Within the hemopoietic system, LAR phosphatase is a T cell lineage-specific adhesion receptor-like protein whose phosphatase activity appears dispensable for T cell development, repertoire selection and function

LAR inhibitory peptide promotes recovery of diaphragm function and multiple forms of respiratory neural circuit plasticity after cervical spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs), up-regulated in and around the lesion after traumatic spinal cord injury (SCI), are key extracellular matrix inhibitory molecules that limit axon growth and consequent recovery of function. CSPG-mediated inhibition occurs via interactions with axonal receptors, including leukocyte common antigen- related (LAR) phosphatase. We tested the effects of a novel LAR inhibitory peptide in rats after hemisection at cervical level 2, a SCI model in which bulbospinal inspiratory neural circuitry originating in the medullary rostral ventral respiratory group (rVRG) becomes disconnected from phrenic motor neuron (PhMN) targets in cervical spinal cord, resulting in persistent partial-to-complete diaphragm paralysis. LAR peptide was delivered by a soaked gelfoam, which was placed directly over the injury site immediately after C2 hemisection and replaced at 1 week post-injury. Axotomized rVRG axons originating in ipsilateral medulla or spared rVRG fibers originating in contralateral medulla were separately assessed by anterograde tracing via AAV2-mCherry injection into rVRG. At 8 weeks post-hemisection, LAR peptide significantly improved ipsilateral hemidiaphragm function, as assessed in vivo with electromyography recordings. LAR peptide promoted robust regeneration of ipsilateral-originating rVRG axons into and through the lesion site and into intact caudal spinal cord to reach PhMNs located at C3-C5 levels. Furthermore, regenerating rVRG axons re-established putative monosynaptic connections with their PhMNs targets. In addition, LAR peptide stimulated robust sprouting of both modulatory serotonergic axons and contralateral-originating rVRG fibers within the PhMN pool ipsilateral/ caudal to the hemisection. Our study demonstrates that targeting LAR-based axon growth inhibition promotes multiple forms of respiratory neural circuit plasticity and provides a new peptide-based therapeutic strategy to ameliorate the devastating respiratory consequences of SCI.

Diverse functions of protein tyrosine phosphatase σ in the nervous and immune systems

Tyrosine phosphorylation is a common means of regulating protein functions and signal transduction in multiple cells. Protein tyrosine phosphatases (PTPs) are a large family of signaling enzymes that remove phosphate groups from tyrosine residues of target proteins and change their functions. Among them, receptor-type PTPs (RPTPs) exhibit a distinct spatial pattern of expression and play essential roles in regulating neurite outgrowth, axon guidance, and synaptic organization in developmental nervous system. Some RPTPs function as essential receptors for chondroitin sulfate proteoglycans that inhibit axon regeneration following CNS injury. Interestingly, certain RPTPs are also important to regulate functions of immune cells and development of autoimmune diseases. PTPσ, a RPTP in the LAR subfamily, is expressed in various immune cells and regulates their differentiation, production of various cytokines and immune responses. In this review, we highlight the physiological and pathological significance of PTPσ and related molecules in both nervous and immune systems.

Protein tyrosine phosphatase σ regulates autoimmune encephalomyelitis development

Protein tyrosine phosphatases (PTPs) play essential roles in regulating signaling events in multiple cells by tyrosine dephosphorylation. One of them, PTPσ, appears important in regulating function of plasmacytoid dendritic cells (pDC). Here we report that PTPσ deletion in knockout mice and inhibition with a selective antagonist peptide exacerbated symptoms of experimental autoimmune encephalomyelitis (EAE) by enhancing axon and myelin damage in the spinal cord. PTPσ-/- mice displayed pro-inflammatory profiles in the spinal cord and lymphoid organs following MOG peptide immunization. PTPσ deletion promoted a pro-inflammatory phenotype in conventional DCs and directly regulated differentiation of CD4+ T cells. It also facilitated infiltration of T lymphocytes, activation of macrophages in the CNS and development of EAE. Therefore, PTPσ is a key negative regulator in EAE initiation and progression, which acts by regulating functions of DCs, T cells, and other immune cells. PTPσ may become an important molecular target for treating autoimmune disorders.

Protein Tyrosine Phosphatase PTPRS Is an Inhibitory Receptor on Human and Murine Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) are primary producers of type I interferon (IFN) in response to viruses. The IFN-producing capacity of pDCs is regulated by specific inhibitory receptors, yet none of the known receptors are conserved in evolution. We report that within the human immune system, receptor protein tyrosine phosphatase sigma (PTPRS) is expressed specifically on pDCs. Surface PTPRS was rapidly downregulated after pDC activation, and only PTPRS(-) pDCs produced IFN-α. Antibody-mediated PTPRS crosslinking inhibited pDC activation, whereas PTPRS knockdown enhanced IFN response in a pDC cell line. Similarly, murine Ptprs and the homologous receptor phosphatase Ptprf were specifically co-expressed in murine pDCs. Haplodeficiency or DC-specific deletion of Ptprs on Ptprf-deficient background were associated with enhanced IFN response of pDCs, leukocyte infiltration in the intestine and mild colitis. Thus, PTPRS represents an evolutionarily conserved pDC-specific inhibitory receptor, and is required to prevent spontaneous IFN production and immune-mediated intestinal inflammation.

