Expression of a human T-cell protein-tyrosine-phosphatase in baby hamster kidney cells.

Abstract

A human T-cell cDNA encoding a 48-kDa protein-tyrosine-phosphatase (PTPase; protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48) was cloned into a mammalian expression vector and introduced into baby hamster kidney cells, and stable colonies were isolated. The expressed PTPase was found to be associated with the particulate fraction of the cells, where it was essentially inactive in an in vitro assay unless first subjected to limited trypsinization; trypsin treatment generated an active fragment of 33 kDa by the removal of a carboxyl-terminal segment of the full-length enzyme. Gel filtration indicated that the expressed enzyme was associated with a complex of >600 kDa. Introduction of a premature stop codon into the T-cell cDNA at position 1012 resulted in the production of a fully active 37-kDa species that distributed between both the particulate and soluble fractions. The truncated form of the enzyme was readily solubilized by detergents and was eluted within its predicted molecular mass range. These results suggest that the carboxyl-terminal segment is important in determining the localization and regulation of the PTPase. The level of protein-tyrosine phosphorylation observed after 5 min of platelet-derived growth factor stimulation was reduced in cells overexpressing either form of the phosphatase, indicating that both are active in vivo. Overexpressing the truncated enzyme resulted in a growth rate that was approximately 50% of that observed in cells transfected with either the full-length PTPase cDNA or the vector alone.

Structure, mapping, and expression of erp, a growth factor-inducible gene encoding a nontransmembrane protein tyrosine phosphatase, and effect of ERP on cell growth.

“…We have also shown that ERP, like VH1, has serine phosphatase activity, indicating that it is a dual phosphatase. Deregulated expression of other nontransmembrane tyrosine phosphatases has also been shown to affect cell growth and to increase the proportion of multinucleated cells, which may result in part from their failure to undergo cytokinesis (13,49). However, from these studies, it is not clear whether the observed phenotype is due to PTPase overexpression per se or instead is the consequence of cellular adaptation to the growth-inhibitory effects of PTPases.…”

Epidermal Growth Factor Receptor and the Adaptor Protein p52Shc Are Specific Substrates of T-Cell Protein Tyrosine Phosphatase

“…The TCPTP cDNA encodes a 48-kDa protein (TC48) that displays 65% sequence identity overall and 74% sequence identity within the conserved catalytic domain with PTP1B, the prototypic PTP (4, 9, 56, 57). Like PTP1B (17), TC48 is targeted to the endoplasmic reticulum (ER) by a stretch of hydrophobic residues at the extreme C terminus (12,35). Alternative splicing of the TCPTP transcript gives rise to a 45-kDa form of the enzyme (TC45) which lacks the hydrophobic C-terminal tail (residues 382 to 418) (7,40,54) and is targeted to the nucleus by a bipartite nuclear localization sequence (35,53,54).…”

“…T-cell PTP (TCPTP) is a ubiquitous PTP originally isolated from a human peripheral T-cell cDNA library (12,13). Although TCPTP was one of the first PTPs to be cloned, its biological function remains unknown.…”

Protein tyrosine phosphatase containing SH2 domains: characterization, preferential expression in hematopoietic cells, and localization to human chromosome 12p12-p13.

“…The known mammalian protein tyrosine phosphatases fall into two broad categories (15). One class is cytoplasmic and includes protein tyrosine phosphatase 1B (PTP1B) (2,6,19), a phosphatase that was initially identified in T cells and termed T-cell protein tyrosine phosphatase (TCPTIP) (9), neuronal phosphatase (STEP) (34), and cytoplasmic phosphatases that contain a region of homology to cytoskeletal proteins (17,84). The second class includes the receptorlike phosphatases human tyrosine phosphatase i (HPTP,B) (33), CD45/LCA/Ly5 (72,74,76), a leukocyte common antigen-related phosphatase (LAR) (66), human protein tyrosine phosphatase a (HPTPa) (33,36,58), human protein tyrosine phosphatase e (HPTPr) (33), human protein tyrosine phosphatase y (HPTPy) (25,33), and human protein tyrosine phosphatase C (HPTPt) (25,33).…”

“…This region contains a high proportion of charged and polar amino acid residues. This is reminiscent of the carboxyl tail of TCPTP, which inhibits enzyme activity (9). Interestingly, this region also contains three nuclear localizationlike motifs (TTKKKLE, aa 518 to 524; KVKKQRSAD, aa 576 to 584; and KNKGSLKRK, aa 587 to 595) (54).…”