Differential Regulation of Myosin Regulatory Light Chain Phosphorylation by Protein Kinase C Isozymes in Human Uterine Myocytes

2018 ◽  
Vol 26 (7) ◽  
pp. 988-996
Author(s):  
Bryan F. Mitchell ◽  
Mei Chi ◽  
Elle Surgent ◽  
Bailey M. Sorochan ◽  
Curtis N. Tracey ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Ex Vivo ◽  
Neonatal Morbidity ◽  
The Novel ◽  
Uterine Contractility ◽  
Uterine Activity ◽  
Kinase C

Background: Preterm birth is the most common cause of neonatal morbidity and mortality and a common precedent to lifelong disability. Current treatment has minimal efficacy. Objective: We assessed the role of isozymes of the protein kinase C (PKC) family in regulating the phosphorylation of myosin regulatory light chains (RLCs), which regulate uterine contractility. We also explored the mechanisms through which these isozymes function. Study Design: We used a previously characterized and validated quantitative in-cell Western (ICW) assay to measure site-specific phosphorylations on myosin RLC and CPI-17. Cultures of human uterine myocytes (hUM) were treated with the potent contractile stimulant oxytocin to induce uterine contractility or a pharmacological mimic of diacyl-glycerol to stimulate the conventional and novel isozymes of the PKC family. Combinations of isozyme-selective inhibitors were used to determine the effects of the conventional and novel classes of isozymes. Results: Stimulation of PKC using phospho-dibutyrate caused immediate, concentration-dependent inhibition of uterine activity ex vivo. Using the ICW assay with hUM, the oxytocin-stimulated increase in the pro-contractile phosphorylations of myosin RLCs at serine19 and threonine18 was completely inhibited by prior treatment with phorbol-12-myristate-13-acetate, which stimulates both convention and novel classes of isozymes. Our results suggest that the conventional class of isozymes cause a reduction in phosphorylations at serine19 and threonine18 by reducing activity of myosin light chain kinase. The novel class of isozymes has 2 mechanisms of action: the first is activation of CPI-17 through phosphorylation at threonine38, which results in reduced activity of myosin light chain phosphatase and increased levels of activated myosin RLC; the second is increased phosphorylation of the N-terminal region of myosin RLC. Conclusions: Specific agonists for the conventional isozymes or inhibitors of the novel isozymes of the PKC family could be useful pharmacological agents for regulation of uterine activity.

scholarly journals The activation-induced decrease in the platelet surface expression of the glycoprotein Ib-IX complex is reversible

Blood ◽  
1994 ◽  
Vol 83 (12) ◽  
pp. 3562-3573 ◽  
Author(s):  
AD Michelson ◽  
SE Benoit ◽  
MH Kroll ◽  
JM Li ◽  
MJ Rohrer ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Light Chain ◽  
Myosin Light Chain Kinase ◽  
Myosin Light Chain ◽  
Surface Expression ◽  
Platelet Surface ◽  
Kinase C ◽  
Von Willebrand ◽  
Willebrand Factor

Abstract Thrombin decreases the platelet surface expression of the glycoprotein (GP) Ib-IX complex. To determine whether this effect is reversible, flow cytometric studies were performed with GPIb-IX-specific monoclonal antibodies. In both whole blood and washed platelet systems, incubation of platelets with thrombin or a combination of adenosine diphosphate and epinephrine resulted in a maximal decrease of the platelet surface expression of GPIb-IX within 5 minutes, after which there was a time- dependent return of the platelet surface GPIb-IX complex, which was maximal by 60 minutes. Exposure of the same platelets to additional exogenous thrombin resulted in a second decrease in platelet surface GPIb-IX, followed by a second reconstitution of platelet surface GPIb- IX. Throughout these experiments there was no measurable release from the platelets of glycocalicin (a proteolytic fragment of GPIb). Experiments in which platelets were preincubated with a biotinylated GPIb-specific MoAb showed that the GPIb molecules that returned to the platelet surface were the same molecules that had been translocated to the intraplatelet pool. The GPIb molecules that returned to the platelet surface were functionally competent to bind von Willebrand factor, as determined by ristocetin-induced platelet agglutination and ristocetin-induced binding of exogenous von Willebrand factor. Inhibitors of protein kinase C and myosin light-chain kinase enhanced the reexpression of platelet surface GPIb. In summary, the activation- induced decrease in the platelet surface expression of the GPIb-IX complex is reversible. Inactivation of protein kinase C and myosin light-chain kinase are important mechanisms in the reexpression of the platelet surface GPIb-IX complex.

scholarly journals Isolation and characterization of protein kinase C from Y-1 adrenal cell cytoskeleton.

