Expression of the spleen focus-forming virus envelope gene in a polarized epithelial cell line.

Friend spleen focus-forming virus (F-SFFV) encodes a glycoprotein designated gp52, which is defective in its intracellular transport and accumulates in the rough endoplasmic reticulum. Only 3-5% of the mature form of gp52 eventually reaches the cell surface. Compared to transport-competent murine leukemia virus (MuLV) glycoproteins, the gp52 molecule exhibits several structural differences which may have resulted in the possible loss of signals required for transport to the cell surface. To determine the effect of these alterations on the specific sites of surface expression of the molecule, the SFFV env gene was expressed from a vaccinia virus recombinant in a polarized epithelial cell line in which retrovirus glycoproteins are expressed exclusively on basolateral surfaces. We also determined the site of expression of a chimeric env protein which contains the external domain of SFFV gp52 the transmembrane, and the cytoplasmic tail residues of Friend MuLV. The wild-type and chimeric env gene products were defective in transport, and remained primarily in an unprocessed form in MDCK cells or CV-1 cells. However, both glycoproteins were detected at low levels on the basolateral surfaces of MDCK cells, a line of polarized epithelial cells. These results indicate that the presence or absence of a cytoplasmic tail as well as a 585-base deletion in the external domain has no affect on the site of polarized expression of a murine retrovirus glycoprotein.