RESUMO
HIV type 1 (HIV-1) was shown to assemble either at the plasma membrane or in the membrane of late endosomes. Now, we report an essential role for human ubiquitin ligase POSH (Plenty of SH3s; hPOSH), a trans-Golgi network-associated protein, in the targeting of HIV-1 to the plasma membrane. Small inhibitory RNA-mediated silencing of hPOSH ablates virus secretion and Gag plasma membrane localization. Reintroduction of native, but not a RING finger mutant, hPOSH restores virus release and Gag plasma membrane localization in hPOSH-depleted cells. Furthermore, expression of the RING finger mutant hPOSH inhibits virus release and induces accumulation of intracellular Gag in normal cells. Together, our results identify a previously undescribed step in HIV biogenesis and suggest a direct function for hPOSH-mediated ubiquitination in protein sorting at the trans-Golgi network. Consequently, hPOSH may be a useful host target for therapeutic intervention.
Assuntos
HIV-1/fisiologia , Ubiquitina-Proteína Ligases/metabolismo , Replicação Viral/fisiologia , Rede trans-Golgi/enzimologia , Membrana Celular/enzimologia , Membrana Celular/virologia , Clonagem Molecular , Produtos do Gene gag/metabolismo , Inativação Gênica , Células HeLa , Humanos , Transporte Proteico , Proteínas Recombinantes/metabolismo , Ubiquitina-Proteína Ligases/genéticaRESUMO
Candida albicans, the most important human fungal pathogen, is a dimorphic fungus that can grow either as a yeast or as a hyphal form in response to medium conditions. A RAS-related C. albicans gene (CaRSR1) was isolated as a suppressor of a cdc24ts bud-emergence mutation of the baker's yeast, Saccharomyces cerevisiae. The deduced protein encoded by CaRSR1 is 248 amino acids long and 56% identical to that encoded by the S. cerevisiae RSR1 (BUD1) gene. Disruption of CaRSR1 in C. albicans indicated that CaRSR1 is involved in both yeast and hypha development. In the yeast phase, CaRSR1 is required for normal (polar) bud site selection and is involved in cell morphogenesis; in the yeast-mycelial transition it is involved in germ tube emergence; and in the development of the hyphae it is involved in cell elongation. The disruption of CaRSR1 leads to reduced virulence in both heterozygote and homozygote disruptants in a dose-dependent manner. The reduced virulence can be attributed to the reduced germination and shorter hyphae resulting from the disruption of CaRSR1.
