title: A novel mechanism underlying the basic defensive response of macrophages against Mycobacterium infection.
abstract: Following inhalation of Mycobacterium tuberculosis, including bacillus Calmette-Guérin (BCG), pathogens enter and grow inside macrophages by taking advantage of their phagocytic mechanisms. Macrophages often fail to eliminate intracellular M. tuberculosis, leading to the induction of host macrophage death. Despite accumulating evidence, the molecular mechanisms underlying M. tuberculosis infection-induced cell death remain controversial. In this study, we show the involvement of two distinct pathways triggered by TLR2 and β2 integrin in BCG infection-induced macrophage apoptosis. First, BCG infection induced activation of ERK1/2, which in turn caused phosphorylation/activation of the proapoptotic protein Bim in mouse macrophage-like Raw 264.7 cells. BCG-infected Raw cells treated with U0126, an MEK/ERK inhibitor, led to the suppression of Bim phosphorylation alongside a remarkable increase in the number of viable macrophages. Small interfering RNA-mediated knockdown of Bim rescued the macrophages from the apoptotic cell death induced by BCG infection. Stimulation with Pam3CSK, a TLR2 agonist, induced macrophage apoptosis with a concomitant increase in the phosphorylation/activation of MEK/ERK and Bim. These observations indicate the important role of the TLR2/MEK/ERK/Bim pathway in BCG infection-induced macrophage apoptosis. Second, we used the β2 integrin agonists C3bi and fibronectin to show that the β2 integrin-derived signal was involved in BCG infection-induced apoptosis, independent of MEK/ERK activation. Interestingly, latex beads coated with Pam3CSK and C3bi were able to induce apoptosis in macrophages to the same extent and specificity as that induced by BCG. Taken together, two distinct pattern-recognition membrane receptors, TLR2 and β2 integrin, acted as triggers in BCG infection-induced macrophage apoptosis, in which MEK/ERK activation played a crucial role following the engagement of TLR2.
authors.affiliation: Department of Molecular Patho-Physiology, Faculty of Pharmaceutical Sciences, Tokyo University of Science, Chiba 278-8510, Japan;
authors.forename: Takuya
authors.initials: T
authors.lastname: Iyoda
authors.forename: Muneaki
authors.initials: M
authors.lastname: Takada
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Fukatsu
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Kumokoshi
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Fujisawa
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Shimada
authors.forename: Noriko
authors.initials: N
authors.lastname: Shimokawa
authors.forename: Takuya
authors.initials: T
authors.lastname: Matsunaga
authors.forename: Kimiko
authors.initials: K
authors.lastname: Makino
authors.forename: Norio
authors.initials: N
authors.lastname: Doi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Terada
authors.forename: Fumio
authors.initials: F
authors.lastname: Fukai
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D018821:CD18 Antigens / Q000276:immunology / Q000378:metabolism; D005434:Flow Cytometry; D047468:Immunoprecipitation; D020287:In Situ Nick-End Labeling; D008264:Macrophages / Q000276:immunology* / Q000382:microbiology; D051379:Mice; D018613:Microscopy, Confocal; D009164:Mycobacterium Infections / Q000276:immunology* / Q000378:metabolism; D009169:Mycobacterium tuberculosis; D034741:RNA, Small Interfering; D015398:Signal Transduction / Q000276:immunology*; D051195:Toll-Like Receptor 2 / Q000276:immunology / Q000378:metabolism
chemical_list: D018821:CD18 Antigens; D034741:RNA, Small Interfering; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2