Smad2 and 3 mediate transforming growth factor-beta1-induced inhibition of chondrocyte maturation

Transforming growth factor-beta (TGF-beta) is a multifunctional regulator of a variety of cellular functions, including proliferation, differentiation, matrix synthesis, and apoptosis. In growth plate chondrocytes, TGF-beta slows the rate of maturation. Because the current paradigm of TGF-beta signaling involves Smad proteins as downstream regulators of target genes, we have characterized their role as mediators of TGF-beta effects on chondrocyte maturation. Both Smad2 and 3 translocated to the nucleus upon TGF-beta1 signaling, but not upon BMP-2 signaling. Cotransfection experiments using the TGF-beta responsive and Smad3 sensitive p3TP-Lux luciferase reporter demonstrated that wild-type Smad3 potentiated, whereas dominant negative Smad3 inhibited TGF-beta1 induced luciferase activity. To confirm the role of Smad2 and 3 as essential mediators of TGF-beta1 effects on chondrocyte maturation, we overexpressed both wild-type and dominant negative Smad2 and 3 in virally infected chondrocyte cultures. Overexpression of both wild-type Smad2 and 3 potentiated the inhibitory effect of TGF-beta on chondrocyte maturation, as determined by colx and alkaline phosphatase activity, whereas dominant negative Smad2 and 3 blocked these effects. Wild-type and dominant negative forms of Smad3 had more pronounced effects than Smad2. Our results define Smad2 and 3 as key mediators of the inhibitory effect of TGF-beta1 signaling on chondrocyte maturation.

Tumor metastasis and the reciprocal regulation of prometastatic and antimetastatic factors by nuclear factor kappaB

To investigate the role of the transcription factor nuclear factor kappaB (NFkappaB) in tumor metastasis, we generated a murine lung alveolar carcinoma cell line (Line 1) defective in NFkappaB-signaling by retroviral delivery of a dominant negative inhibitor of NFkappaB. The NFkappaB signal blockade resulted in the down-regulation of prometastatic matrix metalloproteinase 9, a urokinase-like plasminogen activator, and heparanase and reciprocal up-regulation of antimetastatic tissue inhibitors of matrix metalloproteinases 1 and 2 and plasminogen activator inhibitor 2. NFkappaB signal blockade did not affect tumor cell proliferation in vitro or in vivo but prevented intravasation of tumor cells in an in vivo chick chorioallantoic membrane model of metastasis as well as spontaneous metastasis in a murine model. These findings suggest that NFkappaB plays a central and specific role in the regulation of tumor metastasis and may be an important therapeutic target for development of antimetastatic cancer treatments.

Quantitative small-animal surrogate to evaluate drug efficacy in preventing wear debris-induced osteolysis

Individuals who suffer from severe joint destruction caused by the various arthritidies often undergo total joint arthroplasty. A major limitation of this treatment is the development of aseptic loosening of the prosthesis in as many as 20% of patients. The current paradigm to explain aseptic loosening proposes that wear debris generated from the prosthesis initiates a macrophage-mediated inflammatory response by resident macrophages, leading to osteoclast activation and bone resorption at the implant interface. No therapeutic interventions have been proved to prevent or inhibit aseptic loosening. The development of therapeutic strategies is limited due to the absence of a quantitative surrogate in which drugs can be screened rapidly in large numbers of animals. We have previously described a model in which titanium particles implanted on mouse calvaria induce an inflammatory response with osteolysis similar to that observed in clinical aseptic loosening. Here, we present new methods by which the osteolysis in this model can be quantified. We determined that 6-8-week-old mice in normal health have a sagittal suture area of 50 (+/-6) microm2, which contains approximately five osteoclasts. As a result of the titanium-induced inflammation and osteolysis, the sagittal suture area increases to 197 (+/-27) microm2, with approximately 30 osteoclasts, after 10 days of treatment. The sagittal suture area and the number of osteoclasts in the calvaria of sham-treated mice remained unchanged during the 10 days. We also determined the effects of pentoxifylline, a drug that blocks the responses of tumor necrosis factor-alpha to wear debris, and the osteoclast inhibitor alendronate. We found that both drugs effectively block wear debris-induced osteolysis but not osteoclastogenesis. In conclusion, we found the measurements made with this model to be reproducible and to permit quantitative analysis of agents that are to be screened for their potential to prevent aseptic loosening.

