Activation and mitogen-activated protein kinase regulation of transcription factors Ets and NF-kappaB in Mycobacterium-infected macrophages and role of these factors in tumor necrosis factor alpha and nitric oxide synthase 2 promoter function.

Previous studies have shown that primary murine macrophages infected with Mycobacterium avium produced lower levels of tumor necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase 2 (NOS2) compared to cells infected with nonpathogenic Mycobacterium smegmatis. TNF-alpha and NOS2 levels correlated with and were dependent on the activation of mitogen-activated protein kinases (MAPKs) p38 and extracellular signal-regulated kinase 1/2 (ERK1/2). To define the macrophage transcriptional responses dependent on ERK1/2 activation following a mycobacterial infection, we used RAW 264.7 cells transfected with a TNF-alpha or NOS2 promoter vector. We determined that macrophages infected with M. avium compared to M. smegmatis showed diminished TNF-alpha and NOS2 promoter activity. A more pronounced difference in promoter activity was observed when only the consensus ETS and NF-kappaB binding sites were used as promoters. Mutational analysis of the ETS and NF-kappaB binding sites present on the TNF-alpha and NOS2 promoters, respectively, showed that these sites were essential for a functional promoter. Moreover, the Ets/Elk but not the NF-kappaB transcriptional response was dependent on ERK1/2. This correlated with the requirement for ERK1/2 in TNF-alpha but not NOS2 promoter activity. Our data indicate that the increased Ets/Elk and NF-kappaB promoter activities associated with M. smegmatis-infected macrophages are responsible, at least in part, for the increased TNF-alpha and NOS2 production observed in these infected cells and that ERK1/2 is required for Ets/Elk activity and full TNF-alpha production.