Clusterin/apolipoprotein J is a novel biomarker of cellular senescence that does not affect the proliferative capacity of human diploid fibroblasts

Critical role of lncEPAT in coupling dysregulated EGFR pathway and histone H2A deubiquitination during glioblastoma tumorigenesis

Histone 2A (H2A) monoubiquitination is a fundamental epigenetics mechanism of gene expression, which plays a critical role in regulating cell fate. However, it is unknown if H2A ubiquitination is involved in EGFR-driven tumorigenesis. In the current study, we have characterized a previously unidentified oncogenic lncRNA (lncEPAT) that mediates the integration of the dysregulated EGFR pathway with H2A deubiquitination in tumorigenesis. LncEPAT was induced by the EGFR pathway, and high-level lncEPAT expression positively correlated with the glioma grade and predicted poor survival of glioma patients. Mass spectrometry analyses revealed that lncEPAT specifically interacted with deubiquitinase USP16. LncEPAT inhibited USP16's recruitment to chromatin, thereby blocking USP16-mediated H2A deubiquitination and repressing target gene expression, including CDKN1A and CLUSTERIN. Depletion of lncEPAT promoted USP16-induced cell cycle arrest and cellular senescence, and then repressed GBM cell tumorigenesis. Thus, the EGFR-lncEPAT-ubH2A coupling represents a previously unidentified mechanism for epigenetic gene regulation and senescence resistance during GBM tumorigenesis.

Recurrent pregnancy loss is associated with a pro-senescent decidual response during the peri-implantation window

During the implantation window, the endometrium becomes poised to transition to a pregnant state, a process driven by differentiation of stromal cells into decidual cells (DC). Perturbations in this process, termed decidualization, leads to breakdown of the feto-maternal interface and miscarriage, but the underlying mechanisms are poorly understood. Here, we reconstructed the decidual pathway at single-cell level in vitro and demonstrate that stromal cells first mount an acute stress response before emerging as DC or senescent DC (snDC). In the absence of immune cell-mediated clearance of snDC, secondary senescence transforms DC into progesterone-resistant cells that abundantly express extracellular matrix remodelling factors. Additional single-cell analysis of midluteal endometrium identified DIO2 and SCARA5 as marker genes of a diverging decidual response in vivo. Finally, we report a conspicuous link between a pro-senescent decidual response in peri-implantation endometrium and recurrent pregnancy loss, suggesting that pre-pregnancy screening and intervention may reduce the burden of miscarriage.

Preliminary Study on Clusterin Protein (sCLU) Expression in PC-12 Cells Overexpressing Wild-Type and Mutated (Swedish) AβPP genes Affected by Non-Steroid Isoprenoids and Water-Soluble Cholesterol

In this study we attempted to verify the hypothesis that the mevalonate pathway affects amyloid beta precursor protein (AβPP) processing and regulates clusterin protein levels. AβPP expression was monitored by green fluorescence (FL) and Western blot (WB). WB showed soluble amyloid protein precursor alpha (sAβPPα) presence in AβPP-wt cells and Aβ expression in AβPP-sw cells. Nerve growth factor (NGF)-differentiated rat neuronal pheochromocytoma PC-12 cells were untreated/treated with statins alone or together with non-sterol isoprenoids. Co-treatment with mevalonate, dolichol, ubiquinol, farnesol, geranylgeraniol, or water-soluble cholesterol demonstrated statin-dependent neurotoxicity resulted from the attenuated activity of mevalonate pathway rather than lower cholesterol level. Atorvastatin (50 μM) or simvastatin (50 μM) as well as cholesterol chelator methyl-β-cyclodextrin (0.2 mM) diminished cell viability (p < 0.05) and clusterin levels. Interestingly, co-treatment with mevalonate, dolichol, ubiquinol, farnesol, geranylgeraniol, or water-soluble cholesterol stimulated (p < 0.05) clusterin expression. Effects of non-sterol isoprenoids, but not water soluble cholesterol (Chol-PEG), were the most significant in mock-transfected cells. Geranylgeraniol (GGOH) overcame atorvastatin (ATR)-dependent cytotoxicity. This effect does not seem to be dependent on clusterin, as its level became lower after GGOH. The novelty of these findings is that they show that the mevalonate (MEV) pathway rather than cholesterol itself plays an important role in clusterin expression levels. In mock-transfected, rather than in AβPP-overexpressing cells, GGOH/farnesol (FOH) exerted a protective effect. Thus, protein prenylation with GGOH/FOH might play substantial role in neuronal cell survival.

BACE2, a conditional β-secretase, contributes to Alzheimer's disease pathogenesis

Deposition of amyloid-β protein (Aβ) to form neuritic plaques is the characteristic neuropathology of Alzheimer's disease (AD). Aβ is generated from amyloid precursor protein (APP) by β- and γ-secretase cleavages. BACE1 is the β-secretase and its inhibition induces severe side effects, whereas its homolog BACE2 normally suppresses Aβ by cleaving APP/Aβ at the θ-site (Phe20) within the Aβ domain. Here, we report that BACE2 also processes APP at the β site, and the juxtamembrane helix (JH) of APP inhibits its β-secretase activity, enabling BACE2 to cleave nascent APP and aggravate AD symptoms. JH-disrupting mutations and clusterin binding to JH triggered BACE2-mediated β-cleavage. Both BACE2 and clusterin were elevated in aged mouse brains, and enhanced β-cleavage during aging. Therefore, BACE2 contributes to AD pathogenesis as a conditional β-secretase and could be a preventive and therapeutic target for AD without the side effects of BACE1 inhibition.

Comparison of several commonly used detection indicators of cell senescence

Cell senescence is the state of irreversible growth arrest that can be triggered by a variety of different cellular stresses. Currently, the commonly used detection indicators involved in the study of cell senescence include senescence-associated β-galactosidase, Clusterin, Telomeres/Telomerase, senescence-associated heterochromatin foci, senescence-associated secretory phenotype, senescence marker protein-30, tumor suppressor genes p53 and p16, and other indicators such as Ki67 and decoy receptor 2. These indicators are widely used in the study of cell senescence, each with its own characteristics, advantages, and disadvantages. This review summarizes several commonly used cell senescence indicators and compares their accuracy, credibility, specificity, and the scope of their potential application.

The Na/K-ATPase Oxidant Amplification Loop Regulates Aging

As aging involves oxidant injury, we examined the role of the recently described Na/K-ATPase oxidant amplification loop (NKAL). First, C57Bl6 old mice were given a western diet to stimulate oxidant injury or pNaKtide to antagonize the NKAL. The western diet accelerated functional and morphological evidence for aging whereas pNaKtide attenuated these changes. Next, human dermal fibroblasts (HDFs) were exposed to different types of oxidant stress in vitro each of which increased expression of senescence markers, cell-injury, and apoptosis as well as stimulated the NKAL. Further stimulation of the NKAL with ouabain augmented cellular senescence whereas treatment with pNaKtide attenuated it. Although N-Acetyl Cysteine and Vitamin E also ameliorated overall oxidant stress to a similar degree as pNaKtide, the pNaKtide produced protection against senescence that was substantially greater than that seen with either antioxidant. In particular, pNaKtide appeared to specifically ameliorate nuclear oxidant stress to a greater degree. These data demonstrate that the NKAL is intimately involved in the aging process and may serve as a target for anti-aging interventions.

