title: Clusterin is a short half-life, poly-ubiquitinated protein, which controls the fate of prostate cancer cells.
abstract: 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.
authors.affiliation: Dipartimento di Medicina Sperimentale, Sezione di Biochimica, Biochimica Clinica e Biochimica dell'Esercizio Fisico, Parma, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Rizzi
authors.forename: Alessandro Emanuele
authors.initials: AE
authors.lastname: Caccamo
authors.forename: Lucia
authors.initials: L
authors.lastname: Belloni
authors.forename: Saverio
authors.initials: S
authors.lastname: Bettuzzi
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002453:Cell Cycle / Q000502:physiology; D049109:Cell Proliferation; D051152:Clusterin / Q000235:genetics / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D020868:Gene Silencing; D006801:Humans; D007976:Leupeptins / Q000378:metabolism; D008297:Male; D025821:Polyubiquitin / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000503:physiopathology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D055550:Protein Stability; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051381:Rats; D014407:Tumor Cells, Cultured
chemical_list: D051152:Clusterin; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D025821:Polyubiquitin; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde