The Golgi protein RCAS1 controls cell surface expression of tumor-associated O-linked glycan antigens.
Tumor immunology has received a large impetus from the identification of tumor-associated antigens. Among them, a monoclonal antibody, 22.1.1, was instrumental in defining a novel tumor-associated antigen that was termed "receptor binding cancer antigen expressed on SiSo cells" (RCAS1). RCAS1 was proposed to induce growth arrest and apoptosis on activated immune cells, mediated by a putative death receptor. Structurally, RCAS1 was predicted to exist as a type II transmembrane protein and in a soluble form. Here, we analyzed occurrence, membrane topology, and subcellular localization of the RCAS1-encoded gene product. RCAS1 was shown to be a ubiquitously expressed type III transmembrane protein with a Golgi-predominant localization. Monoclonal antibody 22.1.1 failed to recognize RCAS1, as demonstrated by confocal microscopy. Instead, we showed that the cognate 22.1.1 epitope is identical with the tumor-associated O-linked glycan Tn (N-acetyl-d-galactosamine, GalNAc). Overexpression of RCAS1 in cell lines that are negative for 22.1.1 surface staining led to the generation of Tn and the closely related TF (Thomsen-Friedenreich, Galbeta1-3GalNAc) antigen, thus providing a functional link to the generation of the 22.1.1 epitope. We suggest that RCAS1 modulates surface expression of tumor-associated, normally cryptic O-linked glycan structures and contributes indirectly to the antigenicity of tumor cells.
Engelsberg
Arne
A
Department of Hematology, Oncology and Tumorimmunology, Max-Delbrück Center for Molecular Medicine, Berlin, Germany.
Hermosilla
Ricardo
R
Karsten
Uwe
U
Schülein
Ralf
R
Dörken
Bernd
B
Rehm
Armin
A
D000951:Antigens, Neoplasm / Q000378:metabolism*; D001483:Base Sequence; D019921:Biotinylation; D001943:Breast Neoplasms; D002460:Cell Line; D017931:DNA Primers; D005260:Female; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D007668:Kidney; D016133:Polymerase Chain Reaction; D011134:Polysaccharides / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D019459:Urothelium
D000951:Antigens, Neoplasm; D017931:DNA Primers; C120762:EBAG9 protein, human; D011134:Polysaccharides; D011994:Recombinant Proteins