INHIBITION OF HEAT-SHOCK PROTEIN HSP90-PP60(V-SRC) HETEROPROTEIN COMPLEX-FORMATION BY BENZOQUINONE ANSAMYCINS - ESSENTIAL ROLE FOR STRESS PROTEINS IN ONCOGENIC TRANSFORMATION

The molecular mechanisms by which oncogenic tyrosine kinases induce ce llular transformation are unclear. Herbimycin A, geldanamycin, and cer tain other benzoquinone ansamycins display an unusual capacity to reve rt tyrosine kinase-induced oncogenic transformation, As an approach to the study of v-src-mediated transformation, we examined ansamycin act ion in transformed cells and found that drug-induced reversion could b e achieved without direct inhibition of src phosphorylating activity. To identify mechanisms other than kinase inhibition for drug-mediated reversion, we prepared a solid phase-immobilized geldanamycin derivati ve and affinity precipitated the molecular targets with which the drug interacted. In a range of cell lines, immobilized geldanamycin bound elements of a major class of heat shock protein (HSP90) in a stable an d pharmacologically specific manner. Consistent with these binding dat a, we found that soluble geldanamycin and herbimycin A inhibited speci fically the formation of a previously described src-HSP90 heteroprotei n complex. A related benzoquinone ansamycin that failed to revert tran sformed cells did not inhibit the formation of this complex. These res ults demonstrate that HSP participation in multimolecular complex form ation is required for src-mediated transformation and can provide a ta rget for drug modulation.