Characterization of mouse integrin alpha 3 subunit gene

Integrin alpha 3 beta 1 (VLA-3) is an adhesion receptor for extracellular m atrix proteins including various isoforms of laminin, We have isolated mous e genomic clones encoding the integrin alpha 3 subunit and deduced the exon /intron organization. The mouse integrin alpha 3 subunit gene is encoded by 26 exons spanning 40 kb, The exon/intron structure of the integrin alpha 3 subunit gene resembles that of the integrin ae subunit gene, but differs s omewhat from those of other members of the integrin family. We have demonst rated that the cytoplasmic domain splicing variants of the alpha 3 subunits (alpha 3A and alpha 3B) are generated by alternative exon usage. We also c loned the 5'-flanking region and performed a preliminary analysis of its pr omoter activity in various tumor cell lines with different degrees of integ rin alpha 3 expression. Following transfection, activity in the luciferase assay was found to be roughly correlated with the expression level of integ rin a3 as measured by dow cytometry, Furthermore, the luciferase assay was performed with normal and SV-40- or polyoma virus-transformed fibroblasts. In mouse, human, and hamster fibroblasts, higher levels of luciferase expre ssion were observed in transformed cells than in normal cells. This result is consistent with our previous finding that integrin a3 expression at both the protein and mRNA levels is enhanced upon oncogenic transformation of f ibroblasts by tumor viruses.