THE HIV-1 NEF PROTEIN INHIBITS EXTRACELLULAR SIGNAL-REGULATED KINASE-DEPENDENT DNA-SYNTHESIS IN A HUMAN ASTROCYTIC CELL-LINE

The role of nonproductive infection of astrocytes by human immunodefic iency virus type 1 (HIV-I), characterized by the overexpression of nef , in brain disease progression is largely unknown. We investigated the consequences of stable expression of nef from the HIV-1 strain LAI in the human astrocytic cell line U373. DNA synthesis induced by endothe lin-l (ET-I) was largely decreased by nef. Stable expression of nef di d not affect the ET-1-induced tyrosine phosphorylation of focal adhesi on kinase, an adhesion-dependent pathway known to participate in DNA s ynthesis in astrocytes. Conversely, the activation of extracellular si gnal-regulated kinase (ERK) by ET-I was largely inhibited in cells sta bly or transiently expressing nef. A similar inhibitory action of nef on ERK activation was observed after direct stimulation of G proteins. Furthermore, the inhibitory action of nef did not require protein kin ase C (PKC) and affected mainly the PKC-independent pathway of ERK act ivation. Following chemokine receptor CXCR4-mediated infection of U373 cells stably expressing CXCR4 with the T-tropic HIV-1 strain m7-NDK, ET-l-induced activation of ERK was also inhibited. Altogether, these r esults indicate that intracellular signaling pathways associated with the growth factor activity of ET-I are impaired in nef-expressing and HIV-1-infected astrocytes, suggesting that infection of astrocytes may play a significant role in the neuropathogenesis of HIV-I encephalopa thy.