Abrogation of protein phosphatase 6 promotes skin carcinogenesis induced by DMBA.

Somatic mutations in the gene encoding the catalytic subunit of protein phosphatase 6 (Ppp6c) have been identified in malignant melanoma and are thought to function as a driver in B-raf- or N-ras-driven tumorigenesis. To assess the role of Ppp6c in carcinogenesis, we generated skin keratinocyte-specific Ppp6c conditional knockout mice and performed two-stage skin carcinogenesis analysis. Ppp6c deficiency induced papilloma formation with 7,12-dimethylbenz (a) anthracene (DMBA) only, and development of those papillomas was significantly accelerated compared with that seen following DMBA/TPA (12-O-tetradecanoylphorbol 13-acetate) treatment of wild-type mice. NF-κB activation either by tumor necrosis factor (TNF)-α or interleukin (IL)-1ß was enhanced in Ppp6c-deficient keratinocytes. Overall, we conclude that Ppp6c deficiency predisposes mice to skin carcinogenesis initiated by DMBA. This is the first report showing that such deficiency promotes tumor formation in mice.

Protein phosphatase Dusp26 associates with KIF3 motor and promotes N-cadherin-mediated cell-cell adhesion.

Recent studies have demonstrated essential functions for KIF3, a microtubule-directed protein motor, in subcellular transport of several cancer-related proteins, including the beta-catenin-cadherin(s) complex. In this study, we report identification of the protein-phosphatase Dusp26 as a novel regulator of the KIF3 motor. Here we undertake yeast two-hybrid screening and identify Kif3a, a motor subunit of the KIF3 heterotrimeric complex, as a novel Dusp26-binding protein. Co-immunoprecipitation and colocalization experiments revealed that Dusp26 associates not only with Kif3a, but also with Kap3, another subunit of the KIF3 complex. Dephosphorylation experiments in vitro and analysis using mutant forms of Dusp26 in intact cells strongly suggested that Dusp26 is recruited to the KIF3 motor mainly by interaction with Kif3a, and thereby dephosphorylates Kap3. Forced expression of Dusp26, but not its catalytically inactive mutant, promoted distribution of beta-catenin/N-cadherin, an established KIF3 cargo, to cell-cell junction sites, resulting in increased cell-cell adhesiveness. We also showed that Dusp26 mRNA expression was downregulated in human glioblastoma samples. These results suggest previously unidentified functions of Dusp26 in intracellular transport and cell-cell adhesion. Downregulation of Dusp26 may contribute to malignant phenotypes of glioma.

Protein tyrosine phosphatase epsilonC selectively inhibits interleukin-6- and interleukin- 10-induced JAK-STAT signaling.

Protein tyrosine phosphatase (PTP) epsilon (PTPepsilon) exists as 2 forms generated by alternative promoter usage. It has recently been reported that a cytosolic isoform of PTPepsilon (PTPepsilonC) when over-expressed in murine M1 myeloid cells inhibits interleukin-6 (IL-6)- and leukemia inhibitory factor-induced activation of Janus kinases (JAKs), thereby suppressing STAT3 tyrosine phosphorylation and STAT3 signaling. This study characterizes an inhibitory action of PTPepsilonC on IL-6 signaling and also reveals that PTPepsilonC inhibitory activity is independent of other potential negative regulators, such as SHP-2 and SOCS family proteins. Furthermore, it analyzes the selectivity of PTPepsilonC action toward several cytokines. On IL-6 stimulation, expression of PTPepsilonC-DA, a catalytically inactive mutant of PTPepsilonC, results in an earlier onset of STAT3 tyrosine phosphorylation, suggesting different modes of action between PTPepsilonC and other negative regulators. In addition, the study shows PTPepsilonC-DA enhances activation of STAT1 by IL-6 as well. In terms of specificity to cytokines, over-expressed PTPepsilonC also inhibits IL-10-induced tyrosine phosphorylation of STAT3 in M1 cells, whereas PTPepsilonC does not affect either interferon-beta- and interferon-gamma-induced tyrosine phosphorylation of STATs or expression of STAT transcriptional targets. Among cytokines tested, the inhibitory effect of PTPepsilonC is selective to IL-6- and IL-10-induced JAK-STAT signaling.

Up-regulation of I-2(PP2A)/SET gene expression in rat primary hepatomas and regenerating livers.