Plasma apolipoproteins and physical and cognitive health in very old individuals

Apolipoproteins play a crucial role in lipid metabolism with implications in cardiovascular disease, obesity, diabetes, Alzheimer's disease, and longevity. We quantified 7 apolipoproteins in plasma in 1067 individuals aged 56-105 using immunoassays and explored relationships with APOE polymorphism ε2/3/4, vascular health, frailty, and cognition. ApoA1, ApoA2, ApoB, ApoC3, ApoE, ApoH, and ApoJ decreased from mid-life, although ApoE and ApoJ had U-shaped trends. Centenarians had the highest ApoE levels and the lowest frequency of APOE ε4 allele relative to younger groups. Apolipoprotein levels trended lower in APOE ε4 homozygotes and heterozygotes compared with noncarriers, with ApoE and ApoJ being significantly lower. Levels of all apolipoproteins except ApoH were higher in females. Sex- and age-related differences were apparent in the association of apolipoproteins with cognitive performance, as only women had significant negative associations of ApoB, ApoE, ApoH, and ApoJ in mid-life, whereas associations at older age were nonsignificant or positive. Our findings suggest levels of some apolipoproteins, especially ApoE, are associated with lifespan and cognitive function in exceptionally long-lived individuals.

Cr(VI) induces premature senescence through ROS-mediated p53 pathway in L-02 hepatocytes

Hexavalent Chromium [Cr(VI)], which can be found of various uses in industries such as metallurgy and textile dying, can cause a number of human disease including inflammation and cancer. Unlike previous research that focused on Cr(VI)-induced oxidative damage and apoptosis, this study placed emphasis on premature senescence that can be induced by low-dose and long-term Cr(VI) exposure. We found Cr(VI) induced premature senescence in L-02 hepatocytes, as confirmed by increase in senescence associated-β-galactosidase (SA-β-Gal) activity. Cr(VI) stabilized p53 through phosphorylation at Ser15 and increased expression of p53-transcriptional target p21. Mechanism study revealed Cr(VI) targeted and inhibited mitochondrial respiratory chain complex (MRCC) I and II to enhance reactive oxygen species (ROS) production. By applying antioxidant Trolox, we also confirmed that ROS mediated p53 activation. A tetracycline-inducible lentiviral expression system containing shRNA to p53 was used to knockout p53. We found p53 could inhibit pro-survival genes B-cell lymphoma-2 (Bcl-2), myeloid leukemia-1 (Mcl-1) and S phase related cell cycle proteins cyclin-dependent kinase 2 (CDK2), Cyclin E to induce premature senescence, and the functional role of ROS in Cr(VI)-induced premature senescence is depend on p53. The results suggest that Cr(VI) has a role in premature senescence by promoting ROS-dependent p53 activation in L-02 hepatocytes.

Transcriptome analysis of peripheral blood mononuclear cells in human subjects following a 36 h fast provides evidence of effects on genes regulating inflammation, apoptosis and energy metabolism

There is growing interest in the potential health benefits of diets that involve regular periods of fasting. While animal studies have provided compelling evidence that feeding patterns such as alternate-day fasting can increase longevity and reduce incidence of many chronic diseases, the evidence from human studies is much more limited and equivocal. Additionally, although several candidate processes have been proposed to contribute to the health benefits observed in animals, the precise molecular mechanisms responsible remain to be elucidated. The study described here examined the effects of an extended fast on gene transcript profiles in peripheral blood mononuclear cells from ten apparently healthy subjects, comparing transcript profiles after an overnight fast, sampled on four occasions at weekly intervals, with those observed on a single occasion after a further 24 h of fasting. Analysis of the overnight fasted data revealed marked inter-individual differences, some of which were associated with parameters such as gender and subject body mass. For example, a striking positive association between body mass index and the expression of genes regulated by type 1 interferon was observed. Relatively subtle changes were observed following the extended fast. Nonetheless, the pattern of changes was consistent with stimulation of fatty acid oxidation, alterations in cell cycling and apoptosis and decreased expression of key pro-inflammatory genes. Stimulation of fatty acid oxidation is an expected response, most likely in all tissues, to fasting. The other processes highlighted provide indications of potential mechanisms that could contribute to the putative beneficial effects of intermittent fasting in humans.

ATM regulates insulin-like growth factor 1-secretory clusterin (IGF-1-sCLU) expression that protects cells against senescence

Downstream factors that regulate the decision between senescence and cell death have not been elucidated. Cells undergo senescence through three pathways, replicative senescence (RS), stress-induced premature senescence (SIPS) and oncogene-induced senescence. Recent studies suggest that the ataxia telangiectasia mutant (ATM) kinase is not only a key protein mediating cellular responses to DNA damage, but also regulates cellular senescence induced by telomere end exposure (in RS) or persistent DNA damage (in SIPS). Here, we show that expression of secretory clusterin (sCLU), a known pro-survival extracellular chaperone, is transcriptionally up-regulated during both RS and SIPS, but not in oncogene-induced senescence, consistent with a DNA damage-inducible mechanism. We demonstrate that ATM plays an important role in insulin-like growth factor 1 (IGF-1) expression, that in turn, regulates downstream sCLU induction during senescence. Loss of ATM activity, either by genomic mutation (ATM-deficient fibroblasts from an ataxia telangiectasia patient) or by administration of a chemical inhibitor (AAI, an inhibitor of ATM and ATR), blocks IGF-1-sCLU expression in senescent cells. Downstream, sCLU induction during senescence is mediated by IGF-1R/MAPK/Egr-1 signaling, identical to its induction after DNA damage. In contrast, administration of an IGF-1 inhibitor caused apoptosis of senescent cells. Thus, IGF-1 signaling is required for survival, whereas sCLU appears to protect cells from premature senescence, as IMR-90 cells with sCLU knockdown undergo senescence faster than control cells. Thus, the ATM-IGF-1-sCLU pathway protects cells from lethality and suspends senescence.

Knockdown of clusterin expression increases the in vitro sensitivity of human prostate cancer cells to paclitaxel

Clusterin/apolipoprotein J is a secreted heterodimeric glycoprotein that is implicated in several pathophysiological processes, including tissue remodeling, reproduction, lipid transport, and apoptosis. Although previous studies demonstrated that clusterin is able to protect against apoptosis, the role of the clusterin in cellular proliferation remains elusive. To determine whether clusterin plays an important role in cellular proliferation, the function of clusterin was examined using a small interfering RNA (siRNA) in PC3 human prostate cancer cells. Transient transfection with clusterin siRNA resulted in significant suppression of clusterin mRNA and protein expression. Clusterin knockdown resulted in a decrease in protein expression of phospho-Akt and an increase in expression of proteins phosphatase type 2AC (PP2AC) and phosphorylation of p38. However, treatment with PP2AC siRNA exerted minimal effects on clusterin expression. Interestingly, clusterin mRNA expression was reduced in paclitaxel-treated cells, and the cytotoxic effect of paclitaxel was more potent when cells were incubated with clusterin siRNA. In addition, co-treatment with paclitaxel and clusterin siRNA significantly enhanced PP2AC levels. Taken together, these results indicate that clusterin plays a crucial role in PC3 cell proliferation and that clusterin depletion may contribute to enhanced sensitivity of PC3 cells to anticancer agents such as paclitaxel.

