Targeting the ubiquitin-proteasome system to activate wild-type p53 for cancer therapy

Tripartite motif 8 promotes the progression of hepatocellular carcinoma via mediating ubiquitination of HNF1α

Tripartite motif 8 (TRIM8) is an E3 ligase that plays dual roles in various tumor types. The biological effects and underlying mechanism of TRIM8 in hepatocellular carcinoma (HCC) remain unknown. Hepatocyte nuclear factor 1α (HNF1α) is a key transcriptional factor that plays a significant role in regulating hepatocyte differentiation and liver function. The reduced expression of HNF1α is a critical event in the development of HCC, but the underlying mechanism for its degradation remains elusive. In this study, we discovered that the expression of TRIM8 was upregulated in HCC tissues, and was positively correlated with aggressive tumor behavior of HCC and shorter survival of HCC patients. Overexpression of TRIM8 promoted the proliferation, colony formation, invasion, and migration of HCC cells, while TRIM8 knockdown or knockout exerted the opposite effects. RNA sequencing revealed that TRIM8 knockout suppresses several cancer-related pathways, including Wnt/β-catenin and TGF-β signaling in HepG2 cells. TRIM8 directly interacts with HNF1α, promoting its degradation by catalyzing polyubiquitination on lysine 197 in HCC cells. Moreover, the cancer-promoting effects of TRIM8 in HCC were abolished by the HNF1α-K197R mutant in vitro and in vivo. These data demonstrated that TRIM8 plays an oncogenic role in HCC progression through mediating the ubiquitination of HNF1α and promoting its protein degradation, and suggests targeting TRIM8-HNF1α may provide a promising therapeutic strategy of HCC.

MARCH5 promotes hepatocellular carcinoma progression by inducing p53 ubiquitination degradation

BACKGROUND

Human MARCH5 is a mitochondria-localized E3 ubiquitin-protein ligase that is essential for the regulation of mitochondrial dynamics. A large body of evidence suggests that imbalances in mitochondrial dynamics are strongly associated with cancer. However, the expression, biological function and prognostic significance of MARCH5 in hepatocellular carcinoma (HCC) have not been determined.

MATERIALS AND METHODS

The mRNA and protein expression of MARCH5 in HCC cell lines and tumor tissues was assessed by real-time quantitative PCR, Western blot analysis and immunohistochemistry. The clinical prognostic significance of MARCH5 was evaluated in 135 HCC patients. Knockdown or overexpression of MARCH5 in HCC cells was determined by in vitro cell proliferation, migration and invasion assays, and in vivo tumor growth and metastasis assays. In addition, the intrinsic mechanisms by which MARCH5 regulates HCC cell growth and metastasis were explored.

RESULTS

MARCH5 was significantly overexpressed in HCC cells and was closely associated with patients' poor postoperative prognosis. In vivo and in vitro experiments revealed that MARCH5 significantly promoted the increase and invasive and migratory ability of hepatocellular carcinoma cells, which was mainly due to the promotion of autophagy by MARCH5. Mechanistic studies revealed that MARCH5 promoted autophagy through ubiquitination degradation of p53 leading to malignant progression of hepatocellular carcinoma.

CONCLUSION

Our findings suggest that MARCH5 plays a critical oncogenic role in HCC cells, which provides experimental evidence for the use of MARCH5 as a potential target for HCC therapy.

IL-13/IL-13RA2 signaling promotes colorectal cancer stem cell tumorigenesis by inducing ubiquitinated degradation of p53

Cancer stem cells (CSCs) are considered tumor-initiating cells and the main drivers of disease progression. Targeting these rare cancer cells, however, remains challenging with respect to therapeutic benefit. Here, we report the up-regulation of IL-13RA2 expression in colorectal cancer (CRC) tissues and spheroid cells. The expression of IL-13RA2 was positively correlated with canonical stemness markers in CRC. We further demonstrated that the level of IL-13 was up-regulated in the serum of CRC patients. Biologically, recombinant IL-13 (rIL-13) stimulation promoted the sphere formation, proliferation, and migration of CRC cells in vitro and enhanced tumorigenesis in vivo. This phenotype could be reversed by knocking down IL-13RA2. Mechanistically, IL-13 activated autophagy by inducing LC3I/LC3II transformation in CRC-CSCs, which was crucial for the biological functions of IL-13. We further demonstrated that IL-13RA2 acted as a modular link of the E3 ligase UBE3C and the substrate p53 protein, enhancing the interaction of UBE3C and p53, thereby inducing the K48-linked ubiquitination of p53. In conclusion, the IL-13/IL-13RA2 signaling cascade promotes CRC-CSC self-renewal and tumorigenesis by inducing p53 ubiquitination, adding an important layer to the connection between IL-13 and p53, which can be translated into novel targeted therapies.