I-2(PP2A)/SET, an inhibitor of protein phosphatase 2A, is supposed to be one of the oncoproteins associated with human myeloid leukemia. The I-2(PP2A)/SET gene expression was observed ubiquitously among all the rat tissues examined, but low in liver. Of interest is that the expression in the rat primary hepatomas and hyperplastic nodules was significantly elevated. The experiments using regenerating livers after partial hepatectomy showed that the expression of I-2(PP2A)/SET mRNA was low at the quiescent hepatocytes, but up-regulated at 12-24 h after partial hepatectomy, which corresponds to the mid G1 to S transition in the cell cycle. These results suggested the importance of I-2(PP2A)/SET in the hepatocarcinogenesis and hepatic cell proliferation.

Increased expression of p53 and Bax in the spinal cords of rats with experimental autoimmune encephalomyelitis.

The expression of pro-apoptotic molecules p53 and Bax in the spinal cord of rats with experimental autoimmune encephalomyelitis (EAE) was examined. Apoptosis was confirmed by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method. TUNEL (+) apoptotic cells were mainly either ED1 (+) macrophages or T-cells in the parenchyma of EAE. Western blot analysis showed that both p53 and Bax expression significantly (P<0. 01) increased in the spinal cords of EAE rats at the peak stage, and thereafter declined. An immunohistochemical study showed that inflammatory cells (notably T cells) in the parenchyma express p53 and Bax, while brain cells, including neurons and glia, were devoid of nuclear staining for these molecules. The nuclear expression of p53 largely matches apoptotic cells in the parenchyma of EAE. These findings suggest that the pro-apoptotic molecules p53 and Bax may play an important role in eliminating T cells in the parenchyma in EAE.

Characterization of acute versus chronic relapsing autoimmune encephalomyelitis in DA rats.

This study was undertaken to better understand the role of cytokines in the pathogenesis, especially in the mechanisms of relapse, of experimental autoimmune encephalomyelitis (EAE). For this purpose, we induced acute and chronic relapsing (CR) EAE in DA rats and determined several immunological parameters in rats at various stages of two types of EAE. Histopathological analysis revealed that there was no significant difference in the severity of inflammation in the spinal cord lesions between the two groups. However, demyelination was observed only in rats with CR EAE. Cytokine analysis by competitive PCR demonstrated that levels of TNF-alpha, IL-6 and IL-12 p40 mRNA in the spinal cord at the first attack of CR EAE were significantly higher than those at the peak stage of acute EAE. The mRNA expression of anti-inflammatory cytokines, IL-10 and TGF-beta1, was generally low in both acute EAE and the first attack of CR EAE and upregulated at later stages of CR EAE. These findings suggest that persistent high-level expression of pro-inflammatory cytokines is closely associated with demyelination and relapse of EAE. In contrast, anti-inflammatory cytokines play only a minor role in the relapse.

Protein-tyrosine phosphatase PTPepsilon C inhibits Jak-STAT signaling and differentiation induced by interleukin-6 and leukemia inhibitory factor in M1 leukemia cells.

We engineered and expressed both a wild-type and mutant cytosolic isoform of PTPepsilon (PTPepsilonC) in murine M1 leukemic cells, which can be induced to growth arrest and monocytic differentiation by interleukin (IL)-6 and leukemia inhibitory factor (LIF). Forced expression of PTPepsilonC inhibited IL-6- and LIF-induced monocytic differentiation and apoptosis in M1 cells, whereas expression of PTPepsilonM, a transmembrane isoform of PTPepsilon, did not. PTPepsilonC expression resulted in lower levels of IL-6-induced tyrosine phosphorylation of Jak1, Tyk2, gp130, and Stat3 compared with parent cells. In M1 transfectants expressing an inactive mutant of PTPepsilonC, both tyrosine phosphorylation and apoptosis induced by IL-6 and LIF were potentiated rather than inhibited. These results suggest an important role for PTPepsilonC in negative regulation of IL-6- and LIF-induced Jak-STAT signaling.

Analysis of neurotrophic effects of hepatocyte growth factor in the adult hypoglossal nerve axotomy model.

