Disruption of Hsp90 function results in degradation of the death domain kinase, receptor-interacting protein (RIP), and blockage of tumor necrosis factor-induced nuclear factor-κB activation

The death domain kinase, receptor interacting protein (RIP), is one of the major components of the tumor necrosis factor receptor 1 (TNFR1) complex and plays an essential role in tumor necrosis factor (TNF)-mediated nuclear factor kappa B (NF-kappa B) activation. The activation of NF-kappa B protects cells against TNF-induced apoptosis. Heat-shock proteins (Hsps) are chaperone molecules that confer protein stability and help to restore protein native folding following heat shock and other stresses. The most abundant Hsp, Hsp90, is also involved in regulating the stability and function of a number of cell-signaling molecules. Here we report that RTP is a novel Hsp90-associated kinase and that disruption of Hsp90 function by its specific inhibitor, geldanamycin (GA), selectively causes RIP degradation and the subsequent inhibition of TNF-mediated I kappa B kinase and NP-kappa B activation. MG-132, a specific proteasome inhibitor, abrogated GA-induced degradation of RIP but failed to restore the activation of I kappa B kinase by TNF, perhaps because, in the presence of GA and MG-132, RIP accumulated in a detergent-insoluble subcellular fraction. Most importantly, the degradation of RIP sensitizes cells to TNF-induced apoptosis. These data indicate that Hsp90 plays an important role in TNF-mediated NF-kappa B activation by modulating the stability and solubility of RIP. Thus, inhibition of NF-kappa B activation by GA may be a critical component of the anti-tumor activity of this drug.