The biological role of the protein tyrosine kinase, Pyk2, was explored by targeting the Pyk2 gene by homologous recombination. Pyk2؊͞؊ mice are viable and fertile, without overt impairment in development or behavior. However, the morphology and behavior of Pyk2؊͞؊ macrophages were impaired. Macrophages isolated from mutant mice failed to become polarized, to undergo membrane ruffling, and to migrate in response to chemokine stimulation. Moreover, the contractile activity in the lamellipodia of Pyk2؊͞؊ macrophages was impaired, as revealed by measuring the rearward movement toward the nucleus of fibronectin-coated beads on the lamellipodia in opposition to an immobilizing force generated by optical tweezers. Consistently, the infiltration of macrophages into a carageenan-induced inflammatory region was strongly inhibited in Pyk2؊͞؊ mice. In addition, chemokine stimulation of inositol (1, 4, 5) triphosphate production and Ca 2؉ release, as well as integrin-induced activation of Rho and phosphatidyl inositol 3 kinase, were compromised in Pyk2؊͞؊ macrophages. These experiments reveal a role for Pyk2 in cell signaling in macrophages essential for cell migration and function.

Rapid nerve impulse conduction in myelinated axons requires the concentration of voltage-gated sodium channels at nodes of Ranvier. Myelin-forming oligodendrocytes in the central nervous system (CNS) induce the clustering of sodium channels into nodal complexes flanked by paranodal axoglial junctions. However, the molecular mechanisms for nodal complex assembly in the CNS are unknown. Two isoforms of Neurofascin, neuronal Nfasc186 and glial Nfasc155, are components of the nodal and paranodal complexes, respectively. Neurofascin-null mice have disrupted nodal and paranodal complexes. We show that transgenic Nfasc186 can rescue the nodal complex when expressed in Nfasc−/− mice in the absence of the Nfasc155–Caspr–Contactin adhesion complex. Reconstitution of the axoglial adhesion complex by expressing transgenic Nfasc155 in oligodendrocytes also rescues the nodal complex independently of Nfasc186. Furthermore, the Nfasc155 adhesion complex has an additional function in promoting the migration of myelinating processes along CNS axons. We propose that glial and neuronal Neurofascins have distinct functions in the assembly of the CNS node of Ranvier.

SUMMARY The mechanisms through which the bone marrow (BM) microenvironment regulates hematopoietic stem cell (HSC) fate remain incompletely understood. We examined the role of the heparin-binding growth factor, pleiotrophin (PTN), in regulating HSC function in the niche. PTN−/− mice displayed significantly decreased BM HSC content and impaired hematopoietic regeneration following myelosuppression. Conversely, mice lacking the protein tyrosine phosphatase receptor-zeta (PTPRZ), which is inactivated by PTN, displayed significantly increased BM HSC content. Transplant studies revealed that PTN action was not HSC-autonomous but rather was mediated by the BM microenvironment. Interestingly, PTN was differentially expressed and secreted by BM sinusoidal endothelial cells within the vascular niche. Furthermore, systemic administration of anti-PTN antibody in mice substantially impaired both the homing of hematopoietic progenitor cells to the niche and the retention of BM HSCs in the niche. PTN is a secreted component of the BM vascular niche which regulates HSC self-renewal and retention in vivo.

Protein tyrosine phosphatases (PTPs) represent a super-family of enzymes that play essential roles in normal development and physiology. In this review, we will discuss the PTPs that have a causative role in hereditary diseases in humans. In addition, recent progress in the development and analysis of animal models expressing mutant PTPs will be presented. The impact of PTP signaling on health and disease will be exemplified for the fields of bone development, synaptogenesis and central nervous system diseases. Collectively, research on PTPs since the late 1980's yielded the cogent view that development of PTP-directed therapeutic tools is essential to further combat human disease.Abbreviations AChR, acetylcholine receptor; Akt/PKB, Akt/protein kinase B; AMPAR, a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor; CNS, central nervous system; CNTN-1, contactin-1; CSPG, chondroitin sulfate proteoglycan; cyt, cytosolic; DLAR, ortholog of the mammalian LAR family, type IIa RPTPs; DUSP, dual-specificity PTP; EAE, experimental autoimmune encephalomyelitis; EKO, PTPe knockout; FERM, 4.1 protein/ezrin/radixin/moesin; FNIII, fibronectin type III; GRIP, glutamate receptor interacting protein; HD-PTP, His-domain containing PTP; HSPG, heparan sulfate proteoglycan; IL1RAPL1, interleukin-1 receptor accessory protein-like 1; JNK, c-Jun N-terminal kinase; LAR, leukocyte common antigen related; LTD, long-term depression; LTP, long-term potentiation; LYP, lymphoid tyrosine phosphatase; MAP, mitogenactivated protein; MAPK, mitogen-activated protein kinase; M-CSF/CSF-1, colony stimulating factor 1 (macrophage); (m)GluR, (metabotropic) Glutamate receptor; MKO, Mkp-1 knockout; MS, multiple sclerosis; MuSK, Muscle specific kinase; NGL-3, netrin-G ligand-3; NMDAR, N-methyl-D-aspartate receptor; NMJ, neuromuscular junction; OLG, oligodendrocyte; OPC, oligodendrocyte precursor cell; PDZ, PSD95/disc large tumor suppressor/zona occludens protein; PEZ, PTP/ezrin-like; PSD95, post-synaptic density protein 95; PSTPIP, proline serine threonine-rich phosphatase interacting protein; PTEN, phosphatase and tensin homolog; PTK, protein tyrosine kinase; PTP, protein tyrosine phosphatase; PTP-BL, PTP-BAS-like; PTP-PEST, PTP with proline/glutamate/serine/threonine-rich domains; Pyk2, product of PTK2b gene; RANKL, receptor activator of nuclear factor kappaB ligand; RhoGAP, Rho GTPase activating protein; RPTP, receptor-type PTP; SAP-1, stomach cancer-associated PTP-1; SFK, Src-family tyrosine kinase; SH2, Src homology type 2; SHP, SH2 domain containing PTP; SNP, single nucleotide polymorphism; STEP, striatal-enriched phosphatase; TCPTP, T-cell PTP; TCR, T-cell receptor; TGF-b3 transforming growth factor b3; WASP, Wiskott-Aldrich Syndrome protein.

