Effects Of cGMP-dependent Protein Kinase Research Articles

Effect of cGMP-dependent protein kinase G inhibitor (D)-DT-2 on the lipopolysaccharide-induced hyporesponsiveness of rat vascular ring

Objective To investigate the effect of specific cGMP-dependent protein kinase G (PKG) inhibitor (D)-DT-2 on the contractile function of rat vascular rings after being exposed to lipopolysaccharide (LPS).Methods The experiment was performed in 2 parts.Part Ⅰ:The Sprague-Dawley rat thoracic aortic rings were randomly divided into 3 groups (n =5 each):KH group,DT-2 group and (D)-DT-2 group.KH,DT-2 and (D)-DT-2 were added to the aortic ring after being dilated with 8-Br-cGMP 50 μmol/L for 25 min and the changes in tension of vascular rings were measured.Part Ⅱ:The rat thoracic aortic rings were randomly divided into 4 groups (n =5 each):control group,LPS group,LPS-DT2 group and LPS-(D)-DT2 group.After being incubated with LPS for 3 h in vitro.The Emax and EC50 were compared among the 4 groups.Results Part Ⅰ:Both DT-2 and (D)-DT-2 could contract the vascular rings dilated with 8-Br-cGMP and the Emax was significantly higher in (D)-DT-2 group than DT-2 group (P ＜0.05).Part Ⅱ]:Both DT-2 and (D)-DT-2 significantly improved the contractile function of vascular ring after being exposed to LPS.Emax was significantly higher,while EC50 was lower in groups DT-2 and (D)-DT-2 than in LPS group (P ＜0.01).Emax was significantly increased,while EC50 was decreased in LPS-(D)-DT-2 group as compared with LPS-DT-2 group (P ＜ 0.05).Conclusion PKG inhibitor can improve the contractile function of the vascular rings incubated with LPS and the efficacy of (D)-DT-2 is better than DT-2 in recovering the vascular reactivity. Key words: cGMP-dependent protein kinase G inhibitor; Lipopolysaccharide; Thoracic aortic rings

Abstract 4110: Attenuation of colon cancer cell adaptation to hypoxia by cGMP-dependent protein kinase

Abstract There is growing evidence for the antitumor effects of cGMP-dependent protein kinase (PKG) in colon cancer cells. We reported recently that ectopically expressed PKG resulted in defective angiogenesis in xenografts, and was associated with reduced levels of vascular-endothelial growth factor (VEGF). In order to better understand the therapeutic potential of this enzyme, the present work has examined the mechanism of VEGF regulation by PKG. In contrast to the SW620 xenografts, PKG had no effect on VEGF expression in SW620 cells grown under standard tissue culture conditions in vitro. However, the increase in VEGF expression observed when the cells were subjected to hypoxic stress was significantly attenuated by PKG at both the mRNA and protein levels. Using luciferase reporter assays, PKG was shown to inhibit hypoxia inducible factor (HIF) transcriptional activity in several colon cancer cell lines, including SW620, HCT116, and HT29. The attenuation of HIF by PKG reflected a more fundamental inhibition of the hypoxic response, which was supported by the ability of PKG expression to block the hypoxia-induced activation of glycolytic genes including enolase and hexokinase 2. The reduced levels of glycolytic enzymes in PKG-expressing cells relative to control cells was associated with reduced glycolysis, mitochondrial activity, and cellular ATP levels under hypoxic conditions. While the inhibition of SW620 cell proliferation occurred independently of PKG expression in a 1% O2 environment, PKG reduced cell viability and increased necrosis under these conditions. These findings demonstrate for the first time that PKG can block the adaptation of colon cancer cells to hypoxia, and highlights this enzyme for further evaluation as a potential target for colon cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4110.

