Immunohistochemical study of Skp2 and Jab1, two key molecules in the degradation of P27, in lung adenocarcinoma

Targeting the untargetable: RB1-deficient tumours are vulnerable to Skp2 ubiquitin ligase inhibition

Proteins that regulate the cell cycle are accumulated and degraded in a coordinated manner during the transition from one cell cycle phase to the next. The rapid loss of a critical protein, for example, to allow the cell to move from G1/G0 to S phase, is often regulated by its ubiquitination and subsequent proteasomal degradation. Protein ubiquitination is mediated by a series of three ligases, of which the E3 ligases provide the specificity for a particular protein substrate. One such E3 ligase is SCF^Skp1/Cks1, which has a substrate recruiting subunit called S-phase kinase-associated protein 2 (Skp2). Skp2 regulates cell proliferation, apoptosis, and differentiation, can act as an oncogene, and is overexpressed in human cancer. A primary target of Skp2 is the cyclin-dependent kinase inhibitor p27 (CDKN1b) that regulates the cell cycle at several points. The RB1 tumour suppressor gene regulates Skp2 activity by two mechanisms: by controlling its mRNA expression, and by an effect on Skp2's enzymatic activity. For the latter, the RB1 protein (pRb) directly binds to the substrate-binding site on Skp2, preventing protein substrates from being ubiquitinated and degraded. Inactivating mutations in RB1 are common in human cancer, becoming more frequent in aggressive, metastatic, and drug-resistant tumours. Hence, RB1 mutation leads to the loss of pRb, an unrestrained increase in Skp2 activity, the unregulated decrease in p27, and the loss of cell cycle control. Because RB1 mutations lead to the loss of a functional protein, its direct targeting is not possible. This perspective will discuss evidence validating Skp2 as a therapeutic target in RB1-deficient cancer.

The pivotal oncogenic role of Jab1/CSN5 and its therapeutic implications in human cancer

Jab1/CSN5 is a conserved multifunctional protein involved in ubiquitin-mediated protein degradation. Deregulation of Jab1/CSN5 can exert dramatic effects on diverse cellular functions, including DNA repair, cell cycle control, apoptosis, angiogenesis, and signal transduction, all of which are critical for tumor development. Although increasing evidence has demonstrated that Jab1/CSN5 was overexpressed in a variety of human cancers and usually correlated with poor prognosis, little was known about the underlying regulatory principles that coordinated its function. In this review, we highlight recent advances of the oncogenic role of Jab1/CSN5 and its potential as a therapeutic target for anticancer intervention.

Increased Jab1/COPS5 is associated with therapeutic response and adverse outcome in lung cancer and breast cancer patients

Adjuvant chemotherapy has been established as standard treatment for advanced cancer among multidisciplinary therapies. A simple and instructive biomarker for therapeutic response and recurrence is needed to evaluate the therapeutic effect. Jab1/COPS5 level has been shown to be associated with tumor progression and poor outcomes in many types of cancer patients. This study aims to further evaluate the clinical and prognostic value of Jab1/COPS5 level as a biomarker in lung and breast cancer patients receiving adjuvant chemotherapy. In this study, data of 88 lung cancer and 76 breast cancer patients were retrospectively collected and analyzed to identify the relationship between the Jab1/COPS5 level and the clinical progression and outcome of these patients. Lung cancer patients with increased Jab1/COPS5 level tend to be non-responsive to chemotherapy. Relapsed breast cancer patients had an increased Jab1/COPS5 level and breast cancer patients with increased Jab1/COPS5 level had significantly shorter disease-free survival and overall survival. In a multivariate survival analysis, histological type and Jab1/COPS5 were associated with disease-free survival and overall survival. The Jab1/COPS5 level was found to be a possible biomarker for clinical response to chemotherapy in lung cancer patients and for postoperative relapse in breast cancer patients who received adjuvant chemotherapy. In conclusion, this study identified Jab1/COPS5 as novel prognostic markers for lung cancer and breast cancer.

Prognostic impact of Jab1, p16, p21, p62, Ki67 and Skp2 in soft tissue sarcomas

PURPOSE

The purpose of this study is to clarify the prognostic significance of expression of Jab1, p16, p21, p62, Ki67 and Skp2 in soft tissue sarcomas (STS). Optimised treatment of STS requires better identification of high risk patients who will benefit from adjuvant therapy. The prognostic significance of Jab1, p16, p21, p62, Ki67 and Skp2 in STS has not been sufficiently investigated.

EXPERIMENTAL DESIGN

Tissue microarrays from 193 STS patients were constructed from duplicate cores of viable and representative neoplastic tumor areas. Immunohistochemistry was used to evaluate the expression of Jab1, p16, p21, p62, Ki67 and Skp2.

RESULTS

In univariate analyses, high tumor expression of Ki67 (P = 0.007) and Skp2 (P = 0.050) correlated with shorter disease-specific survival (DSS). In subgroup analysis, a correlation between Skp2 and DSS was seen in patients with malignancy grade 1 or 2 (P = 0.027), tumor size >5 cm (P = 0.018), no radiotherapy given (P = 0.029) and no chemotherapy given (P = 0.017). No such relationship was apparent for Jab1, p16, p21 and p62; but p62 showed a positive correlation to malignancy grade (P = 0.019). Ki67 was strongly positively correlated to malignancy grade (P = 0.001). In multivariate analyses, Skp2 was an independent negative prognostic factor for DSS in women (P = 0.009) and in patients without administered chemotherapy or radiotherapy (P = 0.026).

