CD45 tyrosine phosphatase controls common gamma-chain cytokine-mediated STAT and extracellular signal-related kinase phosphorylation in activated human lymphoblasts: inhibition of proliferation without induction of apoptosis

Different associations of CD45 isoforms with STAT3, PKC and ERK regulate IL-6-induced proliferation in myeloma

In response to interleukin 6 (IL-6) stimulation, both CD45RO and CD45RB, but not CD45RA, translocate to lipid rafts. However, the significance of this distinct translocation and the downstream signals in CD45 isoforms-participated IL-6 signal are not well understood. Using sucrose fractionation, we found that phosphorylated signal transducer and activator of transcription (STAT)3 and STAT1 were mainly localized in lipid rafts in response to IL-6 stimulation, despite both STAT3 and STAT1 localizing in raft and non-raft fractions in the presence or absence of IL-6. On the other hand, extracellular signal-regulated kinase (ERK), and phosphorylated ERK were localized in non-raft fractions regardless of the existence of IL-6. The rafts inhibitor significantly impeded the phosphorylation of STAT3 and STAT1 and nuclear translocation, but had little effect on (and only postponing) the phosphorylation of ERK. This data suggests that lipid raft-dependent STAT3 and STAT1 pathways are dominant pathways of IL-6 signal in myeloma cells. Interestingly, the phosphorylation level of STAT3 but not STAT1 in CD45⁺ cells was significantly higher compared to that of CD45^- cells, while the phosphorylation level of ERK in CD45⁺ myeloma cells was relatively low. Furthermore, exogenously expressed CD45RO/RB significantly enhanced STAT3, protein kinase C (PKC) and downstream NF-κB activation; however, CD45RA/RB inhibited IL-6-induced ERK phosphorylation. CD45 also enhanced the nuclear localization of STAT3 but not that of STAT1. In response to IL-6 stimulation, CD45RO moved into raft compartments and formed a complex with STAT3 and PKC in raft fraction, while CD45RA remained outside of lipid rafts and formed a complex with ERK in non-raft fraction. This data suggests a different role of CD45 isoforms in IL-6-induced signaling, indicating that while CD45RA/RB seems inhibit the rafts-unrelated ERK pathway, CD45RO/RB may actually work to enhance the rafts-related STAT3 and PKC/NF-κB pathways.

Molybdate modulates mitogen and cyclosporin responses of human peripheral blood lymphocytes

The trace element molybdenum (Mo) is an essential component of key physiological systems in animals, plants and microorganisms. The molybdate oxoanion MoO(4)(2-) has been demonstrated to cause diverse yet poorly understood biochemical and pharmacological effects, such as non-specific inhibition of phosphatases and stabilization of steroid receptors. This study aimed to investigate the effects of molybdate on the activation of human peripheral blood lymphocytes (hPBLs) ex vivo and its potential interaction with the widely used immunosuppressant drug cyclosporin A (CsA). Lymphocyte activation was evaluated by performing multiple experiments determining blastogenesis in cultured peripheral blood lymphocytes obtained from 5 healthy volunteers, following stimulation induced by phytohemagglutinin (PHA), in the absence or presence of 0.05-10 mM sodium molybdate or/and 2.5-30 μg/mL CsA. Blastogenesis was assessed by a morphometric assay based on the relative proportions of unactivated lymphocytes, activated lymphoblasts and cells with aberrant morphology after PHA-induced activation. Molybdate concentrations up to 1 mM showed no effect on lymphocyte blastogenesis, while higher concentrations exerted immunosuppressive actions on cultured hPBLs. Co-administration of 0.1 mM sodium molybdate with CsA, at doses up to 20 μg/mL, induced no alteration in the response of cultured hPBLs to CsA. However, molybdate potentiated the immunosuppressive action of higher CsA concentrations, implying a likely dose-related synergistic interaction of the two agents in PHA-stimulated blood lymphocytes. These observations are indicative of the possible biological importance of molybdate oxoanions in the modulation of hPBL activation that may have pharmacological consequences during the therapeutic application of immunomodulatory drugs.

