Toll-like receptor 2 and mitogen- and stress-activated kinase 1 are effectors of Mycobacterium avium-induced cyclooxygenase-2 expression in macrophages.

Understanding how pathogenic mycobacteria subvert the protective immune response is crucial to the development of strategies aimed at controlling mycobacterial infections. Prostaglandin E(2) exerts an immunosuppressive function in the context of mycobacterial infection. Because cyclooxygenase-2 (COX-2) is a rate-limiting enzyme in prostaglandin biosynthesis, there is a need to delineate the mechanisms through which pathogenic mycobacteria regulate COX-2 expression in macrophages. Our studies demonstrate that the NF-kappaB and CRE elements of the COX-2 promoter are critical to Mycobacterium avium-induced COX-2 gene expression. M. avium-triggered signaling originates at the Toll-like receptor 2 (TLR2). Ras associates with TLR2 and activates the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase (ERK), whereas tumor necrosis factor receptor-associated factor 6 (TRAF6)/transforming growth factor beta-activated kinase 1 (TAK1)-dependent signaling activates p38 MAPK. Both ERK and p38 MAPK activation converge to regulate the activation of mitogen- and stress-activated kinase 1 (MSK1). MSK1 mediates the phosphorylation of the transcription factor CREB accounting for its stimulatory effect on CRE-dependent gene expression. M. avium-triggered cytoplasmic NF-kappaB activation following IkappaB phosphorylation is necessary but not sufficient for COX-2 promoter-driven gene expression. MSK1 activation is also essential for M. avium-triggered NF-kappaB-dependent gene expression, presumably mediating nucleosomal modifications. These studies demonstrate that the nuclear kinase MSK1 is necessary in regulating the pathogen-driven expression of a gene by controlling two transcription factors. The attenuation of MSK1 may therefore have potential benefit in restricting survival of pathogenic mycobacteria in macrophages.