Mouse mammary tumor virus superantigens require N-linked glycosylation for effective presentation to T cells.
Mouse mammary tumor viruses (MMTVs) encode superantigens that associate with major histocompatibility complex class II products on antigen-presenting cells and stimulate T cells in a V beta-specific manner. This T cell activation is critical for completion of the viral life cycle and vertical transmission to the next generation. To investigate the functional significance of extensive viral superantigen (Sag) glycosylation, we disrupted the six potential sites for N-linked carbohydrate addition in the Sag encoded by proviral integrant Mtv-1. Shifts in the apparent molecular mass of these mutant glycoproteins suggested that wild-type Mtv-1 Sag is glycosylated on four of its six sites. Intracellular and cell surface staining of the panel of mutants indicated that any decrease in glycosylation resulted in reduced levels of intracellular protein and undetectable surface expression, suggesting that decreased glycosylation leads to rapid Sag degradation and abates trafficking to the plasma membrane. Nevertheless, several mutants with intermediate levels of glycosylation expressed enough Sag on the B cell surface to potently stimulate reactive T cell hybrids. We show there is no specific site bearing N-linked glycosylation that is essential for activity, but at least one carbohydrate addition is necessary for effective B cell presentation of MMTV superantigens to T cells.
McMahon
C W
CW
Department of Immunology, University of Washington, Seattle 98195, USA.
Bogatzki
L Y
LY
Pullen
A M
AM
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D000956:Antigens, Viral / Q000235:genetics / Q000276:immunology*; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D006031:Glycosylation; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D012333:RNA, Messenger; D018089:Superantigens / Q000235:genetics / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*
D000956:Antigens, Viral; D012333:RNA, Messenger; D018089:Superantigens