Plasma membrane subdomain partitioning of Lck in primary human T lymphocytes

Uncovering the plasma membrane distribution of tyrosine kinase Lck is crucial to understanding T lymphocyte triggering. Several studies of Lck species partitioning have given contradictory results. We decided to re-address this point by using phospho-specific antibodies to characterize active and inactive Lck partitioning in raft and non-raft membranes from primary human peripheral blood T lymphocytes. We show that most inactive Lck was localized in rafts and was associated with nearly all CD4 coreceptors and its negative regulator Csk in resting cells, while T cell receptor (TCR) engagement promoted a sustained dephosphorylation of inactive Lck. In contrast, active Lck had a more discrete distribution interacting with only a small number of CD4 coreceptors, and the kinase showed a rapid and short phosphorylation after TCR triggering. The differences in distribution and kinetics may be related to T lymphocyte signalling threshold modulation by Lck species and suggest how TCR triggering is first initiated. This study furthers our knowledge of the TCR activation model in primary human T lymphocytes.

Regulatory role of leukocyte-common-antigen-related molecule (LAR) in thymocyte differentiation

The strength of interaction between the antigenic peptide-loaded MHC (MHC/p) and the TCR determines T-cell fate in the thymus. A high avidity interaction between the TCR and the MHC/p induces apoptosis of self-reactive T cells (negative selection), whereas a moderate avidity interaction rescues thymocytes from apoptosis and permits further differentiation to mature T cells (positive selection). Leukocyte common antigen-related molecule (LAR), a receptor-like protein tyrosine phosphatase, is expressed on immature thymocytes, but its role in thymocyte differentiation has not yet been fully elucidated. We analyzed LAR-deficient mice and demonstrated that LAR deficiency affected the differentiation and expansion of immature thymocytes as well as positive and negative selection. Furthermore, LAR deficiency resulted in a lower Ca2+ response. The results indicate that LAR is an important modulator of TCR signaling that controls thymocyte differentiation.

Identification of Genes Involved in Positive Selection of CD4+8+Thymocytes: Expanding the Inventory

Positive selection of cortical CD4+8+ thymocytes represents crucial and mysterious process in T cell development whereby short-lived precursors are rescued from programmed cell death and induced to differentiate towards long-lived CD4 and CD8 T cells. One reason that this process is not fully understood is that the inventory of genes changing their expression in positively selected CD4+8+ thymocytes is not yet complete. In this work Affymetrics GeneChip cDNA microarrays and cDNA-Representational Difference Analysis were used to search for unknown and known genes that were not identified before as being involved in positive selection. Comparison of transcriptosome of nonstimulated with transcriptosome of PMA/ionomycin stimulated thymoma cell line resembling CD4+8+ thymocytes and subtraction of cDNA of extrathymic tissues from cDNA of purified CD4+8+ thymocytes resulted in identification of 36 genes, which have not been previously reported to change their expression during positive selection. One of them represents a novel, third evolutionarily conserved gene within RAG locus.

Restrictase free generation of targeting vectors for disruption of complex mouse genes

Molecular cloning of targeting vectors (TgVs) is a prerequisite procedure for gene disruption in embryonic stem cells. In cases where target genes display complex features (e.g., gene overlap, alternative exon usage), TgVs must mediate deletions with very high precision to prevent unwanted effects. This is often difficult to achieve by procedures using restriction endonucleases and DNA ligases. Therefore, to prepare TgVs for inactivation of two complex genes of immunological interest: PTPRF and NWC, we employed an alternative method, which involves engineering bacterial artificial chromosomes (BACs) by inducible, plasmid encoded "Red/ET recombinase" expression system. Here, we report rapid and efficient construction of PTPRF and NWC TgVs without using restriction endonucleases.