Involvement of tyrosine phosphatase CD45 in apoptosis

CD45 is a transmembrane molecule with phosphatase activity expressed in all nucleated haematopoietic cells and plays a major role in immune cells. It is a protein tyrosine phosphatase that is essential for antigen-receptor-mediated signal transduction by regulating Src family members that initiate TCR signaling. CD45 is being attributed a new emerging role as an apoptosis regulator. Cross-linking of the extracellular portion of the CD45 by monoclonal antibodies and by galectin-1, can induce apoptosis in T and B cells. Interestingly, this phosphatase has also been involved in nuclear apoptosis induced by mitochondrial perturbing agents. Furthermore, it is involved in apoptosis induced by HIV-1. CD45 defect is implicated in various diseases such as severe-combined immunodeficiency disease (SCID), acquired immunodeficiency syndrome (AIDS), lymphoma and multiple myelomas. The understanding of the mechanisms by which CD45 regulates apoptosis would be very useful in disease treatment.

Anti-CD45RO suppresses human immunodeficiency virus type 1 replication in microglia: role of Hck tyrosine kinase and implications for AIDS dementia

Macrophages and microglia are productively infected by HIV-1 and play a pivotal role in the pathogenesis of AIDS dementia. Although macrophages and microglia express CD45, a transmembrane protein tyrosine phosphatase, whether modulation of its activity affects human immunodeficiency virus type 1 (HIV-1) replication is unknown. Here, we report that of the five human CD45 isoforms, microglia express CD45RB and CD45RO (RB > RO) and treatment of microglia with a CD45 agonist antibody alphaCD45RO (UCHL-1) inhibits HIV-1 replication. alphaCD45RO prevented HIV-1 negative factor (Nef)-induced autophosphorylation of hematopoietic cell kinase (Hck), a myeloid lineage-specific Src kinase. Recombinant CD45 protein also inhibited HIV-1-induced Hck phosphorylation in microglia. Antennapedia-mediated delivery of Hck Src homology domain 3 (SH3), a domain that binds to the Nef PxxP motif with high affinity, reduced HIV-1-induced Hck phosphorylation and HIV-1 production in microglia. HIV-1-induced LTR transactivation was observed in U38 cells stably overexpressing wild-type Hck but not kinase-inactive Hck. In microglia, alphaCD45RO reduced activation of transcription factors (NF-kappaB and CCAAT enhancer binding protein) necessary for LTR transactivation in macrophages. These results establish that in myeloid lineage cells, Nef interacts with the Hck SH3 domain, resulting in autophosphorylation of Hck and an increase in HIV-1 transcription. alphaCD45RO-mediated inhibition of HIV-1 replication in microglia identifies the CD45 protein tyrosine phosphatase as a potential therapeutic target for HIV-1 infection/AIDS dementia.

MUC4-expressing pancreatic adenocarcinomas show elevated levels of both T1 and T2 cytokines: potential pathobiologic implications

OBJECTIVE

The human MUC4 mucin plays an important role in the pathogenesis of pancreatic cancer. Recently, we have demonstrated that MUC4 expression in pancreatic tumor cells is regulated by interferon-gamma (IFNgamma) and by retinoic acid via transforming growth factor beta 2 (TGFbeta-2). In the present study, we established the pathobiological association of various cytokines and MUC4 in pancreatic tumor tissues and tumor cell lines.

METHODS

Using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and/or immunohistochemical analyses, we examined the expression of MUC4, IFNgamma, TGFbetas, and several immunologically relevant cytokines in a panel of 11 pancreatic adenocarcinomas (PA), three normal pancreatic (NP) tissue specimens, and 11 pancreatic tumor cell lines.

