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HIV-1 and Mycobacterium tuberculosis (Mtb) coinfections are a major public health problem but are not well characterized. HIV-1 Tat is secreted by infected cells, generating nanomolar concentrations of Tat in the sera of people living with HIV. Circulating Tat enters cells, binds to PI(4,5)P 2 then undergoes palmitoylation, thereby becoming resident on this phosphoinositide. Here, we found that Tat favors the multiplication of Mtb in macrophages. Moreover, Tat renders zebrafish larvae more sensitive to mycobacterial infection. We found that Tat binding to PI(4,5)P 2 and palmitoylation enable Tat to inhibit the recruitment of the AP-2 adaptor, thereby inhibiting clathrin-mediated endocytosis and in turn autophagy. This inhibition prevents the degradation of intracellular pathogens such as Mtb and opsonized Toxoplasma gondii, but also of lipid droplets, thereby facilitating the access of these pathogens to lipids. We thus identified a mechanism enabling HIV Tat to favor the multiplication of intracellular pathogens such as Mtb.

The Syk tyrosine kinase acts downstream of several immune receptors such as the FcγR. Syk owns two SH2 domains that interact with biphosphorylated ITAMs of the FcγR upon phagocytosis. This results in the activation of Syk by autophosphorylation, triggering phosphorylation of several downstream targets, F-actin polymerization, and phagocytosis of the IgG-opsonized target. We found that Syk is S-acylated upon phagocytosis by macrophages. Palmitoylation is performed on a single Syk-Cys by the DHHC5 enzyme that specifically associates with Syk upon phagocytosis. Syk palmitoylation is important for Syk localization to the phagocytic cup, phosphorylation, and phagocytosis. We observed that another Syk-Cys residue, within a redox motif, is modified by sulfenylation. Nevertheless, Syk desulfenylation seems to occur during phagocytosis, when H 2 O 2 production at the cup decreases, after 3.5 min of phagocytosis. Molecular dynamics studies indicated that desulfenylation increased the exposure of a loop within the Syk interdomain B. This could facilitate phosphorylation of key Syk-Tyr residues by upstream kinases. We thus propose an updated model for Syk activation during FcγR-mediated phagocytosis that involves both Syk palmitoylation and desulfenylation.

Most HIV-1 Tat is unconventionally secreted by infected cells following Tat interaction with phosphatidylinositol (4,5) bisphosphate (PI(4,5)P 2 ) at the plasma membrane. Extracellular Tat is endocytosed by uninfected cells before escaping from endosomes to reach the cytosol and bind PI(4,5)P 2 . It is not clear whether and how incoming Tat concentrates in uninfected cells. Here we show that, in uninfected cells, the S-acyl transferase DHHC-20 together with the prolylisomerases cyclophilin A (CypA) and FKBP12 palmitoylate Tat on Cys31 thereby increasing Tat affinity for PI(4,5)P 2 . In infected cells, CypA is bound by HIV-1 Gag, resulting in its encapsidation and CypA depletion from cells. Because of the lack of this essential cofactor, Tat is not palmitoylated in infected cells but strongly secreted. Hence, Tat palmitoylation specifically takes place in uninfected cells. Moreover, palmitoylation is required for Tat to accumulate at the plasma membrane and affect PI(4,5)P 2 -dependent membrane traffic such as phagocytosis and neurosecretion. It is not clear whether and how incoming HIV-1 Tat accumulates in uninfected cells. Here, Chopard et al. show that, in uninfected cells, incoming Tat is palmitoylated on Cys31 by DHHC-20, which increases its affinity for PI(4,5)P 2 and results in its accumulation at the plasma membrane.