Regulation of the expression of CLU isoforms in endometrial proliferative diseases

Clusterin (CLU) is a nearly ubiquitous multifunctional protein synthesized in different functionally divergent isoforms, sCLU and nCLU, playing a crucial role by keeping a balance between cell proliferation and death. Studying in vivo CLU expression we found a higher mRNA expression both in neoplastic and hyperplastic tissues in comparison to normal endometria; in particular, by RT-qPCR we demonstrated an increase of the specific sCLU isoform in the neoplastic and hyperplastic endometrial diseases. On the contrary, no CLU increase was detected at the protein level. The CLU gene transcriptional activity was upregulated in the hyperplastic and neoplastic tissues, indicating the existence of a fine post-trans-criptional regulation of CLU expression possibly responsible for the protein decrease in the malignant disease. A specific CLU immunoreactivity was present in all the endometrial glandular cells in comparison to the other cellular compartments where CLU immunoreactivity was lower or absent. In conclusion, our results suggest the existence of a complex regulatory mechanism of CLU gene expression during the progression from normal to malignant cells, possibly contributing to endometrial carcinogenesis. Moreover, the specific alteration of the sCLU:nCLU ratio associated with the pathological stage, suggests a possible usage of CLU as molecular biomarker for the diagnosis/prognosis of endometrial proliferative diseases.

Clusterin and FOXL2 act concordantly to regulate pituitary gonadotroph adenoma growth

Pituitary tumors grow slowly and despite their high prevalence are invariably benign. We therefore studied mechanisms underlying pituitary tumor growth restraint. Pituitary tumor transforming gene (PTTG), the index human securin, a hallmark of pituitary tumors, triggers pituitary cell proliferation and murine pituitary tumor development. We show that human gonadotroph cell pituitary tumors, unlike other secreting tumor types, express high levels of gonadotroph-specific forkhead transcription factor FOXL2, and both PTTG and Forkhead box protein L2 (FOXL2) stimulate gonadotroph clusterin (Clu) expression. Both Clu RNA isoforms are abundantly expressed in these nonhormone-secreting human tumors, and, when cultured, these tumor cells release highly abundant levels of secreted Clu. FOXL2 directly stimulates the Clu gene promoter, and we show that PTTG triggers ataxia telangiectasia mutated kinase/IGF-I/p38MAPK DNA damage/chromosomal instability signaling, which in turn also induces Clu expression. Consequently, Clu restrains pituitary cell proliferation by inducing cyclin dependent kinase inhibitors p16 and p27, whereas Clu deletion down-regulates p16 and p27 in the Clu(-/-) mouse pituitary. FOXL2 binds and suppresses the PTTG promoter, and Clu also suppresses PTTG expression, thus neutralizing protumorigenic PTTG gonadotroph tumor cell properties. In vivo, murine gonadotroph LβT2 tumor cell xenografts overexpressing Clu and FOXL2 both grow slower and elicit smaller tumors. Thus, gonadotroph tumor cell proliferation is determined by the interplay between cell-specific FOXL2 with PTTG and Clu.

IGF-1 activates the P13K/AKT signaling pathway via upregulation of secretory clusterin

Secretory clusterin (sCLU) is a type of stress-induced, pro-survival glycoprotein elevated in early-stage cancer. It enhances cancer cell survival and is associated with several types of cancer progression. In this study, we measured the PI3K/AKT signaling activity by determining the phosphorylation level of the AKT protein, namely pAKT. A549 human non-small cell lung carcinoma (NSCLC) cells were treated with insulin-like growth factor-1 (IGF-1) for various periods of time. The results showed that IGF-1 activated the PI3K/AKT signaling pathway in the A549 cells in a time-dependent manner. Western blot analysis was performed to determine the expression of sCLU protein in A549 cells treated with IGF-1. IGF-1 elevated the expression of sCLU. To determine whether sCLU is required for the IGF-1 activation of the PI3K/AKT signaling pathway, the A549 cells were treated with IGF-1 and sCLU antisense oligonuleotide (sCLU ASO). sCLU ASO blocked the IGF-1 activation of the PI3K/AKT signaling pathway. These results demonstrate that IGF-1 activates the P13K/AKT signaling pathway via the upregulation of sCLU. The present study implies that this pathway may uncover a new mechanism for cancer progression and reveal new targets for drug development in the treatment of NSCLC.

The application of a three-step serum proteome analysis for the discovery and identification of novel biomarkers of hepatocellular carcinoma

The representative tumor markers for HCC, AFP, and PIVKA-II are not satisfactory in terms of sensitivity and specificity in the early diagnosis of HCC. In search for novel markers for HCC, three-step proteome analyses were carried out in serum samples obtained from 12 patients with HCC and 10 with LC. As a first step, serum samples were subjected to antibody-based immunoaffinity column system that simultaneously removes twelve of abundant serum proteins. The concentrated flow-through was then fractionated using reversed-phase HPLC. Proteins obtained in each fraction were separated by SDS-PAGE. Serum samples obtained from patient with HCC and with LC were analyzed in parallel and their protein expression patterns were compared. A total of 83 protein bands were found to be upregulated in HCC serum. All the protein bands, the intensity of which was different between HCC and LC groups, were identified. Among them, clusterin was most significantly overexpressed (P = 0.023). The overexpression of serum clusterin was confirmed by ELISA using another validation set of HCC samples. Furthermore, serum clusterin was elevated in 40% of HCC cases in which both AFP and PIVKA-II were within their cut-off values. These results suggested that clusterin is a potential novel serum marker for HCC.

Plasma protein characteristics of long-term hemodialysis survivors

Hemodialysis (HD) patients are under recurrent circulatory stress, and hemodialysis has a high mortality rate. The characteristics of plasma proteomes in patients surviving long-term HD remain obscure, as well as the potential biomarkers in predicting prognoses. This study reports the proteome analyses of patient plasma from non-diabetic long-term HD (LHD, dialysis vintage 14.9±4.1 years, n = 6) and the age/sex/uremic etiology-comparable short-term HD (SHD, dialysis vintage 5.3±2.9 years, n = 6) using 2-DE and mass spectrometry. In addition, a 4-year longitudinal follow-up of 60 non-diabetic HD patients was subsequently conducted to analyze the baseline plasma proteins by ELISA in predicting prognosis. Compared to the SHD, the LHD survivors had increased plasma vitamin D binding proteins (DBP) and decreased clusterin, apolipoprotein A-IV, haptoglobin, hemopexin, complement factors B and H, and altered isoforms of α1-antitrypsin and fibrinogen gamma. During the 45.7±15 months for follow-up of the 60 HD patient cases, 16 patients died. Kaplan-Meier analysis demonstrated that HD patients with the lowest tertile of the baseline plasma DBP level have a significantly higher mortality rate. Multivariate Cox regression analysis further indicated that DBP is an independent predictor of mortality. In summary, the altered plasma proteins in LHD implicated accelerated atherosclerosis, defective antioxidative activity, increased inflammation/infection, and organ dysfunction. Furthermore, lower baseline plasma DBP in HD patients is related to mortality. The results suggest that the proteomic approach could help discover the potential biomarker in HD prognoses.

