Transmembrane signaling of interleukin 2 receptor. Conformation and function of human interleukin 2 receptor (p55)/insulin receptor chimeric molecules

Evolution and synthetic biology

Evolutionary observations have often served as an inspiration for biological design. Decoding of the central dogma of life at a molecular level and understanding of the cellular biochemistry have been elegantly used to engineer various synthetic biology applications, including building genetic circuits in vitro and in cells, building synthetic translational systems, and metabolic engineering in cells to biosynthesize and even bioproduce complex high-value molecules. Here, we review three broad areas of synthetic biology that are inspired by evolutionary observations: (i) combinatorial approaches toward cell-based biomolecular evolution, (ii) engineering interdependencies to establish microbial consortia, and (iii) synthetic immunology. In each of the areas, we will highlight the evolutionary premise that was central toward designing these platforms. These are only a subset of the examples where evolution and natural phenomena directly or indirectly serve as a powerful source of inspiration in shaping synthetic biology and biotechnology.

Differential effects of tumour necrosis factor-alpha and interleukin-12 on isopentenyl pyrophosphate-stimulated interferon-gamma production by cord blood Vgamma9 T cells

Lower numbers of Vgamma9Vdelta2 T cells in cord blood (CB) than in adult peripheral blood (PB), as well as their impaired ability to produce interferon-gamma (IFN-gamma) in response to stimulation, are associated with functional deficiency in the immune system in newborns. In this study, we stimulated CB Vgamma9 T cells with their T-cell receptor-specific ligand, isopentenyl pyrophosphate (IPP), plus exogenous costimulatory cytokines such as interleukin-2 (IL-2), IL-12 and tumour necrosis factor-alpha (TNF-alpha), which are known to play important roles in the activation of PB gammadelta T cells. Our data show that CB Vgamma9 T cells are able to produce IFN-gamma at levels comparable to PB Vgamma9 T cells by the addition of TNF-alpha in the presence of IPP and IL-2; however, under the same culture conditions, IL-12 does not efficiently activate CB Vgamma9 T cells to produce IFN-gamma. The frequency of TNF-alpha receptor II-positive Vgamma9T cells and the expression levels of TNF-alpha receptor II are similar in CB and PB; in contrast, the frequency of IL-12 receptor betaI (IL-12RbetaI) -positive Vgamma9T cells and expression levels of IL-12RbetaI are significantly lower in CB than PB. TNF-alpha but not IL-12 increases the expression of IL-2Rbeta on CB Vgamma9 T cells. These results provide new insights into the role of TNF-alpha in the activation of CB Vgamma9 T cells.

Cord blood leucocyte expression of functionally significant molecules involved in the regulation of cellular immunity

The cellular immune system of the newborn infant is immature and hypo-responsive when compared with adults. The extent to which immaturity of the leucocyte function underlies hyporesponsiveness in the newborn is incompletely understood. In this study flow cytometric techniques were applied to investigate the concurrent expression of a range of surface and intracellular leucocyte functional molecules and cytokines in resting and stimulated cord and adult blood. Production of interleukin (IL)-2 and expression of the components of its receptor, IL-2R alpha/beta/gamma, were investigated. No differences in the proportion of leucocytes producing IL-2R alpha and IL-2R gamma were observed for newborns and adults. A lower proportion of T cells and natural killer (NK) cells from newborns expressed IL-2R beta and upregulation of expression was slower. We hypothesize that reduced IL-2R beta may curtail early autocrine IL-2 activation of immune responses in the newborn. This hypothesis was supported by the observation that an increased proportion of stimulated T cells from newborns produced IL-2 at 4 h poststimulation, but at 24 h the proportion was lower than for adult T cells. The very low levels of interferon (IFN)-gamma produced by neonatal T cells and NK cells may also be partly explained by a curtailment of early autocrine activation of T cells. Expression and kinetics of upregulation for other functional molecules were studied. CD71, HLA-DR, tissue factor and CD152 levels were not significantly different for adults and newborns, suggesting that cord blood leucocytes, in some respects, may demonstrate functional maturity. IL-6 secretion by stimulated monocytes was also comparable in cord and adult blood. However, IL-1 alpha and IL-1 beta were produced by a lower proportion of monocytes from newborns than adults. Similarly, tumour necrosis factor (TNF)-alpha production for monocytes and T cells was lower in cord blood. The mean fluorescence intensity for IL-1 alpha, IL-1 beta and TNF-alpha was also lower for leucocytes from cord blood. These findings are significant in relation to the inability of newborn infants to mount a febrile response to infection. The findings of lower expression of IL-2R beta and lower production of inflammatory cytokines IL-1 alpha, IL-1 beta and TNF-alpha is a basis for improved understanding of the immunological immaturity of leucocytes in the newborn.

