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p38α mitogen-activated protein kinase is essential to cellular homeostasis. Two principal mechanisms to activate p38α exist. The first relies on dedicated dual-specificity kinases such as mitogen-activated protein kinase kinase (MAP2K) 3 (MKK3) or 6 (MKK6), which activate p38α by phosphorylating Thr180 and Tyr182 within the activation segment. The second is by autophosphorylation of Thr180 and Tyr182 in cis, mediated by p38α binding the scaffold protein TAB1. The second mechanism occurs during myocardial ischemia, where it aggravates myocardial infarction. Based on the crystal structure of the p38α-TAB1 complex we replaced threonine 185 of p38α with glycine (T185G) to prevent an intramolecular hydrogen bond with Asp150 from being formed. This mutation did not interfere with TAB1 binding to p38α. However, it disrupted the consequent long-range effect of this binding event on the distal activation segment, releasing the constraint on Thr180 that oriented its hydroxyl for phosphotransfer. Based on assays performed in vitro and in vivo, the autoactivation of p38α(T185G) was disabled, while its ability to be activated by upstream MAP2Ks and to phosphorylate downstream substrates remained intact. Furthermore, myocardial cells expressing p38α(T185G) were resistant to injury. These findings reveal a mechanism to selectively disable p38α autoactivation and its consequences, which may ultimately circumvent the toxicity associated with strategies that inhibit p38α kinase activity under all circumstances, such as with ATP-competitive inhibitors. [ABSTRACT FROM AUTHOR]

Objective: The basal activity of p38 MAPK has recently been shown to impair myocardial contractility. This kinase is activated by ischemia and short-term hibernation. We hypothesized that p38 MAPK activation may contribute to the contractile deficit that characterizes low-flow ischemia. Methods: In Langendorff-perfused isolated C57BL/6 mouse hearts, perfusion pressure was reduced from 85 to 15 or 30 mm Hg for 120 min to induce ischemic left ventricular dysfunction. The effect of the p38 MAPK inhibitor SB203580 (1 μM/l) on contractile function and p38 MAPK activation was assessed. Results: Reduction in perfusion pressure to 15 or 30 mm Hg was accompanied by stable reductions in coronary flow (83±2% and 66±2%, respectively) and developed pressure (84±2% and 61±3%), with minimal infarction (15.6±0.69% and 10.6±0.98% of LV myocardium, respectively), but marked activation of p38 MAPK (reflected in pHSP27 1092±326% basal and 996±301% basal, respectively). The p38 MAPK inhibitor SB203580, present during the last 60 min of reduced pressure perfusion, prevented p38 MAPK activation (pHSP27 281±92% basal, p=0.01 and 186±72% basal, p=0.01) but, despite the presence of a contractile reserve, had no effect on developed pressure. Similarly, early treatment with SB203580 started 5 min after the onset of reduced flow also failed to attenuate contractile dysfunction. Conclusion: The p38 MAPK activation that accompanies short-term hibernation does not appear to contribute to the contractile deficit. [Copyright &y& Elsevier]

p38α mitogen-activated protein kinase (p38α) is activated by a variety of mechanisms, including autophosphorylation initiated by TGFβ-activated kinase 1 binding protein 1 (TAB1) during myocardial ischemia and other stresses. Chemical-genetic approaches and coexpression in mammalian, bacterial and cell-free systems revealed that mouse p38α autophosphorylation occurs in cis by direct interaction with TAB1(371-416). In isolated rat cardiac myocytes and perfused mouse hearts, TAT-TAB1(371-416) rapidly activates p38 and profoundly perturbs function. Crystal structures and characterization in solution revealed a bipartite docking site for TAB1 in the p38α C-terminal kinase lobe. TAB1 binding stabilizes active p38α and induces rearrangements within the activation segment by helical extension of the Thr-Gly-Tyr motif, allowing autophosphorylation in cis. Interference with p38α recognition by TAB1 abolishes its cardiac toxicity. Such intervention could potentially circumvent the drawbacks of clinical pharmacological inhibitors of p38 catalytic activity.