The mitogen-activated protein kinase (MAPK) phosphatases (MKPs) have been considered “undruggable,” but their position as regulators of the MAPKs makes them promising therapeutic targets. MKP5 has been suggested as a potential target for the treatment of dystrophic muscle disease. Here, we identified an inhibitor of MKP5 using a p38α MAPK–derived, phosphopeptide-based small-molecule screen. We solved the structure of MKP5 in complex with this inhibitor, which revealed a previously undescribed allosteric binding pocket. Binding of the inhibitor to this pocket collapsed the MKP5 active site and was predicted to limit MAPK binding. Treatment with the inhibitor recapitulated the phenotype of MKP5 deficiency, resulting in activation of p38 MAPK and JNK. We demonstrated that MKP5 was required for TGF-β1 signaling in muscle and that the inhibitor blocked TGF-β1–mediated Smad2 phosphorylation. TGF-β1 pathway antagonism has been proposed for the treatment of dystrophic muscle disease. Thus, allosteric inhibition of MKP5 represents a therapeutic strategy against dystrophic muscle disease.

丝裂原激活蛋白激酶 (MAPK) 磷酸酶 (MKP) 被认为是“不可成药的”，但它们作为 MAPK 调节剂的地位使其成为有希望的治疗靶点。 MKP5 已被建议作为治疗营养不良性肌肉疾病的潜在靶点。在这里，我们使用 p38α MAPK 衍生的、基于磷酸肽的小分子筛选鉴定了 MKP5 抑制剂。我们解析了 MKP5 与该抑制剂复合物的结构，揭示了一个先前未描述的变构结合袋。抑制剂与该口袋的结合使 MKP5 活性位点塌陷，预计会限制 MAPK 结合。使用抑制剂治疗重现了 MKP5 缺陷的表型，导致 p38 MAPK 和 JNK 激活。我们证明了 MKP5 是肌肉中 TGF-β1 信号传导所必需的，并且该抑制剂阻断了 TGF-β1 介导的 Smad2 磷酸化。 TGF-β1 通路拮抗剂已被提议用于治疗营养不良性肌肉疾病。因此，MKP5 的变构抑制代表了针对营养不良性肌肉疾病的治疗策略。