Hip2 interacts with cyclin B1 and promotes its degradation through the ubiquitin proteasome pathway

Silencing UBE2K inhibits the growth of glioma cells by inducing the autophagy-related apoptosis

Glioma is a central nervous system (CNS) malignant tumor with high heterogeneity and mortality, which severely threatens the health of patients. The overall survival of glioma patients is relatively short and it is critical to identify new molecular targets for developing effective treatment strategies. UBE2K is a ubiquitin conjugating enzyme with oncogenic function in several malignant tumors. However, whether UBE2K participates in gliomas remains unknown. Herein, in glioma cells, UBE2K was found highly expressed in U87 and U251 cells. Subsequently, U87 and U251 cells were transfected with si-UBE2K to silence UBE2K, with the si-NC transfection as the negative control. In both U87 and U251 cells, the cell viability was sharply reduced by transfecting si-UBE2K for 48 and 72 h. Markedly decreased colony number, reduced number of migrated cells and invaded cells, and declined relative wound healing rate were observed in si-UBE2K transfected U87 and U251 cells. Moreover, the Bcl-2 level was markedly reduced, while the Bax and cleaved-caspase-3 levels were sharply increased in U87 and U251 cells after the si-UBE2K transfection. Furthermore, the p62 level was signally declined, while the Beclin-1 and LC-3 II/I levels were greatly increased in U87 and U251 cells by the si-UBE2K transfection. Furthermore, the facilitating effect of si-UBE2K on the apoptosis and autophagy in U87 and U251 cells was abolished by the coculture of 3-MA, an inhibitor of autophagy. Collectively, UBE2K facilitated the in vitro growth of glioma cells, possibly by inhibiting the autophagy-related apoptosis, which might be a promising target for treating glioma.

Cockayne syndrome group A protein localizes at centrosomes during mitosis and regulates Cyclin B1 ubiquitination

Mutations in CSA and CSB proteins cause Cockayne syndrome, a rare genetic neurodevelopment disorder. Alongside their demonstrated roles in DNA repair and transcription, these two proteins have recently been discovered to regulate cytokinesis, the final stage of the cell division. This last finding allowed, for the first time, to highlight an extranuclear localization of CS proteins, beyond the one already known at mitochondria. In this study, we demonstrated an additional role for CSA protein being recruited at centrosomes in a strictly determined step of mitosis, which ranges from pro-metaphase until metaphase exit. Centrosomal CSA exerts its function in specifically targeting the pool of centrosomal Cyclin B1 for ubiquitination and proteasomal degradation. Interestingly, a lack of CSA recruitment at centrosomes does not affect Cyclin B1 centrosomal localization but, instead, it causes its lasting centrosomal permanence, thus inducing Caspase 3 activation and apoptosis. The discovery of this unveiled before CSA recruitment at centrosomes opens a new and promising scenario for the understanding of some of the complex and different clinical aspects of Cockayne Syndrome.

Mechanistic Insights of NAC1 Nuclear Export and Its Role in Ovarian Cancer Resistance to Docetaxel

In this study, we uncovered the nuclear export of nucleus accumbens-associated protein-1 (NAC1) as a novel mechanism involved in ovarian cancer resistance to taxanes, the chemotherapeutic drugs commonly used in treatment of this malignancy. We showed that NAC1, a nuclear factor of the BTB/POZ gene family, has a nuclear export signal (NES) at the N terminus (aa 17-28), and this NES critically contributes to the NAC1 nuclear-cytoplasmic shuttling when tumor cells were treated with docetaxel. Mechanistically, the nuclear-exported NAC1 bound to cullin3 (Cul3) and Cyclin B1 via its BTB and BOZ domains respectively, and the cyto-NAC1-Cul3 E3 ubiquitin ligase complex promotes the ubiquitination and degradation of Cyclin B1, thereby facilitating mitotic exit and leading to cellular resistance to docetaxel. We also showed in in vitro and in vivo experiments that TP-CH-1178, a membrane-permeable polypeptide against the NAC1 NES motif, blocked the nuclear export of NAC1, interfered with the degradation of Cyclin B1 and sensitized ovarian cancer cells to docetaxel. This study not only reveals a novel mechanism by which the NAC1 nuclear export is regulated and Cyclin B1 degradation and mitotic exit are impacted by the NAC1-Cul3 complex, but also provides the nuclear-export pathway of NAC1 as a potential target for modulating taxanes resistance in ovarian cancer and other malignancies.

