Sulfhydryl-dependent dimerization of soluble guanylyl cyclase modulates the relaxation of porcine pulmonary arteries to nitric oxide

BAY58-2667 Activates Different Soluble Guanylyl Cyclase Species by Distinct Mechanisms that Indicate Its Principal Target in Cells is the Heme-Free Soluble Guanylyl Cyclase-Heat Shock Protein 90 Complex

Nitric oxide (NO)-unresponsive forms of soluble guanylyl cyclase (sGC) exist naturally and in disease can disable NO-sGC-cGMP signaling. Agonists like BAY58-2667 (BAY58) target these sGC forms, but their mechanisms of action in living cells are unclear. We studied rat lung fibroblast-6 cells and human airway smooth muscle cells that naturally express sGC and HEK293 cells that we transfected to express sGC and variants. Cells were cultured to build up different forms of sGC, and we used fluorescence and FRET-based measures to monitor BAY58-driven cGMP production and any protein partner exchange or heme loss events that may occur for each sGC species. We found that: (i) BAY58 activated cGMP production by the apo-sGCβ-Hsp90 species after a 5-8 minute delay that was associated with apo-sGCβ exchanging its Hsp90 partner with an sGCα subunit. (ii) In cells containing an artificially constructed heme-free sGC heterodimer, BAY58 initiated an immediate and three times faster cGMP production. However, this behavior was not observed in cells expressing native sGC under any condition. (iii) BAY58 activated cGMP production by ferric heme sGC only after a 30-minute delay, coincident with it initiating a delayed, slow ferric heme loss from sGCβ We conclude that the kinetics favor BAY58 activation of the apo-sGCβ-Hsp90 species over the ferric heme sGC species in living cells. The protein partner exchange events driven by BAY58 account for the initial delay in cGMP production and also limit the speed of subsequent cGMP production in the cells. Our findings clarify how agonists like BAY58 may activate sGC in health and disease. SIGNIFICANCE STATEMENT: A class of agonists can activate cyclic guanosine monophosphate (cGMP) synthesis by forms of soluble guanylyl cyclase (sGC) that do not respond to NO and accumulate in disease, but the mechanisms of action are unclear. This study clarifies what forms of sGC exist in living cells, which of these can be activated by the agonists, and the mechanisms and kinetics by which each form is activated. This information may help to hasten deployment of these agonists for pharmaceutical intervention and clinical therapy.

Conventional and Unconventional Mechanisms for Soluble Guanylyl Cyclase Signaling

Soluble guanylyl cyclase (sGC) is the principal enzyme in mediating the biological actions of nitric oxide. On activation, sGC converts guanosine triphosphate to guanosine 3',5'-cyclic monophosphate (cGMP), which mediates diverse physiological processes including vasodilation, platelet aggregation, and myocardial functions predominantly by acting on cGMP-dependent protein kinases. Cyclic GMP has long been considered as the sole second messenger for sGC action. However, emerging evidence suggests that, in addition to cGMP, other nucleoside 3',5'-cyclic monophosphates (cNMPs) are synthesized by sGC in response to nitric oxide stimulation, and some of these nucleoside 3',5'-cyclic monophosphates are involved in various physiological activities. For example, inosine 3',5'-cyclic monophosphate synthesized by sGC may play a critical role in hypoxic augmentation of vasoconstriction. The involvement of cytidine 3',5'-cyclic monophosphate and uridine 3',5'-cyclic monophosphate in certain cardiovascular activities is also implicated.

The vasodilatory effect of sulfur dioxide via SGC/cGMP/PKG pathway in association with sulfhydryl-dependent dimerization

The present study was designed to explore the role of soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP)/PKG pathway in sulfur dioxide (SO2)-induced vasodilation. We showed that SO2 induced a concentration-dependent relaxation of phenylephrine (PE)-precontracted rat aortic rings in association with an increase in cGMP concentration, whereas l-aspartic acid β-hydroxamate (HDX), an inhibitor of SO2 synthase, contracted rings in a dose-dependent manner. Pretreatment of aortic rings with the sGC inhibitor ODQ (30 μM) attenuated the vasodilatory effects of SO2, suggesting the involvement of cGMP pathway in SO2-induced vasodilation. Mechanistically, SO2 upregulated the protein levels of sGC and PKG dimers, while HDX inhibited it, indicating SO2 could promote cGMP synthesis through sGC activation. Furthermore, the dimerization of sGC and PKG and vasodilation induced by SO2 in precontracted rings were significantly prevented by thiol reductants dithiothreitol (DTT). In addition, SO2 reduced the activity of phosphodiesterase type 5 (PDE5), a cGMP-specific hydrolytic enzyme, implying that SO2 elevated cGMP concentration by inhibiting its hydrolysis. Hence, SO2 exerted its vasodilatory effects at least partly by promoting disulfide-dependent dimerization of sGC and PKG, resulting in an activated sGC/cGMP/PKG pathway in blood vessels. These findings revealed a new mode of action and mechanisms by which SO2 regulated the vascular tone.

