Hsp90 inhibition induces destabilization of actin cytoskeleton in tumor cells: functional significance of Hsp90 interaction with F–actin

ObjectiveTo examine the role of heat shock protein 90 (Hsp 90) in the maintenance of actin cytoskeleton in human neuroblastoma tumor cells.MethodsCo-precipitation experiments were performed to examine Hsp 90 interaction with actin. Hsp 90 and actin interactions were evaluated by protein refolding and acto-myosin motility assays. 17-(Allylamino)-17-demethoxygeldanamycin (17AAG) induced actin-cytoskeleton re-organization was examined by laser scanning confocal microcopy.ResultsIt was shown that inhibition of Hsp 90 by 17AAG accelerates detergent induced cell lysis of neuroblastoma tumor cells through destabilization of actin cytoskeleton. The in vitro co-precipitation experiments showed that functional but not mutant Hsp 90 binds with F-actin. Among biochemical modifications, phopshorylation and oligomerization enhanced Hsp 90 binding with F-actin. F-actin binding to Hsp 90 interfered with Hsp 90 chaperone activity in protein refolding assays, and Hsp 90 binding to F-actin interfered with actin motility on myosin coated flow cell. In the combination treatment, 17AAG irreversibly augmented the effect of cytochalasin D, an inhibitor of actin polymerization.ConclusionsIt can be concluded that Hsp 90 binds to F-actin in tumor cells and maintains the cellular integrity. The results display a novel element of Hsp 90 inhibition in destabilizing the actin cytoskeleton of tumor cells, therefore suggest that 17AAG combination with cytoskeletal disruptor may be effective in combating cancer.