Leishmania donovani lipophosphoglycan : effects on actin and phagosomal maturation

Sammanfattning: Leishmania donovani promastigotes survive intracellularly in macrophages by inhibiting phagosomal maturation. This ability is conferred by surface lipophosphoglycan (LPG), which is transferred to the host-cell plasma and phagosomal membranes during phagocytosis. LPG modulates the biophysical properties of membranes and has several effects on the host cell, including inhibition of protein kinase C alpha (PKCα)-mediated signaling. Our studies were focused on molecular mechanisms operating in the establishment of L. donovani infection, especially effects on host-cell F-actin.We found that L. donovani promastigotes induced accumulation of periphagosomal F-actin, an effect directly dependent on LPG. The F-actin accumulation correlated to inhibition of phagosomal maturation. Cortical F-actin was increased as well. Macrophages overexpressing dominant-negative (DN) PKCα also displayed elevated cortical F-actin, decreased phagocytic capacity, elevated periphagosomal F-actin, and defective phagosomal maturation, effects similar to those seen when exposing the cells to LPG. LPG colocalized with lipid rafts in the host-cell membrane, and lipid rafts were necessary both for translocation of activated PKCα to the membrane, and for the effects of LPG on host cell actin dynamics and phagosomal maturation. Introduction of constitutively active Rac1 and Cdc42 into the host macrophage mimicked the effects of LPG on actin dynamics and phagosomal maturation while DN Rac1 and Cdc42 abrogated LPG's effects on actin.Taken together, our results show that LPG partitions into lipid rafts in macrophages and induces an accumulation of periphagosomal F-actin, which is correlated to inhibition of phagosomal maturation. The effect of LPG on actin involves inhibition of PKCα and depends on active Rac1 and Cdc42.