Recent studies have shown that hepatocyte growth factor (HGF) promotes the survival of embryonic motor neurons. However, it remains unclear whether HGF has trophic effects on mature motor neurons. In the present study, we examined the effects of HGF on adult motoneurons using the hypoglossal nerve transection model. In adult rats, neurons in the hypoglossal nucleus show a dramatic loss of choline acetyltransferase (ChAT) protein and mRNA after the axotomy. This reduction of ChAT was markedly prevented when HGF was administered continuously at the cut end of the nerve using an osmotic pump. The HGF receptor, c-met, protein and mRNA, which were faintly expressed in hypoglossal neurons under normal conditions, gradually increased and reached maximal levels 2 weeks after the axotomy. Administration of HGF reduced this c-met upregulation almost to normal levels. We also quantified HGF mRNA in the tongue and hypoglossal nucleus. The tongue contained abundant HGF mRNA, whereas the nucleus contained only low levels. Interestingly, the HGF mRNA level in the nucleus did not increase after the axotomy. These findings suggest that HGF is principally produced in the tongue and contributes to maintain ChAT expression in the nucleus. HGF produced in the hypoglossal nucleus alone after disconnection from the tongue may not be sufficient for the maintenance of the motor neuron function. Thus, exogenously applied HGF was effective to prevent the downregulation of ChAT activities. These findings provide a strong rationale for the potential clinical use of HGF for the treatment of motor neuron degenerative disease.

Differential role of TNF-alpha and IFN-gamma in the brain of rats with chronic relapsing autoimmune encephalomyelitis.

To elucidate the mechanisms of relapses of the clinical signs in experimental autoimmune encephalomyelitis (EAE), the cytokine profile of chronic relapsing EAE (CR-EAE) in rats was determined by competitive polymerase chain reaction (PCR). By immunization with guinea pig spinal cord homogenate and treatment with low-dose cyclosporin A (CsA), rats developed two attacks of EAE with remission in between. Cytokine analysis revealed that the level of TNF-alpha mRNA increased at the first and second attacks with transient disappearance at the remission phase. In contrast, the level of IFN-gamma mRNA was suppressed at the first attack by CsA and peaked at the second attack. Intraventricular administration of IFN-gamma prior to onset of disease signs induced more relapses, or a severe lethal form. In addition, the intraventricular injection of TNF-alpha caused the persistence of the clinical signs. These findings suggest that TNF-alpha contributes to the first and second attacks of CR-EAE, while IFN-gamma is not required for the first attack but is closely related to the relapse of the disease. With regard to anti-inflammatory cytokines, the levels of both TGF-beta1 and IL-10 mRNA at the second attack were higher than those at the first attack. Taken together, differential involvement of TNF-alpha and IFN-gamma is closely associated with the clinical features of CR-EAE.

Distinct promoters control transmembrane and cytosolic protein tyrosine phosphatase epsilon expression during macrophage differentiation.

We have recently isolated two cDNAs encoding two forms of transmembrane and cytosolic protein tyrosine phosphatase epsilon (PTPepsilon). In this study, the 5' end of the rat PTPepsilon gene was isolated and characterized. Transmembrane PTPepsilon (PTPepsilonM) and cytosolic PTPepsilon (PTPepsilonC) were encoded by a single gene. 5' RACE analysis and RNase protection assay showed that the mRNA of each PTPepsilon isoform was transcribed from different promoters. The putative promoter regions of two alternative first exons lacked a TATA box, but contained potential recognition sites for several transcription factors. Reverse transcription PCR analysis revealed that PTPepsilonC mRNA was up-regulated during interleukin 6-induced differentiation of murine leukemia M1 cells, whereas PTPepsilonM mRNA was down-regulated. With the use of luciferase as a reporter gene, the promoter activities of the 5'-flanking regions were examined during phorbol myristate acetate-induced differentiation of HL-60 cells. In the differentiated HL-60 cells, the activity of the PTPepsilonC promoter, but not that of PTPepsilonM, was dramatically elevated. Furthermore, we found that PTPepsilonC mRNA is highly expressed in mouse peritoneal macrophages and enhanced during activation by lipopolysaccharide. These results suggest that the different promoters control expression of PTPepsilon isoforms during the differentiation and/or activation of macrophages.

A new anti-rheumatic drug, T-614, effectively suppresses the development of autoimmune encephalomyelitis.

In the present study, we examined the therapeutic effects of T-614 (3-formylamino-7-methylsulfonylaminoxy-4H-1-benzopyran-4-one), a new anti-rheumatic drug, on a T cell-mediated autoimmune disease, experimental autoimmune encephalomyelitis (EAE). T-614 dose-dependently suppressed the development of active EAE induced in Lewis rats by immunization with myelin basic protein (MBP) when administered for 2 weeks starting on the day of immunization (day 0 to 14). Amelioration of clinical signs was also obtained by the treatment at the effector phase (day 7 to 14) of the disease. Furthermore, T-614 treatment of recipient rats that had received MBP-sensitized lymphoid cells resulted in suppression of the clinical severity of EAE. Immunohistological examination revealed that the number of TCR alpha beta-expressing T cells and the extent of MHC class II expression in the spinal cord of rats treated with T-614 was markedly reduced. In vitro study using MBP-specific T cells showed that the addition of T-614 inhibited the proliferative responses of T cells and the production of pro-inflammatory cytokines such as IFN-gamma, IL-6 and TNF produced by T and accessory cells. Taken together, these findings imply that T-614 suppresses the development of EAE by inhibiting the proliferation of autoreactive T cells and pro-inflammatory cytokine production not only by T cells but also by macrophages/microglia. This may be attributable to the result that T-614 is more effective at the effector phase rather than the induction phase. Thus, this drug has a potential value for the treatment of various T cell-mediated autoimmune diseases including multiple sclerosis (MS) as well as rheumatoid arthritis.