The adeno-associated virus vector for orthopaedic gene therapy

During the last decade researchers working with recombinant adeno-associated virus have shown the use of this vector for efficient and long-term gene transfer in various tissues including lung, muscle, brain, spinal cord, retina, and liver. In 1999 the first results documenting the use of this vector in transducing joint cells were published. Additional advantages of recombinant adeno-associated virus for in vivo gene therapy are: (1) its ability to transduce nondividing cells; (2) site-specific integration into the host genome; (3) high viral titer (> 10(13)/mL); and (4) the vector is not cytotoxic and does not provoke a significant immune response. Most important, several groups have documented the ability to deliver sustained transgene expression in an immunocompetent host for more than 1 year, and that curative levels of gene product (factor IX), from one injection is sustained long-term in a large animal (hemophilia B dog). Comparable results have not been achieved with any other vector to date. As a result of this work the first Phase I clinical trials using recombinant adeno-associated virus are under way for cystic fibrosis. The history of the recombinant adeno-associated virus vector and its future promise for orthopaedic gene therapies are described. The goal of the current review is to provide the reader with an understanding of the advantages and disadvantages of this vector for treatment of musculoskeletal diseases. Additional information concerning recombinant adeno-associated virus can be obtained in more general reviews.

NF-kappa B regulates VCAM-1 expression on fibroblast-like synoviocytes

Expression of VCAM-1 on synovial fibroblasts is a clinical hallmark of rheumatoid arthritis. The interaction of VCAM-1 and its integrin receptor very late Ag-4 is believed to be critically involved in the recruitment and retention of immune cells in the inflamed joints. To study the regulation of VCAM-1 in synovial fibroblasts, fibroblast-like synoviocytes (FLS) were isolated from the knee joints of normal mice and passaged repeatedly to obtain a homogeneous cell population. We have found that VCAM-1 is constitutively expressed on mouse FLS (mFLS) and that its surface expression is further increased after exposure to TNF-alpha. Nuclear translocation of transcription factor NF-kappa B including P50/P50 homodimer and P65/P50 heterodimer was activated by TNF-alpha treatment. In mFLS stably expressing a dominant-negative mutant of the inhibitory protein I-kappa B alpha- (mI-kappa B), which does not undergo proteolytic degradation, NF-kappa B remains in the cytosol and its activation in response to TNF-alpha is abolished. VCAM-1 protein expression after TNF-alpha stimulation was blocked in cells expressing the mI-kappa B. This effect is likely due to the loss of NF-kappa B-mediated transcription of VCAM-1, because the 5-fold increase in mRNA levels in response to TNF-alpha is absent in the mutant cells. To confirm these findings, we transduced mFLS with an adenoviral vector containing the mI-kappa B transgene. VCAM-1 expression was also blocked by mI-kappa B in this system, whereas cells transduced with a control adenoviral vector remained responsive to TNF-alpha. These results indicate that NF-kappa B mediates TNF-alpha-induced VCAM-1 expression on mFLS.

PTHrP expression in chondrocytes, regulation by TGF-beta, and interactions between epiphyseal and growth plate chondrocytes