Mutation of protein kinase C phosphorylation site S1076 on α-subunits affects BKCachannel activity in HEK-293 cells

Large conductance, calcium- and voltage-activated potassium (BK(Ca)) channels are important modulators of pulmonary vascular smooth muscle membrane potential, and phosphorylation of BK(Ca) channels by protein kinases regulates pulmonary arterial smooth muscle function. However, little is known about the effect of phosphorylating specific channel subunits on BK(Ca) channel activity. The present study was done to determine the effect of mutating protein kinase C (PKC) phosphorylation site serine 1076 (S1076) on transfected human BK(Ca) channel alpha-subunits in human embryonic kidney (HEK-293) cells, a heterologous expression system devoid of endogenous BK(Ca) channels. Results showed that mutating S1076 altered the effect of PKC activation on BK(Ca) channels in HEK-293 cells. Specifically, the phospho-deficient mutation BK(Ca)-alpha(S1076A)/beta(1) attenuated the excitatory effect of the PKC activator phorbol myristate acetate (PMA) on BK(Ca) channels, whereas the phospho-mimetic mutation BK(Ca)-alpha(S1076E)/beta(1) increased the excitatory effect of PMA on BK(Ca) channels. In addition, the phospho-null mutation S1076A blocked the activating effect of cGMP-dependent protein kinase G (PKG) on BK(Ca) channels. Collectively, these results suggest that specific putative PKC phosphorylation site(s) on human BK(Ca) channel alpha-subunits influences BK(Ca) channel activity, which may subsequently alter pulmonary vascular smooth muscle function and tone.

Opposite effects of cGMP-dependent protein kinase on cGMP production by soluble and particular guanylyl cyclase in adult ventricular myocytes

Background Both particulate (pGC) and soluble guanylyl cyclases (sGC) synthesize cGMP. While sGC is activated by nitric oxide (NO), pGC is activated by natriuretic peptides (NPs) such as ANP or BNP. Physiological effects of cGMP are mainly mediated by cGMP-dependent protein kinase (PKG) and cGMP phosphodiesterases (PDEs), namely PDE2 and PDE5. We hypothesised that PKG may underlie regulatory feedback in cGMP signals produced by pGC and sGC activation in adult rat ventricular myocytes (ARVMs).

Effect of PKG activation on recombinant GABAA receptors.

The effect of cGMP-dependent protein kinase (PKG) on recombinant human alpha 1 beta 2 gamma 2L GABAA receptors expressed in Xenopus oocytes was studied using the two-electrode voltage-clamp technique. The cGMP analog 8BrcGMP (1 mM) produced an increase in GABA-gated chloride currents. Intracellular injection of the PKG inhibitor peptide, PKGI, prevented the 8BrcGMP-mediated increase in the GABA response indicating that 8BrcGMP enhances GABAA receptor function via activation of PKG. Previous studies have shown that PKG phosphorylates a fusion protein corresponding to the intracellular loop of the beta 1 subunit [McDonald and Moss, J. Biol. Chem., 269 (1994) 18111-18117]. In the present study, site-directed mutagenesis of this phosphorylation site (beta 2ser410) failed to eliminate the effects of 8BrcGMP on the GABA response. These results suggest that there may be other sites on the receptor which are regulated by PKG or that PKG phosphorylates other proteins which may influence GABAA receptor function.

Phosphorylation of the inositol 1,4,5-trisphosphate receptor by cyclic GMP-dependent protein kinase.

Cyclic GMP (cGMP) inhibits intracellular calcium ([Ca2+]i) mobilization in vascular smooth muscle cells by a mechanism that is not well understood. Because several studies suggest that cGMP inhibits inositol 1,4,5-trisphosphate (IP3) action, we examined the effects of cGMP-dependent protein kinase on IP3 receptor phosphorylation. The purified IP3 receptor was phosphorylated using either the cGMP- or cAMP-dependent protein kinase in vitro. Phosphorylation was time-dependent and stoichiometric using both kinases. Two-dimensional phosphopeptide mapping, high performance liquid chromatography analysis, and amino acid analysis showed that identical sites were phosphorylated using either kinase, and identified serine 1755 as the site of phosphorylation. The synthetic peptide corresponding to serine 1755 (GRRESLTSFG) was phosphorylated with aKm in the range of 30-40 microM by both kinases. The kinetic analysis revealed that this peptide substrate is the best substrate described for cGMP kinase to date. Vascular smooth muscle cells prelabeled with [32P]orthophosphate and treated with atrial natriuretic peptide or sodium nitroprusside to elevate cGMP also resulted in increased labeling of the IP3 receptor. Phosphorylation of IP3 receptor by cGMP kinase may regulate the function of IP3 receptor in vascular smooth muscle cells and contribute to the effect of cGMP to regulate intracellular calcium levels.

