The TAB1-p38a complex aggravates myocardial injury and can be targeted by small molecules

There is considerable evidence that inhibition of p38a mitogen-activated protein kinase diminishes cardiac damage during myocardial ischemia. During myocardial ischemia p38a interacts with TAB1, a scaffold protein, which promotes p38a autoactivation; active p38a (pp38a) then trans-phosphorylates TAB1. Previously, we solved the X-ray structure of the p38a-TAB1(384-412) complex. Here we further characterize the interaction by resolving the structure of the pp38a-TAB1(1-438) complex in the active state. Based on this information we created a global knock-in mouse with substitution of four residues on TAB1 (V390A, Y392A, V408G, M409A) we show are required for docking onto p38a. Whereas ablating p38a or TAB1 results in early embryonal lethality, the TAB1 KI mice are viable, develop normally and have no appreciable alteration in their lymphocyte repertoire or myocardial transcriptional profile. Nonetheless, following in vivo regional myocardial ischemia, infarction volume is significantly reduced and the trans- phosphorylation of TAB1 is disabled. Unexpectedly, the activation of myocardial p38a during ischemia is only mildly attenuated in TAB1 KI hearts, an effect most likely due to the removal of the steric hindrance to MAP2K3 binding. We conclude that it is the phosphorylation of TAB1 by pp38a during ischemia that is associated with cardiac damage. The data reveal that it is possible to selectively inhibit signalling downstream of p38a to attenuate ischemic injury. Our findings validate the p38a-TAB1 complex as a therapeutic target that may circumvent the toxicity associated with ATP-competitive inhibitors of p38a.

现有大量研究证据表明，抑制p38α丝裂原活化蛋白激酶（p38α mitogen-activated protein kinase）可减轻心肌缺血过程中的心脏损伤。在心肌缺血期间，p38α会与支架蛋白TAB1结合，后者可促进p38α的自激活；活化型p38α（pp38α）随后会对TAB1进行反式磷酸化。此前，我们已解析了p38α-TAB1(384-412)复合物的X射线晶体结构。本文中，我们进一步解析了活性状态下pp38α-TAB1(1-438)复合物的结构，以此对二者的相互作用进行深入表征。基于上述研究结果，我们构建了TAB1上携带V390A、Y392A、V408G、M409A四处残基替换的全身性敲入小鼠，并证实这些残基是TAB1与p38α对接结合所必需的关键位点。与敲除p38α或TAB1会导致胚胎早期致死不同，该TAB1敲入（KI）小鼠可正常存活、发育，其淋巴细胞谱系及心肌转录谱均无明显异常。尽管如此，在体局部心肌缺血模型中，该小鼠的梗死体积显著减小，且TAB1的反式磷酸化被完全阻断。出乎意料的是，缺血期间心肌p38α的激活在TAB1 KI小鼠心脏中仅出现轻度减弱，这一现象很可能源于MAP2K3结合的空间位阻被移除。我们的研究结论为：缺血期间pp38α对TAB1的磷酸化是与心脏损伤密切相关的核心因素。本研究数据表明，可通过选择性抑制p38α下游信号通路以减轻缺血性损伤。我们的研究结果验证了p38α-TAB1复合物可作为潜在治疗靶点，有望规避p38α ATP竞争性抑制剂所带来的毒性问题。