p53-induced RING-H2 protein, a novel marker for poor survival in hepatocellular carcinoma after hepatic resection

p53, Pirh2, and L1CAM as Promising Prognostic Biomarkers of Endometrial Carcinoma: An Immunohistochemical and Genetic Study

Endometrial cancer (EC) is the most common gynecologic cancer and the current methods for the prediction of its prognosis and treatment response are unfortunately suboptimal. In this study, we evaluated the prognostic value of p53, Pirh2, and L1CAM in 60 cases of EC using immunohistochemistry (IHC) and polymerase chain reaction. TP53 missense mutations result in nuclear accumulation of p53 protein that can be detected as overexpression by IHC. This is in the form of diffuse strong nuclear positivity involving at least at least >50% of the tumor cells as a whole or if >50% of the tumor cells of a discrete geographical areas. Abnormal p53 IHC expression was expressed in 33.3% of the cases and significantly associated with the tumor grade, myometrial invasion (MI), lymphovascular invasion (LVSI), nodal metastasis, and FIGO stage, and the advanced European Society for Medical Oncology (ESMO) risk groups (P<0.001 for each). High IHC Pirh2 expression was noted in 58.3% of the cases, and significantly associated with MI, LVSI, nodal metastasis, FIGO stage, and high-risk group (P<0.001, P=0.011, P=0.010, P=0.024, P=0.005, respectively). There was a significant upregulation of Pirh2 mRNA expression in EC specimens as compared with the control adjacent tissues (P=0.001). Upregulated Pirh2 mRNA expression had a significant association with Pirh2 immunostaining, tumor grade, tumor stage, MI, lymph node involvement, LVSI, and relapse (P<0.001 for each). Positive L1CAM immunoexpression was noted in 26.7% and was significantly associated with grade, MI, LVSI, nodal metastasis, FIGO stage, and high-risk group (P=0.003, P=0.023, P=0.003, P<0.001, P<0.001, P=0.002, respectively). Analysis of follow-up period revealed that EC with abnormal p53 IHC expression, high pirh2 and positive L1CAM expression exhibited a potent relation with tumor relapse, shorter overall survival and disease-specific survival (P<0.001 for each). Mutant p53, high Pirh2, and L1CAM-positive EC are highly aggressive tumors with a shortened survival rate, dismal outcome, and high risk of relapse after the standard protocol of therapy.

The Role of E3 Ligase Pirh2 in Disease

The p53-dependent ubiquitin ligase Pirh2 regulates a number of proteins involved in different cancer-associated processes. Targeting the p53 family proteins, Chk2, p27Kip1, Twist1 and others, Pirh2 participates in such cellular processes as proliferation, cell cycle regulation, apoptosis and cellular migration. Thus, it is not surprising that Pirh2 takes part in the initiation and progression of different diseases and pathologies including but not limited to cancer. In this review, we aimed to summarize the available data on Pirh2 regulation, its protein targets and its role in various diseases and pathological processes, thus making the Pirh2 protein a promising therapeutic target.

The RNA-binding protein HuR is a novel target of Pirh2 E3 ubiquitin ligase

The RING-finger protein Pirh2 is a p53 family-specific E3 ubiquitin ligase. Pirh2 also ubiquitinates several other important cellular factors and is involved in carcinogenesis. However, its functional role in other cellular processes is poorly understood. To address this question, we performed a proteomic search for novel interacting partners of Pirh2. Using the GST-pulldown approach combined with LC-MS/MS, we revealed 225 proteins that interacted with Pirh2. We found that, according to the GO description, a large group of Pirh2-associated proteins belonged to the RNA metabolism group. Importantly, one of the identified proteins from that group was an RNA-binding protein ELAVL1 (HuR), which is involved in the regulation of splicing and protein stability of several oncogenic proteins. We demonstrated that Pirh2 ubiquitinated the HuR protein facilitating its proteasome-mediated degradation in cells. Importantly, the Pirh2-mediated degradation of HuR occurred in response to heat shock, thereby affecting the survival rate of HeLa cells under elevated temperature. Functionally, Pirh2-mediated degradation of HuR augmented the level of c-Myc expression, whose RNA level is otherwise attenuated by HuR. Taken together, our data indicate that HuR is a new target of Pirh2 and this functional interaction contributes to the heat-shock response of cancer cells affecting their survival.

Regulation of p53 by E3s

More than 40 years of research on p53 have given us tremendous knowledge about this protein. Today we know that p53 plays a role in different biological processes such as proliferation, invasion, pluripotency, metabolism, cell cycle control, ROS (reactive oxygen species) production, apoptosis, inflammation and autophagy. In the nucleus, p53 functions as a bona-fide transcription factor which activates and represses transcription of a number of target genes. In the cytoplasm, p53 can interact with proteins of the apoptotic machinery and by this also induces cell death. Despite being so important for the fate of the cell, expression levels of p53 are kept low in unstressed cells and the protein is largely inactive. The reason for the low expression level is that p53 is efficiently degraded by the ubiquitin-proteasome system and the vast inactivity of the tumor suppressor protein under normal growth conditions is due to the absence of activating and the presence of inactivating posttranslational modifications. E3s are important enzymes for these processes as they decorate p53 with ubiquitin and small ubiquitin-like proteins and by this control p53 degradation, stability and its subcellular localization. In this review, we provide an overview about E3s that target p53 and discuss the connection between p53, E3s and tumorigenesis.

