Galectin-3 has been reported to regulate the functions of a number of immune cell types. We previously reported that galectin-3 is translocated to immunological synapses in T cells upon T-cell receptor engagement, where it associates with ALG-2-interacting protein X (Alix). Alix is known to coordinate with the endosomal sorting complex required for transport (ESCRT) to promote human immunodeficiency virus (HIV)-1 virion release. We hypothesized that galectin-3 plays a role in HIV-1 viral budding. Cotransfection of cells of the Jurkat T line with galectin-3 and HIV-1 plasmids resulted in increased HIV-1 budding, and suppression of galectin-3 expression by RNAi in Hut78 and primary CD4+ T cells led to reduced HIV-1 budding. We used immunofluorescence microscopy to observe the partial colocalization of galectin-3, Alix and Gag in HIV-1-infected cells. Results from co-immunoprecipitation experiments indicate that galectin-3 expression promotes Alix-Gag p6 association, whereas the results of Alix knockdown suggest that galectin-3 promotes HIV-1 budding through Alix. HIV-1 particles released from galectin-3-expressing cells acquire the galectin-3 protein in an Alix-dependent manner, with proteins primarily residing inside the virions. We also found that the galectin-3 N-terminal domain interacts with the proline-rich region of Alix. Collectively, these results suggest that endogenous galectin-3 facilitates HIV-1 budding by promoting the Alix-Gag p6 association.
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