Role of mitogen-activated protein kinases in Thy-1-induced T-lymphocyte activation

The multiple roles of Thy-1 in cell differentiation and regeneration

Thy-1 is a 25-37 kDa glycophosphatidylinositol (GPI)-anchored cell surface protein that was discovered more than 50 years ago. Recent findings have suggested that Thy-1 is expressed on thymocytes, mesenchymal stem cells (MSCs), cancer stem cells, hematopoietic stem cells, fibroblasts, myofibroblasts, endothelial cells, neuronal smooth muscle cells, and pan T cells. Thy-1 plays vital roles in cell migration, adhesion, differentiation, transdifferentiation, apoptosis, mechanotransduction, and cell division, which in turn are involved in tumor development, pulmonary fibrosis, neurite outgrowth, and T cell activation. Studies have increasingly indicated a significant role of Thy-1 in cell differentiation and regeneration. However, despite recent research, many questions remain regarding the roles of Thy-1 in cell differentiation and regeneration. This review aimed to summarize the roles of Thy-1 in cell differentiation and regeneration. Furthermore, since Thy-1 is an outer leaflet membrane protein anchored by GPI, we attempted to address how Thy-1 regulates intracellular pathways through cis and trans signals. Due to the complexity and mystery surrounding the issue, we also summarized the Thy-1-related pathways in different biological processes, and this might provide novel insights in the field of cell differentiation and regeneration.

Thy-1 in Integrin Mediated Mechanotransduction

The glycosylphosphatidylinositol (GPI) anchored glycoprotein Thy-1 has been prevalently expressed on the surface of various cell types. The biological function of Thy-1 ranges from T cell activation, cell adhesion, neurite growth, differentiation, metastasis and fibrogenesis and has been extensively reviewed elsewhere. However, current discoveries implicate Thy-1 also functions as a key mechanotransduction mediator. In this review, we will be focusing on the role of Thy-1 in translating extracellular mechanic cues into intracellular biological cascades. The mechanotransduction capability of Thy-1 relies on trans and cis interaction between Thy-1 and RGD-binding integrins; and will be discussed in depth in the review.

Thy-1 (CD90) Signaling Preferentially Promotes RORγt Expression and a Th17 Response

Thy-1 (CD90) is a glycosylphosphatidylinositol-anchored protein (GPI-AP) with signaling properties that is abundant on mouse T cells. Upon antibody-mediated crosslinking, Thy-1 provides a T cell receptor (TcR)-like signal that is sufficient to drive CD4⁺ T cell proliferation and differentiation into effector cells when costimulatory signals are provided by syngeneic lipopolysaccharide-matured bone marrow-derived dendritic cells. In this study, we investigated the impact of Thy-1 signaling on the production of the T helper (Th) cell subset-associated cytokines, interferon (IFN) γ, interleukin (IL)-4 and IL-17A, as well as the in vitro polarization of highly purified resting CD4⁺ T cells into Th1, Th2, and Th17 cells. Although CD8⁺ T cells expressed more Thy-1 than CD4⁺ T cells, both T cell populations were equally responsive to Thy-1 stimulation. In contrast to TcR stimulation of CD3⁺ T cells, which favored IFNγ and IL-4 production, Thy-1 signaling favored IL-17 synthesis, indicating a previously unidentified difference between the consequences of Thy-1 and TcR signal transduction. Moreover, Thy-1 signaling preferentially induced the Th17-associated transcription factor RORγt in CD4⁺ T cells. As with TcR signaling, Thy-1 stimulation of CD4⁺ T cells under the appropriate polarizing conditions resulted in Th1, Th2 or Th17 cell induction; however, Thy-1 stimulation induced nearly 7- and 2-fold more IL-4 and IL-17A, respectively, but only slightly more IFNγ. The ability to provide a TcR-like signal capable of promoting T helper cell differentiation and cytokine synthesis was not common to all GPI-APs since cross-linking of Ly6A/E with mitogenic mAb did not promote substantial production of IFNγ, IL-4 or IL-17, although there was a substantial proliferative response. The preferential induction of RORγt and Th17 cytokine synthesis as a consequence of Thy-1 signaling suggests a default T helper cell response that may enhance host defense against extracellular pathogens.