Senataxin and R-loops homeostasis: multifaced implications in carcinogenesis

R-loops are inherent byproducts of transcription consisting of an RNA:DNA hybrid and a displaced single-stranded DNA. These structures are of key importance in controlling numerous physiological processes and their homeostasis is tightly controlled by the activities of several enzymes deputed to process R-loops and prevent their unproper accumulation. Senataxin (SETX) is an RNA/DNA helicase which catalyzes the unwinding of RNA:DNA hybrid portion of the R-loops, promoting thus their resolution. The key importance of SETX in R-loops homeostasis and its relevance with pathophysiological events is highlighted by the evidence that gain or loss of function SETX mutations underlie the pathogenesis of two distinct neurological disorders. Here, we aim to describe the potential impact of SETX on tumor onset and progression, trying to emphasize how dysregulation of this enzyme observed in human tumors might impact tumorigenesis. To this aim, we will describe the functional relevance of SETX in regulating gene expression, genome integrity, and inflammation response and discuss how cancer-associated SETX mutations might affect these pathways, contributing thus to tumor development.

p53 ubiquitination co-mediated by HUWE1 and TRAF6 contributes to WSSV infection in crustacean

p53, the guardian of the genome, is a short-lived protein that is tightly controlled at low levels by constant ubiquitination and proteasomal degradation in higher organisms. p53 stabilization and activation are early crucial events to cope with external stimuli in cells. However, the role of p53 ubiquitination and its relevant molecular mechanisms have not been addressed in invertebrates. In this study, our findings revealed that both HUWE1 (HECT, UBA, and WWE domain-containing E3 ubiquitin-protein ligase 1) and TRAF6 (tumor necrosis factor receptor-associated factor 6) could serve as E3 ubiquitin ligases for p53 in mud crabs (Scylla paramamosain). Moreover, the expression of HUWE1 and TRAF6 was significantly downregulated during white spot syndrome virus (WSSV) infection, and therefore the ubiquitination of p53 was interrupted, leading to the activation of apoptosis and reactive oxygen species (ROS) signals through p53 accumulation, which eventually suppressed viral invasion in the mud crabs. To the best of our knowledge, this is the first study to reveal the p53 ubiquitination simultaneously induced by two E3 ligases in arthropods, which provides a novel molecular mechanism of invertebrates for resistance to viral infection.

IMPORTANCE p53, which is a well-known tumor suppressor that has been widely studied in higher animals, has been reported to be tightly controlled at low levels by ubiquitin-dependent proteasomal degradation. However, recent p53 ubiquitination-relevant research mainly involved an individual E3 ubiquitin ligase, but not whether there exist other mechanisms that need to be explored. The results of this study show that HUWE1 and TRAF6 could serve as p53 E3 ubiquitin ligases and synchronously mediate p53 ubiquitination in mud crabs (Scylla paramamosain), which confirmed the diversity of the p53 ubiquitination regulatory pathway. In addition, the effects of p53 ubiquitination are mainly focused on tumorigenesis, but a few are focused on the host immune defense in invertebrates. Our findings reveal that p53 ubiquitination could affect ROS and apoptosis signals to cope with WSSV infection in mud crabs, which is the first clarification of the immunologic functions and mechanisms of p53 ubiquitination in invertebrates.

NEDD4 E3 ubiquitin protein ligase serves an important role in cutaneous melanoma occurrence and development

The present study aimed to discuss the effects and relative mechanisms of NEDD4 E3 ubiquitin protein ligase (NEDD4) in cutaneous melanoma (CMM) occurrence and development. Clinical cancer and adjacent normal tissues samples were collected to analyze pathological changes and protein expression of NEDD4. Moreover, small interfering (si)RNA was used to knockdown NEDD4 expression in SK-MEL-2 and Malme-3M cells. Cellular proliferation, apoptosis, invasiveness and migration were examined using colony formation, flow cytometric, Transwell and wound-healing assays, respectively. In addition, the relative mRNA and protein expression levels of NEDD4, notch receptor 1 (Notch1) and PTEN were evaluated via reverse transcription-quantitative (RT-q) PCR and western blotting. It was found that NEDD4 mRNA and protein expression were significantly upregulated (both P<0.01). Following NEDD4-knockdown, colony number was significantly decreased, while the apoptotic rate was significantly increased, the invasive cell number was significantly inhibited and the wound-healing capacity was significantly decreased. Following si-NEDD4 transfection, RT-qPCR and western blotting revealed that NEDD4 and Notch1 mRNA and protein expression levels were significantly downregulated, while those of PTEN were significantly upregulated in the SK-MEL-2 and Malme-3M cell lines. Collectively, the current results suggest that NEDD4-knockdown effectively suppressed CMM biological activity by regulating the Notch1/PTEN pathway in vitro.

