Owl monkey CCR5 reveals synergism between CD4 and CCR5 in HIV-1 entry

Conformation of HIV-1 Envelope Governs Rhesus CD4 Usage and Simian-Human Immunodeficiency Virus Replication

Infection of rhesus macaques with simian-human immunodeficiency viruses (SHIVs) is the preferred model system for vaccine development because SHIVs encode human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins (Envs)-a key target of HIV-1 neutralizing antibodies. Since the goal of vaccines is to prevent new infections, SHIVs encoding circulating HIV-1 Env are desired as challenge viruses. Development of such biologically relevant SHIVs has been challenging, as they fail to infect rhesus macaques, mainly because most circulating HIV-1 Envs do not use rhesus CD4 (rhCD4) receptor for viral entry. Most primary HIV-1 Envs exist in a closed conformation and occasionally transit to a downstream, open conformation through an obligate intermediate conformation. Here, we provide genetic evidence that open Env conformations can overcome the rhCD4 entry barrier and increase replication of SHIVs in rhesus lymphocytes. Consistent with prior studies, we found that circulating HIV-1 Envs do not use rhCD4 efficiently for viral entry. However, by using HIV-1 Envs with single amino acid substitutions that alter their conformational state, we found that transitions to intermediate and open Env conformations allow usage of physiological levels of rhCD4 for viral entry. We engineered these single amino acid substitutions in the transmitted/founder HIV-1_BG505 Envs encoded by SHIV-BG505 and found that open Env conformation enhances SHIV replication in rhesus lymphocytes. Lastly, CD4-mediated SHIV pulldown, sensitivity to soluble CD4, and fusogenicity assays indicated that open Env conformation promotes efficient rhCD4 binding and viral-host membrane fusion. These findings identify the conformational state of HIV-1 Env as a major determinant for rhCD4 usage, viral fusion, and SHIV replication. IMPORTANCE Rhesus macaques are a critical animal model for preclinical testing of HIV-1 vaccine and prevention approaches. However, HIV-1 does not replicate in rhesus macaques, and thus, chimeric simian-human immunodeficiency viruses (SHIVs), which encode HIV-1 envelope glycoproteins (Envs), are used as surrogate challenge viruses to infect rhesus macaques for modeling HIV-1 infection. Development of SHIVs encoding Envs from clinically relevant, circulating HIV-1 variants has been extremely challenging, as such SHIVs replicate poorly, if at all, in rhesus lymphocytes. This is most probably because many circulating HIV-1 Envs do not use rhesus CD4 efficiently for viral entry. In this study, we identified conformational state of HIV-1 envelope as a key determinant for rhesus CD4 usage, viral-host membrane fusion, and SHIV replication in rhesus lymphocytes.

Rationally Designed ACE2-Derived Peptides Inhibit SARS-CoV-2

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 is a novel and highly pathogenic coronavirus and is the causative agent of the coronavirus disease 2019 (COVID-19). The high morbidity and mortality associated with COVID-19 and the lack of an approved drug or vaccine for SARS-CoV-2 underscores the urgent need for developing effective antiviral therapies. Therapeutics that target essential viral proteins are effective at controlling virus replication and spread. Coronavirus Spike glycoproteins mediate viral entry and fusion with the host cell, and thus are essential for viral replication. To enter host cells, the Spike proteins of SARS-CoV-2 and related coronavirus, SARS-CoV, bind the host angiotensin-converting enzyme 2 (ACE2) receptor through their receptor binding domains (RBDs). Here, we rationally designed a panel of ACE2-derived peptides based on the RBD-ACE2 binding interfaces of SARS-CoV-2 and SARS-CoV. Using SARS-CoV-2 and SARS-CoV Spike-pseudotyped viruses, we found that a subset of peptides inhibits Spike-mediated infection with IC50 values in the low millimolar range. We identified two peptides that bound Spike RBD in affinity precipitation assays and inhibited infection with genuine SARS-CoV-2. Moreover, these peptides inhibited the replication of a common cold causing coronavirus, which also uses ACE2 as its entry receptor. Results from the infection experiments and modeling of the peptides with Spike RBD identified a 6-amino-acid (Glu37-Gln42) ACE2 motif that is important for SARS-CoV-2 inhibition. Our work demonstrates the feasibility of inhibiting SARS-CoV-2 with peptide-based inhibitors. These findings will allow for the successful development of engineered peptides and peptidomimetic-based compounds for the treatment of COVID-19.

