Expression of interleukin-2 receptor gamma chain on human neutrophils

The interleukin-2 (IL-2) receptor gamma is an indispensable functional component of IL-2, IL-4, and IL-7 receptors, and thus, is denoted the common gamma chain, gamma c. The present study was undertaken to determine whether human polymorphonuclear neutrophils (PMNs) expressed gamma c chain. Reverse transcription-polymerase chain reaction and Northern blot analysis showed that fresh human PMN constitutively expressed a remarkable level of gamma c mRNA, which is of the size and intensity of that from the peripheral blood mononuclear cells (PBMCs). Granulocyte macrophage-colony stimulating factor, IL-2, and IL-8, which are known to activate PMN functions, failed to regulate the gamma c gene expression. Western blot analysis with a rabbit anti-gamma c polyclonal antibody identified 64-, 58-, and 50-kD gamma c bands in lysates from PMN, but only 64- and 58-kD bands from PBMCs. After the PMNs and PBMCs were treated with tunicamycin to prevent N-linked glycosylation, Western blot analysis detected a single 39-kD band, which is equal to the calculated molecular weight from the cloned cDNA. Thus, our results indicate that PMNs constitutively express high levels of gamma c and the three forms detected are caused by different glycosylation of a protein translated from a single mRNA species.

The defective gene in X-linked severe combined immunodeficiency encodes a shared interleukin receptor subunit: implications for cytokine pleiotropy and redundancy

The interleukin-2 receptor plays a pivotal role in the regulation of the normal T cell immune response to foreign antigen. The IL-2 receptor gamma-chain is one component of this receptor, and is encoded by the gene that is defective in X-linked severe combined immunodeficiency. The clinical manifestations of this disease led to the hypothesis and subsequent confirmation that the gamma-chain was in fact a subunit shared by multiple cytokine receptors, including those for IL-2, IL-4, and IL-7.

The gamma subunit of the interleukin-2 receptor is expressed in human monocytes and modulated by interleukin-2, interferon gamma, and transforming growth factor beta 1

The interleukin-2 receptor gamma (IL-2R gamma) chain is a newly recognized component of the IL-2R of lymphoid cells that is required for their response to IL-2. We investigated the expression of IL-2R gamma protein in human monocytes by Western blot analysis using an antiserum specific for IL-2R gamma. We found that IL-2R gamma subunit is constitutively expressed in human monocytes and upregulated by the monocyte-activating factors IL-2 and interferon gamma (IFN gamma). Furthermore, we show that transforming growth factor beta 1 (TGF beta 1) downmodulates, in a dose-dependent manner, basal and IL-2-induced, but not IFN gamma-induced, IL-2R gamma chain expression, and this effect may be responsible for TGF beta 1 suppressive activity on IL-2-activated monocytes. Overall, these results show that the expression of the IL-2R gamma subunit in human monocytes is tightly regulated by the cytokine network, suggesting a critical role played by this protein on monocyte activation.

Heterodimerization of the IL-2 receptor beta- and gamma-chain cytoplasmic domains is required for signalling

The interaction of interleukin-2 (IL-2) and IL-2 receptors critically regulates the T-cell immune response following antigen activation. IL-2 can signal through high or intermediate affinity receptors which contain IL-2R alpha (refs 3, 4) +beta (refs 5-8) +gamma (ref. 9) or beta+gamma chains, respectively. IL-2R gamma is a common gamma chain, gamma c, also shared by the IL-7 (ref. 10) and IL-4 (refs 11, 12) receptors, which when mutated results in X-linked severe combined immunodeficiency. Using chimaeric receptor constructs together with monoclonal or bispecific antibodies we demonstrate here that IL-2 signalling requires ligand-induced extracellular-domain-mediated heterodimerization of the beta- and gamma c-chain cytoplasmic domains. Anti-IL-2R alpha monoclonal antibodies trigger proliferation of cells transfected with chimaeric constructs in which the extracellular domains of IL-2R beta and gamma c are replaced by that of IL-2R alpha. Other experiments using chimaeric constructs indicated that IL-2 binds monomerically and monovalently to IL-2R alpha and that the beta-transmembrane domain is not required for receptor chain interactions. Finally, we provide a method for mapping residues in the gamma c cytoplasmic domain even in cells that constitutively express gamma c.

