HIV Type 1nefGene Inhibits Tumor Necrosis Factor α-Induced Apoptosis and Promotes Cell Proliferation through the Action of MAPK and JNK in Human Glial Cells

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Abstract
In neurodegenerative diseases associated with AIDS, reactive astrocytosis plays a central role in the neurotoxicity of the brain parenchyma. Whereas the HIV-1 nef gene is overexpressed during restricted HIV-1 infection of human astrocytes, our previous results have demonstrated that nef expressed in human U251MG glial cells activates the sphingomyelin pathway triggered by TNF-α, increasing ceramide production. Since ceramide is an important regulatory molecule of programmed cell death induced by TNF-α, we examined whether nef could alter TNF-α-induced apoptosis in the U251MG human astrocytoma cell line. Transfection studies indicated that nef could both prevent apoptosis and promote cell proliferation in response to TNF-α stimulation. MAPK and JNK activities were further analyzed in order to elucidate signaling cascades subsequent to the upregulation of ceramide production. After TNF-α treatment, both kinases were shown to be preferentially activated in the presence of nef. These experiments strongly suggest that the HIV-1 Nef protein might modulate the sensitivity of astrocytes to inflammatory molecules, thus contributing to the development of neurodegenerative diseases associated with AIDS.