Moretti Roberta M, Montagnani Marelli Marina, Mai Stefania, Cariboni Anna, Scaltriti Maurizio, Bettuzzi Saverio, Limonta Patrizia
Institute of Endocrinology, University of Milan, Milan, Italy.
Cancer Res. 2007 Nov 1;67(21):10325-33. doi: 10.1158/0008-5472.CAN-07-0516.
Besides a fully processed, secreted form of clusterin (sCLU), an alternative proapoptotic form of the protein targeting the nucleus (nCLU) was recently described. The possible differential roles played by the two clusterin forms in growth and motility of nonmalignant and malignant prostate cells are investigated here. sCLU or nCLU was transiently transfected in both androgen-independent prostate cancer cells (PC3 and DU 145) and immortalized prostate epithelial cells (PNT1A, a nontumoral control). Then, cell growth, motility, and cytoskeleton organization were studied. We found that (a) in PNT1A cells, both sCLU and nCLU significantly decreased cell proliferation and motility; (b) in PC3 and DU 145 cancer cells, only nCLU inhibited cell growth and migration, with sCLU being ineffective; and (c) the antimotility effect of nCLU was accompanied by a dramatic dismantling of the actin cytoskeleton. Moreover, transfection with "full-length" CLU cDNA produced both sCLU and nCLU in nonmalignant PNT1A cells, whereas only sCLU was found in cancer cells. Thus, CLU gene expression might play a crucial role in prostate tumorigenesis by exerting differential biological effects on normal versus tumor cells through differential processing of CLU isoforms in the two cell systems. We also found that nCLU binds to alpha-actinin, a key protein for the regulation of actin cytoskeleton, and that nCLU and alpha-actinin colocalize in the cytoplasm. Thus, the antimotility activity of nCLU and its ability to cause dismantling of the actin cytoskeleton seem to be mediated by its binding to alpha-actinin.
除了一种经过完全加工、分泌形式的聚集素（sCLU）外，最近还发现了该蛋白的另一种靶向细胞核的促凋亡形式（nCLU）。本文研究了这两种聚集素形式在非恶性和恶性前列腺细胞生长及运动中可能发挥的不同作用。sCLU或nCLU分别瞬时转染雄激素非依赖性前列腺癌细胞（PC3和DU 145）以及永生化前列腺上皮细胞（PNT1A，一种非肿瘤对照细胞）。然后，对细胞生长、运动及细胞骨架组织进行了研究。我们发现：（a）在PNT1A细胞中，sCLU和nCLU均显著降低细胞增殖及运动能力；（b）在PC3和DU 145癌细胞中，只有nCLU抑制细胞生长和迁移，而sCLU无此作用；（c）nCLU的抗运动作用伴随着肌动蛋白细胞骨架的显著解体。此外，用“全长”CLU cDNA转染非恶性PNT1A细胞可同时产生sCLU和nCLU，而在癌细胞中仅发现sCLU。因此，通过在两种细胞系统中对CLU异构体进行不同加工，对正常细胞与肿瘤细胞发挥不同生物学效应，CLU基因表达可能在前列腺肿瘤发生中起关键作用。我们还发现nCLU与α-辅肌动蛋白结合，α-辅肌动蛋白是调节肌动蛋白细胞骨架的关键蛋白，且nCLU和α-辅肌动蛋白在细胞质中共定位。因此，nCLU的抗运动活性及其导致肌动蛋白细胞骨架解体的能力似乎是由其与α-辅肌动蛋白的结合介导的。
