Role of MxB in Alpha Interferon-Mediated Inhibition of HIV-1 Infection

Abstract

Type I interferon inhibits viruses through inducing the expression of antiviral proteins, including the myxovirus resistance (Mx) proteins. Compared to the human MxA protein, which inhibits a wide range of viruses, the MxB protein has been reported to specifically inhibit primate lentiviruses, including HIV-1, and herpesviruses. Further, the role of endogenous MxB in alpha interferon-mediated inhibition of HIV-1 infection was questioned by a recent study showing that MxB knockout did not increase the level of infection by HIV-1 which carried the G protein of vesicular stomatitis virus (VSV), allowing infection of CD4-negative HT1080 cells. In order to further examine the anti-HIV-1 activity of endogenous MxB, we have used CRISPR/Cas9 to deplete MxB in different cell lines and observed a substantial restoration of HIV-1 infection in the presence of alpha interferon treatment. However, this rescue effect of MxB knockout became much less pronounced when infection was performed with HIV-1 carrying the VSV G protein. Interestingly, a CRISPR/Cas9 knockout screen of alpha interferon-stimulated genes in U87-MG cells revealed that the genes for interferon-induced transmembrane protein 2 (IFITM2) and IFITM3 inhibited VSV G-pseudotyped HIV-1 much more strongly than the rest of the genes tested, including the gene for MxB. Therefore, our results demonstrate the importance of MxB in alpha interferon-mediated inhibition of HIV-1 infection, which, however, can be underestimated if infection is performed with VSV G protein-pseudotyped HIV-1, due to the high sensitivity of VSV G-mediated infection to inhibition by IFITM proteins. The results of this study reconcile the controversial reports regarding the anti-HIV-1 function of alpha interferon-induced MxB protein. In addition to the different cell types that may have contributed to the different observations, our data also suggest that VSV G protein-pseudotyped HIV-1 is much less inhibited by alpha interferon-induced MxB than HIV-1 itself is. Our results clearly demonstrate an important contribution of MxB to alpha interferon-mediated inhibition of HIV-1 in CD4 T cells, which calls for using HIV-1 target cells and wild-type virus to test the relevance of the anti-HIV-1 activity of endogenous MxB and other restriction factors.

A virus-packageable CRISPR screen identifies host factors mediating interferon inhibition of HIV

“…However, these results show that while MxB does play a role in the IFN-mediated inhibition of VSV-G pseudotyped HIV-1 viruses (compare MxB-KO cells to NTCs in Figure 3D ), this effect is masked by dominant IFITM inhibition of these VSV-G pseudotyped viruses ( Figure 3E ). Similar results have been reported recently elsewhere ( Xu et al, 2018 ). Therefore, viral entry route impacts restriction factor sensitivity and the role of MxB in IFN inhibition of HIV-1 in THP-1s is partially-masked by other ISGs when HIV-1 LAI is pseudotyped by VSV-G.…”

Multiple Pathways To Avoid Beta Interferon Sensitivity of HIV-1 by Mutations in Capsid

“…These results suggest that MxB does not contribute to the IFN-β sensitivity of the RGDA/Q112D virus in T cells, and these findings are similar to those of previous studies that suggested a limited role of MxB in restriction mediated by type I IFN in myeloid THP-1 cells (10, 61). During preparation of the manuscript for this article, Xu et al argued that the limited role of MxB reported previously was due to experimental conditions with HIV-1 carrying the VSV G protein (62). It should be noted that our results were obtained with replication-competent viruses harboring HIV-1 Env (Fig.…”

Novel PF74-like small molecules targeting the HIV-1 capsid protein: Balance of potency and metabolic stability

“…Importantly, HIV-1 core stability and uncoating are also tightly regulated via the interactions between CA and various cellular factors to enable most post entry steps such as cytoplasmic trafficking, nuclear entry, integration, and host restriction 12 , 21 . CA-interacting host factors include TRIM5 α 22 , 23 , cleavage and polyadenylation specific factor 6 (CPSF6) 24 , 25 , nucleoporins 153 26 , 27 , 28 and 358 29 , 30 (NUP153 and NUP358), MxB 31 , 32 , and cyclophilin A 33 , 34 , 35 . Therefore, in addition to potentially inhibiting viral strains resistant to current drug classes, CA-targeting small molecules also have the advantage of conferring both early stage and late stage antiviral phenotypes by disrupting CA‒CA and CA‒host interactions.…”