Transforming growth factor beta-1 up-regulates clusterin synthesis in thyroid epithelial cells

The clusterin connectome: Emerging players in chondrocyte biology and putative exploratory biomarkers of osteoarthritis

Introduction

Clusterin is amoonlighting protein that hasmany functions. It is amultifunctional Q6 holdase chaperone glycoprotein that is present intracellularly and extracellularly in almost all bodily fluids. Clusterin is involved in lipid transport, cell differentiation, regulation of apoptosis, and clearance of cellular debris, and plays a protective role in ensuring cellular survival. However, the possible involvement of clusterin in arthritic disease remains unclear. Given the significant potential of clusterin as a biomarker of osteoarthritis (OA), a more detailed analysis of its complex network in an inflammatory environment, specifically in the context of OA, is required. Based on the molecular network of clusterin, this study aimed to identify interacting partners that could be developed into biomarker panels for OA.

Methods

The STRING database and Cytoscape were used to map and visualize the clusterin connectome. The Qiagen Ingenuity Pathway Analysis (IPA) software was used to analyze and study clusterinassociated signaling networks in OA. We also analyzed transcription factors known to modulate clusterin expression, which may be altered in OA.

Results

The top hits in the clusterin network were intracellular chaperones, aggregate-forming proteins, apoptosis regulators and complement proteins. Using a text-mining approach in Cytoscape, we identified additional interacting partners, including serum proteins, apolipoproteins, and heat shock proteins.

Discussion

Based on known interactions with proteins, we predicted potential novel components of the clusterin connectome in OA, including selenoprotein R, semaphorins, and meprins, which may be important for designing new prognostic or diagnostic biomarker panels.

Diverse functions of clusterin promote and protect against the development of pulmonary fibrosis

Pulmonary fibrosis is a progressive scarring disorder of the lung with dismal prognosis and no curative therapy. Clusterin, an extracellular chaperone and regulator of cell functions, is reduced in bronchoalveolar lavage fluid of patients with pulmonary fibrosis. However, its distribution and role in normal and fibrotic human lung are incompletely characterized. Immunohistochemical localization of clusterin revealed strong staining associated with fibroblasts in control lung and morphologically normal areas of fibrotic lung but weak or undetectable staining in fibrotic regions and particularly fibroblastic foci. Clusterin also co-localized with elastin in vessel walls and additionally with amorphous elastin deposits in fibrotic lung. Analysis of primary lung fibroblast isolates in vitro confirmed the down-regulation of clusterin expression in fibrotic compared with control lung fibroblasts and further demonstrated that TGF-β1 is capable of down-regulating fibroblast clusterin expression. shRNA-mediated down-regulation of clusterin did not affect TGF-β1-induced fibroblast-myofibroblast differentiation but inhibited fibroblast proliferative responses and sensitized to apoptosis. Down-regulation of clusterin in fibrotic lung fibroblasts at least partly due to increased TGF-β1 may therefore represent an appropriate but insufficient response to limit fibroproliferation. Reduced expression of clusterin in the lung may also limit its extracellular chaperoning activity contributing to dysregulated deposition of extracellular matrix proteins.

Clusterin Expression in the Early Process of Pancreas Regeneration in the Pancreatectomized Rat

We have previously reported upregulation of clusterin at the time of islet cell regeneration after beta-cell injury. This led us to speculate that clusterin might be involved in the neogenic regeneration of the pancreas. Clusterin expression was examined throughout the process of pancreatic neogenesis in pancreatectomized rats. For in vitro analysis, duct cells were isolated from the rat pancreas and clusterin cDNA was transfected for its overexpression. Clusterin and its mRNA increased significantly in the early phase of regeneration, particularly at 1-3 days after pancreatectomy. Clusterin was transiently expressed in the differentiating acinar cells but faded afterwards. Interestingly, these clusterin cells were negative for PCNA (proliferating cell nuclear antigen), whereas most epithelial cells in ductules in the regenerating tissue showed extensive proliferative activity. Clusterin expression was also detected in some endocrine cells of the regenerating tissue. Transfection of clusterin cDNA into primary cultured duct cells resulted in a 2.5-fold increase in cell proliferation and induced transformation of non-differentiated duct cells into differentiated cells displaying cytokeratin immunoreactivity. Taken together, these results suggest that clusterin may play essential roles in the neogenic regeneration of pancreatic tissue by stimulating proliferation and differentiation of duct cells.