The Syk tyrosine kinase acts downstream of several immune receptors such as the FcγR. Syk owns two SH2 domains that interact with biphosphorylated ITAMs of the FcγR upon phagocytosis. This results in the activation of Syk by autophosphorylation, triggering phosphorylation of several downstream targets, F-actin polymerization, and phagocytosis of the IgG-opsonized target. We found that Syk is S-acylated upon phagocytosis by macrophages. Palmitoylation is performed on a single Syk-Cys by the DHHC5 enzyme that specifically associates with Syk upon phagocytosis. Syk palmitoylation is important for Syk localization to the phagocytic cup, phosphorylation, and phagocytosis. We observed that another Syk-Cys residue, within a redox motif, is modified by sulfenylation. Nevertheless, Syk desulfenylation seems to occur during phagocytosis, when H2O2 production at the cup decreases, after 3.5 min of phagocytosis. Molecular dynamics studies indicated that desulfenylation increased the exposure of a loop within the Syk interdomain B. This could facilitate phosphorylation of key Syk-Tyr residues by upstream kinases. We thus propose an updated model for Syk activation during FcγR-mediated phagocytosis that involves both Syk palmitoylation and desulfenylation.

Human Immunodeficiency Virus (HIV) and Mycobacterium tuberculosis (M.tb) are among the most lethal human pathogens worldwide, each being responsible for around 1.5 million deaths annually. Moreover, synergy between acquired immune deficiency syndrome (AIDS) and tuberculosis (TB) has turned HIV/M.tb co-infection into a major public health threat in developing countries. In the past decade, autophagy, a lysosomal catabolic process, has emerged as a major host immune defense mechanism against infectious agents like M.tb and HIV. Nevertheless, in some instances, autophagy machinery appears to be instrumental for HIV infection. Finally, there is mounting evidence that both pathogens deploy various countermeasures to thwart autophagy. This mini-review proposes an overview of the roles and regulations of autophagy in HIV and M.tb infections with an emphasis on microbial factors. We also discuss the role of autophagy manipulation in the context of HIV/M.tb co-infection. In future, a comprehensive understanding of autophagy interaction with these pathogens will be critical for development of autophagy-based prophylactic and therapeutic interventions for AIDS and TB.

Human immunodeficiency virus type 1 (HIV‐1) transcription relies on its transactivating Tat protein. Although devoid of a signal sequence, Tat is released by infected cells and secreted Tat can affect uninfected cells, thereby contributing to HIV‐1 pathogenesis. The mechanism and the efficiency of Tat export remained to be documented. Here, we show that, in HIV‐1‐infected primary CD4 + T‐cells that are the main targets of the virus, Tat accumulates at the plasma membrane because of its specific binding to phosphatidylinositol‐4,5‐bisphosphate (PI(4,5)P 2 ). This interaction is driven by a specific motif of the Tat basic domain that recognizes a single PI(4,5)P 2 molecule and is stabilized by membrane insertion of Tat tryptophan side chain. This original recognition mechanism enables binding to membrane‐embedded PI(4,5)P 2 only, but with an unusually high affinity that allows Tat to perturb the PI(4,5)P 2 ‐mediated recruitment of cellular proteins. Tat–PI(4,5)P 2 interaction is strictly required for Tat secretion, a process that is very efficient, as ∼2/3 of Tat are exported by HIV‐1‐infected cells during their lifespan. The function of extracellular Tat in HIV‐1 infection might thus be more significant than earlier thought.

Most macrophages remain uninfected in HIV-1-infected patients. Nevertheless, the phagocytic capacity of phagocytes from these patients is impaired, favouring the multiplication of opportunistic pathogens. The basis for this phagocytic defect is not known. HIV-1 Tat protein is efficiently secreted by infected cells. Secreted Tat can enter uninfected cells and reach their cytosol. Here we found that extracellular Tat, at the subnanomolar concentration present in the sera of HIV-1-infected patients, inhibits the phagocytosis of Mycobacterium avium or opsonized Toxoplasma gondii by human primary macrophages. This inhibition results from a defect in mannose- and Fcγ-receptor-mediated phagocytosis, respectively. Inhibition relies on the interaction of Tat with phosphatidylinositol (4,5)bisphosphate that interferes with the recruitment of Cdc42 to the phagocytic cup, thereby preventing Cdc42 activation and pseudopod elongation. Tat also inhibits FcγR-mediated phagocytosis in neutrophils and monocytes. This study provides a molecular basis for the phagocytic defects observed in uninfected phagocytes following HIV-1 infection. Phagocytic activity of macrophages is reduced in HIV-1-infected patients, but the reason for this is unknown. Here, the authors report that secreted Tat protein inhibits phagocytosis by binding to the phospholipid PI(4,5)P 2 and impairing the recruitment of small GTPase Cdc42 to the phagocytic cup.