Hypoxia-induced UBE2K promotes the malignant progression of HCC

BACKGROUND

Hypoxia critically drives malignant tumor development and is characteristic of hepatocellular carcinoma (HCC), where HIF-1α plays a crucial role. The ubiquitin-conjugating enzyme E2K (UBE2K) is known to participate in the advancement of several human cancers. However, the role of UBE2K in HCC or whether it is a hypoxia-responsive gene remains to be further identified.

METHOD

We performed a microarray to measure the gene expression differences between normoxia and hypoxia. CoCl2 mimicked the hypoxic condition. The protein and RNA expression of HIF-1α, UBE2K, and Actin in HCC cells were measured by western blotting(WB) and RT-qPCR, respectively. Immunohistochemical (IHC) staining analyzed the expression of UBE2K and HIF-1α in HCC tissues. CCK-8 and colony formation assay evaluated the HCC cell growth. Scratch healing and transwell assays were used to detect the migration capability of the cells. Lipofectamine 3000 was used to transfect the plasmids or siRNAs to HCC cells.

RESULTS

We identified UBE2K as a potential hypoxia-responsive gene. Our study showed that hypoxia induced HIF-1α-mediated increase of UBE2K levels in HCC cells, which decreased under HIF-1α deficiency under hypoxia. Further bioinformatics analysis based on UALCAN and GEPIA databases confirmed that UBE2K was highly expressed in HCC tissues and positively associated with HIF-1α expression. Functionally, Hep3B and Huh7 cell proliferation and migration were stimulated upon UBE2K overexpression, while the UBE2K knockdown suppressed such effect. Furthermore, functional rescue experiment proved that depletion of UBE2K inhibited hypoxia-induced cell proliferation and migration in HCC cells. In contrast, enhancing UBE2K levels rescued cell proliferation and migration repression caused by HIF-1α deficiency in hypoxia.

CONCLUSION

Our results established UBE2K as a potential hypoxia-inducible gene in HCC cells, positively regulated by HIF-1α in hypoxia. Moreover, UBE2K served as an oncogene and cooperated with HIF-1α to form a functional HIF-1α/UBE2K axis to trigger HCC progression, highlighting a potential application of UBE2K as a therapeutic target for HCC treatment.

UBE2K promotes the malignant progression of hepatocellular carcinoma by regulating c-Myc

Hepatocellular carcinoma (HCC) is a serious threat to human health and life due to its high morbidity and mortality. Ubiquitin-conjugating enzymes are players in the ubiquitin proteasome system and are responsible for a great number of physiological activities in cells. The action of ubiquitin-conjugating enzyme UBE2K in HCC has not been reported. Therefore, we studied the function and role of UBE2K in the malignant progression of HCC. An analysis of UBE2K expression in HCC cells was performed using RT-qPCR and protein immunoblotting. CCK-8, Transwell and sphere formation assays were used to identify the potential effects of UBE2K in HCC cell proliferation, migration and stemness property. RT-qPCR, and protein immunoblotting experiments was taken to explore the regulation between UBE2K and c-Myc. Here, we discovered that UBE2K expression was elevated in HCC cells, and elevated UBE2K predicts worse prognosis for HCC patients. Functionally, UBE2K promote, while UBE2K knockdown suppressed cell proliferation, migration and stemness property of HCC cells. Furthermore, c-Myc was identified as a downstream target of UBE2K. Moreover, functional rescue experiments finally proved that UBE2K facilitates the malignant progression of HCC cells by upregulating c-Myc. We clarified through in vivo experiments that UBE2K expression promotes tumor growth in HCC. Taken together, our study results proved the molecular regulation of UBE2K and c-Myc in HCC and the oncogenic role of UBE2K/c-Myc axis in HCC progression, thus it provides a promising molecular target for the diagnosis and treatment of HCC.

Reduction of Hip2 suppresses gastric cancer cell proliferation, migration, invasion and tumorigenesis

BACKGROUND

Hip2, a ubiquitin-conjugating enzyme, has been shown to modulate the stability of cyclin B1, a cell cycle regulator. However, the function of Hip2 in gastric cancer (GC) remains largely elusive.

