Hsp90 inhibitors induce the unfolded protein response in bovine and mice lung cells.

The unfolded protein response element protects against endoplasmic reticulum stress and delivers protection towards potentially harmful challenges. The components of this multi-branch molecular machinery, namely the protein kinase RNA-like ER kinase, the activating transcription factor 6, and the inositol-requiring enzyme-1α; expand the endoplasmic reticulum capacity to support cellular function under stress conditions. In the present study, we employed bovine pulmonary aortic endothelial cells and mice to investigate the possibility that the Hsp90 inhibitors Tanespimycin (17-AAG) and Luminespib (AUY-922) exert the capacity to trigger the unfolded protein response. The induction of the unfolded protein response regulators immunoglobulin heavy-chain-binding protein, endoplasmic reticulum oxidoreductin-1alpha; and protein disulfide isomerase was also examined. It appears that both inhibitors capacitate the induction of the unfolded protein response element in vitro, since lung cells exposed to 1, 2 and 10 μM of 17-AAG or AUY-922 for 4, 6, 8, 16 and 48 h demonstrated increased levels of those proteins. Similar events occurred in the lungs of mice treated with AUY-922. Thus, our study demonstrates that Hsp90 inhibition triggers the activities of the unfolded protein response, and suggests that this molecular machinery contributes in the protective action of Hsp90 inhibitors in the lung microvasculature.