PROTEIN-PHOSPHORYLATION DURING PHAGOSOME MATURATION

Phagolysosome biogenesis is driven by a series of interactions between phagosomes and organelles of the biosynthetic and endocytic pathways. The presence of endocytic markers on phagosomes suggests that phagoso mes and endosomes share common structural and functional characteristi cs. In that line of thought, protein phosphorylation has been shown to be involved in regulatory aspects of the fusion properties of endosom es and other vacuolar organelles. To study further the mechanisms invo lved in phagolysosome biogenesis, we have investigated the presence of phagosome proteins that can be phosphorylated in vitro by endogenous phagosome-associated kinases. The results obtained show that proteins phosphorylated on tyrosine residues are present on phagosomes. Moreove r, complex phosphorylation/dephosphorylation cycles appear to occur du ring phagolysosome biogenesis. The addition of endosome fractions to p hagosomes inhibit the phosphorylation of phagosome proteins. These res ults suggest that phosphorylation and dephosphorylation events could p lay roles in the biogenesis of phagolysosomes and regulate, in part, t he complex in vivo interactions between phagosomes and endosomes.