1191

CLU

APO-J|APOJ|CLI|KUB1|NA1/NA2|SGP-2|SGP2|SP-40|TRPM-2|TRPM2;clusterin;CLU;clusterin

aging-associated protein 4|apolipoprotein J|complement cytolysis inhibitor|complement lysis inhibitor|complement-associated protein SP-40,40|ku70-binding protein 1|sulfated glycoprotein 2|testosterone-repressed prostate message 2

8p21-p12

protein-coding

Count: 2; Pubmed_search,Generif

BACKGROUND: Clusterin expression in various types of human cancers may be higher or lower than in normal tissue, and clusterin may promote or inhibit apoptosis, cell motility, and inflammation. We investigated the role of clusterin in tumor development in mouse models of neuroblastoma. METHODS: We assessed expression of microRNAs in the miR-17-92 cluster by real-time reverse transcription-polymerase chain reaction in MYCN-transfected SH-SY5Y and SH-EP cells and inhibited expression by transfection with microRNA antisense oligonucleotides. Tumor development was studied in mice (n = 66) that were heterozygous or homozygous for the MYCN transgene and/or for the clusterin gene; these mice were from a cross between MYCN-transgenic mice, which develop neuroblastoma, and clusterin-knockout mice. Tumor growth and metastasis were studied in immunodeficient mice that were injected with human neuroblastoma cells that had enhanced (by clusterin transfection, four mice per group) or reduced (by clusterin short hairpin RNA [shRNA] transfection, eight mice per group) clusterin expression. All statistical tests were two-sided. RESULTS: Clusterin expression increased when expression of MYCN-induced miR-17-92 microRNA cluster in SH-SY5Y neuroblastoma cells was inhibited by transfection with antisense oligonucleotides compared with scrambled oligonucleotides. Statistically significantly more neuroblastoma-bearing MYCN-transgenic mice were found in groups with zero or one clusterin allele than in those with two clusterin alleles (eg, 12 tumor-bearing mice in the zero-allele group vs three in the two-allele group, n = 22 mice per group; relative risk for neuroblastoma development = 4.85, 95% confidence interval [CI] = 1.69 to 14.00; P = .005). Five weeks after injection, fewer clusterin-overexpressing LA-N-5 human neuroblastoma cells than control cells were found in mouse liver or bone marrow, but statistically significantly more clusterin shRNA-transfected HTLA230 cells (3.27%, with decreased clusterin expression) than control-transfected cells (1.53%) were found in the bone marrow (difference = 1.74%, 95% CI = 0.24% to 3.24%, P = .026). CONCLUSIONS: We report, to our knowledge, the first genetic evidence that clusterin is a tumor and metastasis suppressor gene.

The biological functions of clusterin (CLU, also known as ApoJ, SGP2, TRPM-2, CLI) have been puzzling the researchers since its first discovery in the early 80's. We know that CLU is a single 9-exons gene expressing three protein forms with different sub-cellular localisations and diverse biological functions. Despite the many reports from many research teams on CLU action and its relation to tumourigenesis, contradictions in the data and alternative hypothesis still exist. Understanding the role of CLU in tumourigenesis is complicated not only by the existence of different protein forms but also by the changes of tumours over time and the selection pressures imposed by treatments such as hormone ablation or chemotherapy. This review focuses on recent discoveries concerning the role of CLU in prostate and breast cancer onset and progression. Although CLU acts primarily as a tumour suppressor in the early stages of carcinogenesis, consistent with its role in the involution of the prostate following castration, late stage cancer may overexpress CLU following chemotherapeutic drugs or hormonal ablation therapy. High expression of secreted or cytoplasmic CLU may represent a pro-survival stimulus because it confers increased resistance to killing by anti-cancer drugs or enhances tumour cell survival in specific niches.

The Clusterin (CLU) gene produces different forms of protein products, which vary in their biological properties and distribution within the cell. Both the extra- and intracellular CLU forms regulate cell proliferation and apoptosis. Dis-regulation of CLU expression occurs in many cancer types, including prostate cancer. The role that CLU plays in tumorigenesis is still unclear. We found that CLU over-expression inhibited cell proliferation and induced apoptosis in prostate cancer cells. Here we show that depletion of CLU affects the growth of PC-3 prostate cancer cells. Following siRNA targeting all CLU mRNA variants, all protein products quickly disappeared, inducing cell cycle progression and higher expression of specific proliferation markers (i.e., H3 mRNA, PCNA, and cyclins A, B1, and D) as detected by RT-qPCR and Western blot. Quite surprisingly, we also found that the turnover of CLU protein is very rapid and tightly regulated by ubiquitin-proteasome mediated degradation. Inhibition of protein synthesis by cycloheximide showed that CLU half-life is less than 2 h. CLU protein products were found poly-ubiquitinated by co-immuniprecipitation. Proteasome inhibition by MG132 caused stabilization and accumulation of all CLU protein products, including the nuclear form of CLU (nCLU), and committing cells to caspase-dependent death. In conclusion, proteasome inhibition may induce prostate cancer cell death through accumulation of nCLU, a potential tumor suppressor factor.