βig-h3: A Transforming Growth Factor-β-Responsive Gene Encoding a Secreted Protein That Inhibits Cell AttachmentIn Vitroand Suppresses the Growth of CHO Cells in Nude Mice

Publisher Website
Google Scholar
Abstract
βig-h3 is a novel gene first discovered by differential screening of a cDNA library made from A549 human lung adenocarcinoma cells treated with transforming growth factor-βl (TGF-β1). It encodes a 683-aminoacid protein containing a secretory signal sequence and four homologous internal domains. Here we show that treatment of several types of cells, including human melanoma cells, human mammary epithelial cells, human keratinocytes, and human fibroblasts, with TGF-β resulted in a significant increase in βig-h3 RNA. A portion of the βig-h3 coding sequence was expressed in bacteria, and antisera against the bacterially produced protein was raised in rabbits. This antisera was used to demonstrate that several cell lines secreted a 68-kD βIG-H3 protein after treatment with TGF-β. Transfection of βIG-H3 expression plasmids into Chinese hamster ovary (CHO) cells led to a marked decrease in the ability of these cells to form tumors in nude mice. The βIG-H3 protein was purified from media conditioned by recombinant CHO cells, characterized by immunoblotting and protein sequencing and shown to function in an anti-adhesion assay in that it inhibited the attachment of A549, HeLa, and WI-38 cells to plastic in serum-free media. Sequencing of cDNA clones encoding murine βig-H3 indicated 90.6% conservation at the amino acid level between the murine and human proteins. Finally, the βig-h3 gene was localized to human chromosome 5q31, a region frequently deleted in preleukemic myelodysplasia and leukemia. The corresponding mouse βig-h3 gene was mapped to mouse chromosome 13 region B to Cl, which confirms a region of conservation on human chromosome 5 and mouse chromosome 13. We suggest that this protein be named p68βig-h3.