Mycobacteria directly induce cytoskeletal rearrangements for macrophage spreading and polarization through TLR2-dependent PI3K signaling

Abstract

Macrophage migration and adhesion are important for the control of mycobacterial infection and are critically dependent on the reorganization of the cytoskeleton. Mycobacteria elicit rapid morphological changes, such as cell spreading, a process relevant to in vivo changes of macrophage shape during extravasation and migration. In this study, we investigated the BCG mycobacteria-induced signaling events leading to macrophage cytoskeletal rearrangements employing specific pharmacological inhibitors to suppress distinct kinase pathways known to be elicited by infection. Viable or lysed mycobacteria, as well as purified cell wall lipoprotein p19, TLR2 agonist, induced RAW264.7 cells to extend actin-rich pseudopods, which impart radial spreading within 3 h, leading later to persistent cell polarization. BCG induced rapid activation of phosphatidylinositol 3-kinase, PI3K, activation that was recruited to the activated TLR2 receptor. TLR2- neutralizing antibody inhibited macrophage spreading and PI3K activation induced by p19. Additionally, BCG induced spreading and polarization of bone marrow-derived macrophages from TLR2- expressing mice in contrast to their TLR2-knockout counterparts. Neither MEK1/ERK, p38 MAPK, nor NF-kappaB activation were important for the early cytoskeletal rearrangements observed, although suppression of these pathways is known to inhibit chemokine secretion by activated macrophages. Beta2-integrins blockade with a corresponding antibody inhibited macrophage spreading and polarization but had no effect on pseudopodia protrusions demonstrating the downstream position of integrin-mediated adhesion in PI3K- dependent signaling pathway leading to the motility phenotype. The obtained data demonstrate that the direct effect of mycobacteria on macrophage shape might be mediated through TLR2-dependent PI3K activation.

RP105 Engages Phosphatidylinositol 3-Kinase p110δ To Facilitate the Trafficking and Secretion of Cytokines in Macrophages during Mycobacterial Infection

“…TLR2 and TLR3 have been implicated in the mycobacteriainduced activation of PI3K signaling in macrophages (54)(55)(56). In the present study, we show that in mouse bone marrow-derived macrophages RP105 deficiency abrogated mycobacteria-induced Akt phosphorylation.…”

“…Mycobacteria-induced PI3K signaling in macrophages has been reported to contribute to the production of cytokines (TNF, IL-6, G-CSF) and chemokines (CCL5, CCL8) (55,65), as well as cell polarization (54), bacterial uptake (66), and inhibition of phagosome maturation (67). The positive effects on mycobacteria-induced inflammatory cytokine responses seem to contrast the reported inhibition of proinflammatory cytokine production by PI3K signaling in the context of TLR stimulation, in particular LPS.…”

Neurons are host cells for Mycobacterium tuberculosis

“…However, bacilli that were tightly associated with cytoplasmic structures within neurons appeared to be encased in a sheath-like structure, evidence of cytoskeletal rearrangement upon infection. M. tuberculosis bacillus-induced cytoskeletal rearrangement is known and has previously been reported (41,42), and the observations in this study suggest that similar changes in the neuronal cytoskeleton occur during bacillus invasion. Moreover, it was established that entry of M. tuberculosis bacilli into epithelial cells was dependent on microtubules, which could be inhibited by administration of colchicine and nocodazole, known to cause microtubule depolymerization (43).…”

Inhibitory effects of honokiol on LPS and PMA-induced cellular responses of macrophages and monocytes

“…Taken together, these results imply that honokiol can modulate the cellular responses involved in morphological changes. Because the actin cytoskeleton is known to play a critical role in regulation of flexible changes in cell morphology (18), cytoskeleton rearrangement requires further examination to determine if honokiol is able to directly regulate actin.…”