Molecular Cloning and Characterization of a Transmembrane Surface Antigen in Human Cells

Abstract

The mouse mAb 6C6, raised against a plasma-membrane preparation from human breast-cancer cells, reacts with an antigen that appears to be overexpressed in human breast cancers and other human tumors. Here we describe the cDNA cloning and characterization of the antigen recognized by the 6C6 mAb. The isolated cDNA clone encodes a protein of 246 amino acids, with a predicted molecular mass of 27 991 Da. The protein contains three amino-terminal hydrophobic regions, which could represent transmembrane domains, and a hydrophilic carboxy-terminal region, which we show to be extracellular. The identity of the protein encoded by the cloned cDNA as the 6C6 antigen was confirmed by in vitro translation and immunoprecipitation experiments, and by transfection into cell lines that do not react with the 6C6 mAb, which resulted in the expression of a 28-kDa surface protein that was recognized by the antibody. The 6C6 antigen appears to be a type IT transmembrane protein, with multiple membrane-spanning domains and a long extracellular non-glycosylated carboxy-terminal domain, to which the 6C6 epitope has been mapped. The overall structure of the protein and weak amino acid similarities with a family of multipletransmembrane-spanning-domain proteins that includes some antigens (such as L6, CD63/ME491 and CO-029) that are overexpressed in tumor cells, suggest that the 6C6 antigen may belong to this family of proteins.

Anti-idiotypic antibodies induced by genetic immunisation are directed exclusively against combined VL/VH determinants

“…18 The 6C6 antibody was chosen because its V regions have low homology to those of BCL1. While mAb 6C6 has a light chain and a V H corresponding to family VI, BCL1 light chain is (family I) and the V H corresponds to family XXIV.…”

Endoplasmic Reticulum Membrane-sorting Protein of Lymphocytes (BAP31) Is Highly Expressed in Neurons and Discrete Endocrine Cells

“…Sequential non-covalent interactions between donor and target membrane SNARE proteins, and cytosolic mediators, bring phospholipids of transport vesicles into close proximity to their destined fusion site. Northern blotting analyses have revealed BAP31 RNA transcripts in all tissues examined (Mosser et al 1994;Adachi et al 1996;Li et al 1996), suggesting that BAP31 is important in general cell processes involving early secretory pathway trafficking of proteins and as a mediator of apoptosis. However, associations demonstrated for BAP31 in vitro with nascent IgD (Kim et al 1994), peptide-loaded nascent MHC Class I molecules (Spiliotis et al 2000), and recombinant synaptobrevin, the neuronal synaptic vesicle homologue of cellubrevin (Annaert et al 1997), suggest that BAP31 has a specialized role in regulating export of selected membrane protein cargoes to the Golgi apparatus in lymphocytes and neurons.…”

Tumor antigens as proteogenomic biomarkers in invasive ductal carcinomas

“…However, caspase resistant types of BCAP31 have been observed and the lack of cleavage during apoptosis leads to reduced apoptotic potential [ 84 ]. BCAP31 has previously been reported to be up regulated in the breast cancer tissue as compared to normal tissue [ 85 ].…”