Induction of Inducible Nitric Oxide Synthase-NO· by Lipoarabinomannan of Mycobacterium tuberculosis Is Mediated by MEK1-ERK, MKK7-JNK, and NF-κB Signaling Pathways

Abstract

ABSTRACT Nitric oxide (NO· ) expression by inducible nitric oxide synthase (iNOS) is an important host defense mechanism against Mycobacterium tuberculosis in mononuclear phagocytes. The objective of this investigation was to examine the role of mitogen-activated protein (MAP) kinase (MAPK) and nuclear factor κB (NF-κB) signaling pathways in the regulation of iNOS and NO· by a mycobacterial cell wall lipoglycan known as mannose-capped lipoarabinomannan (ManLAM). Specific pharmacologic inhibition of the extracellular-signal-regulated kinase (ERK) or NF-κB pathway revealed that both these signaling cascades were required in gamma interferon (IFN-γ)-ManLAM-induced iNOS protein and NO 2 − expression in mouse macrophages. Transient cotransfection of dominant-negative protein mutants of the c-Jun NH 2 -terminal kinase (JNK) pathway revealed that the MAP kinase kinase 7 (MKK7)-JNK cascade also mediated IFN-γ–ManLAM induction of iNOS promoter activity whereas MKK4 did not. Overexpression of null mutant IκBα, a potent inhibitor of NF-κB activation, confirmed that the IκBα kinase (IKK)–NF-κB signaling pathway enhanced IFN-γ–ManLAM-induced iNOS promoter activity. By contrast, activated p38 mapk inhibited iNOS induction. These results indicate that combined IFN-γ and ManLAM stimulation induced iNOS and NO· expression and that MEK1-ERK, MKK7-JNK, IKK–NF-κB, and p38 mapk signaling pathways play important regulatory roles.