scholarly journals Unfair competition governs the interaction of pCPI-17 with myosin phosphatase (PP1-MYPT1)

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Joshua J Filter ◽  
Byron C Williams ◽  
Masumi Eto ◽  
David Shalloway ◽  
Michael L Goldberg
Keyword(s):  
Light Chain ◽  
Active Site ◽  
Slow Rate ◽  
Myosin Light Chain ◽  
Muscle Relaxation ◽  
Smooth Muscles ◽  
Unfair Competition ◽  
Myosin Phosphatase ◽  
Myosin Light Chain Phosphatase

The small phosphoprotein pCPI-17 inhibits myosin light-chain phosphatase (MLCP). Current models postulate that during muscle relaxation, phosphatases other than MLCP dephosphorylate and inactivate pCPI-17 to restore MLCP activity. We show here that such hypotheses are insufficient to account for the observed rapidity of pCPI-17 inactivation in mammalian smooth muscles. Instead, MLCP itself is the critical enzyme for pCPI-17 dephosphorylation. We call the mutual sequestration mechanism through which pCPI-17 and MLCP interact inhibition by unfair competition: MLCP protects pCPI-17 from other phosphatases, while pCPI-17 blocks other substrates from MLCP’s active site. MLCP dephosphorylates pCPI-17 at a slow rate that is, nonetheless, both sufficient and necessary to explain the speed of pCPI-17 dephosphorylation and the consequent MLCP activation during muscle relaxation.

Telokin expression and the effect of hypoxia on its phosphorylation status in smooth muscle cells from small and large pulmonary arteries

2008 ◽  
Vol 294 (6) ◽  
pp. L1166-L1173 ◽  
Author(s):  
Jane A. Madden ◽  
Mark W. Dantuma ◽  
Elena A. Sorokina ◽  
Dorothee Weihrauch ◽  
Jack G. Kleinman
Keyword(s):  
Smooth Muscle ◽  
Muscle Cell ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Muscle Relaxation ◽  
Cerebral Arteries ◽  
Pulmonary Arteries ◽  
Smooth Muscle Relaxation ◽  
Myosin Phosphatase ◽  
Mlc Phosphorylation

Small pulmonary arteries (SPA), <500 μm diameter of the cat, constrict when exposed to hypoxia, whereas larger arteries (large pulmonary arteries; LPA), >800 μm diameter, show little or no response. It is unknown why different contractile responses occur within the same vascular bed, but activator or repressor proteins within the smooth muscle cell (SMC) can modify myosin phosphatase and myosin light chain kinase (MLCK), thereby influencing the phosphorylation state of myosin light chain (MLC) and ultimately, contraction. Telokin, a protein with a sequence identical to the COOH-terminal domain of MLCK, is expressed in smooth muscle where in its phosphorylated state it inhibits myosin phosphatase, binds to unphosphorylated myosin, and helps maintain smooth muscle relaxation. We measured telokin mRNA and telokin protein in smooth muscle from different diameter feline pulmonary arteries and sought to determine whether changes in the phosphorylation status of telokin and MLC occurred during hypoxia. In pulmonary arteries, telokin expression varied inversely with artery diameter, but cerebral arteries showed neither telokin protein nor telokin mRNA. Although telokin and MLC were distributed uniformly throughout the SPA muscle cell cytoplasm, they were not colocalized. During hypoxia, telokin dephosphorylated, and MLC became increasingly phosphorylated in SPA SMC, whereas in LPA SMC there was no change in either telokin or MLC phosphorylation. When LPA SMC were exposed to phenylephrine, MLC phosphorylation increased with no change in telokin phosphorylation. These results suggest that in SPA, phosphorylated telokin may help maintain relaxation under unstimulated conditions, whereas in LPA, telokin's function remains undetermined.

scholarly journals Inhibition of smooth-muscle myosin-light-chain phosphatase by Ruthenium Red

2000 ◽  
Vol 349 (3) ◽  
pp. 797-804 ◽  
Author(s):  
Aki YAMADA ◽  
Osamu SATO ◽  
Minoru WATANABE ◽  
Michael P. WALSH ◽  
Yasuo OGAWA ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Smooth Muscles ◽  
Direct Interaction ◽  
Smooth Muscle Contraction ◽  
Ruthenium Red ◽  
Dependent Manner ◽  
Myosin Light Chain Phosphatase ◽  
Concentration Dependent Manner

Ruthenium Red (RuR) is widely used as an inhibitor of ryanodine receptor Ca2+ release channels, but has additional effects such as the induction of Ca2+ sensitization of contraction of permeabilized smooth muscles. To address the mechanism underlying this process, we examined the effects of RuR on contractility in permeabilized guinea-pig ileum and on the activity of myosin-light-chain phosphatase (MP). RuR increased the force at submaximal [Ca2+] (pCa 6.3) approx. 4-fold. This effect was not observed after thiophosphorylation of MP. RuR also seemed capable of preventing the thiophosphorylation of MP, suggesting a direct interaction of RuR with MP. Consistent with this possibility, smooth-muscle MP was inhibited by RuR in a concentration-dependent manner (IC50 23µM). Exogenous calmodulin significantly increased RuR-induced contraction at pCa 6.3 but had little effect on contraction induced by microcystin at this [Ca2+]. Ca2+-independent contraction was induced by RuR (EC50 843µM) and by microcystin (EC50 59nM) but the maximal force induced by RuR was smaller than that induced by microcystin. The addition of 300µM RuR enhanced the contraction induced by 30nM microcystin but markedly decreased that induced by 1µM microcystin. Such a dual action of RuR on microcystin-induced effects was not observed in experiments using purified MP. We conclude that the RuR-induced Ca2+ sensitization of smooth-muscle contraction is due to the direct inhibition of MP by RuR.

