RATIONALE Mechanical ventilation induces heterogeneous lung injury via mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB). Mechanisms regulating regional injury and protective effects of prone positioning are unclear. OBJECTIVES To determine the key regulators of the lung regional protective effects of prone positioning in rodent lungs exposed to injurious ventilation. METHODS Adult rats were ventilated with high (18 mL/Kg, PEEP 0) or low tidal volume (Vt) (6 mL/kg; PEEP 3cmH2O, 3 hours) in supine (SP) or PP. Dorsal-caudal lung mRNA was analyzed by microarray and MKP-1 qPCR. MKP-1-/- or wild type (WT) mice were ventilated with very high (24 ml/kg; PEEP 0) or low Vt (6 - 7 mL/Kg; PEEP 3cmH2O). The MKP-1 regulator PG490-88 (MRx-108, 0.75mg/kg) or PBS was administered pre-ventilation. Injury was assessed by lung mechanics, bronchioalveolar lavage (BAL) cell counts, protein content and lung injury scoring. Immunoblotting for MKP-1, and IκBα and cytokine ELISAs were performed on lung lysates. RESULTS Prone positioning was protective against injurious ventilation in rats. Expression profiling demonstrated MKP-1, 20-fold higher in rats ventilated prone rather than supine and regional reduction in p38 and JNK activation. MKP-/- mice experienced amplified injury. PG490-88 improved static lung compliance and injury scores, reduced BAL cell counts and cytokine levels and induced MKP-1 and IκBα. CONCLUSIONS Injurious ventilation induces MAPK in an MKP-1-dependent fashion. Prone positioning is protective and induces MKP-1. PG490-88 induced MKP-1 and was protective against high Vt in a NFκB-dependent manner. MKP-1 is a potential target for modulating regional effects of injurious ventilation.