Induction of p38 mitogen-activated protein kinase reduces early endosome autoantigen 1 (EEA1) recruitment to phagosomal membranes.

Mycobacterium tuberculosis survives in the infected host by parasitizing macrophages in which the bacillus resides in a specialized phagosome sequestered from the phagolysosomal degradative pathway. Here we report a role of the stress-induced p38 mitogen-activated protein kinase (p38 MAPK) in the component of M. tuberculosis phagosome maturation arrest that has been linked previously to the reduced recruitment of the endosomal and phagosomal membrane-tethering molecule called early endosome autoantigen 1 (EEA1; Fratti, R. A., Backer, J. M., Gruenberg, J., Corvera, S., and Deretic, V. (2001) J. Cell Biol. 154, 631-644). A pharmacological inhibition of M. tuberculosis var. bovis Bacillus Calmette-Guérin-induced p38 MAPK activity caused a marked increase in EEA1 colocalization with mycobacterial phagosomes. Consistent with the increase in EEA1 association and its role in phagosomal maturation, the pharmacological block of p38 activity caused phagosomal acidification and enrichment of the late endocytic markers lysobisphosphatidic acid and CD63 (lysosomal integral membrane protein 1) on mycobacterial phagosomes. A negative regulatory role of p38 MAPK activation in phagosome maturation was further demonstrated by converse experiments with latex bead phagosomes. Artificial activation of p38 MAPK caused a decrease in EEA1 colocalization with model latex bead phagosomes, which normally acquire EEA1 and subsequently mature into the phagolysosome. These findings show that p38 MAPK activity contributes to the arrest of M. tuberculosis phagosome maturation and demonstrate a negative regulatory role of p38 in phagolysosome biogenesis.