Clusterin in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a ubiquitous multifunctional glycoprotein. Following its identification in 1983, clusterin was found to be clearly increased in Alzheimer's disease (AD). Later research demonstrated that clusterin could bind amyloid-beta (Abeta) peptides and prevent fibril formation, a hallmark of AD pathology. In addition to preventing excessive inflammation, intracellular clusterin was found to reduce apoptosis and oxidative stress. Although early studies were inconclusive, two recent large-scale genome-wide association studies (GWAS) independently identified variants within the clusterin gene as risk factors for developing AD. This review focuses on the characteristics of clusterin and possible mechanisms of its relationship to AD.

Comparative analysis of serum proteomes of degenerative scoliosis

Degenerative scoliosis (DS) is an important degenerative lumbar disease causing spinal dysfunction and affecting the quality of life of the elderly, and is associated not only with severe back or leg pain but also with complicated surgical outcomes. The pathogenesis of DS is still unknown. Therefore, it is very important to ascertain the etiology of degenerative scoliosis and establish related molecular markers predicting and controlling the scoliosis. For the first time, we used two-dimensional fluorescence DIGE to compare the serum proteome profiles of 12 DS patients and controls. Proteins found to be differentially expressed were identified by MALDI-TOF mass spectrometric analysis, coupled with database interrogation. Eleven spots that were differentially expressed in the sera of DS patients were found, and eight gene products were identified among these spots. Clusterin, CLU cDNA FLJ57622, ALB cDNA FLJ50830, Hypothetical short protein, HLA-A MHC class 1 antigen. (Fragment), ALB 23 kDa protein, Isoform 1 of G protein-regulated inducer of neurite outgrowth 1 (GPRIN I)and Ficolin-3 were down-regulated in the sera of DS patients. The decreased levels of Clusterin and Ficolin-3 were confirmed by Western blot. The information obtained with this proteomic analysis will be very useful in understanding the pathophysiology of DS as well as in finding candidates as drug targets of DS. These results may provide a novel approach for the pathogenesis study of DS.

Clusterin induces CXCR4 expression and migration of cardiac progenitor cells

Clusterin (CST) is a stress-responding protein with multiple biological functions, including the inhibition of apoptosis and inflammation and transport of lipids. It may also participate in cell traffic and migration. In the process of post-infarct cardiac tissue repair, stem cells migrate into the damaged myocardium under the influence of chemoattractive substances such as stromal cell-derived factor (SDF). This study aimed at testing whether CST enhances expression of stem cell homing receptor and migration of cardiac progenitor cells (CPCs). CPCs isolated from fetal canine hearts transduced by CST cDNA expressed high levels of CXCR4, a receptor for SDF-1. The transfected cells also showed an increased migratory response to SDF-1 stimulation. The SDF-1-mediated migration of the CST-expressing CPCs was attenuated by PI3 kinase inhibitor LY294002 but not by mitogen-activated protein/ERK kinase inhibitor PD98059. Analysis of cell cycle by flow cytometry revealed no significant difference in cell cycle between the transduced and control CPCs. Thus, CST expression may increase CPCs migration via increasing CXCR4 expression and SDF-1/chemokine receptor signaling in a PI3/Akt-dependent manner.

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.

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.

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.

Transcriptional and posttranslational regulation of clusterin by the two main cellular proteolytic pathways

Clusterin/apolipoprotein J (CLU) is a secreted glycoprotein associated with many severe physiological disturbances that represent states of increased oxidative stress, such as aging, cancer, atherosclerosis, diabetes, and renal and neurodegenerative diseases. The aim of our work was to examine the effect of proteasome and lysosome inhibition on CLU expression and to determine whether those proteolytic pathways are implicated in CLU gene regulation and protein degradation. To this end we used two different model systems, namely the U-2 OS osteosarcoma cell line and the WI38 primary human embryonic lung fibroblasts. We report that proteasome inhibition promotes both heat-shock factor 1 (HSF-1)-dependent CLU gene expression induction and protein accumulation due to reduced degradation. In contrast, lysosome inhibition results in elevated levels of CLU protein but does not affect the CLU mRNA levels. We also provide direct evidence that both the intracellular precursor, psCLU, and the mature secreted, sCLU, isoforms constitute proteolytic substrates of the proteasome and the lysosome. Overall our findings indicate that CLU overexpression after proteasome inhibition relates to both positive gene transcriptional regulation by HSF-1 and posttranslational protein accumulation due to reduced proteasomal and lysosomal degradation.

Cellular senescence: molecular mechanisms, in vivo significance, and redox considerations

Cellular senescence is recognized as a critical cellular response to prolonged rounds of replication and environmental stresses. Its defining characteristics are arrested cell-cycle progression and the development of aberrant gene expression with proinflammatory behavior. Whereas the mechanistic events associated with senescence are generally well understood at the molecular level, the impact of senescence in vivo remains to be fully determined. In addition to the role of senescence as an antitumor mechanism, this review examines cellular senescence as a factor in organismal aging and age-related diseases, with particular emphasis on aberrant gene expression and abnormal paracrine signaling. Senescence as an emerging factor in tissue remodeling, wound repair, and infection is considered. In addition, the role of oxidative stress as a major mediator of senescence and the role of NAD(P)H oxidases and changes to intracellular GSH/GSSG status are reviewed. Recent findings indicate that senescence and the behavior of senescent cells are amenable to therapeutic intervention. As the in vivo significance of senescence becomes clearer, the challenge will be to modulate the adverse effects of senescence without increasing the risks of other diseases, such as cancer. The uncoupled relation between cell-cycle arrest and the senescent phenotype suggests that this is an achievable outcome.

Clusterin associates with altered elastic fibers in human photoaged skin and prevents elastin from ultraviolet-induced aggregation in vitro

Clusterin is a secreted glycoprotein with stress-induced expression in various diseased and aged tissues. It shares basic features with small heat shock proteins because it may stabilize proteins in a folding-competent state. Besides its presence in all human body fluids, clusterin associates with altered extracellular matrix proteins, such as beta-amyloid in Alzheimer senile plaques in the brain. Because dermal connective tissue alterations occur because of aging and UV radiation, we explored the occurrence of clusterin in young, aged, and sun-exposed human skin. Immunohistochemical analysis showed that clusterin is constantly associated with altered elastic fibers in aged human skin. Elastotic material of sun-damaged skin (solar elastosis), in particular, revealed a strong staining for clusterin. Because of the striking co-localization of clusterin with abnormal elastic material, we investigated the interaction of clusterin with elastin in vitro. A chaperone assay was established in which elastin was denatured by UV irradiation in the absence or presence of clusterin. This assay demonstrated that clusterin exerted a chaperone-like activity and effectively inhibited UV-induced aggregation of elastin. The interaction of both proteins was further analyzed by electron microscopy, size exclusion chromatography, and mass spectrometry, in which clusterin was found in a stable complex with elastin after UV exposure.

