Mechanism of glutamine inhibition of cytosolic phospholipase a 2 (cPLA 2 ): Evidence of physical interaction between glutamine‐Induced mitogen‐activated protein kinase phosphatase‐1 and cPLA 2

Summary Non‐essential amino acid L‐glutamine (Gln) possesses anti‐inflammatory activity via deactivating cytosolic phospholipase A 2 (cPLA 2 ). We showed previously that Gln deactivated cPLA 2 indirectly via dephosphorylating p38 mitogen‐activated protein kinase (MAPK), the major kinase for cPLA 2 phosphorylation, through inducing MAPK phosphatase‐1 (MKP‐1). In this study, we investigated the precise mechanism underlying Gln deactivation of cPLA 2 . In lipopolysaccharide (LPS)‐treated mice, Gln injection resulted in dephosphorylation of phosphorylated cPLA 2 (p‐cPLA 2 ), which coincided with rapid Gln induction of MKP‐1. MKP‐1 small interfering RNA (siRNA) abrogated the ability of Gln to induce MKP‐1 as well as the dephosphorylation of cPLA 2 . Co‐immunoprecipitation and in‐situ proximity ligation assay revealed a physical interaction between MKP‐1 and p‐cPLA 2 . In a murine model of allergic asthma, we also demonstrated the physical interaction between MKP‐1 and p‐cPLA 2 . Furthermore, Gln suppressed various allergic asthma phenotypes, such as neutrophil and eosinophil recruitments into the airway, airway levels of T helper type 2 (Th2) cytokines [interleukin (IL)‐4, IL‐5 and IL‐13], airway hyperresponsiveness, mucin production and metabolites (leukotriene B 4 and platelet‐activating factor) through inhibiting cPLA 2 in a MKP‐1‐dependent manner. These data suggest that MKP‐1 uses cPLA 2 , in addition to p38, as a substrate, which further potentiates the anti‐inflammatory action of Gln.