Degradation of MK2 with natural compound andrographolide: a new modality for anti-inflammatory therapy.

The p38-MK2 signaling axis functions as an initiator of inflammation. Targeting the p38-MK2 signaling axis represents a direct therapeutic intervention of inflammatory diseases. We described here a novel role of andrographolide (AG), a small-molecule ent-labdane natural compound, as an inhibitor of p38-MK2 axis via MK2 degradation. AG was found to bind to the activation loop of MK2, located at the interface of the p38-MK2 biomolecular complex. This interaction disrupted the complex formation and predisposed MK2 to proteasome-mediated degradation. We showed that AG induced MK2 degradation in a concentration- and time-dependent manner and exerted its anti-inflammatory effects by enhancing the mRNA-destabilizing activity of tristetraprolin, thereby inhibiting pro-inflammatory mediator production (e.g., TNF-α, MCP-1). Administration of AG via intratracheal (i.t.) route to mice induced MK2 downregulation in lung alveolar macrophages, but not lung tissues, and prevented macrophage activation. Our study also demonstrated that the anti-inflammatory effects achieved by AG via MK2 degradation were more durable and sustained than that achieved by the conventional MK2 kinase inhibitors (e.g., PF-3644022). Taken together, our findings illustrated a novel mode of action of AG by modulating the p38-MK2 signaling axis and would pave the way for the development of a novel class of anti-inflammatory agents targeting MK2 for degradation by harnessing the privileged scaffold of AG.