Intermediate- and high-affinity interleukin-2 receptors expressed in an IL-4-dependent T-cell line induce different signals

In order to understand the respective roles of IL-2R alpha and IL-2R beta subunits in transmission of the interleukin-2 (IL-2)-mediated growth signals, we have established two IL-4-dependent murine T-cell clones stably expressing the human IL-2R beta chain and three clones stably expressing the human IL-2R alpha chain. Whereas parental LD8 cells (which express only the murine IL-2R beta chain) do not proliferate in response to IL-2, cell lines stably expressing human IL-2R beta or the chimeric IL-2R alpha beta complex proliferate in response to IL-2. Stably transfected cells expressing the chimeric high-affinity receptor (human IL-2R alpha and murine IL-2R beta) expressed de novo endogenous murine IL-2R alpha when cultured in the presence of IL-2 but not IL-4. Both chimeric and endogenous receptors are functional in response to IL-2, since only addition of both anti-human and anti-murine IL-2R alpha monoclonal antibodies (mAb) inhibited IL-2-induced proliferation. Taken together, our results strongly suggest that human and murine IL-2R beta molecules are different since interaction of IL-2 with human p70 IL-2R is sufficient for transduction of proliferative signals in the absence of p55 IL-2R or, alternatively, that over-expression of the IL-2R beta chain renders cells responsive to IL-2. In addition, IL-2 stimulation of T cells through different forms of IL-2R results in the induction of distinct cellular responses.

Functional dissection of the CD21/CD19/TAPA-1/Leu-13 complex of B lymphocytes

The CD21/CD19/TAPA-1 complex of B lymphocytes amplifies signal transduction through membrane immunoglobulin (mIg), recruits phosphatidylinositol 3-kinase (PI3-kinase), and induces homotypic cellular aggregation. The complex is unique among known membrane protein complexes of the immune system because its components represent different protein families, and can be expressed individually. By constructing chimeric molecules replacing the extracellular, transmembrane, and cytoplasmic regions of CD19 and CD21 with those of HLA-A2 and CD4, we have determined that CD19 and TAPA-1 interact through their extracellular domains, CD19 and CD21 through their extracellular and transmembrane domains, and, in a separate complex, CD21 and CD35 through their extracellular domains. A chimeric form of CD19 that does not interact with CD21 or TAPA-1 was expressed in Daudi B lymphoblastoid cells and was shown to replicate two functions of wild-type CD19 contained within the complex: synergistic interaction with mIgM to increase intracellular free calcium and tyrosine phosphorylation and association with the p85 subunit of PI3-kinase after ligation of mIgM. The chimeric CD19 lacked the capacity of the wild-type CD19 to induce homotypic cellular aggregation, a function of the complex that can be ascribed to the TAPA-1 component. The CD21/CD19/TAPA-1 complex brings together independently functioning subunits to enable the B cell to respond to low concentrations of antigen.