Identification of ubiquitination-related genes in human glioma as indicators of patient prognosis

Ubiquitination is a dynamic and reversible process of a specific modification of target proteins catalyzed by a series of ubiquitination enzymes. Because of the extensive range of substrates, ubiquitination plays a crucial role in the localization, metabolism, regulation, and degradation of proteins. Although the treatment of glioma has been improved, the survival rate of patients is still not satisfactory. Therefore, we explore the role of ubiquitin proteasome in glioma. Survival-related ubiquitination related genes (URGs) were obtained through analysis of the Genotype-Tissue Expression (GTEx) and the Cancer Genome Atlas (TCGA). Cox analysis was performed to construct risk model. The accuracy of risk model is verified by survival, Receiver operating characteristic (ROC) and Cox analysis. We obtained 36 differentially expressed URGs and found that 25 URGs were related to patient prognosis. We used the 25 URGs to construct a model containing 8 URGs to predict glioma patient risk by Cox analysis. ROC showed that the accuracy rate of this model is 85.3%. Cox analysis found that this model can be used as an independent prognostic factor. We also found that this model is related to molecular typing markers. Patients in the high-risk group were enriched in multiple tumor-related signaling pathways. In addition, we predicted TFs that may regulate the risk model URGs and found that the risk model is related to B cells, CD4 T cells, and neutrophils.

Overexpression of ubiquitin-specific peptidase 15 in systemic sclerosis fibroblasts increases response to transforming growth factor β

Objective

Ubiquitination of proteins leads to their degradation by the proteasome, and is regulated by ubiquitin ligases and substrate-specific ubiquitin-specific peptidases (USPs). The ubiquitination process also plays important roles in the regulation of cell metabolism and cell cycle. Here, we found that the expression of several USPs is increased in SSc tenosynovial and skin biopsies, and we demonstrated that USP inhibition decreases TGF-β signalling in primary fibroblast cell lines.

Methods

High-density transcriptomic studies were performed using total RNA obtained from SSc tenosynovial samples. Confirmatory immunostaining experiments were performed on tenosynovial and skin samples. In vitro experiments were conducted in order to study the influence of USP modulation on responses to TGF-β stimulation.

Results

Tenosynovial biopsies from SSc patients overexpressed known disease-associated gene pathways: fibrosis, cytokines and chemokines, and Wnt/TGF-β signalling, but also several USPs. Immunohistochemistry experiments confirmed the detection of USPs in the same samples, and in SSc skin biopsies. Exposure of primary fibroblast cell lines to TGF-β induced USP gene expression. The use of a pan-USP inhibitor decreased SMAD3 phosphorylation, and expression of COL1A1, COL3A1 and fibronectin gene expression in TGF-β-stimulated fibroblasts. The effect of the USP inhibitor resulted in increased SMAD3 ubiquitination, and was blocked by a proteasome inhibitor, thereby confirming the specificity of its action.

Conclusion

Overexpression of several USPs, including USP15, amplifies fibrotic responses induced by TGF-β, and is a potential therapeutic target in SSc.

Inhibition of Ubiquitin-Specific Protease 14 Suppresses Cell Proliferation and Synergizes with Chemotherapeutic Agents in Neuroblastoma

Neuroblastoma is the most common extracranial malignant solid tumor in children, and drug resistance is a major reason for poor outcomes. Elevated proteasome activity plays an important role in neuroblastoma tumor development and resistance to conventional chemotherapy. Ubiquitin-specific protease 14 (USP14), one of three deubiquitinases associated with the regulatory subunit of the proteasome, is emerging as a potential therapeutic target in multiple tumor types. However, the role of USP14 in neuroblastoma is yet to be elucidated. We found that USP14 inhibition in neuroblastoma via knockdown or a specific inhibitor such as b-AP15 suppressed cell proliferation by inducing cell apoptosis. Furthermore, b-AP15 significantly inhibited neuroblastoma tumor growth in NGP and SH-SY5Y xenograft mouse models. For combination treatment, b-AP15 plus conventional chemotherapeutic agents such as doxorubicin or VP-16 resulted in synergistic antitumor effects on neuroblastoma. Our study demonstrates that USP14 is required for cell viability and is a novel therapeutic target in neuroblastoma. Moreover, USP14 inhibition may add value in combination therapy due to its powerful synergistic effects in treating neuroblastoma.

