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

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Abstract
The McDonough strain of feline sarcoma virus encodes a polyprotein that is cotranslationally glycosylated and proteolytically cleaved to yield transforming glycoproteins specified by the viral oncogene v-fms. The major form of the glycoprotein (gp120fms) contains endoglycosidase H-sensitive, N-linked oligosaccharide chains lacking fucose and sialic acid, characteristic of glycoproteins in the endoplasmic reticulum. Kinetic and steady-state measurements showed that most gp1204f4m4s molecules were not converted to mature forms containing complex carbohydrate moieties. Fixed-cell immunofluorescence confirmed that the majority of v-fms-coded antigens were internally sequestered in transformed cells. Dual-antibody fluorescence performed with antibodies to intermediate filaments (IF) showed that of the transformed cells were rearranged, and their distribution coincided with that of v-fms-coded antigens. No specific disruption of action cables was observed. The v-fms gene products cofractionated with IF isolated from virus-transformed cells and reassociated with IF self-assembled in vitro. A minor population of v-fms-coded molecules (gp140fms) acquired endoglycosidase H-resistant, N-linked oligosaccharide chains containing fucose and sialidic acid residues, characteristic of molecules processed in the Golgi complex. Some gp140fms molecules were detected at the plasma membrane and were radiolabeled by lactoperoxidase-catalyzed iodination of live transformed cells. Evidently, v-fms-coded molecules are translated as integral transmembrane glycoproteins, most of which are inhibited in transport through the Golgi complex to the plasma membrane.