A Monoclonal Antibody to a Carbohydrate Epitope Expressed on Glycolipid and on α₃β₁ Integrin on Human Esophageal Carcinoma

A mouse monoclonal antibody (MAb-9) produced by immunization with a human esophageal carcinoma cell line, TE-2 (derived from undifferentiated squamous cell carcinoma) reacted specifically with about 30% of esophageal carcinoma cell lines and tissue sections from clinical samples. MAb-9 showed minimal reactivity with normal esophageal tissue. ¹²⁵I, fluorescent or gold particle labeled MAb-9 bound to TE-2 cell surfaces. ¹²⁵I- radiolabeled MAb-9 was used to detect reactive material from cell extracts in Western blot. Treatment of TE-2 membrane proteins with neuraminidase, N-glycanase or O-glycanase reduced antigen detection. Treatment of cells with periodic acid destroyed antibody binding in ELISA. Lipid extracts from cell membranes, containing glycolipids, also reacted with MAb-9. MAb-9 was used to purify target antigen from detergent solubilized membrane proteins and the prominent bands from subsequent gel electrophoresis were trypsin digested and analyzed by mass spectrometry. Peptides from α₃ and β ₁ integrin chains were identified. These data indicate that α₃β₁ integrin is prominently expressed on certain esophageal carcinomas and that a specific carbohydrate unit is selectively displayed on the α₃ integrin subunit as well as on glycolipid on the cell surface. The α₃β₁ integrin expressed on A-431 carcinoma cells does not display this carbohydrate epitope and is not detected by MAb-9. Thus, expression of the carbohydrate epitope is the basis for the tumor selective reaction of MAb-9 with a subset of esophageal carcinomas.