SB203580, a specific inhibitor of p38-MAPK pathway, is a new reversal agent of P-glycoprotein-mediated multidrug resistance

Interleukin 1alpha (IL-1alpha) induced activation of p38 mitogen-activated protein kinase inhibits glucocorticoid receptor function

Previous studies have demonstrated that interleukinalpha (IL-1alpha) inhibits glucocorticoid receptor (GR) nuclear translocation and dexamethasone (Dex)-induced gene transcription. Given that IL-1alpha is a potent activator of the p38 mitogen-activated protein kinase (MAPK) signal transduction pathway and p38 MAPK has been associated with reduced GR function, we examined the role of p38 MAPK in IL-1alpha-mediated inhibition of GR function in mouse fibroblast cells stably transfected with a GR-mediated reporter gene construct (LMCAT cells). Treatment of LMCAT cells with IL-1alpha (1000 U/ml) for 24 h inhibited Dex (50 nM)-induced GRE-CAT activity by approximately 35%. When cells were cotreated for 24 h with IL-1alpha plus SB-203580 (0.5-1 microM), a selective p38 inhibitor, IL-1alpha's inhibitory effect on GR function as determined by Dex-induced GRE-CAT activity was reversed. Using gel mobility shift assay, SB-203580 was also found to reverse IL-1alpha inhibition of GR-GRE binding. Further confirming the role of p38 pathways, pretreatment of LMCAT cells with antisense oligonucleotides targeted to p38 MAPK completely abrogated IL-1alpha inhibition of Dex-induced GRE-CAT activity. Taken together, these results demonstrate that activation of p38 MAPK pathways are involved in IL-1alpha-mediated inhibition of GR function. In addition, these findings extend the intracellular targets of p38 to include the GR and indicate that p38 inhibitors may have special utility in immunologic and/or neuropsychiatric disorders associated with impaired GR-mediated feedback inhibition.

p38 Mitogen-activated protein kinase mediates a negative inotropic effect in cardiac myocytes

p38 Mitogen-activated protein kinase (MAPK) is one of the most ancient signaling molecules and is involved in multiple cellular processes, including cell proliferation, cell growth, and cell death. In the heart, enhanced activation of p38 MAPK is associated with ischemia/reperfusion injury and the onset of heart failure. In the present study, we investigated the function of p38 MAPK in regulating cardiac contractility and its underlying mechanisms. In cultured adult rat cardiomyocytes, activation of p38 MAPK by adenoviral gene transfer of an activated mutant of its upstream kinase, MKK3bE, led to a significant reduction in baseline contractility, compared with uninfected cells or those infected with a control adenoviral vector (Adv-beta-galactosidase). The inhibitory effect of MKK3bE on contractility was largely prevented by coexpressing a dominant-negative mutant of p38 MAPK or treating cells with a p38 MAPK inhibitor, SB203580. Conversely, inhibition of endogenous p38 MAPK activity by SB203580 rapidly and reversibly enhanced cell contractility in a dose-dependent manner, without altering L-type Ca(2+) currents or Ca(2+)(i) transients. MKK3bE-induced p38 activation had no significant effect on pH(i), whereas SB203580 had a minor effect to elevate pH(i). Furthermore, activation of p38 MAPK was unable to increase troponin I phosphorylation. Thus, we conclude that the negative inotropic effect of p38 MAPK is mediated by decreasing myofilament response to Ca(2+), rather than by altering Ca(2+)(i) homeostasis and that the reduced myofilament Ca(2+) sensitivity is unlikely attributable to troponin I phosphorylation or alterations in pH(i). These findings reveal a novel function of p38 MAPK and shed a new light on our understanding of the coincidence of p38 MAPK activation and the onset of heart failure.