FIG. 7.

Viral determinants for directed virus-like particle release from polarized epithelial cells. MDCK-II cells that stably express GP, Z, and NP in various combinations were grown on Transwell filters (0.4-μm pore size) until polarization was achieved. After cell culture medium replacement with fresh medium containing 2% FCS, cells were further cultivated for 48 h. VLPs from the apical and basolateral chambers were harvested and concentrated by pelleting through a 20% sucrose cushion. The resuspended samples were subjected to SDS-PAGE and immunoblotting using the α-GP-2-C and α-Z antibodies. The viral proteins GP and Z were quantified using the Odyssey infrared quantification system. Average values from four to six independent experiments are expressed as percentage of VLP release. Error bars denote standard deviations. ***, P < 0.001; **, P < 0.01; *, P < 0.05 (t test).