New insights into the role of soluble guanylate cyclase in blood pressure regulation

PURPOSE OF REVIEW

Nitric oxide (NO)-soluble guanylate cyclase (sGC)-dependent signaling mechanisms have a profound effect on the regulation of blood pressure (BP). In this review, we will discuss recent findings in the field that support the importance of sGC in the development of hypertension.

RECENT FINDINGS

The importance of sGC in BP regulation was highlighted by studies using genetically modified animal models, chemical stimulators/activators and inhibitors of the NO/sGC signaling pathway, and genetic association studies in humans. Many studies further support the role of NO/sGC in vasodilation and vascular dysfunction, which is underscored by the early clinical success of synthetic sGC stimulators for the treatment of pulmonary hypertension. Recent work has uncovered more details about the structural basis of sGC activation, enabling the development of more potent and efficient modulators of sGC activity. Finally, the mechanisms involved in the modulation of sGC by signaling gases other than NO, as well as the influence of redox signaling on sGC, have been the subject of several interesting studies.

SUMMARY

sGC is fast becoming an interesting therapeutic target for the treatment of vascular dysfunction and hypertension, with novel sGC stimulating/activating compounds as promising clinical treatment options.

Endothelium-independent hypoxic contraction of porcine coronary arteries may be mediated by activation of phosphoinositide 3-kinase/Akt pathway

Phosphoinositide 3-kinase (PI3K)/Akt signaling pathway plays an essential role in the regulation of vascular tone. The present study aimed to determine its role in hypoxic coronary vasoconstriction. Isometric tension of isolated porcine coronary arteries was measured with organ chamber technique; the protein levels of phosphorylated and total MLC were examined by Western blotting; the activities of PI3K and Rho kinase were determined by the phosphorylation of their respective target protein Akt and MTPT1. Acute hypoxia induced a rapid contraction followed by a short-term relaxation and then a sustained contraction in porcine coronary arteries. The rapid but not the sustained contraction was abolished by endothelium removal. The sustained contraction was attenuated by inhibitors of PI3K (LY294002) and Akt (Akt-I). The attenuation effect caused by LY294002 was not affected by nifedipine, but was abolished by Y27632, an inhibitor of Rho kinase. The sustained hypoxic contraction was associated with altered phosphorylation of MLC and Akt, which was inhibited by LY294002. The sustained hypoxic contraction was also accompanied with increased phosphorylation of MYPT1, which was inhibited by LY294002 and Y27632. This study demonstrates that sustained hypoxia causes porcine coronary artery to contract in an endothelium-independent manner. An increased PI3K/Akt/Rho kinase signaling may be involved.

Preservation of nitric oxide-induced relaxation of porcine coronary artery: roles of the dimers of soluble guanylyl cyclase, phosphodiesterase type 5, and cGMP-dependent protein kinase

Soluble guanylyl cyclase (sGC), phosphodiesterase type 5 (PDE5), and guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase (PKG) are all dimeric. The present study was to determine the role of their dimeric status in nitric oxide-induced vasodilatation. In isolated porcine coronary arteries, after 20 h incubation with serum-free medium, serum-containing medium, or phosphate-buffered saline solution, the protein levels of the dimers of sGC, PDE5, and PKG were diminished while the monomer levels remained unchanged, associated with reduced cGMP elevation in response to DETA NONOate and decreased PDE5 activity; the activity of PKG was not significantly altered. DETA NONOate caused a greater relaxation in arteries incubated for 20 vs. 2 h. The relaxant response was largely abolished by 1H-[1, 2, 4]oxadiazolo[4,3-a]quinoxalin-1-one, an sGC inhibitor. Zaprinast, a PDE5 inhibitor, had no effect on relaxation caused by DETA NONOate of arteries incubated for 20 h but augmented the response incubated for 2 h. A greater relaxation to 8-bromo-guanosine 3'5'-cyclic monophosphate occurred in arteries incubated for 20 than for 2 h. The protein level of the dimers but not monomers of PDE5 was reduced by dithiothreitol and unaffected by hydrogen peroxide, accompanied with decreased PDE5 activity and reduced response to DETA NONOate. These results demonstrate that the dimeric but not monomeric status of sGC and PDE5 of coronary arteries are closely related to their activities. The preserved vasodilator response after 20 h incubation may result in part from a synchronous reduction of the dimer levels of sGC and PDE5 as well as an augmented response to cGMP.