Although PTHrP has been identified as a key regulator of chondrocyte differentiation in the growth plate, the factors directly regulating PTHrP expression have not been identified. Furthermore, while cells from the epiphysis are considered the physiologic source of PTHrP, the relative expression of PTHrP in epiphyseal and growth plate chondrocytes has not been defined. PTHrP expression was examined in chondrocytes isolated from 3- to 5-week-old chick long bones. The expression of PTHrP mRNA was 10-fold higher in epiphyseal chondrocytes compared to cells from the growth plate. Growth plate chondrocytes were isolated into populations with distinct maturational characteristics by countercurrent centrifugal elutriation and analyzed for PTHrP expression. The expression was highest in the least mature cells and progressively declined with the onset of maturation. The regulation of PTHrP expression was further examined in epiphyseal chondrocytes. Both TGF-beta1 and cis-retinoic acid stimulation markedly increased PTHrP mRNA levels, while BMP-2 and PTHrP stimulation decreased the expression of this transcript. The effects of TGF-beta1 (8.9-fold stimulation) and TGF-beta3 (9.2-fold) were slightly greater than the effects of TGF-beta2 (4.9-fold). The effect of TGF-beta was dose-dependent and increases could be detected after 68 h of treatment. To analyze the paracrine effect of epiphyseal and growth plate chondrocytes on each other, these cells were placed in coculture and the mRNA from each of the populations was harvested separately after 24 h. Following coculture the PTHrP mRNA levels increased in the epiphyseal cells while the expression of type X collagen and Indian hedgehog transcripts decreased in growth plate chondrocytes. The results demonstrate potentially important paracrine interactions between these cell populations, possibly mediated by TGF-beta and PTHrP.

Tumor necrosis factor-alpha/nuclear transcription factor-kappaB signaling in periprosthetic osteolysis

Due to irreversible joint destruction caused by the various arthritides, more than 400,000 total joint arthroplasties are performed each year in the United States. As many as 20% of these require revision surgery because of aseptic loosening. The current paradigm to explain aseptic loosening is that wear debris generated from the prosthesis stimulates the release of proinflammatory cytokines (i.e., tumor necrosis factor-alpha and interleukins 1 and 6) following phagocytosis by resident macrophages. These cytokines, in turn, initiate an inflammatory response, with the development of an erosive pannus that stimulates bone resorption by osteoclasts. In support of this model, we have previously shown that human monocytes produce large quantities of tumor necrosis factor-alpha in response to titanium particles in vitro. In the current study, we characterized the role of tumor necrosis factor-alpha/nuclear transcription factor-kappaB signaling in the proinflammatory response to titanium particles in vitro and in vivo. Using the mouse macrophage cell line J774, we showed that these cells produce an amount of tumor necrosis factor-alpha in response to titanium particles similar to that produced by human peripheral blood monocytes. The production of tumor necrosis factor-alpha was preceded by a drop in cellular levels of inhibitory factor-kappaBalpha protein and translocation of p50/p65 nuclear transcription factor-KB to the nucleus 30 minutes after stimulation. Levels of tumor necrosis factor-alpha and inhibitory factor-kappaBalpha mRNA increased 30 minutes after stimulation, consistent with the activation of nuclear transcription factor-kappaB. Interleukin-6 mRNA was first seen 4 hours after the addition of the titanium particles, indicating that the production of this cytokine is secondary to the immediate nuclear transcription factor-kappaB response. To test the relevance of tumor necrosis factor-alpha/nuclear transcription factor-kappaB signaling in response to titanium particles in vivo, we adopted an animal model in which the particles were surgically implanted on the calvaria of mice. The animals displayed a dramatic histological response to the debris, with the formation of fibrous tissue and extensive bone resorption after only 1 week. With use of immunohistochemistry and tartrate-resistant acid phosphatase staining, tumor necrosis factor-alpha and osteoclasts were readily detected at the site of inflammation and bone resorption in the calvaria of the treated mice. By testing mice that genetically over-produce tumor necrosis factor-alpha (hTNFalpha-Tg), those defective in tumor necrosis factor-alpha signaling (TNF-RI-/-), and those that are nuclear transcription factor-kappaB1-deficient (NFkappaB1-/-), we evaluated the importance of tumor necrosis factor-alpha/nuclear transcription factor-kappaB signaling in the biological processes responsible for aseptic loosening. The hTNFalpha-Tg mice had a grossly exaggerated response, the TNF-RI(-/-) mice showed little evidence of inflammation or bone resorption, and the nuclear transcription factor-kappaB1(-/-) mice had an inflammatory response without bone resorption. On the basis of these results, we propose a model for periprosthetic osteolysis in which wear debris particles are phagocytosed by macrophages, resulting in the activation of nuclear transcription factor-kappaB and the production of tumor necrosis factor-alpha. Tumor necrosis factor-alpha directly induces fibroblast proliferation and tissue fibrosis and recruits or activates, or both, osteoclasts to resorb adjacent bone.

