Exogenous nitric oxide (NO) triggers a preconditioning-like effect in heart via a pathway that is dependent on reactive oxygen species. This study examined the signaling pathway by which the NO donor S-nitroso-N-acetylpenicillamine (SNAP, 2 microM) triggers its anti-infarct effect. Isolated rabbit hearts experienced 30 min of regional ischemia and 120 min of subsequent reperfusion. Infarct size was determined by triphenyltetrazolium chloride staining. Infarct size was reduced from 30.5 +/- 3.0% of the risk zone in control hearts to 10.2 +/- 2.0% in SNAP-treated hearts. Bracketing the SNAP infusion with either the guanylyl cyclase blocker 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (2 microM) or the mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel blocker 5-hydroxydecanoate (200 microM) completely blocked the infarct-sparing effect of SNAP (34.3 +/- 3.8 and 32.2 +/- 1.6% infarction, respectively). Pretreatment of hearts with 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (10 microM), which is a cell-permeable cGMP analog that activates protein kinase G, mimicked the preconditioning effect of SNAP by reducing infarct size to 7.5 +/- 1.1% of the risk zone. This salutary effect was abolished by either the free radical scavenger N-(2-mercaptopropionyl)glycine (1 mM) or 5-hydroxydecanoate (100 microM; 28.9 +/- 2.7 and 33.6 +/- 5.0% infarction of the risk zone, respectively). To confirm these functional data and the effect of SNAP on the guanylyl cyclase-protein kinase G signaling pathway, cGMP levels were measured. SNAP increased the level from 0.18 +/- 0.04 to 0.61 +/- 0.14 pmol/mg of protein (P < 0.05). These data suggest that exogenous NO triggers the preconditioning effect by initiating a cascade of events including stimulation of guanylyl cyclase to make cGMP, activation of protein kinase G, opening of mitoK(ATP) channels, and, finally, production of reactive oxygen species.

NO and cGMP have antigrowth and anti-inflammatory effects on the vessel wall in response to injury. It is well established that after vascular injury proinflammatory cytokines are involved in vascular wall remodeling. The purpose of this study was to ascertain the signaling mechanisms involved in cGMP-dependent protein kinase (PKG) suppression by inflammatory cytokines in primary bovine aortic vascular smooth muscle cells (VSMC). Interleukin (IL)-Ibeta, tumor necrosis factor (TNF)-alpha, and LPS decreased the mRNA and protein levels of PKG in VSMC. IL-Ibeta, TNF-alpha, and LPS increased inducible nitric oxide synthase (iNOS) expression and cGMP production. Treatment of cells with selective inhibitors of iNOS or soluble guanylate cyclase (sGC) reversed the downregulation of PKG expression induced by cytokines and LPS. The NO donor (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA NONOate) and 3-(5-hydroxymethyl-2-furyl)-1-benzylindazole (YC-1), a NO-independent sGC activator, decreased PKG mRNA and protein expression in bovine aortic VSMC. Cyclic nucleotide analogs [8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphate (CPT-cGMP) and 8-(4-chlorophenylthio)adenosine 3,5'-cyclic monophosphate (CPT-cAMP)] also suppressed PKG mRNA and protein expression. However, CPT-cAMP was more effective than CPT-cGMP in decreasing PKG mRNA levels. Selective inhibition of PKA with the Rp isomer of 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphorothioate (Rp-8p-CPT cAMPS) prevented the downregulation of PKG by LPS. In contrast, the Rp isomer of 8-(4-chlorophenylthio)guanosine 3,5'-cyclic monophosphorothioate (Rp-8p-CPT cGMPS; inhibitor of PKG) had no effect on LPS-induced inhibition of PKG mRNA and protein expression. These studies suggest that cross-activation of PKA in response to iNOS expression by inflammatory mediators downregulates PKG expression in bovine aortic VSMC.