CONCLUSIONS

Increased expression of Skp2 in patients with soft tissue sarcomas is an independent negative prognostic factor for disease-specific survival in women and in patients not administered chemotherapy or radiotherapy. Besides, further studies are warranted to explore if adjuvant chemotherapy or radiotherapy improve the poor prognosis of STS with high Skp2 expression.

Targeting Jab1/CSN5 in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus-associated head and neck cancer that is most common in eastern Asia. Epstein-Barr virus infection, environmental factors, and genetic susceptibility play important roles in NPC pathogenesis. Jab1/CSN5 is a multifunctional protein that participates in affecting integrin signaling, controlling cell proliferation and apoptosis, and regulating genomic instability and DNA repair. Correlation of Jab1/CSN5 overexpression with poor prognosis for NPC provides evidence that it is involved in the tumorigenic process. In this review, we highlight recent advances in studies of the oncogenic role of Jab1/CSN5 in NPC and its potential as a therapeutic target for this cancer.

Molecular targeting of CSN5 in human hepatocellular carcinoma: a mechanism of therapeutic response

Development of targeted therapy for hepatocellular carcinoma (HCC) remains a major challenge. We have recently identified an elevated expression of the fifth subunit of COP9 signalosome (CSN5) in early HCC as compared to dysplastic stage. In the present study, we explored the possibility of CSN5 being a potential therapeutic target for HCC. Our results show that CSN5 knockdown by small interfering (si) RNA caused a strong induction of apoptosis and inhibition of cell cycle progression in HCC cells in vitro. The downregulation of CSN5 was sufficient to interfere with CSN function as evidenced by the accumulation of neddylated Cullin1 and changes in the protein levels of CSN controlled substrates SKP2, p53, p27 and NF-kB, albeit to a different degree depending on the HCC cell line, which could account for the CSN5 knockdown phenotype. The transcriptomic analysis of CSN5 knockdown signature showed that the anti-proliferative effect was driven by a common subset of molecular alterations including downregulation of CDK6 and ITGB1, which were functionally interconnected with key oncogenic regulators MYC and TGFβ1 involved in the control of proliferation, apoptotic cell death and HCC progression. Consistent with microarray analysis, western blotting revealed that CSN5 depletion increased phosphorylation of Smad 2/3, key mediators of TGFβ1 signaling, decreased the protein levels of ITGB1, CDK6, and cyclin D1 and caused reduced expression of anti-apoptotic Bcl-2 while elevating the levels of pro-apoptotic Bak. A chemically modified variant of CSN5 siRNA was then selected for in vivo application based on the growth inhibitory effect and minimal induction of unwanted immune response. Systemic delivery of the CSN5 3/8 variant by stable-nucleic-acid-lipid-particles (SNALP) significantly suppressed the tumor growth in Huh7-luc⁺ orthotopic xenograft model. Taken together, these results indicate that CSN5 plays a pivotal role in HCC pathogenesis and maybe an attractive molecular target for systemic HCC therapy.

JAB1/CSN5: a new player in cell cycle control and cancer

c-Jun activation domain-binding protein-1 (Jab1) acts as a modulator of intracellular signaling and affects cellular proliferation and apoptosis, through its existence as a monomer or as the fifth component of the constitutive photomorphogenic-9 signalosome (CSN5). Jab1/CSN5 is involved in transcription factor specificity, deneddylation of NEDD8, and nuclear-to-cytoplasmic shuttling of key molecules. Jab1/CSN5 activities positively and negatively affect a number of pathways, including integrin signaling, cell cycle control, and apoptosis. Also, more recent studies have demonstrated the intriguing roles of Jab1/CSN5 in regulating genomic instability and DNA repair. The effects of Jab1/CSN5's multiple protein interactions are generally oncogenic in nature, and overexpression of Jab1/CSN5 in cancer provides evidence that it is involved in the tumorigenic process. In this review, we highlight our current knowledge of Jab1/CSN5 function and the recent discoveries in dissecting the Jab1 signaling pathway. Further, we also discuss the regulation of Jab1/CSN5 in cancers and its potential as a therapeutic target.

Clinicopathological significance of expression of Tspan-1, Jab1 and p27 in human hepatocellular carcinoma

The aim of this study was to investigate the expression of Tspan-1, Jab1 and p27 in human hepatocellular carcinoma (HCC) and their clinicopathological significance. The expression of Tspan-1, Jab1 and p27 was detected in HCC tissues, the tissues around cancer (76 cases), and the normal tissues around the liver hemangiomas (10 cases). The overexpression of Tspan-1 and Jab1 was found in HCC tissues, positively correlated with clinical stage and negatively correlated with survival rate. The expression of p27 was found inversely linked to which of Tspan-1 and Jab1. In conclusion, the expression of Tspan-1, Jab1 and p27 is significantly associated with development of HCC. Overexpression of Tspan-1 and Jab1 suggests poor prognosis but overexpression of p27 may expect good prognosis for patients with HCC.

Jab1/CSN5 induces the cytoplasmic localization and degradation of RUNX3

Runt-related (RUNX) transcription factors play pivotal roles in neoplastic development and have tissue-specific developmental roles in hematopoiesis (RUNX1), osteogenesis (RUNX2), as well as neurogenesis and thymopoiesis (RUNX3). RUNX3 is a tumor suppressor in gastric carcinoma, and its expression is frequently inactivated by DNA methylation or its protein mislocalized in many cancer types, including gastric and breast cancer. Jun-activation domain-binding protein 1 (Jab1/CSN5), a component of the COP9 signalosome (CSN), is critical for nuclear export and the degradation of several tumor suppressor proteins, including p53, p27(Kip1), and Smad4. Here, we find that Jab1 facilitates nuclear export of RUNX3 that is controlled by CSN-associated kinases. RUNX3 sequestered in the cytoplasm is rapidly degraded through a proteasome-mediated pathway. Our results identify a novel mechanism of regulating nuclear export and protein stability of RUNX3 by the CSN complex.