1989 ◽  
Vol 108 (2) ◽  
pp. 553-567 ◽  
Author(s):  
V Papadopoulos ◽  
P F Hall
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Phorbol Esters ◽  
Intact Cells ◽  
Adrenal Cells ◽  
Isolation And Characterization ◽  
Kinase C

The cytoskeletons of Y-1 mouse adrenal tumor cells contain a calcium and phospholipid-dependent protein kinase (protein kinase C) that is bound sufficiently tight to resist extraction by 0.5% Triton but not by 1.0% Triton. The enzyme has been purified to near homogeneity from cytoskeleton and cytosol. It shows features typical of this type of kinase, namely a requirement for Ca2+ and phospholipid, stimulation by tumor promoters but not by nontumor-promoting phorbol esters, and inhibition by trifluoperazine. The enzyme shows specificity for four substrates found in the cytoskeleton, namely 80, 33, 20, and 18 kD. The first three substrates are phosphorylated by the enzyme; the fourth is dephosphorylated and is therefore affected by the kinase indirectly. The 80-kD protein is the kinase enzyme itself which is autophosphorylated in vitro and in the cytoskeleton. The 20-kD protein is myosin light chain. The 33- and 18-kD proteins are unidentified. The same substrates were phosphorylated when Y-1 cells were permeabilized with digitonin and incubated with [gamma-32P]ATP and phorbol-12-myristate-13-acetate. Partly purified protein kinase C changes the extent of phosphorylation of the same substrates when added to cytoskeletons previously extracted to remove endogenous protein kinase C. Addition of Ca2+, phosphatidylserine, and phorbol-12-myristate-13-acetate to cytoskeletons, and addition of these three agents plus protein kinase C to extracted cytoskeletons, causes these structures to undergo a rapid and extensive rounding. A similar change is induced in intact cells by addition of phorbol ester. It is concluded that protein kinase C is capable of changing the shape of adrenal cells by an action that involves autophosphorylation and phosphorylation of myosin light chain. This response may in turn be related to the steroidogenic responses to ACTH and cyclic AMP.

scholarly journals Angiotensin Receptor II type 1 and the activation of Myosin Light-Chain Kinase and Protein Kinase C-βII. Mini Review.

2019 ◽  
Author(s):  
Gerry A. Smith
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Light Chain ◽  
Myosin Light Chain Kinase ◽  
Myosin Light Chain ◽  
Troponin I ◽  
Kinase C ◽  
Skeletal Muscle Contraction ◽  
Agonist Property

The involvement of the angiotensin II type 1 receptor in the Frank-Starling Law of the Heart, where the various activations are very limited, allows simple analysis of the kinase systems involved and thence extrapolation of the mechanism to that of angiotensin control of activation of cardiac and skeletal muscle contraction. The involvement of phosphorylation of the myosin light chain in the control of contraction is accepted but not fully understood. The involvement of troponin-I phosphorylation is also indicated but of unknown mechanism. There is no known signal for activation of myosin light chain kinase or Protein Kinase C-βII other than Ca2+/calmodulin but the former is constitutively active and thus has to be under control of a regulated inhibitor the latter kinase may also be the same. Ca2+/calmodulin is not activated in Frank-Starling, i.e. there are no diastolic or systolic [Ca2+] changes. I suggest here that that the regulated inhibition is by myosin light chain phosphatase and/or β-arrestin. Angiotensin activation is by translocation of the β-arrestin from the sarcoplasm to the PM thus reducing its inhibition in the sarcoplasm, this reduced inhibition has been wrongly attributed to a mythical downstream agonist property of β-arrestin.

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