Vascular smooth muscle cells (VSMC) undergo many phenotypic changes when placed in culture. Several studies have shown that the levels of expression of soluble guanylyl cyclase (sGC) or cGMP-dependent protein kinase (PKG) are altered in cultured VSMC. In this study the mechanisms involved in the coordinated expression of sGC and PKG were examined. Pro-inflammatory cytokines that increase the expression of type II NO synthase (inducible NO synthase, or iNOS) decreased PKG expression in freshly isolated, non-passaged bovine aortic SMC. However, in several passaged VSMC lines (i.e. bovine aortic SMC, human aortic SMC, and A7r5 cells), PKG protein expression was not suppressed by cytokines or NO. sGC was highly expressed in nonpassaged bovine aortic SMC but not in passaged cell lines. Restoration of expression of sGC to passaged bovine SMC using adenovirus encoding the ␣ 1 and ␤ 1 subunits of sGC restored the capacity of the cells to increase cGMP in response to NO. Furthermore, treatment of these sGC-transduced cells with NO donors for 48 h resulted in decreased PKG protein expression. In contrast, passaged rat aortic SMC expressed high levels of NOresponsive sGC but demonstrated reduced expression of PKG. Adenovirus-mediated expression of the PKG catalytically active domain in rat aortic SMC caused a reduction in the expression of sGC in these cells. These results suggest that there is a mechanism for the coordinated expression of sGC and PKG in VSMC and that prolonged activation of sGC down-regulates PKG expression. Likewise, the loss of PKG expression appears to increase sGC expression. These effects may be an adaptive mechanism allowing growth and survival of VSMC in vitro.The nitric oxide (NO)-cGMP signaling pathway plays a critical role in vascular function (1, 2). Cyclic GMP is a second messenger that is generated by cytoplasmic soluble guanylyl cyclases (sGCs), 1 which are activated by NO, or particulate guanylyl cyclases, which are activated by peptide hormones such as atrial natriuretic peptide. sGC is a heterodimer that consists of two subunits, termed ␣ and ␤, which are linked by disulfide bonds, and has a prosthetic heme group covalently bound to the heterodimer (1, 2). NO activates cGMP synthesis by binding to the heme, leading to the conversion of GTP to cGMP. Although two isoforms of each subunit have been cloned from rat and bovine lung, the a 1 b 1 heterodimer has been found in most tissues and cell types, including vascular smooth muscle cells (VSMC) (3-6). NO and cGMP are involved in many physiological processes such as VSMC relaxation, apoptosis, proliferation, migration, and extracellular matrix production (7-10). An important cGMP receptor protein expressed in VSMC is cGMP-dependent protein kinase (PKG), which is ultimately responsible for mediating the effects of cGMP in vascular smooth muscle relaxation (11). There are two distinct genes encoding PKG in mammalian cells, the type I and type II genes (12, 13). Type I, which is the gene product expressed in VSMC, exists as two isoforms, PKG I␣...

Cyclic GMP-dependent protein kinase I plays a pivotal role in regulating smooth muscle cell relaxation, growth, and differentiation. Expression of the enzyme varies greatly in smooth muscle and in other tissues and cell types, yet little is known regarding the mechanisms regulating cGMP-dependent protein kinase gene expression. The present work was undertaken to characterize the mechanisms controlling kinase gene expression in vascular smooth muscle cells. A 2-kb human cGMP-dependent protein kinase I 5-noncoding promoter sequence was characterized by serial deletion, and functional studies demonstrated that a 591-bp 5-promoter construct possessed the highest activity compared with all other constructs generated from the larger promoter. Analysis of the sequence between ؊472 and ؊591 bp from the transcriptional start site revealed the existence of two E-like boxes known to bind upstream stimulatory factors. Electrophoretic mobility shift assays and functional studies using luciferase reporter gene assays identified upstream stimulatory factors as the transcription factors bound to the E-boxes in the 591-bp promoter. Site-directed mutagenesis of the E-boxes abolished the binding of upstream stimulatory factor proteins and decreased the activity of the cGMPdependent protein kinase I 591-bp promoter, thus confirming the involvement of these transcription factors in mediating gene expression. Cotransfection experiments demonstrated that overexpression of upstream stimulatory factors 1 and 2 increased cGMP-dependent protein kinase I promoter activity. Collectively, these data suggest that the human proximal cGMP-dependent protein kinase I promoter is regulated by tandem Eboxes that bind upstream stimulatory factors.The serine/threonine protein kinase, cGMP-dependent protein kinase (PKG), 1 belongs to the large protein kinase family and mediates the actions of nitric oxide (NO) and natriuretic peptides in target cells (1-3). The effects of PKG activation in target cells include smooth muscle relaxation, inhibition of platelet aggregation, calcium homeostasis, intestinal secretion, cell growth, differentiation, and gene regulation (4, 5).Two genes encoding mammalian PKG have been identified, type I and type II (6 -8). The type I PKG (PKG-I) is expressed as two isoforms created by alternative mRNA splicing of the two first coding exons, and these two isoforms are referred to as type I␣ and type I␤. Because these two isoforms differ only in the initial coding region, they contain an identical catalytic domain with identical substrate specificity. Although the two isoforms of PKG-I are rather widely expressed in mammalian tissues, three cell types, smooth muscle, cerebellum Purkinje cells, and platelets, contain the highest levels of the enzyme. The type II PKG is expressed most abundantly in intestinal epithelium, chondrocytes, and certain regions of the brain but is not expressed in smooth muscle (9 -12).In vascular SMC, both PKG-I␣ and -I␤ isoforms are abundant, but expression is highly variable. For instance, upon subc...

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