RESULTS

Our data revealed that both MUC4 and IFNgamma were expressed at moderate to high levels in the majority of PA, while being undetectable in NP. Moreover, transcript for interleukin 2 (IL-2), a known marker of activated T helper 1 (TH1) lymphocytes, exhibited an expression profile similar to IFNgamma, suggesting a role of these immune effector cells as a potential source of IFNgamma in PA. Of note, IFNgamma protein was detected in the inflamed tissues neighboring tumor areas. Furthermore, TGFbetas were expressed by most cell lines and frequently upregulated in PA compared with NP. Interestingly, both IL-12 and IL-10, two key cytokines of the TH1 and TH2 pathways, respectively, were expressed at higher levels in PA relative to NP.

CONCLUSIONS

These observations support the potential implication of IFNgamma and TGFbetas in MUC4 regulation in vivo and suggest a complex interaction of TH1 and TH2 signaling in the pancreatic tumor microenvironment. These findings may provide useful insights into the pathobiology of pancreatic cancer.

Interleukin-4 supports interleukin-12-induced proliferation and interferon-gamma secretion in human activated lymphoblasts and T helper type 1 cells

Interleukin-12 (IL-12) and IL-4 are known to differentially promote T helper (Th) cell differentiation. While IL-12 induces interferon-gamma (IFN-gamma) production and maturation of Th1 cells, IL-4 is thought to antagonize IL-12 and to favour Th2 development. Here we studied the combined action of various concentrations of common gamma-chain (gamma(c)-chain) cytokines, including IL-4 and the Th1 cytokine IL-12, in human activated lymphoblasts and Th1 cells. IL-4 and IL-7 potentiated IL-12-induced proliferation at every concentration tested (1-10 ng/ml) without increasing rescue from apoptosis, indicating that proliferation was directly affected by these cytokine combinations. With regards to cytokine secretion, IL-2 together with IL-12 initiated tumour necrosis factor-alpha synthesis, enhanced IFN-gamma production, and shedding of soluble IL-2 receptor alpha as expected. Importantly, combining IL-4 with IL-12 also enhanced IFN-gamma secretion in lymphoblasts and a Th1 cell line. Investigating signal transduction in lymphoblasts induced by these cytokines, we found that not only IL-2 but also IL-4 enhances signal transducer and activator of transcription 3 (STAT3) tyrosine phosphorylation by IL-12. Tyrosine phosphorylations of janus kinase 2 (JAK-2), tyrosine kinase 2 (TYK2), extracellular signal-regulated kinase (ERK) and STAT4, STAT5 and STAT6 were not potentiated by combinations of these cytokines, suggesting specificity for increased STAT3 phosphorylation. In conclusion, two otherwise antagonizing cytokines co-operate in activated human lymphoblasts and Th1 cells, possibly via STAT3 as a converging signal. These data demonstrate that IL-4 can directly enhance human Th1 cell function independently of its known actions on antigen-presenting cells. These findings should be of importance for the design of cytokine-targeted therapies of human Th-cell-driven diseases.

CD45RA and RO isoforms have distinct effects on cytokine- and B-cell-receptor-mediated signalling in human B cells

The common leucocyte antigen, CD45, is widely expressed on the surface of lymphocytes. In T and B cells, CD45 has an important role in the early events of receptor signalling. However, the role of various CD45 isoforms in B-cell receptor (BCR)- and cytokine-induced signalling and proliferation is still unclear. In the present study, we establish two follicular lymphoma cell lines expressing either CD45RA (HF28RA) or CD45R0 (HF28R0) isoforms. It was observed that the two isoforms had distinct effects on BCR- or cytokine-induced cellular proliferation. BCR stimulation significantly increased the proliferation of HF28R0 cells, in contrast to a decreased proliferation of HF28RA cells. Moreover, proliferation of HF28R0 cells significantly increased after the addition of interleukin-2 (IL-2), IL-4, IL-6, IL-10, IL-12, IL-13, IL-15, interferon-gamma and tumour necrosis factor-alpha cytokines, whereas most of these cytokines significantly inhibited the proliferation of HF28RA cells. In addition, the cell lines had their individual cytokine mRNA expression profiles after BCR stimulation. We also analysed the effect of CD45 isoforms on intracellular signalling after BCR stimulation. It was found out that the kinetics of ERK1/2 MAP kinase phosphorylation was clearly faster in HF28R0 than in HF28RA cells. The phosphorylation of other analysed MAP kinases or PTKs was very similar in the cell lines.

