Reconstitution of protein kinase C-induced contractile Ca2+ sensitization in Triton X-100-demembranated rabbit arterial smooth muscle

Department of Physiology and Biophysics, Georgetown University Medical Center, Washington, DC 20007, USA.
The Journal of Physiology (Impact Factor: 5.04). 11/1999; 520 Pt 1(1):139-52. DOI: 10.1111/j.1469-7793.1999.00139.x
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1. Triton X-100-demembranated smooth muscle loses Ca2+-sensitizing responsiveness to protein kinase C (PKC) activators while intact and alpha-toxin-permeabilized smooth muscles remain responsive. We attempted to reconstitute the contractile Ca2+ sensitization by PKC in the demembranated preparations. 2. Western blot analyses showed that the content of the PKC alpha-isoform (PKCalpha) was markedly reduced and that the smooth muscle-specific protein phosphatase-1 inhibitor protein CPI-17 was not detectable, while the amount of calponin and actin still remained similar to those of intact strips. 3. Unphosphorylated recombinant CPI-17 alone induced a small but significant contraction at constant Ca2+. Isoform-selective PKC inhibitors inhibited unphosphorylated but not pre-thiophosphorylated CPI-17-induced contraction, suggesting that in situ conventional PKC isoform(s) can phosphorylate CPI-17. 4. Exogenously replenishing PKCalpha alone did not induce potentiation of contraction and only slowly increased myosin light chain (MLC) phosphorylation at submaximal Ca2+. 5. PKC in the presence of CPI-17, but not the [T38A]-CPI mutant, markedly induced potentiation of both contraction and MLC phosphorylation. CPI-17 itself was phosphorylated. 6. In in vitro experiments, CPI-17 was a much better substrate for PKCalpha than calponin, caldesmon, MLC and myosin. 7. Our results indicate that PKC requires CPI-17 phosphorylation at Thr-38 but not calponin for reconstitution of the contractile Ca2+ sensitization in the demembranated arterial smooth muscle.

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    • "Since we focused on sustained MLC phosphorylation, our mathematical model does not include MLCK signaling. It is known that CPI-17 inhibits myosin phosphatase in a PKC-mediated phosphorylation-dependent manner [42]. However, thrombin does not induce significant phosphorylation of CPI-17 in endothelial cells [43]. "
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    ABSTRACT: Myosin light chain (MLC) phosphorylation plays important roles in various cellular functions such as cellular morphogenesis, motility, and smooth muscle contraction. MLC phosphorylation is determined by the balance between activities of Rho-associated kinase (Rho-kinase) and myosin phosphatase. An impaired balance between Rho-kinase and myosin phosphatase activities induces the abnormal sustained phosphorylation of MLC, which contributes to the pathogenesis of certain vascular diseases, such as vasospasm and hypertension. However, the dynamic principle of the system underlying the regulation of MLC phosphorylation remains to be clarified. Here, to elucidate this dynamic principle whereby Rho-kinase regulates MLC phosphorylation, we developed a mathematical model based on the behavior of thrombin-dependent MLC phosphorylation, which is regulated by the Rho-kinase signaling network. Through analyzing our mathematical model, we predict that MLC phosphorylation and myosin phosphatase activity exhibit bistability, and that a novel signaling pathway leading to the auto-activation of myosin phosphatase is required for the regulatory system of MLC phosphorylation. In addition, on the basis of experimental data, we propose that the auto-activation pathway of myosin phosphatase occurs in vivo. These results indicate that bistability of myosin phosphatase activity is responsible for the bistability of MLC phosphorylation, and the sustained phosphorylation of MLC is attributed to this feature of bistability.
    PLoS ONE 06/2012; 7(6):e39269. DOI:10.1371/journal.pone.0039269 · 3.23 Impact Factor
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    • "In smooth muscle, CPI-17 is entirely lost after Triton X-100 permeabilization, is reduced by 65% after b-escin permeabilization, and is preserved by a-toxin permeabilization (Kitazawa et al. 1999). Moreover, PKCa/b and ROCK, but not MYPT1 nor MLCK, are also lost from tissues permeabilized with Triton X-100 (Weber et al. 2000; Araki et al. 2001). "
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    Journal of Muscle Research and Cell Motility 06/2011; 32(2):77-88. DOI:10.1007/s10974-011-9253-x · 2.09 Impact Factor
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    • "and [ Thr696 ] antibodies A MYPT1 fragment ( 658 – 714 ) was phosphorylated with ROCK alone , PKA alone , or a mixture of ROCK and PKA . Twenty nanograms of phosphorylated or unphosphorylated fragments were applied onto a urea - lutidine gel ( A ; Kitazawa et al . 1999 ) to separate mono - and di - phosphorylated bands from un - phosphorylated bands . The gel was stained with Coomassie Brilliant Blue ( A ) . The relative intensity of monophosphorylated band in A was 2 , 61 , 62 and 38% , and the diphosphorylated band intensity was 0 , 39 , 38 and 62% for control , ROCK , PKA and ROCK+PKA , respectivel"
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    ABSTRACT: Nitric oxide (NO) from endothelium is a major mediator of vasodilatation through cGMP/PKG signals that lead to a decrease in Ca(2+) concentration. In addition, NO-mediated signals trigger an increase in myosin light chain phosphatase (MLCP) activity. To evaluate the mechanism of NO-induced relaxation through MLCP deinhibition, we compared time-dependent changes in Ca(2+), myosin light chain (MLC) phosphorylation and contraction to changes in phosphorylation levels of CPI-17 at Thr38, RhoA at Ser188, and MYPT1 at Ser695, Thr696 and Thr853 in response to sodium nitroprusside (SNP)-induced relaxation in denuded rabbit femoral artery. During phenylephrine (PE)-induced contraction, SNP reduced CPI-17 phosphorylation to a minimal value within 15 s, in parallel with decreases in Ca(2+) and MLC phosphorylation, followed by a reduction of contractile force having a latency period of about 15 s. MYPT1 phosphorylation at Ser695, the PKG-target site, increased concurrently with relaxation. Phosphorylation of RhoA, MYPT1 Thr696 and Thr853 differed significantly at 5 min but not within 1 min of SNP exposure. Inhibition of Ca(2+) release delayed SNP-induced relaxation while inhibition of Ca(2+) channel, BK(Ca) channel or phosphodiesterase-5 did not. Pretreatment of resting artery with SNP suppressed an increase in Ca(2+), contractile force and phosphorylation of MLC, CPI-17, MYPT1 Thr696 and Thr853 at 10 s after PE stimulation, but had no effect on phorbol ester-induced CPI-17 phosphorylation. Together, these results suggest that NO production suppresses Ca(2+) release, which causes an inactivation of PKC and rapid CPI-17 dephosphorylation as well as MLCK inactivation, resulting in rapid MLC dephosphorylation and relaxation.
    The Journal of Physiology 06/2009; 587(Pt 14):3587-603. DOI:10.1113/jphysiol.2009.172189 · 5.04 Impact Factor
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