Effects of Inner Nuclear Membrane Proteins SUN1/UNC-84A and SUN2/UNC-84B on the Early Steps of HIV-1 Infection

Abstract

Human immunodeficiency virus type 1 (HIV-1) infection of dividing and nondividing cells involves regulatory interactions with the nuclear pore complex (NPC), followed by translocation to the nucleus and preferential integration into genomic areas in proximity to the inner nuclear membrane (INM). To identify host proteins that may contribute to these processes, we performed an overexpression screen of known membrane-associated NE proteins. We found that the integral transmembrane proteins SUN1/UNC84A and SUN2/UNC84B are potent or modest inhibitors of HIV-1 infection, respectively, and that suppression corresponds to defects in the accumulation of viral cDNA in the nucleus. While laboratory strains (HIV-1NL4.3 and HIV-1IIIB) are sensitive to SUN1-mediated inhibition, the transmitted founder viruses RHPA and ZM247 are largely resistant. Using chimeric viruses, we identified the HIV-1 capsid (CA) protein as a major determinant of sensitivity to SUN1, and in vitro-assembled capsid-nucleocapsid (CANC) nanotubes captured SUN1 and SUN2 from cell lysates. Finally, we generated SUN1−/− and SUN2−/− cells by using CRISPR/Cas9 and found that the loss of SUN1 had no effect on HIV-1 infectivity, whereas the loss of SUN2 had a modest suppressive effect. Taken together, these observations suggest that SUN1 and SUN2 may function redundantly to modulate postentry, nuclear-associated steps of HIV-1 infection.IMPORTANCE HIV-1 causes more than 1 million deaths per year. The life cycle of HIV-1 has been studied extensively, yet important steps that occur between viral capsid release into the cytoplasm and the expression of viral genes remain elusive. We propose here that the INM components SUN1 and SUN2, two members of the linker of nucleoskeleton and cytoskeleton (LINC) complex, may interact with incoming HIV-1 replication complexes and affect key steps of infection. While overexpression of these proteins reduces HIV-1 infection, disruption of the individual SUN2 and SUN1 genes leads to a mild reduction or no effect on infectivity, respectively. We speculate that SUN1/SUN2 may function redundantly in early HIV-1 infection steps and therefore influence HIV-1 replication and pathogenesis.

SUN1 Regulates HIV-1 Nuclear Import in a Manner Dependent on the Interaction between the Viral Capsid and Cellular Cyclophilin A

“…Given that SUN1 and SUN2 share many functional similarities, we investigated whether SUN1 regulates HIV-1 infection. During the preparation of this paper, Schaller et al reported that SUN1 overexpression blocks HIV-1 infection in a CA-dependent manner (25). Our results reported here confirm their results.…”

“…5). During the course of our work, Schaller et al (25) reported that SUN1 overexpression inhibits the infection of HIV-1 by reducing the accumulation of the 2-LTR DNA in a CA-dependent manner. Our findings reported here are consistent with theirs.…”

“…Schaller et al reported that SUN1 knockout did not affect infection by NL4-3-GFP (25). They evaluated infection by measuring the percentage of green fluorescent protein (GFP)-positive cells, which is the overall result of many steps.…”

“…Two possible mechanisms can be speculated: (i) CA is directly targeted by SUN1 during the nuclear entry process of the virus, and (ii) CA-mediated nuclear import of the PIC but not CA itself is targeted by SUN1. Schaller et al reported that in vitro-assembled HIV-1 CA-NC nanotubes interacted with SUN1, possibly reflecting a direct interaction between SUN1 and CA (25). However, SUN1 also interacted with the CA-NC nanotubes from an HIV-1 strain that was insensitive to SUN1, suggesting that the interaction between CA and SUN1 may not be the only determi- nant for the sensitivity of the virus to SUN1.…”

The GTPase Domain of MX2 Interacts with the HIV-1 Capsid, Enabling Its Short Isoform to Moderate Antiviral Restriction

“…Detailed methods are provided in the online version of this paper and include the following: cells (Merck Millipore) as previously described (Schaller et al, 2017). Briefly, CANC expression was induced with 1 mM of isopropyl b-D-thiogalactopyranoside (IPTG) for 6 h at 30 C. Cells were collected by centrifugation and lysed by sonication.…”