Synthesis and functional analyses of nuclear clusterin, a cell death protein

Regulation of chemosensitivity and migration by clusterin in non-small cell lung cancer cells

PURPOSE

In terms of drug resistance, cancer cells usually benefit from high clusterin (CLU) expression on chemotherapy. In contrast, CLU expression has been found to be a favorable prognostic factor in lung cancer patients. The aims of this study are to determine the association between CLU expression and chemotherapeutic sensitivity and the potential role of CLU in migration in human non-small-cell lung cancer (NSCLC) cell lines.

METHODS

The levels of clusterin in NSCLC cell lines were altered by short hairpin RNA interference (shRNAi) and overexpression on chemosensitivity assay. Migratory ability of these cell lines was also investigated.

RESULTS

H1355 cells with the highest level of CLU demonstrated the lowest sensitivities to Adriamycin (ADR), docetaxel (DOC), and gemcitabine (GEM) treatment. Inhibition of CLU expression in H1355 cells resulted in higher chemosensitivities. When CLU was stably overexpressed in A549 and H1299 cells, only the chemosensitivity to ADR was reduced. The migratory ability of CLU-overexpressing cells significantly decreased. Moreover, MMP2 transcription was inhibited in CLU-overexpressing H1299 cells. These results indicated lower metastatic potential for cancer cells with high CLU level.

CONCLUSION

Lung cancer cells with high level of CLU have reduced chemosensitivity. High level of CLU may result in migratory inhibition and thus favorable prognosis in lung cancer.

Clusterin confers gemcitabine resistance in pancreatic cancer

Objective

To measure clusterin expression in pancreatic cancer tissues and cell lines and to evaluate whether clusterin confers resistance to gmcitabine in pancreatic cancer cells.

Methods

Immunohistochemistry for clusterin was performed on 50 primary pancreatic cancer tissues and 25 matched backgrounds, and clusterin expression in 5 pancreatic cancer cell lines was quantified by Western blot and PT-PCR. The correlation between clusterin expression level and gmcitabine IC50 in pancreatic cancer cell lines was evaluated. The effect of an antisense oligonucleotide (ASO) against clusterin(OGX-011) on gmcitabine resistance was evaluated by MTT assays. Xenograft model was used to demonstrate tumor growth.

Results

Pancreatic cancer tissues expressed significantly higher levels of clusterin than did normal pancreatic tissues (P < 0.01). Clusterin expression levels were correlated with gmcitabine resistance in pancreatic cancer cell lines, and OGX-011 significantly decreased BxPc-3 cells resistance to gmcitabine (P < 0.01). In vivo systemic administration of AS clusterin and gmcitabine significantly decreased the s.c. BxPC-3 tumor volume compared with mismatch control ODN plus gmcitabine.

Conclusion

Our finding that clusterin expression was significantly higher in pancreatic cancer than in normal pancreatic tissues suggests that clusterin may confer gmcitabine resistance in pancreatic cancer cells.

The conserved clusterin gene is expressed in the developing choroid plexus under the regulation of notch but not IGF signaling in zebrafish

Recent genome-wide association studies have implicated the clusterin gene in the etiology of Alzheimer's disease. The expression and function of clusterin in the developing brain, however, is poorly understood. In this study, we have characterized the zebrafish clusterin gene and determined its structural conservation, developmental expression, and physiological regulation. The structure of the zebrafish clusterin gene and protein is similar to its human orthologue. Biochemical assays show that zebrafish Clusterin is a secreted protein that cannot bind IGFs. In adult zebrafish, clusterin mRNA is detected in many tissues. In early development, clusterin mRNA becomes detectable at 12 h postfertilization, and its levels gradually increase thereafter. In situ hybridization analysis indicates that clusterin mRNA is specifically expressed in the developing diencephalic and myelencephalic choroid plexus. Among various stresses tested, heat shock, but not hypoxic or ionic stresses, increases the levels of clusterin mRNA. Inhibition of the IGF-I receptor-mediated signaling or overexpression of IGF ligands did not change clusterin mRNA levels. In comparison, inhibition or targeted knockdown of Notch signaling significantly increased clusterin mRNA expression in choroid plexus. These results suggest that clusterin is a marker of choroid plexus in zebrafish, and its expression in the developing choroid plexus is under the regulation of Notch but not IGF signaling.

DNA methylation or histone modification status in metastasis and angiogenesis-related genes: a new hypothesis on usage of DNMT inhibitors and S-adenosylmethionine for genome stability

Metastasis is a leading cause of mortality and morbidity in cancer. This process needs angiogenesis. The biology underlying cancer, metastasis, and angiogenesis has been investigated so as to determine the therapeutic targets. Invasive and metastatic cancer cells have undergone numerous genetic and epigenetic changes, manifested by cytoskeletal changes, loss of adhesion, and expression of proteolytic enzymes that degrade the basement membrane. Additionally, in endothelial cells, some epigenetic modifications occur during the formation of angiogenesis. Researchers have used some methylation inhibitors, histone deacetylase inhibitors, or methylating agents (such as S-adenosylmethionine, SAM) against cancer and angiogenesis. Although they are effective to beat these diseases, each one results in differentiation or changes in genome structure. We review epigenetically modified genes related with angiogenesis and metastasis in cancer and endothelial cells, and suggest a new proposal. This hypothesis has discussed the importance of the usage of DNA methylation inhibitors together with SAM to prevent tumor progression and genome instability or changes resulting in additional diseases.

Extracellular chaperones

The maintenance of the levels and correct folding state of proteins (proteostasis) is a fundamental prerequisite for life. Life has evolved complex mechanisms to maintain proteostasis and many of these that operate inside cells are now well understood. The same cannot yet be said of corresponding processes in extracellular fluids of the human body, where inappropriate protein aggregation is known to underpin many serious diseases such as Alzheimer's disease, type II diabetes and prion diseases. Recent research has uncovered a growing family of abundant extracellular chaperones in body fluids which appear to selectively bind to exposed regions of hydrophobicity on misfolded proteins to inhibit their toxicity and prevent them from aggregating to form insoluble deposits. These extracellular chaperones are also implicated in clearing the soluble, stabilized misfolded proteins from body fluids via receptor-mediated endocytosis for subsequent lysosomal degradation. Recent work also raises the possibility that extracellular chaperones may play roles in modulating the immune response. Future work will better define the in vivo functions of extracellular chaperones in proteostasis and immunology and pave the way for the development of new treatments for serious diseases.

Loss of clusterin limits atherosclerosis in apolipoprotein E-deficient mice via reduced expression of Egr-1 and TNF-α

AIM

Whether clusterin/apolipoprotein J is antiatherogenic or proatherogenic is controversial. We reported that clusterin was markedly induced in media and neointima after vascular injury and that reduced clusterin expression reduced the proliferation of vascular smooth muscle cells (VSMCs), which induced G1 arrest via p53 and p21. The purpose of this study was to investigate the physiological function of clusterin in atherosclerosis using double-knockout mice (D-KO) of apolipoprotein E-deficient mice (apoE-KO) and clusterin-deficient mice (CLU-KO).

