APAF1 and gastrointestinal stromal tumor: Bortezomib can bind to Cbl, an E3 ubiquitin-protein ligase, destabilizing the c-KIT-Hsp90Β-Apaf-1 complex and releasing Apaf-1; then KIT was unleashed from the complex, and be internalized and degraded in the cytoplasm of GIST cells.