LPS induces pp60c-src-mediated tyrosine phosphorylation of Hsp90 in lung vascular endothelial cells and mouse lung.

Heat shock protein 90 (Hsp90) inhibitors were initially developed as anticancer agents; however, it is becoming increasing clear that they also possess potent anti-inflammatory properties. Posttranslational modifications of Hsp90 have been reported in tumors and have been hypothesized to affect client protein-and inhibitor-binding activities. In the present study we investigated the posttranslational modification of Hsp90 in inflammation. LPS, a prototypical inflammatory agent, induced concentration- and time-dependent tyrosine (Y) phosphorylation of Hsp90 alpha and Hsp90 beta in bovine pulmonary arterial and human lung microvascular endothelial cells (HLMVEC). Mass spectrometry identified Y309 as a major site of Y phosphorylation on Hsp90 alpha (Y300 of Hsp90 beta). LPS-induced Hsp90 phosphorylation was prevented by the Hsp90 inhibitor 17-allyl-amino-demethoxy-geldanamycin (17-AAG) in vitro as well as in lungs from LPS-treated mice, in vivo. Furthermore, 17-AAG prevented LPS-induced pp60(src) activation. LPS-induced Hsp90 phosphorylation was also prevented by the pp60(src) inhibitor PP2. Additionally, Hsp90 phosphorylation was induced by infecting cells with a constitutively active pp60(src) adenovirus, whereas either a dominant-negative pp60(src) adenovirus or reduced expression of pp60src by a specific siRNA prevented the LPS-induced Y phosphorylation of Hsp90. Transfection of HLMVEC with the nonphosphorylatable Hsp90 beta Y300F mutant prevented LPS-induced Hsp90 beta tyrosine phosphorylation but not pp60(src) activation. Furthermore, the Hsp90 beta Y300F mutant showed a reduced ability to bind the Hsp90 client proteins eNOS and pp60(src) and HLMVEC transfected with the mutant exhibited reduced LPS-induced barrier dysfunction. We conclude that inflammatory stimuli cause posttranslational modifications of Hsp90 that are Hsp90-inhibitor sensitive and may be important to the proinflammatory actions of Hsp90.