METHODS AND RESULTS

Atherosclerotic lesions in the aortic root were quantitated at 20 weeks of age. Atherosclerotic lesions of D-KO were significantly smaller than those of apoE-KO (D-KO: 0.176±0.078 mm(2) vs. apoE-KO: 0.365±0.164 mm(2), p< 0.001). To identify underlying atherosclerotic mechanisms that were blocked by loss of clusterin, we performed immunohistochemical analysis of Egr-1. Egr-1 immunoreactivity in the nuclei of VSMCs in atherosclerotic lesions of apoE-KO was upregulated, whereas it was not in D-KO lesions. Western blotting demonstrated that the expression levels of Egr-1 and TNF-α in the D-KO were significantly lower than those in the apoE-KO. When VSMCs and macrophages were obtained from D-KO and apoE-KO, Western blotting showed that the expression levels of Egr-1 and TNF-α in VSMCs and macrophages of D-KO were significantly lower than those of apoE-KO.

CONCLUSION

Loss of clusterin strongly suppressed apoE-KO-induced atherosclerotic lesions at a step prior to the expression of Egr-1 and TNF-α, suggesting that clusterin is a candidate for an antiatherogenic target.

Clusterin immunoreactivity as a predictive factor for progression of non-muscle-invasive bladder carcinoma

INTRODUCTION

There is a need for prognostic markers which can predict the subset of patients who will not respond sufficiently to conservative management in non-muscle-invasive bladder carcinoma. We analyzed the association of clusterin (CLU) with clinicopathological factors.

MATERIALS AND METHODS

Immunohistochemical CLU expression was investigated in paraffin-embedded archival tissues of initial transurethral resection specimens of 46 patients with non-muscle-invasive bladder carcinoma. The result was expressed as the proportion of the number of CLU-containing tumor cells to the total number of tumor cells detected in each slide and 'percent CLU expression' was calculated for each patient.

RESULTS

Of the 46 cases (35 male, 11 female), 18 were ≥ 65 years of age. CLU expression was significantly higher in male and elderly patients. Following the initial transurethral resection, 39 patients showed tumor recurrence, and progression was seen in 25 patients, of whom 17 progressed to muscle invasion during follow-up. Although there was no significant correlation between CLU expression and recurrence, significant correlation with overall progression and progression to muscle-invasive disease was observed in this cohort of patients (p = 0.001 and p = 0.014, respectively). Among the patients with progression to muscle invasion, 13 underwent radical cystectomy with pT2 tumor in 5 patients in the final pathology of surgical specimens and pT3 and higher in the remainder.

CONCLUSIONS

CLU immunoreactivity showed correlation with age, gender and progression, mainly progression to muscle invasion. Thus, CLU can be used as a molecular marker to predict the potential of progression to muscle-invasive disease in a particular tumor which in turn may prove useful in the decision-making process for early cystectomy without losing time with conservative management.

CLU blocks HDACI-mediated killing of neuroblastoma

Clusterin is a ubiquitously expressed glycoprotein with multiple binding partners including IL-6, Ku70, and Bax. Clusterin blocks apoptosis by binding to activated Bax and sequestering it in the cytoplasm, thereby preventing Bax from entering mitochondria, releasing cytochrome c, and triggering apoptosis. Because increased clusterin expression correlates with aggressive behavior in tumors, clusterin inhibition might be beneficial in cancer treatment. Our recent findings indicated that, in neuroblastoma cells, cytoplasmic Bax also binds to Ku70; when Ku70 is acetylated, Bax is released and can initiate cell death. Therefore, increasing Ku70 acetylation, such as by using histone deacetylase inhibitors, may be therapeutically useful in promoting cell death in neuroblastoma tumors. Since clusterin, Bax, and Ku70 form a complex, it seemed likely that clusterin would mediate its anti-apoptotic effects by inhibiting Ku70 acetylation and blocking Bax release. Our results, however, demonstrate that while clusterin level does indeed determine the sensitivity of neuroblastoma cells to histone deacetylase inhibitor-induced cell death, it does so without affecting histone deacetylase-inhibitor-induced Ku70 acetylation. Our results suggest that in neuroblastoma, clusterin exerts its anti-apoptotic effects downstream of Ku70 acetylation, likely by directly blocking Bax activation.

Plasma clusterin levels in predicting the occurrence of coronary artery lesions in patients with Kawasaki disease

Kawasaki disease (KD) is the leading cause of acquired heart disease during childhood in the developed countries. Coronary artery lesions (CAL) are the major complications of KD. A unique proteomic profiling with increased or decreased fibrinogen, alpha-1-antitrypsin, clusterin, and immunoglobulin free light chains were noted in KD in our previous study. The purpose of this study was to evaluate relations between these biomarkers and CAL in KD and to establish within the markers the appropriate cut-off value with which to predict the occurrence of CAL. A total of 47 KD patients were enrolled, including 14 with CAL and 33 without CAL. Plasma samples from patients with KD before intravenous immunoglobulin administration were indicated for measurement of these biomarkers. A potential relation among CAL, clinical characteristics, and these biomarkers was investigated, and a receiver operating characteristic curve was used to identify a cut-off value of the significant marker that best predicated the occurrence of CAL. Among these biomarkers, only plasma clusterin level was associated with the occurrence of CAL. Using a cut-off value of clusterin <12.0 mg/l, the relative risk for CAL was 4.53-fold (95% confidence interval [CI] 1.060-19.347%, P = 0.014). Results from this study suggest that plasma clusterin level <12.0 mg/l in KD is significantly associated with the occurrence of CAL. Results from this study provide a potential biomarker of KD that may help predict the occurrence of CAL.

Research in castration-resistant prostate cancer: what does the future hold?

Prostate cancer (PCa) is the most common non-skin cancer diagnosed in North America, and it affects 1 in 6 men. Patients with recurrent or metastatic pca will inevitably develop castration-resistant disease after an initial period of hormone responsiveness. The standard first-line treatment for men with castration-resistant pca (CRPC) is docetaxel, but further treatment options are limited. This review summarizes the research being conducted in CRPC, with specific regard to immunotherapy and to novel targeted therapies directed against the androgen axis, vascular endothelial growth factor, chaperone proteins, the phosphoinositide 3 kinase/Akt/phosphatase and tensin homolog/mammalian target of rapamycin pathway, and endothelin-1.

Extracellular Chaperones

The maintenance of the levels and correct folding state of proteins (proteostasis) is a fundamental prerequisite for life. Life has evolved complex mechanisms to maintain proteostasis and many of these that operate inside cells are now well understood. The same cannot yet be said of corresponding processes in extracellular fluids of the human body, where inappropriate protein aggregation is known to underpin many serious diseases such as Alzheimer's disease, type II diabetes and prion diseases. Recent research has uncovered a growing family of abundant extracellular chaperones in body fluids which appear to selectively bind to exposed regions of hydrophobicity on misfolded proteins to inhibit their toxicity and prevent them from aggregating to form insoluble deposits. These extracellular chaperones are also implicated in clearing the soluble, stabilized misfolded proteins from body fluids via receptor-mediated endocytosis for subsequent lysosomal degradation. Recent work also raises the possibility that extracellular chaperones may play roles in modulating the immune response. Future work will better define the in vivo functions of extracellular chaperones in proteostasis and immunology and pave the way for the development of new treatments for serious diseases.

Randomized phase II study of docetaxel and prednisone with or without OGX-011 in patients with metastatic castration-resistant prostate cancer

PURPOSE

To determine the clinical activity of OGX-011, an antisense inhibitor of clusterin, in combination with docetaxel/prednisone in patients with metastatic castration-resistant prostate cancer.