Critical cytoplasmic domains of the common beta subunit of the human GM-CSF, IL-3 and IL-5 receptors for growth signal transduction and tyrosine phosphorylation

The high-affinity receptors for human granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3) and interleukin 5 (IL-5) are composed of two distinct subunits, alpha and beta c. The alpha subunits are specific for each cytokine, whereas the beta subunit (beta c) is shared by the three receptors and is an essential component of signal transduction. We have made a series of mutant beta c cDNAs that delete various regions of the cytoplasmic domain and examined the function of these mutants by coexpressing them with the alpha subunit of the human GM-CSF receptor (hGMR) in an IL-3-dependent mouse pro-B cell line BaF3. Two domains in the membrane-proximal portion of beta c were found to be important for transducing the hGM-CSF-mediated growth signals: one domain between Arg456 and Phe487 appears to be essential for proliferation, and the second domain between Val518 and Asp544 enhances the response to GM-CSF, but is not absolutely required for proliferation. The region between Val518 and Leu626 was responsible for major tyrosine phosphorylation of 95 and 60 kDa proteins. Thus, beta c-mediated major tyrosine phosphorylation of these proteins was apparently separated from proliferation. However, the beta 517 mutant lacking residues downstream of Val518 transmitted a herbimycin-sensitive proliferation signal, suggesting that beta 517 still activates a tyrosine kinase(s). We also evaluated the role of the cytoplasmic domain of the GMR alpha subunit and the results suggest that it is involved in the hGM-CSF-mediated signal transduction, but is not essential.(ABSTRACT TRUNCATED AT 250 WORDS)

Role and regulation of interleukin (IL)-2 receptor alpha and beta chains in IL-2-driven B-cell growth

Substantial proportions of resting B cells constitutively express low levels of IL-2 receptor (IL-2R) alpha and/or beta chains. The expression of these chains is differentially regulated by anti-IgM and IL-2/IL-4. The anti-IgM induces IL-2R alpha chain expression, whereas each of the two cytokines induces IL-2R beta chain expression in a dose-dependent manner. Moreover, IL-2 induces the growth of B cells, when the cells were pretreated with IL-2 or IL-4 for 24 h. The magnitude of this IL-2-driven B-cell growth depends upon the level of IL-2R beta chain expression. Costimulation of the B cells with IL-2 and anti-IgM shifts the dose-response curve, and the cells proliferate at an IL-2 concentration as low as 40 pM. These results indicate that the levels of anti-IgM-induced IL-2R alpha chain and IL-2-induced IL-2R beta chain determine the sensitivity of the cells to IL-2.

Interaction of the IL-2 receptor with the src-family kinase p56lck: identification of novel intermolecular association

In the interleukin-2 (IL-2) system, intracellular signal transduction is triggered by the beta chain of the IL-2 receptor (IL-2R beta); however, the responsible signaling mechanism remains unidentified. Evidence for the formation of a stable complex of IL-2R beta and the lymphocyte-specific protein tyrosine kinase p56lck is presented. Specific association sites were identified in the tyrosine kinase catalytic domain of p56lck and in the cytoplasmic domain of IL-2R beta. As a result of interaction, IL-2R beta became phosphorylated in vitro by p56lck. Treatment of T lymphocytes with IL-2 promotes p56lck kinase activity. These data suggest the participation of p56lck as a critical signaling molecule downstream of IL-2R via a novel interaction.

Soluble interleukin-2 receptor in sera of patients with pulmonary tuberculosis

Interleukin-2 receptor, the complex of IL-2R-alpha and/or IL-2R-beta, is expressed mainly on T-lymphocytes, and the soluble form of IL-2R-alpha (sIL-2R-alpha) has been reported to be detected in the serum of patients with lymphoproliferative disorders or disease characterized by the cellular immune reaction. We measured serum sIL-2R-alpha levels among patients with pulmonary diseases and found that sIL-2R-alpha levels were significantly elevated in patients with active pulmonary tuberculosis (1,327 +/- 209 U/ml) and sarcoidosis (1,037 +/- 115 U/ml) when compared with healthy volunteers (468 +/- 49 U/ml, p less than 0.01). Among patients with pulmonary tuberculosis, the sIL-2R-alpha levels were high in sera from patients with extensive parenchymal lesions on the roentgenogram (2,745 +/- 705 U/ml) and patients with tuberculous pleurisy (2,111 +/- 679 U/ml). In contrast, the sIL-2R-alpha levels in tuberculous patients with minimal lesion (455 +/- 92 U/ml) or moderate lesion (1,082 +/- 189 U/ml) were not significantly elevated when compared with healthy volunteers. After the treatment with antituberculosis agents, serum sIL-2R-alpha levels decreased in accordance with improvement of roentgenographic findings and laboratory data. These results suggest that serum sIL-2R-alpha level may be useful as a monitor for the disease activity in patients with pulmonary tuberculosis.

