55,000-dalton, retrovirus-associated, cell membrane glycoprotein: purification and quantitative measurements of expression in viruses, cells, and tissues.

Abstract

We have purified to homogeneity and characterized a 55,000-dalton rat cell membrane glycoprotein, gp55. This protein was originally identified in preparations of a defective pseudotype of the Kirsten sarcoma virus and shown to be present in several rodent retrovirus particles. The gp55 was purified from this defective virus by concanavalin A and heparin affinity chromatography, as well as by preparative sodium dodecyl sulfate-gel electrophoresis. Both preparations displayed similar purity and antigenic characteristics. The '25I-labeled gp55 was precipitated by antisera against rodent retroviruses, but not by monospecific antisera against purified type C virus structural proteins, thus indicating that gp55 was retrovirus associated, but unrelated to known retrovirus structural proteins. Competition radioimmunoassay with an anti-rat virus serum which recognized rodent group-specific antigens on gp55 indicated: (i) the presence of gp55 antigens in 15 rodent cell lines, but not 10 nonrodent cell lines; (ii) no effect of viral infection or cell transformation on the amount of gp55 expressed; (iii) up to 100-fold increases in the concentration of the gp55 antigens in nine rodent retroviruses, but not in five nonrodent viruses, as compared to cells; (iv) the presence of gp55 in rodent sera, especially of the NZB mouse, where anti-gp55 antibody was also detected; (v) a lymphoid and epithelial tissue distribution of gp55 in rats and mice. Additional competition radioimmunoassays with a broadreacting antivirus serum also detected the presence of gp55 in nonrodent, mink, and human cells and thus distinguished rat type, rodent group, and interspecies antigenic determinants on gp55. In conclusion, gp55 is a cell membrane glycoprotein associated in high concentration with retroviruses.The type C oncoviruses are enveloped ribonucleic acid (RNA) retroviruses which form particles by budding through the plasma membranes of infected cells (25). The virus encodes six structural proteins, of which two form the envelope of the virion and four form the nucleoprotein core (14). During the process of virion budding, the particles also incorporate many cellular components, including nucleic acids (8), lipids (35), histocompatibility antigens (6), adenosine triphosphatases (11), kinases (36, 43), and actin. Whereas the cellular lipids and nucleic acids are both specific and required for virion structure, the role of the other cell components in virions is unknown.We have reported the isolation and characterization of a defective mammalian oncovirus (KW virus), which is comprised of only one virionencoded structural protein (33). Instead, these particles contain several novel proteins incorporated from the rat host cell membranes. The cellular and viral expression of three of these proteins (gpllO, gp55, p20) has been partially characterized (38). gpllO and p20 are transformation related. In contrast, gp55, a 55,000-dalton glycoprotein, appeared common to several rodent retrovirus preparations, but was unrelated to virus transformation. W...

Monoclonal antibodies against baboon endogenous virus and against host cell antigens

“…The immune complex formed with [3H]leucine-labeled virus and F12-9 culture fluid revealed a single band migrating with an apparent molecular weight of 18,000 in a polyacrylamide gel. Whether this polypeptide is analogous to the p16 protein associated with the 70S genome in the virion (23) or whether it can be compared to plSC or plSE protein from murine retroviruses must be further studied.…”