The molecular basis of X-linked severe combined immunodeficiency: the role of the interleukin-2 receptor gamma chain as a common gamma chain, gamma c

X-linked severe combined immunodeficiency is characterized by severe and persistent infections from early life resulting from profound impairment of both cellular and humoral immune function. XSCID is characterized by an absence or diminished number of T cells and histologic evidence of hypoplastic and abnormal differention of the thymic epithelium. The discovery that this disease results from the mutations of the IL-2R gamma chain was surprising since IL-2-deficient mice and human SCID patients had milder phenotypes. This led to the speculation that IL-2R gamma would prove to be a common gamma chain, gamma c, which would play important roles in other cytokine receptors in addition to the IL-2 receptor. There is now compelling evidence to support a role in at least two other cytokine receptors, namely the IL-4 and IL-7 receptors. Thus, with inactivation of gamma c, multiple cytokine systems are simultaneously affected, resulting in the profoundly impaired phenotype of XSCID. It is possible and even likely that gamma c will be found to be a functional component of additional receptors as well. These findings have resulted in a significant improvement in our understanding of the pathophysiologic development of the defects in XSCID and also have important ramifications for prenatal and postnatal diagnosis, carrier female identification, and gene therapy for XSCID.

High-resolution solution structure of the beta chemokine hMIP-1 beta by multidimensional NMR

The three-dimensional structure of a member of the beta subfamily of chemokines, human macrophage inflammatory protein-1 beta (hMIP-1 beta), has been determined with the use of solution multidimensional heteronuclear magnetic resonance spectroscopy. Human MIP-1 beta is a symmetric homodimer with a relative molecular mass of approximately 16 kilodaltons. The structure of the hMIP-1 beta monomer is similar to that of the related alpha chemokine interleukin-8 (IL-8). However, the quaternary structures of the two proteins are entirely distinct, and the dimer interface is formed by a completely different set of residues. Whereas the IL-8 dimer is globular, the hMIP-1 beta dimer is elongated and cylindrical. This provides a rational explanation for the absence of cross-binding and reactivity between the alpha and beta chemokine subfamilies. Calculation of the solvation free energies of dimerization suggests that the formation and stabilization of the two different types of dimers arise from the burial of hydrophobic residues.

Interleukin-2 receptor gamma chain: a functional component of the interleukin-7 receptor

The interleukin-2 receptor gamma chain (IL-2R gamma) is a necessary component of functional IL-2 receptors. IL-2R gamma mutations result in X-linked severe combined immunodeficiency (XSCID) in humans, a disease characterized by the presence of few or no T cells. In contrast, SCID patients with IL-2 deficiency and IL-2-deficient mice have normal numbers of T cells, suggesting that IL-2R gamma is part of more than one cytokine receptor. By using chemical cross-linking, IL-2R gamma was shown to be physically associated with the IL-7 receptor. The presence of IL-2R gamma augmented both IL-7 binding affinity and the efficiency of internalization of IL-7. These findings may help explain the defects of XSCID. Given its role in more than one cytokine receptor system, the common gamma chain (gamma c) is proposed as the designation for IL-2R gamma.

Tyrosine kinase(s) regulate apoptosis and bcl-2 expression in a growth factor-dependent cell line

Apoptosis (programmed cell death) plays a critical role in many physiological processes, but the mechanism(s) which regulate apoptosis are poorly understood. We demonstrate that in a hematopoietic cell line, which can grow in either interleukin (IL)-2 or IL-3, both of these growth factors can increase bcl-2 mRNA levels and prevent apoptosis normally seen following growth factor withdrawal. Herbimycin A, a protein tyrosine kinase inhibitor, blocks the ability of IL-2 and IL-3 to up-regulate bcl-2 mRNA levels and induces apoptosis. Transfection of a bcl-2 expression vector not only prolongs survival following growth factor withdrawal but also confers resistance to the effect of herbimycin A. We conclude that herbimycin A-sensitive protein tyrosine kinases are involved in the regulation of apoptosis and bcl-2 expression, but these protein tyrosine kinases appear not to be required for the action of Bcl-2 since Bcl-2 can exert its growth survival effect even in the presence of herbimycin A.