Murine interleukin 2 receptor beta chain: dysregulated gene expression in lymphoma line EL-4 caused by a promoter insertion

The functional, high-affinity interleukin 2 receptor (IL-2R) consists of at least two receptor components, IL-2R alpha (p55) and IL-2R beta (p70-75). The cDNA encoding the murine IL-2R beta has been isolated by using the previously cloned cDNA for human IL-2R beta as a probe. Analysis of the cDNA revealed that the murine IL-2R beta shows a marked homology with the human IL-2R beta and that it is also structurally related to other cytokine receptors such as erythropoietin receptor. The cDNA-directed murine IL-2R beta formed high-affinity IL-2R in conjunction with the endogenous IL-2R alpha in a murine pro-B-cell line and could transduce IL-2-induced growth signal. In mouse lymphoma line EL-4, the IL-2R beta gene was found to be rearranged by the insertion of the long terminal repeat sequence of an intracisternal A particle, giving rise to constitutive expression of the IL-2R beta mRNA.

Why are multiple chains required for the interleukin 2 receptor?

The interleukin 2 receptor (IL-2R) is composed of at least two proteins, that is, a 55 kDa L chain (p55, alpha chain) and a 75 kDa H chain (p75, beta chain). The high-affinity binding of IL-2 results in the formation of the ternary complex consisting of IL-2, the L chain and the H chain. Kinetic studies on the IL-2 binding to the high-affinity IL-2R have shown that the association of IL-2 to the L chain is the first step of the ternary complex formation and that expression of a larger number of L chains accelerates the association of IL-2 to the high-affinity IL-2R in agreement with the stepwise binding/affinity conversion model. This conclusion was supported by experiments using several monoclonal antibodies directed to either H or L chain and murine T cell lines which was transfected by the human L chain cDNA. Temperature-sensitive IL-2 binding to the high-affinity receptor is also consistent with the above conclusion. Signal transduction by the IL-2R appears to involve the activation of tyrosine protein kinase. IL-2 signal transduction seems to require the H chain and another yet unidentified molecule, which might have the kinase activity.

Human interleukin 2 (IL 2) receptor beta chain allows transduction of IL 2-induced proliferation signal(s) in a murine cell line

Interleukin 2 (IL 2) delivers cell growth signal by virtue of its interaction with the high-affinity receptor complex, which consists of two distinct IL 2-binding molecules: the IL 2 receptor alpha (IL 2R alpha) and beta (IL 2R beta) chains. Unlike many known growth factor receptors, neither of the IL 2R chains seems to contain a tyrosine kinase domain. In this report, we have shown that the human IL 2R beta chain expressed in a murine IL 3-dependent, non-lymphoid cell line can transduce IL 2-induced cell proliferation signal(s) in combination with the autologous mouse IL 2R alpha chain. This observation should provide a tool to dissect IL 2-induced signal transduction pathway in lymphoid and non-lymphoid cells.

A restricted cytoplasmic region of IL-2 receptor beta chain is essential for growth signal transduction but not for ligand binding and internalization

The functional, high affinity form of interleukin-2 receptor (IL-2R) is composed of two receptor components, the IL-2R alpha (p55) and IL-2R beta (p70-75) chains. Unlike the IL-2R alpha chain, the IL-2R beta chain contains a large cytoplasmic domain that shows no obvious tyrosine kinase motif. In the present study, we report the establishment of a system in which the cDNA-directed human IL-2R beta allows growth signal transduction in a mouse pro-B cell line. This system enabled us to identify a unique region within the cytoplasmic domain of the human IL-2R beta chain essential for ligand-mediated signal transduction. We also demonstrate that certain cytoplasmic deletion mutants in the IL-2R beta chain, although deficient in signal transduction, can still form high affinity IL-2R in conjunction with endogenous mouse IL-2R alpha chain; the mutants are still able to internalize the ligand as well.