Pirh2, an E3 ligase, regulates the AIP4-p73 regulatory pathway by modulating AIP4 expression and ubiquitination

Pirh2 is an E3 ligase belonging to the RING-H2 family and shown to bind, ubiquitinate and downregulate p73 tumor suppressor function without altering p73 protein levels. AIP4, an E3 ligase belonging to the HECT domain family, has been reported to be a negative regulatory protein that promotes p73 ubiquitination and degradation. Herein, we found that Pirh2 is a key regulator of AIP4 that inhibits p73 function. Pirh2 physically interacts with AIP4 and significantly downregulates AIP4 expression. This downregulation is shown to involve the ubiquitination of AIP4 by Pirh2. Importantly, we demonstrated that the ectopic expression of Pirh2 inhibits the AIP4-p73 negative regulatory pathway, which was restored when depleting endogenous Pirh2 utilizing Pirh2-siRNAs. We further observed that Pirh2 decreases AIP4-mediated p73 ubiquitination. At the translational level and specifically regarding p73 cell cycle arrest function, Pirh2 still ensures the arrest of p73-mediated G1 despite AIP4 expression. Our study reveals a novel link between two E3 ligases previously thought to be unrelated in regulating the same effector substrate, p73. These findings open a gateway to explain how E3 ligases differentiate between regulating multiple substrates that may belong to the same family of proteins, as it is the case for the p53 and p73 proteins.

Ubiquitin, SUMO, and Nedd8 as Therapeutic Targets in Cancer

Ubiquitin defines a family of approximately 20 peptidic posttranslational modifiers collectively called the Ubiquitin-like (UbLs). They are conjugated to thousands of proteins, modifying their function and fate in many ways. Dysregulation of these modifications has been implicated in a variety of pathologies, in particular cancer. Ubiquitin, SUMO (-1 to -3), and Nedd8 are the best-characterized UbLs. They have been involved in the regulation of the activity and/or the stability of diverse components of various oncogenic or tumor suppressor pathways. Moreover, the dysregulation of enzymes responsible for their conjugation/deconjugation has also been associated with tumorigenesis and cancer resistance to therapies. The UbL system therefore constitutes an attractive target for developing novel anticancer therapeutic strategies. Here, we review the roles and dysregulations of Ubiquitin, SUMO, and Nedd8 pathways in tumorigenesis, as well as recent advances in the identification of small molecules targeting their conjugating machineries for potential application in the fight against cancer.

Combined use of murine double minute-2 promoter methylation and serum AFP improves diagnostic efficiency in hepatitis B virus-related hepatocellular carcinoma

Objective: Hepatocellular carcinoma (HCC) accounts for approximately 85% of all cases of liver cancer. In China, chronic hepatitis B virus-related HCC (HBV-related HCC) is the most common type of HCC. However, the majority of HBV-related HCC patients are asymptomatic, and the best opportunities for treating these patients are missed. The precise diagnosis of HBV-related HCC is crucial. The main purpose of this study was to evaluate the diagnostic value of murine double minute-2 (MDM2) promoter methylation in HBV-related HCC patients. Methods: The methylation status of the MDM2 promoter was detected by methylation-specific PCR. The MDM2 expression levels were validated by quantitative real-time PCR. Enzyme-linked immunosorbent assay was used to determine the levels of interleukin-6 (IL-6) and tumor-necrosis factor-α (TNF-α) in plasma. Results: The methylation frequency of the MDM2 promoter was decreased in HBV-related HCC patients. The MDM2 mRNA levels of patients with HBV-related HCC were higher than those of patients with liver cirrhosis and chronic hepatitis B. The plasma levels of IL-6 and TNF-α were significantly higher in HBV-related HCC patients than that in liver cirrhosis and chronic hepatitis B patients. The TNF-α levels were higher in the unmethylated MDM2 promoter group than in the methylated MDM2 promoter group in HBV-related HCC patients. Moreover, the combination of MDM2 promoter methylation and alpha-fetoprotein (AFP) improved the diagnosis of HBV-related HCC. Conclusions: Our study indicates, for the first time, that MDM2 promoter hypomethylation is present in HBV-related HCC patients. The combination of MDM2 promoter methylation and AFP can greatly improve diagnostic efficiency in HBV-related HCC, which might provide a new method for HBV-related HCC diagnosis.

Inverse correlation between Naa10p and Pirh2 expression and the combined prognostic value in oral squamous cell carcinoma patients

BACKGROUND

This study aims to explore the associations between N-α-acetyltransferase 10 protein (Naa10p) and p53-induced protein with a RING-H2 domain (Pirh2) expression and clinicopathological characteristics in oral squamous cell carcinoma (OSCC).

