Heat Shock Protein 70 (Hsp70) Suppresses RIP1-dependent Apoptotic and Necroptotic Cascades.

Hsp70 is a molecular chaperone that binds to "client" proteins and protects them from protein degradation. Hsp70 is essential for the survival of many cancer cells, but it is not yet clear which of its clients are involved. Using structurally distinct chemical inhibitors, we found that many of the well-known clients of the related chaperone, Hsp90, are not strikingly responsive to Hsp70 inhibition. Rather, Hsp70 appeared to be important for the stability of the RIP1 (RIPK1) regulators: cIAP1/2 (BIRC1 and BIRC3), XIAP, and cFLIPS/L (CFLAR). These results suggest that Hsp70 limits apoptosis and necroptosis pathways downstream of RIP1. Consistent with this model, MDA-MB-231 breast cancer cells treated with Hsp70 inhibitors underwent apoptosis, while cotreatment with zVAD. fmk switched the cell death pathway to necroptosis. In addition, cell death in response to Hsp70 inhibitors was strongly suppressed by RIP1 knockdown or inhibitors. Thus, these data indicate that Hsp70 plays a previously unrecognized and important role in suppressing RIP1 activity. 68. (C) 2017 AACR.