Interleukin-6 triggers the association of its receptor with a possible signal transducer, gp130

Interleukin-6 mediates pleiotropic functions in various types of cells through its specific receptor (IL-6-R), the cDNA of which has already been cloned. We report here that an 80 kd single polypeptide chain (IL-6-R) is involved in IL-6 binding and that IL-6 triggers the association of this receptor with a non-ligand-binding membrane glycoprotein, gp130. The association takes place at 37 degrees C within 5 min and is stable for at least 40 min in the presence of IL-6, but does not occur at 0 degree C. Human IL-6-R can associate with a murine gp130 homolog and is functional in murine cells. Mutant IL-6-R lacking the intracytoplasmic portion is functional, suggesting that the two polypeptide chains interact to involve their extracellular portion. In fact, a soluble IL-6-R lacking the transmembrane and intracytoplasmic domains can associate with gp130 in the presence of IL-6 and mediate its function. These findings indicate that the complex of IL-6 and IL-6-R can interact with a non-ligand-binding membrane glycoprotein, gp130, extracellularly and can provide the IL-6 signal.

Binding specificity and intramolecular signal transmission of uncleaved insulin proreceptor in transformed lymphocytes from a patient with extreme insulin resistance

An alteration of an amino acid sequence in the processing site of the insulin proreceptor by a point mutation of the insulin receptor gene produced extreme insulin resistance. We characterized functional properties of the unprocessed insulin receptor in transformed lymphocytes from a patient. Insulin binding to intact cells and to a partially purified insulin receptor preparation was radically decreased to 20% and 18% of the control values, respectively. In competitive insulin binding to intact cells, [LeuA3]-, [LeuB24]-, [SerB24]-insulin, and mini-proinsulin ([ B(1-29)-Ala-Ala-Lys-A(1-21)]-insulin) had the same relative binding activity in both the patient's and the control cells, but proinsulin and IGF-I were markedly less able to displace 125I-insulin in the patient's cells. In contrast to the study in intact cells, proinsulin and IGF-I as well as other insulin analogues had the same relative binding activity to bind to the partially lectin-purified insulin receptor preparations from both the patient's and the control cells. As regards the signal transduction after receptor binding, insulin-stimulated autophosphorylation of the unprocessed insulin proreceptor occurred proportionally to the amount of decreased insulin binding. With 0.025% trypsin treatment, the abnormal binding characteristics and autophosphorylation were normalized through conversion to functionally normal receptors. In spite of the abnormal processing, self-association of receptors into oligomeric structures was observed in the proreceptor. These results suggest that the unprocessed insulin proreceptor in the plasma membranes has an altered conformation which affects its binding characteristics but not its intramolecular signal transmission.

Interleukin-2 receptor beta chain gene: generation of three receptor forms by cloned human alpha and beta chain cDNA's

Interleukin-2 (IL-2) binds to two distinct receptor molecules, the IL-2 receptor alpha (IL-2R alpha, p55) chain and the newly identified IL-2 receptor beta (IL-2R beta, p70-75) chain. The cDNA encoding the human IL-2R beta chain has now been isolated. The overall primary structure of the IL-2R beta chain shows no apparent homology to other known receptors. Unlike the IL-2R alpha chain, the IL-2R beta chain has a large cytoplasmic region in which a functional domain (or domains) mediating an intracellular signal transduction pathway (or pathways) may be embodied. The cDNA-encoded beta chain binds and internalizes IL-2 when expressed on T lymphoid cells but not fibroblast cells. Furthermore, the cDNA gives rise to the generation of high-affinity IL-2 receptor when co-expressed with the IL-2R alpha chain cDNA.