METHODS

Immunohistochemistry was performed to detect Naa10p and Pirh2 levels containing 118 OSCC specimens, and additional analyses were used to determine correlations between Naa10p and Pirh2 expressions, generate survival curves, and perform univariate and multivariate statistical analyses. Further, quantitative real-time PCR (qRT-PCR) and western blot were employed to examine Naa10p and Pirh2 expression level in OSCC patients' samples. We further validated the result using RNAseq data from The Cancer Genome Atlas (TCGA) and mRNA array data from GSE31056 and GSE30784.

RESULTS

Naa10p and Pirh2 are overexpression, and the protein level of Naa10p was negatively correlated with that of Pirh2 in OSCC tissues. Multivariate Cox proportional hazard regression analysis showed that positive Naa10p expression and negative Pirh2 expression were both independent good prognostic factors for OSCC patients. Furthermore, the Naa10p-positive/Pirh2-negative group has the best prognosis among all OSCC patients. Results from qRT-PCR showed the higher expression level of Naa10 and lower expression level of Pirh2 in tumor tissues than adjacent normal tissues. TCGA database and data from GSE31056 and GSE30784 showed the similar result. The correlation analysis showed that the mRNA level of Naa10 was negatively correlated that of Pirh2.

CONCLUSION

The expression of Naa10p is negatively correlated with that of Pirh2, and positive Naa10p and negative Pirh2 might be independent biomarkers for better OSCC prognoses.

Identification of a 3,3-difluorinated tetrahydropyridinol compound as a novel antitumor agent for hepatocellular carcinoma acting via cell cycle arrest through disturbing CDK7-mediated phosphorylation of Cdc2

Tetrahydropyridinol derivatives were recently reported to exhibit good biological activities, and the incorporation of fluorine into organic molecules may have profound effects on their physical and biological properties. Therefore, we investigated the anticancer activities of six fluorinated tetrahydropyridinol derivatives that we synthesized previously. We found that only one compound, 3,3-difluoro-2,2-dimethyl-1,6-diphenyl-5-tosyl-1,2,3,6-tetrahydropyridin-4-ol, showed significant antiproliferative activity on human hepatocellular carcinoma HepG2 and HMCCLM3 cells (the IC₅₀ values were 21.25 and 29.07 μM, respectively). We also found that this compound mediated cell cycle arrest in the G0/G1 phase at 30-40 μM. Western blot analysis demonstrated that the cell cycle arrest induced by this compound in HepG2 and HMCCLM3 cells was associated with a significant decrease in Cdc2 and cyclin B1, which led to the accumulation of the phosphorylated-Tyr¹⁵ (inactive) form of Cdc2 and low expression of M phase-promoting factor (cyclin B1/Cdc2). Moreover, cells treated with this compound exhibited decreased expression of cyclin-dependent kinase (CDK)-activating kinase (CDK7/cyclin H). This compound also induced cell apoptosis via activation of caspase-3. A xenograft model in nude mice demonstrated anti-liver cancer activity and the mechanism of action of this compound. These findings indicated that the anticancer effect of this compound was partially due to G0/G1 cell cycle arrest via inhibition of CDK7-mediated expression of Cdc2, and this compound may be a promising anticancer candidate for further investigation.

p53-Pirh2 Complex Promotes Twist1 Degradation and Inhibits EMT

Epithelial-mesenchymal transition (EMT) is a critical process involved in cancer metastasis and chemoresistance. Twist1 is a key EMT-inducing transcription factor, which is upregulated in multiple types of cancers and has been shown to promote tumor cell invasiveness and support tumor progression. Conversely, p53 is a tumor suppressor gene that is frequently mutated in cancers. This study demonstrates the ability of wild-type (WT) p53 to promote the degradation of Twist1 protein. By forming a complex with Twist1 and the E3 ligase Pirh2, WT p53 promotes the ubiquitination and proteasomal degradation of Twist1, thus inhibiting EMT and maintaining the epithelial phenotype. The ability of p53 to induce Twist1 degradation is abrogated when p53 is mutated. Consequently, the loss of p53-induced Twist1 degradation leads to EMT and the acquisition of a more invasive cancer phenotype.Implication: These data provide new insight into the metastatic process at the molecular level and suggest a signaling pathway that can potentially be used to develop new prognostic markers and therapeutic targets to curtail cancer progression.

E3 ubiquitin ligase Pirh2 enhances tumorigenic properties of human non-small cell lung carcinoma cells

The product of RCHY1 human gene, Pirh2, is a RING-finger containing E3 ligase that modifies p53 with ubiquitin residues resulting in its subsequent degradation in proteasomes. Transcription of RCHY1 is regulated by p53 itself thus forming a negative regulatory feedback loop. Functionally, by eliminating p53, Pirh2 facilitates tumorigenesis. However, the role of Pirh2 in cancer cells lacking p53 is yet not well understood. Therefore, we decided to elucidate the role of Pirh2 in p53-negative human non-small cell lung carcinoma cells, H1299. We found that ectopic expression of Pirh2 enhanced cell proliferation, resistance to doxorubicin, and increased migration potential. Ablation of Pirh2 by specific shRNA reversed these phenotypes. Mechanistically, Pirh2 increased mRNA and protein levels of the c-Myc oncogene. The bioinformatics data indicate that co-expression of both c-Myc and Pirh2 strongly correlated with poor survival of lung cancer patients. Collectively, our results suggest that Pirh2 can be considered as a potential pharmacological target for developing anticancer therapies to treat p53-negative cancers.

