Down-regulation of MARCKS-related protein (MRP) in macrophages infected with Leishmania

Leishmania, a protozoan parasite of macrophages, has been shown to interfer e with host cell signal transduction pathways including protein kinase C (P KC)-dependent signaling. Myristoylated alanine-rich C kinase substrate (MAR CKS) and MARCKS-related protein (MRP, MacMARCKS) are PKC substrates in dive rse cell types, MARCKS and MRP are thought to regulate the actin network an d thereby participate in cellular responses involving cytoskeletal rearrang ement. Because MRP is a major PKC substrate in macrophages, we examined its expression in response to infection by Leishmania, Activation of murine ma crophages by cytokines increased MRP expression as determined by Western bl ot analysis. Infection with Leishmania promastigotes at the time of activat ion or up to 48 h postactivation strongly decreased MRP levels. Leishmania- dependent MRP depletion was confirmed by [H-3]myristate labeling and by imm unofluorescence microscopy. All species or strains of Leishmania parasites tested, including lipophosphoglycan-deficient Leishmania major L119, decrea sed MRP levels. MRP depletion was not obtained with other phagocytic stimul i including zymosan, latex beads, or heat-killed Streptococcus mitis, a Gra m-positive bacterium. Experiments with [H-3]myristate labeled proteins reve aled the appearance of lower molecular weight fragments in Leishmania-infec ted cells suggesting that MRP depletion may be due to proteolytic degradati on.