Panoply™ Human LAMP1 Over-expressing Stable Cell Line

Lassa virus (LASV) cellular invasion is mediated by the interaction of the viral glycoprotein complex (GPC) with α-dystrophic proteoglycans on the cell surface, followed by binding to LAMP1 in late endosomes. However, LAMP1 is not absolutely necessary for LASV fusion, as the virus can infect LAMP1-deficient cells. Here, researchers investigated the role of human LAMP1 (hLAMP1) in the fusion of LASV with human and avian cells expressing LAMP1 homologs that do not support LASV invasion using LASV GPC pseudoviruses, LASV virus-like particles, and recombinant lymphocytic choriomeningitis virus expressing LASV GPC. The results showed that ectopic expression of hLAMP1 accelerated the formation kinetics of small fusion pores but only slightly improved the efficient fusion and infectivity of LASV with human and avian cells. To assess the role of hLAMP1 in the absence of essential endosome host factors, researchers forced LASV fusion with the plasma membrane by applying a low pH. Unlike the traditional LASV invasion pathway, ectopic expression of hLAMP1 significantly promotes the initial and complete expansion of pores formed on the plasma membrane via forced fusion. Further investigation revealed that while the soluble hLAMP1 extracellular domain accelerates the formation kinetics of new pores, it fails to promote efficient pore expansion, indicating that the hLAMP1 transmembrane domain is involved in the later stages of LASV fusion.

Here, we investigated the effect of hLAMP1 expression on infection with a recombinant LCMV virus carrying LASV GPC (LCMV-LASV GPC). After LAMP1-WT overexpression, LAMP1-d384 overexpression, and control A549 and DF-1 cells were inoculated with LCMV-LASV GPC and immunostained for LCMV NP protein, infection was quantitatively analyzed using microscopy (Figure 1A). Consistent with the results of LASVpp infection, ectopic expression of hLAMP1 slightly increased infection with recombinant LASV in both cell lines (Figure 1B). However, unlike the significantly enhanced infection of LASVpp and LASV-VLP fusions in hLAMP1-overexpressing cells, the infection of LCMV-LASV GPCs in hLAMP1-overexpressing cells was only increased approximately 6-fold (Figure 1C). Thus, although the extent to which hLAMP1 affects fusion/infection of pseudoviruses, VLPs, and recombinant arenaviruses varies, forcing GPC-mediated plasma membrane fusion is always more dependent on ectopic hLAMP1 expression than fusion via the traditional endosomal entry pathway.

Figure 1. LAMP1 expression enhances recombinant LCMV/LASV-GPC infection of A549 and DF-1 cells. (Zhang Y, et al., 2022)