T-lymphocyte proliferation: tyrosine kinases in interleukin 2 signal transduction

T cell signaling and Treg dysfunction correlate to disease kinetics in IL-2Rα-KO autoimmune mice

IL-2Rα, in part, comprises the high affinity receptor for IL-2, a cytokine important in immune proliferation, activation, and regulation. IL-2Rα deficient mice (IL-2Rα-KO) develop systemic autoimmune disease and die from severe anemia between 18 and 80 days of age. These mice develop kinetically distinct autoimmune progression, with approximately a quarter dying by 21 days of age and half dying after 30 days. This research aims to define immune parameters and cytokine signaling that distinguish cohorts of IL-2Rα-KO mice that develop early- versus late-stage autoimmune disease. To investigate these differences, we evaluated complete blood counts (CBC), antibody binding of RBCs, T cell numbers and activation, hematopoietic progenitor changes, and signaling kinetics, during autoimmune hemolytic anemia (AIHA) and bone marrow failure. We identified several alterations that, when combined, correlate to disease kinetics. Early onset disease correlates with anti-RBC antibodies, lower hematocrit, and reduced IL-7 signaling. CD8 regulatory T cells (Tregs) have enhanced apoptosis in early disease. Further, early and late end stage disease, while largely similar, had several differences suggesting distinct mechanisms drive autoimmune disease kinetics. Therefore, IL-2Rα-KO disease pathology rates, driven by T cell signaling, promote effector T cell activation and expansion and Treg dysfunction.

Association of SRC-related kinase Lyn with the interleukin-2 receptor and its role in maintaining constitutive phosphorylation of JAK/STAT in human T-cell leukemia virus type 1-transformed T cells

Human T-cell leukemia virus type 1 (HTLV-1) infection and transformation are associated with an incremental switch in the expression of the Src-related protein tyrosine kinases Lck and Lyn. We examined the physical and functional interactions of Lyn with receptors and signal transduction proteins in HTLV-1-infected T cells. Lyn coimmunoprecipitates with the interleukin-2 beta receptor (IL-2Rβ) and JAK3 proteins; however, the association of Lyn with the IL-2Rβ and Lyn kinase activity was independent of IL-2 stimulation. Phosphorylation of Janus kinase 3 (JAK3) and signal transducers and activator of transcription 5 (STAT5) proteins was reduced by treatment of cells with the Src kinase inhibitor PP2 or by ectopic expression of a dominant negative Lyn kinase protein.

Effects of lentinan on broiler splenocyte proliferation, interleukin-2 production, and signal transduction

Lentinan (LEN) is an intensively studied beta-glucan that has been shown to have immunostimulating and antitumor functions. However, it currently is not used in veterinary practice and animal production. This study was conducted to investigate the impacts of LEN on broiler splenocyte proliferation, interleukin-2 (IL-2) production, and to explore its effects on receptor signal transduction by determining signaling molecules, including nitric oxide (NO), cytosolic-free Ca2+, cytosolic cyclic adenosine monophosphate (cAMP), and cyclic guanosine monophosphate (cGMP). The results showed that compared to the control all three measured doses, including 40, 80, and 160 microg/mL LEN, increased splenocyte proliferation and IL-2 production (P < 0.05). Lentinan increased splenocyte NO production and cytosolic-free calcium concentration in a dose-dependent manner (P < 0.001). After incubating splenocytes for 20 min, LEN increased intracellular cAMP and cGMP concentrations at a dose of 80 and 160 microg/mL, respectively. However, after incubating the splenocytes for 60 min, LEN had no effect on cytosolic cAMP and cGMP concentration irrespective of the LEN dosage. Those results indicated that LEN had immunostimulatory effects on splenocytes by increasing splenocyte proliferation and IL-2 production and by activating splenocyte receptor signal transduction.

