Leishmania donovani Exploits Myeloid Cell Leukemia 1 (MCL-1) Protein to Prevent Mitochondria-dependent Host Cell Apoptosis

Abstract

Apoptosis is one of the mechanisms used by host cells to remove unwanted intracellular organisms, and often found to be subverted by pathogens through use of host anti-apoptotic proteins. In the present study, with the help of in vitro and in vivo approaches, we documented that the macrophage anti-apoptotic protein myeloid cell leukemia 1 (MCL-1) is exploited by the intra-macrophage parasite Leishmania donovani to protect their "home" from actinomycin D-induced mitochondria-dependent apoptosis. Among all the anti-apoptotic BCL-2 family members, infection preferentially up-regulated expression of MCL-1 at both the mRNA and protein levels and compared with infected control, MCL-1-silenced infected macrophages documented enhanced caspase activity and increased apoptosis when subjected to actinomycin D treatment. Phosphorylation kinetics and ChIP assay demonstrated that infection-induced MCL-1 expression was regulated by transcription factor CREB (cAMP-response element-binding protein) and silencing of CREB resulted in reduced expression of MCL-1 and increased apoptosis. During infection, MCL-1 was found to be localized in mitochondria and this was significantly reduced in Tom70-silenced macrophages, suggesting the active role of TOM70 in MCL-1 transport. In the mitochondria, MCL-1 interacts with the major pro-apoptotic protein BAK and prevents BAK-BAK homo-oligomer formation thereby preventing cytochrome c release-mediated mitochondrial dysfunction. Silencing of MCL-1 in the spleen of infected mice showed decreased parasite burden and increased induction of splenocyte apoptosis. Collectively our results showed that L. donovani exploited the macrophage anti-apoptotic protein MCL-1 to prevent BAK-mediated mitochondria-dependent apoptosis thereby protecting its niche, which is essential for disease progression.Leishmania donovani, an obligate intracellular parasite, is the causative agent of the fatal visceral leishmaniasis (1). After entry into the macrophages, it survives and replicates inside the acidified phagolysosomes of macrophages (2). Its persistence to resist the host immune system determines the extent of pathogenicity and requires extensive manipulation of macrophage defense (3). One of the vital mechanisms by which host cells defend themselves against intracellular pathogens is the induction of apoptosis (4, 5). On the contrary, pathogens relentlessly try to defeat the host defense systems and evolved a number of ways to inhibit host cell apoptosis, which allows them more time to replicate (6). Various studies have documented the molecular mechanisms in virus (7), bacteria (8), and protozoan parasites (9) that tamper with the host defensive apoptotic machinery. Leishmania, being an obligate intracellular parasite, makes host cells resistant to a variety of pro-apoptotic signals in murine and human cell lines. L. donovani infection protects bone marrow-derived macrophages (BMDM) 2 from growth factor withdrawal-induced apoptosis (10). Infection with Leishmania infantum reduces actinomycin D-induced cell dea...

The Mitochondrial Outer Membrane Protein Tom70-Mediator in Protein Traffic, Membrane Contact Sites and Innate Immunity

“…MCL-1 targets TOM70 at the surface of mitochondria and subsequently acts as an inhibitor of apoptosis due to its structural similarity to Bcl-2. Interestingly, MCL-1 binds to TOM70 due to an internal EELD motif, which resembles the EEVD motif found at the C-terminus of cytosolic chaperones [ 175 , 187 ]. The prevention of host cell apoptosis by exploitation of the anti-apoptotic Bcl-2 family protein MCL-1 is also a feature of some other intracellular pathogens including Staphylococcus aureus, Chlamydia trachomatis and Mycobacterium tuberculosis [ 188 , 189 , 190 ].…”

Leishmania Hijacks Myeloid Cells for Immune Escape

“…In addition, L. donovani triggers AKT activation of the anti-apoptotic β-catenin, inhibiting the pro-apoptotic transcriptional regulator FOXO-1 ( Gupta et al, 2016 ). L. donovani also prevents mitochondria-dependent apoptosis by inducing anti-apoptotic protein MCL-1 ( Giri et al, 2016 ). Some factors encoded by the parasite, like the orthologs of the cytokine macrophage migration inhibitory factor (MIF), are involved in blocking macrophage apoptosis and prevent clearance of internalized parasites upon L. major infection ( Holowka et al, 2016 ).…”

The enemy within: Targeting host–parasite interaction for antileishmanial drug discovery

“…Since the seminal study of Moore and Matlashewski suggesting a Leishmania -dependent inhibition of host cell apoptosis [ 52 ], this observation has been confirmed by various reports [ 53 , 54 ]. More recent reports studying the anti-apoptotic effect observed in the VL mouse model proposed molecular mechanisms involving Leishmania -CpG motifs, host myeloid cell leukemia 1 factor (MCL-1), and the cAMP response element binding protein (CREB) transcription factor [ 55 , 56 ].…”