Exon-skipping strategy by ratio modulation between cytoprotective versus pro-apoptotic clusterin forms increased sensitivity of LNCaP to cell death

Therapeutic Potential of Clusterin Inhibition in Human Cancer

Clusterin (CLU) protein is involved in various pathophysiological processes including carcinogenesis and tumor progression. In recent years, the role of the secretory isoform has been demonstrated in tumor cells, where it inhibits apoptosis and favors the acquisition of resistance to conventional treatments used to treat cancer. To determine the possible therapeutic potential of inhibiting this protein, numerous studies have been carried out in this field. In this article, we present the existing knowledge to date on the inhibition of this protein in different types of cancer and analyze the importance it could have in the development of new therapies targeted against this disease.

Plexina4 and cell survival in the developing zebrafish hindbrain

BACKGROUND

Growth factors are important in the developing and mature nervous system to support the survival of neurons. Developmental signaling molecules are known for their roles in controlling neurogenesis and neural circuit formation. Whether or not these molecules also have roles in cell survival in the developing nervous system is poorly understood. Plexins are a family of transmembrane receptors that bind Semaphorin ligands and are known to function in the guidance of developing axons and blood vessels.

RESULTS

In embryonic zebrafish, plexina4 is expressed widely in the brain, becoming largely restricted to the hindbrain as neurogenesis and differentiation proceed. Apoptosis is increased in the embryonic hindbrain of a plexina4ca307/ca307 CRISPR mutant. Based on the literature, we tested the secreted heat shock protein, Clusterin, as a candidate ligand to mediate cell survival through Plexina4. clusterin is expressed by the floor plate of the embryonic zebrafish hindbrain, in proximity to plexina4-expressing hindbrain cells. Morpholino-mediated knockdown of Clusterin increases cell apoptosis in the hindbrain, with additional cell death observed in epistasis experiments where Clusterin is knocked down in a plexina4 mutant background.

CONCLUSIONS

Our data suggest that Plexina4 promotes cell survival in the developing zebrafish hindbrain, likely through a pathway independent of Clusterin.

The Ins and Outs of Clusterin: Its Role in Cancer, Eye Diseases and Wound Healing

Clusterin (CLU) is a glycoprotein originally discovered in 1983 in ram testis fluid. Rapidly observed in other tissues, it was initially given various names based on its function in different tissues. In 1992, it was finally named CLU by consensus. Nearly omnipresent in human tissues, CLU is strongly expressed at fluid-tissue interfaces, including in the eye and in particular the cornea. Recent research has identified different forms of CLU, with the most prominent being a 75-80 kDa heterodimeric protein that is secreted. Another truncated version of CLU (55 kDa) is localized to the nucleus and exerts pro-apoptotic activities. CLU has been reported to be involved in various physiological processes such as sperm maturation, lipid transportation, complement inhibition and chaperone activity. CLU was also reported to exert important functions in tissue remodeling, cell-cell adhesion, cell-substratum interaction, cytoprotection, apoptotic cell death, cell proliferation and migration. Hence, this protein is sparking interest in tissue wound healing. Moreover, CLU gene expression is finely regulated by cytokines, growth factors and stress-inducing agents, leading to abnormally elevated levels of CLU in many states of cellular disturbance, including cancer and neurodegenerative conditions. In the eye, CLU expression has been reported as being severely increased in several pathologies, such as age-related macular degeneration and Fuch's corneal dystrophy, while it is depleted in others, such as pathologic keratinization. Nevertheless, the precise role of CLU in the development of ocular pathologies has yet to be deciphered. The question of whether CLU expression is influenced by these disorders or contributes to them remains open. In this article, we review the actual knowledge about CLU at both the protein and gene expression level in wound healing, and explore the possibility that CLU is a key factor in cancer and eye diseases. Understanding the expression and regulation of CLU could lead to the development of novel therapeutics for promoting wound healing.

