Cloning and Characterization of Rat Density-Enhanced Phosphatase-1, a Protein Tyrosine Phosphatase Expressed by Vascular Cells

Abstract

We have cloned from cultured vascular smooth muscle cells a protein tyrosine phosphatase, rat density-enhanced phosphatase-1 (rDEP-1), which is a probable rat homologue of DEP-1/HPTPη. rDEP-1 is encoded by an 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 mouse chromosome 2 (region 2E). The cDNA sequence predicts a transmembrane protein consisting of a single phosphatase catalytic domain in the intracellular region, a single transmembrane domain, and eight fibronectin type III repeats in the extracellular region (GenBank accession number U40790 ). In situ hybridization analysis demonstrates that rDEP-1 is widely expressed in vivo but that expression is highest in cells that form epithelioid monolayers. In cultured cells with epitheliod morphology, including endothelial cells and newborn smooth muscle cells, but not in fibroblast-like cells, rDEP-1 transcript levels are dramatically upregulated as population density increases. In vivo, quiescent endothelial cells in normal arteries express relatively high levels of rDEP-1. During repair of vascular injury, expression of rDEP-1 is downregulated in migrating and proliferating endothelial cells. In vivo, rDEP-1 transcript levels are present in very high levels in megakaryocytes, and circulating platelets have high levels of the rDEP-1 protein. In vitro, initiation of differentiation of the human megakaryoblastic cell line CHRF-288-11 with phorbol 12-myristate 13-acetate leads to a very strong upregulation of rDEP-1 transcripts. The deduced structure 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 cell-matrix contact.

Murine DEP-1, a receptor protein tyrosine phosphatase, is expressed in macrophages and is regulated by CSF-1 and LPS

“…Expression in macrophages has not previously been reported for either human or rat DEP-1. We found no evidence for the expression of mDEP-1 in the vasculature, smooth muscle, epithelia, or other mesenchymal tissues of the developing mouse that might have been inferred from the study of rDEP-1 in the adult tissues of the rat [14]. The conclusions are not necessarily incompatible.…”

“…hDEP-1 was isolated separately from a human myeloid cell line and referred to as HPTPh [13]. A rat Dep-1 homolog (rDEP-1) was cloned recently and was also found to be regulated in response to density-dependent inhibition of growth in vascular cells, although curiously not in fibroblasts [14]. In this study we show that mDEP-1 is indeed a marker for macrophage differentiation and that the expression is highly regulated in mature macrophages.…”

“…The presence of a large extracellular domain containing multiple fibronectin type III repeats, and evidence that similar proteins such as RPTB␤ are involved in adhesion to the extracellular matrix, has led to speculation that DEP-1 is involved in anchorage-and/or contact-dependent regulation of proliferation [14]. This cannot be true of macrophages because the proliferation of BMMs is neither anchoragenor density-dependent.…”

Thrombospondin-1 acts as a ligand for CD148 tyrosine phosphatase

“…CD148 (DEP-1/PTPη) is a receptor-type PTP composed of an extracellular segment of fibronectin type Z (FNZ) repeats, a transmembrane domain, and a single intracellular PTP domain (1). CD148 is expressed in vascular endothelial cells, duct epithelial cells, and hematopoietic lineages (2)(3)(4)(5). Growing evidence indicates a prominent role for CD148 in the negative regulation of cell proliferation and transformation.…”

An extracellular ligand increases the specific activity of the receptor-like protein tyrosine phosphatase DEP-1

“…Immunohistochemical stainings have revealed a broad tissue distribution of DEP-1; prominent expression was found in thymus, and also on many epithelial cell types with glandular or endocrine di erentiation (Autschbach et al, 1999). DEP-1 expression is enhanced in high cell density cultures of ®broblasts and in contactinhibited endothelial cells (Borges et al, 1996;O È stman et al, 1994), and heterologous expression of DEP-1 in bovine aortic endothelial cells leads to inhibition of cfos and Cyclin A promotor activity (Suzuki et al, 2000). DEP-1 expression has also been shown to be upregulated after di erentiation of breast cancer cells (Keane et al, 1996) and thyroid cells (Martelli et al, 1998;Zhang et al, 1997).…”