Molecular cloning and anti-HIV-1 activities of APOBEC3s from northern pig-tailed macaques (Macaca leonina)

IFI27 inhibits HIV-1 replication by degrading Gag protein through the ubiquitin-proteasome pathway

Type I interferon (IFN-I) and its downstream genes play a profound role in HIV infection. In this study, we found that an IFN-inducible gene, IFI27, was upregulated in HIV-1 infection, which in turn efficiently suppressed HIV-1 replication, specially degraded the viral gag protein, including p24 and p55 subunits. Notably, the anti-HIV-1 activity of IFI27 in Old World monkeys surpassed that in New World monkeys, and IFI27 has a higher potentially inhibitory effect on HIV-1 than simian immunodeficiency virus (SIV). Our initial observations showed that NPM-IFI27, the IFI27 variant in northern pig-tailed macaque (Macaca leonina, NPM), exhibited a strong anti-HIV-1 activity. Further investigation demonstrated that NPM-IFI27 degraded p24 and p55 via the ubiquitin-proteasome pathway, with NPM-IFI27-37-115 interacting with the p24-N domain, and the NPM-IFI27-76-122 domain was closely associated with K48 ubiquitin recruitment. Additionally, Skp2 was identified as the probable E3 ubiquitin ligase responsible for the degradation of p24 and p55. Similarly, human IFI27 (Hu-IFI27) showed a mechanism similar to NPM-IFI27 in HIV-1 inhibition. These findings underscore the pivotal role of NPM-IFI27 in HIV-1 infection and provide a potential strategy for clinical anti-HIV-1 therapy.IMPORTANCEHIV-1 infection can trigger the production of IFN-I, which subsequently activates the expression of various IFN-stimulated genes (ISGs) to antagonize the virus. Therefore, discovering novel host antiviral agents for HIV-1 treatment is crucial. Our previous study revealed that IFI27 can influence HIV-1 replication. In this study, we observed that the NPM-IFI27 complex specifically inhibited HIV-1 by targeting its Gag protein. Further exploration demonstrated that IFI27 interacted with the HIV-1 p24 and p55 proteins, leading to their degradation through the ubiquitin-proteasome pathway. Notably, the NPM-IFI27-37-122 variant exhibited potent anti-HIV-1 activity, comparable to that of SAMHD1. These findings highlight the critical role and inhibitory mechanism of NPM-IFI27 in HIV-1 infection, providing a potential strategy for clinical antiviral therapy.

An Alu Element Insertion in Intron 1 Results in Aberrant Alternative Splicing of APOBEC3G Pre-mRNA in Northern Pig-Tailed Macaques (Macaca leonina) That May Reduce APOBEC3G-Mediated Hypermutation Pressure on HIV-1

APOBEC3 family members, particularly APOBEC3F and APOBEC3G, inhibit the replication and spread of various retroviruses by inducing hypermutation in newly synthesized viral DNA. Viral hypermutation by APOBEC3 is associated with viral evolution, viral transmission, and disease progression. In recent years, increasing attention has been paid to targeting APOBEC3G for AIDS therapy. Thus, a controllable model system using species such as macaques, which provide a relatively ideal in vivo system, is needed for the study of APOBEC3-related issues. To appropriately utilize this animal model for biomedical research, important differences between human and macaque APOBEC3s must be considered. In this study, we found that the ratio of APOBEC3G-mediated/APOBEC3-mediated HIV-1 hypermutation footprints was much lower in peripheral blood mononuclear cells (PBMCs) from northern pig-tailed macaques than in PBMCs from humans. Next, we identified a novel and conserved APOBEC3G pre-mRNA alternative splicing pattern in macaques, which differed from that in humans and resulted from an Alu element insertion into macaque APOBEC3G gene intron 1. This alternative splicing pattern generating an aberrant APOBEC3G mRNA isoform may significantly dilute full-length APOBEC3G and reduce APOBEC3G-mediated hypermutation pressure on HIV-1 in northern pig-tailed macaques, which was supported by the elimination of other possibilities accounting for this hypermutation difference between the two hosts.IMPORTANCE APOBEC3 family members, particularly APOBEC3F and APOBEC3G, are important cellular antiviral factors. Recently, more attention has been paid to targeting APOBEC3G for AIDS therapy. To appropriately utilize macaque animal models for the study of APOBEC3-related issues, it is important that the differences between human and macaque APOBEC3s are clarified. In this study, we identified a novel and conserved APOBEC3G pre-mRNA alternative splicing pattern in macaques, which differed from that in humans and which may reduce the APOBEC3G-mediated hypermutation pressure on HIV-1 in northern pig-tailed macaques (NPMs). Our work provides important information for the proper application of macaque animal models for APOBEC3-related issues in AIDS research and a better understanding of the biological functions of APOBEC3 proteins.

Superior intestinal integrity and limited microbial translocation are associated with lower immune activation in SIVmac239-infected northern pig-tailed macaques (Macaca leonina)

Microbial translocation is a cause of systemic immune activation in HIV/SIV infection. In the present study, we found a lower CD8+ T cell activation level in Macaca leonina (northern pig-tailed macaques, NPMs) than in Macaca mulatta (Chinese rhesus macaques, ChRMs) during SIVmac239 infection. Furthermore, the levels of plasma LPS-binding protein and soluble CD14 in NPMs were lower than those in ChRMs. Compared with ChRMs, SIV-infected NPMs had lower Chiu scores, representing relatively normal intestinal mucosa. In addition, no obvious damage to the ileum or colon epithelial barrier was observed in either infected or uninfected NPMs, which differed to that found in ChRMs. Furthermore, no significant microbial translocation (Escherichia coli) was detected in the colon or ileum of infected or uninfected NPMs, which again differed to that observed in ChRMs. In conclusion, NPMs retained superior intestinal integrity and limited microbial translocation during SIV infection, which may contribute to their lower immune activation compared with ChRMs.

Host Restriction Factors APOBEC3G/3F and Other Interferon-Related Gene Expressions Affect Early HIV-1 Infection in Northern Pig-Tailed Macaque (Macaca leonina)

The northern pig-tailed macaques (NPMs) lack TRIM5α, an antiviral restriction factor, and instead have TRIM5-CypA. In our previous study, we demonstrated that HIV-1NL4-3 successfully infected NPMs and formed a long-term viral reservoir in vivo. However, the HIV-1-infected NPMs showed relatively high viremia in the first 6 weeks of infection, which declined thereafter suggesting that HIV-1 NL4-3 infection in these animals was only partly permissive. To optimize HIV-1 infection in NPMs therefore, we generated HIV-1NL4-R3A and stHIV-1sv, and infected NPMs with these viruses. HIV-1NL4-R3A and stHIV-1sv can replicate persistently in NPMs during 41 weeks of acute infection stage. Compared to the HIV-1NL4-R3A, stHIV-1sv showed a notably higher level of replication, and the NPMs infected with the latter induced a more robust neutralizing antibody but a weaker cellular immune response. In addition, IFN-I signaling was significantly up-regulated with the viral replication, and was higher in the stHIV-1sv infected macaques. Consequently, the sequences of pro-viral env showed fewer G-A hyper-mutations in stHIV-1sv, suggesting that vif gene of SIV could antagonize the antiviral effects of APOBEC3 proteins in NPMs. Taken together, NPMs infected with HIV-1NL4-R3A and stHIV-1sv show distinct virological and immunological features. Furthermore, interferon-related gene expression might play a role in controlling primary HIV-1NL4-R3A and stHIV-1sv replication in NPMs. This result suggests NPM is a potential HIV/AIDS animal model.