Characterization of the human interleukin-2 receptor beta-chain gene promoter: regulation of promoter activity by ets gene products

The interleukin-2 receptor (IL-2R) beta chain (IL-2R beta) is an essential signaling component of high- and intermediate-affinity IL-2Rs. Our laboratory previously reported that a DNA fragment containing 857 bp of 5'-flanking sequence of the human IL-2R beta gene exhibited promoter activity. We have now further characterized the promoter and delineated cis-acting regulatory regions. The region downstream of -363 is critical for basal and phorbol myristate acetate-inducible IL-2R beta promoter activity and contains at least three enhancer-like regions. Among them, the -56 to -34 enhancer was the most potent and had high-level activity in two T-cell lines but not in nonlymphoid HeLaS3 and MG63 cells. This enhancer contains a GGAA Ets binding site which bound two Ets family proteins, Ets-1 and GA-binding protein in vitro. Mutation of the Ets motif strongly diminished both promoter and enhancer activities. We conclude that this Ets binding site plays a key role in regulating basal and phorbol myristate acetate-inducible IL-2R beta promoter activity and may also contribute to tissue-specific expression of the IL-2R beta gene.

Characterization of cDNAs encoding the murine interleukin 2 receptor (IL-2R) gamma chain: chromosomal mapping and tissue specificity of IL-2R gamma chain expression

The IL-2R gamma chain (IL-2R gamma) is an essential component of high- and intermediate-affinity IL-2Rs, playing critical roles for ligand binding and internalization. Recently, our laboratory has demonstrated that IL-2R gamma mutation results in X chromosome-linked severe combined immunodeficiency in humans, suggesting that IL-2R gamma plays a vital role in thymic maturation of human T cells. We now report the isolation and characterization of cDNAs encoding murine IL-2R gamma. The open reading frame encodes 369 aa, identical in length to that encoded by the human IL-2R gamma cDNA. Murine IL-2R gamma and human IL-2R gamma have 69% and 70% identity at the nucleotide and amino acid levels, respectively. As expected, the murine IL-2R gamma retains the WSXWS motif and four cysteine residues characteristic of cytokine receptor superfamily members. IL-2R gamma mRNA distribution shows significant tissue specificity, with particularly high-level expression in spleen and thymus, and higher expression in single-positive (CD4+8- or CD4-8+)-enriched thymocytes than in double-negative (CD4-8-) thymocytes. Finally, we have localized the murine IL-2R gamma gene, Il2rg, to the X chromosome between Rsvp and Plp and demonstrated that a defect in IL-2R gamma is not responsible for the X chromosome-linked xid mutation, which maps to this same region. The cloning of the murine IL-2R gamma cDNA will facilitate the investigation of the role of this protein in lymphocyte function and thymic development.