Jab1 has negative effects on p53-mediated genotoxic stresses

In this study, we use promoter analysis to show that interaction between Jab1 and p53 induces suppression of p53 activation in U2OS and H1299 cells. Interaction between p53 and Jab1 was further confirmed by immunoprecipitation and immunofluorescent analyses. In particular, Jab1 was able to induce nuclear export of p53 as previously reported. When Jab1 was overexpressed in U2OS cells followed by etoposide or hydrogen peroxide (H(2)O(2)), cell death induced by such stresses was protected against. On the contrary, when the level of Jab1 was suppressed in U2OS cells, cytotoxicity imposed by etoposide and H(2)O(2) was dramatically increased, suggesting a cell protective role for Jab1. These results indicate that Jab1 is a negative regulator of p53 and a plausible oncogene.

Immunohistochemically detected expression of p27(Kip1) and Skp2 predicts survival in patients with intrahepatic cholangiocarcinomas

In intrahepatic cholangiocarcinomas (ICCs), the prognostic significance of p27(Kip1), a cyclin-dependent kinase inhibitor, remains controversial, and there have been no studies of degradation pathway associated proteins, S-phase kinase-interacting protein (Skp2), and Jun activation domain-binding protein-1 (Jab1). In the present study of 74 patients with ICC-mass forming type (ICC-MF) undergoing radical surgery, we determined immunohistochemical expression of p27(Kip1), Skp2, and Jab1 and examined relationships with clinicopathologic findings and patient survival. On the basis of the average of labeling indices, we set cutoff values to define high and low expressors and divided the cases into two groups. A statistically significant correlation was found between low p27(Kip1) expression and lymph node metastasis (P = .009). Patient survival in the low p27(Kip1) expression group (n = 25) was also significantly worse than that in the high p27(Kip1) expression group (n = 49, P = .0007). A significant inverse correlation was found between p27(Kip1) and Skp2 expression (P = .016). High Skp2 expression (n = 36) was significantly associated with poor prognosis (P = .0046). High Jab1 expression was observed in 32 cases, but there was no statistically significant relationship with clinicopathologic findings or patient survival. The multivariate analysis revealed that low p27(Kip1) and high Skp2 expression are independent and significant factors of poor prognosis. The results suggest that low p27(Kip1) and high Skp2 expression are associated with aggressive tumor behavior, and these cell-cycle regulators are useful markers to predict outcome of patients with ICC-MF.

p27(Kip1)is overexpressed in very early stages of hepatocarcinogenesis

Hepatocellular carcinoma (HCC) associated with chronic liver disease evolves from precancerous lesions and early HCC to more malignant forms. Despite the demonstrated importance of cell-cycle regulators in tumor biology, there have been few studies of their role in multistep hepatocarcinogenesis. Expression of p27(Kip1) and a degradation pathway associated protein, S-phase kinase-interacting protein 2 (Skp2), was therefore evaluated in surgically resected specimens of eight adenomatous hyperplasias, 16 early HCC and 126 classical HCC. Immunohistochemistry revealed no p27(Kip1) expression in the majority of hepatocytes from normal and cirrhotic liver, whereas positive staining for p27(Kip1) protein was found in 75.0% and 93.8% of adenomatous hyperplasias and early HCC, respectively. The average p27(Kip1) labeling indices (LI) for adenomatous hyperplasias, early HCC, well differentiated HCC, moderately differentiated HCC and poorly differentiated HCC were 36.99, 43.59, 47.73, 49.24, and 30.21, respectively. Real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses confirmed the increases. Skp2 LI were also significantly elevated in accordance with stepwise progression of hepatocarcinogenesis. Increased expression of Skp2 mRNA was observed most frequently in less differentiated tumors and Kaplan-Meier survival analysis showed a significantly association with a poor prognosis (P = 0.0496). In conclusion, a high level of p27(Kip1) expression is evident from early stages of hepatocarcinogenesis, indicating that this parameter could be a useful diagnostic marker for precancerous lesions and early HCC. In addition, Skp2 expression correlates with tumor dedifferentiation and may contribute to biological aggression in HCC.

Stable form of JAB1 enhances proliferation and maintenance of hematopoietic progenitors

Overexpression of JAB1 is observed in a variety of human cancers, but how JAB1 is involved in tumor development remained to be investigated. Here we analyzed mice with modified Jab1 expression. Mice ectopically expressing a more stable form of JAB1 protein under the control of a constitutive promoter were rescued from the embryonic lethality caused by the Jab1(-/-) allele and developed a myeloproliferative disorder in a gene dosage-dependent manner. Hematopoietic cells from the bone marrow of Jab1 transgenic mice had a significantly larger stem cell population and exhibited higher and transplantable proliferative potential. In contrast, Jab1(+/-) mice, which express approximately 70% as much JAB1 protein as their wild-type littermates, showed inefficient hematopoiesis. Expression of the tumor suppressor p16(INK4a) was inversely correlated with that of JAB1, and the oncoprotein SMYD3, a newly identified JAB1 interactor, suppressed transcription of p16 in cooperation with JAB1. Thus, the expression and function of JAB1 are critical for the proliferation and maintenance of hematopoietic progenitors.

