Induction of inducible nitric oxide synthase-NO center dot by lipoarabinomannan of Mycobacterium tuberculosis is mediated by MEK1-ERK, MKK7-JNK, and NF-kappa B signaling pathways

Nitric oxide (NO.) expression by inducible nitric oxide synthase (iNOS) is an important host defense mechanism against Mycobacterium tuberculosis in m ononuclear phagocytes. The objective of this investigation was to examine t he role of mitogen-activated protein (MAP) kinase (MAPK) and nuclear factor kappaB (NF-kappaB) signaling pathways in the regulation of iNOS and NO. by a mycobacterial cell wall lipoglycan known as mannose-capped lipoarabinoma nnan (ManLAM). Specific pharmacologic inhibition of the extracellular-signa l-regulated kinase (ERK) or NF-kappaB pathway revealed that both these sign aling cascades were required in gamma interferon (IFN-gamma)-ManLAM induced iNOS protein and NO2- expression in mouse macrophages. Transient cotransfe ction of dominant-negative protein mutants of the c-Jun NH2-terminal kinase (JNK) pathway revealed that the MAP kinase kinase 7 (MKK7)-JNK cascade als o mediated IFN-gamma -ManLAM induction of iNOS promoter activity whereas MK K4 did not. Overexpression of null mutant I kappaB alpha, a potent inhibito r of NF-kappaB activation, confirmed that the I kappaB alpha kinase (IKK)-N F-kappaB signaling pathway enhanced IFN-gamma -ManLAM-induced iNOS promoter activity. By contrast, activated p38(mapk) inhibited iNOS induction. These results indicate that combined IFN-gamma and ManLAM stimulation induced iN OS and NO. expression and that MEK1-ERK, MKK7-JNK, IKK-NF-kappaB, and p38(m apk) signaling pathways play important regulatory roles.