Mitogen-activated protein kinase inhibitors suppress prostaglandin F(2alpha)-induced myosin-light chain phosphorylation and contraction in iris sphincter smooth muscle

Casein kinase 2 inhibition impairs spontaneous and oxytocin-induced contractions in late pregnant mouse uterus

NEW FINDINGS

What is the central question of this study? Does the inhibition of the protein kinase casein kinase 2 (CK2) alter the uterine contractility? What is the main finding and its importance? Inhibition of CK2 impaired the spontaneous and oxytocin-induced contractility in late pregnant mouse uterus. This finding suggests that CK2 is a novel pathway mediating oxytocin-induced contractility in the uterus and thus opens up the possibility for this class of drugs to be developed as a new class of tocolytics.

ABSTRACT

The protein kinase casein kinase 2 (CK2) is a ubiquitously expressed serine or threonine kinase known to phosphorylate a number of substrates. The aim of this study was to assess the effect of CK2 inhibition on spontaneous and oxytocin-induced uterine contractions in 19 day pregnant mice. The CK2 inhibitor CX-4945 elicited a concentration-dependent relaxation in late pregnant mouse uterus. CX-4945 and another selective CK2 inhibitor, apigenin, also inhibited the oxytocin-induced contractile response in late pregnant uterine tissue. Apigenin also blunted the prostaglandin F_2α response, but CX-4945 did not. Casein kinase 2 was located in the lipid raft fractions of the cell membrane, and disruption of lipid rafts was found to reverse its effect. The results of the present study suggest that CK2, located in lipid rafts of the cell membrane, is an active regulator of spontaneous and oxytocin-induced uterine contractions in the late pregnant mouse.

MAPK mediates PKC-dependent contraction of cat esophageal and lower esophageal sphincter circular smooth muscle

Esophageal (ESO) circular muscle contraction and lower esophageal sphincter (LES) tone are PKC dependent. Because MAPKs may be involved in PKC-dependent contraction, we examined ERK1/ERK2 and p38 MAPKs in ESO and LES. In permeabilized LES muscle cells, ERK1/2 antibodies reduced 1,2-dioctanoylglycerol (DG)- and threshold ACh-induced contraction, which are PKC dependent, but not maximal ACh, which is calmodulin dependent. LES tone was reduced by the ERK1/2 kinase inhibitor PD-98059 and by the p38 MAPK inhibitor SB-203580. In permeable ESO cells, ACh contraction was reduced by ERK1/ERK2 and p38 MAPK antibodies and by PD-98059 and SB-203580. ACh increased MAPK activity and phosphorylation of MAPK and of p38 MAPK. The 27-kDa heat shock protein (HSP27) antibodies reduced ACh contraction. HSP27 and p38 MAPK antibodies together caused no greater inhibition than either one alone. p38 MAPK and HSP27 coprecipitated after ACh stimulation, suggesting that HSP27 is linked to p38 MAPK. These data suggest that PKC-dependent contraction in ESO and LES is mediated by the following two distinct MAPK pathways: ERK1/2 and HSP27-linked p38 MAPK.

Essential role of growth factor receptor-mediated signal transduction through the mitogen-activated protein kinase pathway in early embryogenesis of the echinoderm

In this study it was shown that growth factor receptors (GFR) play a crucial role in early embryogenesis of the echinoderms Hemicentrotus pulcherrimus and Clypeaster japonicus by transmitting signals to the mitogen-activated protein kinase (MAPK) pathway. The phosphorylation ratio of extracellular signal-regulated kinase 1 (ERK1) changed dynamically during early embryogenesis and showed a peak at the swimming blastula (sBl) stage. Suramin, an inhibitor of GFR, when applied during the sBl stage perturbed morphogenesis, including primary mesenchyme cell (PMC) migration, cell proliferation, archenteron elongation, spiculogenesis, pigment cell differentiation and phosphorylation of myosin light chains (MLC). Genistein, a receptor-type protein tyrosine kinase inhibitor, severely inhibited PMC migration, gastrulation and the phosphorylation of MLC. Manumycin A, a Ras inhibitor, inhibited spiculogenesis and invagination. PD98059, a MAPK/ERK kinase inhibitor, perturbed early PMC migration and pigment cell differentiation, but not spiculogenesis and gastrulation (although these two events were significantly delayed). PMC ingression was not perturbed by genistein, suramin, manumycin A or PD98059. All of the inhibitors perturbed the phosphorylation of ERK1, which was completely restored by exogenous platelet-derived growth factor (PDGF)-AB. PDGF-AB also partially restored elongation of the archenteron by restoring cell proliferation that had been perturbed by suramin.

Evidence for the role of p38 MAP kinase in hypoxia-induced pulmonary vasoconstriction

Mitogen-activated protein (MAP) kinases regulate smooth muscle cell contraction. Hypoxia contracts pulmonary arteries by mechanisms that are incompletely understood. We hypothesized that hypoxic contraction of pulmonary arteries involves activation of the MAP kinases. To test this hypothesis, we studied the effects of SB-202190, a p38 MAP kinase inhibitor, PD-98059 and UO-126, two structurally different MEKK inhibitors, and anisomycin, a stimulator of p38 MAP kinase on acute hypoxia-induced contraction in rat conduit pulmonary artery rings precontracted with phenylephrine or KCl. Hypoxia induced a transient contraction, followed by a relaxation, and then a slowly developing sustained contraction. Hypoxia also significantly increased phosphorylation of p38 MAP kinase. SB-202190 did not affect the transient phase but abrogated the sustained phase of hypoxic contraction, whereas anisomycin enhanced both phases of contraction. SB-202190 also attenuated and anisomycin enhanced the phenylephrine-induced contraction. In contrast, PD-98059 and UO-126 had minimal effects on either hypoxic or phenylephrine-induced contraction. None of the treatments modified KCl-induced contraction. We conclude that p38, but not the ERK1/ERK2 MAP kinase pathway, mediates the sustained phase of hypoxic contraction in isolated rat pulmonary arteries.