Inhibition of granulocyte-macrophage colony-stimulating factor signaling and microglial proliferation by anti-CD45RO: role of Hck tyrosine kinase and phosphatidylinositol 3-kinase/Akt

Increasing evidence suggests that CD45, a transmembrane protein tyrosine phosphatase, is an important modulator of macrophage activation. Microglia, resident brain macrophages, express CD45 and proliferate under pathologic conditions. In this study, we examined the role of CD45 in modulating GM-CSF-induced proliferation and signal transduction in primary human microglial cultures. Soluble, but not immobilized anti-CD45RO induced tyrosine phosphatase activity and inhibited GM-CSF-induced microglial proliferation. Microglial proliferation was also inhibited by PP2 (Src inhibitor), LY294002 (PI3K inhibitor), and U0126 (MEK inhibitor). GM-CSF induced phosphorylation of Jak2, Stat5, Hck (the myeloid-restricted Src kinase), Akt, Stat3, and Erk MAPKs in microglia. Of these, anti-CD45RO inhibited phosphorylation of Hck and Akt, and PP2 inhibited phosphorylation of Hck and Akt. In a macrophage cell line stably overexpressing wild-type or kinase-inactive Hck, GM-CSF increased proliferation of the control (empty vector) and wild-type but not kinase-inactive cells, and this was inhibited by anti-CD45RO. Together, these results demonstrate that, in macrophages, Hck tyrosine kinase is activated by GM-CSF, and that Hck plays a pivotal role in cell proliferation and survival by activating the PI3K/Akt pathway. Ab-mediated activation of macrophage and microglial CD45 tyrosine phosphatase may have therapeutic implications for CNS inflammatory diseases.

Extranuclear detection of histones and nucleosomes in activated human lymphoblasts as an early event in apoptosis

OBJECTIVE

To evaluate the presence of histones and nucleosomes in cell lysates of freshly isolated peripheral blood mononuclear cells (PBMC), fully activated lymphoblasts, or lymphoblasts after induction of apoptosis.

METHODS

Each histone class (H1, H2A, H2B, H3, and H4) was detected by western blot analysis with specific antibodies. Annexin V/propidium iodide (PI) staining was performed for each treatment to distinguish viable, early, and late apoptotic, and necrotic cells. DNA degradation was evaluated by PI staining in a hypotonic buffer.

RESULTS

All five histones were detected in cell lysates of activated lymphoblasts in higher concentrations than in lysates of PBMC. An additional significant increase of H2A, H2B, H3, H4, and complete nucleosomes in cell lysates of lymphoblasts was found during interleukin (IL)2 deprivation for 8 or 24 hours. The content of these histones or nucleosomes in cell lysates decreased after delayed IL2 readdition. H1 content in cell lysates was not affected by IL2 deprivation or addition. Quantities of H2A, H2B, H3, and H4 in cell lysates correlated significantly with signs of early apoptosis. UV-B light exposure or etoposide treatment of lymphoblasts resulted in a distinct increase for each histone class in cell lysates compared with standard curves. No bands for post-translationally modified histones were detected in cell lysates in contrast with signals in nuclear preparations.

CONCLUSION

Extranuclear accumulation of histones and nucleosomes is an early event of apoptosis in human lymphoblasts. Dysregulation of early apoptosis might support the induction of autoimmunity against nuclear components.

