DISRUPTION OF THE RAF-1-HSP90 MOLECULAR-COMPLEX RESULTS IN DESTABILIZATION OF RAF-1 AND LOSS OF RAF-1-RAS ASSOCIATION

Cytosolic Raf-1 exists in a high molecular weight complex with the heat shock protein Hsp90, the purpose of which is unknown. The benzoquinone ansamycin, geld-anamycin, specifically binds to Hsp90 and disrupts certain multimolecular complexes containing this protein, Using this drug, we are able to demonstrate rapid dissociation of both Raf-1-Hsp90 and Raf-1-Ras multimolecular complexes, concomitant with a markedly decreased half-life of the Raf-1 protein. Continued disruption of the Raf-1-Hsp90 complex results in apparent loss of Raf-1 protein from the cell, although Raf-1 synthesis is actually increased. Prevention of Raf-1-Hsp90 complex formation interferes with trafficking of newly synthesized Raf-1 from cytosol to plasma membrane. These data indicate that association with Hsp90 is essential for both Raf-1 protein stability and its proper localization in the cell.