12 Ca2+/Calmodulin-dependent myosin light-chain kinases

Kamm, Kristine E.; Krueger, Joanna K.; Lin, Pei Ju; Luby-Phelps, Katherine; Zhi, Gang

doi:10.1016/s1040-7952(97)80015-8

Cited by 19 publications

(12 citation statements)

References 33 publications

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“…CSMC transfected with 16D-HSP20 cDNA showed significant decreases in 1) phosphorylation of HSP27 (ser78); 2) phosphorylation of PKC-␣ (ser657); 3) phosphorylation of TM and CaD (ser789); 4) ACh-induced phosphorylation of myosin light chain; 5) ACh-induced association of TM with HSP27; and 6) ACh-induced dissociation of TM from caldesmon (CaD). We thus propose the crucial physiological relevance of molecular signaling switch (phosphorylation state of HSP27 and HSP20), which dictates 1) the phosphorylation states of TM and CaD and 2) their dissociations from each other.relaxation; heat shock protein; molecular signaling switch; molecular mechanical switch; smooth muscle contraction AGONIST-INDUCED INCREASES in intracellular Ca 2ϩ concentrations have been implicated in the initiation of smooth muscle contraction (42,46, 54,61). Although phosphorylation of regulatory myosin light chains (MLC 20 ) by activation of Ca 2ϩ / calmodulin-dependent myosin light chain kinase (MLCK) is the key mechanism for initiation of smooth muscle contraction, inactivation of myosin light chain phosphatase (MLCP) is the key mechanism for maintenance of smooth muscle contraction (25).…”

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“…relaxation; heat shock protein; molecular signaling switch; molecular mechanical switch; smooth muscle contraction AGONIST-INDUCED INCREASES in intracellular Ca 2ϩ concentrations have been implicated in the initiation of smooth muscle contraction (42,46,54,61). Although phosphorylation of regulatory myosin light chains (MLC 20 ) by activation of Ca 2ϩ / calmodulin-dependent myosin light chain kinase (MLCK) is the key mechanism for initiation of smooth muscle contraction, inactivation of myosin light chain phosphatase (MLCP) is the key mechanism for maintenance of smooth muscle contraction (25).…”

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Phosphorylated HSP20 modulates the association of thin-filament binding proteins: caldesmon with tropomyosin in colonic smooth muscle

Somara

Gilmont

Varadarajan

et al. 2010

American Journal of Physiology-Gastrointestinal and Liver Physi

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Somara S, Gilmont RR, Varadarajan S, Bitar KN. Phosphorylated HSP20 modulates the association of thin-filament binding proteins: caldesmon with tropomyosin in colonic smooth muscle. Am J Physiol Gastrointest Liver Physiol 299: G1164 -G1176, 2010. First published September 9, 2010 doi:10.1152/ajpgi.00479.2009.-Small heat shock proteins HSP27 and HSP20 have been implicated in regulation of contraction and relaxation in smooth muscle. Activation of PKC-␣ promotes contraction by phosphorylation of HSP27 whereas activation of PKA promotes relaxation by phosphorylation of HSP20 in colonic smooth muscle cells (CSMC). We propose that the balance between the phosphorylation states of HSP27 and HSP20 represents a molecular signaling switch for contraction and relaxation. This molecular signaling switch acts downstream on a molecular mechanical switch [tropomyosin (TM)] regulating thin-filament dynamics. We have examined the role of phosphorylation state(s) of HSP20 on HSP27-mediated thin-filament regulation in CSMC. CSMC were transfected with different HSP20 phosphomutants. These transfections had no effect on the integrity of actin cytoskeleton. Cells transfected with 16D-HSP20 (phosphomimic) exhibited inhibition of acetylcholine (ACh)-induced contraction whereas cells transfected with 16A-HSP20 (nonphosphorylatable) had no effect on ACh-induced contraction. CSMC transfected with 16D-HSP20 cDNA showed significant decreases in 1) phosphorylation of HSP27 (ser78); 2) phosphorylation of PKC-␣ (ser657); 3) phosphorylation of TM and CaD (ser789); 4) ACh-induced phosphorylation of myosin light chain; 5) ACh-induced association of TM with HSP27; and 6) ACh-induced dissociation of TM from caldesmon (CaD). We thus propose the crucial physiological relevance of molecular signaling switch (phosphorylation state of HSP27 and HSP20), which dictates 1) the phosphorylation states of TM and CaD and 2) their dissociations from each other.relaxation; heat shock protein; molecular signaling switch; molecular mechanical switch; smooth muscle contraction AGONIST-INDUCED INCREASES in intracellular Ca 2ϩ concentrations have been implicated in the initiation of smooth muscle contraction (42,46, 54,61). Although phosphorylation of regulatory myosin light chains (MLC 20 ) by activation of Ca 2ϩ / calmodulin-dependent myosin light chain kinase (MLCK) is the key mechanism for initiation of smooth muscle contraction, inactivation of myosin light chain phosphatase (MLCP) is the key mechanism for maintenance of smooth muscle contraction (25). However, maintenance of force upon decrease in intracellular calcium concomitant with decrease in phosphorylation of MLC 20 is associated with thin-filament regulation (18,36,38,64). Thin-filament regulation explains the maintenance of tone at low MLC 20 phosphorylation. Thin-filament regulation modulates the interaction of actin molecules of the thin filament with myosin heads of the thick filament for contraction to occur (10,20,53,65).Relaxation of smooth muscle occurs either as a result of removal of the con...