Suppression of the Ubiquitin Pathway by Small Molecule Binding to Ubiquitin Enhances Doxorubicin Sensitivity of the Cancer Cells

Development of inhibitors for ubiquitin pathway has been suggested as a promising strategy to treat several types of cancers, which has been showcased by recent success of a series of novel anticancer drugs based on inhibition of ubiquitin pathways. Although the druggability of enzymes in ubiquitin pathways has been demonstrated, ubiquitin itself, the main agent of the pathway, has not been targeted. Whereas conventional enzyme inhibitors are used to silence the ubiquitination or reverse it, they cannot disrupt the binding activity of ubiquitin. Herein, we report that the scaffolds of sulfonated aryl diazo compounds, particularly Congo red, could disrupt the binding activity of ubiquitin, resulting in the activity equivalent to inhibition of ubiquitination. NMR mapping assay demonstrated that the chemical directly binds to the recognition site for ubiquitin processing enzymes on the surface of ubiquitin, and thereby blocks the binding of ubiquitin to its cognate receptors. As a proof of concept for the druggability of the ubiquitin molecule, we demonstrated that Congo red acted as an intracellular inhibitor of ubiquitin recognition and binding, which led to inhibition of ubiquitination, and thereby, could be used as a sensitizer for conventional anticancer drugs, doxorubicin.

Regulation of Organic Anion Transporting Polypeptides (OATP) 1B1- and OATP1B3-Mediated Transport: An Updated Review in the Context of OATP-Mediated Drug-Drug Interactions

Organic anion transporting polypeptides (OATP) 1B1 and OATP1B3 are important hepatic transporters that mediate the uptake of many clinically important drugs, including statins from the blood into the liver. Reduced transport function of OATP1B1 and OATP1B3 can lead to clinically relevant drug-drug interactions (DDIs). Considering the importance of OATP1B1 and OATP1B3 in hepatic drug disposition, substantial efforts have been given on evaluating OATP1B1/1B3-mediated DDIs in order to avoid unwanted adverse effects of drugs that are OATP substrates due to their altered pharmacokinetics. Growing evidences suggest that the transport function of OATP1B1 and OATP1B3 can be regulated at various levels such as genetic variation, transcriptional and post-translational regulation. The present review summarizes the up to date information on the regulation of OATP1B1 and OATP1B3 transport function at different levels with a focus on potential impact on OATP-mediated DDIs.

Overexpression of ubiquitin specific proteases 44 promotes the malignancy of glioma by stabilizing tumor-promoter securin

Ubiquitin specific peptidase 44 (USP44) has been identified as an important component of spindle assemble checkpoint (SAC) to prevent the formation of aneuploidy. However, recent study raised a controversy about the effect of USP44 in tumor. Here, we first confirmed the intranuclear localization of USP44 by testing several specific antibodies to recognize endogenous USP44. Then, data from IHC and qRT-PCR assay indicated that the high expression of USP44 existed in high-grade glioma tissues and signified a poor prognosis. Knockdown of USP44 inhibited proliferation, migration and invasion, induced apoptosis, and arrested cell cycle in G2/M phase in the established glioma cell lines. Down-regulation of oncoprotein securin was detected in USP44 deficient cells, and the interaction of endogenous USP44 and securin was confirmed by immunoprecipitation in U251MG cells, which indicated that securin was a substrate of USP44, and might be stabilized by USP44. In vivo, knockdown of USP44 inhibited the tumorigenicity of U87MG cells significantly. Consequently, our findings suggested that overexpression of USP44 could enhance the malignancy of glioma via securin. USP44 might serve as a predictive biomarker, and the USP44-securin pathway might provide a new therapeutic strategy for the treatment of glioma.

miR-100 antagonism triggers apoptosis by inhibiting ubiquitination-mediated p53 degradation

During tumourigenesis, p53 functions as 'the guardian of the genome' because p53-dependent apoptosis strongly regulates the fate of cancer cells. Therefore, p53 regulation must be sensitive and accurate. p53 activity is regulated through its ubiquitination and deubiquitination. However, the role of microRNA in ubiquitin-mediated p53 degradation has not been previously studied. Our previous studies indicated that miR-100 is required for apoptosis. In the current study, the mechanism of p53 protein ubiquitination mediated by miR-100 was characterized. An analysis of primary tumour samples from gastric cancer patients showed a significant correlation between miR-100 upregulation and primary human gastric tumourigenesis and progression. The in vivo and in vitro data indicated that miR-100 antagonism specifically induced the apoptosis of poorly differentiated gastric cancer cells but not non-cancerous gastric cells, indicating that miR-100 has a crucial role in regulating the progression of gastric tumours. In the regulation of p53-dependent apoptosis, miR-100 antagonism inhibited ubiquitin-mediated p53 protein degradation by activating RNF144B, an E3 ubiquitination ligase. Consequently, the miR-100-RNF144B-pirh2-p53-dependent pathway was initiated. Our findings highlight a novel mechanism of ubiquitin-mediated p53 protein degradation in apoptosis.

