Molecular cloning, nucleotide sequence and expression of a cDNA encoding an intracellular protein tyrosine phosphatase, PTPase-2, from mouse testis and T-cells

Role of protein tyrosine phosphatases in regulating the immune system: implications for chronic intestinal inflammation

Current hypothesis suggests that genetic, immunological, and bacterial factors contribute essentially to the pathogenesis of inflammatory bowel disease. Variations within the gene loci encoding protein tyrosine phosphatases (PTPs) have been associated with the onset of inflammatory bowel disease. PTPs modulate the activity of their substrates by dephosphorylation of tyrosine residues and are critical for the regulation of fundamental cellular signaling processes. Evidence emerges that expression levels of PTPN2, PTPN11, and PTPN22 are altered in actively inflamed intestinal tissue. PTPN2 seems to be critical for protecting intestinal epithelial barrier function, regulating innate and adaptive immune responses and finally for maintaining intestinal homeostasis. These observations have been confirmed in PTPN2 knockout mice in vivo. Those animals are clearly more susceptible to intestinal and systemic inflammation and feature alterations in innate and adaptive immune responses. PTPN22 controls inflammatory signaling in lymphocytes and mononuclear cells resulting in aberrant cytokine secretion pattern and autophagosome formation. PTPN22 deficiency in vivo results in more severe colitis demonstrating the relevance of PTPN22 for intestinal homeostasis in vivo. Of note, loss of PTPN22 promotes mitogen-activated protein kinase-induced cytokine secretion but limits secretion of nuclear factor κB-associated cytokines and autophagy in mononuclear cells. Loss of PTPN11 is also associated with increased colitis severity in vivo. In summary, dysfunction of those PTPs results in aberrant and uncontrolled immune responses that result in chronic inflammatory conditions. This way, it becomes more and more evident that dysfunction of PTPs displays an important factor in the pathogenesis of chronic intestinal inflammation, in particular inflammatory bowel disease.

Requirement of protein tyrosine kinase and phosphatase activities for human sperm exocytosis

The acrosome is a membrane-limited granule that overlies the nucleus of the mature spermatozoon. In response to physiological or pharmacological stimuli, sperm undergo calcium-dependent exocytosis termed the acrosome reaction, which is an absolute prerequisite for fertilization. Protein tyrosine phosphorylation and dephosphorylation are a mechanisms by which multiple cellular events are regulated. Here we report that calcium induces tyrosine phosphorylation in streptolysin O (SLO)-permeabilized human sperm. As expected, pretreatment with tyrphostin A47-a tyrosine kinase inhibitor-abolishes the calcium effect. Interestingly, the calcium-induced increase in tyrosine phosphorylation has a functional correlate in sperm exocytosis. Masking of phosphotyrosyl groups with a specific antibody or inhibition of tyrosine kinases with genistein, tyrphostin A47, and tyrphostin A51 prevent the acrosome reaction. By reversibly sequestering intra-acrosomal calcium with a photo-inhibitable chelator, we show a requirement for protein tyrosine phosphorylation late in the exocytotic pathway, after the efflux of intra-acrosomal calcium. Both mouse and human sperm contain highly active tyrosine phosphatases. Importantly, this activity declines when sperm are incubated under capacitating conditions. Inhibition of tyrosine phosphatases with pervanadate, bis(N,N-dimethylhydroxoamido)hydroxovanadate, ethyl-3,4-dephostatin, and phenylarsine oxide prevents the acrosome reaction. Our results show that both tyrosine kinases and phosphatases play a central role in sperm exocytosis.

A nuclear protein tyrosine phosphatase TC-PTP is a potential negative regulator of the PRL-mediated signaling pathway: dephosphorylation and deactivation of signal transducer and activator of transcription 5a and 5b by TC-PTP in nucleus

In the present study we examined involvement of nuclear protein tyrosine phosphatase TC-PTP in PRL-mediated signaling. TC-PTP could dephosphorylate signal transducer and activator of transcription 5a (STAT5a) and STAT5b, but the apparent dephosphorylation activity of TC-PTP was weaker than that of cytosolic PTP1B 30 min after PRL stimulation in transfected COS-7 cells, whereas both STAT5a and STAT5b were dephosphorylated to the same extent by recombinant TC-PTP and PTP1B in vitro. Tyrosine-phosphorylated STAT5 was coimmunoprecipitated with substrate trapping mutants of TC-PTP, suggesting that STAT5 is a specific substrate of TC-PTP. These observations were further extended in mammary epithelial COMMA-1D cells stably expressing TC-PTP. A time-course study revealed that dephosphorylation of STAT5 by TC-PTP was delayed compared with that by cytosolic PTP1B due to nuclear localization of TC-PTP throughout PRL stimulation in mammary epithelial cells. Endogenous beta-casein gene expression and beta-casein gene promoter activation in COS-7 cells were largely suppressed by TC-PTP wild type as well as catalytically inactive mutants, suggesting that stable complexes formed between STAT5 and TC-PTP in the nucleus. Taken together, we conclude that TC-PTP is catalytically competent with respect to dephosphorylation and deactivation of PRL-activated STAT5 in the nucleus.