Characterization of the human interleukin-2 receptor gamma chain gene

The interleukin-2 (IL-2) receptor gamma chain is an essential component of high and intermediate affinity IL-2 receptors (IL-2Rs), playing critical roles for ligand binding and internalization. We report here the isolation and characterization of the genomic locus for human IL-2R gamma, which, like IL-2R beta, is a member of the cytokine receptor superfamily. The IL-2R gamma gene is composed of eight exons and seven introns and spans approximately 4.2 kilobases. Analogous to the IL-2R beta gene, the two pairs of conserved cysteines typical of cytokine receptor superfamily proteins are located in adjacent exons, and the conserved WSXWS motif is located in the exon preceding the one that encodes the transmembrane domain and a small part of the cytoplasmic domain. In each gene, the remainder of the cytoplasmic domain is encoded by the final two exons. Southern blot analysis suggests that IL-2R gamma is encoded by a single copy gene. Cross-hybridizing sequences were detected in DNA derived from a number of other mammalian species but not from yeast. Primer extension analysis and ribonuclease protection assays revealed that there are three principal transcription initiation sites located 32-38 nucleotides 5' to the translation initiation AUG codon. These sites are upstream of the 5' end of the published IL-2R gamma cDNA sequence. The region 5' to the transcription initiation sites exhibited promoter activity when cloned upstream of the luciferase reporter gene. With this study, the organization of the genes encoding all three chains (alpha, beta, and gamma) of the IL-2 receptor has been determined and promoters for each identified.

Interleukin-2 receptor gamma chain mutation results in X-linked severe combined immunodeficiency in humans

The interleukin-2 (IL-2) receptor gamma chain (IL-2R gamma) is a component of high and intermediate affinity IL-2 receptors that is required to achieve full ligand binding affinity and internalization. We have localized the IL-2R gamma gene to human chromosome Xq13. Genetic linkage analysis indicates that the IL-2R gamma gene and the locus for X-linked severe combined immunodeficiency (XSCID) appear to be at the same position. Moreover, we demonstrate that each of three unrelated patients with XSCID has a different mutation in his IL-2R gamma gene resulting in a different premature stop codon and predicted C-terminal truncation. These data establish that XSCID is associated with mutations of the IL-2R gamma gene product. Since XSCID is characterized by absent or markedly reduced numbers of T cells, our findings imply that IL-2R gamma plays a vital role in thymic maturation of T cells. These results also have important implications for prenatal and postnatal diagnosis, carrier female detection, and gene therapy for XSCID.

Characterization of a receptor for macrophage inflammatory protein 1 alpha and related proteins on human and murine cells

Macrophage inflammatory protein 1 alpha (MIP-1 alpha) is a potent stem cell inhibitor and a member of a large and expanding family of related cytokines. In an effort to understand the molecular basis of the activities of MIP-1 alpha, we have sought to characterize the cellular receptors for this molecule. Our results demonstrate the presence of abundant MIP-1 alpha receptors on both human and murine cells. The receptor on K562 cells can bind a range of members of the MIP-1 alpha family and may thus be a general MIP-1 alpha family receptor. Murine FDCPmix cells also bind a range of members of this peptide family, although the receptor(s) that they express appear somewhat more selective for peptides capable of displaying stem cell inhibitory properties. The human and murine receptors do not bind members of the related interleukin 8 family of peptides and are thus distinct from the recently cloned interleukin 8 receptor. We suggest that the receptor on the murine cell is a candidate for the receptor responsible for articulating stem cell inhibitory signals following MIP-1 alpha binding.

Activation of tumor necrosis factor-alpha production from human neutrophils by IL-2 via IL-2-R beta

In addition to T cells, NK cells, B cells, and monocytes, we provide new evidence that human polymorphonuclear neutrophils (PMN) can be functionally activated by IL-2 via binding to IL-2R beta expressed on the cell surface. Brief exposure of normal PMN to human rIL-2 enhanced both transcriptional and translational expression of TNF-alpha. The release of TNF-alpha protein by IL-2-treated PMN was inhibitable by a specific mAb against human IL-2-R beta. The response to IL-2 was dose and time dependent with the increase in TNF-alpha mRNA detected maximally 3 h after IL-2 exposure, followed by a continuous maintenance of high mRNA levels up to 18 h. The TNF-alpha mRNA was significantly increased above the medium control level, with as little as 10 U/ml of IL-2. Maximal transcription was obtained with 1000 U/ml of IL-2, which achieved the level observed with known neutrophil activating factors such as granulocyte-macrophage-CSF, IL-8, and Candida albicans. Using actinomycin D, it was found that new and continuous synthesis of a labile TNF-alpha mRNA was responsible for the observed high levels of transcripts. Of significance was the observation that cycloheximide could selectively modulate TNF-alpha mRNA transcription in neutrophils, depending on the cytokine used. Cycloheximide did not affect or alter TNF-alpha mRNA induction in IL-2-treated neutrophils but abrogated it in granulocyte-macrophage-CSF-treated neutrophils and superinduced transcription in C. albicans-treated neutrophils. Thus various control elements must be involved in the transcription of the TNF-alpha genes that are responsive to different cytokines and activating factors. The induction of TNF-alpha and functional activation of neutrophils by IL-2 is therefore an important immunomodulatory property of IL-2 that has not heretofore been recognized.

