Nonmuscle myosin light-chain kinase mediates microglial migration induced by HIV Tat: Involvement of -1 integrins

One of the hallmark features of HIVassociated neurological disease is increased activation and migration of microglia. HIV transactivator of transcription (Tat) is released from infected cells and has the ability to recruit microglia. The purpose of this study was to investigate molecular mechanisms by which recombinant Tat_1-72, but not heated-inactive Tat_1-72, induces migration of rat primary microglia. Using primary microglia in Boyden chambers, we demonstrated the role of nonmuscle myosin light-chain kinase (nmMYLK) in Tat_1-72 (14.4 nM)-mediated increased microglial migration (up to 171.85%). These findings were validated using microglia isolated from wild-type (WT) or nmMYLK^-/- mice in Dunn chamber assays. Tat_1-72- mediated activation of nmMYLK resulted in "insideout" activation of β1 integrin, followed by "outside-in" activation of c-Src, Pyk2, and Cdc42-GTP (using GLISA in primary and nmMYLK^-/-microglia) and, subsequently, actin polymerization (flow cytometry and Western blot assays). In vivo corroboration of these findings demonstrated decreased migration of nmMYLK ^-/-microglia (2×10⁵ cells transplanted into corpus callosum) compared with WT microglia toward microinjected Tat_1-72 (2 μg/mouse) in hippocampus. Up-regulation of nmMYLK in microglia was also detected in sections of basal ganglia from humans with HIV-encephalitis compared with uninfected controls. nmMYLK is thus critical for eliciting microglial migration during the innate immune response.-Yao, H., Duan, M., Yang, L., Buch, S. Nonmuscle myosin lightchain kinase mediates microglial migration induced by HIV Tat: Involvement of β1 integrins. FASEB J. 27, 1532-1548 (2013). www.fasebj.org.