Empirical advantages of adeno associated viral vectors in vivo gene therapy for arthritis

OBJECTIVE

To evaluate the utility of the adeno associated viral (AAV) vector for gene delivery to joint cells in vivo and in vitro, and to assess its potential as a vector for arthritis gene therapy.

METHODS

A recombinant AAV (rAAV) vector expressing the bacterial beta-galactosidase (beta-gal) gene (rAAV-CMV-LacZ) was directly introduced into healthy-normal mouse knees, or arthritic knees in mice overexpressing tumor necrosis factor-alpha (hTNFalpha-Tg). Beta-gal expression levels were determined by immunohistochemistry and chemiluminescence. The transduction efficiency of this vector on primary fibroblast-like synoviocytes (FLS) in vitro was determined by FACS. The effects of UV and gamma-irradiation as well as TNF-alpha on transduction efficiency were determined using the same methods.

RESULTS

We found little evidence of rAAV transduction in the joint cells of healthy mice. Target gene expression was detected in all animals at Day 3, and peaked at Day 7 before returning to baseline levels 21 days after injection. In contrast, synoviocytes, articular chondrocytes, and meniscal cells of diseased mice were transduced by rAAV-CMV-LacZ in hTNFalpha-Tg animals. Transduction efficiencies correlated with joint damage, and target gene expression was up to 10-fold greater than that seen in the normal mice. In vitro, we found that rAAV transduction of FLS can be enhanced by pretreatment with UV or gamma-irradiation and TNF-alpha stimulation.

CONCLUSION

We find that rAAV vectors have several empirical advantages for in vivo gene therapy for arthritis: (1) rAAV preferentially transduces arthritic joint cells in vivo. (2) rAAV can transduce both FLS and chondrocytes in vivo. (3) rAAV transduction of FLS can be augmented by pretreatment with agents that induce DNA repair enzymes.

Anti-TNF-alpha therapy as a clinical intervention for periprosthetic osteolysis

Aseptic loosening of total joint arthroplastics due to periprosthetic osteolysis is a frequent cause of implant failure. The absence of clinical interventions to arrest or prevent this complication limits the use of total joint replacement especially in younger patients. Here we review recent studies implicating tumor necrosis factor (TNF)-alpha in periprosthetic osteolysis and the rationale for clinical studies of anti-TNF therapy and other interventions for periprosthetic loosening.

NF-kappaB-mediated inhibition of apoptosis is required for encephalomyocarditis virus virulence: a mechanism of resistance in p50 knockout mice

Apoptosis is a central host defense mechanism to eliminate virus-infected cells. Activation of NF-kappaB suppresses apoptosis following some types of stimulation in vitro. To test the physiological importance of this pathway in vivo, we studied murine encephalomyocarditis virus (EMCV) infection in mice and cell lines defective in NF-kappaB1 (p50) signaling. As previously reported, we find that all p50 knockout (p50 -/-) mice survive an EMCV infection that readily kills normal mice. By introducing the p50 mutation into interferon (IFN) type I receptor knockout (IFNRI -/-) mice, we find that this resistance is not mediated by IFN-beta as previously thought. While no IFNRI -/- mice survive, the double-knockout mice survive 60% of the time. The survival is tightly linked to the animals' ability to clear the virus from the heart in vivo. Using murine embryonic fibroblasts (MEF) derived from wild-type, p50 -/-, and p65 -/- embryos, we found that NF-kappaB is not required for the replication cycle of EMCV. However, during these experiments we observed that p50 -/- and p65 -/- MEF infected with EMCV undergo enhanced, premature cytotoxicity. Upon examination of this cell death, we found that EMCV infection induced both plasma membrane and nuclear changes typical of apoptosis in all cell lines. These apoptotic processes occurred in an accelerated and pronounced way in the NF-kappaB-defective cells, as soon as 6 h after infection, when virus is beginning to be released. Previously, only the RelA (p65) subunit of NF-kappaB has been shown to play a role in suppressing apoptosis. In our studies, we find that p50 is equally important in suppressing apoptosis during EMCV infection. Additionally, we show that suppression of apoptosis by NF-kappaB1 is required for EMCV virulence in vivo. The attenuation in p50 -/- mice can be explained by rapid apoptosis of infected cells which allows host phagocytes to clear infected cells before the viral burst leading to a reduction of the viral burden and survival of the mice.

