Human and simian immunodeficiency virus capsid proteins are major viral determinants of early, postentry replication blocks in simian cells

Abstract

The cells of most Old World monkey species exhibit early, postentry restrictions on infection by human immunodeficiency virus type 1 (HIV-1) but not by simian immunodeficiency virus of macaques (SIV(mac)). Conversely, SIV(mac), but not HIV-1, infection is blocked in most New World monkey cells. By using chimeric HIV-1/SIV(mac) viruses capable of a single round of infection, we demonstrated that a major viral determinant of this restriction is the capsid (CA) protein. The efficiency of early events following HIV-1 and SIV(mac) entry is apparently determined by the interaction of the incoming viral CA and species-specific host factors.

FIG. 1.

HIV-1/SIV_mac recombinants. The name of the construct reflects the HIV-1 or SIV proviral backbone, and the names in parentheses designate the source of the CA or CA-p2 sequences (H = HIV-1; S = SIV_mac). The amino-terminal portions of the Gag polyproteins of the recombinant viruses used in this study are shown beneath the wild-type HIV-1 (white) and SIV_mac239 (black) sequences. The locations of the matrix (MA), CA, p2, and NC proteins are shown. The numbers represent the boundaries of the HIV-1 CA sequence that was replaced by the SIV_mac sequence. The locations of the N- and C-terminal domains of the CA proteins are shown. The asterisk represents the approximate location of a threonine-to-cysteine change at residue 58 of the HIV-1 CA protein.

FIG. 2.

Virion proteins produced by HIV-1/SIV_mac chimeras. 293T cells were transfected with plasmids HIV.GFP (lane 1), HIV(S/HCA).GFP (lane 2), HIV(H/SCA).GFP (lane 3), HIV(SCA).GFP (lane 4), HIV(T58C).GFP (lane 5), SIV.GFP (lane 6), and SIV(HCA-p2).GFP (lane 7). Following transfection, the cells were labeled with [³⁵S]methionine. Virions released into the cell supernatants were pelleted through 20% sucrose and resuspended in radioimmunoprecipitation assay buffer before analysis by sodium dodecyl sulfate-12.5% polyacrylamide gel electrophoresis and autoradiography. The location of the CA proteins is shown on the left. The values on the right are molecular sizes in kilodaltons.

FIG. 3.

Infection of cells by HIV-1/SIV_mac recombinants. Supernatants containing the indicated single-round HIV-1 and SIV_mac vectors, which encode GFP, were assessed for reverse transcriptase (RT) activity. The indicated number of RT units of virus was added to cells, which were incubated for 3 days prior to fluorescence-activated cell sorting analysis for GFP expression. The cells in the top row (A) are permissive for both HIV-1 and SIV_mac, the cells in the second row (B) are permissive for SIV_mac but restricted for HIV-1, and the cells in panel C are permissive for HIV-1 but restricted for SIV_mac. The symbols and lines used for the viruses are as follows: viruses with HIV-1 CA sequences, open symbols and dotted lines; viruses with SIV_mac CA sequences, black symbols and solid lines; virus with CA sequences derived from SIV_mac and HIV-1, gray symbol and dashed line.