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confidence: 99%

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confidence: 99%

Phosphorylated HSP20 modulates the association of thin-filament binding proteins: caldesmon with tropomyosin in colonic smooth muscle

Somara

Gilmont

Varadarajan

et al. 2010

American Journal of Physiology-Gastrointestinal and Liver Physi

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“…Ca 2ϩ binds to calmodulin (CaM) and activates myosin light chain kinase (MLCK) (16). MLCK regulates myosin by phosphorylating the 20-kDa myosin regulatory light chain (MRLC) at Ser 19 (41). Ser 19 -MRLC phosphorylation increases myosin's actin-activated ATPase activity by approximately 1,000-fold (28).…”

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Cooperative attachment of cross bridges predicts regulation of smooth muscle force by myosin phosphorylation

Rembold¹,

Wardle²,

Wingard³

et al. 2004

American Journal of Physiology-Cell Physiology

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Serine 19 phosphorylation of the myosin regulatory light chain (MRLC) appears to be the primary determinant of smooth muscle force development. The relationship between MRLC phosphorylation and force is nonlinear, showing that phosphorylation is not a simple switch regulating the number of cycling cross bridges. We reexamined the MRLC phosphorylation-force relationship in slow, tonic swine carotid media; fast, phasic rabbit urinary bladder detrusor; and very fast, tonic rat anococcygeus. We found a sigmoidal dependence of force on MRLC phosphorylation in all three tissues with a threshold for force development of approximately 0.15 mol P(i)/mol MRLC. This behavior suggests that force is regulated in a highly cooperative manner. We then determined whether a model that employs both the latch-bridge hypothesis and cooperative activation could reproduce the relationship between Ser(19)-MRLC phosphorylation and force without the need for a second regulatory system. We based this model on skeletal muscle in which attached cross bridges cooperatively activate thin filaments to facilitate cross-bridge attachment. We found that such a model describes both the steady-state and time-course relationship between Ser(19)-MRLC phosphorylation and force. The model required both cooperative activation and latch-bridge formation to predict force. The best fit of the model occurred when binding of a cross bridge cooperatively activated seven myosin binding sites on the thin filament. This result suggests cooperative mechanisms analogous to skeletal muscle that will require testing.

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“…When the intracellular Ca 2ϩ concentration increases upon stimulation of cells by Ca 2ϩ influx through Ca 2ϩ channels in the plasma membrane or through Ca 2ϩ release from intracellular Ca 2ϩ stores, Ca 2ϩ binds to calmodulin. Ca 2ϩ /calmodulin binds to the calmodulin-binding sequence of the kinase, resulting in displacement of the autoinhibitory segment and exposure of the catalytic site for RLC phosphorylation (12,13).…”

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Properties of Filament-bound Myosin Light Chain Kinase

Lin

Luby-Phelps

Stull

1999

Journal of Biological Chemistry

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Myosin light chain kinase binds to actin-containing filaments from cells with a greater affinity than to Factin. However, it is not known if this binding in cells is regulated by Ca 2؉ /calmodulin as it is with F-actin. Therefore, the binding properties of the kinase to stress fibers were examined in smooth muscle-derived A7r5 cells. Full-length myosin light chain kinase or a truncation mutant lacking residues 2-142 was expressed as chimeras containing green fluorescent protein at the C terminus. In intact cells, the full-length kinase bound to stress fibers, whereas the truncated kinase showed diffuse fluorescence in the cytoplasm. After permeabilization with saponin, the fluorescence from the truncated kinase disappeared, whereas the fluorescence of the full-length kinase was retained on stress fibers. Measurements of fluorescence intensities and fluorescence recovery after photobleaching of the full-length myosin light chain kinase in saponin-permeable cells showed that Ca 2؉ /calmodulin did not dissociate the kinase from these filaments. However, the filament-bound kinase was sufficient for Ca 2؉ -dependent phosphorylation of myosin regulatory light chain and contraction of stress fibers. Thus, dissociation of myosin light chain kinase from actin-containing thin filaments is not necessary for phosphorylation of myosin light chain in thick filaments. We note that the distance between the N terminus and the catalytic core of the kinase is sufficient to span the distance between thin and thick filaments.

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12 Ca2+/Calmodulin-dependent myosin light-chain kinases

Cited by 19 publications

References 33 publications

Phosphorylated HSP20 modulates the association of thin-filament binding proteins: caldesmon with tropomyosin in colonic smooth muscle

Phosphorylated HSP20 modulates the association of thin-filament binding proteins: caldesmon with tropomyosin in colonic smooth muscle

Cooperative attachment of cross bridges predicts regulation of smooth muscle force by myosin phosphorylation

Properties of Filament-bound Myosin Light Chain Kinase

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