Functional interdependence and colocalization of endothelial nitric oxide synthase and heat shock protein 90 in cerebral arteries

Heat shock protein 90 (HSP90), an essential component of several signal tra nsduction systems, participates in the activation of endothelial nitric oxi de synthase (eNOS) in cells. The objective of the current study was to dete rmine if HSP90 and eNOS were functionally interdependent and colocalized in the cerebral circulation. The authors used isometric force recording, cycl ic 3'5'-guanosine monophosphate (cGMP) radioimmunoassay (RIA), and immunogo ld electron microscopy (EM) to study canine basilar artery. They found that gel-danamycin (0.1 to 10 mug/mL), a selective HSP90 inhibitor, caused conc entration-dependent contractions in arterial rings (n = 6 dogs). Contractio ns to geldanamycin were unaffected by a cyclooxygenase inhibitor, indometha cin (10 mu mol/L; P < 0.05, n = 6). Functional evidence for interaction bet ween HSP90 and nitric oxide (NO)-mediated signaling included observations t hat the contractile effect of geldanamycin was the following: (1) endotheli um-dependent, (2) abolished by N-g-nitro-L-arginine methylester (L-NAME; 0. 3 mmol/L), and (3) nonadditive with the contractile effect of this NOS inhi bitor (P < 0.01, n = 6 for each). Furthermore, RIA showed significant reduc tion in cGMP levels in arteries treated with geldanamycin (3 mug/mL; P < 0. 02, n = 8), whereas immunogold EM demonstrated areas of colocalization of H SP90 and eNOS selectively in the cytoplasm of endothelial cells. The curren t findings suggest that in cerebral arteries, endothelial HSP90 plays an im portant role in modulation of basal NO-mediated signaling. This interaction may be particularly important in stress-induced up-regulation of HSP90 wit h subsequent alteration of vasomotor function.