Ubiquitin-protein ligase E3C promotes glioma progression by mediating the ubiquitination and degrading of Annexin A7

The ubiquitin-protein ligase E3C (UBE3C) belongs to the E3 ligase enzyme family and implicates in the ubiquitin-proteasome pathway, thus regulates physiological and cancer-related processes. Here, we investigated the expression and roles of UBE3C in glioma. We demonstrated that UBE3C was overexpressed in glioma tissues and cell lines. Inhibition of UBE3C expression in glioma cells significantly decreased cell migration and invasion in vitro. Mechanistically, we disclosed that UBE3C physically interacted with and ubiquitinated tumor suppressor gene annexin A7 (ANXA7), resulting in ubiquitination and degradation of ANXA7. Our results also revealed that increased UBE3C expression was accompanied by a reduction in ANXA7 protein expression in glioma tissues, but not ANXA7 mRNA. Importantly, the inhibition of ANXA7 expression in gliomas cells with UBE3C interference could rescue the cell invasion. Clinically, UBE3C overexpression significantly correlated with high-grade tumors (p < 0.05), poor overall survival, and early tumor recurrence. Thus, our data reveal that high UBE3C expression contributes to glioma progression by ubiquitination and degradation of ANXA7, and thus presents a novel and promising target for glioma therapy.

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.

p53 abnormalities and potential therapeutic targeting in multiple myeloma

p53 abnormalities are regarded as an independent prognostic marker in multiple myeloma. Patients harbouring this genetic anomaly are commonly resistant to standard therapy. Thus, various p53 reactivating agents have been developed in order to restore its tumour suppressive abilities. Small molecular compounds, especially, have gained popularity in its efficacy against myeloma cells. For instance, promising preclinical results have steered both nutlin-3 and PRIMA-1 into phase I/II clinical trials. This review summarizes different modes of p53 inactivation in myeloma and highlights the current p53-based therapies that are being utilized in the clinic. Finally, we discuss the potential and promise that the novel small molecules possess for clinical application in improving the treatment outcome of myeloma.

Expression of neddylation-related proteins in melanoma cell lines and the effect of neddylation on melanoma proliferation

Neddylation promotes the process of ubiquitination, which plays a critical role in the degradation of numerous proteins, including cell cycle and apoptosis regulators. In our previous study, an increase in neddylation was identified in melanoma cell lines. In the present study, the upregulation of neddylation was detected in melanoma tissues which confirmed the results of our previous study on melanoma cell lines. To explore the mechanism by which the process of neddylation was increased, the enzymes that regulate the process were investigated. These neddylation-related regulatory enzymes are potential targets for melanoma therapy. Downregulation of UBA3, a subunit of the E1 enzyme, by RNA interference caused cell cycle arrest at G0^/G1 in the M14 cell line. In addition, cyclin D expression declined, whereas p27, p21 and bax expression increased. These findings suggest that interfering with the neddylation pathway may decrease the proliferation of melanoma through the modulation of cell cycle regulators and apoptosis promoters.

p53 in neurodegenerative diseases and brain cancers

More than thirty years elapsed since a protein, not yet called p53 at the time, was detected to bind SV40 during viral infection. Thousands of papers later, p53 evolved as the main tumor suppressor involved in growth arrest and apoptosis. A lot has been done but the protein has not yet revealed all its secrets. Particularly important is the observation that in totally distinct pathologies where apoptosis is either exacerbated or impaired, p53 appears to play a central role. This is exemplified for Alzheimer's and Parkinson's diseases that represent the two main causes of age-related neurodegenerative affections, where cell death enhancement appears as one of the main etiological paradigms. Conversely, in cancers, about half of the cases are linked to mutations in p53 leading to the impairment of p53-dependent apoptosis. The involvement of p53 in these pathologies has driven a huge amount of studies aimed at designing chemical tools or biological approaches to rescue p53 defects or over-activity. Here, we describe the data linking p53 to neurodegenerative diseases and brain cancers, and we document the various strategies to interfere with p53 dysfunctions in these disorders.

