SEQUENCE AND TISSUE DISTRIBUTION OF THE INTEGRIN-ALPHA-9 SUBUNIT, A NOVEL PARTNER OF BETA-1 THAT IS WIDELY DISTRIBUTED IN EPITHELIA AND MUSCLE

The integrin family of adhesion receptors consists of several heterodimeric glycoproteins, each composed of one alpha and one beta subunit. A novel integrin alpha subunit partial cDNA isolated from TGF-beta stimulated guinea pig airway epithelial cells has previously been reported (Erle, D. J., D. Sheppard, J. Bruess, C. Ruegg, and R. Pytela. 1991. Am. J. Respir. Cell Mol. Biol. 5:170-177). We have now determined cDNA and amino acid sequence for the human homolog of this subunit, named alpha9, from a human lung cDNA library, a human small intestine cDNA library, and cDNA from the cell lines U937, HL-60 and Tera-2. This sequence is predicted to encode a 1006-amino acid mature protein that shares 39% identity with the previously identified integrin subunit alpha4. By Northern blot analysis, alpha9 mRNA was detected in the human carcinoma cell lines Tera-2 and Caco-2. Anti-peptide antibodies against the predicted COOH-terminal sequence of alpha9 immunoprecipitated a heterodimer (140 kD/115 kD nonreduced; 150 kD/130 kD reduced) from Tera-2 lysates. Immunodepletion of beta1-containing integrins with Tera-2 lysates removed alpha9 immunoreactivity, suggesting that beta1 is the principal subunit partner for alpha9 in these cells. Alpha9 was detected by immunohistochemistry in airway epithelium, in the basal layer of squamous epithelium, and in smooth muscle, skeletal muscle, and hepatocytes.