Activation of tumor necrosis factor-alpha production from human neutrophils by IL-2 via IL-2-R beta

In addition to T cells, NK cells, B cells, and monocytes, we provide new evidence that human polymorphonuclear neutrophils (PMN) can be functionally activated by IL-2 via binding to IL-2R beta expressed on the cell surface. Brief exposure of normal PMN to human rIL-2 enhanced both transcriptional and translational expression of TNF-alpha. The release of TNF-alpha protein by IL-2-treated PMN was inhibitable by a specific mAb against human IL-2-R beta. The response to IL-2 was dose and time dependent with the increase in TNF-alpha mRNA detected maximally 3 h after IL-2 exposure, followed by a continuous maintenance of high mRNA levels up to 18 h. The TNF-alpha mRNA was significantly increased above the medium control level, with as little as 10 U/ml of IL-2. Maximal transcription was obtained with 1000 U/ml of IL-2, which achieved the level observed with known neutrophil activating factors such as granulocyte-macrophage-CSF, IL-8, and Candida albicans. Using actinomycin D, it was found that new and continuous synthesis of a labile TNF-alpha mRNA was responsible for the observed high levels of transcripts. Of significance was the observation that cycloheximide could selectively modulate TNF-alpha mRNA transcription in neutrophils, depending on the cytokine used. Cycloheximide did not affect or alter TNF-alpha mRNA induction in IL-2-treated neutrophils but abrogated it in granulocyte-macrophage-CSF-treated neutrophils and superinduced transcription in C. albicans-treated neutrophils. Thus various control elements must be involved in the transcription of the TNF-alpha genes that are responsive to different cytokines and activating factors. The induction of TNF-alpha and functional activation of neutrophils by IL-2 is therefore an important immunomodulatory property of IL-2 that has not heretofore been recognized.

Function associated with IL-2 receptor-beta on human neutrophils. Mechanism of activation of antifungal activity against Candida albicans by IL-2

Polymorphonuclear neutrophils (PMN) are essential components of the host defense system against a wide variety of pathogens. We report here the novel finding that freshly isolated human PMN constitutively express detectable surface levels of IL-2R beta, but not IL-2R alpha, as analyzed by flow cytometry. Northern blot analysis confirmed the constitutive expression of mRNA for IL-2R beta in PMN. Scatchard analysis using 125I-labeled IL-2 demonstrated the presence of approximately 600 intermediate binding IL-2R per PMN, with a dissociation constant of 1.1 x 10(-9) M, similar to that of IL-2 binding to YT-1 tumor cells that specifically express IL-2R beta. More importantly, PMN were able to respond functionally to IL-2 by enhanced growth-inhibitory activity against an opportunistic fungal pathogen, Candida albicans. IL-2 activation of antifungal activity was dose-dependent, with some functional activation detected at 1 U/ml of rIL-2 and maximal activation at 1000 U/ml. The action of IL-2 was rapid, with maximal PMN activation after 30-min incubation with IL-2. The IL-2 enhancement of antifungal activity could be blocked by a specific antibody against IL-2R beta, but not by anti-IL-2R alpha. Analysis of the mechanism of IL-2 activation of PMN indicated that oxidative metabolism, as measured by superoxide anion production, was not involved. Instead, PMN release of lactoferrin appeared to be responsible for the heightened activity against C. albicans in IL-2-treated PMN. Not only was lactoferrin detected in the supernatants of IL-2-treated PMN, but also the antifungal activity of PMN activated by IL-2 could be blocked in the presence of antilactoferrin. These results, taken together, indicate that normal PMN are capable of functionally responding to IL-2 via expression of the IL-2R beta chain.

