Using the "one-bead one-
peptide" combinatorial technology, a library of random cyclic octapeptides and nonapeptides, consisting of natural and unnatural
amino acids, was synthesized on
polystyrene beads. This library was used to screen for
peptides that promoted attachment and proliferation of
bronchioloalveolar carcinoma cells (H1650), employing a "cell growth on bead" assay. Consensus
peptide sequences of cNleDXXXXc and cXNleDXXXXc (where Nle is
norleucine) were identified. With
alanine scanning and site-directed deletion, a typical
ligand consisted of a motif of -NleDI/V/Nle- with two flanking cysteines. These
peptide ligands were specific for promoting cell attachment of the H1650 cells and the cells of lymphoid
cancers (Jurkat and Raji) but not other selected human cell lines of
lung cancer and fibroblast. In an antibody blocking assay,
integrin alpha(4)beta(1), which was overexpressed in H1650, Jurkat, and Raji, was identified as a putative receptor for these
peptide ligands. Using Chinese hamster ovary cells transfected with either wild-type or mutant
integrin alpha(4), a critical binding site for these
peptides was localized to the
glycine residue at position 190 of
integrin alpha(4).