Skp2 expression is associated with high risk and elevated Ki67 expression in gastrointestinal stromal tumours

Background

Gastrointestinal stromal tumors (GIST) exhibit an unpredictable clinical course and can rapidly progress to lethality. Predictions about the biological behavior of GIST are based on a number of canonical clinical and pathologic parameters whose validity in distinguishing between a benign and a malignant tumour is still imperfect. The aim of our study was to investigate the role of morphologic parameters and expression of cells cycle regulators as prognosticators in GIST.

Methods

We performed an immunohistochemical analysis for Ki67, p27^Kip1, Jab1, and Skp2, on a Tissue Microarray (TMA) containing 94 GIST. Expression of the above proteins was correlated to classically used prognosticators, as well as to risk groups. Clinical significance of histologic and immunohistochemical features were evaluated in 59 patients for whom follow-up information was available.

Results

Overexpression of Ki67 and Skp2, and p27^Kip1 loss directly correlated with the high risk group (p = 0.03 for Ki67 and Skp2, p = 0.05 for p27^Kip1). Jab1 expression did not exhibit correlation with risk. In 59 cases provided with clinical follow-up, high cellularity, presence of necrosis, and Ki67 overexpression were predictive of a reduced overall survival in a univariate model. The same parameters, as well as mitotic rate, tumour size, and p27^Kip1 loss were indicative of a shortened relapse free survival interval. High cellularity, and high mitotic rate retained their prognostic significance by multivariate analysis.

Conclusion

Our data suggest that a number of histologic parameters in combination with immunohistochemical expression of cell cycle regulators can facilitate risk categorization and predict biologic behavior in GIST. Importantly this study demonstrates, for the first time, that Skp2 expression correlates with Ki67 expression and high risk in GIST.

PI3K/Akt/p27kip1 pathway mediates chemoresistance to Etoposide and Doxorubicin in gastric carcinoma cell line BGC-823 and its mechanism

AIM: To investigate the effect of chemo-resistance to Etoposide and Doxorubicin mediated by the PI3K/Akt/p27 pathway on human gastric carcinoma cell line BGC-823 and its mechanism.

METHODS: Cultured BGC-823 gastric cancer cells were divided into control group, PI3K/Akt/p27 Kip1 channel inhibitor Wort (Wort) group, Etoposide (Eto) group, Doxorubicin (Dox) group, Eto + Wort group and Dox + Wort group. Cell survival was assessed with MTT method. Cell cycle and apoptosis were detected using a flow cytometer (FCM). Expression level of p27 Kip1 and p27 gene mRNA was determined by Western blotting analysis and reverse transcription-polymerase chain reaction, respectively.

RESULTS: The cell survival rate at 24 h was lower in Wort group, Eto +Wort group and Dox +Wort group than in control group (57.8%, 46.5%, 44.3% vs 46.5%, 44.3%, P < 0.01). The cell ratio in G₀-G₁ phase was higher in Wort group, Eto +Wort group and Dox + Wort group than in control group (85.0 ± 3.54, 91.5 ± 3.63, 92.4 ± 3.64 vs 71.5 ± 3.25, P < 0.01) and the protein expression was increased at 12 h and 24 h. The cell survival rate in Eto and Dox groups was higher than that in control group, but no obvious change was found in G₀ - G₁ phase. The p27 mRNA expression was similar in different groups.

CONCLUSION: Activation of PI3K/Akt/p27 channel can mediate chemo-resistance to tumor cells.

Hepatitis B virus pre-S2 mutant surface antigen induces degradation of cyclin-dependent kinase inhibitor p27Kip1 through c-Jun activation domain-binding protein 1

The hepatitis B virus (HBV) large surface antigen (LHBS) mutant with deletion at the pre-S(2) region accumulates in endoplasmic reticulum (ER) and is associated with HBV-induced hepatocellular carcinogenesis. In this study, we found that the pre-S(2) LHBS mutant directly interacts with the Jun activation domain-binding protein 1 (JAB1). Association of pre-S(2) LHBS with JAB1 dissociated JAB1 from the JAB1/IRE1 complex in ER. The free (active) JAB1 then translocated into cell nuclei and rendered the Cdk inhibitor p27(Kip1) to cytosolic proteasome for degradation. The pre-S(2) LHBS mutant induced hyperphosphorylation of tumor suppressor retinoblastoma (RB) via cyclin-dependent kinase 2 (Cdk2), a downstream molecule regulated by p27(Kip1). This effect is independent of the ER stress signaling pathway. The transgenic mice carrying the pre-S(2) mutant LHBS gene also exhibited Cdk2 activation, p27(Kip1) degradation, as well as RB hyperphosphorylation. The mouse hepatocytes exhibited morphologic abnormalities such as chromatin condensation, multinucleation, and dysplasia of hepatocytes. In summary, the pre-S(2) LHBS mutant causes p27(Kip1) degradation through direct interaction with JAB1. The pre-S(2) mutant LHBS is suggested to be a potential oncoprotein for HBV-related hepatocellular carcinoma.

The E3 ubiquitin ligase skp2 regulates neural differentiation independent from the cell cycle

Background

The SCF^skp2 complex is an E3 ubiquitin ligase that is known to target a number of cell cycle regulators, including cyclin-dependent kinase inhibitors, for proteolysis. While its role in regulation of cell division has been well documented, additional functions in differentiation, including in the nervous system, have not been investigated.

