Clusterin Has Chaperone-like Activity Similar to That of Small Heat Shock Proteins

Humphreys, David T.; Carver, John A.; Easterbrook‐Smith, Simon B.; Wilson, Mark R.

doi:10.1074/jbc.274.11.6875

Cited by 409 publications

(406 citation statements)

References 42 publications

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“…Clusterin was not found in hydrophilic extractions. It has been known that heterodimeric sCLU possesses binding activity to hydrophobic domains of various proteins [11]. Our results demonstrated the presence of clusterin in normal spermatozoa, within the membrane structures.…”

Section: Discussionsupporting

confidence: 66%

Presence, localization, and origin of clusterin in normal human spermatozoa

Han

Wang

Cheng

et al. 2012

J Assist Reprod Genet

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Purpose Clusterin in mammalian semen is a secretory form of clusterin (sCLU) with the heterodimeric structure. It is secreted by the epididymis and seminal vesicle. It is generally agreed that clusterin mainly exists on the surface of abnormal spermatozoa and is implicated in decreased sperm motility, sperm aggregation and infertility. However, few studies observe clusterin in normal spermatozoa, which is presumed to be a novel form. Up to now, the systematical information about the presence, localization, origin and function of clusterin in normal human spermatozoa has yet not been established. The aim of our current study is to systematically research clusterin in normal human spermatozoa.Methods We detected the presence of clusterin via western blot, explored the localization of clusterin using immunofluorescence, and investigated the origin and distribution of clusterin in human testis by western blot and immunohistochemistry. Results We found native clusterin in the inner plasma membrane of normal human spermatozoa. It was derived from the testis and showed similar molecular weight and heterodimeric structure compared with sCLU in semen and on the surface of abnormal spermatozoa. Conclusion Clusterin in normal spermatozoa should be self-synthesized during the later stage of spermatogenesis. The different localization and origin suggested that the clusterin observed by us may be a novel form compared with conventional sCLU on the surface of abnormal spermatozoa.

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Section: Discussionsupporting

confidence: 66%

Presence, localization, and origin of clusterin in normal human spermatozoa

Han

Wang

Cheng

et al. 2012

J Assist Reprod Genet

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“…4 The gene codes for an initial precursor peptide glycosylated and cleaved into two a and b chains of 40 kDa each, held together by a unique five disulfide bond motif in the extracellular mature form. 1 This secreted form of CLU has been suggested to act as a molecular chaperone following stress-induced injury, 5 clearing extracellular debris. 6 However, it has been reported the existence of an inactive, cytoplasmic form of CLU produced by alternative splicing that is converted by ionizing irradiation to a truncated mature nuclear isoform, 7 which binds the Ku70/Ku80 complex in cell-free systems 8 inhibiting cell growth and survival 7 probably by a caspase-3-independent mechanism.…”

mentioning

confidence: 99%

Ca2+ depletion induces nuclear clusterin, a novel effector of apoptosis in immortalized human prostate cells

et al. 2004

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Clusterin (CLU) is a secreted heterodimeric glycoprotein thatcan be produced almost ubiquitously in mammalians tissues.1Its gene expression is subjected to complex regulation and canchange enormously according to different stimuli.2 Cloned andidentified as the most potently induced gene in the regressingrat ventral prostate following androgen-ablation,3 CLU wasalmost simultaneously characterized and isolated by differentresearch groups working in widely divergent areas.2 CLU iscoded by a single copy gene, located on chromosome 8.4 Thegene codes for an initial precursor peptide glycosylated andcleaved into two a and b chains of 40 kDa each, held togetherby a unique five disulfide bond motif in the extracellular matureform.1 This secreted form of CLU has been suggested to act asa molecular chaperone following stress-induced injury,5clearing extracellular debris.6 However, it has been reportedthe existence of an inactive, cytoplasmic form of CLUproduced by alternative splicing that is converted by ionizingirradiation to a truncated mature nuclear isoform,7 which bindsthe Ku70/Ku80 complex in cell-free systems8 inhibiting cellgrowth and survival7 probably by a caspase-3-independentmechanism.9 Other alternative CLU isoforms, produced eitherby exon skipping10 or by post-translational modificationsactivated by apoptosis,11,12 were recently described. Thesedifferent isoforms of CLU have been suggested to beantiapoptotic6,13 or proapoptotic.7,10,12,14–16These controversial reports on the role of CLU might berelated to specific proteomic profiles that are produced bydifferent apoptotic stimuli (i.e. the general protein pattern ofCLU and the relative ratio between different CLU isoforms).This might explain why CLU has been involved in a plethora ofpathophysiological processes, including cell–cell and cell–matrix adhesion, cell differentiation, transformation, aging17,18and cancer,19 but its biological role still remains to be clearlyestablished. Reports suggesting that CLU may be a potentialtumor suppressor gene include the finding that CLU suppressesNF-kB activity and the metastatic phenotype ofneuroblastoma cells.20 We have previously reported that CLUoverexpression inhibits cell cycle progression of simian virus40(SV40)-immortalized human prostate PNT2 and PNT1Aepithelial cells.21To further assess the role of CLU in apoptotic processes wehave studied its expression pattern during the regulation ofcalcium homeostasis. Ca2þ is an important regulator ofapoptosis and cell survival.22,23,24 Both pathological increaseof Ca2þ concentration in the cytosol compartment byinophores25 and depletion of intracellular Ca2þ stores maytrigger apoptosis by disrupting intracellular architecture andallowing effectors to gain access to their substrates.24,26,27Activation of apoptotic endonucleases28 eliciting DNA cleavageand chromatin condensation has beenwell documented.29,30,31A tight buffering of intracellular Ca2þ is required for normalgrowth. In fact, apoptosis can be induced by Ca2þ mobilizationfrom intracellular pools,23,24,27 chelati...