PATIENTS AND METHODS

Patients were randomly assigned 1:1 to receive docetaxel/prednisone either with (arm A) or without (arm B) OGX-011 640 mg intravenously weekly. The primary end point was the proportion of patients with a prostate-specific antigen (PSA) decline of ≥ 50% from baseline, with the experimental therapy being considered of interest if the proportion of patients with a PSA decline was more than 60%. Secondary end points were objective response rate, progression-free survival (PFS), overall survival (OS), and changes in serum clusterin.

RESULTS

Eighty-two patients were accrued, 41 to each arm. OGX-011 adverse effects included rigors and fevers. After cycle 1, median serum clusterin decreased by 26% in arm A and increased by 0.9% in arm B (P < .001). PSA declined by ≥ 50% in 58% of patients in arm A and 54% in arm B. Partial response occurred in 19% and 25% of patients in arms A and B, respectively. Median PFS and OS times were 7.3 months (95% CI, 5.3 to 8.8 months) and 23.8 months (95% CI, 16.2 months to not reached), respectively, in arm A and 6.1 months (95% CI, 3.7 to 8.6 months) and 16.9 months (95% CI, 12.8 to 25.8 months), respectively, in arm B. Baseline factors associated with improved OS on exploratory multivariate analysis were an Eastern Cooperative Oncology Group performance status of 0 (hazard ratio [HR], 0.27; 95% CI, 0.14 to 0.51), presence of bone or lymph node metastases only (HR, 0.45; 95% CI, 0.25 to 0.79), and treatment assignment to OGX-011 (HR, 0.50; 95% CI, 0.29 to 0.87).

CONCLUSION

Treatment with OGX-011 and docetaxel was well tolerated with evidence of biologic effect and was associated with improved survival. Further evaluation is warranted.

Low-dose radiation-induced responses: focusing on epigenetic regulation

PURPOSE

With the widespread use of ionising radiation, the risks of low-dose radiation have been increasingly highlighted for special attention. This review introduces the potential role of epigenetic elements in the regulation of the effects of low-dose radiation.

MATERIALS AND METHODS

The related literature has been analysed according to the topics of DNA methylation, histone modifications, chromatin remodelling and non-coding RNA modulation in low-dose radiation responses.

RESULTS

DNA methylation and radiation can reciprocally regulate effects, especially in the low-dose radiation area. The relationship between histone methylation and radiation mainly exists in the high-dose radiation area; histone deacetylase inhibitors show a promising application to enhance radiation sensitivity, both in the low-dose and high-dose areas; phosphorylated histone 2 AX (H2AX) shows a low sensitivity with 1-15 Gy irradiation as compared with lower dose radiation; and histone ubiquitination plays an important role in DNA damage repair mechanisms. Moreover, chromatin remodelling has an integral role in the repair of DNA double-strand breaks and the response of chromatin to ionising radiation. Finally, the effect of radiation on microRNA expression seems to vary according to cell type, radiation dose, and post-irradiation time point.

CONCLUSION

Small advances have been made in the understanding of epigenetic regulation of low-dose radiation responses. Many questions and blind spots deserve to be investigated. Many new epigenetic elements will be identified in low-dose radiation responses, which may give new insights into the mechanisms of radiation response and their exploitation in radiotherapy.

Evaluation of serum clusterin as a surveillance tool for human hepatocellular carcinoma with hepatitis B virus related cirrhosis

BACKGROUND AND AIM

Hepatocellular carcinoma (HCC) is a common human cancer worldwide. The levels of serum clusterin in HCC patients and its potential diagnostic significance is not clear. We aimed to evaluate the clinical use of serum clusterin levels as a surveillance tool for HCC with hepatitis B virus (HBV) related cirrhosis.

METHODS

Twenty-two cases of healthy subjects, 31 cases of HBV carriers, 26 patients with chronic hepatitis B, 29 patients with cirrhosis, and 76 patients with HCC were enrolled in this study. Serum levels of clusterin were measured by a sandwich enzyme-linked immunosorbent assay.

RESULTS

The serum clusterin levels in HCC patients were significantly lower than that in healthy, HBV carriers and chronic hepatitis B, but statistically higher than in cirrhosis patients. Receiver operator characteristic (ROC) curve indicated that a serum clusterin value of 50 microg/mL yielded the best sensitivity (91%) and specificity (83%) for differentiating HCC patients with HBV-related cirrhosis from those with HBV-related cirrhosis. The optimal alpha fetoprotein (AFP) cutoff value was 15 ng/mL and was inferior to the clusterin value of 50 microg/mL, the area under the ROC curves being 0.937 versus 0.781, respectively (P < 0.05).

CONCLUSIONS

Serum clusterin was more sensitive and specific than serum AFP for differentiating HCC patients with HBV-related cirrhosis from those with HBV-related liver cirrhosis, and may be a useful surveillance tool of HCC based on HBV-related cirrhosis.

Clusterin expression is associated with decreased disease-free survival of patients with colorectal carcinomas

AIMS

It has been demonstrated that increased clusterin expression is involved in malignant progression and that anticlusterin treatment leads to selective apoptosis. The aim of this study was to determine the clinicopathological significance of clusterin expression in human colorectal carcinomas.

METHODS AND RESULTS

The expression of clusterin was examined in 31 adenomas and 103 colorectal carcinomas. Normal epithelial cells were always negative for clusterin expression, but clusterin expression was present in 16% (5/31) of adenomas and this percentage increased in colorectal carcinomas (30%, 31/103). Immunopositivity always presented an apical cytoplasmic pattern. The expression level of clusterin did not correlate with age, gender, grade or stage. However, its expression was significantly associated with a decrease in disease-free survival (P < 0.05). In a multivariate Cox proportional hazards model, clusterin expression remained a significant independent predictor.

CONCLUSIONS

Clusterin expression may have a role in colonic carcinogenesis and may help identify patients with more aggressive tumours who may benefit from targeted therapy.

Clinical significance of clusterin expression in esophageal squamous cell carcinoma

AIM: To investigate the expression of clusterin mRNA in esophageal squamous cell carcinoma (ESCC), measure preoperative and postoperative serum clusterin protein levels in ESCC patients, and evaluate their correlations with clinicopathological parameters in ESCC.

METHODS: The expression of full-length clusterin mRNA in ESCC tissue was detected by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). Serum clusterin level was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS: The expression of clusterin mRNA was significantly down-regulated in ESCC tissue compared with matched tumor-adjacent non-cancerous tissue. The median level of serum clusterin in postoperative ESCC patients was significantly higher than that in preoperative patients (25.71 mg/L vs 3.23 mg/L, P < 0.0001). The level of serum clusterin is correlated with tumor size, but not with age, gender, tumor differentiation, tumor grade, lymph node metastasis and biochemical parameters.

CONCLUSION: The expression of clusterin mRNA is down-regulated in ESCC. Serum clusterin level decreases in ESCC patients. Clusterin might be a potential tumor suppressor gene in ESCC. Dynamic measurement of serum clusterin level might aid to evaluate the progression of ESCC.

Effects of clusterin over-expression on metastatic progression and therapy in breast cancer

Background

Clusterin is a secreted glycoprotein that is upregulated in a variety of cell lines in response to stress, and enhances cell survival. A second nuclear isoform of clusterin that is associated with cell death has also been identified. The aim of this study was to determine the role(s) of the secretory isoform in breast tumor progression and metastasis.

