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Expression of DEP-1, a receptor-like protein-tyrosine-phosphatase, is enhanced with increasing cell density.

ABSTRACT: cDNA encoding a receptor-like protein-tyrosine-phosphatase (PTP) termed DEP-1 was isolated from a HeLa cell library. The cDNA predicts an enzyme consisting of an extracellular segment containing eight fibronectin type III repeats, a single transmembrane segment, and a single intracellular PTP domain. Following expression of DEP-1 cDNA in COS cells a glycoprotein of 180 kDa was detected and PTP activity was demonstrated in immunocomplexes with a C-terminal peptide antiserum. Endogenous DEP-1 was detected in WI-38 human embryonic lung fibroblasts by immunoblotting and immunocomplex PTP assays. Immunoblot analysis of DEP-1 expression in WI-38 cells revealed dramatically increased levels and activity of the PTP in dense cultures relative to sparse cultures. Also, DEP-1 activity, detected in PTP assays of immunocomplexes, was increased in dense cell cultures. In contrast, the expression levels of PTP-1B did not change with cell density. This enhancement of DEP-1 expression with increasing cell density was also observed in another fibroblast cell line, AG1518. The increase in DEP-1 occurs gradually with increasing cell contact and is initiated before saturation cell density is reached. These observations suggest that DEP-1 may contribute to the mechanism of contact inhibition of cell growth.

SUBMITTER: Ostman A

PROVIDER: S-EPMC44880 | biostudies-other | 1994 Oct

REPOSITORIES: biostudies-other

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Expression of DEP-1, a receptor-like protein-tyrosine-phosphatase, is enhanced with increasing cell density.

Ostman A A Yang Q Q Tonks N K NK

Proceedings of the National Academy of Sciences of the United States of America 19941001 21

cDNA encoding a receptor-like protein-tyrosine-phosphatase (PTP) termed DEP-1 was isolated from a HeLa cell library. The cDNA predicts an enzyme consisting of an extracellular segment containing eight fibronectin type III repeats, a single transmembrane segment, and a single intracellular PTP domain. Following expression of DEP-1 cDNA in COS cells a glycoprotein of 180 kDa was detected and PTP activity was demonstrated in immunocomplexes with a C-terminal peptide antiserum. Endogenous DEP-1 was ...[more]

PMID: 7937872

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Project description:Renal vascular development is a coordinated process that requires ordered endothelial cell proliferation, migration, intercellular adhesion, and morphogenesis. In recent decades, studies have defined the pivotal role of endothelial receptor tyrosine kinases (RPTKs) in the development and maintenance of renal vasculature. However, the expression and the role of receptor tyrosine phosphatases (RPTPs) in renal endothelium are poorly understood, though coupled and counterbalancing roles of RPTKs and RPTPs are well defined in other systems. In this study, we evaluated the promoter activity and immunolocalization of two endothelial RPTPs, VE-PTP and PTP?, in developing and adult renal vasculature using the heterozygous LacZ knock-in mice and specific antibodies. In adult kidneys, both VE-PTP and PTP? were expressed in the endothelium of arterial, glomerular, and medullary vessels, while their expression was highly limited in peritubular capillaries and venous endothelium. VE-PTP and PTP? promoter activity was also observed in medullary tubular segments in adult kidneys. In embryonic (E12.5, E13.5, E15.5, E17.5) and postnatal (P0, P3, P7) kidneys, these RPTPs were expressed in ingrowing renal arteries, developing glomerular microvasculature (as early as the S-shaped stage), and medullary vessels. Their expression became more evident as the vasculatures matured. Peritubular capillary expression of VE-PTP was also noted in embryonic and postnatal kidneys. Compared to VE-PTP, PTP? immunoreactivity was relatively limited in embryonic and neonatal renal vasculature and evident immunoreactivity was observed from the P3 stage. These findings indicate 1) VE-PTP and PTP? are expressed in endothelium of arterial, glomerular, and medullary renal vasculature, 2) their expression increases as renal vascular development proceeds, suggesting that these RPTPs play a role in maturation and maintenance of these vasculatures, and 3) peritubular capillary VE-PTP expression is down-regulated in adult kidneys, suggesting a role of VE-PTP in the development of peritubular capillaries.

Project description:Fms-like tyrosine kinase 3 (FLT3) plays an important role in hematopoietic differentiation, and constitutively active FLT3 mutant proteins contribute to the development of acute myeloid leukemia. Little is known about the protein-tyrosine phosphatases (PTP) affecting the signaling activity of FLT3. To identify such PTP, myeloid cells expressing wild type FLT3 were infected with a panel of lentiviral pseudotypes carrying shRNA expression cassettes targeting different PTP. Out of 20 PTP tested, expressed in hematopoietic cells, or presumed to be involved in oncogenesis or tumor suppression, DEP-1 (PTPRJ) was identified as a PTP negatively regulating FLT3 phosphorylation and signaling. Stable 32D myeloid cell lines with strongly reduced DEP-1 levels showed site-selective hyperphosphorylation of FLT3. In particular, the sites pTyr-589, pTyr-591, and pTyr-842 involved in the FLT3 ligand (FL)-mediated activation of FLT3 were hyperphosphorylated the most. Similarly, acute depletion of DEP-1 in the human AML cell line THP-1 caused elevated FLT3 phosphorylation. Direct interaction of DEP-1 and FLT3 was demonstrated by "substrate trapping" experiments showing association of DEP-1 D1205A or C1239S mutant proteins with FLT3 by co-immunoprecipitation. Moreover, activated FLT3 could be dephosphorylated by recombinant DEP-1 in vitro. Enhanced FLT3 phosphorylation in DEP-1-depleted cells was accompanied by enhanced FLT3-dependent activation of ERK and cell proliferation. Stable overexpression of DEP-1 in 32D cells and transient overexpression with FLT3 in HEK293 cells resulted in reduction of FL-mediated FLT3 signaling activity. Furthermore, FL-stimulated colony formation of 32D cells expressing FLT3 in methylcellulose was induced in response to shRNA-mediated DEP-1 knockdown. This transforming effect of DEP-1 knockdown was consistent with a moderately increased activation of STAT5 upon FL stimulation but did not translate into myeloproliferative disease formation in the 32D-C3H/HeJ mouse model. The data indicate that DEP-1 is negatively regulating FLT3 signaling activity and that its loss may contribute to but is not sufficient for leukemogenic cell transformation.

Dataset Information

Expression of DEP-1, a receptor-like protein-tyrosine-phosphatase, is enhanced with increasing cell density.

Publications

Expression of DEP-1, a receptor-like protein-tyrosine-phosphatase, is enhanced with increasing cell density.

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