Clusterin transcript variants expression in thyroid tumor: a potential marker of malignancy?

BACKGROUND

Clusterin (CLU) is a ubiquitous multifunctional factor involved in neoplastic transformation. The CLU transcript variants and protein forms play a crucial role in balancing cells proliferation and death.

METHODS

We investigated the regulation of CLU transcript variants expression in an in vivo model system consisting of both neoplastic tissues and fine needle aspiration biopsy (FNAB) samples isolated from patients undergoing thyroidectomy.

RESULTS

The immunohistochemical analyses showed an overall CLU up-regulation in papillary carcinoma. A specific CLU2 transcript variant increase was registered using qPCR in papillary carcinomas while CLU1 decreased. In addition, the analysis of CLU transcripts expression level showed an increase of the CLU2 transcript in the TIR 3 patients with histologically confirmed thyroid cancer.

CONCLUSIONS

Our results suggest the existence of a specific alteration of CLU2:CLU1 ratio towards CLU2, thus providing the first circumstantial evidence for the potential use of CLU transcript variants as effective biomarkers for a more accurate assessment of the so called "indeterminate" thyroid nodules.

ERp29 deficiency affects sensitivity to apoptosis via impairment of the ATF6-CHOP pathway of stress response

Endoplasmic reticulum protein 29 (ERp29) belongs to the redox-inactive PDI-Dβ-subfamily of PDI-proteins. ERp29 is expressed in all mammalian tissues examined. Especially high levels of expression were observed in secretory tissues and in some tumors. However, the biological role of ERp29 remains unclear. In the present study we show, by using thyrocytes and primary dermal fibroblasts from adult ERp29(-/-) mice, that ERp29 deficiency affects the activation of the ATF6-CHOP-branch of unfolded protein response (UPR) without influencing the function of other UPR branches, like the ATF4-eIF2α-XBP1 signaling pathway. As a result of impaired ATF6 activation, dermal fibroblasts and adult thyrocytes from ERp29(-/-) mice display significantly lower apoptosis sensitivities when treated with tunicamycin and hydrogen peroxide. However, in contrast to previous reports, we could demonstrate that ERp29 deficiency does not alter thyroglobulin expression levels. Therefore, our study suggests that ERp29 acts as an escort factor for ATF6 and promotes its transport from ER to Golgi apparatus under ER stress conditions.

Clusterin mediates TGF-β-induced epithelial-mesenchymal transition and metastasis via Twist1 in prostate cancer cells

TGF-β promotes epithelial-mesenchymal transition (EMT) and induces clusterin (CLU) expression, linking these genes to cancer metastasis. CLU is a pleiotropic molecular chaperone that confers survival and proliferative advantage to cancer cells. However, the molecular mechanisms by which TGF-β regulates CLU expression and CLU affects metastasis remain unknown. In this study, we report that the transcription factor Twist1 mediates TGF-β-induced CLU expression. By binding to E-boxes in the distal promoter region of CLU gene, Twist1 regulated basal and TGF-β-induced CLU transcription. In addition, CLU reduction reduced TGF-β induction of the mesenchymal markers, N-cadherin and fibronectin, thereby inhibiting the migratory and invasive properties induced by TGF-β. Targeted inhibition of CLU also suppressed metastasis in an in vivo model. Taken together, our findings indicate that CLU is an important mediator of TGF-β-induced EMT, and suggest that CLU suppression may represent a promising therapeutic option for suppressing prostate cancer metastatic progression.

