Down-regulation of 7SL RNA Expression and Impairment of Vesicular Protein Transport Pathways by Leishmania Infection of Macrophages

Smita Misra,Manish K Tripathi,Gautam Chaudhuri

doi:10.1074/jbc.m504162200

Smita Misra, Manish K Tripathi + Show 1 more

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https://doi.org/10.1074/jbc.m504162200

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Abstract

The parasitic protozoan Leishmania specifically manipulates the expression of host macrophage genes during initial interactions, as revealed by mRNA differential display reverse transcription-PCR and cDNA microarray analyses. The genes that are down-regulated in mouse (J774G8) or human (U937) macrophages upon exposure to Leishmania include small RNA transcripts from the short interspersed element sequences. Among the short interspersed element RNAs that are down-regulated is 7SL RNA, which is the RNA component of the signal recognition particle. Because the microbicidal functions of macrophages profoundly count on vesicular protein transport processes, down-regulation of 7SL RNA may be significant in the establishment of infection by Leishmania in macrophage phagolysosomes. To evaluate whether down-regulation of 7SL RNA results in inhibition of signal recognition particle-mediated vesicular protein transport processes, we have tested and found that the targeting of proteins to the endoplasmic reticulum and plasma membrane and the secretion of proteins by macrophages are compromised in Leishmania-infected J774G8 and U937 cells. Knocking down 7SL RNA using small interfering RNA mimicked the effect of exposure of macrophages to Leishmania. The overexpression of 7SL RNA in J774G8 or U937 cells made these cells resistant to Leishmania infection, suggesting the possible biological significance of down-regulation of 7SL RNA synthesis in the establishment of infection by Leishmania. We conclude that Leishmania down-regulates 7SL RNA in macrophages to manipulate the targeting of many proteins that use the vesicular transport pathway and thus favors its successful establishment of infection in macrophages.

Highlights

Pathogenic microbes often develop strategies to evade host immune responses, learn to adapt to the host environment, and/or manipulate the host system to make it more hospitable for the establishment of infection and propagation [1,2,3]
Our data suggest that the exposure of macrophages to Leishmania induces the up- and down-regulation of many genes (Table I)
To evaluate whether the consequences of leishmanial knockdown of 7SL RNA may be alleviated by the overexpression of 7SL RNA in macrophages, we developed stable J774G8 and undifferentiated U937 cell lines in which 7SL RNA was overexpressed from the H1 RNA promoter

Summary

Introduction

Pathogenic microbes often develop strategies to evade host immune responses, learn to adapt to the host environment, and/or manipulate the host system to make it more hospitable for the establishment of infection and propagation [1,2,3]. The parasitic protozoan Leishmania has the uncanny ability to evade the immune reactions of macrophages and is able to establish infection inside macrophage phagolysosomes and to propagate inside tissue macrophages [1,2,3]. To survive inside the macrophage and to escape immunity, Leishmania has developed mechanisms that deactivate macrophage immune functions, including inhibition of the respiratory burst and interleukin-12 and nitric oxide synthesis and down-regulation of major histocompatibility complex class II molecules as well as promotion of the synthesis of inhibitory cytokines such as transforming growth factor-␤ and interleukin-10 and induction of the suppressor of cytokine signaling [5, 6]. Proper targeting of the receptor molecules specific for those activating factors on the cell surface is very important for the optimal function of macrophages. The RNA component of the SRP (7SL RNA) contains two elements related to the human and rodent Alu families of interspersed repetitive DNA sequences connected by a unique sequence, the S domain [11]. 7SL RNA associates with six proteins in mammalian cells termed SRP72, SRP68, SRP54, SRP19, SRP14, and SRP9 [11]

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