N-terminal DNA-binding domains contribute to differential DNA-binding specificities of NF-kappa B p50 and p65

We previously reported that either oxidation or alkylation of NF-kappa B in vitro abrogates DNA binding. We used this phenomenon to help elucidate structural determinants of NF-kappa B binding. We now demonstrate that Cys-62 of NF-kappa B p50 mediates the redox effect and lies within an N-terminal region required for DNA binding but not for dimerization. Several point mutations in this region confer a transdominant negative binding phenotype to p50. The region is highly conserved in all Rel family proteins, and we have determined that it is also critical for DNA binding of NF-kappa B p65. Replacement of the N-terminal region of p65 with the corresponding region from p50 changes its DNA-binding specificity towards that of p50. These data suggest that the N-terminal regions of p50 and p65 are critical for DNA binding and help determine the DNA-binding specificities of p50 and p65. We have defined within the N-terminal region a sequence motif, R(F/G)(R/K)YXCE, which is present in Rel family proteins and also in zinc finger proteins capable of binding to kappa B sites. The potential significance of this finding is discussed.

Function associated with IL-2 receptor-beta on human neutrophils. Mechanism of activation of antifungal activity against Candida albicans by IL-2

Polymorphonuclear neutrophils (PMN) are essential components of the host defense system against a wide variety of pathogens. We report here the novel finding that freshly isolated human PMN constitutively express detectable surface levels of IL-2R beta, but not IL-2R alpha, as analyzed by flow cytometry. Northern blot analysis confirmed the constitutive expression of mRNA for IL-2R beta in PMN. Scatchard analysis using 125I-labeled IL-2 demonstrated the presence of approximately 600 intermediate binding IL-2R per PMN, with a dissociation constant of 1.1 x 10(-9) M, similar to that of IL-2 binding to YT-1 tumor cells that specifically express IL-2R beta. More importantly, PMN were able to respond functionally to IL-2 by enhanced growth-inhibitory activity against an opportunistic fungal pathogen, Candida albicans. IL-2 activation of antifungal activity was dose-dependent, with some functional activation detected at 1 U/ml of rIL-2 and maximal activation at 1000 U/ml. The action of IL-2 was rapid, with maximal PMN activation after 30-min incubation with IL-2. The IL-2 enhancement of antifungal activity could be blocked by a specific antibody against IL-2R beta, but not by anti-IL-2R alpha. Analysis of the mechanism of IL-2 activation of PMN indicated that oxidative metabolism, as measured by superoxide anion production, was not involved. Instead, PMN release of lactoferrin appeared to be responsible for the heightened activity against C. albicans in IL-2-treated PMN. Not only was lactoferrin detected in the supernatants of IL-2-treated PMN, but also the antifungal activity of PMN activated by IL-2 could be blocked in the presence of antilactoferrin. These results, taken together, indicate that normal PMN are capable of functionally responding to IL-2 via expression of the IL-2R beta chain.

Interleukin (IL)-2 and IL-3 induce distinct but overlapping responses in murine IL-3-dependent 32D cells transduced with human IL-2 receptor beta chain: involvement of tyrosine kinase(s) other than p56lck