Clusterin/Apolipoprotein J up-regulation after zinc exposure, replicative senescence or differentiation of human haematopoietic cells

Clusterin/Apolipoprotein J (CLU) is a cellular senescence biomarker implicated in several physiological processes. In this work we have investigated CLU expression and function in human haematopoietic cells. We found that early passage human T cell clones (TCC) express minimal endogenous amounts of CLU, which are significantly elevated in late passage cells. Moreover, exposure of TCC to increased levels of the essential micronutrient zinc in culture resulted in intense induction of CLU. Because haematopoietic cells cease proliferation following induction of terminal differentiation, we also studied the expression profile of CLU in the leukemic progenitor cell lines K562 and HL-60. We found that, like TCC, both cell lines express minimal endogenous levels of CLU in their actively proliferating state. However, when induced to differentiate into their distinct cell types, CLU was found to be up-regulated specifically in those cells expressing the main differentiation markers. Enforced stable over-expression of CLU in K562 cells inhibited the expression of the CD14 differentiation marker and blocked differentiation to either monocytes/megacaryoblasts or to erythrocytes. Overall, our results suggest that CLU is actively involved in both replicative senescence and terminal differentiation in different types of human haematopoietic cells.

Development of resistance to chemotherapeutic drugs in human osteosarcoma cell lines largely depends on up-regulation of Clusterin/Apolipoprotein J

Clusterin/Apolipoprotein J (CLU) is differentially regulated during in vivo cancer progression. We have addressed the role of CLU during the acquisition and maintenance of human cancer cells resistance to chemotherapeutic drugs. We used two osteosarcoma (OS) cell lines, namely U-2 OS and KH OS, and selected three generations of doxorubicin (DXR)-resistant cells (R1, R2 and R3; resistant to 0.0035, 0.035 and 0.35 microM DXR, respectively) by continuous exposure to increasing, clinically relevant, DXR concentrations. Our studies showed that the DXR-resistant OS cell lines were cross-resistant to a variety of unrelated cytotoxic agents. Analysis of the CLU mRNA and protein expression levels revealed a minimal CLU up-regulation in the U-2 OS R2 cells and a significant, more than 4-fold, induction in the KH OS R2 and R3 cells. Antibody-mediated neutralization of the extracellular CLU, or silencing of CLU gene expression via small interfering RNA (siRNA) partially sensitized KH OS R2 cells to the drugs assayed. Moreover, siRNA-mediated CLU knock down in the absence of DXR induced high levels of endogenous spontaneous apoptosis in both the parental and R2 OS cell lines. This effect was enhanced by more than 60% in the KH OS R2 cells as compared to their parental counterparts, indicating that the high CLU levels in the KH OS R2 cells are essential for survival. Overall, we suggest that CLU up-regulation in the multi-drug resistant OS cells relates to enhanced drug resistance. Therefore, CLU may represent a predictive marker, which correlates to response of cancer cells to chemotherapy.

Regulation of clusterin/apolipoprotein J, a functional homologue to the small heat shock proteins, by oxidative stress in ageing and age-related diseases

Clusterin/apolipoprotein J (CLU) gene has a nearly ubiquitous expression pattern in human tissues. The two main CLU protein isoforms in human cells include the conventional glycosylated secreted heterodimer (sCLU) and a truncated nuclear form (nCLU). CLU has been implicated in various physiological processes and in many severe physiological disturbance states including ageing, cancer progression, vascular damage, diabetes, kidney and neuron degeneration. Although unrelated in their etiology and clinical manifestation, these diseases represent states of increased oxidative stress, which in turn, promotes amorphous aggregation of target proteins, increased genomic instability and high rates of cellular death. Among the various properties attributed to CLU so far, those mostly investigated and invariably appreciated are its small heat shock proteins-like chaperone activity and its involvement in cell death regulation, which are both directly correlated to the main features of oxidant injury. Moreover, the presence of both a heat shock transcription factor-1 and an activator protein-1 element in the CLU gene promoter indicate that CLU gene can be an extremely sensitive biosensor to reactive oxygen species. This review emphasizes on CLU gene regulation by oxidative stress that is the common link between all pathological conditions where CLU has been implicated.

Genes, ageing and longevity in humans: problems, advantages and perspectives

Many epidemiological data indicate the presence of a strong familial component of longevity that is largely determined by genetics, and a number of possible associations between longevity and allelic variants of genes have been described. A breakthrough strategy to get insight into the genetics of longevity is the study of centenarians, the best example of successful ageing. We review the main results regarding nuclear genes as well as the mitochondrial genome, focusing on the investigations performed on Italian centenarians, compared to those from other countries. These studies produced interesting results on many putative "longevity genes". Nevertheless, many discrepancies are reported, likely due to the population-specific interactions between gene pools and environment. New approaches, including large-scale studies using high-throughput techniques, are urgently needed to overcome the limits of traditional association studies performed on a limited number of polymorphisms in order to make substantial progress to disentangle the genetics of a trait as complex as human longevity.

Characterization and functional consequences of underexpression of clusterin in rheumatoid arthritis

We previously compared by microarray analysis gene expression in rheumatoid arthritis (RA) and osteoarthritis (OA) tissues. Among the set of genes identified as a molecular signature of RA, clusterin (clu) was one of the most differentially expressed. In the present study we sought to assess the expression and the role of CLU (mRNA and protein) in the affected joints and in cultured fibroblast-like synoviocytes (FLS) and to determine its functional role. Quantitative RT-PCR, Northern blot, in situ hybridization, immunohistochemistry, and Western blot were used to specify and quantify the expression of CLU in ex vivo synovial tissue. In synovial tissue, the protein was predominantly expressed by synoviocytes and it was detected in synovial fluids. Both full-length and spliced isoform CLU mRNA levels of expression were lower in RA tissues compared with OA and healthy synovium. In synovium and in cultured FLS, the overexpression of CLU concerned all protein isoforms in OA whereas in RA, the intracellular forms of the protein were barely detectable. Transgenic overexpression of CLU in RA FLS promoted apoptosis within 24 h. We observed that CLU knockdown with small interfering RNA promoted IL-6 and IL-8 production. CLU interacted with phosphorylated IkappaBalpha. Differential expression of CLU by OA and RA FLS appeared to be an intrinsic property of the cells. Expression of intracellular isoforms of CLU is differentially regulated between OA and RA. We propose that in RA joints, high levels of extracellular CLU and low expression of intracellular CLU may enhance NF-kappaB activation and survival of the synoviocytes.

Reduced expression levels of the senescence biomarker clusterin/apolipoprotein j in lymphocytes from healthy centenarians

Clusterin/apolipoprotein J (CLU) is a conserved, ubiquitously expressed secreted glycoprotein that has been implicated in several physiological processes and was found to accumulate in many severe physiological disturbances. We have previously shown that the CLU gene and protein are upregulated during replicative senescence, stress-induced premature senescence, in vivo aging, and in several age-related diseases. In this study we have examined the CLU gene relationship to human longevity. We recruited and further analyzed 96 blood samples from Italian and Greek healthy donors of different ages, including 49 centenarians. We found that although the CLU gene expression levels increase during aging, in the centenarians' samples CLU levels were lower than those found in old donors. We then investigated the possible existence of a genetic polymorphism related to longevity at the CLU structural locus. A neutral noncoding sequence variant was detected 35 nucleotides upstream from exon 6, which does not correlate, however, with the age of the donor. We conclude that CLU gene accumulation during in vivo aging does not directly relate to chronological age, but rather indicates increased levels of organismal stress due to a progressive failure of homeostasis and/or to prolonged exposure to a stressful environment.