EGF and TGF-β1 Effects on Thyroid Function

Normal epithelial thyroid cells in culture are inhibited by TGF-β1. Instead, transformed thyroid cell lines are frequently resistant to its growth inhibitory effect. Loss of TGF-β responsiveness could be due to a reduced expression of TGF-β receptors, as shown in transformed rat thyroid cell lines and in human thyroid tumors, or to alterations of other genes controlling TGF-β signal transduction pathway. However, in thyroid neoplasia, a complex pattern of alterations occurring during transformation and progression has been identified. Functionally, TGF-β1 acts as a tumor suppressor in the early stage of transformation or as a tumor promoter in advanced cancer. This peculiar pleiotropic behaviour of TGF-β may result from cross-talk with signalling pathways mediated by other growth factors, among which EGF-like ligands play an important role. This paper reports evidences on TGF-β1 and EGF systems in thyroid tumors and on the cross-talk between these growth factors in thyroid cancer.

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.

Role of transforming growth factor beta in the regulation of thyroid function and growth

Transforming growth factor beta (TGF-beta) exists in nature as three isoforms. They exert their effects by binding to a type II receptor located at the cell membrane. The TGF-beta-type II receptor complex then recruits type I receptor, and this new complex stimulates the phosphorylation of Smads 2 and 3, which are subsequently transferred to the nucleus, where they regulate gene transcription. The thyroid gland expresses the TGF-beta1 gene mRNA and synthesizes the protein, which under physiologic conditions regulates thyroid growth and function. Different studies have demonstrated that TGF-beta1 inhibits cell proliferation and a number of functional parameters. These include cyclic adenosine monophosphate (AMP) formation, iodine uptake and organification, hormone secretion, and the expression of thyroglobulin, thyroid peroxidase, and Na(+)/I(-) symporter. The expression of the TGF-beta1 gene and protein may be stimulated by iodine under normal conditions. Since TGF-beta1 mimics some of the inhibitory actions of iodine, its participation in thyroid autoregulation has been proposed; however, this concept is still debated. In thyroid tumors, the inhibitory action of TGF-beta1 on cell proliferation is progressively lost as the tumor becomes more undifferentiated. The alterations in the signaling pathway of TGF-beta1 are not the same in tumors from different species. Even within the same species, such as the pig thyroid, the results may be different depending on whether monolayers or follicular suspensions are employed. The data suggest that it is not entirely possible to apply the results obtained in animal studies to normal or pathological human thyroid tissue. More studies are required to provide the information needed to develop treatments, based on targeting the signaling pathway of TGF-beta1, for undifferentiated thyroid cancer and other thyroid diseases.

Functional association of the morphogenic factors with the clusterin for the pancreatic beta-cell differentiation

Several differentiation or morphogenic factors have known to be involved in the developmental process of endocrine pancreas. However, mechanism of action and functional relation of these molecules are not well elucidated particularly in beta-cell formation from adult pancreatic stem cells. We hypothesized that adult pancreatic stem cells could be activated by the functional resumption of the morphogenic factors that were involved in embryonic development of pancreas in the duct system under the specific conditions such as tissue injuries. Besides the well-established genes including Pdx-1 and Ngn-3, we propose the nestin and clusterin as the new morphogenic factors for beta-cell neogenesis and their functional associations. We found extensive in vivo formation of ductules showing a higher replicating ability following the experimental tissue injury. These neogenic ductules were lined with low epithelial cells positive for the nestin, which has been known as neuronal stem cell marker. In in vitro culture, the nestin-rich epithelial cells of the neogenic ductules also displayed extensive self-replication leading to monolayer of epithelial cell explants and transformed into the insulin secreting beta cells as well as duct cells. Thus, we depicted them as nestin-positive duct stem (NPDS) cells. We found a neogenesis specific protein 'clusterin' in the regenerating pancreatic tissues with concomitant increase of Pdx-1 and Ngn-3 expression. The protein is expressed predominantly in the neogenic pancreas undergoing differentiation. In vitro over-expression of the clusterin gene strongly induces beta-cell transformation from neogenic ductal cells. Insulin expression, both insulin mRNA and peptide levels, was increased and showed glucose dependent manner by ectopic expression of clusterin upon the culture of neogenic ductules when compared to the mock-transfected control, implying that the duct cells transformed functional beta cells. We observed that clusterin over-expression led to up-regulation of Pdx-1 and Ngn-3, and clusterin levels were increased upon the transfection of cDNAs of Pdx-1 or Ngn-3, suggesting a close functional association of these morphogenic factors. In conclusion, we suggest that adult pancreatic stem cells can be recapitulated for neogenesis of insulin secreting beta cells not only by reactivation Pdx-1 and Ngn-3, the classical differentiation factors for pancreas development, but also by the intervention of new morphogenic factors including nestin and clusterin. In particular, by modulation of Pdx-1 and Ngn-3, clusterin induces remarkable differentiation of the functional beta cells secreting insulin in response to glucose stimulation.

Proteomics analysis of plasma for potential biomarkers in the diagnosis of Alzheimer's disease

The objective of this study was to search for biological markers associated with Alzheimer's disease (AD). Plasma specimens obtained from ten pathologically diagnosed AD patients and ten non-demented (ND) control subjects were analyzed by a combination of 2-DE and MS. This strategy allowed us to identify six plasma proteins (alpha-1-antitrypsin, vitamin D-binding protein, inter-alpha-trypsin inhibitor family heavy chain-related protein, apolipoprotein J precursor, cAMP-dependent protein kinase catalytic subunit alpha 1, and an orf) whose 2-DE spot densities were different between the AD and ND groups. Due to their involvements in AD amyloid plaque formation, the plasma concentrations of alpha-1-antitrypsin and apolipoprotein J were further validated using either ELISA or Western blot. The results revealed that the plasma levels of alpha-1-antitrypsin in AD were higher than those of controls, confirming the 2-DE findings. However, no difference in total apolipoprotein J concentration was observed between the AD and ND groups. Considering the difference in resolving power to differentially quantitate protein isoforms provided by 2-DE and Western blot, 2-DE analysis combined with MS protein identification offers distinctive advantages when a disease-related protein isoform-specific variance is investigated.

Challenge and promise: roles for clusterin in pathogenesis, progression and therapy of cancer

Clusterin (CLU) has been implicated in various cell functions involved in carcinogenesis and tumour progression. There are two known CLU protein isoforms generated in human cells. A nuclear form of CLU protein (nCLU) is proapoptotic, and a secretory form (sCLU) is prosurvival. CLU expression has been associated with tumorigenesis of various malignancies, including tumours of prostate, colon, and breast. Furthermore, CLU expression is modulated by many factors that are believed to regulate tumour growth and/or apoptosis, including 1,25-dihydroxyvitamin D3, transforming growth factor beta-1, ultraviolet radiation, and IR. sCLU upregulation appears to be a general molecular stress response. Presently, preliminary results indicate that therapeutic modalities targeting CLU may be effective in cancer treatment. However, such strategies should make sure that nCLU is not eliminated or reduced. This review summarizes our present understanding of the importance of CLU in various physiological functions including tumour growth, and discusses its relevance to future cancer therapy.

Differential effects of clusterin/apolipoprotein J on cellular growth and survival

The secreted clusterin/apolipoprotein J (CLU) protein form is a ubiquitously expressed heterodimeric glycoprotein which is differentially regulated in many severe physiological disturbance states including cell death, ageing, cancer progression, and various neurological diseases. Despite extensive efforts CLU function remains an enigma, the main cause being the intriguingly distinct and usually opposed functions in various cell types and tissues. In the current report we investigated the effects of CLU on cellular growth and survival in three human osteosarcoma (OS) cell lines, namely KH OS, Sa OS, and U-2 OS that express very low, moderate, and high endogenous steady-state CLU amounts, respectively. We found that exposure of these established OS cell lines or primary OS cells to genotoxic stress results in CLU gene induction at distinct levels that correlate negatively to CLU endogenous amounts. Following CLU-forced overexpression by means of an artificial transgene, we found that although extracellular CLU inhibits cell death in all three OS cell lines, intracellular CLU has different effects on cellular proliferation and survival in these cell lines. Transgenic KH OS cell lines adapted to moderate intracellular CLU levels were growth-retarded and became resistant to genotoxic and oxidative stress. In contrast, transgenic Sa OS and U2 OS cell lines adapted to high intracellular CLU amounts were sensitive to genotoxic and oxidative stress. In these two cell lines, the proapoptotic CLU function could be rescued by caspase inhibition. To monitor the immediate effects of heterologous CLU overexpression prior to cell adaptation, we performed transient transfections in all three OS cell lines. We found that induction of high intracellular CLU amounts increases spontaneous apoptosis in KH OS cells and reduces DNA synthesis in all three cell lines assayed. On the basis of these novel findings we propose that although extracellular CLU as well as intracellular CLU at low/moderate levels is cytoprotective, CLU may become highly cytostatic and/or cytotoxic if it accumulates intracellularly in high amounts either by direct synthesis or by uptake from the extracellular milieu.

