p38 MAPK autophosphorylation drives macrophage IL-12 production during intracellular infection

The intracellular protozoan Toxoplasma gondii triggers rapid MAPK activation in mouse macrophages (M phi). We used synthetic inhibitors and dominant-negative M phi mutants to demonstrate that T. gondii triggers IL-12 production in dependence upon p38 MAPK. Chemical inhibition of stress-activated protein kinase/JNK showed that this MAPK was also required for parasite-triggered IL-12 production. Examination of upstream MAPK kinases (MKK) 3, 4, and 6 that function as P38 MAPK activating kinases revealed that parasite infection activates only MKK3 Nevertheless, in MKK3(-/-) M phi, p38 MAPK activation was near normal and IL-12 production was unaffected. Recently, MKK-independent p38 alpha MAPK activation via autophosphorylation was described. Autophosphorylation depends upon p38a MAPK association with adaptor protein, TGF-beta-activated protein kinase 1-binding protein-1. We observed TGF-beta-activated protein kinase 1-binding protein-1-p38 alpha MAPK association that closely paralleled p38 MAPK phosphorylation during Toxoplasma infection of M phi. Furthermore, a synthetic p38 catalytic-site inhibitor blocked tachyzoite-induced p38 alpha MAPK phosphorylation. These data are the first to demonstrate p38 MAPK autophosphorylation triggered by intracellular infection.