Methods

To investigate the role of secretory clusterin in the biology of breast cancer tumor growth and resistance to therapy we have engineered an MCF-7 cell line (MCF-7CLU) that over-expresses clusterin. We have measured the in vitro effects of clusterin over-expression on cell cycle, cell death, and sensitivity to TNFalpha and tamoxifen. Using an orthotopic model of breast cancer, we have also determined the effects of over-expression of clusterin on tumor growth and metastatic progression.

Results

In vitro, over-expression of secretory clusterin alters the cell cycle kinetics and decreases the rate of cell death, resulting in the enhancement of cell growth. Over-expression of secretory clusterin also blocks the TNFalpha-mediated induction of p21 and abrogates the cleavage of Bax to t-Bax, rendering the MCF-7CLU cells significantly more resistant to the cytokine than the parental cells. Orthotopic primary tumors derived from MCF-7CLU cells grow significantly more rapidly than tumors derived from parental MCF-7 cells and, unlike the parental cells, metastasize frequently to the lungs.

Conclusions

These data suggest that secretory clusterin, which is frequently up-regulated in breast cancers by common therapies, including anti-estrogens, may play a significant role in tumor growth, metastatic progression and subsequent drug resistance in surviving cells.

Novel targeted therapies for prostate cancer

This article reviews the concepts and rationale behind targeted agents that are currently in clinical testing for patients with castration resistant prostate cancer (CRPC). Advances in our understanding of the molecular mechanisms underlying prostate cancer progression has translated into a variety of treatment approaches. Agents targeting androgen receptor activation and local steroidogenesis, angiogenesis, apoptosis, chaperone proteins, the insulinlike growth factor pathway, RANK ligand, endothelin receptors, and Src family kinases are entering, or have recently completed, accrual to phase III trials for patients with CRPC. There has also been interest generated by data from early-phase studies evaluating multitargeted tyrosine kinase inhibitors, agents effecting signal transduction pathways, and novel cytotoxics.

Targeting the cytoprotective chaperone, clusterin, for treatment of advanced cancer

Many strategies used to kill cancer cells induce stress-responses that activate survival pathways to promote emergence of a treatment resistant phenotype. Secretory clusterin (sCLU) is a stress-activated cytoprotective chaperone up-regulated by many varied anticancer therapies to confer treatment resistance when overexpressed. sCLU levels are increased in several treatment recurrent cancers including castrate resistant prostate cancer, and therefore sCLU has become an attractive target in cancer therapy. sCLU is not druggable with small molecule inhibitors, therefore nucleotide-based strategies to inhibit sCLU at the RNA level are appealing. Preclinical studies have shown that antisense oligonucleotide (ASO) or siRNA knockdown of sCLU have preclinical activity in combination with hormone- and chemotherapy. Phase I and II clinical trial data indicate that the second generation ASO, custirsen (OGX-011), has biologic and clinical activity, suppressing sCLU expression in prostate cancer tissues by more than 90%. A randomized study comparing docetaxel-custirsen to docetaxel alone in men with castrate resistant prostate cancer reported improved survival by 7 months from 16.9 to 23.8 months. Strong preclinical and clinical proof-of-principle data provide rationale for further study of sCLU inhibitors in randomized phase III trials, which are planned to begin in 2010.

Chibby interacts with NBPF1 and clusterin, two candidate tumor suppressors linked to neuroblastoma

The NBPF genes are members of a gene family that underwent a remarkable increase in their copy number during recent primate evolution. The NBPF proteins contain 5 to 40 copies of a domain known as the NBPF repeat or DUF1220. Very little is known about the function of these domains or about the NBPF proteins. We performed a yeast two-hybrid screening with the aminoterminal domain of NBPF11 and found that Chibby, a documented repressor of Wnt signaling, interacts with multiple NBPF proteins. More specifically, a coiled-coil region in the NBPF proteins interacts with the coiled-coil domain in the carboxyterminal region of Chibby. Nonetheless, this interaction did not influence the repressor function of Chibby in a TOPFLASH reporter assay. Using Chibby as bait in a new yeast two-hybrid screening, we identified clusterin as a binding protein. Chibby and clusterin were co-immunoprecipitated with NBPF1, suggesting the formation of a tri-molecular complex. Although we have not pinpointed the role of these mutual interactions, the possible formation of a macromolecular complex of three candidate tumor suppressor proteins, including the enigmatic NBPF1, points at important functional implications.

Chapter 9: Oxidative stress in malignant progression: The role of Clusterin, a sensitive cellular biosensor of free radicals

Clusterin/Apolipoprotein J (CLU) gene is expressed in most human tissues and encodes for two protein isoforms; a conventional heterodimeric secreted glycoprotein and a truncated nuclear form. CLU has been functionally implicated in several physiological processes as well as in many pathological conditions including ageing, diabetes, atherosclerosis, degenerative diseases, and tumorigenesis. A major link of all these, otherwise unrelated, diseases is that they are characterized by increased oxidative injury due to impaired balance between production and disposal of reactive oxygen or nitrogen species. Besides the aforementioned diseases, CLU gene is differentially regulated by a wide variety of stimuli which may also promote the production of reactive species including cytokines, interleukins, growth factors, heat shock, radiation, oxidants, and chemotherapeutic drugs. Although at low concentration reactive species may contribute to normal cell signaling and homeostasis, at increased amounts they promote genomic instability, chronic inflammation, lipid oxidation, and amorphous aggregation of target proteins predisposing thus cells for carcinogenesis or other age-related disorders. CLU seems to intervene to these processes due to its small heat-shock protein-like chaperone activity being demonstrated by its property to inhibit protein aggregation and precipitation, a main feature of oxidant injury. The combined presence of many potential regulatory elements in the CLU gene promoter, including a Heat-Shock Transcription Factor-1 and an Activator Protein-1 element, indicates that CLU gene is an extremely sensitive cellular biosensor of even minute alterations in the cellular oxidative load. This review focuses on CLU regulation by oxidative injury that is the common molecular link of most, if not all, pathological conditions where CLU has been functionally implicated.

Chapter 2: Clusterin (CLU): From one gene and two transcripts to many proteins

Clusterin (CLU) has kept many researchers engaged for a long time since its first discovery and characterization in the attempt to unravel its biological role in mammals. Although there is a general consensus on the fact that CLU is supposed to play important roles in nearly all fundamental biological phenomena and in many human diseases including cancer, after about 10 years of work CLU has been defined as an "enigmatic" protein. This sense of frustration among the researchers is originated by the fact that, despite considerable scientific production concerning CLU, there is still a lack of basic information about the complex regulation of its expression. The CLU gene is a single 9-exon gene expressed at very different levels in almost all major tissues in mammals. The gene produces at least three protein forms with different subcellular localization and diverse biological functions. The molecular mechanism of production of these protein forms remains unclear. The best known is the glycosylated mature form of CLU (sCLU), secreted with very big quantitative differences at different body sites. Hormones and growth factors are the most important regulators of CLU gene expression. Before 2006, it was believed that a unique transcript of about 1.9 kb was originated by transcription of the CLU gene. Now we know that alternative transcriptional initiation, possibly driven by two distinct promoters, may produce at least two distinct CLU mRNA isoforms differing in their unique first exon, named Isoform 1 and Isoform 2. A third transcript, named Isoform 11036, has been recently found as one of the most probable mRNA variants. Approaches like cloning, expression, and functional characterization of the different CLU protein products have generated a critical mass of information teaching us an important lesson about CLU gene expression regulation. Nevertheless, further studies are necessary to better understand the tissue-specific regulation of CLU expression and to identify the specific signals triggering the expression of different/alternative transcript isoforms and protein forms in different cell types at appropriate time.