Interleukin-2 as a neuroregulatory cytokine

Interleukin-2 (IL-2), the cytokine also known as T-cell growth factor, has multiple immunoregulatory functions and biological properties not only related to T-cells. In the past decade, substantial evidence accumulated to suggest that IL-2 is also a modulator of neural and neuroendocrine functions. First, extremely potent effects of IL-2 on neural cells were discovered, including activities related to cell growth and survival, transmitter and hormone release and the modulation of bioelectric activities. IL-2 may be involved in the regulation of sleep and arousal, memory function, locomotion and the modulation of the neuroendocrine axis. Second, the concept that IL-2 could act as a neuroregulatory cytokine has been supported by reports on the presence in rodent and human brain tissues of IL-2-like bioactivity, IL-2-like immunoreactivity, IL-2-like mRNA, IL-2 binding sites, IL-2 receptor (IL-2R alpha) and beta chain mRNA and IL-2R immunoreactivity. IL-2 and/or IL-2R molecules mainly localize to the frontal cortex, septum, striatum, hippocampal formation, hypothalamus, locus coeruleus, cerebellum, the pituitary and fiber tracts, such as the corpus callosum, where they are likely expressed by both neuronal and glial cells. Although the molecular biology of the brain IL-2/IL-2R system (including its relation to IL-15/IL-15R alpha) is not yet fully established by cloning and complete sequencing of all respective components, similarities (and to some extent differences) to peripheral counterparts are now apparent. The ability of IL-2 to readily penetrate the blood-brain barrier further suggests that this cytokine could regulate interactions between peripheral tissues and the central nervous system. Taken together, these data suggest that IL-2 of either immune and CNS origin can have access to functional IL-2R molecules on neurons and glia under normal conditions. Additionally, dysregulation of the IL-2/IL-2 receptor system could lead or contribute to functional and pathological alterations in the brain as in the immune system. Understanding the neurobiology of the IL-2/IL-2 receptor system should also help to explain neurologic, neuropsychiatric and neuroendocrine side effects occurring during IL-2 treatment of peripheral and brain tumors. Immunopharmacological manipulation either aiming at the activation or suppression of IL-2 signaling should consider functional interference with constitutive and inducible IL-2 receptors on brain cells in order to fulfil the high expectations associated with the use of this cytokine as a promising agent in immunotherapies, especially of brain tumors.

Defects in antigen-driven lymphocyte responses in common variable immunodeficiency (CVID) are due to a reduction in the number of antigen-specific CD4+ T cells

T cells from patients with CVID have defects that may relate to the failure in vivo of B cell production of antibodies. Antigen-driven responses of T cells from CVID patients and normal subjects have been assessed by measuring DNA synthesis in vitro. Low density cells enriched for antigen-presenting dendritic cells were pulsed with purified protein derivative (PPD) and cultured with autologous T cells. Overall, T cells from CVID patients showed a significantly low mean response to PPD, although non-specific DNA synthesis induced in CVID T cells by IL-2 was within the normal range. However, mean PPD-specific T cell responses in CVID were not restored by IL-2 irrespective of the presence of monocytes. Depletion of CD8+ cells also failed to restore the mean PPD response of CVID CD4+ T cells. Limiting dilution analysis showed that in CVID there was a reduced frequency of antigen-specific cells within the T cell preparations. The mean frequency of the PPD-specific T cells in cultures from patients vaccinated with bacille Calmette-Guérin (BCG) was reduced to 1 in 109,000 T cells compared with 1 in 18,600 T cells in BCG-vaccinated normal donors. These data show that the reduced PPD-specific response in CVID is due to a partial peripheral loss of antigen-specific cells.

