Clusterin is a chaperone protein that is synthesized in response to cellular stress. It often appears in cells undergoing apoptosis - both as part of developmental programmes such as tissue involution and in numerous pathological conditions - but has also been reported to confer resistance to apoptosis in some cases. Whether it is a pro-survival or a pro-death molecule is therefore unclear. Laure Debure and co-workers have examined the effects of clusterin expression in COS-7 cells (see ). They find that clusterin can accumulate in juxtanuclear aggregates that exhibit features characteristic of aggresomes (inclusion bodies thought to prevent misfolded proteins spreading throughout the cell). They have a vimentin cage, for example, and can be disrupted by treatment with the chaperone Hsp70 or microtubule-depolymerising drugs. The authors also observe, however, that clusterin expression disrupts mitochondria and induces apoptosis through the mitochondrial pathway - this can be prevented by expression of the pro-survival molecule Bcl-2 or inhibition of caspases. Debure and co-workers reconcile these seemingly conflicting effects on cell survival by suggesting that clusterin is an anti-apoptotic, aggresome-forming chaperone but can be cytotoxic if it accumulates.