Involvement of p44/42 mitogen-activated protein kinases in regulating angiotensin II- and endothelin-1-induced contraction of rat thoracic aorta

In order to elucidate the signal transduction pathway of vascular smooth muscle contraction induced by the activation of receptors for angiotensin II and endothelin-1, we examined whether tyrosine kinases and mitogen-activated protein (MAP) kinases are involved in the development of force of contraction in the rat aorta. Isolated aortic smooth muscles without endothelium were incubated in a modified Krebs-Henseleit solution and stimulated with angiotensin II (100 nM) or endothelin-1 (10 nM). A tyrosine kinase inhibitor genistein (10 microM) reduced the angiotensin II- and endothelin-1-induced aortic contraction, while 10 microM of daidzein (an inactive analogue of genistein) did not. The K(+) depolarization-induced contraction was not attenuated by 10 microM of genistein. Selective inhibitors of MAP kinase/extracellular signal-regulated kinase (Erk) kinase (MEK) such as PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] and U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] inhibited the angiotensin II- and endothelin-1-induced vasocontraction. The p44/42 MAP kinases were phosphorylated in cultured aortic smooth muscle cells and in physiologically contracted aortic vessels stimulated with angiotensin II and endothelin-1 for 5 min. The angiotensin II- and endothelin-1-induced phosphorylations of p44/42 MAP kinases were inhibited by PD98059 as well as U0126 in the intact aorta. These results suggest that the activation of genistein-sensitive tyrosine kinases and p44/42 MAP kinases is involved in the angiotensin II- and endothelin-1-induced rat aortic contraction.

Myosin light chain phosphorylation facilitates in vivo myosin filament reassembly after mechanical perturbation

Phosphorylation of the 20-kDa regulatory myosin light chain (MLC) of smooth muscle is known to cause monomeric myosins in solution to self-assemble into thick filaments. The role of MLC phosphorylation in thick filament formation in intact muscle, however, is not clear. It is not known whether the phosphorylation is necessary to initiate thick filament assembly in vivo. Here we show, by using a potent inhibitor of MLC kinase (wortmannin), that the MLC phosphorylation and isometric force in trachealis muscle could be abolished without affecting calcium transients. By measuring cross-sectional densities of the thick filaments electron microscopically, we also show that inhibition of MLC phosphorylation alone did not cause disassembly of the filaments. The unphosphorylated thick filaments, however, partially dissolved when the muscle was subjected to oscillatory strains (which caused a 25% decrease in the thick filament density). The postoscillation filament density recovered to the preoscillation level only when wortmannin was removed and the muscle was stimulated. The data suggest that in vivo thick filament reassembly after mechanical perturbation is facilitated by the cyclic MLC phosphorylation associated with repeated stimulation.

Cross talk between cyclic nucleotides and polyphosphoinositide hydrolysis, protein kinases, and contraction in smooth muscle

This article provides an update of a minireview published in 1996 (Abdel-Latif AA. Proc Soc Exp Biol Med 211:163-177, 1996), the purpose of which was to examine in nonvascular smooth muscle the biochemical and functional cross talk between the sympathetic nervous system, which governs the formation of cAMP and muscle relaxation, and the parasympathetic nervous system, which governs the generation of IP3 and diacylglycerol, from the polyphosphoinositides, Ca2+ mobilization, and contraction. This review examines further evidence, both from nonvascular and vascular smooth muscle, for cross talk between the cyclic nucleotides, cAMP and cGMP via their respective protein kinases, and the Ca2+-dependent- and Ca2+-independent-signaling pathways involved in agonist-induced contraction. These include the IP3-Ca2+-CaM- myosin light chain kinase (MLCK) pathway and the Ca2+-independent pathways, including protein kinase C-, MAP kinase-, and Rho-kinase. In addition, MLC phosphorylation and contraction can also be increased by a decrease in myosin phosphatase activity. A summary of the cross talk between the cyclic nucleotides and these signaling pathways was presented. In smooth muscle, there are several targets for cyclic nucleotide inhibition and consequent relaxation, including the receptor, G proteins, phospholipase C-beta1-4 isoforms, IP3 receptor, Ca2+ mobilization, MLCK, MAP kinase, Rho-kinase, and myosin phosphatase. While significant progress has been made in the past four years on this cross talk, the precise mechanisms underlying the biochemical basis for the cyclic nucleotide inhibition of Ca2+ mobilization and consequently muscle contraction remain to be established. Although it is well established that second-messenger cross talk plays an important role in smooth muscle relaxation, the many sources which exist in smooth muscle for Ca2+ mobilization, coupled with the multiple signaling pathways involved in agonist-induced contraction, contribute appreciably to the difficulties found by many investigators in identifying the targets for cyclic nucleotide inhibition and consequent relaxation. Better methodology and more novel interdisciplinary approaches are required for elucidating the mechanism(s) of cAMP- and cGMP-inhibition of smooth muscle contraction.