Inhibitor-κB kinase attenuates Hsp90-dependent endothelial nitric oxide synthase function in vascular endothelial cells.

ABSTRACT

Endothelial nitric oxide (NO) synthase (eNOS) is the predominant isoform that generates NO in the blood vessels. Many different regulators, including heat shock protein 90 (Hsp90), govern eNOS function. Hsp90-dependent phosphorylation of eNOS is a critical event that determines eNOS activity. In our earlier study we demonstrated an inhibitor-κB kinase-ß (IKKß)-Hsp90 interaction in a high-glucose environment. In the present study we further define the putative binding domain of IKKß on Hsp90. Interestingly, IKKß binds to the middle domain of Hsp90, which has been shown to interact with eNOS to stimulate its activity. This new finding suggests a tighter regulation of eNOS activity than was previously assumed. Furthermore, addition of purified recombinant IKKß to the eNOS-Hsp90 complex reduces the eNOS-Hsp90 interaction and eNOS activity, indicating a competition for Hsp90 between eNOS and IKKß. The pathophysiological relevance of the IKKß-Hsp90 interaction has also been demonstrated using in vitro vascular endothelial growth factor-mediated signaling and an Ins2(Akita) in vivo model. Our study further defines the preferential involvement of α- vs. ß-isoforms of Hsp90 in the IKKß-eNOS-Hsp90 interaction, even though both Hsp90α and Hsp90ß stimulate NO production. These studies not only reinforce the significance of maintaining a homeostatic balance of eNOS and IKKß within the cell system that regulates NO production, but they also confirm that the IKKß-Hsp90 interaction is favored in a high-glucose environment, leading to impairment of the eNOS-Hsp90 interaction, which contributes to endothelial dysfunction and vascular complications in diabetes.