MicroRNA-424 inhibits Akt3/E2F3 axis and tumor growth in hepatocellular carcinoma

By comparing the expression profiles of miRNAs in different subtypes of HCC, we identified miR-424 as a HCC related miRNA. We found that the expression of miR-424 was significantly decreased in HCC tissues and six liver cancer cell lines. Significantly, its expression levels were correlated with tumor size, multiple nodules, vein invasion, TNM stage and overall survival of HCC. We showed that up-regulated miR-424 suppressed HCC cell proliferation in vivo and in vitro. Multi-pathway reporter arrays suggested that miR-424 suppressed the pRb-E2F pathway. Consistently, Akt3 and E2F3 were identified as the targets of miR-424 as evidenced by that ectopic miR-424 expression suppressed Akt3 and E2F3 expressions. Silencing Akt3 and E2F3 by siRNA pheno-copied the effect of ectopic miR-424 on HCC growth. Whereas, overexpression of Akt3 and E2F3 attenuated the effect of miR-424 on HCC growth. Together, our data demonstrated a tumor suppressor role for miR-424 in HCC development and progression with therapeutic implications. The strong correlation of miR-424 expression with HCC patient survival suggests that miR-424 could be a valuable biomarker for HCC prognosis.

Prognostic significance of Nemo-like kinase expression in patients with hepatocellular carcinoma

Nemo-like kinase (NLK) is an evolutionarily conserved serine/threonine protein kinase and belongs to the extracellular signal-regulated kinases/microtubule-associated protein kinase families (Erks/MAPKs). Previous studies have indicated that abnormal expressions of NLK played critical roles in various types of human cancers. Recent studies suggested that NLK expression was significantly upregulated in the hepatocellular carcinoma (HCC) specimens. However, the clinical significance of NLK expression in HCC remains largely unknown. In this study, we focused on the clinical significance of NLK in HCC and found that high expression of NLK was significantly associated with Edmondson-Steiner grade (P = 0.002), tumor size (P = 0.022), and no. of tumor nodules (P < 0.001), and NLK was positively correlated with proliferation marker Ki-67 (P < 0.01). Univariate analysis suggested that NLK expression was associated with poor prognosis (P < 0.001). Multivariate analysis indicated that NLK expression was an independent prognostic indicator for HCC (P = 0.0370). In conclusion, NLK overexpression is associated with poor overall survival in patients with HCC, it might be an independent poor prognostic marker for HCC.

Decreased STAT4 indicates poor prognosis and enhanced cell proliferation in hepatocellular carcinoma

AIM: To investigate the role of signal transduction and activation of transcription 4 (STAT4) in the development and progression of human hepatocellular carcinoma (HCC).

METHODS: Recent genetic investigations have identified that a genetic variant of STAT4 is associated with hepatitis B virus (HBV)-related HCC. The level of STAT4 in 90 HCC patients was examined via Western blot and immunohistochemical analyses. The correlation between STAT4 expression and the clinicopathological characteristics of the patients was analyzed. The level of STAT4 expression in the HCC liver tissues was significantly lower than that in the non-HCC liver tissues and correlated with tumor size, histological grade of HCC and serum hepatitis B surface antigen level in HCC patients. The data were statistically analyzed using SPSS. Furthermore, siRNA oligos targeting STAT4 were employed to investigate the influence of STAT4 RNA interference on HCC cell physiology. Based on Cell Counting Kit-8 and flow cytometric assays, we found that depletion of STAT4 expression significantly enhanced the proliferation of L02 cells.

RESULTS: STAT4 protein expression was significantly lower in HCC tissues than in normal liver tissues. Immunohistochemistry followed by statistical analysis revealed that the expression of STAT4 negatively correlated with Ki67 expression (r = 0.851; P < 0.05) and positively correlated with maximal tumor size (P < 0.05), HBV (P = 0.012) and histological grade (P < 0.05). Kaplan-Meier analysis revealed significant differences in the survival curves between HCC patients expressing low and high levels of STAT4 and Ki67 (P < 0.05). Based on a multivariate Cox proportional hazard model, STAT4 expression was an independent prognostic indicator for HCC patients who underwent curative resection. In vitro, following the release of L02 cell lines from serum starvation, the expression of STAT4 was downregulated, and transfection of L02 cells with siRNA targeting STAT4 inhibited cell proliferation.

CONCLUSION: Our data indicate that STAT4 may inhibit HCC development by modulating HCC cell proliferation.