METHODS

The expression of Hip2 in GC cell lines was analyzed by RT-qPCR, Western Blotting and Immunohistochemical Staining. shRNA was utilized to knock down the expression of Hip2. Cell growth, cell cycle, migration, invasion and tumorigenesis were performed by CCK-8, BrdU staining, flow cytometry, wound healing, transwell migration and invasion, and xenograft assay, respectively.

RESULTS

Hip2 was highly expressed in GC cell lines and patients. High level of Hip2 indicated poor prognosis. Knockdown of Hip2 suppressed cell growth, lead to G2/M phase arrest, and reduced cell migration and invasion in vitro. Furthermore, downregulation of Hip2 inhibited tumorigenesis in vivo.

CONCLUSIONS

Elevated expression of HIP2 in GC patients suggested poor prognosis. Reduction of Hip2 suppressed GC progression, indicating that Hip2 may be a potential target for the management of GC.

Hip2 ubiquitin-conjugating enzyme has a role in UV-induced G1/S arrest and re-entry

Regulation of cell cycle arrest and re-entry triggered by DNA damage is vital for cell division and growth and is also involved in cell survival. UV radiation can generate lesions in the DNA, which results in cell cycle arrest and the induction of the DNA repair process. However, the mechanism of promoting cell cycle progression following DNA repair is elusive. The primary aim of this study is to investigate whether Hip2 ubiquitin-conjugating enzyme has a role in UV-induced G1/S arrest and re-entry. The phase of HEK293 cells was synchronized at the G1/S border using thymidine. The synchronously proliferating cells were exposed to UV radiation to cause DNA damage. We investigated the expression of p53, Hip2, p21, cyclin D and E proteins that are involved in the cell cycle progression. Finally, we examined changes in the phosphorylation of Hip2 after UV radiation treatment using the pIMAGO™ assay. When cells were exposed to UV radiation, expression of p53 was elevated, and the cell cycle was arrested at the G1/S boundary. In response to the increased p53 level, Hip2 became phosphorylated and activated through the inhibition of its degradation. The phosphorylated Hip2 inhibited p53, thereby suppressing the expression of p21, a downstream signal, and sequentially stimulating cyclin D and cyclin E to induce re-entry to the cell cycle. Our studies demonstrate that Hip2 works as a regulator in UV-induced cell cycle arrest and re-entry.

C6orf106 is a novel inhibitor of the interferon-regulatory factor 3-dependent innate antiviral response

Host recognition of intracellular viral RNA and subsequent induction of cytokine signaling are tightly regulated at the cellular level and are a target for manipulation by viruses and therapeutics alike. Here, we characterize chromosome 6 ORF 106 (C6orf106) as an evolutionarily conserved inhibitor of the innate antiviral response. C6orf106 suppresses the synthesis of interferon (IFN)-α/β and proinflammatory tumor necrosis factor (TNF) α in response to the dsRNA mimic poly(I:C) and to Sendai virus infection. Unlike canonical inhibitors of antiviral signaling, C6orf106 blocks interferon-regulatory factor 3 (IRF3) and, to a lesser extent, NF-κB activity without modulating their activation, nuclear translocation, cellular expression, or degradation. Instead, C6orf106 interacts with IRF3 and inhibits IRF3 recruitment to type I IFN promoter sequences while also reducing the nuclear levels of the coactivator proteins p300 and CREB-binding protein (CBP). In summary, we have defined C6orf106 as a negative regulator of antiviral immunity that blocks IRF3-dependent cytokine production via a noncanonical and poorly defined mechanism. This work presents intriguing implications for antiviral immunity, autoimmune disorders, and cancer.

Ataxin-1 is involved in tumorigenesis of cervical cancer cells via the EGFR-RAS-MAPK signaling pathway

Ataxin-1 (ATXN1) is a coregulator protein within which expansion of the polyglutamine tract causes spinocerebellar ataxia type 1, an autosomal dominant neurodegenerative disorder. Previously, we reported that ATXN1 regulates the epithelial–mesenchymal transition of cervical cancer cells. In the present study, we demonstrate that ATXN1 is involved in cervical cancer tumorigenesis by promoting the proliferation of human cervical cancer cells. Chromatin immunoprecipitation assays showed that ATXN1 bound to the promoter region within cyclin D1 and activated cyclin D1 transcription, resulting in cell proliferation. ATXN1 promoted cyclin D1 expression through the EGFR–RAS–MAPK signaling pathway. Mouse xenograft tumorigenicity assays showed that ATXN1 downregulation inhibited tumorigenesis in cervical cancer cell lines in nude mice. Human cervical cancer tissue microarrays and immunohistochemical techniques showed that ATXN1 was significantly upregulated in many such tissues. Our results suggest that ATXN1 plays an important role in cervical cancer tumorigenesis and is a prognostic marker for cervical cancer.