Quantitative analysis of pro- and anti-inflammatory cytokine mRNA in neural graft rejection.

The central nervous system (CNS) has been considered an immunologically privileged site. However, this concept is now changing because rejection of histoincompatible neural grafts is commonly observed in the CNS. To be able to use neural transplantation as therapy for human diseases, it is important to determine factors that are related to brain-graft rejection. In the present study, we examined the phenotype of infiltrating T cells around grafts in the cerebra that had received xenogeneic (mouse to rat) neural transplants. Furthermore, the amount of pro- and anti-inflammatory cytokine mRNA was determined by competitive PCR at various time points after the neural transplantation. Immunohistochemical examination revealed that both CD4-positive and CD8-positive T cells infiltrated the CNS parenchyma. In competitive PCR analysis, levels of IFN-gamma and perforin in xenografts on days 10 and 13 post-transplantation (PT) were higher than those in isografts (rat to rat) at the same stage, whereas the levels of TNF-alpha, which was detected only on day 7 PT, were not significantly different between the two groups. With regard to anti-inflammatory cytokines, TGF-beta1 mRNA was recognized throughout the examination period, but there was no significant difference between xeno- and iso-grafts at most time points. These findings suggest that IFN-gamma and perforin secreted by infiltrating CD4-positive and CD8-positive T cells, respectively, play an important role in neural graft rejection. The responses of anti-inflammatory cytokines seem to be nonspecific reactions to grafts or surgical procedures.

Role of natural killer cells and TCR gamma delta T cells in acute autoimmune encephalomyelitis.

To elucidate the role of NK cells and TCR gamma delta+ T cells in acute experimental autoimmune encephalomyelitis (EAE) induced in Lewis rats, the distribution, number and function of these cells were studied using several methods. Immunohistochemical and flow cytometric analysis revealed that a certain number of NK cells (17 of the total inflammatory cells) infiltrated the central nervous system (CNS) at the peak stage of EAE and were mainly located in the perivascular region. On the other hand, virtually no TCR gamma delta+ T cells were found in the CNS. NK-T (NKR-P1+TCR alpha beta+) cells were few and did not increase in number in the CNS and lymphoid organs. In the cytotoxic assay using YAC-1 cells, effector cells isolated from the spleen of rats at the peak of EAE showed essentially the same cytotoxicity as those isolated from normal controls although the total number of NK cells decreased to one fifth of that of normal rats. Furthermore, in vivo administration of anti-NK cell (3.2.3 and anti-asialo GM1), but not of anti-TCR gamma delta (V65), antibodies exacerbated the clinical features of EAE and induced fatal EAE in some rats. These findings suggest that NK cells play a suppressive role in acute EAE whereas TCR gamma delta+ T cells are not involved in the development of or recovery from the disease.

Myosin-induced autoimmune polymyositis in the rat.

Experimental autoimmune myositis (EAM) was induced in Lewis rats by immunization with partially purified and purified skeletal myosin. Although clinical signs such as muscle weakness were very mild, multiple inflammatory lesions in the skeletal muscle, but not in the heart, were found by histological examination. Immunohistochemical staining revealed that muscle fiber-infiltrating cells were CD8+ and CD11b+ cells and that CD4+, TCR alphabeta+, B and NK cells were mainly located in the endomysium and interfiber connective tissue. These findings were in contrast to those obtained in experimental autoimmune encephalomyelitis lesions in which CD4+ cells predominate over CD8+ cells. T cells and sera isolated from myosin-immunized animals responded vigorously to myosin. However, neither sensitized lymphoid cells mainly comprising CD4+ cells nor purified anti-myosin immunoglobulin G mediated the disease into naive rats, suggesting that T cells other than CD4+ cells such as CD8+ cells may be the final effector. Taken together, EAM induced in Lewis rats is similar to human polymyositis (PM). EAM can serve as a good model for human PM and give insight into the pathogenesis of the disease.