Several lines of evidence suggest that tyrosine phosphorylation is a key element in myelin formation, differentiation of oligodendrocytes and Schwann cells, and recovery from demyelinating lesions. Multiple sclerosis is a demyelinating disease of the human central nervous system, and studies of experimental demyelination indicate that remyelination in vivo requires the local generation, migration or maturation of new oligodendrocytes, or some combination of these. Failure of remyelination in multiple sclerosis could result from the failure of any of these processes or from the death of oligodendrocytes. Ptprz encodes protein tyrosine phosphatase receptor type Z (Ptpz, also designated Rptpbeta), which is expressed primarily in the nervous system but also in oligodendrocytes, astrocytes and neurons. Here we examine the susceptibility of mice deficient in Ptprz to experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. We observe that mice deficient in Ptprz show impaired recovery from EAE induced by myelin oligodendrocyte glycoprotein (MOG) peptide. This sustained paralysis is associated with increased apoptosis of mature oligodendrocytes in the spinal cords of mutant mice at the peak of inflammation. We further demonstrate that expression of PTPRZ1, the human homolog of Ptprz, is induced in multiple sclerosis lesions and that the gene is specifically expressed in remyelinating oligodendrocytes in these lesions. These results support a role for Ptprz in oligodendrocyte survival and in recovery from demyelinating disease.

The six members of the contactin (CNTN) family of neural cell adhesion molecules are involved in the formation and maintenance of the central nervous system (CNS) and have been linked to mental retardation and neuropsychiatric disorders such as autism. Five of the six CNTNs bind to the homologous receptor protein tyrosine phosphatases gamma (PTPRG) and zeta (PTPRZ), but the biological roles of these interactions remain unclear. We report here the cocrystal structure of the carbonic anhydrase-like domain of PTPRZ bound to tandem Ig repeats of CNTN1 and combine these structural data with binding assays to show that PTPRZ binds specifically to CNTN1 expressed at the surface of oligodendrocyte precursor cells. Furthermore, analyses of glial cell populations in wild-type and PTPRZ-deficient mice show that the binding of PTPRZ to CNTN1 expressed at the surface of oligodendrocyte precursor cells inhibits their proliferation and promotes their development into mature oligodendrocytes. Overall, these results implicate the PTPRZ/CNTN1 complex as a previously unknown modulator of oligodendrogenesis.

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The human interferon alpha‐receptor (IFNAR gene product) is a transmembranal protein of 557 amino acids with an intracytoplasmic domain of 100 amino acids containing four tyrosines. Antibodies to a C‐terminal peptide (residues 521‐536) were developed which efficiently immunoprecipitate the 105 kDa IFNAR protein from detergent extracts of human cells. We show that the IFNAR protein becomes tyrosine phosphorylated within 5 min after treatment of human myeloma U266 cells with IFN‐alpha 2, IFN‐alpha 8 or IFN‐beta. The IFNAR chain interacts with both IFN‐alpha 2 and IFN‐beta, as demonstrated by cross‐linking. Among elements involved in signal transduction by type I IFNs, the tyrosine kinase Tyk2 but not Jak1, and the ISGF3 transcription factor subunit Stat2 (p113) but not Stat1 (p91), are found associated with the IFNAR protein. After IFN‐beta treatment for 5 min, a tyrosine‐phosphorylated protein of approximately 95 kDa (beta‐PTyr) is found bound to IFNAR, but can be dissociated by denaturation. The beta‐PTyr protein is present on the cell surface, like IFNAR, as shown by extracellular biotin tagging. The ratio of beta‐PTyr to IFNAR tyrosine phosphorylation is much higher with IFN‐beta than with IFN‐alpha 2 or 8. Both are IFN dependent and abrogated by a monoclonal antibody which blocks IFNAR action. The beta‐PTyr component may represent an important difference in the action of IFN‐beta as compared with IFN‐alpha in their shared receptor system.