Regulation of the DNA damage response by ubiquitin conjugation

In response to DNA damage, cells activate a highly conserved and complex kinase-based signaling network, commonly referred to as the DNA damage response (DDR), to safeguard genomic integrity. The DDR consists of a set of tightly regulated events, including detection of DNA damage, accumulation of DNA repair factors at the site of damage, and finally physical repair of the lesion. Upon overwhelming damage the DDR provokes detrimental cellular actions by involving the apoptotic machinery and inducing a coordinated demise of the damaged cells (DNA damage-induced apoptosis, DDIA). These diverse actions involve transcriptional activation of several genes that govern the DDR. Moreover, recent observations highlighted the role of ubiquitylation in orchestrating the DDR, providing a dynamic cellular regulatory circuit helping to guarantee genomic stability and cellular homeostasis (Popovic et al., 2014). One of the hallmarks of human cancer is genomic instability (Hanahan and Weinberg, 2011). Not surprisingly, deregulation of the DDR can lead to human diseases, including cancer, and can induce resistance to genotoxic anti-cancer therapy (Lord and Ashworth, 2012). Here, we summarize the role of ubiquitin-signaling in the DDR with special emphasis on its role in cancer and highlight the therapeutic value of the ubiquitin-conjugation machinery as a target in anti-cancer treatment strategy.

Expression and prognostic significance of p21-activated kinase 6 in hepatocellular carcinoma

BACKGROUND

p21-activated protein kinase (PAK) 6 is a serine-threonine kinase belonging to the PAK family. Previous studies have indicated that abnormal expressions of PAK1, PAK2, and PAK5 played critical roles in hepatocellular carcinoma (HCC). Recent studies suggested that deregulation of PAK6 expression played an important role in oncogenesis. To explore the potential roles of PAK6 in HCC, expression of PAK6 was detected in human HCC specimens.

METHODS

Immunohistochemistry and Western blot analysis were performed for PAK6 in 121 HCC samples. The data were correlated with clinicopathologic features. The univariate and multivariate survival analyses were also performed to determine their clinical prognostic significance.

RESULTS

PAK6 was overexpressed in HCC as compared with the adjacent noncancerous liver tissues. High expression of PAK6 was associated with Edmondson-Steiner grade (P = 0.006) and number of tumor nodules (P < 0.001), and PAK6 was positively correlated with proliferation marker Ki-67 (P < 0.01). Univariate analysis suggested that PAK6 expression was associated with poor prognosis (P < 0.001). Multivariate analysis indicated that PAK6 and Ki-67 protein expressions were independent prognostic markers for HCC (P = 0.0245 and 0.0331, respectively).

CONCLUSIONS

Our results suggest that PAK6 overexpression is involved in the pathogenesis of HCC; it may be an independent poor prognostic factor for HCC.

The role and therapeutic implications of RING-finger E3 ubiquitin ligases in hepatocellular carcinoma

Increasing evidence indicates that deregulation of RING-finger ubiquitin-protein ligases (E3s) involves in the development of hepatocellular carcinoma (HCC). These RING-finger E3s serve as oncoproteins or tumor suppressors in HCC under specific conditions. In this review, we summarize current knowledge about abnormal RING-finger E3s and their clinical significance in the development of HCC, and discuss parts of critical substrates for these RING-finger E3s in detail. Furthermore, in light of success of Bortezomib in treating hematological malignancies, we describe the preclinical and clinical studies of therapeutic approaches targeting aberrant RING-finger E3s in HCC.

Residues 240-250 in the C-terminus of the Pirh2 protein complement the function of the RING domain in self-ubiquitination of the Pirh2 protein

Pirh2 is a p53 inducible gene that encodes a RING-H2 domain and is proposed to be a main regulator of p53 protein, thus fine tuning the DNA damage response. Pirh2 interacts physically with p53 and promotes its MDM2-independent ubiquitination and subsequent degradation as well as participates in an auto-regulatory feedback loop that controls p53 function. Pirh2 also self-ubiquitinates. Interestingly, Pirh2 is overexpressed in a wide range of human tumors. In this study, we investigated the domains and residues essential for Pirh2 self-ubiquitination. Deletions were made in each of the three major domains of Pirh2: the N-terminal domain (NTD), Ring domain (RING), and C-terminal domain (CTD). The effects of these deletions on Pirh2 self-ubiquitination were then assessed using in vitro ubiquitination assays. Our results demonstrate that the RING domain is essential, but not sufficient, for Pirh2 self-ubiquitination and that residues 240–250 of the C-terminal domain are also essential. Our results demonstrate that Pirh2 mediated p53 polyubiquitination occurs mainly through the K48 residue of ubiquitin in vitro. Our data further our understanding of the mechanism of Pirh2 self-ubiquitination and may help identify valuable therapeutic targets that play roles in reducing the effects of the overexpression of Pirh2, thus maximizing p53's response to DNA damage.

MicroRNA-140-5p suppresses tumor growth and metastasis by targeting transforming growth factor β receptor 1 and fibroblast growth factor 9 in hepatocellular carcinoma

By comparing the expression profiles of microRNAs (miRNAs) in different hepatocellular carcinoma (HCC) subtypes, we identified miR-140-5p as an HCC-related miRNA. We found that miR-140-5p was significantly decreased in HCC tissues and all of six liver cancer cell lines examined and its expression levels were correlated with multiple nodules, vein invasion, capsular formation, and differentiation, as well as overall and disease-free survival of HCC. We also found that miR-140-5p suppressed HCC cell proliferation and HCC metastasis. Multipathway reporter arrays suggested that miR-140-5p inhibited transforming growth factor β (TGF-β) and mitogen-activated protein kinase / extracellular signal-regulated kinase (MAPK/ERK) signaling. TGFB receptor 1 (TGFBR1) and fibroblast growth factor 9 (FGF9) were then characterized as the direct targets for miR-140-5p after it was found that ectopic miR-140-5p expression suppressed TGFBR1 and FGF9 expression. Silencing TGFBR1 and FGF9 by small interfering RNA (siRNA) resembled the phenotype resulting from ectopic miR-140-5p expression, while overexpression of TGFBR1 and FGF9 attenuated the effect of miR-140-5p on HCC growth and metastasis.

