Second Generation Monoclonal Antibodies to the Human Integrin α6β4

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Abstract
Second generation monoclonal antibodies to the α6β4 subunits of human integrins have been prepared. MAbs 450-9D, 10D, and 11A1 react at different sites on the β4 molecule and MAbs 450-30A1 and 33D react at the same site on the α6 subunit. Double determinant (two-site) radioimmunoassays using combinations of these MAbs have been developed. Two assays for β4 distinguish between the whole β4 molecule and the β4 molecule truncated from the C-terminus (form c) while another assay measures the presence of α6 subunits. Data from the two-site assays support the following conclusions: (1) Colon tumors and normal colon mucosa express large amounts of α6β4 although only form c of the β4 was detected; (2) There is no evidence for α6β4 expression in colon; however, some of this complex may be present in certain lung tumors. The extracellular domains of α6 and β4 can associate with each other even if the cytoplasmic domain of the β4 subunit is not present. MAbs to specific domains of the β4 molecule may be useful in analyses of forms a and c in normal and malignant tissue. The fact that only the largest β4 molecule "a" retains the phosphorylation site may have functional significance.