RESUMO
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.
Assuntos
Apoptose/fisiologia , Adesão Celular/fisiologia , Células Epiteliais/química , Células Epiteliais/fisiologia , Glicoproteínas/metabolismo , Chaperonas Moleculares/metabolismo , Proteínas Nucleares/metabolismo , Próstata/citologia , Transporte Ativo do Núcleo Celular/fisiologia , Anoikis/fisiologia , Caspases/metabolismo , Ciclo Celular/fisiologia , Linhagem Celular Transformada , Clusterina , Meios de Cultura Livres de Soro/metabolismo , Regulação para Baixo/fisiologia , Indução Enzimática/fisiologia , Células Epiteliais/enzimologia , Quinase 1 de Adesão Focal , Proteína-Tirosina Quinases de Adesão Focal , Genes/fisiologia , Glicoproteínas/química , Glicoproteínas/genética , Humanos , Queratinócitos/metabolismo , Masculino , Chaperonas Moleculares/química , Chaperonas Moleculares/genética , Peso Molecular , Proteínas Nucleares/química , Fosforilação , Poli Adenosina Difosfato Ribose/metabolismo , Isoformas de Proteínas/química , Isoformas de Proteínas/metabolismo , Proteínas Tirosina Quinases/metabolismo , Proteínas/metabolismoRESUMO
Clusterin is a highly conserved, widely distributed glycoprotein whose biological significance is still debated. Involved in many biological processes and disease states, clusterin is induced by cell injury and tissue regression, but is repressed during cell proliferation. We have previously reported that clusterin mRNA induction is associated with epithelial cell atrophy in the rat prostate and both clusterin transcript and protein accumulated in quiescent normal human skin fibroblasts. Here we show that transient clusterin overexpression, in SV40-immortalized human prostate epithelial cells (PNT2), resulted in increased accumulation of cells in the G(0)/G(1) phases of the cell cycle, accompanied by slowdown of cell cycle progression and decrease of DNA synthesis. The activities of ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC), and the level of histone H3 mRNA (markers of cell proliferation) concomitantly decreased, while Gas1 mRNA (a marker of cell quiescence) accumulated. Thus it appears that clusterin, by opposing the effect of SV40 on the proliferation rate of PNT2 cells, acts as an anti-oncogene in the prostate, suggesting a role for this gene in controlling proliferation of normal and transformed prostate epithelial cells.