Dysregulation of HNF1B/Clusterin axis enhances disease progression in a highly aggressive subset of pancreatic cancer patients

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy and is largely refractory to available treatments. Identifying key pathways associated with disease aggressiveness and therapeutic resistance may characterize candidate targets to improve patient outcomes. We used a strategy of examining the tumors from a subset of PDAC patient cohorts with the worst survival to understand the underlying mechanisms of aggressive disease progression and to identify candidate molecular targets with potential therapeutic significance. Non-negative matrix factorization (NMF) clustering, using gene expression profile, revealed three patient subsets. A 142-gene signature specific to the subset with the worst patient survival, predicted prognosis and stratified patients with significantly different survival in the test and validation cohorts. Gene-network and pathway analysis of the 142-gene signature revealed dysregulation of Clusterin (CLU) in the most aggressive patient subset in our patient cohort. Hepatocyte nuclear factor 1 b (HNF1B) positively regulated CLU, and a lower expression of HNF1B and CLU was associated with poor patient survival. Mechanistic and functional analyses revealed that CLU inhibits proliferation, 3D spheroid growth, invasiveness and epithelial-to-mesenchymal transition (EMT) in pancreatic cancer cell lines. Mechanistically, CLU enhanced proteasomal degradation of EMT-regulator, ZEB1. In addition, orthotopic transplant of CLU-expressing pancreatic cancer cells reduced tumor growth in mice. Furthermore, CLU enhanced sensitivity of pancreatic cancer cells representing aggressive patient subset, to the chemotherapeutic drug gemcitabine. Taken together, HNF1B/CLU axis negatively regulates pancreatic cancer progression and may potentially be useful in designing novel strategies to attenuate disease progression in PDAC patients.

The Dual Roles of Clusterin in Extracellular and Intracellular Proteostasis

Clusterin (CLU) was the first reported secreted mammalian chaperone and impacts on serious diseases associated with inappropriate extracellular protein aggregation. Many studies have described intracellular CLU in locations outside the secretory system and recent work has shown that CLU can be released into the cytosol during cell stress. In this article, we critically evaluate evidence relevant to the proposed origins of cellular CLU found outside the secretory system, and advance the hypothesis that the cytosolic release of CLU induced by stress serves to facilitate the trafficking of misfolded proteins to the proteasome and autophagy for degradation. We also propose future research directions that could help establish CLU as a unique chaperone performing critical and synergic roles in both intracellular and extracellular proteostasis.

Clusterin as modulator of carcinogenesis: A potential avenue for targeted cancer therapy

Clusterin (CLU) is an evolutionary conserved molecular chaperone present in different human tissues and fluids and established to be a significant cancer regulator. It controls several cancer-associated cellular events, including cancer cell proliferation, stemness, survival, metastasis, epithelial-mesenchymal transition, therapy resistance, and inhibition of programmed cell death to support cancer growth and recurrence. This multifunctional role of CLU makes it an ideal target for cancer control. More importantly, genetic and antisense-mediated (OGX-011) inhibition of CLU enhances the anticancer potential of different FDA-approved chemotherapeutic drugs at the clinical level, improving patient's survival. In this review, we have discussed the detailed mechanism of CLU-mediated modulation of different cancer-associated signaling pathways. We have also provided updated information on the current preclinical and clinical findings that drive trials in various cancer types for potential targeted cancer therapy.

Secretory Clusterin as a Novel Molecular-targeted Therapy for Inhibiting Hepatocellular Carcinoma Growth

BACKGROUND

Although secretory clusterin (sCLU) plays a crucial role in Hepatocellular Carcinoma (HCC) cells proliferation, Multiple Drug Resistance (MDR), metastasis and so on, its targeted effects and exact mechanism are still unknown. This review summarizes some new progress in sCLU as a molecular-targeted therapy in the treatment of HCC.

METHODS

A systematic review of the published English-language literature about sCLU and HCC has been performed using the PubMed and bibliographic databases. Some valuable studies on sCLU in HCC progression were searched for relevant articles with the keywords: HCC, diagnosis, MDR, as molecular-targeted in treatment, and so on.

RESULTS

The incidence of the positive rate of sCLU was significantly higher in HCC tissues as compared to the surrounding tissues at mRNA or protein level, gradually increasing with tumor-nodemetastasis staging (P<0.05). Also, the abnormal level of sCLU was related to poor differentiation degree, and considered as a useful marker for HCC diagnosis or independent prognosis for patients. Hepatic sCLU could be silenced at mRNA level by specific sCLU-shRNA or by OGX-011 to inhibit cancer cell proliferation with an increase in apoptosis, cell cycle arrest, reversal MDR, alteration of cell migration or invasion behaviors, and a decrease in GSK-3β or AKT phosphorylation in vitro, as well as significant suppression of the xenograft growth by down-regulating β-catenin, p-GSK3β, and cyclinD1 expression in vivo.

CONCLUSION

Abnormal hepatic sCLU expression should not only be a new diagnostic biomarker but also a novel promising target for inhibiting HCC growth.

Secretory clusterin promotes hepatocellular carcinoma progression by facilitating cancer stem cell properties via AKT/GSK-3β/β-catenin axis

Background

To explore the modulatory effects and mechanism of secretory clusterin (sCLU) on cancer stem cell (CSC) properties in hepatocellular carcinoma (HCC).

Methods

The effects of sCLU repression or overexpression on chemoresistance, migration, invasion, and tumor growth were detected by MTT, wound healing, transwell assays, and xenograft assay, respectively. The tumor sphere assay was performed to evaluate the self-renewal ability of HCC cells. In addition, the molecular regulation between sCLU and AKT/GSK-3β/β-catenin axis in HCC cells were discovered by western blotting, quantitative real-time PCR (qRT-PCR), and immunofluorescence. The expression status of sCLU and β-catenin in HCC tissues were investigated by immunohistochemistry.

Results

Knockdown or overexpressing sCLU remarkably inhibited or promoted the chemoresistance against sorafenib/doxorubicin, metastasis, and tumor growth of HCC cells, respectively. HepG2 and HCCLM3-derived spheroids showed higher expression of sCLU than that in attached cells. Additionally, repressing sCLU impaired the self-renewal capacity of HCC cells and CSC-related chemoresistance while overexpression of sCLU enhanced these CSC properties. Knockdown or overexpression of sCLU inhibited or increased the expressions of β-catenin, cyclinD1, MMP-2 and MMP-9, and the phosphorylation of AKT or GSK3β signaling, respectively. However, LiCl or LY294002 abrogated the effects mediated by sCLU silencing or overexpression on chemoresistance, metastasis, and CSC phenotype. Furthermore, co-expression of sCLU and β-catenin in HCC tissues indicated poor prognosis of HCC patients.

Conclusions

Taken together, the oncogenic sCLU might promote CSC phenotype via activating AKT/GSK3β/β-catenin axis, suggesting that sCLU was a potential molecular-target for HCC therapy.

Clusterin inhibition mediates sensitivity to chemotherapy and radiotherapy in human cancer

Since its discovery in 1983, the protein clusterin (CLU) has been isolated from almost all human tissues and fluids and linked to the development of different physiopathological processes, including carcinogenesis and tumor progression. During the last few years, several studies have shown the cytoprotective role of secretory CLU in tumor cells, inhibiting their apoptosis and enhancing their resistance to conventional treatments including hormone depletion, chemotherapy, and radiotherapy. In an effort to determine the therapeutic potential that the inhibition of this protein could have on the development of new strategies for cancer treatment, numerous studies have been carried out in this field, with results, in most cases, satisfactory but sometimes contradictory. In this document, we summarize for the first time the current knowledge of the effects that CLU inhibition has on sensitizing tumor cells to conventional cancer treatments and discuss its importance in the development of new strategies against cancer.

