HIV-1 Vpr enhances production of receptor of activated NF-kappaB ligand (RANKL) via potentiation of glucocorticoid receptor activity.

The HIV-1 accessory protein Vpr potentiates glucocorticoid (GC)-induced inhibition of a variety of immunologically important cytokines. We report the first instance of synergy between Vpr and GC in induction of a T cell cytokine, one which may underlie a metabolic complication of HIV infection. Accelerated bone resorption is an important complication of HIV disease and its treatment. Receptor of activated NF-kappaB ligand (RANKL) is the final effector of osteoclast differentiation and bone resorption. It is induced by exogenous GC, a prominent cofactor in bone mineral loss, as well as by elevated levels of endogenous GC, found in many patients with HIV disease. We document Vpr-mediated upregulation of RANKL, the dependence of this effect on GC receptor integrity, its function through a classic GC receptor motif, and its independence from Vpr-mediated G(2) cell cycle arrest. These data suggest a positive regulatory role for Vpr in transcriptional control of a cytokine that may be critical to one metabolic complication of HIV.

Interactions among human immunodeficiency virus (HIV)-1, interferon-gamma and receptor of activated NF-kappa B ligand (RANKL): implications for HIV pathogenesis.

We reported recently that exposure of human T cells to soluble HIV-1 envelope glycoprotein gp120 induced biologically active tumour necrosis factor (TNF)-alpha-related cytokine receptor of activated NF-kappaB ligand (RANKL), the primary drive to osteoclast differentiation and bone resorption. Furthermore, certain anti-HIV protease inhibitors linked clinically to accelerated bone loss in HIV disease blocked the physiological control of RANKL activity by interferon (IFN)-gamma through inhibition of degradation of the RANKL nuclear adapter signalling protein, TNF receptor associated protein 6 (TRAF6). We now report a series of reciprocal interactions among HIV-1, RANKL and IFN-gamma. RANKL augmented HIV replication in acutely and chronically infected cells of T lymphocyte and monocyte lineage, effects which occurred at a transcriptional level in conjunction with activation of NF-kappaB. TNF-alpha and RANKL were markedly synergistic in induction of HIV. Low pharmacological levels of IFN-gamma (0.75-3 ng/ml) suppressed RANKL-driven enhancement of HIV replication, as did L-T6DP-1, a cell-permeable peptide inhibitor of TRAF6. In contrast, HIV replication induced by TNF-alpha and phorbol ester were not inhibited, and in some cases augmented, by IFN-gamma. We conclude that a positive feedback loop exists between RANKL production and HIV replication, which may be relevant to both the pathophysiology of HIV-linked osteopenia and control of HIV growth. This pathway appears distinct from those of other cytokine activators of HIV, with respect to its utilization of TRAF6 and its suppression by IFN-gamma. These data raise the possibility that TRAF-specific inhibitory peptides, alone or in conjunction with IFN-gamma, could be used to regulate HIV activation in vivo.

Metalloprotease activity in a small heat shock protein of the human malaria parasite Plasmodium vivax.

The malaria parasite affects millions of people each year, lives and multiplies in two different hosts, and synthesizes a large number of proteases and heat shock proteins (HSPs) for its survival. We describe here the characterization of a metalloprotease activity which resides in the small HSP (PVHSP28) of the common but noncultivable human malaria parasite Plasmodium vivax. The protein is expressed by erythrocytic stages of the parasite. It is expressed as a approximately 55-kDa polypeptide which is then processed to the 28-kDa mature protein. The latter was found to be an active protease in gelatin zymography. This protease showed its optimal activity at 37 degrees C (pH 7.6). It also retained its proteolytic activity at higher temperatures of up to 55 degrees C. The enzyme belongs to the metalloprotease class, as its proteolytic activity was most effectively blocked by 1,10-phenanthroline and was restored to a maximal level by the addition of zinc metal ions. Inhibitors for the cysteine, serine, and aspartate classes of proteases were ineffective against this enzyme. A homology search indicates that PVHSP28 probably belongs to a new class of HSPs which possess the metalloprotease signature sequence.