The protein tyrosine phosphatase CD45 is required for interleukin 6 signaling in U266 myeloma cells

The objective of this study was to examine whether CD45 mediates interleukin 6 (IL-6) signaling in human multiple myeloma (MM) cells. We chose U266 MM cells as a study model and isolated cells into CD45+ and CD45- subpopulations. CD45+ and CD45- U266 cells were cocultured with bone marrow stromal cells (BMSCs). IL-6-induced proliferation in CD45+ U266 cells was inhibited by vanadate, a potent protein tyrosine phosphatase inhibitor. However, IL-6-independent CD45- U266 cell growth was not affected by vanadate. CD45+ U266 cells, but not CD45- U266 cells, have the capability of cell adhesion concomitant with actin filament polymerization at the adherent cells. Adhesion of CD45+ U266 cells to BMSCs was impaired by vanadate. We clarified the signaling differences between CD45+ and CD45- U266 cells in response to IL-6. In CD45+ U266 cells, IL-6 increased tyrosine phosphorylation of gp130 and STAT3 and stimulated the level of Mcl-1 protein expression. An association between CD45 and the Src-family protein tyrosine kinase, Lyn, was maintained in the presence of IL-6; the formation of the CD45/Lyn complex was impaired by vanadate. Additionally, IL-6-induced Lyn kinase activity in CD45+ U266 cells was increased by the cross-linking of CD45, and this increase was due to the dephosphorylation of Tyr507 at Lyn. In conclusion, IL-6-dependent MM cells require CD45 to initiate IL-6 signaling and to maintain Lyn kinase activity, both of which are essential for cell proliferation and cell adhesion.

Defective suppressor function of human CD4+ CD25+ regulatory T cells in autoimmune polyglandular syndrome type II

In autoimmune polyglandular syndromes (APS), several organ-specific autoimmune diseases are clustered. Although APS type I is caused by loss of central tolerance, the etiology of APS type II (APS-II) is currently unknown. However, in several murine models, depletion of CD4⁺ CD25⁺ regulatory T cells (T_regs) causes a syndrome resembling human APS-II with multiple endocrinopathies. Therefore, we hypothesized that loss of active suppression in the periphery could be a hallmark of this syndrome. T_regs from peripheral blood of APS-II, control patients with single autoimmune endocrinopathies, and normal healthy donors showed no differences in quantity (except for patients with isolated autoimmune diseases), in functionally important surface markers, or in apoptosis induced by growth factor withdrawal. Strikingly, APS-II T_regs were defective in their suppressive capacity. The defect was persistent and not due to responder cell resistance. These data provide novel insights into the pathogenesis of APS-II and possibly human autoimmunity in general.

A role for interleukin-12 in the regulation of T cell plasma membrane compartmentation

The immunological synapse initiates the clustering and stabilization of the T cell receptor by the formation of a large lipid microdomain that accumulates (e.g. CD4/CD8) and segregates (e.g. CD45 and LFA-1) some proteins of the T cell plasma membrane. This work shows that a fraction of transmembrane glycoproteins CD26 and CD45 (the R0 isoform in particular) is present in the rafts of fresh and activated human T lymphocytes. CD26 is proposed as the costimulator of TCR-dependent activation, and CD45 is essential to the T cell activation process because it dephosphorylates at least the inhibitory site of Src kinases. These findings support a more complex model of compartmentation, depending on the stage of T cell maturation and post-transcriptional and post-translational regulation. In addition, interleukin 12 (IL-12; inducer of TH1 responses) drives CD26 and CD45R0 to particular microdomains, thereby involving interleukins in the rules governing raft inclusion or exclusion. The physical association of CD26 and CD45R0 has long been reported. The results presented in this work fit a model in which IL-12 up-regulates a certain type of CD26 expression that interacts on the cell surface with CD45R0, near but outside of the raft core. The use of antisense oligonucleotides for the CD26 mRNAs demonstrated that both events (enhanced by IL-12), CD26-CD45R0 association and membrane compartment redistribution, are related. Thus, CD26 could be part of a shuttling mechanism for CD45 that regulates membrane tyrosine-phosphatase activities, e.g. to control IL-12 receptor-dependent signal transduction.