The T-cell protein tyrosine phosphatase

In recent years, the T-cell protein tyrosine phosphatase (TC-PTP) has become an important member of the protein-tyrosine phosphatase (PTP) family in two aspects. Firstly, TC-PTP has been reported to act on downstream signalling events initiated by the epidermal growth receptor, suggesting that it may act as an important modulator of receptor tyrosine kinases and mitogenic signalling. Secondly, the finding of immune deficiency and lethality observed in TC-PTP null mice emphasizes the importance of this small PTP in the hematopoietic system. In this review, we provide a summary of the recent literature published on the TC-PTP and its various orthologs. Although much remains to be uncovered, some recent findings on the function of this small PTP suggest that it plays a critical role in regulating mammalian cell signalling.

Protein tyrosine phosphatase gene expression analysis in Swiss 3T3 fibroblasts

The aim of this study was to identify protein tyrosine phosphatases (PTPs) expressed in Swiss 3T3 fibroblasts and to examine their expression levels as well as to characterize quantitative aspects of RT-PCR based on degenerate deoxyoligonucleotides. By using an RT-PCR assay based on degenerate deoxyoligonucleotide primers, expression of mRNAs for two cytoplasmic- and six transmembrane-type PTPs in Swiss 3T3 cells was detected. The sequences of two of them are new. Among nine analyzed PTPs expressed to widely varied extends, only three have mRNA levels high enough to be seen on Northern blots with 10 microg of total RNA per lane. The frequencies with which the examined PTPs are represented among the PCR amplification products, correlate stronger with the primer fidelity, defined as the number of mismatches between the primer- and the cDNA target-sequences, rather than with the PTP expression levels. In conclusion, an RT-PCR assay based on degenerate primers can be successfully used to sample the expressed PTPs and to identify new members of this gene family. However, reliable quantification of their mRNA levels can only be achieved using the classical approaches, like Northern, RNase protection assay or nondegenerate quantitative RT-PCR.

RPTP delta and the novel protein tyrosine phosphatase RPTP psi are expressed in restricted regions of the developing central nervous system

Transmembrane receptor-type protein tyrosine phosphatases (RPTPs) form a novel and potentially important class of cell regulatory proteins. To identify RPTPs expressed during neural development we have characterized RPTPs transcribed in embryonic day (E)13.5 rat neural tube. Nine different phosphatases, one of which was novel, were identified. We examined the expression of the novel phosphatase, called RPTP psi, and of two other phosphatases, RPTP delta and RPTP mu, whose expression in the developing nervous system has not yet been described in detail. The expression of RPTP mu in small blood capillaries in developing neural tissue is consistent with an involvement in angiogenesis. In contrast, the temporally and spatially regulated expression of RPTP psi and RPTP delta in neuroepithelium suggests a role in early neural development. In the spinal cord, early expression of RPTP delta in the roof plate is followed by its expression in differentiating motor neurons. RPTP psi mRNA is also transiently detectable in the roof plate as well as in floor plate cells. In the telencephalon as well as in the hindbrain at E13.5, the reciprocal expression patterns of RPTP delta and RPTP psi are consistent with a sequential function, RPTP psi exerting its activity in undifferentiated progenitor cells and RPTP delta functioning during neuronal differentiation.

Protein tyrosine phosphatases expressed in developing brain and retinal Müller glia

Regulation of protein function through tyrosine phosphorylation is critical to many developmental processes involving cell-cell communication. A number of protein tyrosine phosphatases (PTPs) have been identified in the early postnatal and mature central nervous system (CNS), but the PTPs expressed during its development have not been well characterized. Using a polymerase chain reaction with degenerate primers, we analyzed PTPs expressed in fetal (E18) rat brain and Müller glia cultures from embryonic chick retina, two systems in which cell-to-cell contacts are numerous. Fetal rat brain expressed four known receptor-like PTPs (PTP delta, LAR, LAR-PTP2, LRP (PTP alpha)) and the non-receptor phosphatase PTP1B. Müller glia exhibited a distinct but overlapping pattern of expression: four known receptor PTPs (PTP alpha, PTP gamma, PTP delta, PTP zeta) and PTP1B. In addition, two novel PTPs, termed MG-PTP1 and 2 (Müller glia PTP 1 and 2) were identified in Müller glia cDNA. MG-PTP1 was related to, but distinct from PTP delta, while MG-PTP2 was related to, but distinct from the cytosolic T-cell phosphatase. These results demonstrate that a distinct but overlapping set of PTPs is expressed in the developing brain and retinal Müller glia, including two novel PTPs that may participate in neural cell communication.