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HIV-1 inhibits autophagy in bystander macrophage/monocytic cells through Src-Akt and STAT3.

Van Grol J, Subauste C, Andrade RM, Fujinaga K, Nelson J, Subauste CS - PLoS ONE (2010)

Bottom Line: Little is known about the role of altered regulatory signaling in disorders associated with defective autophagy.These studies revealed that a pathogen can impair autophagy in non-infected cells by activating counter-regulatory pathways.The fact that pharmacologic manipulation of cell signaling restored autophagy in cells exposed to HIV-1-infected cells raises the possibility of therapeutic manipulation of cell signaling to restore autophagy in HIV-1 infection.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America.

ABSTRACT
Autophagy is a homeostatic mechanism of lysosomal degradation. Defective autophagy has been linked to various disorders such as impaired control of pathogens and neurodegeneration. Autophagy is regulated by a complex array of signaling pathways that act upstream of autophagy proteins. Little is known about the role of altered regulatory signaling in disorders associated with defective autophagy. In particular, it is not known if pathogens inhibit autophagy by modulation of upstream regulatory pathways. Cells infected with HIV-1 blocked rapamycin-induced autophagy and CD40-induced autophagic killing of Toxoplasma gondii in bystander (non-HIV-1 infected) macrophage/monocytic cells. Blockade of autophagy was dependent on Src-Akt and STAT3 triggered by HIV-1 Tat and IL-10. Neutralization of the upstream receptors VEGFR, beta-integrin or CXCR4, as well as of HIV-1 Tat or IL-10 restored autophagy in macrophage/monocytic cells exposed to HIV-1-infected cells. Defective autophagic killing of T. gondii was detected in monocyte-derived macrophages from a subset of HIV-1(+) patients. This defect was also reverted by neutralization of Tat or IL-10. These studies revealed that a pathogen can impair autophagy in non-infected cells by activating counter-regulatory pathways. The fact that pharmacologic manipulation of cell signaling restored autophagy in cells exposed to HIV-1-infected cells raises the possibility of therapeutic manipulation of cell signaling to restore autophagy in HIV-1 infection.

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STAT3 and Akt are required for HIV-1 and IL-10 to inhibit autophagy.A, MonoMac6 cells were transfected with siRNA against STAT3 or control siRNA. Expression of STAT3 and actin were examined 72 h post-transfection. B, MonoMac6 cells transfected with control siRNA or siRNA directed against STAT3 or Akt were transfected with LC3-eGFP. Cells were incubated with or without HIV-1 Tat or IL-10 (both at 100 pg/ml) overnight followed by stimulation with rapamycin. Autophagy was assessed by examining expression of large LC3+ structures. Data are representative of 3 independent experiments presented as means ± SEM; ***p≤0.001, ∧p≥0.05.
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pone-0011733-g007: STAT3 and Akt are required for HIV-1 and IL-10 to inhibit autophagy.A, MonoMac6 cells were transfected with siRNA against STAT3 or control siRNA. Expression of STAT3 and actin were examined 72 h post-transfection. B, MonoMac6 cells transfected with control siRNA or siRNA directed against STAT3 or Akt were transfected with LC3-eGFP. Cells were incubated with or without HIV-1 Tat or IL-10 (both at 100 pg/ml) overnight followed by stimulation with rapamycin. Autophagy was assessed by examining expression of large LC3+ structures. Data are representative of 3 independent experiments presented as means ± SEM; ***p≤0.001, ∧p≥0.05.

Mentions: STAT3 is a major signaling molecule downstream of IL-10 [49], [50]. Thus, we examined the role of STAT3 in the inhibition of autophagy induced by HIV-1 and IL-10. Transfection of MonoMac6 cells with siRNA directed against STAT3 reduced expression of this protein (Figure 7A). Silencing of STAT3 prevented IL-10 and HIV-1 Tat from inhibiting autophagy induced by rapamycin (Figure 7B). The PI3K/Akt pathway has also been reported to mediate IL-10 signaling [51], [52], [53]. Indeed, silencing of Akt prevented IL-10 from inhibiting autophagy induced by rapamycin (Figure 7B). Therefore, IL-10 signaling through STAT3 and Akt is necessary for blockade of autophagy. IL-10 appears unlikely to be the sole mediator of inhibition of autophagy. In this regard, the concentration of IL-10 (30 pg/ml) detected in MDM cultures after HIV-1 Tat treatment was insufficient for blockade of rapamycin-induced autophagy (data not shown). Moreover, IL-10 production induced by HIV-1 Tat is reported to be independent of the basic and RGD domains while these sites are required for inhibition of autophagy [54], [55]. Taken together, these results support a model whereby HIV-1 and IL-10 act in cooperation through Akt and STAT3 to impair autophagy in bystander macrophage/monocytic cells (Figure 8).


