Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.12 (PKG)
 2,515 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Focal adhesions are specialized regions of cell membranes that are foci for the transmission of signals between the outside and the inside of the cell. Intracellular signaling events are important in the organization and stability of these structures. In previous work, we showed that the counter-adhesive extracellular matrix proteins, thrombospondin, tenascin, and SPARC, induce the disassembly of focal adhesion plaques and we identified the active regions of these proteins. In order to determine the mechanisms whereby the anti-adhesive matrix proteins modulate cytoskeletal organization and focal adhesion integrity, we examined the role of protein kinases in mediating the loss of focal adhesions by these proteins. Data from these studies show that cGMP-dependent protein kinase is necessary to mediate focal adhesion disassembly triggered by either thrombospondin or tenascin, but not by SPARC. In experiments using various protein kinase inhibitors, we observed that selective inhibitors of cyclic GMP-dependent protein kinase, KT5823 and Rp-8-Br-cGMPS, blocked the effects of both the active sequence of thrombospondin 1 (hep I) and the alternatively-spliced segment (TNfnA-D) of tenascin-C on focal adhesion disassembly. Moreover, early passage rat aortic smooth muscle cells which have high levels of cGMP-dependent protein kinase were sensitive to hep I treatment, in contrast to passaged cGMP-dependent protein kinase deficient cells which were refractory to hep I or TNfnA-D treatment, but were sensitive to SPARC. Transfection of passaged smooth muscle cells with the catalytic domain of PKG I alpha restored responsiveness to hep I and TNfnA-D. While these studies show that cGMP-dependent protein kinase activity is necessary for thrombospondin and tenascin-mediated focal adhesion disassembly, kinase activity alone is not sufficient to induce disassembly as transfection of the catalytic domain of the kinase in the absence of additional stimuli does not result in loss of focal adhesions.
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PMID:Cyclic GMP-dependent protein kinase is required for thrombospondin and tenascin mediated focal adhesion disassembly. 892 11

Vascular lesions resulting from injury are characterized by a thickening of the intima brought about in part through the production of increased amounts of extracellular matrix proteins by the vascular smooth muscle cells (VSMCs). In this study, we tested the hypothesis that cGMP-dependent protein kinase (PKG), an important mediator of NO and cGMP signaling in VSMCs, inhibits the production of two extracellular matrix proteins, osteopontin and thrombospondin, which are involved in the formation of the neointima. VSMCs deficient in PKG were stably transfected with cDNAs encoding either the holoenzyme PKG-Ialpha or the constitutively active catalytic domain of PKG-I in order to directly examine the effects of PKG on osteopontin and thrombospondin production. Cells expressing either of the PKG constructs had dramatically reduced levels of osteopontin and thrombospondin-1 protein compared with control-transfected PKG-deficient cells. PKG transfection also altered the morphology of the VSMCs. These results indicate that PKG may be involved in suppressing extracellular matrix protein expression, which is one important characteristic of synthetic secretory VSMCs. Suppression of these matrix proteins may underlie the effects of NO-cGMP signaling to inhibit VSMC migration and phenotypic modulation.
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PMID:Cyclic GMP-dependent protein kinase inhibits osteopontin and thrombospondin production in rat aortic smooth muscle cells. 946 84

The role of cGMP-dependent protein kinase (PKG) in the regulation of rat aortic vascular smooth muscle cells (VSMC) phenotype was examined using a transfected cell culture system. Repetitively passaged VSMC do not express PKG and exist in the synthetic phenotype. Transfection of PKG-l alpha cDNA, or the active catalytic domain of PKG-l alpha, resulted in the appearance of VSMC having a morphology consistent with the contractile phenotype. PKG-expressing cells also contained markers for the contractile phenotype (for example, smooth muscle specific myosin heavy chain, calponin, alpha-actin) and reduced levels of synthetic phenotype markers (osteopontin, thrombospondin). PKG-transfected VSMC have also reduced the levels of fibroblast growth factor receptors 1 and 2, consistent with the establishment of a more contractile phenotype. The regulation of PKG expression in VSMC is largely undefined; however, continuous exposure of cultured bovine aortic smooth muscle cells with nitric oxide (NO)-donor drugs or cyclic nucleotide analogues reduced the expression of PKG. These results suggest that PKG occupies a critical role in VSMC phenotype and that suppression of PKG expression during inflammation or injury promotes a more synthetic state of the VSMC.
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PMID:Nitric oxide--cyclic GMP pathway regulates vascular smooth muscle cell phenotypic modulation: implications in vascular diseases. 988 73

