CLONING AND CHARACTERIZATION OF RAT DENSITY-ENHANCED PHOSPHATASE-1, APROTEIN-TYROSINE-PHOSPHATASE EXPRESSED BY VASCULAR CELLS

We have cloned from cultured vascular smooth muscle cells a protein ty rosine phosphatase, rat density-enhanced phosphatase-l (rDEP-1), which is a probable rat homologue of DEP-1/HPTP eta. rDEP-1 is encoded by a n 8.7-kb transcript and is expressed as a 180- to 220-kD protein. The rDEP-1 gene is located on human chromosome 11 (region p11.2) and on mo use chromosome 2 (region 2E). The cDNA sequence predicts a transmembra ne protein consisting of a single phosphatase catalytic domain in the intracellular region, a single transmembrane domain, and eight fibrone ctin type III repeats in the extracellular region (GenBank accession n umber U40790). In situ hybridization analysis demonstrates that rDEP-1 is widely expressed in vivo but that expression is highest in cells t hat form epithelioid monolayers. In cultured cells with epithelioid mo rphology, including endothelial cells and newborn smooth muscle cells, but not in fibroblast-like cells, rDEP-1 transcript levels are dramat ically upregulated as population density increases. In vivo, quiescent endothelial cells in normal arteries express relatively high levels o f rDEP-1. During repair of vascular injury, expression of rDEP-1 is do wnregulated in migrating and proliferating endothelial cells. In vivo, rDEP-1 transcript levels are present in very high levels in megakaryo cytes, and circulating platelets have high levels of the rDEP-1 protei n. In vitro, initiation of differentiation of the human megakaryoblast ic cell line CHRF-288-11 with phorbol 12-myristate 13-acetate leads to a very strong upregulation of rDEP-1 transcripts. The deduced structu re and the regulation of expression of rDEP-1 suggest that it may play a role in adhesion and/or signaling events involving cell-cell and ce ll-matrix contact.