A myosin phosphatase targeting subunit isoform transition defines a smooth muscle developmental phenotypic switch

2000 ◽  
Vol 278 (3) ◽  
pp. C589-C600 ◽  
Author(s):  
Wessel P. Dirksen ◽  
Franjo Vladic ◽  
Steven A. Fisher
Keyword(s):  
Smooth Muscle ◽  
Alternative Splicing ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Muscle Relaxation ◽  
Smooth Muscle Relaxation ◽  
Myosin Phosphatase ◽  
Mrna Isoforms ◽  
Regulatory Myosin Light Chain ◽  
Muscle Tissues

Smooth muscle myosin phosphatase dephosphorylates the regulatory myosin light chain and thus mediates smooth muscle relaxation. The activity of this myosin phosphatase is dependent upon its myosin-targeting subunit (MYPT1). Isoforms of MYPT1 have been identified, but how they are generated and their relationship to smooth muscle phenotypes is not clear. Cloning of the middle section of chicken and rat MYPT1 genes revealed that each gene gave rise to isoforms by cassette-type alternative splicing of exons. In chicken, a 123-nucleotide exon was included or excluded from the mature mRNA, whereas in rat two exons immediately downstream were alternative. MYPT1 isoforms lacking the alternative exon were only detected in mature chicken smooth muscle tissues that display phasic contractile properties, but the isoform ratios were variable. The patterns of expression of rat MYPT1 mRNA isoforms were more complex, with three major and two minor isoforms present in all smooth muscle tissues at varying stoichiometries. Isoform switching was identified in the developing chicken gizzard, in which the exon-skipped isoform replaced the exon-included isoform around the time of hatching. This isoform switch occurred after transitions in myosin heavy chain and myosin light chain (MLC17) isoforms and correlated with a severalfold increase in the rate of relaxation. The developmental switch of MYPT1 isoforms is a good model for determining the mechanisms and significance of alternative splicing in smooth muscle.

scholarly journals Abnormal myosin phosphatase targeting subunit 1 phosphorylation and actin polymerization contribute to impaired myogenic regulation of cerebral arterial diameter in the type 2 diabetic Goto-Kakizaki rat

2016 ◽  
Vol 37 (1) ◽  
pp. 227-240 ◽  
Author(s):  
Khaled S Abd-Elrahman ◽  
Olaia Colinas ◽  
Emma J Walsh ◽  
Hai-Lei Zhu ◽  
Christine M Campbell ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Light Chain ◽  
Actin Polymerization ◽  
Myosin Light Chain ◽  
Intraluminal Pressure ◽  
Myogenic Response ◽  
Myosin Phosphatase ◽  
Myosin Light Chain Phosphatase ◽  
Myogenic Regulation

The myogenic response of cerebral resistance arterial smooth muscle to intraluminal pressure elevation is a key physiological mechanism regulating blood flow to the brain. Rho-associated kinase plays a critical role in the myogenic response by activating Ca2+ sensitization mechanisms: (i) Rho-associated kinase inhibits myosin light chain phosphatase by phosphorylating its targeting subunit myosin phosphatase targeting subunit 1 (at T855), augmenting 20 kDa myosin regulatory light chain (LC20) phosphorylation and force generation; and (ii) Rho-associated kinase stimulates cytoskeletal actin polymerization, enhancing force transmission to the cell membrane. Here, we tested the hypothesis that abnormal Rho-associated kinase-mediated myosin light chain phosphatase regulation underlies the dysfunctional cerebral myogenic response of the Goto-Kakizaki rat model of type 2 diabetes. Basal levels of myogenic tone, LC20, and MYPT1-T855 phosphorylation were elevated and G-actin content was reduced in arteries of pre-diabetic 8–10 weeks Goto-Kakizaki rats with normal serum insulin and glucose levels. Pressure-dependent myogenic constriction, LC20, and myosin phosphatase targeting subunit 1 phosphorylation and actin polymerization were suppressed in both pre-diabetic Goto-Kakizaki and diabetic (18–20 weeks) Goto-Kakizaki rats, whereas RhoA, ROK2, and MYPT1 expression were unaffected. We conclude that abnormal Rho-associated kinase-mediated Ca2+ sensitization contributes to the dysfunctional cerebral myogenic response in the Goto-Kakizaki model of type 2 diabetes.

scholarly journals Arachidonic acid inhibits myosin light chain phosphatase and sensitizes smooth muscle to calcium.

1992 ◽  
Vol 267 (30) ◽  
pp. 21492-21498
Author(s):  
M.C. Gong ◽  
A Fuglsang ◽  
D Alessi ◽  
S Kobayashi ◽  
P Cohen ◽  
...  
Keyword(s):  
Arachidonic Acid ◽  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Myosin Light Chain Phosphatase
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