. Novel complexes of guanylate cyclase with heat shock protein 90 and nitric oxide synthase. Am J Physiol Heart Circ Physiol 285: H669-H678, 2003. First published April 3, 2003 10.1152/ajpheart.01025.2002 is an important downstream intracellular target of nitric oxide (NO) that is produced by endothelial NO synthase (eNOS) and inducible NO synthase (iNOS). In this study, we demonstrate that sGC exists in a complex with eNOS and heat shock protein 90 (HSP90) in aortic endothelial cells. In addition, we show that in aortic smooth muscle cells, sGC forms a complex with HSP90. Formation of the sGC/eNOS/HSP90 complex is increased in response to eNOS-activating agonists in a manner that depends on HSP90 activity. In vitro binding assays with glutathione S-transferase fusion proteins that contain the ␣-or ␤-subunit of sGC show that the sGC ␤-subunit interacts directly with HSP90 and indirectly with eNOS. Confocal immunofluorescent studies confirm the subcellular colocalization of sGC and HSP90 in both endothelial and smooth muscle cells. Complex formation of sGC with HSP90 facilitates responses to NO donors in cultured cells (cGMP accumulation) as well as in anesthetized rats (hypotension). These complexes likely function to stabilize sGC as well as to provide directed intracellular transfer of NO from NOS to sGC, thus preventing inactivation of NO by superoxide anion and formation of peroxynitrite, which is a toxic molecule that has been implicated in the pathology of several vascular diseases.smooth muscle cells; endothelium; vascular endothelial growth factor; bradykinin; cGMP accumulation SOLUBLE GUANYLATE CYCLASE (sGC), an ␣/␤-heterodimeric heme protein, catalyzes the conversion of GTP to cGMP in many cells including vascular endothelial cells (ECs) and vascular smooth muscle cells (SMCs). Activation of sGC is by direct binding of nitric oxide (NO) to the sGC heme prosthetic group. Formation of the nitrosyl heme adduct induces a conformational change in sGC that results in an increase in its enzymatic activity (21). The NO that activates sGC in various cells is the product of a reaction that is catalyzed by one of three distinct NO synthase (NOS) molecules, which catalyze the oxidation of L-arginine to produce L-citrulline and NO (1). In ECs, NO production is mediated by the constitutively expressed endothelial NOS (eNOS). Activation of eNOS is by Ca 2ϩ -calmodulin (CaM) after agonist-stimulated elevations in intracellular Ca 2ϩ concentrations. Two signaling pathways exist that involve eNOS and sGC. The first is an intercellular pathway whereby NO, which is produced by eNOS in ECs, diffuses to the underlying SMCs and promotes blood vessel relaxation (16). The second is an intracellular eNOS-sGC pathway that is essential for vascular endothelial growth factor (VEGF)-induced increases in EC permeability and proliferation (24,25,30).Initially, eNOS was thought to function as an isolated homodimer. It is now known, however, that eNOS exists in multiprotein complexes in which it interacts with other proteins. These pr...

OBJECTIVE Pulmonary Hypertension (PH) is a progressive disease arising from remodeling and narrowing of pulmonary arteries (PA) resulting in high pulmonary blood pressure and ultimately right ventricular failure. Elevated production of reactive oxygen species (ROS) by NADPH oxidase 4 (Nox4) is associated with increased pressure in PH. However, the cellular location of Nox4 and its contribution to aberrant vascular remodeling in PH remains poorly understood. Therefore, we sought to identify the vascular cells expressing Nox4 in PA and determine the functional relevance of Nox4 in PH. APPROACH AND RESULTS Elevated expression of Nox4 was detected in hypertensive PA from 3 rat PH models and human PH using qRT-PCR, Western blot, and immunofluorescence. In the vascular wall, Nox4 was detected in both endothelium and adventitia and perivascular staining was prominently increased in hypertensive lung sections, colocalizing with cells expressing fibroblast and monocyte markers and matching the adventitial location of ROS production. Small molecule inhibitors of Nox4 reduced adventitial ROS generation and vascular remodeling as well as ameliorating right ventricular hypertrophy and non-invasive indices of PA stiffness in monocrotaline (MCT)-treated rats as determined by morphometric analysis and high resolution digital ultrasound. Nox4 inhibitors improved PH in both prevention and reversal protocols and reduced the expression of fibroblast markers in isolated PA. In fibroblasts, Nox4 over-expression stimulated migration and proliferation and was necessary for matrix gene expression. CONCLUSIONS These findings indicate that Nox4 is prominently expressed in the adventitia and contributes to altered fibroblast behavior, hypertensive vascular remodeling and the development of PH.

Hsp90 inhibitors may offer a new pharmacological tool in the management of severe sepsis and severe sepsis-induced ALI.