Diagnostic and prognostic significance of secretory clusterin expression in patients with hepatocellular carcinoma

The upregulation of secretory clusterin (sCLU) is associated with tumor progression by contributing to angiogenesis, chemo-resistance, cell survival, and metastasis. However, its diagnostic or prognostic values for hepatocellular carcinoma (HCC) still remain to be clarified. The average serum sCLU level analyzed by an enzyme-linked immunosorbent assay was significantly higher (P < 0.001) in HCC patients than that in any of cases with cirrhosis, chronic hepatitis, or healthy control. The area under receiver operating characteristic curve and diagnostic sensitivity were 0.75 and 74.7 % in sCLU, and 0.74 and 58.7 % in α-fetoprotein (AFP), respectively. The combining detections of sCLU and AFP rose up to 90.7 % for HCC diagnosis. In liver, sCLU by immunohistochemistry was significantly higher (P < 0.001) in the HCC (77.3 %) group than that in their para-cancerous group (33.3 %). Abnormal serum or tissue sCLU expression was closely associated with tumor-node-metastasis (TNM) classification of malignant tumors and lymph node metastasis, as an independent prognosis factor (hazard ratio, 2.287; 95 % confidence interval, 1.044-5.007; P = 0.039), and higher sCLU expression significantly correlated (χ (2) = 4.252, P = 0.039) with poor survival of HCC patients analyzed by multivariate Cox regression or Kaplan-Meier method, suggesting that abnormal sCLU expression associated with tumor progression could be a potential diagnostic and prognostic biomarker for HCC.

Silencing clusterin gene transcription on effects of multidrug resistance reversing of human hepatoma HepG2/ADM cells

Abnormal clusterin (CLU) expression is associated with multidrug resistance (MDR) of hepatocellular carcinoma (HCC). In the present study, the CLU expression was analyzed in human hepatoma cells and chemoresistant counterpart HepG2/ADM cells. Compared with L02 cells, the overexpression of cellular CLU was identified in HepG2, HepG2/ADM, SMMC7721, Hep3B ,and PLC cells and relatively lower expression in Bel-7404, SNU-739, and MHCC97H cells. Specific short hairpin RNAs (shRNAs) to silence CLU gene transcription were designed, and the most effective sequences were screened. After the HepG2/ADM cells transfected with shRNA-1, the inhibition of CLU expression was 73.68 % at messenger RNA (mRNA) level by real-time quantitative RT-PCR with obvious enhancement in cell chemosensitivity, increasing apoptosis induced by doxorubicin using fluorescence kit, and Rh-123 retention qualified with flow cytometry. Knockdown CLU also significantly decreased the drug efflux pump activity through the depression of MDR1/P-glycoprotein (q = 11.739, P < 0.001). Moreover, silencing CLU led to downregulation of β-catenin (q = 13.544, P = 0.001), suggesting that downregulation of CLU might be a key point to reverse multidrug resistance of HepG2/ADM cells.

Downregulating sCLU enhances the sensitivity of hepatocellular carcinoma cells to gemcitabine by activating the intrinsic apoptosis pathway

PURPOSE

The purpose of this study was to investigate whether the therapeutic activity of gemcitabine (GCB) in hepatocellular carcinoma (HCC) could be increased by the down-regulation of secretory clusterin (sCLU), a glycoprotein that is considered to play a cytoprotective role in the resistance to chemotherapy.

METHODS

The expression of sCLU was detected in HCC tumor tissues and cell lines. A cell viability and apoptosis assay were performed in parental HCC cells or the same cells transfected with sCLU shRNA and treated with or without GCB. The potential downstream pathways were investigated using the Human Apoptosis RT(2) Profiler™ PCR Array.

RESULTS

The expression levels of sCLU in HCC tissues were significantly higher than in adjacent non-tumor liver tissues and were associated with the histological grade and transarterial chemoembolization. sCLU overexpression was also found in three HCC cell lines and hepatocytes. The depletion of sCLU synergistically increased GCB sensitivity in Bel7402 and SMMC7721 cells and induced cell apoptosis. Based on the PCR array analysis, sCLU depletion also resulted in the up-regulation of BNIP1, GADD45A, TNFRSF10A, and TRADD and down-regulation of AKT1 in Bel7402 and SMMC7721 cells compared with the parental controls. These results were further supported by a Western blot analysis, which showed increased GADD45a protein expression and the decreased expression of phosphorylated AKT. GADD45a overexpression also increased the sensitivity to GCB in the Bel7402 and SMMC7721 cells.