The degradation of p53 and its major E3 ligase Mdm2 is differentially dependent on the proteasomal ubiquitin receptor S5a

p53 and its major E3 ligase Mdm2 are both ubiquitinated and targeted to the proteasome for degradation. Despite the importance of this in regulating the p53 pathway, little is known about the mechanisms of proteasomal recognition of ubiquitinated p53 and Mdm2. In this study, we show that knockdown of the proteasomal ubiquitin receptor S5a/PSMD4/Rpn10 inhibits p53 protein degradation and results in the accumulation of ubiquitinated p53. Overexpression of a dominant-negative deletion of S5a lacking its ubiquitin-interacting motifs (UIM)s, but which can be incorporated into the proteasome, also causes the stabilization of p53. Furthermore, small-interferring RNA (siRNA) rescue experiments confirm that the UIMs of S5a are required for the maintenance of low p53 levels. These observations indicate that S5a participates in the recognition of ubiquitinated p53 by the proteasome. In contrast, targeting S5a has no effect on the rate of degradation of Mdm2, indicating that proteasomal recognition of Mdm2 can be mediated by an S5a-independent pathway. S5a knockdown results in an increase in the transcriptional activity of p53. The selective stabilization of p53 and not Mdm2 provides a mechanism for p53 activation. Depletion of S5a causes a p53-dependent decrease in cell proliferation, demonstrating that p53 can have a dominant role in the response to targeting S5a. This study provides evidence for alternative pathways of proteasomal recognition of p53 and Mdm2. Differences in recognition by the proteasome could provide a means to modulate the relative stability of p53 and Mdm2 in response to cellular signals. In addition, they could be exploited for p53-activating therapies. This work shows that the degradation of proteins by the proteasome can be selectively dependent on S5a in human cells, and that this selectivity can extend to an E3 ubiquitin ligase and its substrate.

Deubiquitinase inhibition of 19S regulatory particles by 4-arylidene curcumin analog AC17 causes NF-κB inhibition and p53 reactivation in human lung cancer cells

Proteasome inhibitors have been suggested as potential anticancer agents in many clinical trials. Recent evidence indicates that proteasomal deubiquitinase (DUB) inhibitors, bearing a different mechanism from that of traditional proteasome inhibitors, would be appropriate candidates for new anticancer drug development. In the present study, we describe the deubiquitinase inhibition of 19S regulatory particles (19S RP) by AC17, a 4-arylidene curcumin analog synthesized in our laboratory. Although 4-arylidene curcumin analogs were reported to act as inhibitory κB (IκB) kinase (IKK) inhibitors, AC17 instead induced a rapid and marked accumulation of ubiquitinated proteins without inhibiting proteasome proteolytic activities. In contrast to its parent compound, curcumin, which is a proteasome proteolytic inhibitor, AC17 serves as an irreversible deubiquitinase inhibitor of 19S RP, resulting in inhibition of NF-κB pathway and reactivation of proapoptotic protein p53. In addition, in a murine xenograft model of human lung cancer A549, treatment with AC17 suppresses tumor growth in a manner associated with proteasome inhibition, NF-κB blockage, and p53 reactivation. These results suggest that 4-arylidene curcumin analogs are novel 19S deubiquitinase inhibitors with great potential for anticancer drug development.

Ubiquitin pathway and ovarian cancer

The ubiquitin-proteasome pathway is a common cellular process in eukaryotic tissue. Ubiquitin binds to proteins and tags them for destruction; this tagging directs proteins to the proteosome in the cell that degrades and recycles unneeded proteins. The ubiquitin-proteasome pathway plays an important role in the regulation of cellular proteins with respect to cell cycle control, transcription, apoptosis, cell adhesion, angiogenesis, and tumour growth. This review article discusses the various ways that the ubiquitin pathway is involved in ovarian cancer, such as modulating the ovarian-cancer-related gene BRCA1 and tumour suppressor p53, and interfering with the erk pathway, the cyclin-dependent cell cycle regulation process, and ERBB2 gene expression.

UHRF2, another E3 ubiquitin ligase for p53

UHRF2, ubiquitin-like with PHD and ring finger domains 2, is a nuclear E3 ubiquitin ligase, which is involved in cell cycle and epigenetic regulation. UHRF2 interacts with multiple cell cycle proteins, including cyclins (A2, B1, D1, and E1), CDK2, and pRb; moreover, UHRF2 could ubiquitinate cyclin D1 and cyclin E1. Also, UHRF2 has been shown to be implicated in epigenetic regulation by associating with DNMTs, G9a, HDAC1, H3K9me2/3 and hemi-methylated DNA. We found that UHRF2 associates with tumor suppressor protein p53, and p53 is ubiquitinated by UHRF2 in vivo and in vitro. Given that both UHRF2 and p53 are involved in cell cycle regulation, this study may suggest a novel signaling pathway on cell proliferation.

