gms | German Medical Science

Objective: The proteolipid plasmolipin (PLLP) is a tetraspan membrane protein expressed primarily in brain and kidney epithelial cells. In the brain, PLLP is associated with the myelin sheath and is thought to play a role in the regulation of myelin maintenance. Recently PLLP has been identified as a receptor for a mouse endogenous retrovirus McERV, which can infect cells from different mammalian species but has a restricted tissue tropism. Kidney cells have been shown to be susceptible to McERV infection, but cell targets in the brain are unknown. The aim of the study is to characterize the expression of PLLP in different types of glioma stem-like cells (GSCs) and assess their infectability with a lentiviral vector encoding green fluorescent protein (LeGo-G) and pseudotyped with either McERV Env protein or, as a control, the glycoprotein from the vesicular stomatitis virus (VSV-G).

Method: Five GSCs lines established from surgical GBM specimens were tested for susceptibility to McERV in vitro. GSCs were plated at 5x104 cells per well in 24 well plates 24 hours prior infection in Neurobasal medium (Invitrogen) supplemented with bFGF (10 ng/ml) and EGF (20 ng/ml). The next day, the cells were exposed to 0.01 to 0.05 ml of cell supernatants containing equivalent titers of either LeGo-G(McERV) or LeGo-G(VSV) viral particles. To evaluate the rate of infection, GSCs were analyzed for GFP expression by flow cytometry two days after exposure to the virus. PLLP expression in GSCs was assessed by western blot or immunofluorescence staining.

Results: From the five lines of GSCs, two lines were found susceptible to LeGo-G(McERV). PLLP assessments revealed that the rate of infectability correlates with the expression of PLLP. Interestingly, the susceptible lines show a more differentiated phenotype compared to non-susceptible lines, suggesting that, in addition to PLLP abundance, the degree of differentiation may be a determining factor of GSCs infectability by McERV.

Conclusions: PLLP expression and PLLP-associated infectability of GSCs offers an opportunity to target specifically the stem cell compartment in GBM. Our data suggests PLLP as in GSCs a potential novel therapeutic target for McERV-mediated therapy in GBM.