Silencing the PTEN gene is protective against neuronal death induced by human immunodeficiency virus type 1 Tat

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Neurons are targets of toxicity induced by the human immunodeficiency virus (HIV)-1 protein Tat (transactivator of transcription). Exposure to Tat increases [Ca(2+)](i) in striatal neurons and activates multiple cell death pathways. In earlier studies the authors showed that Tat activated both caspase-3 and endonuclease-G, a caspase-independent effector of apoptosis, and that Tat-induced neurotoxicity was not attenuated by a caspase-3 inhibitor. Because Tat activates multiple, parallel death pathways, the authors attempted to reduce Tat-induced neurotoxicity by manipulating signaling pathways upstream of mitochondrial apoptotic events. PTEN (phosphatase and tensin homolog deleted on chromosome 10), a negative regulator of Akt/PKB (protein kinase B) phosphorylation, was chosen as a target for silencing. Akt/PKB activity directs multiple downstream pathways mediated by GSK3beta, BAD, forkhead transcription factors, nuclear factor kappa B (NFkappaB), and others, in a manner that promotes proliferation and survival. Striatal neurons were nucleofected with short interfering RNA (siRNA) vectors targeting PTEN, or a negative-control siRNA. Although Tat(1-86) significantly increased the death of neurons transfected with control construct by 72 h, PTEN-silenced neurons were completely protected. These findings indicate that Akt is a critical intermediary in the direct neurotoxicity induced by HIV-1 Tat, and identify Akt regulation as a possible therapeutic strategy for Tat-induced neurotoxicity in HIV encephalitis (HIVE).