Zebrafish p53 protein enhances the translation of its own mRNA in response to UV irradiation and CPT treatment

p53 protein is an important regulatory factor involved in cell growth and development. In our previous study, we demonstrated that recombined zebrafish p53 protein could specifically bind to its own mRNA in vitro. To determine if a similar interaction exists in zebrafish and if this interaction affects zebrafish development, in the present study, we investigated the interaction of p53 protein and its mRNA in zebrafish embryos. Our results revealed that expressed zebrafish p53 protein could bind with its own mRNA in zebrafish embryos. Furthermore, the endogenous activated or ectopically expressed p53 protein could enhance the relative activity of Renilla luciferase fused with p53 3'UTR in response to UV irradiation and CPT treatment, and retarded development of zebrafish embryos was observed.

Ubiquitination and the Ubiquitin-Proteasome System as regulators of transcription and transcription factors in epithelial mesenchymal transition of cancer

Epithelial to Mesenchymal Transition (EMT) in cancer is a process that allows cancer cells to detach from neighboring cells, become mobile and metastasize and shares many signaling pathways with development. Several molecular mechanisms which regulate oncogenic properties in neoplastic cells such as proliferation, resistance to apoptosis and angiogenesis through transcription factors or other mediators are also regulators of EMT. These pathways and downstream transcription factors are, in their turn, regulated by ubiquitination and the Ubiquitin-Proteasome System (UPS). Ubiquitination, the covalent link of the small 76-amino acid protein ubiquitin to target proteins, serves as a signal for protein degradation by the proteasome or for other outcomes such as endocytosis, degradation by the lysosome or directing these proteins to specific cellular compartments. This review discusses aspects of the regulation of EMT by ubiquitination and the UPS and underlines its complexity focusing on transcription and transcription factors regulating EMT and are being regulated by ubiquitination.

Pharmacological activation of p53 in cancer cells

Tumor suppressor p53 is a transcription factor that regulates a large number of genes and guards against genomic instability. Under multiple cellular stress conditions, p53 functions to block cell cycle progression transiently unless proper DNA repair occurs. Failure of DNA repair mechanisms leads to p53-mediated induction of cell death programs. p53 also induces permanent cell cycle arrest known as cellular senescence. During neoplastic progression, p53 is often mutated and fails to efficiently perform these functions. It has been observed that cancers carrying a wild-type p53 may also have interrupted downstream p53 regulatory signaling leading to disruption in p53 functions. Therefore, strategies to reactivate p53 provide an attractive approach for blocking tumor pathogenesis and its progression. p53 activation may also lead to regression of existing early neoplastic lesions and therefore may be important in developing cancer chemoprevention protocols. A large number of small molecules capable of reactivating p53 have been developed and some are progressing through clinical trials for prospective human applications. However, several questions remain to be answered at this stage. For example, it is not certain if pharmacological activation of p53 will restore all of its multifaceted biological responses, assuming that the targeted cell is not killed following p53 activation. It remains to be demonstrated whether the distinct biological effects regulated by specific post-translationally modified p53 can effectively be restored by refolding mutant p53. Mutant p53 can be classified as a loss-of-function or gain-of-function protein depending on the type of mutation. It is also unclear whether reactivation of mutant p53 has similar consequences in cells carrying gain-of-function and loss-of-function p53 mutants. This review provides a description of various pharmacological approaches tested to activate p53 (both wild-type and mutant) and to assess the effects of activated p53 on neoplastic progression.

Acetylation of the pro-apoptotic factor, p53 in the hippocampus following cerebral ischemia and modulation by estrogen

BACKGROUND

Recent studies demonstrate that acetylation of the transcription factor, p53 on lysine(373) leads to its enhanced stabilization/activity and increased susceptibility of cells to stress. However, it is not known whether acetylation of p53 is altered in the hippocampus following global cerebral ischemia (GCI) or is regulated by the hormone, 17β-estradiol (17β-E(2)), and thus, this study examined these issues.

METHODOLOGY/PRINCIPAL FINDINGS

The study revealed that Acetyl p53-Lysine(373) levels were markedly increased in the hippocampal CA1 region after GCI at 3 h, 6 h and 24 h after reperfusion, an effect strongly attenuated by 17β-E(2). 17β-E(2) also enhanced interaction of p53 with the ubiquitin ligase, Mdm2, increased ubiquitination of p53, and induced its down-regulation, as well as attenuated elevation of the p53 transcriptional target, Puma. We also observed enhanced acetylation of p53 at a different lysine (Lys(382)) at 3 h after reperfusion, and 17β-E(2) also markedly attenuated this effect. Furthermore, administration of an inhibitor of CBP/p300 acetyltransferase, which acetylates p53, was strongly neuroprotective of the CA1 region following GCI. In long-term estrogen deprived (LTED) animals, the ability of 17β-E(2) to attenuate p53 acetylation was lost, and intriguingly, Acetyl p53-Lysine(373) levels were markedly elevated in sham (non-ischemic) LTED animals. Finally, intracerebroventricular injections of Gp91ds-Tat, a specific NADPH oxidase (NOX2) inhibitor, but not the scrambled tat peptide control (Sc-Tat), attenuated acetylation of p53 and reduced levels of Puma following GCI.

