Proline-Proline-Glutamic Acid (PPE) Protein Rv1168c of Mycobacterium tuberculosis Augments Transcription from HIV-1 Long Terminal Repeat Promoter

Khalid Hussain Bhat,Chinta Krishna Chaitanya,Nazia Parveen,Raja Varman,Sudip Ghosh,Sangita Mukhopadhyay

doi:10.1074/jbc.m111.327825

Abstract

Cells of the monocyte/macrophage lineage are shown to play a role in the pathogenesis of human immunodeficiency virus (HIV). The occurrence of HIV type 1 (HIV-1) infection is found to be accelerated in people infected with Mycobacterium tuberculosis, but the mechanism by which mycobacterial protein(s) induces HIV-1 LTR trans-activation is not clearly understood. We show here that the M. tuberculosis proline-proline-glutamic acid (PPE) protein Rv1168c (PPE17) can augment transcription from HIV-1 LTR in monocyte/macrophage cells. Rv1168c interacts specifically with Toll-like receptor-2 (TLR2) resulting in downstream activation of nuclear factor-κB (NF-κB) resulting in HIV-1 LTR trans-activation. Another PPE protein, Rv1196 (PPE18), was also found to interact with TLR2 but had no effect on HIV-1 LTR trans-activation because of its inability to activate the NF-κB signaling pathway. In silico docking analyses and mutation experiments have revealed that the N-terminal domain of Rv1168c specifically interacts with LRR motifs 15-20 of TLR2, and this site of interaction is different from that of Rv1196 protein (LRR motifs 11-15), indicating that the site of interaction on TLR2 dictates the downstream signaling events leading to activation of NF-κB. This information may help in understanding the mechanism of pathogenesis of HIV-1 during M. tuberculosis co-infection.

Highlights

Mycobacterium tuberculosis stimulates human immunodeficiency virus (HIV)-1 long terminal repeat (LTR) transcription in co-infected individuals
Recombinant Rv1168c Protein Activates HIV type 1 (HIV-1) LTR-driven Chloramphenicol Acetyltransferase Expression in THP-1 Cells— To examine whether rRv1168c increases HIV-1 LTR transcription, human monocytic THP-1 cells were co-transfected with a CAT reporter gene driven by a full-length HIV-1 LTR (HIV-1 LTR-CAT) and a ␤-galactosidase reporter driven by a constitutive CMV promoter used as a control to determine the transfection efficiency
Treatment of THP-1 cells with rRv1168c resulted in dose-dependent increase in the HIV-1 LTR-driven CAT expression, whereas rRv1168c had no effect on ␤-galactosidase expression (Fig. 1A)

Summary

Background

Mycobacterium tuberculosis stimulates HIV-1 LTR transcription in co-infected individuals. In silico docking analyses and mutation experiments have revealed that the N-terminal domain of Rv1168c interacts with LRR motifs 15–20 of TLR2, and this site of interaction is different from that of Rv1196 protein (LRR motifs 11–15), indicating that the site of interaction on TLR2 dictates the downstream signaling events leading to activation of NF-␬B This information may help in understanding the mechanism of pathogenesis of HIV-1 during M. tuberculosis co-infection. Activation of monocytes by LPS, IL-6, or TNF-␣ results in enhanced HIV replication, a process that correlates well with NF-␬B activity (20 –22) Induction of these proinflammatory cytokines during mycobacterial infection has been postulated to be one of the important factors that drive hyper-transcription from the LTR promoter [13, 14, 23, 24]. Our data presented indicate that Rv1168c interacts with the LRR motifs 15–20 of TLR2 and activates NF-␬B signaling cascades that leads to HIV-1 LTR hyper-activation in a Tat-independent manner

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION