Subcellular localization of glycoproteins encoded by the viral oncogene v-fms

Area of Science:

• Molecular Biology
• Virology
• Cell Biology

Background:

• Feline sarcoma virus (FSV) encodes a polyprotein processed into transforming glycoproteins via the viral oncogene v-fms.
• These glycoproteins are cotranslationally glycosylated and proteolytically cleaved.

Purpose of the Study:

• To investigate the post-translational modifications and cellular localization of v-fms-coded glycoproteins.
• To understand the transport and potential interactions of these viral glycoproteins within infected cells.

Main Methods:

• Endoglycosidase H digestion to analyze oligosaccharide chains.
• Fixed-cell immunofluorescence and dual-antibody staining to assess protein localization and intermediate filament (IF) interactions.
• Cofractionation studies and in vitro self-assembly assays to examine v-fms protein and IF association.
• Lactoperoxidase-catalyzed iodination to label cell surface proteins.

Main Results:

• The major glycoprotein (gp120fms) exhibited endoglycosidase H-sensitive glycans, indicating retention in the endoplasmic reticulum, and was largely sequestered intracellularly.
• v-fms antigens showed rearranged distribution coinciding with intermediate filaments (IFs) in transformed cells, with no actin disruption observed.
• v-fms gene products cofractionated with and reassociated with IFs.
• A minor glycoprotein form (gp140fms) was endoglycosidase H-resistant, indicating Golgi processing, and was detected at the plasma membrane.

Conclusions:

• Most v-fms-coded glycoproteins are synthesized as transmembrane proteins but are largely inhibited from transport through the Golgi complex to the plasma membrane.
• The intracellular accumulation of v-fms glycoproteins is associated with rearrangements of intermediate filaments (IFs).
• A small subset of v-fms glycoproteins does reach the cell surface, suggesting partial completion of the transport pathway.