Thy-1 stimulation of mouse T cells induces a delayed T cell receptor-like signal that results in Ca2+‑independent cytotoxicity

Antibody-mediated crosslinking of Thy-1 [also known as cluster of differentiation (CD)90], results in a T cell receptor (TcR)‑like signal; however, the impact of Thy‑1 stimulation in comparison to TcR stimulation on T cell activation and effector function has yet to be fully elucidated. In the present study, the outcome of Thy‑1‑ and TcR‑induced stimulation of T cells was investigated in mice, using fragment crystalizable (Fc) receptor‑bound antibodies and costimulatory signals provided by syngeneic lipopolysaccharide‑matured bone marrow‑derived dendritic cells. Compared with TcR signaling, Thy‑1 signaling initiated a less robust proliferative response in T cells, as determined by tritiated‑thymidine incorporation. In addition, enzyme‑linked immunosorbent assays revealed that interleukin‑2 production was reduced, and the expression of CD25 and cyclin D3 was weaker in Thy‑1‑stimulated cells, as determined by western blotting; however, the expression of cyclin‑dependent kinase 6 was similar to that in TcR‑induced T cells. Furthermore, western blotting demonstrated that the phosphorylation of ζ-chain‑associated protein kinase 70 and extracellular signal‑regulated kinase 1/2 was delayed following Thy‑1 stimulation. DNA fragmentation assays revealed that cytotoxic effector function was also slower to develop in Thy‑1‑stimulated T cells, required more time to be effective and was largely Ca2+‑independent; these findings suggested that Fas ligand rather than granule‑associated perforin was involved in T cell effector function. In conclusion, the present results suggested that Thy‑1 signaling may contribute to the regulation of T cell homeostasis and the development of non‑specific T cell‑mediated cytotoxicity. However, further studies are required to elucidate the exact physiological roles of TcR‑like signals that result from Thy‑1 crosslinking and to investigate the molecular mechanisms that are involved.

Pharmacodynamic endpoints as clinical trial objectives to answer important questions in oncology drug development

Analyzing the molecular interplay between malignancies and therapeutic agents is rarely a straightforward process, but we hope that this special issue of Seminars has highlighted the clinical value of such endeavors as well as the relevant theoretical and practical considerations. Here, we conclude with both an overview of the various high-value applications of clinical pharmacodynamics (PD) in developmental therapeutics and an outline of the framework for incorporating PD analyses into the design of clinical trials. Given the increasingly recognized importance of determining and administering the biologically effective dose (BED) and schedule of targeted agents, we explain how clinical PD biomarkers specific to the agent mechanism of action (MOA) can be used for the development of pharmacodynamics-guided biologically effective dosage regimens (PD-BEDR) to maximize the efficacy and minimize the toxicity of targeted therapies. In addition, we discuss how MOA-based PD biomarker analyses can be used both as patient selection diagnostic tools and for designing novel drug combinations targeting the specific mutational signature of a given malignancy. We also describe the role of PD analyses in clinical trials, including for MOA confirmation and dosage regimen optimization during phase 0 trials as well as for correlating molecular changes with clinical efficacy when establishing proof-of-concept in phase I/II trials. Finally, we outline the critical technological developments that are needed to enhance the quality and quantity of future clinical PD data collection, broaden the types of molecular questions that can be answered in the clinic, and, ultimately, improve patient outcomes.

