TI - Calpain-mediated regulation of the distinct signaling pathways and cell migration in human neutrophils . AB - We studied the mechanisms underlying calpain inhibition-mediated human neutrophil migration . MAPKs , including ERK , p38 , and JNK , MEK1/2 , MAPK kinase 3/6 ( MKK3/6 ) , PI-3K/Akt , c-Raf , and p21-activated kinase ( PAK ; an effector molecule of Rac ) were rapidly ( within 30 s ) activated in neutrophils upon exposure to calpain inhibitors ( PD150606 and N-acetyl-Leu-Leu-Nle-CHO ) but not PD145305 ( inactive analog of PD150606 ) . Following activation of these pathways , neutrophils displayed active migration ( chemotaxis ) , which was sustained for more than 45 min . The studies with pharmacological inhibitors suggest that calpain inhibition-mediated neutrophil migration is mediated by activation of MEK/ERK , p38 , JNK , PI-3K/Akt , and Rac . NSC23766 (Rac inhibitor) and pertussis toxin ( PTX ) suppressed calpain inhibitor -induced phosphorylation of distinct signaling molecules ( PAK , c-Raf , MEK1/2 , ERK , MKK3/6 , p38 , JNK , and Akt ) as well as cell migration , suggesting that the PTX-sensitive G protein and Rac axis may be a possible key target of calpain inhibitors . Differentiated neutrophil-like HL-60 cells but not undifferentiated cells displayed cell migration and activation of MAPKs and PI-3K/Akt on calpain inhibition . These findings suggest that constitutively active calpain negatively regulates activation of the distinct signaling pathways and cell migration in resting neutrophils , and this regulatory system develops during differentiation into mature neutrophils .