Competitive PCR quantification of pro- and anti-inflammatory cytokine mRNA in the central nervous system during autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the central nervous system that can be induced by immunization with myelin basic protein (MBP)/complete Freund's adjuvant and serves as a model for multiple sclerosis. Recent studies have suggested that cytokines play a crucial role in the clinical course of EAE. To clarify the roles of cytokines in EAE, we examined levels of interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-beta1 (TGF-beta1) and interleukin-10 (IL-10) mRNA in isolates from infiltrating inflammatory cells in EAE lesions induced in Lewis rats. The non-radioactive and sensitive competitive PCR method was employed to quantify the relative amounts of cytokine mRNA. Levels of both IFN-gamma and TNF-alpha mRNA were increased at the early stage of EAE and rapidly decreased at the peak stage. On the other hand, TGF-beta1 mRNA was demonstrated throughout the course of EAE as well as under normal conditions and its amount paralleled the severity of EAE. IL-10 mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR) under normal conditions, but was below the level of detection of competitive PCR. IL-10 mRNA expression peaked at the early stage of EAE and declined gradually thereafter. Taken together, these results suggest that IFN-gamma and TNF-alpha might play a crucial role in the development of EAE. Furthermore, it appears that the peak expression of IL-10 mRNA at the early stage and the following marked TGF-beta1 expression at the peak stage might represent an important endogenous mechanism to limit the extent of inflammation and to prevent relapse in the course of acute monophasic EAE.

Pretreatment with T cell receptor peptides using a conventional immunization protocol does not induce effective protection against autoimmune encephalomyelitis.

It was previously reported that vaccination with synthetic peptides corresponding to the CDR2 or CDR3 region of T cell receptor (TCR) protected susceptible animals from the development of experimental autoimmune encephalomyelitis (EAE). However, recent studies by several research groups have revealed that TCR peptide therapy often confers little or no protection from autoimmune disease. In the present study, we attempted to find more appropriate peptides that is capable of conferring effective protection against the development of EAE. Four peptides corresponding to parts of the V beta region (13-23, 24-36, 39-59, and 64-74) were selected by epitope scanning and hydrophilicity searching, and their protective abilities were tested. All these peptides were, however, ineffective in protecting rats from the disease. We also generated three different synthetic peptides corresponding to the TCR J region of encephalitogenic T cells. Vaccination with the J-region peptides did not protect animals from the development of EAE. Rather, one of the peptides (V beta-DSS-J beta 2.6) enhanced the clinical severity of EAE and induced fatal disease in some rats. Taken together, TCR peptide therapy appears to be generally ineffective and elucidation of the mechanism by which EAE is enhanced after TCR peptide vaccination should provide insight into the pathogenesis of this disease.

The subarachnoid space as a site for precursor T cell proliferation and effector T cell selection in experimental autoimmune encephalomyelitis.

To characterize the phenotype of inflammatory cells in the central nervous system (CNS) in experimental autoimmune encephalomyelitis (EAE), Lewis rats were immunized with guinea pig myelin basic protein and frozen sections of the spinal cord with EAE were examined immunohistochemically using a panel of monoclonal antibodies against T cells and adhesion molecules. In addition, double immunostaining was performed with glial and T cells markers to examine the interaction between infiltrating T cells and reactive brain cells during the course of EAE. In the early stage of EAE, inflammatory cells first appeared in the subarachnoid space (SAS) and infiltrated the subpial region. The majority of inflammatory cells in SAS expressed TCR alpha beta and either CD4 or CD8 molecules. However, only CD4+ T cells infiltrated the parenchyma while the majority of CD8+ cells remained in SAS. A similar differential localization of T cells was observed with regard to CD45RC molecules. Inflammatory cells in SAS consisted of both CD45RC+ and CD45RC- population, while those in the parenchyma were largely CD45RC-. With regard to adhesion molecules, the leptomeninges constitutively expressed fibronectin (FN) and intercellular adhesion molecule 1 (ICAM-1). Most SAS inflammatory cells expressed very late activation antigen 4 (VLA-4) and, to lesser extent, lymphocyte function-associated antigen 1 (LFA-1) in the early stage of EAE. On the other hand, parenchymal infiltrating cells expressed LFA-1 more strongly in the peak stage. Double staining for V beta 8.2 TCR and microglia demonstrated an increase in the number of microglia together with morphological changes into rod-shape cells in the vicinity of infiltrating T cells.(ABSTRACT TRUNCATED AT 250 WORDS)