Isolation, cloning, and sequence analysis of the integrin subunit α10, a β1-associated collages binding integrin expressed on chondrocytes

We have found that chondrocytes express a novel collagen type II-binding integrin, a new member of the beta 1-integrin family. The integrin alpha subunit, which has a M(r) of 160 kDa reduced, was isolated from bovine chondrocytes by collagen type II affinity purification. The human homologue was obtained by screening a human chondrocyte library with a bovine cDNA probe. Cloning and cDNA sequence analysis of the human integrin alpha subunit designated alpha 10 show that it shares the general structure of other integrin alpha subunits, The predicted amino acid sequence consists of a 1167-amino acid mature protein, including a signal peptide (22 amino acids), a long extracellular domain (1098 amino acids), a transmembrane domain (25 amino acids), and a short cytoplasmic domain (22 amino acids). The extracellular part contains a 7-fold repeated sequence, an I-domain (199 amino acids) and three putative divalent cation-binding sites. The deduced amino acid sequence of alpha 10 is 35% identical to the integrin subunit (alpha 2 and 37% identical to the integrin subunit alpha 1. Northern blot analysis shows a single mRNA of 5.4 kilobases in chondrocytes. A peptide antibody against the predicted sequence of the cytoplasmic domain of alpha 10 immunoprecipitated two proteins with masses of 125 and 160 kDa from chondrocyte lysates under reducing conditions. The peptide antibody specifically stained chondrocytes in tissue sections of human articular cartilage, showing that alpha 10 beta 1 is expressed in cartilage tissue.