The HIV‐1 Nef Protein Inhibits Extracellular Signal‐Regulated Kinase‐Dependent DNA Synthesis in a Human Astrocytic Cell Line

Abstract

Abstract: The role of nonproductive infection of astrocytes by human immunodeficiency virus type 1 (HIV‐1), 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 endothelin‐1 (ET‐1) was largely decreased by nef. Stable expression of nef did not affect the ET‐1‐induced tyrosine phosphorylation of focal adhesion kinase, an adhesion‐dependent pathway known to participate in DNA synthesis in astrocytes. Conversely, the activation of extracellular signal‐regulated kinase (ERK) by ET‐1 was largely inhibited in cells stably 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 kinase C (PKC) and affected mainly the PKC‐independent pathway of ERK activation. Following chemokine receptor CXCR4‐mediated infection of U373 cells stably expressing CXCR4 with the T‐tropic HIV‐1 strain m7‐NDK, ET‐1‐induced activation of ERK was also inhibited. Altogether, these results indicate that intracellular signaling pathways associated with the growth factor activity of ET‐1 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‐1 encephalopathy.