MOLECULAR-CLONING AND EXPRESSION OF THE CDNA FOR ALPHA-3 SUBUNIT OF HUMAN ALPHA-3-BETA-1 (VLA-3), AN INTEGRIN RECEPTOR FOR FIBRONECTIN, LAMININ, AND COLLAGEN

alpha-3-beta-1 (VLA-3), a member of the integrin family of cell adhesion receptors, may function as a receptor for fibronectin, laminin, and collagen. A partial cDNA clone (2.4 kb) for the human alpha-3 subunit was selected from an endothelial cell lambda-gt11 cDNA library by specific antibody screening. Several overlapping cDNA clones were subsequently obtained, of a total length of 4.6 kb from various cDNA libraries. The reconstructed alpha-3 cDNA was expressed on the surface of chinese hamster ovary cells as detected by an alpha-3-specific mAb after transfection, suggesting that the cDNA is authentic. Within this sequence was an open reading frame, encoding for 1,051 amino acids, including a signal peptide of 32 residues, a long extracellular domain (959 residues), a transmembrane domain (28 residues), and a short cytoplasmic segment (32 residues). Overall, the alpha-3 amino acid sequence was 25-37% similar to the other integrin alpha-subunits that are cleaved, with most similarity to the alpha-6 sequence (37%), and less similarity to those alpha-subunits that have I domains (15-20%, excluding the I domain sequence itself). Features most like those in other alpha subunits are (a) the positions of 18/19 cysteine residues, (b) three potential metal binding domains of the general structure DX(D/N)X(D/N)GXXD, and (c) the predicted transmembrane domain. The mass of alpha-3 calculated from its amino acid sequence is 113,505. The human-alpha-3 sequence was 89% identical to hamster galactoprotein b3, and 70% similar to the chicken CSAT antigen band 2 protein partial sequence, suggesting that these two polypeptides are homologues of human alpha-3.