Leishmania donovaniAmastigotes Impair Gamma Interferon-Induced STAT1α Nuclear Translocation by Blocking the Interaction between STAT1α and Importin-α5

Abstract

The protozoan parasite Leishmania donovani, the etiological agent of visceral leishmaniasis, is renowned for its capacity to sabotage macrophage functions and signaling pathways stimulated by activators such as gamma interferon (IFN-␥). Our knowledge of the strategies utilized by L. donovani to impair macrophage responsiveness to IFN-␥ remains fragmentary. In the present study, we investigated the impact of an infection by the amastigote stage of L. donovani on IFN-␥ responses and signaling via the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway in mouse bone marrow-derived macrophages. The levels of IFN-␥-induced expression of major histocompatibility complex class II and inducible nitric oxide synthase (iNOS) were strongly reduced in L. donovani amastigote-infected macrophages. As the expression of those genes is mediated by the transcription factors STAT1␣ and IFN regulatory factor 1 (IRF-1), we investigated their activation in amastigote-infected macrophages treated with IFN-␥. We found that whereas STAT1␣ protein levels and the levels of phosphorylation on Tyr701 and Ser727 were normal, IRF-1 expression was inhibited in infected macrophages. This inhibition of IRF-1 expression correlated with a defective nuclear translocation of STAT1␣, and further analyses revealed that the IFN-␥-induced STAT1␣ association with the nuclear transport adaptor importin-␣5 was compromised in L. donovani amastigote-infected macrophages. Taken together, our results provide evidence for a novel mechanism used by L. donovani amastigotes to interfere with IFN-␥-activated macrophage functions and provide a better understanding of the strategies deployed by this parasite to ensure its intracellular survival.Protozoan parasites of the genus Leishmania cause a spectrum of diseases in humans, ranging from self-healing ulcers to potentially fatal visceral leishmaniasis, which affect millions of people worldwide. These parasites are transmitted to mammals under their promastigote form upon the blood meal of infected sand flies. Following their phagocytosis by macrophages, promastigotes differentiate into amastigotes, the mammalian stage of the parasite which resides and replicates inside phagolysosomes. To ensure their survival within macrophages, Leishmania parasites have evolved strategies to sabotage signaling pathways that modulate host cell microbicidal properties (8,14,19,20,26). Hence, Leishmania-infected macrophages are characterized by the abnormal expression of activation-associated functions and by an unresponsiveness to activators such as gamma interferon (IFN-␥) (2,9,12,17,25,33,34).The signaling events initiated by IFN-␥ have been investigated in great detail (29, 36). Binding of IFN-␥ to its multisubunit receptor triggers tyrosine phosphorylation of the IFN-␥ receptor-associated kinases Janus kinase 1 (JAK1) and JAK2, which in turn phosphorylate the transcription factor signal transducer and activator of transcription 1␣ (STAT1␣) on residue Tyr701. Tyrosine-phosphorylated STAT1␣ molecules ...

A Metronidazole-Resistant Isolate of Blastocystis spp. Is Susceptible to Nitric Oxide and Downregulates Intestinal Epithelial Inducible Nitric Oxide Synthase by a Novel Parasite Survival Mechanism

“…In fact L-arginine bioavailability controls nitric oxide production without affecting iNOS mRNA levels in the cell (18).On the contrary, we observed a downregulation of iNOS mRNA expression in live enterocytes cocultured with Blastocystis ST-7 (B), as seen in Toxoplasma (35)-and Leishmania (25)-infected macrophages. Although iNOS-inhibiting Blastocystis strain ST-7 (B) possesses much higher arginase activity than ST-4 (WR-1), the inhibition of Caco-2 NO production by ST-7 (B) (without altering host cell viability) is primarily due to the downregulation of epithelial iNOS mRNA expression, as reported for Toxoplasma-and Leishmania-infected macrophages (25,35). A secondary role of Blastocystis arginase in inhibiting epithelial NO production (as seen in cases of H. pylori and Giardia infections) cannot be ruled out.…”

“…Inhibition of iNOS activity under both conditions occurs at a posttranscriptional level and does not involve downregulation of iNOS mRNA. On the other hand, infections of intracellular parasites such as Toxoplasma (35) and Leishmania (25) lead to downregulation of iNOS mRNA expression in microglial cells and macrophages, respectively. Noninvasive, lumen-dwelling, extracellular pathogens like Giardia and Blastocystis seldom come in contact with macrophages.…”

Synaptotagmin XI Regulates Phagocytosis and Cytokine Secretion in Macrophages

“…RNA was reverse-transcribed (39), and PCR was performed with a DNA thermal cycler (Perkin-Elmer Corporation, version 2.3) with the following primer pairs, and an annealing temperature of 55˚C. Hypoxanthine phosphoribosyltransferase (HPRT): F-AD55: 59-GTTGGATACAGGCCA-GACTTTGTTG-39, R-AD56: 59-GATTCAACTTGCGCTCATCTTAGGC-39; Syt IV: F-AD476: 59-CACCTACCGAAATCTGATGTGTC-39, R-AD477: 59-GACCAACCGTCCAATCACCTC-39; Syt XI: F-AD445: 59-CAATG-CGTTTTCTGCCGTAGTAGA-39, R-AD446: 59-CTGACCAGGGACATC-ATCAAGAG-39.…”

Karyopherin Alpha Proteins Regulate Oligodendrocyte Differentiation

“…For example, it has been shown that Kpna1 mediates type I interferon-induced ISGF3 (Stat1/Stat2/IRF9) complex nucleocytoplasmic import [37]. In addition, Kpna1 is also implicated in Stat1 import in response to type II interferon signaling activation [38]. Other paralogs may similarly function downstream of and in coordination with specific extrinsic cues, warranting further exploration.…”