Polydom: a secreted protein with pentraxin, complement central protein, epidermal growth factor and von Willebrand factor A domains

To identify extracellular proteins with epidermal growth factor (EGF) domai ns that are potentially involved in the control of haemopoiesis, we perform ed degenerate reverse-transcriptase-mediated PCR on the murine bone-marrow stromal cell line MS-5 and isolated a new partial cDNA encoding EGF-like do mains related to those in the Notch proteins. Cloning and sequencing of the full-length cDNA showed that it encoded a new extracellular multi-domain p rotein that we named polydom. This 387 kDa mosaic protein contained a signa l peptide followed by a new association of eight different protein domains, including a pentraxin domain and a von Willebrand factor type A domain, te n EGF domains, and 34 complement control protein modules. The human polydom mRNA is strongly expressed in placenta, its expression in the other tissue s being weak or undetectable. The particular multidomain structure of the e ncoded protein suggests an important biological role in cellular adhesion a nd/or in the immune system.