CONCLUSIONS/SIGNIFICANCE

The studies demonstrate that p53 undergoes enhanced acetylation in the hippocampal CA1 region following global cerebral ischemia, and that the neuroprotective agent, 17β-E(2), markedly attenuates the ischemia-induced p53 acetylation. Furthermore, following LTED, the suppressive effect of 17β-E(2) on p53 acetylation is lost, and p53 acetylation increases in the hippocampus, which may explain previous reports of increased sensitivity of the hippocampus to ischemic stress following LTED.

Translating p53 into the clinic

Mutations in the TP53 gene are a feature of 50% of all reported cancer cases. In the other 50% of cases, the TP53 gene itself is not mutated but the p53 pathway is often partially inactivated. Cancer therapies that target specific mutant genes are proving to be highly active and trials assessing agents that exploit the p53 system are ongoing. Many trials are aimed at stratifying patients on the basis of TP53 status. In another approach, TP53 is delivered as a gene therapy; this is the only currently approved p53-based treatment. The p53 protein is overexpressed in many cancers and p53-based vaccines are undergoing trials. Processed cell-surface p53 is being exploited as a target for protein-drug conjugates, and small-molecule drugs that inhibit the activity of MDM2, the E3 ligase that regulates p53 levels, have been developed by several companies. The first MDM2 inhibitors are being trialed in both hematologic and solid malignancies. Finally, the first agent found to restore the active function of mutant TP53 has just entered the clinic. Here we discuss the basis of these trials and the future of p53-based therapy.

Ubiquitin becomes ubiquitous in cancer: emerging roles of ubiquitin ligases and deubiquitinases in tumorigenesis and as therapeutic targets

By virtue of its ability to regulate both protein turnover and non-proteolytic signalling functions, ubiquitin protein conjugation has been implicated in the control of multiple cellular processes, including protein localization, cell cycle control, transcription regulation, DNA damage repair, and endocytosis. Ubiquitin metabolism enzymes have been identified as either oncogenes or tumor suppressors in a variety of cancers. Given that ubiquitin metabolism is governed by enzymes--E1, E2, E3, E4, deubiquitinases (DUBs), and the proteasome- the system as a whole is ripe for target and drug discovery in cancer. Of the ubiquitin/proteasome system components, the E3's and DUBs can recognize substrates with the most specificity, and are thus of key interest as drug targets in cancer. This review examines the molecular role in cancer, relevant substrates, and potential for pharmacologic development, of E3's and DUBs that have been associated thus far with human malignancies as oncogenes or tumor suppressors.

A comparative genome analysis of gene expression reveals different regulatory mechanisms between mouse and human embryo pre-implantation development

BACKGROUND

Pre-implantation development is a crucial step in successful implantation and pregnancy in mammals. It has been studied in depth, but mostly in laboratory animal models. Less is known about the regulatory mechanism involved in the pre-implantation development in humans and about the comparative aspects.

METHODS

Here, we employed the microarray datasets from the public database library of GEO and applied comparative analysis of genome wide temporal gene expression data based on statistical analysis and functional annotation for both mouse and human, demonstrating the discordance between the regulatory mechanisms of both mouse and human pre-implantation development.

RESULTS

There were differences between mouse and human pre-implantation development both in the global gene expression pattern and in the expression changes of individual genes at each stage, including different major transient waves of transcription profiles and some stage-specific genes and significantly related pathways. There also appeared to be different functional changes from one stage to another between mouse and human.

CONCLUSIONS

The analysis presented here lead to interesting and complementary conclusions that the regulatory mechanism of human pre-implantation development is not completely the same as the mouse. Not as the fact that 1-cell to 2-cell stage is important for mouse pre-implantation development, the 4-cell stage and 8-cell stage are both essential for human. Unlike in mouse, of which most of pathways found were related to energy, RNA and protein metabolism, the identified pathways in human were mostly disease-related and associated with human pre-implantation embryonic development. All of these suggest that a further comparative analysis should be required for applying the result of mouse expression data to human research or therapy, particularly in pre-implantation developments. Our study provides several potential targets of genes and pathways for studying the regulatory mechanism of human pre-implantation development using mouse model.