Results

Using Xenopus as a model system, here we demonstrate that skp2 has an additional role in regulation of differentiation of primary neurons, the first neurons to differentiate in the neural plate. Xenopus skp2 shows a dynamic expression pattern in early embryonic neural tissue and depletion of skp2 results in generation of extra primary neurons. In contrast, over-expression of skp2 inhibits neurogenesis in a manner dependent on its ability to act as part of the SCF^skp2 complex. Moreover, inhibition of neurogenesis by skp2 occurs upstream of the proneural gene encoding NeuroD and prior to cell cycle exit. We have previously demonstrated that the Xenopus cyclin dependent kinase inhibitor Xic1 is essential for primary neurogenesis at an early stage, and before these cells exit the cell cycle. We show that SCF^skp2 degrades Xic1 in embryos and this contributes to the ability of skp2 to regulate neurogenesis.

Conclusion

We conclude that the SCF^skp2 complex has functions in the control of neuronal differentiation additional to its role in cell cycle regulation. Thus, it is well placed to be a co-ordinating factor regulating both cell proliferation and cell differentiation directly.

Potential role of Jun activation domain-binding protein 1 as a negative regulator of p27kip1 in pancreatic adenocarcinoma

Reduced expression of p27 has been associated with poor prognosis in most human cancers, including pancreatic adenocarcinoma. Jun activation domain-binding protein 1 (JAB1), an activator protein (AP-1) coactivator, previously implicated in p27 degradation, is overexpressed in various tumors and correlates with low p27 expression. We examined JAB1 and p27 in normal and neoplastic pancreatic tissues. Increased JAB1 expression was seen in pancreatic carcinoma samples but not in paired normal pancreatic tissues. Immunohistochemical analysis using tissue microarrays showed that JAB1 was overexpressed in all 32 (100%) pancreatic adenocarcinoma samples tested, predominantly nuclear in 23 (72%) samples and predominantly cytoplasmic in 9 (28%) tumors. When 10% was used as a cutoff for p27 positivity, p27 was expressed in 11 (34%) of tumors; however, p27 expression was localized in the nuclei of tumor cells in only 4 (13%) of the samples. Overexpression of the JAB1 in the pancreatic carcinoma cell lines Panc-1, Mia PaCa-2, and Panc-28 resulted in decreased p27 expression. Conversely, down-regulation of JAB1 by short interfering RNA substantially increased p27 expression and inhibited progression from G(1) to S phase of the cell cycle. Interestingly, JAB1-mediated p27 degradation was not impaired when S-phase kinase-interacting protein 2 (Skp2), an F-box protein required for the ubiquitination and consequent degradation of p27, was silenced. Thus, JAB1 may have an Skp2-independent p27 degradation mechanism in pancreatic cancer cells. These findings suggest that JAB1 overexpression is involved in the pathogenesis of pancreatic cancer through JAB1-mediated p27 degradation and that control of JAB1 expression is a novel therapeutic target in patients with pancreatic adenocarcinomas.

Inverse expression of Jun activation domain binding protein 1 and cell cycle inhibitor p27Kip1: influence on proliferation in hepatocellular carcinoma

Recently, the functional role of Jun activation domain binding protein 1 (Jab1) as a putative novel oncogene in hepatocellular carcinoma (HCC) has been postulated. We show that expression of p27(Kip1), a negative cell cycle regulator, correlates inversely with Jab1 expression in HCC (P = .014). We observed nuclear Jab1 expression in 57% (55/97) and p27(Kip1) expression in 32% (31/97) of HCCs. Neither Jab1 nor p27(Kip1) nor inverse Jab1 and p27(Kip1) expression correlated with clinicopathological parameters. However, HCCs lacking p27(Kip1) with increased proliferative activity were frequently found to express Jab1 (P = .048). Normal liver tissue, cirrhosis, and tumor-like lesions (focal nodular hyperplasia, dysplastic nodules in cirrhotic liver) showed no significant Jab1 expression. In transfection studies in the hepatoma cell line Huh 7, Jab1 overexpression resulted in reduced p27(Kip1) protein levels. We conclude that Jab1 expression may lead to down-regulation of the negative cell cycle regulator p27(Kip1), pointing to a possible mechanism that promotes hepatocarcinogenesis.

c-Met activation in lung adenocarcinoma tissues: an immunohistochemical analysis

c-Met is often overexpressed in non-small cell lung cancer, but it remains unsolved whether its overexpression leads to its activation. We used an antibody specific to phospho-c-Met (Tyr1235) to investigate c-Met activation immunohistochemically in 130 surgically resected lung adenocarcinomas. The expression of c-Met and hepatocyte growth factor (HGF) was also investigated. Phospho-c-Met was positive in 21.5% (28/130) of cases. c-Met was positive in 74.6% of cases (97/130) and was expressed at high levels in 36.1% of cases (47/130). HGF was expressed at high levels in 31.5% of cases (41/130). Phospho-c-Met was correlated with high levels of HGF (P =0.0010) and high levels c-Met expression (P = 0.0303), but it was also found to be positive in 12 cases with little to no HGF expression. Phospho-c-Met expression was significantly associated with tumor differentiation (P = 0.0023) and papillary histology (P = 0.0011), but not with pathological stage, lymph node metastasis or survival. High levels of c-Met and HGF were also associated with papillary histology (P = 0.0056 and P = 0.0396, respectively), but not with tumor differentiation. Phospho-c-Met was correlated with phospho-Akt (P = 0.0381), but not with phospho-Erk or phospho-Stat3. Phospho-Akt expression was marginally correlated with the expression of phospho-epidermal growth factor receptor (EGFR) (P = 0.0533) and, importantly, it was strongly correlated with the expression of either phospho-c-Met or phospho-EGFR (P = 0.0013). The data suggest that in lung adenocarcinoma tissue, c-Met activation may take place either ligand-dependently or ligand-independently via c-Met overexpression. c-Met activation may play special roles in the papillary subtype and in well differentiated lung adenocarcinomas.

