Mapping of two new epitopes on the apomucin encoded by MUC5AC gene: Expression in normal GI tract and colon tumors

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Abstract
Three hybridomas secreting monoclonal antibodies (MAbs) against human (62M MAb) or rat (463M and 589M MAbs) gastric mucins were isolated. These MAbs immunoreacted against a human recombinant protein encoded by the 3′ region of the MUC5AC gene. We have mapped 2 new gastric mucin epitopes and the M1‐f epitope previously characterized by the 19/21M1 MAbs on MUC5AC‐encoded apomucin. The M1‐f, 463/589M and 62M epitopes are located in the MUC11p15/von Willebrand factor (vWF)‐A3uD4 domain, in the D4‐(vWF)‐like domain and in the C‐ and CK‐vWF‐like domains of MUC5AC, respectively. The 463/589M and 62M MAbs stained the surface epithelium of human gastric mucosae, but not the normal colon mucosae (except 463/589M MAbs, which immunoreacted with 5 of 49 cases). All hyperplastic polyps are stained strongly with the 463/589M MAbs and faintly with the 62M MAb. In addition, 463/589M epitope was detected in 64% of the adenomas and in 93% of the mucosae adjacent to adenocarcinomas; in contrast, only 9% of the adenomas and 29% of the mucosae adjacent to adenocarcinomas expressed the 62M epitope. The expression pattern of the 463/589M epitope in colonic carcinogenesis is different from that of the 19/21M1 epitope, although the 2 epitopes are encoded by MUC5AC gene.