HIV-1 coat protein gp120 stimulates interleukin-1beta secretion from human neuroblastoma cells: evidence for a role in the mechanism of cell death

1. The role of the pro-inflammatory cytokine interleukin-1beta (IL-1beta) in the mechanism of cell death induced by the human immunodeficiency virus type 1 (HIV-1) recombinant coat glycoprotein, gp120 IIIB, has been studied in the human CHP100 neuroblastoma cell line maintained in culture. 2. Death of neuroblastoma cells typically elicited by 10 pM gp120 or by human recombinant IL-1beta (10 ng x ml(-1)) has been minimized by the antagonist of IL-1 receptor, i.e. IL-1ra (0.5 and 50 ng x ml(-1), respectively), an endogenous molecule that antagonizes most of the biological actions of IL-1beta, or by an antibody (5 and 50 ng x ml(-1)) which blocks the human IL-1 receptor type I (IL-1RI). 3. ELISA experiments have established that gp120 enhances immunoreactive IL-1beta levels in the culture medium and this is prevented by exposure to the IL-1 converting enzyme (ICE) inhibitor t-butoxycarbonyl-L-aspartic acid benzyl ester-chloromethylketone [Boc-Asp(OBzl)-CMK] used at a concentration (2.5 microM) which significantly (P<0.001) reduces cell death. 4. Death of CHP100 cells induced by gp120 is also prevented by acetyl-Tyr-Val-Ala-Asp-chloromethylketone (Ac-YVAD-CMK; 10-100 microM), a second inhibitor of ICE, supporting the concept that the viral protein stimulates the conversion of the 31 kDa pro-IL-1beta in to the 17 kDa mature cytokine which is then secreted to cause death. 5. In conclusion, our present data demonstrate that gp120 stimulates the secretion of IL-1beta which then triggers CHP100 neuroblastoma cell death via stimulation of IL-1 receptor type I.

Evidence that increases of mitochondrial immunoreactive IL-1beta by HIV-1 gp120 implicate in situ cleavage of pro-IL-1beta in the neocortex of rat

Immunoelectron microscopy analysis of brain tissue sections and rat-specific sandwich ELISA allowed the localization of interleukin-1beta (IL-1beta) immunoreactivity in the mitochondria and cytosol of neocortical tissue preparations from the brain of naive, untreated, rats and rats receiving a single daily injection into one lateral cerebral ventricle (i.c.v.) of bovine serum albumin (BSA; 100 ng/day) for seven consecutive days. Interestingly, seven days i.c.v. treatment with the HIV-1 coat protein gp120 (100 ng/day) enhances IL-1beta immunoreactivity in the cellular fractions studied. Elevation of mitochondrial immunoreactive IL-1beta levels seems to originate from the conversion operated by the interleukin converting enzyme (ICE) of mitochondrial pro-IL-1beta; in fact, IL-1beta increases reported in the ELISA experiments were paralleled by a decrease of the mitochondrial pro-IL-1beta 31-kDa band in conjunction with enhanced expression of the p20 component of activated ICE. In conclusion, the present results demonstrate that gp120-enhanced neocortical expression of IL-1beta originates, at least in part, from in situ cleavage of mitochondrial pro-IL-1beta and suggest that this, together with the central role of the mitochondrion in the expression of programmed cell death, may be important for apoptosis induced by the viral coat protein in the brain of rats.

Apoptosis induced by gp120 in the neocortex of rat involves enhanced expression of cyclooxygenase type 2 and is prevented by NMDA receptor antagonists and by the 21-aminosteroid U-74389G

The effects of a single dose of the HIV-1 coat protein gp120 given into one lateral cerebral ventricle (i.c.v.) on the expression of cyclooxygenase type 2 (COX-2) and PGE(2) levels have been studied using Western blotting and ELISA techniques applied to brain tissue extracts obtained from the neocortex of individual rats, one of the regions of the central nervous system where the viral protein causes apoptosis. The results demonstrate that COX-2 expression is almost doubled 6 h after a single dose (100 ng) of gp120 and this is paralleled by a statistically significant elevation of PGE(2). Enhanced COX-2 expression is implicated in the mechanisms of apoptosis evoked by gp120 because the latter is prevented by NS398 (10 mg/kg i.p.), a selective inhibitor of COX-2 activity. Protection is also afforded by NMDA receptor antagonists, such as MK801 (0.3 mg/kg i.p.) and CGP040116 (10 mg/kg i.p.), and by the free radical scavenger, U-74389G (10 mg/kg i.p.), supporting a glutamate-mediated, excitotoxic, mechanism of apoptotic death induced by gp120. These data together with the observation that MK801 failed to prevent gp120-enhanced COX-2 expression indicate that products of the arachidonic cascade may be responsible for elevation of synaptic glutamate leading neocortical cells to oxidative stress and excitotoxic apoptosis.