Received for publication April 24, 2006.
Revised June 21, 2006.
Accepted for publication June 21, 2006.

HIV-1 VIRAL ENVELOPE GLYCOPROTEIN GP120 TRIGGERS AN INFLAMMATORY RESPONSE IN CULTURED RAT ASTROCYTES AND REGULATES THE FUNCTIONAL EXPRESSION OF P-GLYCOPROTEIN

Abstract

In the present work, we have examined i) the ability of gp120, an HIV-1 viral envelope glycoprotein, to trigger the innate immune response in astrocytes, an HIV-1 brain cellular target, and ii) investigated the functional expression of the ABC membrane transporter P-glycoprotein (P-gp), in primary cultures of rat astrocytes treated with gp120 or cytokines (TNF-, IL-1, IL-6). Standard MTT and D-mannitol uptake assays confirmed that HIV-1_96ZM651 gp120 treatment did not alter cell viability or membrane permeability. Semiquantitative RT-PCR analysis and ELISA demonstrated increased TNF-, IL-1 and IL-6 mRNA and protein expression in cultures treated with HIV-1_96ZM651 gp120, suggesting in vitro activation of immune responses. Cytokine secretion was detected when CXCR4, but not CCR5, was inhibited with a specific antibody, implying cytokine secretion is primarily mediated via CCR5 in astrocytes triggered with HIV-1_96ZM651 gp120. P-gp protein expression was increased in astrocyte cultures exposed to TNF- (2.9-fold) or IL-1 (1.6-fold) but profoundly decreased in the presence of IL-6 (8.9-fold), suggesting IL-6 is primarily involved in modulating P-gp expression. In parallel, following HIV-1_96ZM651 gp120 treatment, immunoblotting analysis showed a significant decrease in P-gp expression (4.7-fold). Furthermore, the accumulation of two P-gp substrates, digoxin and saquinavir (an HIV-1 protease inhibitor) was enhanced (1.5-1.8-fold) in HIV-1_96ZM651 gp120 treated astrocyte monolayers but not altered by P-gp inhibitors (i.e., PSC833, GF120918) suggesting a loss of transport activity. Taken together, these data imply that HIV-1_96ZM651 gp120 or cytokine treatment modulate P-gp functional expression in astrocytes which may lead to complex drug-transporter interactions during HIV-1 encephalitis-associated immune responses.

Key words: Interleukins, Tumor necrosis factor, MDR/p-Glycoprotein, Antiviral drugs

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