Nuclear clusterin accumulation during heat shock response: implications for cell survival and thermo-tolerance induction in immortalized and prostate cancer cells

Clusterin (CLU), whose role is still debated, is differentially regulated in several patho-physiological processes and invariably induced during apoptosis. In heat shock response, CLU is considered a stress-inducible, pro-survival/cyto-protective factor via an HSE element present in his promoter. In both human prostate PNT1A and PC-3 epithelial cells we found that apoptotic stimuli induced nuclear localization of CLU (nCLU), and that overexpression of nCLU is pro-apoptotic. We show here that CLU time-course accumulation kinetic is different from that of HSP70 in these cells, thus other factor(s) might mediate HSF-1 activation and CLU expression. Sub-lethal heat shock inhibited the secretion of CLU (sCLU), leading to increased cytoplasm accumulation of CLU (cCLU) in association to cell survival. At difference, lethal heat stress caused massive accumulation of pro-apoptotic nCLU in cells dying by caspase-3-dependent apoptosis. Double heat stress (sub-lethal heat shock followed by recovery and lethal stress) induced HSP70 and thermo-tolerance in PNT1A cells, but not in PC-3 cells. In PNT1A cells, CLU secretion was inhibited and cCLU was accumulated, suggesting that cCLU might be pro-survival, while in PC-3 cells accumulation of nCLU was concomitant to caspase-3 induction and PARP activation instead. Thus, CLU expression/sub-cellular localization is strictly related to cell fate. In particular, nCLU and physiological levels of HSP70 affected cell survival in an antagonistic fashion. Prevalence of heat-induced nCLU, not allowing PC-3 cells to cope with heat shock, could be the rational explaining why malignant cells are more sensitive to heat when delivered by minimally invasive procedures for ablation of localized prostate cancer.

Cellular effect of high doses of silica-coated quantum dot profiled with high throughput gene expression analysis and high content cellomics measurements

Quantum dots (Qdots) are now used extensively for labeling in biomedical research, and this use is predicted to grow because of their many advantages over alternative labeling methods. Uncoated Qdots made of core/shell CdSe/ZnS are toxic to cells because of the release of Cd2+ ions into the cellular environment. This problem has been partially overcome by coating Qdots with polymers, poly(ethylene glycol) (PEG), or other inert molecules. The most promising coating to date, for reducing toxicity, appears to be PEG. When PEG-coated silanized Qdots (PEG-silane-Qdots) are used to treat cells, toxicity is not observed, even at dosages above 10-20 nM, a concentration inducing death when cells are treated with polymer or mercaptoacid coated Qdots. Because of the importance of Qdots in current and future biomedical and clinical applications, we believe it is essential to more completely understand and verify this negative global response from cells treated with PEG-silane-Qdots. Consequently, we examined the molecular and cellular response of cells treated with two different dosages of PEG-silane-Qdots. Human fibroblasts were exposed to 8 and 80 nM of these Qdots, and both phenotypic as well as whole genome expression measurements were made. PEG-silane-Qdots did not induce any statistically significant cell cycle changes and minimal apoptosis/necrosis in lung fibroblasts (IMR-90) as measured by high content image analysis, regardless of the treatment dosage. A slight increase in apoptosis/necrosis was observed in treated human skin fibroblasts (HSF-42) at both the low and the high dosages. We performed genome-wide expression array analysis of HSF-42 exposed to doses 8 and 80 nM to link the global cell response to a molecular and genetic phenotype. We used a gene array containing approximately 22,000 total probe sets, containing 18,400 probe sets from known genes. Only approximately 50 genes (approximately 0.2% of all the genes tested) exhibited a statistically significant change in expression level of greater than 2-fold. Genes activated in treated cells included those involved in carbohydrate binding, intracellular vesicle formation, and cellular response to stress. Conversely, PEG-silane-Qdots induce a down-regulation of genes involved in controlling the M-phase progression of mitosis, spindle formation, and cytokinesis. Promoter analysis of these results reveals that expression changes may be attributed to the down-regulation of FOXM and BHLB2 transcription factors. Remarkably, PEG-silane-Qdots, unlike carbon nanotubes, do not activate genes indicative of a strong immune and inflammatory response or heavy-metal-related toxicity. The experimental evidence shows that CdSe/ZnS Qdots, if appropriately protected, induce negligible toxicity to the model cell system studied here, even when exposed to high dosages. This study indicates that PEG-coated silanized Qdots pose minimal impact to cells and are a very promising alternative to uncoated Qdots.

Induction of clusterin/apoJ expression by histone deacetylase inhibitors in neural cells

The regulation of clusterin expression is poorly characterized although some regulatory elements have been identified, such as CpG-rich methylation domain. Environmental stress, aging, diet and diseases regulate DNA methylation and protein acetylation status but interestingly, the same insults increase clusterin expression in vivo. Our purpose was to elucidate whether histone deacetylase inhibitors, such as TSA, SAHA and M344, as well as an inhibitor of DNA methylation, 5'-aza-2'-deoxycytidine, could regulate the expression of clusterin in cultured neural cells. We observed that histone deacetylase inhibitors induced the expression of clusterin mRNA and protein in all neural cells studied. The induction of clusterin mRNA was blocked by actinomycin D which indicates that TSA regulates clusterin expression at the transcriptional level. An inhibitor of DNA methylation, 5'-aza-2'-deoxycytidine, itself did not affect the expression of clusterin mRNA but strongly potentiated the TSA-induced expression of clusterin. Proteasomal stress (MG-132 and PI-1 treatments) and apoptotic stress (okadaic acid treatment) did not affect clusterin expression which indicates that the induction of clusterin expression requires more specific inducers than cellular stress in general. Furthermore, LPS did not affect clusterin expression in N9 microglia although activated NF-kappaB signaling and IL-6 expression. CAPE and helenalin, inhibitors of NF-kappaB signalling, did not affect the clusterin mRNA expression either in non-treated or in TSA-treated N9 microglia. These observations suggest that clusterin induction is NF-kappaB-independent and unrelated to the inflammatory response in N9 microglia.

Bcl-2 but not clusterin/apolipoprotein J protected human diploid fibroblasts and immortalized keratinocytes from ceramide-induced apoptosis: role of p53 in the ceramide response

The role of clusterin/apolipoprotein J (Clu/ApoJ) and Bcl-2 on C(2)-ceramide-induced apoptosis of embryonic human diploid fibroblasts, MRC-5 and immortalized adult skin keratinocytes, HaCaT was investigated. C(2)-ceramide-induced apoptosis of HaCaT in a time- and dose-dependent manner, while in MRC-5 only at higher concentrations. There was a dose-dependent accumulation of Clu/ApoJ and downregulation of Bcl-2 which correlated with C(2)-ceramide-induced apoptosis of MRC-5. While overexpression of Bcl-2 suppressed C(2)-ceramide-mediated apoptosis in both cell types, Clu/ApoJ failed to do so, accessed by morphological changes, DNA fragmentation and PARP cleavage. There was no change in the expression of endogenous p53 or p21(Waf1/Cip1) upon C(2)-ceramide treatment of MRC-5. However, mutant p53(143ala) increased the sensitivity of MRC-5 to C(2)-ceramide-induced apoptosis by markedly downregulating Bcl-2, pointing to a role for p53. These results suggested that whereas downregulation of Bcl-2 may be a crucial factor involved in C(2)-ceramide-induced apoptosis, accumulation of Clu/ApoJ may be a signal of stress response. Moreover, the ceramide-activated apoptotic pathway may be regulated by p53.

