Signal transduction and phagosome biogenesis in human macrophages during phagocytosis of Mycobacterium bovis BCG.

Downstream signal transduction via heterotrimeric GTP-binding proteins to protein kinase C has been reported to be a central event in induction of rapid phagocytosis of extracellular particles by macrophages. However, the signalling pathway involved in mycobacterial uptake and phagosome biogenesis is poorly understood, and there is lack of information about in situ localization of PKC, cytoskeletal proteins, and G-proteins in mycobacterial vacuoles. Employing immunocytochemical methods, we provide evidence that alpha-subunits of stimulatory and inhibitory G-proteins and PKC beta as well as two major cytoskeletal components, microfilaments and microtubules, participate in uptake of Mycobacterium bovis BCG by human macrophages and co-localize in phagosomes. This implies that cellular signalling via G-proteins and PKC beta may occur not only at the level of the plasma membrane; rather, the alpha-subunit of G-proteins and PKC beta may be translocated to the effector proteins involved in phagosomal biogenesis. A similar pattern of accumulation of G-proteins, PKC, and both microfilamental and microtubular cytoskeleton around vacuoles containing internalized latex beads indicates their general role in phagocytosis.