title: Exogenous Nef is an inhibitor of Mycobacterium tuberculosis-induced tumor necrosis factor-alpha production and macrophage apoptosis.
abstract: Human immunodeficiency virus-1 (HIV-1) impairs tumor necrosis factor-alpha (TNF-alpha)-mediated macrophage apoptosis induced by Mycobacterium tuberculosis (Mtb). HIV Nef protein plays an important role in the pathogenesis of AIDS. We have tested the hypothesis that exogenous Nef is a factor that inhibits TNF-alpha production/apoptosis in macrophages infected with Mtb. We demonstrate that Mtb and Nef individually trigger TNF-alpha production in macrophages. However, TNF-alpha production is dampened when the two are present simultaneously, probably through cross-regulation of the individual signaling pathways leading to activation of the TNF-alpha promoter. Mtb-induced TNF-alpha production is abrogated upon mutation of the Ets, Egr, Sp1, CRE, or AP1 binding sites on the TNF-alpha promoter, whereas Nef-mediated promoter activation depends only on the CRE and AP1 binding sites, pointing to differences in the mechanisms of activation of the promoter. Mtb-dependent promoter activation depends on the mitogen-activated kinase (MAPK) kinase kinase ASK1 and on MEK/ERK signaling. Nef inhibits ASK1/p38 MAPK-dependent Mtb-induced TNF-alpha production probably by inhibiting binding of ATF2 to the TNF-alpha promoter. It also inhibits MEK/ERK-dependent Mtb-induced binding of FosB to the promoter. Nef-driven TNF-alpha production occurs in an ASK1-independent, Rac1/PAK1/p38 MAPK-dependent, and MEK/ERK-independent manner. The signaling pathways used by Mtb and Nef to trigger TNF-alpha production are therefore distinctly different. In addition to attenuating Mtb-dependent TNF-alpha promoter activation, Nef also reduces Mtb-dependent TNF-alpha mRNA stability probably through its ability to inhibit ASK1/p38 MAPK signaling. These results provide new insight into how HIV Nef probably exacerbates tuberculosis infection by virtue of its ability to dampen Mtb-induced TNF-alpha production.
authors.affiliation: Department of Chemistry, Bose Institute, 93/1 APC Road, Kolkata 700009, India.
authors.forename: Kuldeep
authors.initials: K
authors.lastname: Kumawat
authors.forename: Sushil Kumar
authors.initials: SK
authors.lastname: Pathak
authors.forename: Anna-Lena
authors.initials: AL
authors.lastname: Spetz
authors.forename: Manikuntala
authors.initials: M
authors.lastname: Kundu
authors.forename: Joyoti
authors.initials: J
authors.lastname: Basu
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000378:metabolism* / Q000382:microbiology; D051698:Activating Transcription Factor 2 / Q000378:metabolism; D017209:Apoptosis; D002460:Cell Line; D015497:HIV-1 / Q000378:metabolism* / Q000472:pathogenicity; D006801:Humans; D048848:MAP Kinase Kinase Kinase 5 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008264:Macrophages / Q000378:metabolism* / Q000382:microbiology / Q000821:virology; D009169:Mycobacterium tuberculosis / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D020871:RNA Stability / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D020218:Response Elements; D014376:Tuberculosis / Q000378:metabolism* / Q000821:virology; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D054311:nef Gene Products, Human Immunodeficiency Virus / Q000378:metabolism* / Q000494:pharmacology; D054462:p21-Activated Kinases / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
chemical_list: C497105:ATF2 protein, human; D051698:Activating Transcription Factor 2; C064269:FOSB protein, human; D016760:Proto-Oncogene Proteins c-fos; C107953:RAC1 protein, human; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D054311:nef Gene Products, Human Immunodeficiency Virus; C514837:nef protein, Human immunodeficiency virus 1; C515903:PAK1 protein, human; D054462:p21-Activated Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048848:MAP Kinase Kinase Kinase 5; C482858:MAP3K5 protein, human; D020830:rac1 GTP-Binding Protein