Multiple Restrictions of Human Immunodeficiency Virus Type 1 in Feline Cells

Abstract

The productive replication of human immunodeficiency virus type 1 (HIV-1) occurs exclusively in defined cells of human or chimpanzee origin, explaining why heterologous animal models for HIV replication, pathogenesis, vaccination, and therapy are not available. This lack of an animal model for HIV-1 studies prompted us to examine the susceptibility of feline cells in order to evaluate the cat (Felis catus) as an animal model for studying HIV-1. Here, we report that feline cell lines harbor multiple restrictions with respect to HIV-1 replication. The feline CD4 receptor does not permit virus infection. Feline T-cell lines MYA-1 and FeT-1C showed postentry restrictions resulting in low HIV-1 luciferase reporter activity and low expression of viral Gag-Pol proteins when pseudotyped vectors were used. Feline fibroblastic CrFK and KE-R cells, expressing human CD4 and CCR5, were very permissive for viral entry and HIV-long terminal repeat-driven expression but failed to support spreading infection. KE-R cells displayed a profound block with respect to release of HIV-1 particles. In contrast, CrFK cells allowed very efficient particle production; however, the CrFK cellderived HIV-1 particles had low specific infectivity. We subsequently identified feline apolipoprotein B-editing catalytic polypeptide 3 (feAPOBEC3) proteins as active inhibitors of HIV-1 particle infectivity. CrFK cells express at least three different APOBEC3s: APOBEC3C, APOBEC3H, and APOBEC3CH. While the feAPOBEC3C did not significantly inhibit HIV-1, the feAPOBEC3H and feAPOBEC3CH induced G to A hypermutations of the viral cDNA and reduced the infectivity ϳ10-to ϳ40-fold.Like many retroviruses, human immunodeficiency virus type 1 (HIV-1) has a very limited host range; spreading replication is seen only in Homo sapiens and by artificial inoculation in the close relative the chimpanzee (Pan troglodytes) (2, 16), preventing the setup of an efficient small animal model for HIV-1 research. Many reasons argue against the widespread use of chimpanzees in research, including the ethical problems involved in the use of an endangered species, budgetary problems, and the very low induction of simian AIDS either from HIV-1 or its ancestor simian immunodeficiency virus cpz (SIVcpz) in infected chimpanzees (25,26,30,57,58,60,63).In general, the tropism of HIV-1 in human tissue is determined by the expression of its receptor protein CD4 together with CCR5 or CXCR4 chemokine receptors. Simian CD4 but not murine CD4 supports entry of HIV-1 (15, 33). HIV-1 entry through receptor-mediated membrane fusion is required for reverse transcription of the viral genomic RNA into a doublestranded DNA molecule. Murine T cells show early postentry restriction of HIV-1 at reverse transcription (3). In simian cells, a related restriction of HIV-1, but not of SIVs (5, 10, 53), involves the simian TRIM5␣ protein, which leads to increased viral uncoating and thereby suppresses reverse transcription (73). Since HIV-1 does not show spreading replication in nonhuman cells, cell type-and t...

Restriction of Equine Infectious Anemia Virus by Equine APOBEC3 Cytidine Deaminases

“…The discovery of the cellular antiviral cytidine deaminase A3G in search for the Vif cofactor explained many in vitro observations regarding the replication of HIV-1 and HIV-1 ⌬vif in specific human cells (5,49,78,91,100). It also contributed to explain the narrow host range of HIV-1 that shows spreading replication only in humans and chimpanzees (49,59). Such defined interactions of Vif proteins with cognate A3 proteins had been shown so far only for HIV, SIV, and Feline immunodeficiency virus (49,58,74).…”

Productive Replication of vif -Chimeric HIV-1 in Feline Cells

“…Three closely related feline A3C (fA3C) proteins (fA3Ca, fA3Cb, and fA3Cc) are active against feline foamy virus but not vif-deficient FIV (60). In contrast, the two other proteins (fA3H and fA3CH) have antilentiviral effects, as they restrict ⌬vif FIV and HIV-1 with vif intact (60,61). fA3CH, the only two-domain feline A3 protein, is an unusual hybrid encoded by exons 1 to 3 of fA3Ca, exon 4 of fA3Cb, and exons 2 to 5 of fA3H (60).…”

“…Murine T cells also display a postentry block to HIV-1 (3). Even if all necessary human dependency factors can be identified and made to function in a nonprimate animal with transgenic methods, HIV-1 replication is inhibited in the cells of many primate (29,74,87) and nonprimate (32,50,61,76,84) species by the antiviral activity of species-specific restriction factors, such as TRIM5␣, TRIMCyp, and APOBEC3 (A3) proteins. The APOBEC3 proteins are DNA and RNA cytidine deaminases, some of which have antiviral activity.…”

“…fA3CH, the only two-domain feline A3 protein, is an unusual hybrid encoded by exons 1 to 3 of fA3Ca, exon 4 of fA3Cb, and exons 2 to 5 of fA3H (60). fA3H and fA3CH mediate hypermutation of wild-type HIV-1 (61). Whether fA3 proteins act through other mechanisms as well, whether any Vif protein of any lentivirus triggers fA3 degradation, or whether any Vif can protect HIV-1 against them has not been determined.…”

Inhibition of Alpharetrovirus Replication by a Range of Human APOBEC3 Proteins

“…Analysis of other mammalian species has shown that the mouse genome contains a single APOBEC3 gene (the mA3 gene), while cats express at least three distinct APOBEC3 proteins (11,37). While nonmammalian vertebrates, such as birds and fish, do not carry any genes encoding any APOBEC3 proteins, all vertebrates do carry genes encoding activation-induced deaminase (AID), a DNA-editing enzyme that plays a role in the diversification of antibody genes (11).…”