Chapter 8: Clusterin: A multifacet protein at the crossroad of inflammation and autoimmunity

For years, clusterin has been recognized as a secreted protein and a large number of works demonstrated that this ubiquitously expressed protein has multiple activities. Among the described activities several were related to inflammation and immunity such as its regulatory activity on complement. Then it became clear that a nuclear form of the protein with proapoptotic property existed and more recently that a cytoplasmic form could regulate NF-kappaB pathway. Again, these activities have a strong repercussion in inflammation and immunity. On the other hand, data available on the exact role of CLU in these processes and autoimmunity were quite scarce until recently. Indeed, in the last few years, a differential CLU expression in subtype of T cells, the regulation of CLU expression by proinflammatory cytokines and molecules, the regulation of expression and function of CLU depending on its subcellular localization, the interaction of CLU with nuclear and intracellular proteins were all reported. Adding these new roles of CLU to the already reported functions of this protein allows a better understanding of its role and potential involvement in several inflammatory and immunological processes and, in particular, autoimmunity. In this sense, rheumatoid arthritis appears to be a very attractive disease to build a new paradigm of the role and function of CLU because it makes the link between proliferation, inflammation, and autoimmunity. We will try to see in this review how to bring altogether the old and new knowledge on CLU with inflammation and autoimmunity. Nevertheless, it is clear that CLU has not yet revealed all its secrets in inflammation and autoimmunity.

Chapter 5: Nuclear CLU (nCLU) and the fate of the cell

The possible biological role played by Clusterin (CLU) has been puzzling researchers for a long time since its first discovery and characterization. CLU has been often described as an "enigmatic" gene, a clear indication that too many aspects of this issue have been obscure or difficult to interpret for long. The good news is that this is certainly no longer true. Since the beginning, CLU was believed to play important roles in nearly all most important biological phenomena. The diversity, sometime the contradictions, of its biological action is now likely explained by the existence of different protein products all generated by the same single copy CLU gene. The relatively recent discovery that CLU can be retained inside the cell and targeted to many intracellular sites and organelles, including the nucleus, provided us a very different view from that solely deriving from its possible role in the outer cellular environment. In particular, nuclear localization of CLU (nCLU) was found to trigger cell death in many systems. In this chapter, a critical review of previous work will enable us to reinterpret old data and observations in the attempt to progressively unravelling the CLU "enigma" by considering its localization inside and outside the cell. The final picture would supposedly reconciliate different or alternative hypothesis. Starting with an "historical" approach demonstrating that nCLU was right under our eyes since the beginning, up to the more recent contributions we will describe which stimuli would inhibit secretion and maturation of CLU leading at least one protein product to target the nucleus and kill the cell. A better understanding of this complex issue is not an easy work, considering the thoughtfulness in reviewing the existing literature and the known controversial reports. We hope that the information contained in this article will be useful for the reader to enlighten this field.

Chapter 4: Regulation of Clusterin activity by calcium

In this chapter, the attention is put on Ca(2+) effect on Clusterin (CLU) activity. We showed that two CLU forms (secreted and nuclear) are differently regulated by Ca(2+) and that Ca(2+) fluxes affect CLU gene expression. A secretory form (sCLU) protects cell viability whereas nuclear form (nCLU) is proapoptotic. Based on available data we suggest, that different CLU forms play opposite roles, depending on intracellular Ca(2+) concentration, time-course of Ca(2+) current, intracellular Ca(2+) compartmentalization, and final Ca(2+) targets. Discussion will be motivated on how CLU acts on cell in response to Ca(2+) waves. The impact of Ca(2+) on CLU gene activity and transcription, posttranscriptional modifications, translation of CLU mRNA, and posttranslational changes as well as biological effects of CLU will be discussed. We will also examine how Ca(2+) signal and Ca(2+)-dependent proteins are attributable to changes in CLU characteristics. Some elucidation of CLU gene activity, CLU protein formation, maturation, secretion, and intracellular translocations in response to Ca(2+) is presented. In response to cell stress (i.e., DNA damage) CLU gene is activated. We assume that commonly upregulated mRNA for nCLU versus sCLU and vice versa are dependent on Ca(2+) accessibility and its intracellular distribution. It looks as if at low intracellular Ca(2+) the delay in cell cycle allows more time for DNA repair; otherwise, cells undergo nCLU-dependent apoptosis. If cells are about to survive, intrinsic apoptosis is abrogated by sCLU interacting with activated Bax. In conclusion, a narrow range of intracellular Ca(2+) concentrations is responsible for the decision whether nCLU is mobilized (apoptosis) or sCLU is appointed to improve survival. Since the discovery of CLU, a huge research progress has been done. Nonetheless we feel that much work is left ahead before remaining uncertainties related to Ca(2+) signal and the respective roles of CLU proteins are unraveled.

Chapter 6: The chaperone action of Clusterin and its putative role in quality control of extracellular protein folding

The function(s) of clusterin may depend upon its topological location. A variety of intracellular "isoforms" of clusterin have been reported but further work is required to better define their identity. The secreted form of clusterin has a potent ability to inhibit both amorphous and amyloid protein aggregation. In the case of amorphous protein aggregation, clusterin forms stable, soluble high-molecular-weight complexes with misfolded client proteins. Clusterin expression is increased during many types of physiological and pathological stresses and is thought to function as an extracellular chaperone (EC). The pathology of a variety of serious human diseases is thought to arise as a consequence of the inappropriate aggregation of specific extracellular proteins (e.g., Abeta peptide in Alzheimer's disease and beta(2)-microglobulin in dialysis-related amyloidosis). We have proposed that together with other abundant ECs (e.g., haptoglobin and alpha(2)-macroglobulin), clusterin forms part of a previously unknown quality-control (QC) system for protein folding that mediates the recognition and disposal of extracellular misfolded proteins via receptor-mediated endocytosis and lysosomal degradation. Characterizing the mechanisms of this extracellular QC system will thus have major implications for our understanding of diseases of this type and may eventually lead to the development of new therapies.

The role of clusterin (CLU) in malignant transformation and drug resistance in breast carcinomas

Breast cancer is the main cause of cancer-related death among women in Western countries. Current research is focused on identifying antiapoptotic proteins which could be a possible target for novel chemotherapeutic drugs. Secretory clusterin (sCLU) is an extracellular chaperone that has been functionally implicated in DNA repair, cell-cycle regulation, apoptotic cell death and tumorigenesis. The implication of sCLU in carcinogenesis and the progression of breast carcinomas make it an interesting gene, worthy of investigation. It has been reported to present powerful antiapoptotic activity and to perform a prosurvival function with most therapeutic treatments for breast cancer. This review summarizes our current understanding of the role of CLU in tumorigenesis, progression, and response to treatment in breast carcinomas.