Gene Transfer in Adeno-Associated Virus Seropositive Rhesus Macaques Following Rapamycin Treatment and Subcutaneous Delivery of AAV6, but Not Retargeted AAV6 Vectors

Adeno-associated virus (AAV) vectors such as AAV6, which shows tropism for primary human CD4⁺ T cells in vitro, are being explored for delivery of anti-HIV therapeutic modalities in vivo. However, pre-existing immunity and sequestration in nontarget organs can significantly hinder their performance. To overcome these challenges, we investigated whether immunosuppression would allow gene delivery by AAV6 or targeted AAV6 derivatives in seropositive rhesus macaques. Animals were immune suppressed with rapamycin before intravenous (IV) or subcutaneous (SC) delivery of AAV, and we monitored vector biodistribution, gene transfer, and safety. Macaques received phosphate-buffered saline, AAV6 alone, or an equal dose of AAV6 and an AAV6-55.2 vector retargeted to CD4 through a direct ankyrin repeat protein (DARPin). AAV6 and AAV6-55.2 vector genomes were found in peripheral blood mononuclear cells and most organs up to 28 days postadministration, with the highest levels seen in liver, spleen, lymph nodes (LNs), and muscle, suggesting that retargeting did not prevent vector sequestration. Despite vector genome detection, gene expression from AAV6-55.2 was not detected in any tissue. SC injection of AAV6 facilitated efficient gene expression in muscle adjacent to the injection site, plus low-level gene expression in spleen, LNs, and liver, whereas gene expression following IV injection of AAV6 was predominantly seen in the spleen. AAV vectors were well tolerated, although elevated liver enzymes were detected in three of four AAV-treated animals 14 days after rapamycin withdrawal. One SC-injected animal had muscle inflammation proximal to the injection site, plus detectable T cell responses against transgene and AAV6 capsid at study finish. Overall, our data suggest that rapamycin treatment may offer a possible strategy to express anti-HIV therapeutics such as broadly neutralizing antibodies from muscle. This study provides important safety and efficacy data that will aid study design for future anti-HIV gene therapies.

The Robust Restriction of Zika Virus by Type-I Interferon in A549 Cells Varies by Viral Lineage and Is Not Determined by IFITM3

Type-I interferon (IFN-I) is a major antiviral host response but its impact on Zika virus (ZIKV) replication is not well defined, particularly as it relates to different circulating strains. Interferon stimulated genes (ISGs) that inhibit ZIKV, such as IFITM3, have been identified largely using overexpression studies. Here, we tested whether diverse ZIKV strains differed in their susceptibility to IFN-I-mediated restriction and the contribution of IFITM3 to this restriction. We identified a robust IFN-I-mediated antiviral effect on ZIKV replication (>100-fold reduction) in A549 cells, a commonly used cell line to study ZIKV replication. The extent of inhibition depended on the IFN-I type and the virus strain tested. Viruses from the American pathogenic outbreak were more sensitive to IFNα (p = 0.049) and IFNβ (p = 0.09) than African-lineage strains, which have not been linked to severe pathogenesis. Knocking out IFITM3 expression did not dampen the IFN-I antiviral effect and only high overexpression of IFITM3 led to ZIKV inhibition. Moreover, IFITM3 expression levels in different cells were not associated with IFN-mediated ZIKV inhibition. Taken together, our findings indicate that there is a robust IFN-I-mediated antiviral effect on ZIKV infection, particularly for American viruses, that is not due to IFITM3. A549 cells, which are a commonly used cell line to study ZIKV replication, present an opportunity for the discovery of novel antiviral ISGs against ZIKV.

5-HT1B Receptor-Mediated Activation of ERK1/2 Requires Both Gαi/o and β-Arrestin Proteins

5-HT_1B receptors modulate synaptic serotonin (5-HT) levels and play a significant role in the regulation of emotional behaviors. These receptors are Gα_i/o-coupled and inhibit adenylyl cyclase but have also been reported to activate MAP kinases; however, the details of signaling cascades downstream of 5-HT_1B receptor activation remain unclear, particularly in neuronal cells. We generated a stable 5-HT_1B receptor-expressing Neuro2A (N2A-1B) neuronal cell line and demonstrate that activation of these receptors by the selective 5-HT_1B agonist CP-94253 results in activation of ERK1/2 but not of other closely related MAP kinases. Phosphoproteomics revealed four novel phosphorylation sites on the third intracellular loop of the 5-HT_1B receptor, and mutations of serine-256 and serine-291 to alanine led to reduced levels of ERK1/2 phosphorylation following receptor activation. Inhibition of Gα_i/o signaling with pertussis toxin, as well as MEK1/2 inhibition with U0126, also reduced 5-HT_1B-mediated ERK1/2 phosphorylation. Finally, we found that knockout of either β-arrestin 1 or β-arrestin 2 prevented 5-HT_1B-mediated phosphorylation of ERK1/2. Taken together, these results show that 5-HT_1B receptor activation selectively induces ERK1/2 activation through both the Gα_i subunit and β-arrestin proteins. This work elucidates the signal transduction pathway of 5-HT_1B receptors, as well as key phosphorylation sites within the receptor that modulate ERK1/2 activation, and further characterizes the intracellular mechanisms that underlie 5-HT_1B receptor function.