Two orphan seven-transmembrane segment receptors which are expressed in CD4-positive cells support simian immunodeficiency virus infection

Abstract

Clinical isolates of primate immunodeficiency viruses, including human immunodeficiency virus type 1 (HIV-1), enter target cells by sequential binding to CD4 and the chemokine receptor CCR5, a member of the seven-transmembrane receptor family. HIV-1 variants which use additional chemokine receptors are present in the central nervous system or emerge during the course of infection. Simian immunodeficiency viruses (SIV) have been shown to use CCR5 as a coreceptor, but no other receptors for these viruses have been identified. Here we show that two orphan seven-transmembrane segment receptors, gpr1 and gpr15, serve as coreceptors for SIV, and are expressed in human alveolar macrophages. The more efficient of these, gpr15, is also expressed in human CD4(+) T lymphocytes and activated rhesus macaque peripheral blood mononuclear cells. The gpr15 and gpr1 proteins lack several hallmarks of chemokine receptors, but share with CCR5 an amino-terminal motif rich in tyrosine residues. These results underscore the potential diversity of seven-transmembrane segment receptors used as entry cofactors by primate immunodeficiency viruses, and may contribute to an understanding of viral variation and pathogenesis.

Figure 1

CAT activity in Cf2Th cells expressing CD4 alone or together with gpr1, gpr15, CCR5, or CXCR4 after incubation with HIV-1 recombinant viruses carrying the SIV_mac239, SIV_mac316, or HIV-1 (YU2, HXBc2, 89.6, or ADA) envelope glycoproteins. A representative experiment is shown. The amount of target cell lysate used was equivalent for all the experiments shown. CAT activity was determined by calculating the percentage of chloramphenicol present in acetylated forms (three uppermost spots) to the total amount of chloramphenicol. The nonacetylated form of chloramphenicol is present in the spot closest to the origin, which is near the bottom of the figure.

Figure 2

Expression of gpr1 and gpr15 RNA in cells. The cDNA libraries from U87 and CEM×174 cells and from human alveolar macrophages, as well as cDNA prepared from human CD4⁺ T lymphocytes, were PCR amplified using gpr1- or gpr15-specific primers.

Figure 3

An alignment of human gpr1, human gpr15, rhesus CCR5 (rccr5), and human CCR5 from the NH₂-terminus through the first cysteine of CCR5 is shown. Tyrosines shown to be important for HIV-1 and SIV_mac239 entry are shown in bold. Other residues similarly positioned in these proteins are underlined. Sequences for gpr1 and gpr15 are provided in references and , respectively.