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The role of Mcl-1 in S. aureus-induced cytoprotection of infected macrophages.

Koziel J, Kmiecik K, Chmiest D, Maresz K, Mizgalska D, Maciag-Gudowska A, Mydel P, Potempa J - Mediators Inflamm. (2013)

Bottom Line: Consistent with this, we proved a crucial role of Mcl-1 in S. aureus-induced cytoprotection, since silencing of MCL1 by siRNA profoundly reversed the cytoprotection of infected cells leading to apoptosis.Increased MCL1 expression in infected cells was associated with enhanced NFκB activation and subsequent IL-6 secretion, since the inhibition of both NFκB and IL-6 signalling pathways abrogated Mcl-1 induction and cytoprotection.Finally, we confirmed our observation in vivo in murine model of septic arthritis showing the association between the severity of arthritis and Mcl-1 expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Ul. Gronostajowa 7, 30-387 Kraków, Poland. joanna.koziel@uj.edu.pl

ABSTRACT
As a facultative intracellular pathogen, Staphylococcus aureus invades macrophages and then promotes the cytoprotection of infected cells thus stabilizing safe niche for silent persistence. This process occurs through the upregulation of crucial antiapoptotic genes, in particular, myeloid cell leukemia-1 (MCL-1). Here, we investigated the underlying mechanism and signal transduction pathways leading to increased MCL-1 expression in infected macrophages. Live S. aureus not only stimulated de novo synthesis of Mcl-1, but also prolonged the stability of this antiapoptotic protein. Consistent with this, we proved a crucial role of Mcl-1 in S. aureus-induced cytoprotection, since silencing of MCL1 by siRNA profoundly reversed the cytoprotection of infected cells leading to apoptosis. Increased MCL1 expression in infected cells was associated with enhanced NFκB activation and subsequent IL-6 secretion, since the inhibition of both NFκB and IL-6 signalling pathways abrogated Mcl-1 induction and cytoprotection. Finally, we confirmed our observation in vivo in murine model of septic arthritis showing the association between the severity of arthritis and Mcl-1 expression. Therefore, we propose that S. aureus is hijacking the Mcl-1-dependent inhibition of apoptosis to prevent the elimination of infected host cells, thus allowing the intracellular persistence of the pathogen, its dissemination by infected macrophages, and the progression of staphylococci diseases.

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Mcl-1 expression induced by S. aureus is mediated by IL-6. (a) hMDMs were preincubated with anti-IL6 receptor antibodies (1 μg/mL) for 30 min and then infected with S. aureus at an MOI of 1 : 50 and/or stimulated with IL-6 (200 ng/mL). At 7 h p.i., RNA was extracted and relative MCL1 expression was measured by qRT-PCR. Diagram shows the mean values calculated from the results of at least three independent real-time reactions using hMDMs derived from different donors. Bars represent mean relative expression ± SD. *P < 0.05. (b) hMDMs were preincubated with anti-IL6 receptor (1 μg/mL) antibodies for 30 min and then infected with S. aureus Newman at an MOI of 1 : 50. The effect of S. aureus on Mcl-1 protein synthesis was measured 20 h after-infection by immunoblot. Shown is a representative immunoblot from three separate experiments performed on hMDMs derived from different donors.
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fig5: Mcl-1 expression induced by S. aureus is mediated by IL-6. (a) hMDMs were preincubated with anti-IL6 receptor antibodies (1 μg/mL) for 30 min and then infected with S. aureus at an MOI of 1 : 50 and/or stimulated with IL-6 (200 ng/mL). At 7 h p.i., RNA was extracted and relative MCL1 expression was measured by qRT-PCR. Diagram shows the mean values calculated from the results of at least three independent real-time reactions using hMDMs derived from different donors. Bars represent mean relative expression ± SD. *P < 0.05. (b) hMDMs were preincubated with anti-IL6 receptor (1 μg/mL) antibodies for 30 min and then infected with S. aureus Newman at an MOI of 1 : 50. The effect of S. aureus on Mcl-1 protein synthesis was measured 20 h after-infection by immunoblot. Shown is a representative immunoblot from three separate experiments performed on hMDMs derived from different donors.

Mentions: IL-6 upregulates Mcl-1 in human myeloma cells [18]. To determine whether IL-6 was also playing a role in S. aureus-induced Mcl-1 expression in hMDMs, macrophages were infected with S. aureus, what leads to IL-6 secretion within 24 h after infection (Supplement Figure 3). Both high mRNA and protein Mcl-1 expression observed after bacteria phagocytosis (Figures 5(a) and 5(b), resp.) was markedly reduced upon treatment of cells with IL-6 receptor (R) neutralising antibodies. Together, these results demonstrated that S. aureus-induced Mcl-1 expression is partly mediated by IL-6.