Negative regulation of T cell activation by placental protein 14 is mediated by the tyrosine phosphatase receptor CD45

CD45 is the major protein tyrosine phosphatase receptor on T cell surfaces that functions as both a positive and a negative regulator of T cell receptor (TCR) signaling. Although CD45 is required for the activation of TCR-associated Src family kinases, it also dephosphorylates phosphoproteins involved in the TCR-signaling cascade. This study links CD45 to the inhibitory activity of placental protein 14 (PP14), a major soluble protein of pregnancy that is now known to be a direct modulator of T cells and to function by desensitizing TCR signaling. PP14 and CD45 co-capped with each other, pointing to a physical linkage between the two. Interestingly, however, the binding of PP14 to T cell surfaces was not restricted to CD45 alone, with evidence showing that PP14 binds to other surface molecules in a carbohydrate-dependent fashion. Notwithstanding the broader molecular binding potential of PP14, its interaction with CD45 appeared to have special functional significance. Using transfected derivatives of the HPB. ALL mutant T cell line that differ in CD45 expression, we established that the inhibitory effects of PP14 are dependent upon the expression of intact CD45 on T cell surfaces. Based upon these findings, we propose a new immunoregulatory model for PP14, wherein one of its surface molecular targets, CD45, mediates its T cell inhibitory activity, accounting for the intriguing capacity of PP14 to elevate TCR activation thresholds and thereby down-regulate T cell activation.

CD45 tyrosine phosphatase inhibits erythroid differentiation of umbilical cord blood CD34+ cells associated with selective inactivation of Lyn

CD45 is a membrane-associated tyrosine phosphatase that dephosphorylates Src family kinases and Janus kinases (JAKs). To clarify the role of CD45 in hematopoietic differentiation, we examined the effects of anti-CD45 monoclonal antibody NU-L(PAN) on the proliferation and differentiation of umbilical cord blood CD34(+) cells. NU-L(PAN) showed a prominent inhibition of the proliferation of CD34(+) cells induced by the mouse bone marrow stromal cell line MS-5 or erythropoietin (EPO). However, NU-L(PAN) did not affect the proliferation induced by interleukin 3. NU-L(PAN) also inhibited MS-5-induced or EPO-induced erythroid differentiation of CD34(+) cells. The cells stimulated with EPO in the presence of NU-L(PAN) morphologically showed differentiation arrest at the stage of basophilic erythroblasts after 11 days of culture, whereas the cells treated with EPO without NU-L(PAN) differentiated into mature red blood cells. The Src family kinase Lyn and JAK2 were phosphorylated when erythroblasts obtained after 4 days of culture of CD34(+) cells in the presence of EPO were restimulated with EPO. Overnight NU-L(PAN) treatment before addition of EPO reduced the phosphorylation of Lyn but not that of JAK2. Simultaneously, the enhancement of Lyn kinase activity after restimulation with EPO was reduced by NU-L(PAN) treatment. These results indicate selective inactivation of Lyn by CD45 activated with NU-L(PAN) and could partly explain the inhibitory mechanism on erythropoiesis exhibited by EPO. These findings suggest that CD45 may play a pivotal role in erythropoiesis.

CD45 controls interleukin-4-mediated IgE class switch recombination in human B cells through its function as a Janus kinase phosphatase

CD45 plays a critical regulatory role in receptor signaling through its protein tyrosine phosphatase and Janus kinase (JAK) phosphatase activities. To investigate whether CD45 also plays a regulatory role in Ig class switching in human B cells, we examined the effects of CD45 triggering on Ig class switching to IgE and its relationship with CD45 JAK phosphatase activity. Anti-CD45 triggering of CD45 significantly inhibited interleukin-4 + anti-CD40-induced switch recombination in a switch recombination vector assay in stably transfected Ramos 2G6 human B cells, as well as Ig epsilon germ-line transcription and Smu-Sepsilon switch recombination in primary human B cells. These negative regulatory effects on Ig class switching were concomitant with the ability of CD45 to dephosphorylate the induced phosphorylation of JAK1, JAK3, and signal transducer and activator of transcription 6, but not on stress-activated/mitogen-activated protein kinases. We also showed that phosphorylated JAK1 and JAK3 were directly dephosphorylated by recombinant CD45 in vitro. These results indicate that CD45 is able to function as JAK phosphatase in human B cells and that this activity is directly associated with the negative regulation of the class switch recombination to IgE. CD45 may be an appropriate target drug for modulating IgE in allergic diseases.