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

Abstract

Normal human fibroblasts have a limited replicative potential in culture and eventually reach a state of irreversible growth arrest, termed senescence. In a previous study aiming to identify genes that are differentially regulated during cellular senescence we have cloned clusterin/apolipoprotein J (Apo J), a 80 kDa secreted glycoprotein. In the current report we pursue our studies and show that senescence of human diploid fibroblasts is accompanied by up-regulation of both Apo J mRNA and protein levels, but with no altered biogenesis, binding partner profile or intracellular distribution of the two Apo J forms detected. To analyze the causal relationship between senescence and Apo J protein accumulation, we stably overexpressed the Apo J gene in primary as well as in SV40 T antigenimmortalized human fibroblasts and we showed no alteration of the proliferative capacity of the transduced cells. Despite previous reports on tumor-derived cell lines, overexpression of Apo J in human fibroblasts did not provide protection against apoptosis or growth arrest induced by hydrogen peroxide. Overall, our results suggest that Apo J overexpression does not induce senescence but it is rather a secondary consequence of the senescence phenotype. To our knowledge this is the first report that provides a functional analysis of human Apo J during replicative senescence. ß

Apoptosis, necrosis and cellular senescence: chaperone occupancy as a potential switch

“…Apolipoprotein J (clusterin), an extracellular chaperone, has been described as a biomarker of senescence, and is implicated in the p revention/delay of apoptosis (Petropoulou et al ., 2001;Trougakos & Gonos, 2002). As another example, impaired Hsp90 function leads to the activation of HSF-1, restoration of the heat shock response and slower chronological aging of non-dividing Saccharomyces cerevisiae (Harris et al ., 2001).…”

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

“…By using the DMSO-polybrene method, HaCaT cells were transfected with pcDNA3.1B (Invitrogen, Life Technologies, USA), pcDNA3.1/hApoJ that carries the human clusterin/ApoJ cDNA and neo [28] or pcDNA3/hBcl-2 that carries human Bcl-2 cDNA and neo [29], respectively. After being selected in 500 µg/ml G418 for 3 weeks, several stably transfected HaCaTBcl-2 or HaCaTApoJ clones were picked out and subjected to immunoblotting for the expression of clusterin/ApoJ.…”

“…In agreement with previous studies on the various forms of ApoJ and their processing, a diffuse doublet of 36-40 kD band that corresponds to α-and β-chains of the secreted 75-80 kD clusterin/ApoJ was detected as the cleavage product at the Asp 227 -Ser 228 residues after the reduction of the protein (sClu). And a 60 kD band that corresponds to the cytoplasmic form of clusterin/Apo J (cClu) which is not reduced still retained inside the cells [18,28]. Similarly, human clusterin/ApoJ was also overexpressed in HaCaTApoJ clone 2.…”

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

“…the general protein pattern of CLU and the relative ratio between different CLU isoforms). This might explain why CLU has been involved in a plethora of pathophysiological processes, including cell-cell and cellmatrix adhesion, cell differentiation, transformation, aging 17,18 and cancer, 19 but its biological role still remains to be clearly established. Reports suggesting that CLU may be a potential tumor suppressor gene include the finding that CLU suppresses NF-kB activity and the metastatic phenotype of neuroblastoma cells.…”