IL-27 Reduces Cell-Surface LDLR in Human Macrophages and Restricts VSV-G-Pseudotyped HIV infection

Low-density lipoprotein receptor (LDLR) is a major cellular receptor for vesicular stomatitis virus glycoprotein (VSV-G), which is widely used to pseudo-type viral vectors. We previously showed that IL-27 suppresses infection by VSV-G-pseudotyped HIV encoding luciferase (VSV-G-HIVLuc) in macrophages; although IL-27 induced multiple anti-virus genes in cell, the underlying mechanism of VSVG-HIVLuc inhibition remains poorly understood. Here, we examined whether IL-27 regulates LDLR expression and contributes to suppression of VSV-G-HIVLuc infection. Monocyte-derived macrophages differentiated with M-CSF or GM-CSF, with or without IL-27, were analyzed for cell-surface LDLR by flow cytometry, LDLR transcripts by quantitative RT-PCR, and total LDLR protein by Western blotting. Viral binding, proviral DNA, and reporter expression were evaluated by cell-associated p24 antigen, late reverse-transcription products, and luciferase activity, respectively. IL-27 reduced surface LDLR to 38.3 ± 2.6 % in M-CSF-derived macrophages (p<0.01) and 31.4± 3.2 % in GM-CSF-derived macrophages (p<0.01). Western Blotting demonstrated that total LDLR protein decreased to 48 ± 0.8 % in IL-27-treated M-CSF-derived macrophages (27M-Mac) (p<0.01) while it was not significantly changed in IL-27-treated GM-CSF-derived macrophages (27GM-Mac), although approximately 1.6~1.9-fold increase in LDLR transcripts following IL-27 treatment in both macrophages (p<0.01). Viral binding decreased to nearly 50 % in 27GM but not significantly changed on 27M-Mac whereas late reverse-transcription products decreased to 23 ± 2.1% (p<0.0001) and 44 ± 1.5% (p<0.0001). Luciferase activity was further reduced to 5.8 ± 0.4 % and 5.9 ± 2.1 % (both p<0.0001). These findings demonstrate that IL-27 downregulates cell-surface LDLR in human macrophages, suggesting that IL-27 restricts VSV-G-pseudo-typed Lenti virus infection through both receptor-associated and additional post-entry mechanisms.