CONCLUSION

These data elucidated a tumor suppressor role for miR-140-5p in HCC development and progression with therapeutic potential. Our correlation studies in clinical HCC samples further suggest that miR-140-5p could be a valuable biomarker for HCC prognosis.

A portrayal of E3 ubiquitin ligases and deubiquitylases in cancer

E3 ubiquitin ligases and deubiquitylating enzymes (DUBs) are the key components of ubiquitin proteasome system which plays a critical role in cellular protein homeostasis. Any shortcoming in their biological roles can lead to various diseases including cancer. The dynamic interplay between ubiquitylation and deubiquitylation determines the level and activity of several proteins including p53, which is crucial for cellular stress response and tumor suppression pathways. In this review, we describe the different types of E3 ubiquitin ligases including those targeting tumor suppressor p53, SCF ligases and RING type ligases and accentuate on biological functions of few important E3 ligases in the cellular regulatory networks. Tumor suppressor p53 level is tightly regulated by multiple E3 ligases including Mdm2, COP1, Pirh2, etc. SCF ubiquitin ligase complexes are key regulators of cell cycle and signal transduction. BRCA1 and VHL RING type ligases function as tumor suppressors and play an important role in DNA repair and hypoxia response respectively. Further, we discuss the biological consequences of deregulation of the E3 ligases and the implications for cancer development. We also describe deubiquitylases which reverse the process of ubiquitylation and regulate diverse cellular pathways including metabolism, cell cycle control and chromatin remodelling. As the E3 ubiquitin ligases and DUBs work in a substrate specific manner, an improved understanding of them can lead to better therapeutics for cancer.

Arsenic suppresses cell survival via Pirh2-mediated proteasomal degradation of ΔNp63 protein

Transcription factor p63, a member of the p53 family, shares a high degree of sequence similarity with p53. Because of transcription from two distinct promoters, the p63 gene encodes two isoforms, TAp63 and ΔNp63. Although TAp63 acts as a tumor suppressor, ΔNp63 functions as an oncogene and is often overexpressed in squamous cell carcinomas. Thus, therapeutic agents targeting ΔNp63 might be used to manage tumors that overexpress ΔNp63. Here we found that arsenic trioxide, a frontline agent for acute promyelocytic leukemia, inhibits ΔNp63 but not TAp63 expression in time- and dose-dependent manners. In addition, we found that arsenic trioxide decreases the stability of ΔNp63 protein via a proteasome-dependent pathway but has little effect on the level of ΔNp63 transcript. Furthermore, we found that arsenic trioxide activates the Pirh2 promoter and consequently induces Pirh2 expression. Consistent with this, we found that knockdown of Pirh2 inhibits, whereas ectopic expression of Pirh2 enhances, arsenic-induced degradation of ΔNp63 protein. Importantly, we found that knockdown of ΔNp63 sensitizes, whereas ectopic expression of ΔNp63 inhibits, growth suppression induced by arsenic. Together, these data suggest that arsenic degrades ΔNp63 protein at least in part via Pirh2-dependent proteolysis and that inhibition of ΔNp63 expression facilitates tumor cells to arsenic-induced death.

High expression of P53-induced Ring-h2 protein is associated with poor prognosis in clear cell renal cell carcinoma

PURPOSE

This study was carried out to examine P53-induced Ring-h2 protein (Pirh2) expression and investigate its clinical and prognostic significance in patients with clear cell renal cell carcinoma (ccRCC).

METHODS

Pirh2 mRNA and protein expressions were detected by quantitative reverse-transcription polymerase chain reaction (Q-RT PCR) and Western blotting in 35 frozen renal cancer tissue specimens and 35 adjacent normal renal tissue specimens of the same patients. Pirh2 protein expression was assessed by immunohistochemical analysis in 92 paraffin-embedded specimens of human ccRCC and 30 specimens of adjacent normal renal tissue. Correlations between Pirh2 and clinicopathologic features and prognosis were analyzed statistically.

RESULTS

Pirh2 mRNA and protein levels in ccRCC samples were increased significantly as compared with the adjacent normal renal tissues (P < 0.001). Pirh2 mRNA overexpression correlated with high stage and grade of the renal cancer (P < 0.001 and P < 0.001 respectively). Pirh2 protein expression was negative in most normal renal tissue specimens (23/30) but positive in 52.2% (48/92) of ccRCC specimens (P = 0.006). Pirh2 protein expression correlated with tumor grade and stage (P < 0.001 and P < 0.001 respectively). The median follow-up interval was 42.0 months. Overexpression of Pirh2 protein in ccRCC was significantly associated with shorter overall survival and recurrence-free survival (P = 0.001 and P = 0.003, respectively). Multivariate analysis showed that Pirh2 expression was an independent prognostic factor for ccRCC patients (P = 0.037).

