Subcellular trafficking of exogenously expressed interferon-β in Madin-Darby canine kidney cells

We have recently demonstrated that when IFN-β was exogenously expressed in epithelial cells, transiently expressed IFN-β was predominantly secreted from the cell side to which the transfection was performed, while stably expressed one was almost equally secreted to the apical and basolateral sides. In the present study, we analyzed the subcellular transport of IFN-β using confocal imaging with green fluorescent protein (GFP)-tagged IFN-β in Madin-Darby canine kidney (MDCK) cells. Stably expressed and transiently expressed human IFN-β (HulFN-β)-GFPs were seen in upper regions of the nucleus. In stable HulFN β-GFP-producing transformants, transiently expressed mouse IFN-β (MulFN-β) was apparently colocalized with the bulk of the constitutive HulFN β-GFP proteins at TGN, and a significant quantity of them then appeared to pass into distinct post-TGN vesicles, accepting either type of IFN. Meanwhile, when cells were co-transfected with both expression vectors, transiently expressed both IFNs tended to co-localize not only at TGN but in post-TGN vesicles. These results suggest that stably and transiently expressed IFN-βs, albeit co-localized at TGN, were transported through apparently discriminated post-TGN routes.