Clusterin (CLU) and lung cancer

Lung cancer is the leading cause of cancer-related mortality. It is categorized into two histological groups that have distinct clinical behaviors, the nonsmall cell lung cancers (NSCLC) and the small cell lung cancer (SCLC). When identified at an early stage, NSCLC is treated by surgical resection. However, patients who undergo surgical resection still have a relative low survival rate, primarily for tumor recurrence. Unfortunately, advances in cytotoxic therapy have reached a plateau and new approaches to treatment are needed together with new and better parameters for more accurate prediction of the outcome and more precise indication of the efficacy of the treatment. Several in vitro studies have examined the role of Clusterin (CLU) in carcinogenesis, lung cancer progression, and response to chemo- and radiotherapy. Studies performed in lung cancer cell lines and animal models showed that CLU is upregulated after exposure to chemo- and radiotherapy. A potential role proposed for the protein is cytoprotective. In vitro, CLU silencing by antisense oligonucleotides (ASO) and small-interfering RNAs (siRNA) directed against CLU mRNA in CLU-rich lung cancer cell lines sensitized cells to chemotherapy and radiotherapy and decreased their metastatic potential. In vivo, a recent work analyzed the prognostic role of CLU in NSCLC, showing that CLU-positive patients with lung cancer had a better overall survival and disease-free survival than those with CLU-negative tumors. These data are contradictory to the promising in vitro results. From the results of these studies we may hypothesize that in early-stage lung cancers CLU represents a positive biomarker correlating with better overall survival. In advanced patients, already treated with chemo- and radiotherapy, the induction of CLU may confer resistance to the treatments. However, many studies are needed to better understand the role of CLU in early-stage and advanced lung cancers with the aim to discriminate patients and specific local conditions that could benefit for a CLU knocking down treatment.

Identification of clusterin domain involved in NF-kappaB pathway regulation

Clusterin (CLU) is a ubiquitous protein that has been implicated in tumorigenesis, apoptosis, inflammation, and cell proliferation. We and others have previously shown that CLU is an inhibitor of the NF-kappaB pathway. However, the exact form of CLU and the region(s) of CLU involved in this effect were unknown. Using newly generated molecular constructs encoding for CLU and various regions of the molecule, we demonstrated that the presecretory form of CLU (psCLU) form bears the NF-kappaB regulatory activity. Sequence comparison analysis showed sequence motif identity between CLU and beta-transducin repeat-containing protein (beta-TrCP), a main E3 ubiquitin ligase involved in IkappaB-alpha degradation. These homologies were localized in the disulfide constraint region of CLU. We generated a specific molecular construct of this region, named DeltaCLU, and showed that it has the same NF-kappaB regulatory activity as CLU. Neither the alpha-chain nor the beta-chain of CLU had any NF-kappaB regulatory activity. Furthermore, we showed that following tumor necrosis factor-alpha stimulation of transfected cells, we could co-immunoprecipitate phospho-IkappaB-alpha with DeltaCLU. Moreover, we showed that DeltaCLU could localize both in the cytoplasm and in the nucleus. These results demonstrate the identification of a new CLU activity site involved in NF-kappaB pathway regulation.

Transcriptome profiling of a TGF-beta-induced epithelial-to-mesenchymal transition reveals extracellular clusterin as a target for therapeutic antibodies

Transforming growth factor (TGF)-beta plays a dual role in tumorigenesis, switching from acting as a growth inhibitory tumor suppressor early in the process, to a tumor promoter in late-stage disease. Since TGF-beta's prometastatic role may be linked to its ability to induce tumor cell epithelial-to-mesenchymal transition (EMT), we explored TGF-beta's EMT-promoting pathways by analysing the transcriptome changes occurring in BRI-JM01 mammary tumor epithelial cells undergoing a TGF-beta-induced EMT. We found the clusterin gene to be the most highly upregulated throughout most of the TGF-beta time course, and showed that this results in an increase of the secreted form of clusterin. By monitoring several hallmark features of EMT, we demonstrated that antibodies targeting secreted clusterin inhibit the TGF-beta-induced EMT of BRI-JM01 cells, as well as the invasive phenotype of several other breast and prostate tumor cell lines (4T1, NMuMG, MDA-MB231LM2 and PC3), without affecting the proliferation of these cells. These results indicate that secreted clusterin is a functionally important EMT mediator that lies downstream within TGF-beta's EMT-promoting transcriptional cascade, but not within its growth-inhibitory pathways. To further investigate the role played by secreted clusterin in tumor metastasis, we assessed the effect of several anti-clusterin monoclonal antibodies in vivo using a 4T1 syngeneic mouse breast cancer model and found that these antibodies significantly reduce lung metastasis. Taken together, our results reveal a role for secreted clusterin as an important extracellular promoter of EMT, and suggest that antibodies targeting clusterin may inhibit tumor metastasis without reducing the beneficial growth inhibitory effects of TGF-beta.

A unique plasma proteomic profiling with imbalanced fibrinogen cascade in patients with Kawasaki disease

Kawasaki disease (KD) is the leading cause of acquired heart disease during childhood in the developed countries. The mechanism and biomarkers of KD remain to be determined. In this study, we sought to elucidate potential plasma proteomic markers in KD patients in comparison to that in febrile controls. Plasma samples from KD patients and febrile controls were subjected to two-dimensional polyacrylamide gel electrophoresis analysis. Differential protein displays between KD patients and febrile controls were determined. Fibrinogen beta and gamma chains, alpha-1-antitrypsin (A1AT), CD5 antigen-like precursor (CD5L), and clusterin were increased in KD patients, whereas immunoglobulin free light chains were decreased, as compared with controls. The differential protein displays were validated with enzyme-linked immunosorbent assay tests. We found higher fibrinogen-related proteins (fibrinogen, A1AT, clusterin, and CD5L), along with a lower level of the immunoglobulin free light chains that involve fibrin degradation in KD. Results from this study showing a unique proteomic profiling with abnormal fibrinogen cascade may afford a good biomarker of KD and a better strategy to prevent cardiovascular complications of KD by correcting abnormal fibrin deposition or degradation.

Clusterin in stool: a new biomarker for colon cancer screening?

OBJECTIVES

The identification of useful markers for early diagnosis of human colon cancer is a major goal still in progress. Clusterin is a pleiotropic protein with a broad range of functions. It has recently drawn much attention because of its association with cancer promotion and metastasis. It is involved in prosurvival and apoptosis processes that are carried out by two different isoforms. Secreted clusterin isoform (sCLU) is cytoprotective and its prosurvival function is the basis of the current phase I/II clinical trials against prostate, lung, and breast cancers. We have already shown that in colorectal cancer (CRC) there is an increased expression of sCLU. In this report, we investigated whether sCLU is released in the blood and stool of colon cancer patients in order to study sCLU as a potential diagnostic molecular marker for colon cancer screening.

METHODS

The quantitative expression of sCLU was determined by dot blot immunodosage in the serum and stool of CRC patients (n=63) and age-matched controls without clinical history of neoplasia, CRC, or systemic or bowel inflammatory disease (n=50). Unpaired t-tests and Mann-Whitney U-tests were used for continuous variables. The diagnostic performance of clusterin was appraised by means of receiver operating characteristic (ROC) curves.

