Phosphorylation of p57/coronin‐1 regulates phagocytosis through the modulation of actin‐binding activity

Abstract

The actin‐binding protein p57/coronin‐1, a member of the coronin protein family, is selectively expressed in hematopoietic cells and plays crucial roles in the immune response through reorganization of the actin cytoskeleton. We have studied on the intracellular distribution of p57/coronin‐1 in differentiated HL60 cells during phagocytosis, and found that p57/coronin‐1 and F‐actin were transiently accumulated on phagosomes and then dissociated from phagosomes before phagosome‐lysosome fusion. When the cells were treated with inhibitors of protein kinase C (PKC), p57/coronin‐1 and F‐actin remained on phagosomes without dissociation. This phenomenon seems to be similar to that observed after phagocytosis of Mycobacterium bovis BCG. Since we found that p57/coronin‐1 was phosphorylated by PKC, we assumed that the phosphorylation of p57/coronin‐1 triggered its dissociation from phagosomes and is an essential step for phagosome‐lysosome fusion. Recently, we reported that phosphorylation at Thr‐412 of p57/coronin‐1 regulated its actin‐binding activity and increased during phagocytosis. These studies provide mechanistic insights into roles of p57/coronin‐1 in phagosome‐lysosome fusion and bacterial parasitism.