Thy1 (CD90) controls adipogenesis by regulating activity of the Src family kinase, Fyn

Worldwide obesity rates are at epidemic levels, and new insight into the regulation of obesity and adipogenesis are required. Thy1 (CD90), a cell surface protein with an enigmatic function, is expressed on subsets of fibroblasts and stem cells. We used a diet-induced obesity model to show that Thy1-null mice gain weight at a faster rate and gain 30% more weight than control C57BL/6 mice. During adipogenesis, Thy1 expression is lost in mouse 3T3-L1 cells. Overexpression of Thy1 blocked adipocyte formation and reduced mRNA and protein expression of an adipocyte marker, fatty acid-binding protein 4, by 5-fold. Although preadipocyte fibroblasts expressed Thy1 mRNA and protein, adipocytes from mouse and human fat tissue had almost undetectable Thy1 levels. Thy1 decreases the activity of the adipogenic transcription factor PPARγ by more than 60% as shown by PPARγ-dependent reporter assays. Using both genetic and pharmacologic approaches, we show Thy1 expression dampens PPARγ by inhibiting the activity of the Src-family kinase, Fyn. Thus, these studies reveal Thy1 blocks adipogenesis and PPARγ by inhibiting Fyn and support the idea that Thy1 is a novel therapeutic target in obesity.

Role of Mitogen-Activated Protein Kinases in Myocardial Ischemia-Reperfusion Injury during Heart Transplantation

In solid organ transplantation, ischemia/reperfusion (IR) injury during organ procurement, storage and reperfusion is an unavoidable detrimental event for the graft, as it amplifies graft inflammation and rejection. Intracellular mitogen-activated protein kinase (MAPK) signaling pathways regulate inflammation and cell survival during IR injury. The four best-characterized MAPK subfamilies are the c-Jun NH2-terminal kinase (JNK), extracellular signal- regulated kinase-1/2 (ERK1/2), p38 MAPK, and big MAPK-1 (BMK1/ERK5). Here, we review the role of MAPK activation during myocardial IR injury as it occurs during heart transplantation. Most of our current knowledge regarding MAPK activation and cardioprotection comes from studies of preconditioning and postconditioning in nontransplanted hearts. JNK and p38 MAPK activation contributes to myocardial IR injury after prolonged hypothermic storage. p38 MAPK inhibition improves cardiac function after cold storage, rewarming and reperfusion. Small-molecule p38 MAPK inhibitors have been tested clinically in patients with chronic inflammatory diseases, but not in transplanted patients, so far. Organ transplantation offers the opportunity of starting a preconditioning treatment before organ procurement or during cold storage, thus modulating early events in IR injury. Future studies will need to evaluate combined strategies including p38 MAPK and/or JNK inhibition, ERK1/2 activation, pre- or postconditioning protocols, new storage solutions, and gentle reperfusion.

Human CD90 identifies Th17/Tc17 T cell subsets that are depleted in HIV-infected patients

By revisiting CD90, a GPI-anchored glycoprotein, we show that CD90 is expressed by a subset of CD4(+) and CD8(+) human T cells. CD4(+)CD90(+) cells share similarities with Th17 cells because they express the Th17-specific transcription factor RORC2 and produce IL-17A. CD4(+)CD90(+) cells are activated memory T cells that express the gut mucosal markers CCR6, CD161, and the α(4) and β(7) integrins. Compared with CD90-depleted CCR6(+) memory Th17 cells, CD4(+)CD90(+) cells express higher levels of IL-22 and proinflammatory cytokines (IL-6, TNF-α and GM-CSF), but they produce lower levels of IL-21 and no IL-9. Analyses of CD8(+)CD90(+) cells reveal that they express RORC2 and are able to produce higher levels of IL-17A, IL-22, and CCL20 compared with CD90-depleted CD8(+) cells. These data show that CD90 identifies Th17 and Tc17 cells with a peculiar cytokine profile. Studies of circulating CD90(+) cells in HIV patients show that CD90(+) cells are decreased with an imbalance of the CD4(+)CD90(+)/regulatory T cell ratio in nontreated patients compared with treated patients and healthy donors. Overall, human CD90 identifies a subset of Th17 and Tc17 cells within CD4(+) and CD8(+) T cells, respectively, which are depleted during HIV infection.

