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Expression of the spleen focus-forming virus envelope gene in a polarized epithelial cell line
D R Kilpatrick1, R V Srinivas, R W Compans
1Department of Microbiology, University of Alabama, Birmingham 35294.
Abstract:
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.
Insights
Friend spleen focus-forming virus (F-SFFV) glycoprotein gp52 shows defective transport. Structural changes in gp52 do not affect its polarized cell surface expression site.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Friend spleen focus-forming virus (F-SFFV) produces a glycoprotein, gp52, with impaired intracellular transport.
- Gp52 accumulates in the endoplasmic reticulum, with minimal surface expression, unlike transport-competent murine leukemia virus (MuLV) glycoproteins.
Purpose of the Study:
- To investigate the impact of structural alterations in F-SFFV gp52 on its cell surface expression.
- To determine the polarized expression site of F-SFFV gp52 and a chimeric protein in epithelial cells.
Main Methods:
- Expression of wild-type and chimeric F-SFFV env genes using vaccinia virus recombinants.
- Analysis of glycoprotein transport and localization in polarized epithelial cell lines (MDCK and CV-1).
- Comparison of gp52 with a chimeric protein containing MuLV transmembrane and cytoplasmic tail residues.
Main Results:
- Both wild-type and chimeric gp52 proteins exhibited defective transport and remained largely unprocessed in MDCK and CV-1 cells.
- Low levels of both glycoproteins were detected on the basolateral surfaces of polarized MDCK cells.
- Neither the presence/absence of a cytoplasmic tail nor a deletion in the external domain altered the polarized expression site.
Conclusions:
- The structural differences in F-SFFV gp52, including a 585-base deletion, do not influence the site of polarized expression.
- Cytoplasmic tail modifications do not affect the basolateral targeting of this murine retrovirus glycoprotein.
- Defective transport is a characteristic of F-SFFV gp52, irrespective of its specific structural domains.