 deubiquitylates and stabilizes E2F1 to promote tumour formation.

Hyperactivation of the transcriptional factor E2F1 occurs frequently in human cancers and contributes to malignant progression. E2F1 activity is regulated by proteolysis mediated by the ubiquitin-proteasome system. However, the deubiquitylase that controls E2F1 ubiquitylation and stability remains undefined. Here we demonstrate that the deubiquitylase POH1 stabilizes E2F1 protein through binding to and deubiquitylating E2F1. Conditional knockout of Poh1 alleles results in reduced E2F1 expression in primary mouse liver cells. The POH1-mediated regulation of E2F1 expression strengthens E2F1-downstream prosurvival signals, including upregulation of Survivin and FOXM1 protein levels, and efficiently facilitates tumour growth of liver cancer cells in nude mice. Importantly, human hepatocellular carcinomas (HCCs) recapitulate POH1 regulation of E2F1 expression, as nuclear abundance of POH1 is increased in HCCs and correlates with E2F1 overexpression and tumour growth. Thus, our study suggests that the hyperactivated POH1-E2F1 regulation may contribute to the development of liver cancer.