Chronic hypoxia triggers pulmonary vascular remodeling, which is associated with a modulation of the vascular smooth muscle cell (SMC) phenotype from a contractile, differentiated to a synthetic, dedifferentiated state. We previously reported that acute hypoxia represses cGMP-dependent protein kinase (PKG) expression in ovine fetal pulmonary venous SMCs (FPVSMCs). Therefore, we tested if altered expression of PKG could explain SMC phenotype modulation after exposure to hypoxia. Hypoxia-induced reduction in PKG protein expression strongly correlated with the repressed expression of SMC phenotype markers, myosin heavy chain (MHC), calponin, vimentin, alpha-smooth muscle actin (alphaSMA), and thrombospondin (TSP), indicating that hypoxic exposure of SMC induced phenotype modulation to dedifferentiated state, and PKG may be involved in SMC phenotype modulation. PKG-specific small interfering RNA (siRNA) transfection in FPVSMCs significantly attenuated calponin, vimentin, and MHC expression, with no effect on alphaSMA and TSP. Treatment with 30 microM Drosophila Antennapedia (DT-3), a membrane-permeable peptide inhibitor of PKG, attenuated the expression of TSP, MHC, alphaSMA, vimentin, and calponin. The results from PKG siRNA and DT-3 studies indicate that hypoxia-induced reduction in protein expression was also similarly impacted by PKG inhibition. Overexpression of PKG in FPVSMCs by transfection with a full-length PKG construct tagged with green fluorescent fusion protein (PKG-GFP) reversed the effect of hypoxia on the expression of SMC phenotype marker proteins. These results suggest that PKG could be one of the determinants for the expression of SMC phenotype marker proteins and may be involved in the maintenance of the differentiated phenotype in pulmonary vascular SMCs in hypoxia.
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PMID:Modulation of pulmonary vascular smooth muscle cell phenotype in hypoxia: role of cGMP-dependent protein kinase. 1732 85

Platelet alpha-granules constitute the major rapidly releasable reservoir of thrombospondin-1 in higher animals. Although some fragments and peptides derived from thrombospondin-1 stimulate or inhibit platelet aggregation, its physiologic function in platelets has remained elusive. We now show that endogenous thrombospondin-1 is necessary for platelet aggregation in vitro in the presence of physiologic levels of nitric oxide (NO). Exogenous NO or elevation of cGMP delays thrombin-induced platelet aggregation under high shear and static conditions, and exogenous thrombospondin-1 reverses this delay. Thrombospondin-1-null murine platelets fail to aggregate in response to thrombin in the presence of exogenous NO or 8Br-cGMP. At physiologic concentrations of the NO synthase substrate arginine, thrombospondin-1-null platelets have elevated basal cGMP. Ligation of CD36 or CD47 is sufficient to block NO-induced cGMP accumulation and mimic the effect of thrombospondin-1 on aggregation. Exogenous thrombospondin-1 also reverses the suppression by NO of alphaIIb/beta3 integrin-mediated platelet adhesion on immobilized fibrinogen, mediated in part by increased GTP loading of Rap1. Thrombospondin-1 also inhibits cGMP-mediated activation of cGMP-dependent protein kinase and thereby prevents phosphorylation of VASP. Thus, release of thrombospondin-1 from alpha-granules during activation provides positive feedback to promote efficient platelet aggregation and adhesion by overcoming the antithrombotic activity of physiologic NO.
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PMID:Thrombospondin-1 stimulates platelet aggregation by blocking the antithrombotic activity of nitric oxide/cGMP signaling. 1789 Apr 48

Thrombospondin-1 is a secreted protein that modulates vascular cell behavior via several cell surface receptors. In vitro, nanomolar concentrations of thrombospondin-1 are required to alter endothelial and vascular smooth muscle cell adhesion, proliferation, motility, and survival. Yet, much lower levels of thrombospondin-1 are clearly functional in vivo. This discrepancy was explained with the discovery that the potency of thrombospondin-1 increases more than 100-fold in the presence of physiological levels of nitric oxide (NO). Thrombospondin-1 binding to CD47 inhibits NO signaling by preventing cGMP synthesis and activation of its target cGMP-dependent protein kinase. This potent antagonism of NO signaling allows thrombospondin-1 to acutely constrict blood vessels, accelerate platelet aggregation, and if sustained, inhibit angiogenic responses. Acute antagonism of NO signaling by thrombospondin-1 is important for hemostasis but becomes detrimental for tissue survival of ischemic injuries. New therapeutic approaches targeting thrombospondin-1 or CD47 can improve recovery from ischemic injuries and overcome a deficit in NO-responsiveness in aging. (Part of a Multi-author Review).
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PMID:Thrombospondin-1: a physiological regulator of nitric oxide signaling. 1819 60