Induction of CD4(+)CD25(+)Foxp3(-) regulatory T cells by Thy-1 stimulation of CD4(+) T cells

Thy-1 (CD90) on mouse T cells has been reported to have both T-cell activating and regulatory roles. In this study, we show that monoclonal antibody (mAb)-mediated crosslinking of Thy-1 on CD4(+) mouse T-cells-induced regulatory T (T(reg)) cells that expressed CD25, CD39 and glucocorticoid-induced tumor necrosis factor receptor family-related gene, but not CD73, CD122 or Foxp3. The proliferation of CD4(+) T(responder) cells in response to anti-CD3/anti-CD28mAb-coated T-cell expander beads or syngeneic dendritic cells and soluble anti-CD3mAb was inhibited by Thy-1-induced T(reg) cells, in spite of elevated IL-2 levels in the co-cultures. Interestingly, stimulation with T-cell expander beads caused Thy-1-induced T(reg) cells to synthesize large amounts of interleukin-2 (IL-2). IL-10 was also elevated in co-cultures of activated T(responder) cells and Thy-1-induced T(reg) cells. However, mAb-mediated neutralization of IL-10 did not restore T(responder)-cell proliferation to control levels, which excluded IL-10 as a potential mediator of Thy-1-induced T(reg)-cell suppressor function. In addition, Thy-1-induced T(reg) cells did not inhibit IL-2-dependent proliferation of CTLL-2 cells, suggesting that IL-2 receptor signaling remained intact in the presence of Thy-1-induced T(reg) cells. We suggest that T(reg) cells induced by Thy-1 ligation in vivo may contribute to the maintenance of T-cell homeostasis.

Modulation of IL-2 expression after uptake of hepatitis C virus non-enveloped capsid-like particles: the role of p38 kinase

Hepatitis C virus (HCV) has been shown to actively replicate in cells of the immune system, altering both their function and cytokine expression. Naked nucleocapsids have been reported in the serum of infected patients. We investigated interference of recombinant non-enveloped capsid-like particles with signaling pathways in T cells. HCV non-enveloped particles (HCVne) internalization was verified in Jurkat and Hut 78 T cells, as well as primary human peripheral blood and intrahepatic mononuclear cells. HCVne uptake leads to activation of the MAPKs-p38 signaling pathway. Using specific phosphoantibodies, signaling pathways inhibitors, and chemical agents, it was demonstrated that p38 activation in T cells correlated with IL-2 transcriptional activation and was accompanied by a parallel increase of IL-2 cytokine secretion. c-fos and egr-1, two transcription factors, essential for IL-2 promoter activity, were also found to be elevated. We propose that HCVne uptake by T lymphocytes results in increased MAPKs-p38 activity and IL-2 expression, thus altering the host immune response.

Salutary effects of 17beta-estradiol on Peyer's patch T cell functions following trauma-hemorrhage

Although 17beta-estradiol (E2) administration following trauma-hemorrhage (T-H) improves immune functions in male rodents, it remains unclear whether E2 has salutary effects on Peyer's patch (PP) T cell functions. We hypothesized that T-H induces PP T cell dysfunction and E2 administration following T-H will improve PP T cell function. T-H was induced in male C3H/HeN mice (6-8weeks) by midline laparotomy and approximately 90min of hemorrhagic shock (blood pressure 35mmHg), followed by fluid resuscitation (4x the shed blood volume in the form of Ringer's lactate). Estrogen receptor (ER)-alpha agonist propyl pyrazole triol (PPT; 5microg/kg), ER-beta agonist diarylpropionitrile (DPN; 5microg/kg), E2 (50microg/kg), or vehicle was injected subcutaneously at resuscitation onset. Two hours later, mice were sacrificed and PP T cells isolated. PP T cell capacity to produce cytokines in response to in vitro stimulation, PP T cell proliferation and MAPK (p38, ERK-1/2, JNK) activation were measured. Results indicate PP T cell proliferation, cytokine production and MAPK activation decreased significantly following T-H. E2, PPT or DPN administration normalized these parameters. Since PPT or DPN administration following T-H was effective in normalizing PP T cell functions, the salutary effects of E2 are mediated via ER-alpha and ER-beta.