Effects of SDF-1α and gp120_IIIB on apoptotic pathways in SK-N-SH neuroblastoma cells

Abstract

CXCR4, a chemokine receptor constitutively expressed in the brain, binds both ligands, the chemokine SDF-1α and the HIV envelope glycoprotein gp120_IIIB. There seem to be intracellular differences between the neuronal apoptosis induced by SDF-1α and that induced by gp120_IIIB, but the apoptotic pathways involved have not been compared in human neuronal cells. In this study, we characterized the apoptotic intracellular pathways activated by neurotoxic concentrations of SDF-1α and gp120_IIIB in human neuroblastoma cells SK-N-SH.

SDF-1α (10 nM) and gp120_IIIB (2 nM) induced similar levels of apoptosis after 24 h of incubation (49 ± 4% and 48 ± 3%, respectively, of the neurons were apoptotic). SDF1α-induced apoptosis was completely abolished by the inhibition of Src phosphorylation by PP2. Exposure to SDF-1α (10 nM) triggered an increase in Src phosphorylation, with a maximum after 20 min of incubation (1.80 ± 0.24 times higher than control, P = 0.01). NMDA calcium flux was enhanced only if cells were incubated with SDF-1α for 20 min before applying NMDA. By contrast, gp120_IIIB-induced apoptosis was not affected by the inhibition of Src phosphorylation. Moreover, gp120_IIIB enhanced NMDA calcium flux immediately, without modifying Src phosphorylation status. Finally, levels of phospho-JNK increased following exposure to gp120_IIIB (by a factor of 1.46 ± 0.4 at 120 min, P = 0.03), but not after exposure to SDF-1α. Thus, SDF-1α and gp120_IIIB induced a similar level of neuronal apoptosis, but by activating different intracellular pathways. SDF-1α enhanced NMDA activity indirectly via Src phosphorylation, whereas gp120_IIIB probably activated the NMDA receptor directly and phosphorylated JNK.