Macrophage migration inhibitory factor induces phospholamban phosphorylation in cardiac muscle

• MIF promoted PLN phosphorylation and increased store Ca 2+ content in cardiomyocytes. • CD74 and CXCR7 were supposed to form a major cardiac MIF receptor complex. • MIF-induced CXCR7 activation sequentially stimulated PI3K, AKT and eNOS. • Arginine accelerated eNOS-mediated NO synthesis in MIF-treated cardiomyocytes. • Upon the MIF stimulation, CaMKII became NO-dependently active to phosphorylate PLN. The pleiotropic cytokine macrophage migration inhibitory factor (MIF) elevates sarcoplasmic reticulum (SR) Ca 2+ content and enhances Ca 2+ transient in cardiac muscle. Our imaging and immunoblot data indicated that the MIF-evoked effect is caused mainly by the phosphorylation of the SR Ca 2+ -pump regulator phospholamban (PLN). Gene expression data suggested that the cluster of differentiation 74 (CD74) and the C-X-C motif chemokine receptor 7 (CXCR7) form a major MIF receptor complex in cardiomyocytes, but CXCR7 activation alone seemed sufficient to exert the MIF-evoked effect. Our pharmacological assessments suggested that phosphoinositide 3-kinase (PI3K), AKT kinase and endothelial nitric oxide synthase (eNOS) were continuously stimulated in the downstream of CXCR7 activation. Furthermore, NO thus generated likely reacted to activate Ca 2+ /calmodulin-dependent protein kinase II (CaMKII), leading to PLN phosphorylation and subsequent SR Ca 2+ -pump activation. Therefore, the CXCR7-PI3K-AKT-eNOS-CaMKII-PLN axis is proposed as a central pathway for MIF-evoked potentiation of cardiac Ca 2+ signaling.