Identification of human galactoprotein b3, an oncogenic transformation-induced membrane glycoprotein, as VLA-3 alpha subunit: the primary structure of human integrin alpha 3.

Galactoprotein b3 is one of the cell membrane glycoproteins of fibroblasts showing enhanced expression in association with oncogenic transformation. Analysis of cDNA for this glycoprotein from hamster fibroblasts indicated that the glycoprotein is a member of the integrin superfamily [Tsuji, T., Yamamoto, F., Miura, Y., Takio, K., Titani, K., Pawar, S., Osawa, T., & hakomori, S. (1990) J. Biol. Chem. 265, 7016-7021]. In the present study, we examined the change in the amounts of mRNA for the mouse and human counterparts in fibroblasts after oncogenic transformation by Northern blot analysis using hamster galactoprotein b3 cDNA as a probe. In both human and murine fibroblasts transformed with SV-40, the homologous mRNA to galactoprotein b3 was also found to increase as compared with the progenitor cells. The human homologue of galactoprotein b3 cDNA was cloned from human bladder carcinoma cell line (T24) cDNA library. The cDNA codes for a single polypeptide of which the N-terminal sequence (21 amino acids) is identical with that of human VLA-3 alpha subunit. Based on this sequence identity and the structural similarities (i.e. the positions of most cysteine residues, the presence of a transmembrane domain near the C-terminus and the presence of metal binding sequences) with other integrins so far cloned, we conclude that human galactoprotein b3 is an integrin alpha 3 subunit. The mature integrin alpha 3 polypeptide was composed of 1,019 amino acid residues, and the overall structure was quite similar to the hamster counterpart.(ABSTRACT TRUNCATED AT 250 WORDS)