Intracellular pathogenic microorganisms and toxins exploit host cell mechanisms to enter, exert their deleterious effects as well as hijack host nutrition for their development. A potential approach to treat multiple pathogen infections and that should not induce drug resistance is the use of small molecules that target host components. We identified the compound 1-adamantyl (5-bromo-2-methoxybenzyl) amine (ABMA) from a cell-based high throughput screening for its capacity to protect human cells and mice against ricin toxin without toxicity. This compound efficiently protects cells against various toxins and pathogens including viruses, intracellular bacteria and parasite. ABMA provokes Rab7-positive late endosomal compartment accumulation in mammalian cells without affecting other organelles (early endosomes, lysosomes, the Golgi apparatus, the endoplasmic reticulum or the nucleus). As the mechanism of action of ABMA is restricted to host-endosomal compartments, it reduces cell infection by pathogens that depend on this pathway to invade cells. ABMA may represent a novel class of broad-spectrum compounds with therapeutic potential against diverse severe infectious diseases.

The non-receptor Spleen tyrosine kinase Syk acts downstream of several receptors of the immune system such as the FcγR. Syk is composed of a kinase domain and two SH2 domains that interact with the bi- phosphorylated ITAMs motifs of the FcγR upon phagocytosis. This results in the activation of Syk by auto- phosphorylation, triggering phosphorylation of several downstream targets in a process that will culminate in F-actin polymerization and phagocytosis of the IgG-opsonized target. We found that Syk is S-acylated upon phagocytosis by macrophages. Palmitoylation is performed on a single Syk-Cys by the protein S-acyl transferase DHHC5 that specifically associates with Syk upon phagocytosis. Syk palmitoylation is required for Syk localization to the phagocytic cup, Syk phosphorylation/activation, Cdc42 recruitment to the cup, F-actin polymerization and phagocytosis. We also observed that another Syk-Cys residue is modified by sulfenylation. Mutation of the sulfenylated Cys that belongs to a redox-motif inactivated the Syk catalytic activity and phagocytosis. We found that Syk desulfenylation occurs during phagocytosis. Molecular dynamics studies indicated that desulfenylation increased the mobility and exposure of a loop within the Syk interdomain B, likely facilitating phosphorylation of key Syk-Tyr residues by upstream effectors such as Src kinases. We thus propose an original updated model for Syk activation during FcγR-mediated phagocytosis that involves both Syk palmitoylation and desulfenylation.

HIV-1 and Mycobacterium tuberculosis (Mtb) coinfections are a major public health problem but are not well characterized. HIV-1 Tat is secreted by infected cells, generating nanomolar concentrations of Tat in the sera of people living with HIV. Circulating Tat enters cells, binds to PI(4,5)P2 then undergoes palmitoylation, thereby becoming resident on this phosphoinositide. Here, we found that Tat favors the multiplication of Mtb in macrophages. Moreover, Tat renders zebrafish larvae more sensitive to mycobacterial infection. We found that Tat binding to PI(4,5)P2 and palmitoylation enable Tat to inhibit the recruitment of the AP-2 adaptor, thereby inhibiting clathrin-mediated endocytosis and in turn autophagy. This inhibition prevents the degradation of intracellular pathogens such as Mtb and opsonized Toxoplasma gondii, but also of lipid droplets, thereby facilitating the access of these pathogens to lipids. We thus identified a mechanism enabling HIV Tat to favor the multiplication of intracellular pathogens such as Mtb.