Identification of a third evolutionarily conserved gene within the RAG locus and its RAG1-dependent and -independent regulation

Recombination-activating gene (RAG)1 and RAG2 encode T and B lymphocyte-specific endonucleases indispensable for rearrangements of antigen-receptor gene segments but also capable of causing deleterious chromosome rearrangements. The mechanisms regulating RAG expression and repression are not clear. Here we identify NWC, a third evolutionarily conserved gene within the RAG locus, and show that it is ubiquitously expressed, with the notable exception of RAG-nonexpressing immature and mature T and B lymphocytes because in lymphocytes it is regulated by the RAG1 promoter and transcribed as RAG1-NWC hybrid mRNA molecules. We also show that in all other cells NWC is controlled by the RAG2 intragenic promoter, which in immature and mature T and B lymphocytes is silent. The possible implications of these findings for understanding the activation and inactivation of RAG genes in lymphocytes and their repression in other cells are discussed.

Delayed peripheral nerve regeneration and central nervous system collateral sprouting in leucocyte common antigen-related protein tyrosine phosphatase-deficient mice

Cell adhesion molecule-like receptor-type protein tyrosine phosphatases have been shown to be important for neurite outgrowth and neural development in several animal models. We have previously reported that in leucocyte common antigen-related (LAR) phosphatase deficient (LAR-deltaP) mice the number and size of basal forebrain cholinergic neurons, and their innervation of the hippocampal area, is reduced. In this study we compared the sprouting response of LAR-deficient and wildtype neurons in a peripheral and a central nervous system lesion model. Following sciatic nerve crush lesion, LAR-deltaP mice showed a delayed recovery of sensory, but not of motor, nerve function. In line with this, neurofilament-200 immunostaining revealed a significant reduction in the number of newly outgrowing nerve sprouts in LAR-deltaP animals. Morphometric analysis indicated decreased axonal areas in regenerating LAR-deltaP nerves when compared to wildtypes. Nonlesioned nerves in wildtype and LAR-deltaP mice did not differ regarding myelin and axon areas. Entorhinal cortex lesion resulted in collateral sprouting of septohippocampal cholinergic fibres into the dentate gyrus outer molecular layer in both genotype groups. However, LAR-deltaP mice demonstrated less increase in acetylcholinesterase density and fibre number at several time points following the lesion, indicating a delayed collateral sprouting response. Interestingly, a lesion-induced reduction in number of (septo-entorhinal) basal forebrain choline acetyltransferase-positive neurons occurred in both groups, whereas in LAR-deltaP mice the average cell body size was reduced as well. Thus, regenerative and collateral sprouting is significantly delayed in LAR-deficient mice, reflecting an important facilitative role for LAR in peripheral and central nervous system axonal outgrowth.

Liprin beta 1, a member of the family of LAR transmembrane tyrosine phosphatase-interacting proteins, is a new target for the metastasis-associated protein S100A4 (Mts1)

Metastasis-associated protein S100A4 (Mts1) induces invasiveness of primary tumors and promotes metastasis. S100A4 belongs to the family of small calcium-binding S100 proteins that are involved in different cellular processes as transducers of calcium signal. S100A4 modulates properties of tumor cells via interaction with its intracellular targets, heavy chain of non-muscle myosin and p53. Here we report identification of a new molecular target of the S100A4 protein, liprin beta1. Liprin beta1 belongs to the family of leukocyte common antigen-related (LAR) transmembrane tyrosine phosphatase-interacting proteins that may regulate LAR protein properties via interaction with another member of the family, liprin alpha1. We showed by the immunoprecipitation analysis that S100A4 interacts specifically with liprin beta1 in vivo. Immunofluorescence staining demonstrated the co-localization of S100A4 and liprin beta1 in the cytoplasm and particularly at the protrusion sites of the plasma membrane. We mapped the S100A4 binding site at the C terminus of the liprin beta1 molecule between amino acid residues 938 and 1005. The S100A4-binding region contains two putative phosphorylation sites by protein kinase C and protein kinase CK2. S100A4-liprin beta1 interaction resulted in the inhibition of liprin beta1 phosphorylation by both kinases in vitro.

Gene expression signatures define novel oncogenic pathways in T cell acute lymphoblastic leukemia

Human T cell leukemias can arise from oncogenes activated by specific chromosomal translocations involving the T cell receptor genes. Here we show that five different T cell oncogenes (HOX11, TAL1, LYL1, LMO1, and LMO2) are often aberrantly expressed in the absence of chromosomal abnormalities. Using oligonucleotide microarrays, we identified several gene expression signatures that were indicative of leukemic arrest at specific stages of normal thymocyte development: LYL1+ signature (pro-T), HOX11+ (early cortical thymocyte), and TAL1+ (late cortical thymocyte). Hierarchical clustering analysis of gene expression signatures grouped samples according to their shared oncogenic pathways and identified HOX11L2 activation as a novel event in T cell leukemogenesis. These findings have clinical importance, since HOX11 activation is significantly associated with a favorable prognosis, while expression of TAL1, LYL1, or, surprisingly, HOX11L2 confers a much worse response to treatment. Our results illustrate the power of gene expression profiles to elucidate transformation pathways relevant to human leukemia.