ISOLATION, CLONING, AND SEQUENCE-ANALYSIS OF THE INTEGRIN SUBUNIT ALPHA-10, A BETA-1-ASSOCIATED COLLAGES BINDING INTEGRIN EXPRESSED ON CHONDROCYTES

We have found that chondrocytes express a novel collagen type II-bindi ng 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 b ovine chondrocytes by collagen type II affinity purification. The huma n 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 gen eral structure of other integrin alpha subunits, The predicted amino a cid sequence consists of a 1167-amino acid mature protein, including a signal peptide (22 amino acids), a long extracellular domain (1098 am ino acids), a transmembrane domain (25 amino acids), and a short cytop lasmic domain (22 amino acids). The extracellular part contains a 7-fo ld repeated sequence, an I-domain (199 amino acids) and three putative divalent cation-binding sites. The deduced amino acid sequence of alp ha 10 is 35% identical to the integrin subunit (alpha 2 and 37% identi cal to the integrin subunit alpha 1. Northern blot analysis shows a si ngle mRNA of 5.4 kilobases in chondrocytes. A peptide antibody against the predicted sequence of the cytoplasmic domain of alpha 10 immunopr ecipitated two proteins with masses of 125 and 160 kDa from chondrocyt e 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.