In a recent study published on the Research Square preprint server*, researchers evaluated the effect of SARS-CoV-2 (SARS-CoV-2) and SARS-CoV (E) envelope proteins on respiratory syndrome severe acute on human immunodeficiency virus type 1 (HIV-1) infectivity.
Study: SARS-CoV-2 and SARS-CoV envelope proteins potentially reduce human immunodeficiency virus type 1 (HIV-1) infectivity. Image Credit: RAJ CREATIONZS/Shutterstock
Virus-encoded ion channels are called viroporins and are involved in virus assembly and release. Influenza A virus and HIV-1 encode viroporins. SARS-CoV-2 encodes at least two viroporins: the envelope protein (E) and the open reading frame (ORF)-3a. In terms of size, membrane position, ion channel activity, and roles in promoting virus release, CoV E proteins resemble HIV-1 viral protein U (Vpu). Because of these similarities, the team determined the biological characteristics of the SARS-CoV-2 E protein relative to HIV-1 to assess whether it could replace HIV-1 Vpu.
About the study
In the present study, the researchers assessed HIV-1 replication in the presence of beta-coronavirus E proteins.
The team first evaluated the intracellular expression of the SARS-CoV-2 E protein. The SARS-CoV-2 E protein was expressed in COS-7 cells using a vector labeled in the C-terminus with a hemagglutinin (HA) tag. E protein was immunostained using anti-HA antibody, as well as antibodies against LAMP-1 (late endosomes/lysosomes), endoplasmic reticulum (ER) – Golgi intermediate compartment (ERGIC53), and Golgin97 (trans-Golgi). The team then co-transfected cells with plasmids expressing E-HA protein and vectors expressing ER-MoxGFP (RER), TGN38-GFP (TGN), or giantin-GFP (cis/medial Golgi) to study the co-localization of protein E and the ER, TGN and cis-medial Golgi. These co-transfections involved the fixation of cells that were permeabilized and immunostained with an anti-HA antibody to detect the E protein.
In addition, the team compared the intracellular localization of SARS-CoV-2 E with SARS-CoV, Middle East respiratory syndrome (MERS)-CoV and HCoV-OC43 E proteins. tested the amount of infectious HIV-1 or vpuHIV-1 produced to determine whether the SARS-CoV-2 E protein would increase or decrease the amount. The empty pcDNA3.1(+) vector, which encoded the SARS-CoV-2 E protein, herpes simplex virus type 1 (HSV-1) glycoprotein D (gD), which was a positive control for the restriction, or gD[TMCT] that was secreted by cells and did not restrict HIV-1, and pNL4-3 were co-transfected into HEK293 cells.
results
The results of the study showed that ER, ERGIC, TGN, trans-Golgi and cis-medial Golgi markers co-localized with protein E. However, neither the cell plasma membrane nor lysosomes possessed protein E .This suggested that the three E proteins were localized similarly to the SARS-CoV-2 E protein inside the cell. The presence of the SARS-CoV-2 E protein dramatically reduced the amount of infectious HIV-1 released. SARS-CoV-2 E and gD proteins present in cell lysates were well expressed during co-transfections as demonstrated by immunoblots. In addition, the team noted that in the absence of the Vpu protein, bone marrow stromal cell antigen 2 (BST-2) decreased the amount of HIV-1.
The team observed that co-transfection with vectors encoding the HIV-1 vpu genome, BST-2 and the SARS-CoV-2 E protein reduced the infectious virus produced, although not as significantly as the HSV-1 gD protein. Immunoblots of cell lysates for gD, BST-2, and SARS-CoV-2 E protein showed that these proteins showed significant expression during co-transfections. Together, the team noted that the SARS-CoV-2 E protein prevented the growth of both viruses and that it could not replace the function of the Vpu protein.
Examination of the intracellular expression of these E proteins revealed that, similar to the SARS-CoV-2 E protein, they were localized exclusively to the ER and Golgi compartments of the cell without showing any expression on the cell surface. Although gD was present, it did not affect the amount of infectious HIV-1 released. Instead, he limited his pitching. SARS-CoV-2 and SARS-CoV-related E proteins significantly decreased the amount of infectious HIV-1 released by 1.3% and 1.4%, respectively. A lower restriction was observed for MERS-CoV and HCoV-OC43 E proteins at nearly 37% and 16% of the pcDNA3.1(+) control, respectively.
SARS-CoV-2 and MERS-CoV E proteins shared about 37% of their amino acid sequences, while SARS-CoV-2 and HCoV-OC43 E proteins shared about 26%. The expression of gD and E proteins was verified by immunoprecipitation from cell lysates obtained from the restriction tests. These findings provide further insight into the specificity of HIV-1 restriction.
Overall, the results of the study demonstrated the ability of SARS-CoV-2 and SARS-CoV E proteins to significantly prevent the development of infectious HIV-1 infection. The study found that protein synthesis was most likely inhibited and apoptosis triggered due to the expression of the SARS-CoV-2 E protein. These findings provided evidence that a virus viroporin it can prevent another virus from infecting cells.
*Important news
Research Square publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice or health-related behavior, or be treated as established information.