Mechanism of down regulation of RNA polymerase III‐transcribed ncRNA genes in macrophages by Leishmania

Abstract

Most of the non‐coding RNA (ncRNA) genes including those of several miRNAs are transcribed by RNA polymerase III (Pol III). The parasitic protozoan Leishmania invades mammalian macrophages to establish infection. We reported previously that Leishmania manipulates the expression of several non‐coding RNA genes in the macrophages to favor the establishment of their infection in the phagolysosomes of these cells. We report here the potential mechanism of these down regulations. We found that the ncRNA genes that are repressed by Leishmania infection in macrophages contain a ‘B‐box’ at their promoters and thus require the Pol III transcription factor TFIIIC110 for their expression. Leishmania promastigotes through their surface protease activate the thrombin receptor PAR1 in the macrophages. This activation of PAR1 increases the levels of cytosolic Ca2+ which in turn activates the Ca2+‐dependent protease calpain 1. Calpain 1 then degrades TFIIIC110 to inhibit the expression of the selected ncRNA genes. Immunofluorescence microscopy showed that PAR1 is abundantly expressed on the surface of the macrophages. Avirulent stock of Leishmania does not express surface gp63 and could not down regulate ncRNAs in the exposed macrophages. Inhibition of PAR1 or calpain 1 in macrophages made them relatively resistant to Leishmania infection. Supported by NIH NIAID grants R01AI042327 and R21AI076757 to GC.