HIV-1 inhibits autophagy in bystander macrophage/monocytic cells through Src-Akt and STAT3.

Van Grol J, Subauste C, Andrade RM, Fujinaga K, Nelson J, Subauste CS - PLoS ONE (2010)

STAT3 and Akt are required for HIV-1 and IL-10 to inhibit autophagy.A, MonoMac6 cells were transfected with siRNA against STAT3 or control siRNA. Expression of STAT3 and actin were examined 72 h post-transfection. B, MonoMac6 cells transfected with control siRNA or siRNA directed against STAT3 or Akt were transfected with LC3-eGFP. Cells were incubated with or without HIV-1 Tat or IL-10 (both at 100 pg/ml) overnight followed by stimulation with rapamycin. Autophagy was assessed by examining expression of large LC3+ structures. Data are representative of 3 independent experiments presented as means ± SEM; ***p≤0.001, ∧p≥0.05.
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Related In: Results  -  Collection

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pone-0011733-g007: STAT3 and Akt are required for HIV-1 and IL-10 to inhibit autophagy.A, MonoMac6 cells were transfected with siRNA against STAT3 or control siRNA. Expression of STAT3 and actin were examined 72 h post-transfection. B, MonoMac6 cells transfected with control siRNA or siRNA directed against STAT3 or Akt were transfected with LC3-eGFP. Cells were incubated with or without HIV-1 Tat or IL-10 (both at 100 pg/ml) overnight followed by stimulation with rapamycin. Autophagy was assessed by examining expression of large LC3+ structures. Data are representative of 3 independent experiments presented as means ± SEM; ***p≤0.001, ∧p≥0.05.
Mentions: STAT3 is a major signaling molecule downstream of IL-10 [49], [50]. Thus, we examined the role of STAT3 in the inhibition of autophagy induced by HIV-1 and IL-10. Transfection of MonoMac6 cells with siRNA directed against STAT3 reduced expression of this protein (Figure 7A). Silencing of STAT3 prevented IL-10 and HIV-1 Tat from inhibiting autophagy induced by rapamycin (Figure 7B). The PI3K/Akt pathway has also been reported to mediate IL-10 signaling [51], [52], [53]. Indeed, silencing of Akt prevented IL-10 from inhibiting autophagy induced by rapamycin (Figure 7B). Therefore, IL-10 signaling through STAT3 and Akt is necessary for blockade of autophagy. IL-10 appears unlikely to be the sole mediator of inhibition of autophagy. In this regard, the concentration of IL-10 (30 pg/ml) detected in MDM cultures after HIV-1 Tat treatment was insufficient for blockade of rapamycin-induced autophagy (data not shown). Moreover, IL-10 production induced by HIV-1 Tat is reported to be independent of the basic and RGD domains while these sites are required for inhibition of autophagy [54], [55]. Taken together, these results support a model whereby HIV-1 and IL-10 act in cooperation through Akt and STAT3 to impair autophagy in bystander macrophage/monocytic cells (Figure 8).

Bottom Line: Little is known about the role of altered regulatory signaling in disorders associated with defective autophagy.These studies revealed that a pathogen can impair autophagy in non-infected cells by activating counter-regulatory pathways.The fact that pharmacologic manipulation of cell signaling restored autophagy in cells exposed to HIV-1-infected cells raises the possibility of therapeutic manipulation of cell signaling to restore autophagy in HIV-1 infection.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America.

ABSTRACT
Autophagy is a homeostatic mechanism of lysosomal degradation. Defective autophagy has been linked to various disorders such as impaired control of pathogens and neurodegeneration. Autophagy is regulated by a complex array of signaling pathways that act upstream of autophagy proteins. Little is known about the role of altered regulatory signaling in disorders associated with defective autophagy. In particular, it is not known if pathogens inhibit autophagy by modulation of upstream regulatory pathways. Cells infected with HIV-1 blocked rapamycin-induced autophagy and CD40-induced autophagic killing of Toxoplasma gondii in bystander (non-HIV-1 infected) macrophage/monocytic cells. Blockade of autophagy was dependent on Src-Akt and STAT3 triggered by HIV-1 Tat and IL-10. Neutralization of the upstream receptors VEGFR, beta-integrin or CXCR4, as well as of HIV-1 Tat or IL-10 restored autophagy in macrophage/monocytic cells exposed to HIV-1-infected cells. Defective autophagic killing of T. gondii was detected in monocyte-derived macrophages from a subset of HIV-1(+) patients. This defect was also reverted by neutralization of Tat or IL-10. These studies revealed that a pathogen can impair autophagy in non-infected cells by activating counter-regulatory pathways. The fact that pharmacologic manipulation of cell signaling restored autophagy in cells exposed to HIV-1-infected cells raises the possibility of therapeutic manipulation of cell signaling to restore autophagy in HIV-1 infection.

Show MeSH
Related in: MedlinePlus