Abstract
CD63, a member of the tetraspanin family, is involved in virion production by human immunodeficiency virus type 1 (HIV-1), but its mechanism is unknown. In this study, we showed that a small GTP-binding protein, Rab3a, interacts with CD63. When Rab3a was exogenously expressed, the amounts of CD63 decreased in cells. The Rab3a-mediated reduction of CD63 was suppressed by lysosomal and proteasomal inhibitors. The amount of CD63 was increased by reducing the endogenous Rab3a level using a specific shRNA. These results indicate that Rab3a binds to CD63 to induce the degradation of CD63. Rab3a is thought to be involved in exocytosis, but we found that another function of Rab3a affects the fate of CD63 in lysosomes. CD63 interacted with Rab3a and was incorporated into HIV-1 particles. However, Rab3a was not detected in HIV-1 virions, thereby indicating that Rab3a-free CD63, but not Rab3a-bound CD63, is incorporated into HIV-1 particles. Overexpression or silencing of Rab3a moderately reduced HIV-1 virion formation. Overexpression of Rab3a decreased CD63 levels, but did not affect the incorporation of CD63 into HIV-1 particles. This study showed that Rab3a binds to CD63 to induce the degradation of CD63, and only Rab3a-free CD63 is incorporated into HIV-1 particles.
Highlights
The main targets of human immunodeficiency virus type 1 (HIV-1) are CD4-positive T lymphocytes, but it is important to understand the mechanism of HIV-1 virion production in fibroblast cell lines
CD63 wild type (WT)-GFP protein was detected in the virion-containing pellets, only when 293T cells were transfected with the HIV-1 vector construction plasmids (Figure 1B)
We found that Rab3a binds to CD63 to induce the degradation of CD63
Summary
The main targets of human immunodeficiency virus type 1 (HIV-1) are CD4-positive T lymphocytes, but it is important to understand the mechanism of HIV-1 virion production in fibroblast cell lines. The HIV-1 vector is constructed by transfecting 293T or COS7 fibroblast cells expressing the T antigen of simian virus 40 (SV40), which induces DNA replication of SV40 replication origin-containing plasmids. Understanding the mechanism of HIV-1 virion production in these cell lines would contribute to the construction of highly efficient or cell type-specific HIV-1 vectors. Some members of the tetraspanin family are associated with HIV-1 replication. Tetraspanin family members including CD9, CD63, CD81, and CD82 are membrane-spanning proteins with four transmembrane domains, and these proteins form tetraspanin-enriched microdomains (TEMs) in plasma membranes. Tetraspanins and TEMs participate in many physiological and pathological events (Andreu and Yanez-Mo, 2014; Mazzocca et al, 2014; Jiang et al, 2015)
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