Preparation and characterization of monoclonal antibodies against mouse Jab1/CSN5 protein

Jab1, also known as the fifth component of the COP9 signalosome complex (CSN5), directly interacts with and regulates the activity and stability of multiple intracellular regulatory molecules, such as c-Jun, p27, p53, Cullin, Smad4, and HIF1alpha. In addition, a high level of Jab1 is observed in a variety of human cancers and is sometimes correlated with a poor prognosis, suggesting that Jab1 contributes to cancer cell proliferation and survival and could be a novel target of cancer therapy. In this report, we generated five mouse monoclonal antibodies to a bacterially produced recombinant mouse Jab1 protein and examined their capabilities and limitations in commonly used assays, including enzyme linked immunosorbent assay (ELISA), Western blotting with denatured and native polyacrylamide gel electrophoresis (PAGE), immunoprecipitation, and immunofluorescence microscopy, finding the most suitable antibody for each application. Because these antibodies proved useful for immunohistochemical staining for Jab1 in fixed sections of human cancer samples, they should be useful in determining the expression and subcellular distribution of Jab1 in human tumors.

Downregulation of the KIP family members p27(KIP1) and p57(KIP2) by SKP2 and the role of methylation in p57(KIP2) inactivation in nonsmall cell lung cancer

Knowing the status of molecules involved in cell cycle control in cancer is vital for therapeutic approaches aiming at their restoration. The p27(KIP1) and p57(KIP2) cyclin-dependent kinase inhibitors are nodal factors controlling normal cell cycle. Their expression in normal lung raises the question whether they have a mutual exclusive or redundant role in nonsmall cell lung cancer (NSCLC). A comparative comprehensive analysis was performed in a series of 70 NSCLCs. The majority of cases showed significantly reduced expression of both members compared to normal counterparts. Low KIP protein levels correlated with increased proliferation, which seems to be histological subtype preponderant. At mechanistic level, degradation by SKP2 was demonstrated, in vivo and in vitro, by siRNA-methodology, to be the most important downregulating mechanism of both KIPs in NSCLC. Decreased p57(KIP) (2)-transcription complements the above procedure in lowering p57(KIP2)-protein levels. Methylation was the main cause of decreased p57(KIP) (2)-mRNA levels. Allelic loss and imprinting from LIT1 mRNA contribute also to decreased p57(KIP2) transcription. In vitro recapitulation of the in vivo findings, in A549 lung cells (INK4A-B((-/-))), suggested that inhibition of the SKP2-degradation mechanism restores p27(KIP1) and p57(KIP2) expression. Double siRNA treatments demonstrated that each KIP is independently capable of restraining cell growth. An additional demethylation step is required for complete reconstitution of p57(KIP2) expression in NSCLC.

Cytoplasmic localization of p63 is associated with poor patient survival in lung adenocarcinoma

AIMS

To determine the significance of p63 protein expression in the development and progression of lung adenocarcinoma.

METHODS AND RESULTS

The expression of p63 was immunohistochemically investigated in 92 cases of lung adenocarcinoma with a maximum diameter of 30 mm or less. p63 expression was observed not only in the nuclei (46/92 cases, 50%), but also in the cytoplasm of neoplastic cells (47/92, 51%). Nuclear localization of p63 was correlated with nuclear accumulation of p53 (P=0.0120), whereas the presence of nuclear p63 had no apparent effect on patient survival. Cytoplasmic localization of p63 was found to be correlated with shorter survival periods by univariate and multivariate analyses (P=0.0486 and P=0.0488, respectively) and the relation was independent of clinicopathological factors. Cytoplasmic localization of p63 was further confirmed by immunoblots of the cytoplasmic fraction of HLC-1, a lung adenocarcinoma cell line which predominately expressed DeltaNp63alpha transcript relative to TAp63 transcript by quantitative reverse transcriptase-polymerase chain reaction.

CONCLUSIONS

Cytoplasmic expression of p63 is an adverse prognostic factor in patients with adenocarcinoma of the lung.

Depletion of Jab1 inhibits proliferation of pancreatic cancer cell lines

Jab1 overexpression is observed in many human cancers, but its physiological significance remains to be investigated. We reduced the level of Jab1 expression in pancreatic cancer cell lines, MIA PaCa-2 and PANC-1 by the RNA interference and found that Jab1-knockdown resulted in impaired cell proliferation and enhanced apoptosis regardless of the genotype of the tumor suppressor p53. This growth inhibition was rescued by the introduction of siRNA-resistant mouse Jab1 cDNA. Jab1-knocked-down cells expressed a higher level of c-myc, and additional depletion of c-myc rescued cells from Jab1-knockdown-mediated growth suppression. Thus, Jab1 overexpression contributes to pancreatic cancer cell proliferation and survival. Jab1 could be a novel target in cancer therapy.

Overexpression of Jun activation domain-binding protein 1 in nonsmall cell lung cancer and its significance in p27 expression and clinical features

BACKGROUND

Decreased expression of p27, which is an inhibitor of cyclin-dependent kinase, is associated with cancer aggressiveness. It is believed that Jun activation domain-binding protein 1 (Jab1) plays a role in p27 degradation in a manner that is independent from the role played by S-phase kinase-associated protein 2 (Skp2). To examine the clinical significance of Jab1 in nonsmall cell lung cancer (NSCLC), the protein expression of Jab1 in tumor tissues was investigated with regard to the expression of p27 and Skp2.

METHODS

The clinicopathologic features and immunohistochemical expression levels of Jab1, p27, and Skp2 proteins were studied in 138 specimens from patients who underwent surgical resection for NSCLC. Survival analyses were performed by using the Kaplan-Meier method and Cox regression models.