Identification of differentially expressed proteins in senescent human embryonic fibroblasts

Normal human fibroblasts undergo a limited number of divisions in culture, a process known as replicative senescence (RS). Although several senescence-specific genes have been identified, analysis at the level of protein expression can provide additional insights into the mechanisms that regulate RS. We have performed a proteomic comparison between young and replicative senescent human embryonic WI-38 fibroblasts and we have identified 13 proteins, which are differentially expressed in senescent cells. Some of the identified proteins are components of the cellular cytoskeleton, while others are implicated in key cellular functions including metabolism and energy production, Ca(2+) signalling, nucleo-cytoplasmic trafficking and telomerase activity regulation. In summary, our analysis contributes to the list of senescence-associated proteins by identifying new biomarkers and provides novel information on functional protein networks that are perturbed during replicative senescence of human fibroblast cultures.

Comparative studies on cellular gene regulation by HIV-1 based vectors: implications for quality control of vector production

Among the recent gene therapy protocols, vectors that can stably express transgenes, for example, HIV-1-based vectors, are particularly desirable. There have been no direct reports on insertional mutagenesis by lentiviral vectors; however, the severe pathogenic nature of their parental virus (HIV-1) is still a major safety concern surrounding these vectors and prevents the progress with their clinical application. We reason that by investigating the host response we shall be able to assess the safety and potential effects of the vectors on targeted cells and understand the interaction between vectors and the host. For this, two major sets of experiments were conducted. Initially, we used cDNA microarray methodology to examine cellular gene profile in human primary umbilical cord endothelial cells (HUVECs) after HIV-1-based VSV-G/GFP vector transduction and observed a modest effect of HIV-1-based vectors on HUVECs. The represented functional categories include transcription and translation factors, tumour antigens, complement factors and signal transduction factors. Some of the differentially expressed genes, for example, Clusterin, CD151, Ku antigen and eIF4gamma, could have oncogenic potential. In the second approach, we systematically compared five different viral vectors, that is, HIV-1-based VSV-G/Empty, VSV-G/GFP, VSV-G/puro, Amph/GFP and MLV-based Amph/Laz, for the effects of individual viral components on cellular gene regulation. Our comparative results demonstrated a regulatory function of Gag/Pol proteins on cellular gene expression. The significance of our findings in relation to the safety of HIV-1 vectors and the importance of quality control of vector production will be presented and discussed.

Delayed Activation of Insulin-like Growth Factor-1 Receptor/Src/MAPK/Egr-1 Signaling Regulates Clusterin Expression, a Pro-survival Factor

Secretory clusterin protein (sCLU) is a general genotoxic stress-induced, pro-survival gene product implicated in aging, obesity, heart disease, and cancer. However, the regulatory signal transduction processes that control sCLU expression remain undefined. Here, we report that induction of sCLU is delayed, peaking 72 h after low doses of ionizing radiation, and is dependent on the up-regulation of insulin-like growth factor-1 as well as phosphorylation-dependent activation of its receptor (IGF-1 and IGF-1R, respectively). Activated IGF-1R then stimulates the downstream Src-Mek-Erk signal transduction cascade to ultimately transactivate the early growth response-1 (Egr-1) transcription factor, required for sCLU expression. Thus, ionizing radiation exposure causes stress-induced activation of IGF-1R-Src-Mek-Erk-Egr-1 signaling that regulates the sCLU pro-survival cascade pathway, important for radiation resistance in cancer therapy.

DNA microarray allows molecular profiling of rheumatoid arthritis and identification of pathophysiological targets

This study was undertaken to evaluate the possibility to obtain a molecular signature of rheumatoid arthritis (RA) comparatively osteoarthritis (OA), and to lay the bases to develop new diagnostic tools and identify new targets. Microarray technology was used for such an analysis. The gene expression profiles of synovial tissues from patients with confirmed RA, and patients with OA were established and compared. A set of 63 genes was selected, based, more specifically, on their overexpression or underexpression in RA samples compared to OA. Results for six of these genes have been verified by quantitative PCR using both samples identical to those used in the microarray experiments and entirely separate samples. Expression profile of the 48 known genes allowed the correct classification of additional RA and OA patients. Furthermore, the distinct expression of three of the selected genes was also studied by quantitative RT-PCR in cultured synovial cells. Detailed analysis of the expression profile of the selected genes provided evidence for dysregulated biological pathways, pointed out to chromosomal location and revealed novel genes potentially involved in RA. It is proposed that such an approach allows valuable diagnosis/prognostics tools in RA to be established and potential targets for combating the disease to be identified.

Repeated exposure of human skin fibroblasts to UVB at subcytotoxic level triggers premature senescence through the TGF-β1 signaling pathway

Premature senescence of human diploid fibroblasts (HDFs) can be induced by exposures to a variety of oxidative stress and DNA damaging agents. In this study we developed a robust model of UVB-induced premature senescence of skin HDFs. After a series of 10 subcytotoxic (non-proapoptotic) exposures to UVB at 250 mJ/cm2, the so-called biomarkers of senescence were markedly expressed: growth arrest, senescence-associated β-galactosidase activity, senescence-associated gene overexpression, deletion in mitochondrial DNA. A set of 44 stress- and senescence-associated genes were found to be differentially expressed in this model, among which clusterin/apolipoprotein J (apo J) and transforming growth factor-β1 (TGF-β1). Transfection of apo J cDNA provided protection against premature senescence-inducing doses of UVB and other stressful agents. Neutralizing antibodies against TGF-β1 or its receptor II (TβRII) sharply attenuated the senescence-associated features, suggesting a role for TGF-β1 in UVB-induced premature senescence. Both the latent and active forms of TGF-β1 were increased with time after the last UVB stress. Proteasome inhibition was ruled out as a potential mechanism of UVB-induced stress-induced premature senescence (SIPS). This model represents an alternative in vitro model in photoaging research for screening potential anti-photoaging compounds.

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.

Clusterin overexpression in both malignant and nonmalignant prostate epithelial cells induces cell cycle arrest and apoptosis

Expression of the castration-induced clusterin protein is incompatible with the survival of human prostate cancer cells in tissues and in cell culture. To investigate the fate of human prostate epithelial cells, when engineered to maintain expression of clusterin protein, we have used an IRES-hyg vector and hygromycin selection. PC-3 prostate tumour cells were substantially more sensitive to clusterin expression than nonmalignant PNT1a cells, showing multiple phenotypic changes including cell cycle arrest and increased apoptosis. The results strengthen the hypothesis that clusterin expression is proapoptotic. Expression of exogenous clusterin in both cell types resulted in its relocation from the cytoplasm and a nuclear accumulation of the protein, as was also seen in the same cells when apoptosis was induced by etoposide treatment. To survive clusterin expression, the PC-3 tumour cells developed apoptosis-inhibitory properties. This could have significance for the resistance of prostate cancers to chemo/radiotherapy, where clusterin overexpression is observed.

