現地観測に基づく河川流の乱流特性に関する研究

博士（工学）神戸大

A Conserved Acidic Residue in the C-Terminal Flexible Loop of HIV-1 Nef Contributes to the Activity of SERINC5 and CD4 Downregulation

The host transmembrane protein SERINC5 is incorporated into retrovirus particles and inhibits HIV-1 infectivity. The lentiviral Nef protein counteracts SERINC5 by downregulating it from the cell surface and preventing its incorporation into virions. The ability of Nef to antagonize the host factor varies in magnitude between different HIV-1 isolates. After having identified a subtype H nef allele unable to promote HIV-1 infectivity in the presence of SERINC5, we investigated the molecular determinants responsible for the defective counteraction of the host factor. Chimeric molecules with a subtype C Nef highly active against SERINC5 were constructed to locate Nef residues crucial for the activity against SERINC5. An Asn at the base of the C-terminal loop of the defective nef allele was found in place of a highly conserved acidic residue (D/E 150). The conversion of Asn to Asp restored the ability of the defective Nef to downregulate SERINC5 and promote HIV-1 infectivity. The substitution was also found to be crucial for the ability of Nef to downregulate CD4, but not for Nef activities that do not rely on the internalization of receptors from the cell surface, suggesting a general implication in promoting clathrin-mediated endocytosis. Accordingly, bimolecular fluorescence complementation revealed that the conserved acidic residue contributes to the recruitment of AP2 by Nef. Altogether, our results confirm that Nef downregulates SERINC5 and CD4 by engaging a similar machinery and indicates that, in addition to the di-leucine motif, other residues in the C-terminal flexible loop are important for the ability of the protein to sustain clathrin-mediated endocytosis

The decrease in T cell transduction efficiency by SIV_MAC is not explained by differences in reporter gene expression.

<p>(A) CRFK cells (left panel) and Jurkat T cells (right panel) were transduced with VSV G-pseudotyped, single-cycle, two-part HIV-1_NL4-3GFP or SIV_MAC239-GFP vectors, as in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005050#ppat.1005050.g001" target="_blank">Fig 1</a>_. Virus stocks were normalized by reverse transcriptase activity prior to transduction. 48 hrs after transduction, cells were visualized by phase contrast and fluorescence microscopy. Shown are representative fields for each condition at 100x magnification. Fluorescence intensity of individual T cells transduced with SIV_MAC239-GFP is at least as strong as that in cells transduced with HIV-1_NL4-3GFP. (B) VSV G-pseudotyped, HIV-1_NL4-3 (black squares) and SIV_MAC239 (white circles) three-part vectors were generated by plasmid transfection of 293T cells. In each case, the viral genomic RNA was designed to transduce an identical SFFV-GFP reporter gene. Vector stocks were normalized by titer on CRFK cells, and then used to challenge Jurkat T cells. 48 hrs post vector challenge, the percentage GFP-expressing cells was determined by FACS. Data is plotted as percent GFP⁺ (infected) cells (Y axis) versus CRFK infectious units (IU) x 1,000 (X axis).</p

SIV_MAC transduction of human peripheral blood mononuclear cells or of monocyte derived dendritic cells is less efficient than by HIV-1.

<p>(A) VSV G-pseudotyped HIV-1_NL4-3GFP (black squares) and SIV_MAC239GFP (white circles) two-part vectors were generated by plasmid transfection of 293T cells. Vector stocks were normalized by titer on CRFK cells, and then used to challenge human peripheral blood mononuclear cells. (B) VSV G-pseudotyped, HIV-1_NL4-3 (black squares) and SIV_MAC239 (white circles) three-part vectors were generated by plasmid transfection of 293T cells. In each case, the viral genomic RNA was designed to transduce an identical SFFV-GFP reporter gene. Vector stocks were normalized by titer on CRFK cells, and then used to challenge monocyte derived dendritic cells (DCs). 2 days post-challenge, the percentage of GFP-expressing cells was determined by FACS. Data is plotted as percent GFP⁺ (infected) cells (Y axis) versus CRFK infectious units (IU) x 1,000 (X axis). Shown are representative data with cells from 4 independent blood donors.</p