Mammalian orthoreovirus T3D infects U-118 MG cell spheroids independent of junction adhesion molecule-A

In the canonical pathway, Infection of cells by the wild-type mammalian orthoreovirus Type 3 Dearing (T3D) is dependent on the interaction of the viral spike protein σ1 with the high-affinity cellular receptor junction adhesion molecule-A (JAM-A). We previously demonstrated that the human Glioblastoma cell line U-118 MG does not express JAM-A and resists reovirus T3D Infection in standard Cell Culture conditions (SCCC). Heterologous JAM-A expression sensitises U-118 MG cells to reovirus T3D. Here we studied reovirus Infection in U-118 MG cells grown in spheroid cultures with the premise that cells in such cultures resemble cells in tumours more than those grown under standard adherent Cell Culture conditions on a plastic surface. Although the U-118 MG cells in spheroids do not express JAM-A, they are susceptible to reovirus T3D Infection. We show that this can be attributed to factors secreted by cells in the spheroids. The concentration of active extracellular proteases Cathepsin B and L in the medium of spheroid cultures was increased 19- and 24-fold, respectively, as compared with SCCC. These Enzymes can convert the reovirus particles into a form that can infect the U-118 MG cells independent of JAM-A. Taken together, these data demonstrate that Infection of tumour cells by wild-type reovirus T3D is not strictly dependent on the expression of JAM-A on the cell surface.