CONCLUSION

Targeting sCLU may be a useful method to enhance the cytotoxic effect of GCB in hepatocellular carcinoma.

Clusterin: a key player in cancer chemoresistance and its inhibition

Clusterin is a heterodimeric disulfide-linked glycoprotein (449 amino acids) isolated in the rat prostate after castration. It is widely distributed in different tissues and highly conserved in species. There are two isoforms (1 and 2) with antagonistic actions regarding apoptosis. Clusterin is implicated in a number of biological processes, including lipid transport, membrane recycling, cell adhesion, programmed cell death, and complement cascade, representing a truly multifunctional protein. Isoform 2 is overexpressed under cellular stress conditions and protects cells from apoptosis by impeding Bax actions on the mitochondrial membrane and exerts other protumor activities, like phosphatidylinositol 3-kinase/protein kinase B pathway activation, modulation of extracellular signal-regulated kinase 1/2 signaling and matrix metallopeptidase-9 expression, increased angiogenesis, modulation of the nuclear factor kappa B pathway, among others. Its overexpression should be considered as a nonspecific cellular response to a wide variety of tissue insults like cytotoxic chemotherapy, radiation, excess of free oxygen radicals, androgen or estrogen deprivation, etc. A review of the recent literature strongly suggests potential roles for custirsen in particular, and proapoptosis treatments in general, as novel modalities in cancer management. Inhibition of clusterin is known to increase the cytotoxic effects of chemotherapeutic agents, and custirsen, a second-generation antisense oligonucleotide that blocks clusterin, is being tested in a Phase III clinical trial after successful results were achieved in Phase II studies. A major issue in cancer evolution that remains unanswered is whether clusterin represents a driving force of tumorigenesis or a late phenomenon after chemotherapy. This review presents preclinical data that encourages trials in various types of cancer other than advanced castration-resistance prostate cancer and discusses briefly the appropriate timing for clusterin inhibition in the clinical context.

Non-secreted clusterin isoforms are translated in rare amounts from distinct human mRNA variants and do not affect Bax-mediated apoptosis or the NF-κB signaling pathway

Clusterin, also known as apolipoprotein J, is expressed from a variety of tissues and implicated in pathological disorders such as neurodegenerative diseases, ischemia and cancer. In contrast to secretory clusterin (sCLU), which acts as an extracellular chaperone, the synthesis, subcellular localization and function(s) of intracellular CLU isoforms is currently a matter of intense discussion. By investigating human CLU mRNAs we here unravel mechanisms leading to the synthesis of distinct CLU protein isoforms and analyze their subcellular localization and their impact on apoptosis and on NF-κB-activity. Quantitative PCR-analyses revealed the expression of four different stress-inducible CLU mRNA variants in non-cancer and cancer cell lines. In all cell lines variant 1 represents the most abundant mRNA, whereas all other variants collectively account for no more than 0.34% of total CLU mRNA, even under stressed conditions. Overexpression of CLU cDNAs combined with in vitro mutagenesis revealed distinct translational start sites including a so far uncharacterized non-canonical CUG start codon. We show that all exon 2-containing mRNAs encode sCLU and at least three non-glycosylated intracellular isoforms, CLU_1‑449, CLU_21‑449 and CLU_34‑449, which all reside in the cytosol of unstressed and stressed HEK‑293 cells. The latter is the only form expressed from an alternatively spliced mRNA variant lacking exon 2. Functional analysis revealed that none of these cytosolic CLU forms modulate caspase-mediated intrinsic apoptosis or significantly affects TNF-α-induced NF-κB-activity. Therefore our data challenge some of the current ideas regarding the physiological functions of CLU isoforms in pathologies.