Inhibitors of Mitogen-activated Protein Kinase Kinase Potentiated Agonist-induced Airway Smooth Muscle Contraction

Content Provider	Semantic Scholar
Author	Alan Koh H. M. Fred Wong W. S.
Copyright Year	2002
Abstract	PD 098059 (2'-amino-3' methoxyflavone) has been shown to inhibit the activation of mitogen-activated protein kinase kinase-1 (MAPKK 1) by Raf-1 or mitogen activated and extracellular regulated kinase kinase (MEK kinase) in vitro while Ħ [1,4-diamino-2,3dicyano-1,4-bis(2-aminophenylthio)butadiene] was found to functionally antagonized AP-1 transcriptional activity via noncompetitive inhibition of dual specificity kinase, MEK 1 and MEK 2. The present study was conducted to examine the potentiation effects of these two MAPKK inhibitors, PD 098059 and Ħ, on agonistinduced bronchial smooth muscle contraction. PD 098059 (10-50μM) pontentiated both histamineand leukotriene D4 (LTD4)induced bronchial smooth muscle contraction. 30μM of Ħ has potentiated the LTD4induced bronchial smooth muscle contraction, as well as that by histamine. Our data show that MAPKK inhibitors can potentiate agonistinduced airway smooth muscle contraction in vitro, probably via the inhibition of relaxant prostanoids production. INTRODUCTION MAPKK is part of the Ras/MAPK signaling pathway that engages in various activities such as metabolic processes, cell cycles, cell migration, cell shape, cell proliferation as well as cell differentiation. PD 098059 and Ħ (Fig. 1) are two well-known specific MAPKK inhibitors that have been used to study the importance of this pathway (Alessi et al., 1995; Favata et al., 1998). Histamine and LTD4 are the two main mediators that cause bronchoconstriciton by mediating a certain degree of tone in airway smooth muscle in vitro (Ellis and Undem, 1994). Our previous study showed that histamine-induced bronchial contraction was significantly potentiated by PD 098059 (Tsang et al., 1998). In the present study, we examined the potentiation effects of PD 098059 and Ħ on agonistinduced bronchial smooth muscle contraction. Our findings show PD 098059 (10-50μM) and Ħ (30μM) potentiated both histamineand LTD4-induced bronchial smooth muscle contractions. This potentiation effect is likely due to the inhibition of relaxant prostanoids production in the airways by PD 098059 and Ħ. 1 Student 2 Laboratory Officer 3 Senior Lecturer Figure 1. PD 098059 (left) and Ħ (right) METHODS The guinea pigs were sacrificed for their lungs. The lungs were cut and trimmed to obtain the bronchial rings. These rings were suspended (Fig. 2) under a tension of 2 g in organ bath that contained Krebs-bicarbonate solution, aerated with oxygen. The study was done in the presence or absence of MAPKK inhibitor treatments, with dimethyl sulfoxide as negative control and indomethacin as positive control. The contractile responses were monitored and the data was analysed by using one-way analysis of variance (ANOVA) followed by Tukey test. The critical level for significance was set at P <0.05. Figure 2. Tissue suspension (left) in organ bath system (right) RESULTS Based on our previous studies (Tsang et al., 1998), PD 098059 markedly potentiated bronchial ring contraction induced by histamine. To determine whether the potentiation effect of PD 098059 on agonist-induced bronchial smooth muscle is dose-dependent or not, we evaluate the effects of increasing concentrations of PD 098059 on histamineor LTD4-induced bronchial contraction. PD 098059 (10μM-50μM) potentiated both histamineand LTD4-induced bronchial contraction, but did not show dose-dependent effect (Fig. 3A and Fig. 3B). To determine whether Ħ might have the same effects as PD 098059 on agonistinduced bronchial smooth muscle contraction, we evaluate the effects of 30 μM Ħ on histamineor LTD4-induced bronchial contraction. Ħ (30μM) significantly (P<0.05) potentiated bronchial ring contraction induced by LTD4 (Fig. 4B), as well as that by histamine (Fig. 4A).
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