Activity of cyclin B1 in HL-60 cells treated with etoposide

Cyclin B1 triggers G2/M phase transition phosphorylating with its catalytical partner - Cdc2 many of the molecular targets essential for cell cycle progression. Human leukemia cell line HL-60 were treated with increasing doses of etoposide (ETP) (0.5; 0.75; 1μM) to investigate how the drug affects cell morphology, viability, cell cycle distribution and expression of cyclin B1. To achieve this aim we applied light and transmission electron microscopy to observe morphological and ultra structural changes, image-based cytometry for apoptosis evaluation and cell cycle analysis, and then we conducted immunohistochemical and immunofluorescence staining to visualize cyclin localization and expression. Quantitive data about cyclin B1 expression were obtained from flow cytometry. Etoposide caused decrease in cell viability, induced apoptosis and G2/M arrest accompanied by enhanced expression of cyclin B1. Changes in expression and localization of cyclin B1 may constitute a part of the mechanism responsible for resistance of HL-60 cells to etoposide. Our results may reflect involvement of cyclin B1 in opposite processes - apoptosis induction and maintenance of cell viability in leukemia cells. We hypothesized possible roles and pathways by which cyclin B1 takes part in drug treatment response and chemosensitivity.

USP22 promotes the G1/S phase transition by upregulating FoxM1 expression via β-catenin nuclear localization and is associated with poor prognosis in stage II pancreatic ductal adenocarcinoma

Ubiquitin-specific protease 22 (USP22), a newly discovered member of ubiquitin hydrolase family, exhibits a critical function in cell cycle progression and tumorigenesis. The forkhead box M1 (FoxM1) transcription factor plays a crucial role in cell proliferation, differentiation and transformation. However, the expression and functions of USP22 in pancreatic ductal adenocarcinoma (PDA) and whether FoxM1 is involved in USP22-mediated cell cycle regulation have not been studied. We examined the expression of USP22 and FoxM1 in 136 stage II PDA tissues by immunohistochemistry. Clinical significance was analyzed by multivariate Cox regression analysis, Kaplan-Meier curves and log-rank test. RT-PCR, western blot analysis, luciferase and immunofluorescence assays were used to investigate the molecular function of USP22 and FoxM1 in PDA fresh tissues and cell lines. USP22 and FoxM1 were significantly upregulated in PDA tissues compared with the paired normal carcinoma-adjacent tissues. A statistical correlation was observed between USP22 and FoxM1 expression. The expression of USP/FoxM1 and co-expression of both factors correlated with tumor size, lymph node metastasis and overall survival. Multivariate Cox regression analysis revealed that the expression of USP22/FoxM1, especially the co-expression of both factors, is an independent, unfavorable prognostic factor. USP22 overexpression is accompanied by an increase in FoxM1 expression and USP22 increases FoxM1 expression to promote G1/S transition and cell proliferation through promoting β-catenin nuclear translocation in PDA cell lines. USP22 promotes the G1/S phase transition by upregulating FoxM1 expression via promoting β-catenin nuclear localization. USP22 and FoxM1 may act as prognostic markers and potential targets for PDA.

Hip2 ubiquitin-conjugating enzyme overcomes radiation-induced G2/M arrest

Radiation induces cell cycle arrest and/or cell death in mammalian cells. In the present study, we show that Hip2, a ubiquitin-conjugating enzyme, can overcome radiation-induced G2/M cell cycle arrest and trigger the entry into mitosis. Ionizing radiation increased the levels of Hip2 by preventing its degradation but not its gene transcription. The stability of Hip2 in irradiated cells was further confirmed using live cell fluorescence imaging. Flow cytometric and molecular analyses revealed that Hip2 abrogated radiation-induced G2/M arrest, promoting entry into mitosis. Bimolecular fluorescence complementation assays and co-immunoprecipitation experiments showed that Hip2 interacted with and targeted p53 for degradation via the ubiquitin proteasome system, resulting in the activation of cdc2-cyclin B1 kinase to promote mitotic entry. These results contribute to our understanding of the mechanisms that regulate cell cycle progression and DNA damage-induced G2/M checkpoint cellular responses.