Cloning and characterization of cellular senescence-associated genes in human fibroblasts by suppression subtractive hybridization

Cellular senescence marks the end of the proliferative life span of normal cells in tissue culture and occurs after cells have undergone a certain number of population doublings (PDLs). It is accompanied by alterations in the pattern of gene expression. A specific human embryonic lung diploid fibroblast cell line, 2BS, has been studied as a model of senescence in our laboratory. Here, we report a set of cellular senescence-associated genes identified from suppression subtractive cDNA libraries from senescent and young 2BS cells. They include three novel genes and six previously identified genes of unknown function. The genes whose functions are known belong to various functional pathways that have been reported to change with the onset of senescence. These include three pre-mRNA splicing factors with reduced expression in senescent cells, indicating that the regulation of mRNA splicing is altered during cell senescence. In addition, the expression of the gene TOM1 (target of Myb 1), which has not previously been associated with cellular senescence, is shown to increase in senescent cells, and we demonstrate that the expression of antisense TOM1 gene in 2BS cells can delay the progress of senescence.

Ectopic expression of clusterin/apolipoprotein J or Bcl-2 decreases the sensitivity of HaCaT cells to toxic effects of ropivacaine

Local anesthetics inhibit cell proliferation and induce apoptosis in various cell types. Ropivacaine, a unique, novel tertiary amine-type anesthetic, was shown to inhibit the proliferation of several cell types including keratinocytes. We found that Ropivacaine could inhibit the proliferation and induce apoptosis in an immortalized human keratinocyte line, HaCaT, in a dose- and time-dependent manner and with the deprivation of serum. The dose-dependent induction of apoptosis by ropivacaine was demonstrated by DNA fragmentation analysis and the proteolytic cleavage of a caspase-3 substrate-poly (ADP-ribose) polymerase (PARP). In addition, ropivacaine downregulated the expression of clusterin/ apoliporotein J, a protein with anti-apoptotic properties, in a dose-dependent manner, which well correlated with the induction of apoptosis of HaCaT cells. To investigate the role of clusterin/apoliporotein J in ropivacaine-induced apoptosis, HaCaT cells overexpressing clusterin/apoliporotein J were generated and compared to cells expressing the well established anti-apoptotic Bcl-2 protein. Ectopic overexpression of the secreted form of clusterin/apoliporotein J or Bcl-2 decreased the sensitivity of HaCaT cells to toxic effects of ropivacaine as demonstrated by DNA fragmentation, the proteolytic cleavage of PARP and by a reduction in procaspase-3 expression. Furthermore, the downregulation of endogenous clusterin/apolipoprotein J levels by ropivacaine suggested that this might be one mechanism by which ropivacaine induced cell death in HaCaT cells. In conclusion, the ability of ropivacaine to induce antiproliferative responses and to suppress the expression of the anti-apoptotic protein clusterin/apolipoprotein J, combined with previously reported anti-inflammatory activity and analgesic property of the drug, suggests that ropivacaine may have potential utility in the local treatment of tumors.

Aging theories of primary osteoarthritis: from epidemiology to molecular biology

Osteoarthritis is the most common disabling condition of humans in the western world. It has been known for a very long time that aging is the most prominent risk factor for the initiation and progression of the disease, but the explanations for this phenomenon have changed over time. The most longstanding theory is that osteoarthritis develops because of continuous mechanical wear and tear. However, osteoarthritis can also be the result of time/age-related modifications to cartilage matrix components. One of the simplest biological explanations for the initiation and progression of osteoarthritic cartilage degeneration is a mere loss of viable cells, due to apoptosis or other mechanisms. Overall, the most likely scenario is that the cells and the matrix of articular cartilage get older over time, and eventually the tissue enters a senescence-like state that makes it more prone to enter the osteoarthritic degeneration pathway. Thus, patients with osteoarthritis might progress more quickly to the senescence phenotype compared to others. Moreover, stressful conditions associated with the osteoarthritic disease process might further promote chondrocyte senescence. Primary osteoarthritis in this model would be a "premature" degeneration of the joint due to a premature chondrocyte senescence. By analogy to neurodegenerative disorders, one could refer to osteoarthritis as the "M. Alzheimer" of articular cartilage. One of the most important implications of this hypothesis is that it points to issues of cellular degeneration as the basis for understanding the initiation and progression of osteoarthritis. Equally important, it emphasizes that whatever treatment we envisage for osteoarthritis, we must take into account that we are dealing with aged/(pre)senescent cells that no longer have the ability of their juvenile counterparts to counteract the many mechanical, inflammatory, and/or other assaults to the tissue.

Functional analysis of clusterin/apolipoprotein J in cellular death induced by severe genotoxic stress

Clusterin/apolipoprotein J (CLU) is a secreted heterodimeric glycoprotein that is reportedly upregulated during tumorigenesis, as well as during cell injury or death. Despite extensive efforts, CLU function during cellular death remains largely elusive. We are using as a model system to study CLU function three human osteosarcoma (OS) cell lines, namely, Sa OS, KH OS, and U-2 OS cells, induced to die after exposure to severe genotoxic stress mediated by the chemotherapeutic drug doxorubicin (DXR). We initially applied small interfering RNA (siRNA)-mediated specific knockdown of the CLU protein in OS cells. In all three cell lines, CLU knockdown resulted in increased sensitization to DXR-induced apoptosis. Supportively, moderate levels of forced transgene-mediated CLU stable overexpression in KH OS cells could rescue them from DXR-mediated apoptosis. In contrast, stable overexpression of high CLU levels in Sa OS and U-2 OS cells augmented apoptosis induced by cell exposure to severe DXR-mediated genotoxic stress. In summary, our data provide evidence that, although CLU is essential for cellular homeostasis, it may become highly cytotoxic in certain cellular contexts when it accumulates in high amounts intracellularly either by direct synthesis or by uptake from the extracellular milieu.

Cell detachment and apoptosis induction of immortalized human prostate epithelial cells are associated with early accumulation of a 45 kDa nuclear isoform of clusterin

Clusterin, ubiquitously distributed in mammalians, was cloned and identified as the most potently induced gene during rat prostate involution following androgen deprivation. Also found to be involved in many other patho-physiological processes, its biological significance is still controversial, particularly with regard to apoptosis. We previously showed that transient over-expression of clusterin blocked cell cycle progression of simian-virus-40-immortalized human prostate epithelial cell lines PNT1A and PNT2. We show in the present study that the accumulation of an intracellular 45 kDa clusterin isoform was an early event closely associated with death of PNT1A cells caused by cell detachment followed by apoptosis induction (anoikis). Cell morphological changes, decreased proliferation rate and cell cycle arrest at G0/G1-S-phase checkpoint were all strictly associated with the production and early translocation to the nucleus of a 45 kDa clusterin isoform. Later, nuclear clusterin was found accumulated in detached cells and apoptotic bodies. These results suggest that a 45 kDa isoform of clusterin, when targeted to the nucleus, can decrease cell proliferation and promotes cell-detachment-induced apoptosis, suggesting a possible major role for clusterin as an anti-proliferative gene in human prostate epithelial cells.