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“…It was characterized as a potent small heat shock protein-like chaperone that inhibits stress-induced amorphous protein aggregation and the fibrillar aggregation of many amyloidogenic proteins and peptides. CLU forms highmolecular-weight 'solubilized' complexes with heat-or reduction-stressed proteins, inhibiting their precipitation [62]. CLU can stabilize stressed proteins but, like small heat shock proteins, cannot catalyze protein refolding.…”

Section: Chaperone Activity and Proteinase Inhibitionmentioning

confidence: 99%

Clusterin in the eye: An old dog with new tricks at the ocular surface

Fini

Bauskar

Jeong

et al. 2016

Experimental Eye Research

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, M. R. (2016). Clusterin in the eye: an old dog with new tricks at the ocular surface. Experimental Eye Research, Clusterin in the eye: an old dog with new tricks at the ocular surface AbstractThe multifunctional protein clusterin (CLU) was first described in 1983 as a secreted glycoprotein present in ram rete testis fluid that enhanced aggregation ('clustering') of a variety of cells in vitro. It was also independently discovered in a number of other systems. By the early 1990s, CLU was known under many names and its expression had been demonstrated throughout the body, including in the eye. Its homeostatic activities in proteostasis, cytoprotection, and anti-inflammation have been well documented, however its roles in health and disease are still not well understood. CLU is prominent at fluid-tissue interfaces, and in 1996 it was demonstrated to be the most highly expressed transcript in the human cornea, the protein product being localized to the apical layers of the mucosal epithelia of the cornea and conjunctiva. CLU protein is also present in human tears. Using a preclinical mouse model for desiccating stress that mimics human dry eye disease, the authors recently demonstrated that CLU prevents and ameliorates ocular surface barrier disruption by a remarkable sealing mechanism dependent on attainment of a critical all-or-none concentration in the tears. When the CLU level drops below the critical all-or-none threshold, the barrier becomes vulnerable to desiccating stress. CLU binds selectively to the ocular surface subjected to desiccating stress in vivo, and in vitro to LGALS3 (galectin-3), a key barrier component. Positioned in this way, CLU not only physically seals the ocular surface barrier, but it also protects the barrier cells and prevents further damage to barrier structure. CLU depletion from the ocular surface epithelia is seen in a variety of inflammatory conditions in humans and mice that lead to squamous metaplasia and a keratinized epithelium. This suggests that CLU might have a specific role in maintaining mucosal epithelial differentiation, an idea that can now be tested using the mouse model for desiccating stress. Most excitingly, the new findings suggest that CLU could serve as a novel biotherapeutic for dry eye disease. Competing Interests: US patent 9,241,974 B2 entitled "Clusterin pharmaceuticals and treatment methods using the same" (inventors: MEF and SJ), assigned to the University of Southern California, is connected with this work. MEF holds a management position with Proteris Biotech, Inc., Pasadena, CA, which is developing Protearin for dry eye based on clusterin. MRW declares that he has no competing interests. Page 3 of 65 AbstractThe multifunctional protein clusterin (CLU) was first described in 1983 as a secreted glycoprotein present in ram rete testis fluid that enhanced aggregation ('clustering') of a variety of cells in vitro. It was also independently discovered in a number of other systems. By the early 1990s, CLU was known under many names and its expression had bee...

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Clusterin Has Chaperone-like Activity Similar to That of Small Heat Shock Proteins

Cited by 409 publications

References 42 publications

Presence, localization, and origin of clusterin in normal human spermatozoa

Presence, localization, and origin of clusterin in normal human spermatozoa

Ca2+ depletion induces nuclear clusterin, a novel effector of apoptosis in immortalized human prostate cells

Clusterin in the eye: An old dog with new tricks at the ocular surface

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