Proteasome-mediated degradation of STAT1alpha following infection of macrophages with Leishmania donovani.
Activation of the Janus-activated kinase 2 (JAK2)/STAT1alpha signaling pathway is repressed in Leishmania-infected macrophages. This represents an important mechanism by which this parasite subverts the microbicidal functions of the cell to promote its own survival and propagation. We recently provided evidence that the protein tyrosine phosphatase (PTP) SHP-1 was responsible for JAK2 inactivation. However, STAT1 translocation to the nucleus was not restored in the absence of SHP-1. In the present study, we have used B10R macrophages to study the mechanism by which this Leishmania-induced STAT1 inactivation occurs. STAT1alpha nuclear localization was shown to be rapidly reduced by the infection. Western blot analysis revealed that cellular STAT1alpha, but not STAT3, was degraded. Using PTP inhibitors and an immortalized bone marrow-derived macrophage cell line from SHP-1-deficient mice, we showed that STAT1 inactivation was independent of PTP activity. However, inhibition of macrophage proteasome activity significantly rescued Leishmania-induced STAT1alpha degradation. We further demonstrated that degradation was receptor-mediated and involved protein kinase C alpha. All Leishmania species tested (L. major, L. donovani, L. mexicana, L. braziliensis), but not the related parasite Trypanosoma cruzi, caused STAT1alpha degradation. Collectively, results from this study revealed a new mechanism for STAT1 regulation by a microbial pathogen, which favors its establishment and propagation within the host.
Centre de Recherche en Infectiologie and Département de Biologie Médicale, Centre Hospitalier Universitaire de Québec, Université Laval, Québec G1V 4G2, Canada.
Geneviève
G
Forget
David J
DJ
Gregory
Martin
M
Olivier
D021581:Active Transport, Cell Nucleus; D000818:Animals; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015180:Electrophoresis, Gel, Two-Dimensional; D004791:Enzyme Inhibitors / Q000494:pharmacology; D050832:Interferon-Stimulated Gene Factor 3; D047908:Intracellular Signaling Peptides and Proteins; D007893:Leishmania donovani / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D051571:Protein Kinase C-alpha; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D013045:Species Specificity; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D050832:Interferon-Stimulated Gene Factor 3; D047908:Intracellular Signaling Peptides and Proteins; D061988:Proteasome Inhibitors; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; C079868:gamma interferon activation factor; C496630:Prkca protein, mouse; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C509248:Ptpn6 protein, mouse; D046988:Proteasome Endopeptidase Complex