CONCLUSIONS

Pirh2 was up-regulated in ccRCC at both transcriptional and translational levels compared with normal renal tissues, suggesting that Pirh2 may be a potential prognostic marker for ccRCC.

SCYL1 binding protein 1 promotes the ubiquitin-dependent degradation of Pirh2 and has tumor-suppressive function in the development of hepatocellular carcinoma

Pirh2 is a Ring-H2 domain containing E3 ubiquitin ligase that targets several important tumor suppressor genes for proteasomal degradation. Overexpression of Pirh2 is frequently detected in many clinical tumor tissues including hepatocellular carcinoma (HCC). However, the molecular mechanism of Pirh2 activation in tumorigenesis still remains poorly understood. In this study, we find a Pirh2-binding protein, SCYL1 binding protein 1 (SCYL1BP1), that can promote the ubiquitin-dependent degradation of Pirh2. SCYL1BP1 colocalized with Pirh2 in the cytoplasm and prevented its localization to the nucleus. Ectopic expression of SCYL1BP1 increased the expression of p53 and further inhibited the G(1)/S transition of HCC cell lines. Conversely, knock down of SCYL1BP1 restored the expression of Pirh2 and inhibited p53 at protein level. Functional assays found that reintroduction of SCYL1BP1 into HCC cell lines significantly inhibited cell proliferation, foci formation, colony formation in soft agar and tumor formation in nude mice, suggesting the strong tumor-suppressive function of SCYL1BP1 in HCC progression. Furthermore, SCYL1BP1 was found to be frequently downregulated in HCC clinical specimens compared to their paired non-tumor tissues by immunohistochemical staining. Taken together, our data suggested that the interaction of SCYL1BP1/Pirh2 could accelerate Pirh2 degradation through an ubiquitin-dependent pathway. SCYL1BP1 may function as an important tumor suppressor gene in HCC development.

Pirh2 RING-finger E3 ubiquitin ligase: its role in tumorigenesis and cancer therapy

The ubiquitin-dependent proteasome system plays a critical role in many cellular processes and pathogenesis of various human diseases, including cancer. Although there are a large number of E3 ubiquitin ligases, the majority are RING-finger type E3s. Pirh2, a target of p53 transcription factor, contains a highly conserved C(3)H(2)C(3) type RING domain. Importantly, Pirh2 was found to regulate a group of key factors dedicated to the DNA damage response, such as p53, p73, PolH, and c-Myc. Interestingly, Pirh2 was upregulated or downregulated in different types of cancers. These suggest that Pirh2 is implicated in either promoting or suppressing tumor progression in a tissue-dependent manner. This review will focus on the major findings in these studies and discuss the potential to explore Pirh2 as a cancer therapeutic target.

The involvement of a Nanog, Klf4 and c-Myc transcriptional circuitry in the intertwining between neoplastic progression and reprogramming

One undisputed milestone of traditional oncology is neoplastic progression, which consists of a progressive selection of dedifferentiated cells driven by a chance sequence of genetic mutations. Recently it has been demonstrated that the overexpression of well-defined transcription factors reprograms somatic cells to the pluripotent stem status. The demonstration raises crucial questions as to whether and to what extent this reprogramming contributes to tumorigenesis, and whether the epigenetic changes involved in it are reversible. Here, we show for the first time that a tumor produced in vivo by a chemical carcinogen is the product of the interaction between neoplastic progression and reprogramming. The experimental model employed the prototype of ascites tumors, the Yoshida AH130 hepatoma and other neoplasias, including human melanoma. AH130 hepatoma was started in the liver by the carcinogen o-aminoazotoluene. This compound binds to and abolishes the p53 protein, producing a genomic instability that promotes both the neoplastic progression and the hepatoma reprogramming. Eventually this tumor contained 100% CD133(+) elements and pO(2)-dependent percentages of the three embryonic transcription factors Nanog, Klf4 and c-Myc. Once transferred into aerobic cultures, the minor cellular fraction expressing this triad generates various types of adherent cells, which are progressively substituted by non-tumorigenic elements committed to fibromuscular, neuronal and glial differentiation. This reprogramming appears to be accomplished stepwise, with the assembly of the triad into a sophisticated transcriptional, oxygen-dependent circuitry, in which Nanog and Klf4 antagonistically regulate c-Myc, and hence, cell hypoxia survival and cell cycle activation.

FBI-1 promotes cell proliferation and enhances resistance to chemotherapy of hepatocellular carcinoma in vitro and in vivo

BACKGROUND

The so-called factor that binds to inducer of short transcripts-1 (FBI-1) purportedly plays an important role in tumorigenesis; however, its role in hepatocellular carcinoma (HCC) remains unknown. The objective of this study was to investigate the expression level, clinical relevance, and biologic function of FBI-1 in HCC.

METHODS

Real-time quantitative reverse transcriptase-polymerase chain reaction analysis, Western blot analysis, and immunohistochemical staining were used to detect expression levels of FBI-1 and to analyze its relation to clinicopathologic parameters and to the prognosis of patients with HCC. In addition, the biologic functions of FBI-1 in regulating cell proliferation, migration, and reaction to chemotherapy were detected by using HepG2 cells and SMMC-7721 cells; subsequently, the molecular mechanism of FBI-1 also was investigated. Finally, a xenograft mouse model was used to validate the observations obtained from in vitro studies.