Exposure of human skin diploid fibroblasts to repeated subcytotoxic doses of ultraviolet-B induces the overexpression of transforming growth factor-beta1 mRNA

In this work we show that the steady state mRNA level of TGF-beta1 is significantly increased in UVB-induced premature senescence.

Clusterin/apolipoprotein J in human aging and cancer

Clusterin/Apolipoprotein J (ApoJ) is a heterodimeric highly conserved secreted glycoprotein being expressed in a wide variety of tissues and found in all human fluids. Despite being cloned since 1989, no genuine function has been attributed to ApoJ so far. The protein has been reportedly implicated in several diverse physiological processes such as sperm maturation, lipid transportation, complement inhibition, tissue remodeling, membrane recycling, cell-cell and cell-substratum interactions, stabilization of stressed proteins in a folding-competent state and promotion or inhibition of apoptosis. ApoJ gene is differentially regulated by cytokines, growth factors and stress-inducing agents, while another defining prominent and intriguing ApoJ feature is its upregulation in many severe physiological disturbances states and in several neurodegenerative conditions mostly related to advanced aging. Moreover, ApoJ accumulates during the viable growth arrested cellular state of senescence, that is thought to contribute to aging and to tumorigenesis suppression; paradoxically ApoJ is also upregulated in several cases of in vivo cancer progression and tumor formation. This review focuses on the reported data related to ApoJ cell-type and signal specific regulation, function and site of action in normal and cancer cells. We discuss the role of ApoJ during cellular senescence and tumorigenesis, especially under the light of the recently demonstrated various ApoJ intracellular protein forms and their interaction with molecules involved in signal transduction and DNA repair, raising the possibility that its overexpression during cellular senescence might cause a predisposition to cancer.

Enhanced expression of plasminogen activator inhibitor-1 by dedifferentiated thyrocytes

Porcine thyrocytes in vitro in the presence of TSH adopt follicular-like morphology. Epidermal growth factor, phorbol esters or transforming growth factor beta-1 (TGFbeta-1) induce a rapid spreading of the cells and dedifferentiation. In addition to thyroglobulin, dedifferentiated thyrocytes secreted into the culture medium three proteins in abundant quantities. Two of them have been previously identified as thrombospondin-1 and clusterin, respectively. Using the microsequencing method we identified the third one, a M(r) 45,000 glycosylated protein, as plasminogen activator inhibitor-1 (PAI-1). EGF, phorbol esters or TGF-beta1 predominantly increased PAI-1 protein expression in TSH-treated cells. The maximal increase of PAI-1 mRNA steady-state level was observed 6 h after EGF treatment and sustained up to 48 h. Recombinant PAI-1 inhibited cell-associated plasmin activity and delayed cell spreading. Enhanced synthesis and secretion of PAI-1 upon treatment with different growth factors during dedifferentiation process and spreading may be considered a feed-back defence mechanism of the cells to harmful extracellular stimuli.

