RESUMO
Second generation monoclonal antibodies to the alpha 6 beta 4 subunits of human integrins have been prepared. MAbs 450-9D, 10D, and 11A1 react at different sites on the beta 4 molecule and MAbs 450-30A1 and 33D react at the same site on the alpha 6 subunit. Double determinant (two-site) radioimmunoassays using combinations of these MAbs have been developed. Two assays for beta 4 distinguish between the whole beta 4 molecule and the beta 4 molecule truncated from the C-terminus (form c) while another assay measures the presence of alpha 6 subunits. Data from the two-site assays support the following conclusions: (1) Colon tumors and normal colon mucosa express large amounts of alpha 6 beta 4 although only form c of the beta 4 was detected; (2) There is no evidence for alpha 6 beta 1 expression in colon; however, some of this complex may be present in certain lung tumors. The extracellular domains of alpha 6 and beta 4 can associate with each other even if the cytoplasmic domain of the beta 4 subunit is not present. MAbs to specific domains of the beta 4 molecule may be useful in analyses of forms a and c in normal and malignant tissue. The fact that only the largest beta 4 molecule "a" retains the phosphorylation site may have functional significance.