Vimentin is transiently co-localized with and phosphorylated by cyclic GMP-dependent protein kinase in formyl-peptide-stimulated neutrophils.

The effects of cGMP-dependent protein kinase (G-kinase), a major cellular receptor of cGMP, were investigated in activated human neutrophils. Immunocytochemistry demonstrated that G-kinase translocated from a diffuse localization in the cytoplasm to the cytoskeleton and nucleus after stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP), and transiently co-localized with the intermediate filament protein, vimentin. During this time period, the most remarkable co-localization of G-kinase and vimentin was observed between 1-2.5 min stimulation with fMLP. At that time co-localization of G-kinase and vimentin was predominantly confined to filaments which extended from regions adjacent to the nucleus into the uropod. Distinctive localization for only G-kinase was observed at the microtubule organizing center and euchromatin of the nucleus. The filamentous staining pattern for G-kinase and vimentin was enhanced in the presence of 8-Br-cGMP. Coincident with co-localization of G-kinase and vimentin in adherent neutrophils was a transient increase in cGMP levels and an increase in the phosphorylation of vimentin in fMLP-stimulated cells. The increase in cGMP levels was dependent upon cell adherence, was enhanced by preincubating neutrophils with L-arginine (the precursor for nitric oxide synthesis), and attenuated with the nitric oxide synthase inhibitor, NG-monomethyl-L-arginine. Phosphorylation of vimentin in the fMLP-stimulated neutrophil was observed in the presence or absence of exogenous cGMP, although in the presence of low concentrations of 8-Br-cGMP a more rapid phosphorylation of vimentin was observed that correlated with the enhanced co-localization of G-kinase and vimentin. Phosphorylation of vimentin was not observed in non-activated cells treated with 8-Br-cGMP, suggesting that phosphorylation only occurs when G-kinase is co-localized with vimentin. The presence of the protein kinase C inhibitors, staurosporine or H-7, did not inhibit vimentin phosphorylation during fMLP stimulation, while 8-Br-cGMP enhanced phosphorylation in fMLP-treated cells. This suggests that neither protein kinase C nor cAMP-dependent protein kinase catalyze the phosphorylation of vimentin in neutrophils activated by fMLP. These results indicate that vimentin and G-kinase are co-localized in neutrophils and that vimentin is phosphorylated by G-kinase in response to the co-localization of the two proteins. A model for the targeting of G-kinase and vimentin is presented which hypothesizes that the transient redistribution of G-kinase may regulate neutrophil activation.

Effects of 8-bromo-cGMP on Ca2+ levels in vascular smooth muscle cells: possible regulation of Ca2+-ATPase by cGMP-dependent protein kinase.

The effects of 8-bromo-cGMP on intracellular calcium concentrations in cultured rat aortic smooth muscle cells were studied. Both angiotensin II and depolarizing concentrations of K+ stimulated Ca2+ accumulation in the cytoplasm. The increase in Ca2+ due to angiotensin II was associated with an increase in inositol phosphates, while that due to K+ was not. Preincubation of cells with 8-bromo-cGMP (100 microM) caused an inhibition of peak Ca2+ accumulation to either angiotensin II or K+. To probe the mechanism of action of cGMP in vascular smooth muscle, the effects of cGMP-dependent protein kinase on Ca2+-ATPase from the cultured cell particulate material were investigated. Ca2+-activated ATPase was stimulated approximately equal to 2-fold by exogenous calmodulin and up to 4-fold by low concentrations of purified cGMP-dependent protein kinase. The inclusion of both calmodulin and cGMP-dependent protein kinase resulted in an additive stimulation of Ca2+-ATPase. Stimulation of Ca2+-ATPase activity was observed at all Ca2+ concentrations tested (0.01-1.0 microM). cAMP-dependent protein kinase catalytic subunit and protein kinase C were either ineffective or less effective than cGMP-dependent protein kinase in stimulating the Ca2+-ATPase from rat aortic smooth muscle cells. These results suggest a possible mechanism of action for cGMP in mediating decreases in cytosolic Ca2+ through activation of a Ca2+-ATPase and the subsequent removal of Ca2+ from the cell.