The role of Mcl-1 in S. aureus-induced cytoprotection of infected macrophages.

Koziel J, Kmiecik K, Chmiest D, Maresz K, Mizgalska D, Maciag-Gudowska A, Mydel P, Potempa J - Mediators Inflamm. (2013)

Mcl-1 expression induced by S. aureus is mediated by IL-6. (a) hMDMs were preincubated with anti-IL6 receptor antibodies (1 μg/mL) for 30 min and then infected with S. aureus at an MOI of 1 : 50 and/or stimulated with IL-6 (200 ng/mL). At 7 h p.i., RNA was extracted and relative MCL1 expression was measured by qRT-PCR. Diagram shows the mean values calculated from the results of at least three independent real-time reactions using hMDMs derived from different donors. Bars represent mean relative expression ± SD. *P < 0.05. (b) hMDMs were preincubated with anti-IL6 receptor (1 μg/mL) antibodies for 30 min and then infected with S. aureus Newman at an MOI of 1 : 50. The effect of S. aureus on Mcl-1 protein synthesis was measured 20 h after-infection by immunoblot. Shown is a representative immunoblot from three separate experiments performed on hMDMs derived from different donors.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3569898&req=5

fig5: Mcl-1 expression induced by S. aureus is mediated by IL-6. (a) hMDMs were preincubated with anti-IL6 receptor antibodies (1 μg/mL) for 30 min and then infected with S. aureus at an MOI of 1 : 50 and/or stimulated with IL-6 (200 ng/mL). At 7 h p.i., RNA was extracted and relative MCL1 expression was measured by qRT-PCR. Diagram shows the mean values calculated from the results of at least three independent real-time reactions using hMDMs derived from different donors. Bars represent mean relative expression ± SD. *P < 0.05. (b) hMDMs were preincubated with anti-IL6 receptor (1 μg/mL) antibodies for 30 min and then infected with S. aureus Newman at an MOI of 1 : 50. The effect of S. aureus on Mcl-1 protein synthesis was measured 20 h after-infection by immunoblot. Shown is a representative immunoblot from three separate experiments performed on hMDMs derived from different donors.
Mentions: IL-6 upregulates Mcl-1 in human myeloma cells [18]. To determine whether IL-6 was also playing a role in S. aureus-induced Mcl-1 expression in hMDMs, macrophages were infected with S. aureus, what leads to IL-6 secretion within 24 h after infection (Supplement Figure 3). Both high mRNA and protein Mcl-1 expression observed after bacteria phagocytosis (Figures 5(a) and 5(b), resp.) was markedly reduced upon treatment of cells with IL-6 receptor (R) neutralising antibodies. Together, these results demonstrated that S. aureus-induced Mcl-1 expression is partly mediated by IL-6.

Bottom Line: Consistent with this, we proved a crucial role of Mcl-1 in S. aureus-induced cytoprotection, since silencing of MCL1 by siRNA profoundly reversed the cytoprotection of infected cells leading to apoptosis.Increased MCL1 expression in infected cells was associated with enhanced NFκB activation and subsequent IL-6 secretion, since the inhibition of both NFκB and IL-6 signalling pathways abrogated Mcl-1 induction and cytoprotection.Finally, we confirmed our observation in vivo in murine model of septic arthritis showing the association between the severity of arthritis and Mcl-1 expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Ul. Gronostajowa 7, 30-387 Kraków, Poland. joanna.koziel@uj.edu.pl

ABSTRACT
As a facultative intracellular pathogen, Staphylococcus aureus invades macrophages and then promotes the cytoprotection of infected cells thus stabilizing safe niche for silent persistence. This process occurs through the upregulation of crucial antiapoptotic genes, in particular, myeloid cell leukemia-1 (MCL-1). Here, we investigated the underlying mechanism and signal transduction pathways leading to increased MCL-1 expression in infected macrophages. Live S. aureus not only stimulated de novo synthesis of Mcl-1, but also prolonged the stability of this antiapoptotic protein. Consistent with this, we proved a crucial role of Mcl-1 in S. aureus-induced cytoprotection, since silencing of MCL1 by siRNA profoundly reversed the cytoprotection of infected cells leading to apoptosis. Increased MCL1 expression in infected cells was associated with enhanced NFκB activation and subsequent IL-6 secretion, since the inhibition of both NFκB and IL-6 signalling pathways abrogated Mcl-1 induction and cytoprotection. Finally, we confirmed our observation in vivo in murine model of septic arthritis showing the association between the severity of arthritis and Mcl-1 expression. Therefore, we propose that S. aureus is hijacking the Mcl-1-dependent inhibition of apoptosis to prevent the elimination of infected host cells, thus allowing the intracellular persistence of the pathogen, its dissemination by infected macrophages, and the progression of staphylococci diseases.

Show MeSH
Related in: MedlinePlus