Clusterin expression is significantly enhanced in prostate cancer cells following androgen withdrawal therapy

INTRODUCTION AND OBJECTIVES

Progression of prostate cancer to androgen independence (AI) results in part from the upregulation of anti-apoptotic genes following androgen withdrawal, and androgen-independent disease remains the primary obstacle to improved survival. Testosterone-repressed prostate message-2 (TRPM-2) encodes the anti-apoptotic protein clusterin, which is upregulated in response to cellular compromise as observed in normal and malignant tissues undergoing apoptosis. Systemic administration of antisense clusterin oligonucleotides in prostate cancer xenograft models delays progression to AI and enhances chemosensitivity. The objective of this study was to define changes in clusterin expression following neoadjuvant hormone therapy (NHT) in prostate cancer patients.

MATERIALS AND METHODS

Archival radical prostatectomy (RP) specimens were obtained for 128 patients who received either no NHT or treatment for 2-8 weeks, 3 months, or 8 months. Paired needle biopsy specimens were acquired for 30 patients and all tissues were subjected to clusterin immunohistochemistry. Western blot analysis was performed on frozen tissue from 5 untreated and 5 treated patients.

RESULTS

Clusterin expression in malignant prostatic tissue was significantly greater in patients who underwent preoperative NHT (P < 0.001). Needle biopsies obtained prior to NHT consistently demonstrated lower staining intensity than corresponding RP specimens (P < 0.001). Western blot analysis confirmed clusterin levels increased 17-fold beginning within 4 weeks after androgen withdrawal.

CONCLUSIONS

Upregulation of clusterin levels following androgen ablation therapy may represent an adaptive cell survival response following apoptotic signals like androgen withdrawal. These findings support clusterin as a valid therapeutic target in strategies employing novel multimodality therapy for advanced prostate cancer.

Subcytotoxic H2O2 stress triggers a release of transforming growth factor-beta 1, which induces biomarkers of cellular senescence of human diploid fibroblasts

Stress-induced premature senescence (SIPS) is induced 3 days after exposure of human diploid fibroblasts to subcytotoxic oxidative stress with H(2)O(2), with appearance of several biomarkers of replicative senescence. In this work, we show that transforming growth factor-beta1 (TGF-beta1) regulates the induction of several of these biomarkers in SIPS: cellular morphology, senescence-associated beta-galactosidase activity, increase in the steady-state level of fibronectin, apolipoprotein J, osteonectin, and SM22 mRNA. Indeed, the neutralization of TGF-beta1 or its receptor (TGF-beta RII) using specific antibodies decreases sharply the percentage of cells positive for the senescent-associated beta-galactosidase activity and displaying a senescent morphology. In the presence of each of these antibodies, the steady-state level of fibronectin, osteonectin, apolipoprotein J, and SM22 mRNA is no more increased at 72 h after stress. Results obtained on fibroblasts retrovirally transfected with the human papillomavirus E7 cDNA suggest that retinoblastoma protein (Rb) regulates the expression of TGF-beta1 in stressful conditions, leading to SIPS and overexpression of these four genes.

Subcellular distribution, secretion, and posttranslational modifications of clusterin in thyrocytes

A prominent secretory glycoprotein was detected in the culture medium of porcine thyrocytes which was identified as clusterin by microsequencing. Treatment of thyrocytes with thyroid stimulating hormone revealed a tight regulation of both synthesis and secretion of clusterin, with a distinct fraction of clusterin being always associated with the cells. At least three N-bound glycans were found on each subunit of clusterin, receiving most of the incorporated [(32)P]phosphate-label. Binding of clusterin to the immobilized cation-independent mannose 6-phosphate (M6P) receptor indicated that part of the phosphate label was contained in M6P moieties. Immunolabeling of cultured thyrocytes and of thyrocytes in situ showed clusterin on the apical cell surfaces where it colocalized with gp330/megalin, which is known to serve as a binding site for clusterin. The association with the apical plasma membrane, which, in thyrocytes, carries the iodinating system, was confirmed by biosynthetic iodination, an as yet unknown posttranslational modification of clusterin. On the basolateral plasma membranes clusterin was found within distinct, bipartite patches, suggesting that it is a constituent of cell-adhesion complexes and that it participates in cell-cell and cell-matrix interactions.