RESULTS

High Jab1 expression (>50% of cancer cell nuclei stained) was observed in 81 specimens (59%). In Skp2-negative specimens (n = 81), an inverse correlation between the protein expression of p27 and Jab1 was observed both with the chi-square test (P = .02) and with the Mann-Whitney U test (P = .02). High Jab1 expression levels were related to poor outcomes in 118 patients who underwent complete resection, with a 5-year overall survival rate of 43.9% for patients who had high Jab1 expression and 63.1% for patients who had low Jab1 expression (P = .01). This difference was greater in patients who had Skp2-negative specimens (51.9% vs. 79.3% (P = .02), but it was not significant in patients who had Skp2-positive specimens. The multivariate analysis revealed that Jab1 expression was an independent prognostic factor for survival in patients with NSCLC (relative risk, 2.247; P = .01).

CONCLUSIONS

The current results showed for the first time that high Jab1 protein expression is related to poor outcome in patients with NSCLC and that this protein may be a target of therapy in NSCLC.

Jab1 Induces the Cytoplasmic Localization and Degradation of p53 in Coordination with Hdm2

The biological mechanisms for maintaining the basal level of p53 in normal cells require nuclear exclusion and cytoplasmic degradation. Here, we showed that Jab1 facilitates p53 nuclear exclusion and its subsequent degradation in coordination with Hdm2. p53 was excluded from the nucleus in the presence of Jab1; this exclusion was prevented by leptomycin B treatment. Nuclear export of p53 was accompanied by a decrease in the levels of p53, as well as of its target proteins, which include p21 and Bax. Domain analyses of Jab1 showed that the N-terminal domain, 1-110, was capable of inducing cytoplasmic translocation of p53. Furthermore, 110-191 was required to facilitate the degradation of p53. Neither of these mutants incorporated into the CSN complex, indicating that Jab1 could affect the levels of p53 independent of intact CSN complex. Conversely, Jab1 was incapable of translocating and degrading two p53 mutants, W23S and 6KR, neither of which could be modified by Hdm2. Moreover, Jab1 did not affect the cellular localization or protein levels of p53 in p53 and Hdm2 double-null mouse embryo fibroblasts. We further observed that the ablation of endogenous Jab1 by small interfering RNA prevented Hdm2-mediated p53 nuclear exclusion. Under stressed conditions, which could sequester Hdm2 in its inactive state, Jab1 did not affect p53. Our studies implicate that Jab1 is required to remove post-translationally modified p53 and provide a novel target for p53-related cancer therapies.

Ubiquitin ligases: cell-cycle control and cancer

A driving force of the cell cycle is the activation of cyclin-dependent kinases (CDKs), the activities of which are controlled by the ubiquitin-mediated proteolysis of key regulators such as cyclins and CDK inhibitors. Two ubiquitin ligases, the SKP1-CUL1-F-box-protein (SCF) complex and the anaphase-promoting complex/cyclosome (APC/C), are responsible for the specific ubiquitylation of many of these regulators. Deregulation of the proteolytic system might result in uncontrolled proliferation, genomic instability and cancer. Cumulative clinical evidence shows alterations in the ubiquitylation of cell-cycle regulators in the aetiology of many human malignancies. A better understanding of the ubiquitylation machinery will provide new insights into the regulatory biology of cell-cycle transitions and the development of anti-cancer drugs.

The emerging role of the COP9 signalosome in cancer

In the last several years, multiple lines of evidence have suggested that the COP9 signalosome (CSN) plays a significant role in the regulation of multiple cancers and could be an attractive target for therapeutic intervention. First, the CSN plays a key role in the regulation of Cullin-containing ubiquitin E3 ligases that are central mediators of a variety of cellular functions essential during cancer progression. Second, several studies suggest that the individual subunits of the CSN, particularly CSN5, might regulate oncogenic and tumor suppressive functions independently of, or coordinately with, the CSN holocomplex. Thus, deregulation of CSN subunit function can have a dramatic effect on diverse cellular functions, including the maintenance of DNA fidelity, cell cycle control, DNA repair, angiogenesis, and microenvironmental homeostasis that are critical for tumor development. Additionally, clinical studies have suggested that the expression or localization of some CSN subunits correlate to disease progression or clinical outcome in a variety of tumor types. Although the study of CSN function in relation to tumor progression is in its infancy, this review will address current studies in relation to cancer initiation, progression, and potential for therapeutic intervention.

Prognostic value of p27 kip1 expression in adenocarcinoma of the pancreatic head region

BACKGROUND

p27(kip1) is a tumour suppressor gene, functioning as a cyclin-dependent kinase inhibitor, and an independent prognostic factor in breast, colon, and prostate adenocarcinomas. Conflicting data are reported for adenocarcinoma of the pancreas. The aim of this study was to establish the prognostic value of p27(kip1) expression in adenocarcinoma of the pancreatic head region.

PATIENTS AND METHODS

The study included 45 patients (male/female ratio 2:1; mean age 59, range 38-82 years) with adenocarcinomas of the pancreatic head region: 24 - pancreatic head, 18 - periampullary and 3 - uncinate process. The patients underwent the Kausch-Whipple pancreatoduodenectomy (n=39), pylorus-preserving pancreatoduodenectomy (n=5), or nearly total pancreatectomy (n=1). Eight patients received adjuvant chemotherapy postoperatively. Follow-up time ranged from 3 to 60 months. Tumours were staged according to the pTNM classification (UICC 1997). Immunohistochemistry was done on paraffin-embedded blocks from tumour sections. Quantitative determination of p27(kip1) expression was based on the proportion of p27(kip1) -positive cells (< 5% = negative). Survival analysis was carried out using the Kaplan-Meier method and Cox regression model.

