Hsp90 Inhibition Accelerates Cell Lysis

Abstract

The 90 kDa heat shock protein, Hsp90, is an abundant molecular chaperone participating in the cytoprotec- tion of eukaryotic cells. Here we analyzed the involve- ment of Hsp90 in the maintenance of cellular integrity using partial cell lysis as a measure. Inhibition of Hsp90 by geldanamycin, radicicol, cisplatin, and novobiocin induced a significant acceleration of detergent- and hy- potonic shock-induced cell lysis. The concentration and time dependence of cell lysis acceleration was in agree- ment with the Hsp90 inhibition characteristics of the N-terminal inhibitors, geldanamycin and radicicol. Glu- tathione and other reducing agents partially blocked geldanamycin-induced acceleration of cell lysis but were largely ineffective with other inhibitors. Indeed, geldanamycin treatment led to superoxide production and a change in membrane fluidity. When Hsp90 content was diminished using anti-Hsp90 hammerhead ri- bozymes, an accelerated cell lysis was also observed. Hsp90 inhibition-induced cell lysis was more pro- nounced in eukaryotic (yeast, mouse red blood, and hu- man T-lymphoma) cells than in bacteria. Our results indicate that besides the geldanamycin-induced super- oxide production, and a consequent increase in cell ly- sis, inhibition or lack of Hsp90 alone can also compro- mise cellular integrity. Moreover, cell lysis after hypoxia and complement attack was also enhanced by any type of Hsp90 inhibition used, which shows that the mainte- nance of cellular integrity by Hsp90 is important in physiologically relevant lytic conditions of tumor cells.