Cystatin cures visceral leishmaniasis by NF-kappa B-mediated proinflammatory response through co-ordination of TLR/MyD88 signaling with p105-Tpl2-ERK pathway

Cystatin could completely cure experimental visceral leishmaniasis by switching the differentiation of Th2 cells to Th1 type, as well as upregulating NO, and activation of NF-kappa B played a major role in these processes. Analysis of upstream signaling events revealed that TLR 2/4-mediated MyD88-dependent participation of IL-1R-activated kinase (IRAK) 1, TNF receptor-associated factor (TRAF) 6 and TGF beta-activated kinase (TAK)1 is essential to induce cystatin-mediated I kappa B kinase (IKK)/NF-kappa B activation in macrophages. Cystatin plus IFN-gamma activated the IKK complex to induce phosphorylation-mediated degradation of p105, the physiological partner and inhibitor of the MEK kinase, tumor progression locus 2 (Tpl-2). Consequently, Tpl-2 was liberated from p105, thereby stimulating activation of the MEK/ERK MAPK cascade. Cystatin plus IFN-gamma-induced IKK-beta post-transcriptionally modified p65/RelA subunit of NF-kappa B by dual phosphorylation in infected phagocytic cells. IKK induced the phosphorylation of p65 directly on Ser-536 residue whereas phosphorylation on Ser 276 residue was by sequential activation of Tpl-2/MEK/ERK/MSK1. Collectively, the present study indicates that cystatin plus IFN-gamma-induced MyD88 signaling may bifurcate at the level of IKK, leading to a divergent pathway regulating NF-kappa B activation by I kappa B alpha phosphorylation and by p65 transactivation through Tpl-2/MEK/ERK/MSK1.