Heat shock protein90 suppressing apoptosis by preventing the cleavage of Bid in NIH3T3 fibroblasts

OBJECTIVE:To investigate the underlying mechanism of HSP90 suppressing tumor necrosis factor α(TNFα) and cycloheximide(CHX)-induced apoptosis. METHODS:We used electroporation to establish stable HSP90 overexpression clones;using laser confocal microscopy and flowcytometry to observe apoptosis induced by TNF-α/CHX;using Western blotting and immunoprecipitation to show whether HSP90 binds directly with Bid(BH3 interacting death agonist) and monitor the changes of Bid and the function of HSP90’s inhibitor geldanamycin in this event. RESULTS:HSP90 suppressed TNFα/CHX-induced apoptosis in stable HSP90-overexpressing NIH3T3 cells; The mechanism by which HSP90 suppressed TNFα-induced apoptosis was that HSP90 prevented the cleavage of Bid through direct binding with Bid; disrupting the function of HSP90 by the addition of its specific inhibitor,geldanamycin,blocked HSP90’s protection of Bid cleavage. CONCLUSION:The abundant existence of HSP90, even in physiological conditions, plays an important role in preventing cell apoptosis and maintaining cellular homeostasis, not only by promoting protein folding, but also by preventing Bid cleavag and keeping proapoptotic factors in an inert state;one mechanism by which HSP90’s inhibitor acts as an anti-cancer drug could be to promote the release of Bid from the HSP90 complex,and this event promotes cancer cell apoptosis.