We have established IL-3-dependent 32D myeloid progenitor cells stably expressing the human IL-2 receptor beta chain (IL-2R beta). Whereas parental 32D cells proliferated only in response to IL-3, the transduced cells also proliferated in response to IL-2. Transduced cells expressed high- and intermediate-affinity IL-2Rs, resulting from expression of human IL-2R beta and murine IL-2R alpha chain (IL-2R alpha). IL-2 induced phenotypic changes not induced by IL-3, including the upregulated expression of endogenous murine IL-2R alpha and IL-2R beta and an increase in cell size. Therefore, the transduced IL-2R beta was not merely coupling with the IL-3 signaling pathway. IL-3 augmented several IL-2-induced responses including the up-regulation of IL-2R alpha. Both IL-2- and IL-3-induced proliferation and IL-2 induced IL-2R alpha expression were inhibited by the tyrosine kinase inhibitor herbimycin A. Thus, both IL-2- and IL-3-mediated effects required tyrosine kinase activity. The identity of the tyrosine kinase(s) mediating the IL-2 signals in these cells is not known but cannot be p56lck, a tyrosine kinase found in T cells, since 32D-IL-2R beta cells do not express p56lck.

Interleukin (IL)-2 activation of p21ras in murine myeloid cells transfected with human IL-2 receptor beta chain

The T cell growth factor interleukin-2 (IL-2) induces p21ras activation in T lymphocytes. To determine whether the IL-2 receptor (IL-2R) can regulate p21ras when expressed in a non-T cell environment we have examined the ability of IL-2 to activate p21ras in 32D murine myeloid progenitor cells transduced with human IL-2R beta chains. These cells are denoted beta 53 cells. 32D cells normally proliferate in response to IL-3 but the expression of the IL-2R beta chain confers IL-2 responsiveness to the cells. Our data show that IL-3 is able to activate p21ras in the parental 32D cells and both IL-2 and IL-3 can stimulate p21ras in the IL-2R-expressing beta 53 clone of 32D. In T lymphocytes, activation of protein kinase C (PKC) with phorbol esters is sufficient to stimulate p21ras. However, in 32D and beta 53 cells activation of PKC with phorbol esters does not result in p21ras activation even though these cells express functional PKC. It appears, therefore, that a PKC-mediated pathway for p21ras regulation exists in T lymphocytes but not in 32D cells. The IL-2R can couple to p21ras independently of the concomitant presence of the PKC pathway for p21ras regulation. These data imply that multiple intracellular mechanisms may exist to regulate p21ras and that cells of different lineages may differ with regard to p21ras regulation.

The gene encoding the Act-2 cytokine. Genomic structure, HTLV-I/Tax responsiveness of 5' upstream sequences, and chromosomal localization

Act-2 is a cytokine that belongs to a superfamily of structurally related proteins. Act-2 expression is rapidly induced in T cells, B cells, and monocytes upon mitogenic stimulation. The Act-2 genomic locus is on chromosome 17q. The exons and exon/intron splice junctions have been sequenced, as have the sequences upstream of exon 1. A classical TATA box is located immediately upstream of the transcription initiation site. The upstream sequences possess promoter activity and can be functionally activated after treatment of Jurkat T cells with phythohemagglutinin plus phorbol myristrate acetate. In addition, Act-2 promoter chloramphenicol acetyltransferase constructs are expressed in human T cell lymphotropic virus type I (HTLV-I)-infected MT-2 cells and in Jurkat cells which can be induced to express the transactivator gene (tax) product of HTLV-I.

Modulation of transcription factor NF-kappa B binding activity by oxidation-reduction in vitro

NF-kappa B is a widely used regulator of inducible and tissue-specific gene control. In the cytosol, when complexed to an inhibitory molecule, I kappa B, NF-kappa B is in an inactive form and cannot bind DNA. Activation of cells with appropriate stimuli results in the dissociation of NF-kappa B from I kappa B and its translocation to the nucleus as an active binding protein. We now demonstrate that NF-kappa B binding in vitro can be inhibited by agents that modify free sulfhydryls. Binding is eliminated after treatment with N-ethylmaleimide, an alkylating agent, and diamide, an oxidizing agent. The diamide effect can be reversed by 2-mercaptoethanol. Further, 2-mercaptoethanol acts synergistically with deoxycholate plus Nonidet P-40 in converting inactive cytosolic NF-kappa B to an active DNA-binding form. It is therefore possible that modulation of the redox state of NF-kappa B could represent a post-translational control mechanism for this factor.