Project #1. Impact of HIV-1 on the Rho GTPase-mediated neuronal cell development. It is now well accepted that the HIV-1 regulatory protein, Tat, has a neurotoxic effect and that treatment of both human and rodent neurons with Tat induces apoptosis by mechanisms that are not fully understood. The cellular protein, Pur-alpha, is a key target of Tat for directing the regulation of HIV-1 transcription, translation, and viral RNA transport. Indeed, both Pur-alpha and Tat have been detected in the same cells within HIVE infected lesions. Results in the Pur-alpha knockout mouse model have revealed a critical role for Pur-alpha during development, particularly in the coordinated development and differentiation of neuronal cells throughout the brain. Over the past several years, it has become clear that the RhoGTPases and related molecules play an important role in neuronal cell development, including neurite outgrowth, differentiation, axon pathfinding, dendritic spine formation, as well as neuronal cell maintenance. Results from our studies indicate that Tat has the ability to disturb this pathway by stimulating RhoA activation, an event that is accompanied by conversion of RhoA?GDP to RhoA?GTP by interacting with guanine nucleotide exchange factor (GEF) family members including PDZ-RhoGEF. Indeed, our preliminary results suggest that Tat may mediate RhoA activity via interaction with PDZ-RhoGEF. Upon its activation, RhoA is usually positioned in the plasma membrane, and via a series of signaling pathways that involve Rock, MAPK, and JNK1, NFkB induces neurite retraction. Moreover, activation of RhoA via heteromeric G-proteins including Ga12 and G
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