The 90-kDa heat shock protein (hsp90) regulates the stability and function of many client proteins, including members of the NO-cGMP signaling pathway. Soluble guanylyl cyclase (sGC), an NO receptor, was recently reported to be an hsp90-interacting partner. In the present study, we show that hsp90 binds to both subunits of the most common sGC form (␣ 1 ␤ 1 ) when these are expressed individually but only interacts with ␤ 1 in the heterodimeric form of the enzyme. Characterization of the region of hsp90 required to bind each subunit in immunoprecipitation experiments revealed that residues 310 to 456 of hsp90 interact with the sGC subunits. The region of ␤ 1 responsible for binding to hsp90␤ was mapped using in vitro binding assays and immunoprecipitation experiments and was found to lie in the regulatory domain. The physiological importance of the hsp90/sGC interaction was investigated by treating rat smooth muscle cells with the hsp90 inhibitors radicicol and geldanamycin (GA) and determining both sGC activity and protein levels. Long-term (24 or 48 h) inhibition of hsp90 resulted in a strong decrease of both ␣ 1 and ␤ 1 protein levels and sGC activity. Moreover, incubation of smooth muscle cells with the proteasome inhibitor N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132) blocked the GA-induced down-regulation of sGC. We conclude that the N-terminal region of the ␤ 1 subunit mediates binding of the heterodimeric form of sGC to hsp90 and that this interaction involves the M domain of hsp90. Hsp90 binding to sGC regulates the pool of active enzymes by affecting the protein levels of the two subunits.The 90-kDa heat shock protein (hsp90) is one of the most abundant cytosolic proteins in eukaryotes, amounting to 1 to 2% of the total soluble protein, even under resting conditions.

Background and purpose: Superoxide anions produced during vascular disease scavenge nitric oxide (NO), thereby reducing its biological activity. The aim of the present study was to investigate whether reactive oxygen species (ROS) have a direct effect on soluble guanylyl cyclase (sGC) subunit levels and function and to ascertain the mechanism(s) involved. Experimental approach: Rat aortic smooth muscle cells (RASM) or freshly isolated vessels were exposed to reactive oxygen species (ROS)-generating agents and sGC subunit expression was determined at the mRNA and/or protein level. cGMP accumulation was also determined in RASM exposed to ROS. Key results: Incubation of smooth muscle cells with H 2 O 2 , xanthine/xanthine oxidase (X/XO) or menadione sodium bisulphite (MSB) significantly decreased protein levels of a1 and b1 subunits of sGC and reduced SNP-induced cGMP formation. Similarly, sGC expression was reduced in freshly isolated vessels exposed to ROS-generating agents. The ROS-triggered inhibition of a1 and b1 levels was not blocked by proteasome inhibitors, suggesting that decreased sGC protein was not due to protein degradation through this pathway. Real time RT-PCR analysis demonstrated a 68% reduction in steady state mRNA levels for the a1 subunit following exposure to H 2 O 2 . In addition, a1 promoter-driven luciferase activity in RASM decreased by 60% after H 2 O 2 treatment. Conclusion and implications:We conclude that oxidative stress triggers a decrease in sGC expression and activity that results from reduced sGC steady state mRNA levels. Altered sGC expression is expected to contribute to the changes in vascular tone and remodeling observed in diseases associated with ROS overproduction.

Background: It has been shown that interleukin (IL)-18 levels in induced sputum are reduced in asthmatic and healthy smokers. However, in chronic obstructive pulmonary disease (COPD) patients, recent data show an overproduction in the lungs and increased serum levels of IL-18, suggesting that IL-18 may be involved in the pathogenesis of COPD. Method: In order to assess the relation of IL-18 with pulmonary function and airway inflammation in COPD, IL-18, tumour necrosis factor-a, and IL-8 levels were measured by ELISA in sputum supernatants obtained from patients with bronchitis type COPD (n Z 28), and healthy subjects (18 smokers and 17 non-smokers). Cellular localization of IL-18 was assessed by immunocytochemistry.Results: The levels of IL-18 were significantly higher in sputum supernatants of COPD patients compared to healthy smokers and non-smokers (p < 0.05). IL-18 production was localized to sputum macrophages. IL-18 levels were inversely correlated with FEV 1 (% predicted) (r Z À0.572, p Z 0.002) and FEV 1 /FVC ratio in COPD smokers (r Z À0.608, p Z 0.001). No correlations were found between IL-18 levels and inflammatory markers studied in induced sputum obtained from COPD patients, healthy smokers and non-smokers. Conclusion:In patients with COPD, increased levels of IL-18 in induced sputum were associated with airflow limitation, suggesting that IL-18 may be implicated in the pathogenesis of COPD.