RESULTS

Positive p27(kip1) expression was detected in 22 tumours (49%), whereas 23 tumours (51%) were p27(kip1)-negative. There were no significant correlations between p27(kip1) index and stage or lymph node involvement. Median survival time in patients with p27(kip1)-positive tumours was 19 months, whereas in patients with p27(kip1)-negative tumours it was 18 months (p=0.53). A significant relationship was found between p27(kip1)-negative tumours and radical resection (p=0.04). Multivariate survival analysis revealed that the localization of the tumour (pancreatic head/uncinate process vs periampullary) was the only significant and independent prognosticator (p = 0.01, Cox regression model). Resection margins involvement and grade remained nearly significant prognostic factors (p=0.07 and p=0.09, respectively).

CONCLUSION

We conclude that p27(kip1) has limited overall prognostic utility in resected carcinoma of the pancreatic head region, but its potential role as a marker of residual disease needs to be further assessed.

Expression and correlations of S-phase kinase associated protein 2 and P27 protein in pancreatic cancer tissues: an analyses of 51 cases

AIM: To detect the expression of S-phase kinase associated protein 2 (SKP2) and P27 protein in human pancreatic ductal carcinoma and chronic pancreatitis, and to investigate the clinical significance and their correlations in the pancreatic ductal carcinoma.

METHODS: SP immunohistochemical method was used to detect the expression of SKP2 and P27 in the routinely paraffin-embedded sections of specimens from patients with pancreatic ductal carcinoma (n = 51) and chronic pancreatitis (n = 10)..

RESULTS: The positive rate of SKP2 expression in the pancreatic ductal carcinoma (28/51, 54.9%) was significantly higher than that in the chronic pancreatitis (2/10, 20.0%, P < 0.05), while the rate of P27 was significantly lower [25/51(49.0%) vs 9/10(90.0%), P < 0.05]. The positive rates of SKP2 expression was significantly lower in the well-differentiated (7/20, 35.0%) and non-metastasis cases (5/16, 31.2%) than those in the poorly-differentiated (14/19, 73.7%) and metastasis ones (23/35, 65.7%) (P < 0.05), while the rate of P27 expression was significantly higher in the well-differentiated (13/20, 65.0%) and non-metastasis cases (12/16, 75.0%) than those in the poorly-differentiated (6/19, 31.5%) and metastasis ones (13/35, 37.1%) (P < 0.05 or P < 0.01). The expression of SKP2 and P27 were closely correlated in the pancreatic ductal carcinoma tissue (χ² = 14.33, P < 0.01)..

CONCLUSION: SKP2 and P27 are important biological markers for reflecting the carcinogenesis, progression, and prognosis of pancreatic ductal carcinoma. The positive expression of SKP2 or the negative expression of P27 reveals more serious status of the illness, the tendency of metastasis and unfavorable prognosis. There may be a co-regulatory relationship between SKP2 and P27 expression.

Loss of TSLC1 expression in lung adenocarcinoma: relationships with histological subtypes, sex and prognostic significance

The TSLC1 (tumor suppressor in lung cancer 1) gene is a tumor suppressor recently identified through functional complementation in a lung adenocarcinoma cell line A549. In this study we immunohistochemically examined the loss of TSLC1 expression in 93 cases of surgically resected lung adenocarcinoma, and investigated its correlation with clinicopathological parameters, including histological subtypes of tumors. The prognostic significance of loss of TSLC1 expression was analyzed by univariate and multivariate analyses, in parallel with other prognostic markers such as p53, p27, and Ki-67. In non-cancerous lung tissue, TSLC1 was weakly positive in bronchial and bronchiolar epithelial cells, type II pneumocytes and bronchial glands. Overall, TSLC1 was negative in 60 of 93 lung adenocarcinomas. TSLC1 was mainly localized in the cytoplasm of the cells, but cell membrane staining was also observed, especially at sites of cell-cell adhesion. TSLC1-negative tumors were more frequently observed in male cases (41/54 cases, 70.0%) than in female cases (19/39 cases, 48.7%) (P < 0.01). Notably, TSLC1 expression was preserved in a non-invasive, bronchiolo-alveolar histological pattern of tumor cells (P < 0.0001). Survival analyses showed that loss of TSLC1 expression was associated with lower patient survival in univariate and multivariate analyses (P < 0.05 and P = 0.059, respectively). Subset analyses further showed that the prognostic impact of loss of TSLC1 was significant for male patients (P = 0.0089), but not for female patients. We conclude that TSLC1 is expressed in a subset of lung adenocarcinomas, especially in those with bronchiolo-alveolar spread pattern. Loss of TSLC1 is associated with lower patient survival, supporting its role as a tumor suppressor.

Small Jab1-containing subcomplex is regulated in an anchorage- and cell cycle-dependent manner, which is abrogated by ras transformation

Jab1 interacts with a variety of cell cycle and signal transduction regulators to control cell proliferation, differentiation, and tumorigenesis. In this study, we employed a non-denaturing gel electrophoresis method to separate different Jab1-containing complexes, the COP9 signalosome complex and the small Jab1-containing subcomplex. The formation of the small Jab1 complex was dependent on a low cell density and anchorage to a solid support, and enhanced during the early G1 phase of the cell cycle, which was abrogated in ras-transformed cells. The small Jab1-containing subcomplex may be a novel mediator of anchorage and cell-cell contact-dependent signal transduction.