RESULTS

We found a significant increase of sCLU in the serum and stool of CRC patients (P=0.0002 and P<0.000, respectively) as compared with controls. ROC curves provided cutoff points showing a trade-off between sensitivity and specificity. With a cutoff point of 88.5 microg/ml, sCLU in blood showed a 55.6% sensitivity and 100% specificity, and with a cutoff point of 34.6 microg/g, the stool test reached 66.7% sensitivity and 84% specificity in discriminating between nonneoplastic and colorectal neoplastic lesions. Human cancer xenografts in nude mice indicated a positive correlation between increasing serum clusterin level and tumor size.

CONCLUSIONS

This study highlights the potential of clusterin detection in stool to be a valuable tool to improve the effectiveness and efficiency of large-scale clinical cancer screening.

Clusterin as a diagnostic and prognostic marker for transitional cell carcinoma of the bladder

We investigated the feasibility of profiling and measuring the concentration of clusterin in urine and serum for individuals with transitional cell carcinoma (TCC) of the bladder and comparing it with nontumor controls. In addition, we analyzed the correlation of expression of clusterin in specimens of TCC to various clinicopathologic parameters and prognosis of bladder cancer. Blood and urine samples were used from 68 patients with TCC of the bladder and from 61 patients with benign urological diseases. Enzyme-linked immunosorbent assays (ELISA) were performed for clusterin from serum and urine. Quantitation of clusterin mRNA was carried out in 68 bladder tumor specimens from radical cystectomy or transurethral resection and 26 normal bladder specimens from BPH patients by using RT-PCR method. Correlation for the expression of clusterin mRNA with clinicopathologic parameters was analyzed. Serum and urine clusterin was significantly higher in individuals with bladder cancer than control (p = 0.001). Sensitivity and specificity of serum and urine clusterin as a tumor marker for TCC of the bladder was found to be 80%, 91%, 87.1% and 96.7% respectively. Clusterin expression was significantly higher in TCC specimens than normal tissue specimens (P < 0.001). Expression of clusterin was significantly higher in patients with invasive TCC of the bladder than that in patients with superficial TCC and control (P < 0.001). Overexpression of clusterin mRNA was significantly associated with tumor recurrence and overall survival (p < 0.001). The recurrence-free survival time of patients with overexpression of clusterin was significantly shorter than that of patients with weak expression of clusterin (9.8 months vs. 35.2 months). Clusterin may be considered as a potential diagnostic and prognostic biomarker for bladder cancer using urine, serum and/or molecular biology techniques.

Clusterin: a forgotten player in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a versatile chaperone molecule which contains several amphipathic and coiled-coil alpha-helices, typical characteristics of small heat shock proteins. In addition, clusterin has three large intrinsic disordered regions, so-called molten globule domains, which can stabilize stressed protein structures. Twenty years ago, it was demonstrated that the expression of clusterin was clearly increased in Alzheimer's disease (AD). Later it was observed that clusterin can bind amyloid-beta peptides and prevent their fibrillization. Clusterin is also involved in the clearance of amyloid-beta peptides and fibrils by binding to megalin receptors and enhancing their endocytosis within glial cells. Clusterin is a complement inhibitor and can suppress complement activation observed in AD. Clusterin is also present in lipoprotein particles and regulates cholesterol and lipid metabolism of brain which is disturbed in AD. Clusterin is a stress-induced chaperone which is normally secreted but in conditions of cellular stress, it can be transported to cytoplasm where it can bind to Bax protein and inhibit neuronal apoptosis. Clusterin can also bind to Smad2/3 proteins and potentiate the neuroprotective TGFbeta signaling. An alternative splicing can produce a variant isoform of clusterin which can be translocated to nuclei where it induces apoptosis. The role of nuclear clusterin in AD needs to be elucidated. We will review here the extensive literature linking clusterin to AD and examine the recent progress in clusterin research with the respect to AD pathology. Though clusterin can be viewed as a multipotent guardian of brain, it is unable to prevent the progressive neuropathology in chronic AD.

Castration-resistant prostate cancer: from new pathophysiology to new treatment targets

CONTEXT

Castration-resistant prostate cancer (CRPC) refers to patients who no longer respond to surgical or medical castration. Standard treatment options are limited.

OBJECTIVE

To review the concepts and rationale behind targeted agents currently in late-stage clinical testing for patients with CRPC.

EVIDENCE ACQUISITION

Novel targeted therapies in clinical trials were identified from registries. The MEDLINE database was searched for all relevant reports published from 1996 to October 2009. Bibliographies of the retrieved articles and major international meeting abstracts were hand-searched to identify additional studies.

EVIDENCE SYNTHESIS

Advances in our understanding of the molecular mechanisms underlying prostate cancer (PCa) progression has translated into a variety of treatment approaches. Agents targeting androgen receptor (AR) activation and local steroidogenesis, angiogenesis, immunotherapy, apoptosis, chaperone proteins, the insulin-like growth factor (IGF) pathway, RANK-ligand, endothelin receptors, and the Src family kinases are entering or have recently completed accrual to phase 3 trials for patients with CRPC.

CONCLUSIONS

A number of new agents targeting mechanisms of PCa progression with early promising results are in clinical trials and have the potential to provide novel treatment options for CRPC in the near future.

Vanadium-induced apoptosis of HaCaT cells is mediated by c-fos and involves nuclear accumulation of clusterin

Vanadium exerts a variety of biological effects, including antiproliferative responses through activation of the respective signaling pathways and the generation of reactive oxygen species. As epidermal cells are exposed to environmental insults, human keratinocytes (HaCaT) were used to investigate the mechanism of the antiproliferative effects of vanadyl(IV) sulfate (VOSO(4)). Treatment of HaCaT cells with VOSO(4) inhibited proliferation and induced apoptosis in a dose-dependent manner. Inhibition of proliferation was associated with downregulation of cyclins D1 and E, E2F1, and the cyclin-dependent kinase inhibitors p21(Cip1/Waf1) and p27(Kip1). Induction of apoptosis correlated with upregulation of the c-fos oncoprotein, changes in the expression of clusterin (CLU), an altered ratio of antiapoptotic to proapoptotic Bcl-2 protein family members, and poly(ADP-ribose) polymerase-1 cleavage. Forced overexpression of c-fos induced apoptosis in HaCaT cells that correlated with secretory CLU downregulation and upregulation of nuclear CLU (nCLU), a pro-death protein. Overexpression of Bcl-2 protected HaCaT cells from vanadium-induced apoptosis, whereas secretory CLU overexpression offered no cytoprotection. In contrast, nCLU sensitized HaCaT cells to apoptosis. Our data suggest that vanadium-mediated apoptosis was promoted by c-fos, leading to alterations in CLU isoform processing and induction of the pro-death nCLU protein.

Clusterin, a haploinsufficient tumor suppressor gene in neuroblastomas

BACKGROUND

Clusterin expression in various types of human cancers may be higher or lower than in normal tissue, and clusterin may promote or inhibit apoptosis, cell motility, and inflammation. We investigated the role of clusterin in tumor development in mouse models of neuroblastoma.