Structural domains of interleukin-2 receptor beta critical for signal transduction: kinase association and nuclear complex-formation

The structural domains of interleukin-2 receptor beta (IL-2R beta) were examined, characterizing the protein domains, associated phosphoproteins and nuclear complexes of IL-2-induced signal transduction. A series of IL-2R beta cytoplasmic deletion mutants were constructed and transfected into a murine pre-B-cell line, Ba/F3. The proliferative response of characterized clones was determined. A minimal linear cytoplasmic sequence required for proliferation and a sequence motif (PQPLXP) needed along with Box1-Box2 for IL-2-induced proliferation were identified. Anti-phosphotyrosine Western-blot analysis of a stimulated biologically active clone showed several IL-2-induced tyrosylphosphorylated proteins with molecular masses ranging from 45 to 116 kDa. In vitro kinase studies of biologically active clone-receptor complexes showed a 116 kDa protein (p116) to be the major tyrosine-phosphorylated component. The presence of the p116 kinase in the receptor complex correlates with IL-2-induced proliferation. An IL-2-inducible p116 kinase has recently been characterized as a Jak kinase family member and named Jak3. Nuclear complexes were formed with the GRR oligomer only when the IL-2R beta mutant supported proliferation. This led us to conclude that Box1-Box2 and PQPLXP motifs associate with Jak3 and that this association is an essential element in the IL-2 signal-transduction pathway culminating in the formation of a nuclear complex.

Interleukin-2 induces tyrosine phosphorylation and nuclear translocation of stat3 in human T lymphocytes

An early biochemical event associated with T cell activation through the interleukin-2 receptor (IL-2R) is tyrosine phosphorylation of several intracellular substrates. The exact mechanism by which IL-2 regulates transcription of different genes is presently unknown. Here, we report that stimulation through the IL-2R induced tyrosine phosphorylation and subsequent nuclear translocation of stat3, a newly identified member of the signal transducers and activators of transcription (STAT) family of proteins. In contrast, stat1 proteins were not tyrosine phosphorylated after IL-2 ligation, whereas tyrosine-phosphorylated stat1 proteins (91 and 84 kDa proteins) were translocated to the nucleus following interferon-gamma treatment of HeLa cells. Apart from stat3, another cytoplasmic protein was tyrosine phosphorylated and subsequently translocated to the nucleus in response to IL-2. This protein had an apparent molecular mass of 84 kDa and was not recognized by stat3 or stat1 mAb or antisera. Since IL-2 induced nuclear translocation of the 84 kDa protein and stat3 followed identical kinetics, p84 is a candidate for a new, yet undefined, member of the STAT family. Taken together, we report that IL-2 induces tyrosine phosphorylation and subsequent nuclear translocation of stat3 and an as yet undefined 84-kDa protein in antigen-specific human T cell lines.

Cooperative interactions between the interleukin 2 receptor alpha and beta chains alter the interleukin 2-binding affinity of the receptor subunits

The interleukin 2 (IL-2) receptor (IL-2R) is a multisubunit receptor that includes three major IL-2 binding subunits, the IL-2R alpha, beta, and gamma chains. We have detected and analyzed cooperative interactions between the IL-2R alpha and beta chains (IL-2R alpha and IL-2R beta, respectively) in COS cells transfected with cDNAs encoding the IL-2R alpha, the IL-2R beta, or both cDNAs. We demonstrated that IL-2 F42A, an analog that fails to bind to the isolated IL-2R alpha subunit and would be predicted by the hierarchical affinity-conversion model to have impaired binding to cells expressing both chains, instead readily binds to the IL-2R alpha/beta heterodimer in COS cells. Furthermore, this binding is abolished by the antibody HIEI that separates the two IL-2R subunits. The monoclonal antibodies anti-Tac and Mik-beta 1 directed at the IL-2-binding sites on IL-2R alpha and IL-2R beta, respectively, block ligand binding to the heterodimer. This binding pattern is inconsistent with the strict hierarchical affinity-conversion model that mandates an initial binding of IL-2 to IL-2R alpha followed by binding of the IL-2/IL-2R alpha complex to IL-2R beta. Instead, our results support an alternative model of preformed complexes of IL-2R beta with other IL-2R subunits. In this alternative model, IL-2R alpha and -beta exist in part as preformed complexes in which the affinity of IL-2R beta for IL-2 is altered by the proximity of IL-2R alpha, through mechanisms that do not require the prior binding of IL-2 to IL-2R alpha.