Mycobacterium tuberculosis RecA is indispensable for inhibition of the mitogen-activated protein kinase-dependent bactericidal activity of THP-1-derived macrophages in vitro

Our knowledge about the mechanisms utilized by Mycobacteriumtuberculosis to survive inside macrophages is still incomplete. One of the mechanism that protects M.tuberculosis from the host's microbicidal products and allows bacteria to survive involves DNA repair systems such as the homologous recombination (HR) and nonhomologous end-joining (NHEJ) pathways. It is accepted that any pathway that contributes to genome maintenance should be considered as potentially important virulence factor. In these studies, we investigated reactive oxygen species, nitric oxide and tumor necrosis factor- production by macrophages infected with wild-type M.tuberculosis, with an HR-defective mutant (recA), with an NHEJ-defective mutant [(ku,ligD)], with a mutant defective for both HR and NHEJ [(ku,ligD,recA)], or with appropriate complemented strains. We also assessed the involvement of extracellular signal-regulated kinases (ERKs) 1 and 2 in the response of macrophages to infection with the above-mentioned strains, and ERK1/2 phosphorylation in M.tuberculosis-infected macrophages. We found that mutants lacking RecA induced a greater bactericidal response by macrophages than did the wild-type strain or an NHEJ-defective mutant, and activated ERK1/2 was involved only in the response of macrophages to recA deletion mutants [(ku,ligD,recA) and recA]. We also demonstrated that only the triple mutant induced ERK1/2 phosphorylation in phorbol-12-myristate-13-acetate-stimulated macrophages. Moreover, HR-defective mutants induced lower amounts of tumor necrosis factor- secretion than did the wild-type or (ku,ligD). Our results indicate that RecA contributes to M.tuberculosis virulence, and also suggest that diminished ERK1/2 activation in macrophages infected with M.tuberculosis possessing recA may be an important mechanism by which wild-type mycobacteria escape intracellular killing.