METHODS

We assessed expression of microRNAs in the miR-17-92 cluster by real-time reverse transcription-polymerase chain reaction in MYCN-transfected SH-SY5Y and SH-EP cells and inhibited expression by transfection with microRNA antisense oligonucleotides. Tumor development was studied in mice (n = 66) that were heterozygous or homozygous for the MYCN transgene and/or for the clusterin gene; these mice were from a cross between MYCN-transgenic mice, which develop neuroblastoma, and clusterin-knockout mice. Tumor growth and metastasis were studied in immunodeficient mice that were injected with human neuroblastoma cells that had enhanced (by clusterin transfection, four mice per group) or reduced (by clusterin short hairpin RNA [shRNA] transfection, eight mice per group) clusterin expression. All statistical tests were two-sided.

RESULTS

Clusterin expression increased when expression of MYCN-induced miR-17-92 microRNA cluster in SH-SY5Y neuroblastoma cells was inhibited by transfection with antisense oligonucleotides compared with scrambled oligonucleotides. Statistically significantly more neuroblastoma-bearing MYCN-transgenic mice were found in groups with zero or one clusterin allele than in those with two clusterin alleles (eg, 12 tumor-bearing mice in the zero-allele group vs three in the two-allele group, n = 22 mice per group; relative risk for neuroblastoma development = 4.85, 95% confidence interval [CI] = 1.69 to 14.00; P = .005). Five weeks after injection, fewer clusterin-overexpressing LA-N-5 human neuroblastoma cells than control cells were found in mouse liver or bone marrow, but statistically significantly more clusterin shRNA-transfected HTLA230 cells (3.27%, with decreased clusterin expression) than control-transfected cells (1.53%) were found in the bone marrow (difference = 1.74%, 95% CI = 0.24% to 3.24%, P = .026).

CONCLUSIONS

We report, to our knowledge, the first genetic evidence that clusterin is a tumor and metastasis suppressor gene.

Development of reverse phase protein microarrays for the validation of clusterin, a mid-abundant blood biomarker

Background

Many putative disease blood biomarkers discovered in genomic and proteomic studies await validation in large clinically annotated cohorts of patient samples. ELISA assays require large quantities of precious blood samples and are not high-throughput. The reverse phase protein microarray platform has been developed for the high-throughput quantification of protein levels in small amounts of clinical samples.

Results

In the present study we present the development of reverse-phase protein microarrays (RPPMs) for the measurement of clusterin, a mid-abundant blood biomarker. An experimental protocol was optimized for the printing of serum and plasma on RPPMs using epoxy coated microscope slides and a non-denaturing printing buffer. Using fluorescent-tagged secondary antibodies, we achieved the reproducible detection of clusterin in spotted serum and plasma and reached a limit of detection of 780 ng/mL. Validation studies using both spiked clusterin and clinical samples showed excellent correlations with ELISA measurements of clusterin.

Conclusion

Serum and plasma spotted in the reverse phase array format allow for reliable and reproducible high-throughput validation of a mid-abundant blood biomarker such as clusterin.

Hepatitis delta virus epigenetically enhances clusterin expression via histone acetylation in human hepatocellular carcinoma cells

Both isoforms of the hepatitis delta antigen (HDAg) of hepatitis delta virus (HDV) are highly associated with virus proliferation and may act as co-activators of cellular gene expression. Human hepatocellular carcinoma (HCC) cell line Huh7, which stably expresses HDAgs, was differentially screened and the results showed that clusterin gene expression was enhanced. The mechanisms for HDAg-mediated clusterin gene upregulation were investigated. Expression of HDAgs was associated with enhanced histone H3 acetylation within the clusterin promoter in a chromatin immunoprecipitation assay. Transient transfection of HDAg-expressing plasmids into Huh7 cells also enhanced clusterin expression and histone acetylation. Furthermore, HDV replication was associated with histone hyperacetylation and clusterin induction. The effect of increased clusterin expression was determined by a chemosensitivity assay with adriamycin treatment. These data indicated that HDV-induced clusterin protein increases cell survival potential. Thus, it is possible that epigenetic regulation by HDV contributes to a pathological outcome of hepatitis D/hepatitis B viral hepatitis and HCC.

Interleukin-6 affects cell death escaping mechanisms acting on Bax-Ku70-Clusterin interactions in human colon cancer progression

Activation of pro-survival pathways and apoptotic cell death escape are considered hallmarks of oncogenic cell transformation. Tissue microenvironment strongly influences tumorigenesis, redirecting some pathways versus a persisting pro-survival state. Here, we report evidence on the role of interleukin 6 (IL-6) in affecting pro-survival pathways in colon cancer progression, modulating the expression and the molecular interactions among the pro-apoptotic factor Bax, the DNA repair proteins Ku70/86 and Clusterin isoforms. In human colorectal carcinomas (n = 50) at different stages of disease, we found an increased IL-6 production, the loss of Ku86 and Clusterin 50-55 kDa pro-apoptotic isoform. Conversely, we observed the overexpression of Bax and the 40 kDa prosurvival sClusterin (sCLU) isoform. Bax co-localized with Ku70 that was found atypically expressed in the cytoplasm of advanced stage colon cancers (Dukes'C-D; n = 22). IL-6 treatment of a colon cancer cell line, Caco-2, modulated the expression of genes involved in tumor invasion and apoptosis, as observed by microarrays. In particular, IL-6 downmodulated Bax expression at mRNA level. Concomitantly, IL-6 exposure influenced Bax also at protein level acting on the Bax-Ku70-sCLU physical interactions in the cytoplasm, by affecting the Ku70 acetylation and phosphorylation state, thus leading to the inhibition of Bax pro-apoptotic activity. In addition, we found that IL-6 treatment induced a significant downregulation of Ku86 and a strong increase of sCLU, confirming tumor biopsies data. In contrast Somatostatin treatment of Caco-2 cells was able to restore apoptosis, demonstrating that Ku70-Bax-CLU interactions could be dynamically modulated. Hence, IL-6 could favor tumor expansion, promoting cell survival and apoptosis escape throughout the different stages of tumor evolution. Uncovering the molecular mechanisms of action of these factors may offer strategies for selectively manipulate the cancer cells sensitivity to therapy.

Differential age-associated regulation of clusterin expression in prostate lobes of brown Norway rats

BACKGROUND

Serum androgen concentrations decline with age in male Brown Norway rats and castration induces apoptosis of luminal secretory epithelial cells in the ventral but not in the dorsal and lateral prostate lobes. Clusterin has been described as an androgen-repressed gene and a protein with either anti- or pro-apoptotic actions.

METHODS

We measured clusterin mRNA and protein levels, the effects of aging and castration on clusterin protein levels and clusterin immunolocalization within the prostatic ductal network in the prostate lobes of young and aged rats.

RESULTS

Whereas levels of clusterin mRNA and protein expression measured by RT-PCR and Western blot, respectively, were higher in the ventral and lateral lobes of aged (24 months) compared to young (4 months) rats, no age-dependent differences were observed in the dorsal lobe. Clusterin expression was localized by immunohistochemistry exclusively to the proximal duct segment of young rats, but extended to the distal segment of the ventral and lateral lobes of aged rats. Despite an age-related decrease in serum testosterone concentration, clusterin gene expression was not altered in the dorsal lobe. After castration, levels of clusterin expression increased significantly in the ventral and lateral lobes despite the absence of epithelial cell apoptosis in the latter. In castrated rats, clusterin expression extended throughout the proximal-distal duct regions of the prostate lobes of young and aged rats.

CONCLUSION

Regulation of clusterin expression in the prostate lobes of aging rats appears complex and is neither directly repressed by androgen nor dependent on apoptotic-induced stress.