RESULTS

Expression levels of FBI-1 messenger RNA and protein were elevated significantly in HCC tissues compared with adjacent nontumorous liver tissues (ANLTs). Increased FBI-1 expression was correlated with multiple tumor nodes, Edmondson-Steiner grade, and a poor prognosis in patients with HCC (P < .05). In vitro studies revealed that FBI-1 was capable of promoting cell proliferation (but not cell migration) by regulating the cell cycle regulation proteins p53, p21, and p27. In addition, FBI-1 could inhibit cell death induced by 5-fluorouracil or doxorubicin through suppressing the activation of p53. Consistent with the in vitro data, FBI-1 was capable of promoting cell proliferation and enhancing chemotherapy resistance of HCC in vivo.

CONCLUSIONS

The current findings indicated that FBI-1 plays an important role in HCC carcinogenesis and chemotherapy tolerance, and FBI-1 may served as a novel prognostic marker and therapeutic target for HCC.

A novel oncoprotein Pirh2: rising from the shadow of MDM2

Pirh2 (p53-induced RING-H2) is an E3 ubiquitin ligase that can target p53 for degradation and thereby repress a diverse group of biological activities regulated by p53. Notably, Pirh2, rather than MDM2, is the primary degrader of active p53 under conditions of DNA damage. Moreover, Pirh2 is highly expressed in multiple cancer cell lines regardless of p53 status. Recent research has shown that Pirh2 is involved in many signalling pathways related to the genesis and evolution of cancer. This review aims to summarize a comprehensive picture of the role of Pirh2 in cellular processes and its significance to tumorigenesis. Furthermore, this review focuses on its potential role as a cancer therapeutic target.

Expression of Pirh2, a p27(Kip1) ubiquitin ligase, in hepatocellular carcinoma: correlation with p27(Kip1) and cell proliferation

p53-Induced ring-H2 protein (Pirh2), a recently identified ubiquitin-protein ligase, interacts with p27(Kip1) to promote ubiquitination of p27(Kip1) independently of p53. High Pirh2 and low p27(Kip1) immunoreactivity are associated with a poor prognosis in several cancers, including resistant phenotypes. In the present study, we investigated the role of Pirh2 and p27(Kip1) in human hepatocellular carcinoma (HCC) progression. Immunohistochemical analysis was performed on formalin-fixed paraffin sections of 87 specimens. Statistical analysis showed that expression of Pirh2 was negatively related to p27(Kip1) expression (r = 0.787; P < .05), and Pirh2 expression correlated significantly with histologic grade (P < .001), venous invasion (P = .004), tumor size (P = .024), and the presence of multiple tumor-bearing lymph nodes (P = .017), whereas p27(Kip1) expression correlated significantly with histologic grade (P < .001), venous invasion (P = .048), and cirrhosis (P = .028). By Kaplan-Meier analysis, the survival curves of low versus high expressers of Pirh2 and p27(Kip1) showed significant separation (P < .01). Molecular interaction could be demonstrated between Pirh2 and p27(Kip1) in three HCC cell lines. In vitro, following release of two HCC cell lines from serum starvation, the expression of Pirh2 was upregulated, whereas p27(Kip1) was downregulated. Our results suggest that Pirh2 mediates the degradation of p27(Kip1) and participates in cell proliferation in human HCC. These findings provide a rational framework for further development of Pirh2 inhibitors as a novel class of anti-tumor agents.

The antagonism between MCT-1 and p53 affects the tumorigenic outcomes

Background

MCT-1 oncoprotein accelerates p53 protein degradation via a proteosome pathway. Synergistic promotion of the xenograft tumorigenicity has been demonstrated in circumstance of p53 loss alongside MCT-1 overexpression. However, the molecular regulation between MCT-1 and p53 in tumor development remains ambiguous. We speculate that MCT-1 may counteract p53 through the diverse mechanisms that determine the tumorigenic outcomes.

Results

MCT-1 has now identified as a novel target gene of p53 transcriptional regulation. MCT-1 promoter region contains the response elements reactive with wild-type p53 but not mutant p53. Functional p53 suppresses MCT-1 promoter activity and MCT-1 mRNA stability. In a negative feedback regulation, constitutively expressed MCT-1 decreases p53 promoter function and p53 mRNA stability. The apoptotic events are also significantly prevented by oncogenic MCT-1 in a p53-dependent or a p53-independent fashion, according to the genotoxic mechanism. Moreover, oncogenic MCT-1 promotes the tumorigenicity in mice xenografts of p53-null and p53-positive lung cancer cells. In support of the tumor growth are irrepressible by p53 reactivation in vivo, the inhibitors of p53 (MDM2, Pirh2, and Cop1) are constantly stimulated by MCT-1 oncoprotein.

Conclusions

The oppositions between MCT-1 and p53 are firstly confirmed at multistage processes that include transcription control, mRNA metabolism, and protein expression. MCT-1 oncogenicity can overcome p53 function that persistently advances the tumor development.