Calx, a Na-Ca exchanger gene of Drosophila melanogaster

We have cloned Calx, a gene that encodes a Na-Ca exchanger of Drosophila melanogaster. Calx encodes two repeated motifs, Calx-alpha and Calx-beta, that overlap domains required for exchanger activity and regulation. Calx has multiple transcripts in adults, including at least one expressed in the retina. The Calx genomic locus comprises >/=35 kb between the Atpalpha and rudimentary-like genes in chromosomal region 93B. In Xenopus oocytes, microinjected Calx cRNA induces calcium uptake like that of its homolog, the 3Na+-1Ca2+ exchanger of mammalian heart. Implications of Calx-alpha motifs for the mechanism of Na-Ca exchange are discussed.

Structure-function studies of p38 mitogen-activated protein kinase. Loop 12 influences substrate specificity and autophosphorylation, but not upstream kinase selection

Several mitogen-activated protein kinase (MAPK) cascades have been identified in eukaryotic cells. The activation of MAPKs is carried out by distinct MAPK kinases (MEKs or MKKs), and individual MAPKs have different substrate preferences. Here we have examined how amino acid sequences encompassing the dual phosphorylation motif located in the loop 12 linker (L12) between kinase subdomains VII and VIII and the length and amino acid sequence of L12 influence autophosphorylation, substrate specificity, and upstream kinase selectivity for the MAPK p38. Conversion of L12 of p38 to an "ERK-like" structure was accomplished in several ways: (i) by replacing glycine with glutamate in the dual phosphorylation site, (ii) by placing a six-amino acid sequence present in L12 of ERK (but absent in p38) into p38, and (iii) by mutations of amino acid residues in loop 12. Two predominant effects were noted: (i) the Xaa residue in the dual phosphorylation motif Thr-Xaa-Tyr as well as the length of L12 influence p38 substrate specificity, and (ii) the length of L12 plays a major role in controlling autophosphorylation. In contrast, these modifications do not result in any change in the selection of p38 by individual MAPK kinases.

Immunological defects in mice with a targeted disruption in Bcl-3

The proto-oncogene bcl-3 is a member of the IkappaB family. The Bcl-3 protein is known to interact specifically with the p50 and p52 subunits of NFkappaB. However, the function of this interaction is not well understood. To determine the in vivo role of Bcl-3, mice were generated that lack the bcl-3 gene, Bcl 3(-/-). Here we report that Bcl 3(-/-) mice appear developmentally normal, but exhibit severe defects in humoral immune responses and protection from in vivo pathogenic challenges. Relative to wild-type mice, Bcl 3(-/-) mice are unable to clear L. monocytogenes and are more susceptible to infection with S. pneumoniae. This phenotype is similar to that observed in the p50(-/-) mice and the cross between the Bcl-3(-/-) and p50(-/-) mice generates animals with an enhanced phenotype. In accordance with the observed defects in their immune response, the Bcl 3(-/-) mice have normal immunoglobulin levels before and after immunization, but fail to produce antigen-specific antibodies. Additionally, spleens from Bcl-3(-/-) mice are abnormal and void of germinal centers. In contrast, the p50(-/-) mice have normal germinal centers. We propose that in in vivo, Bcl-3 can function independently of p50.

Anomalous regulation of the Drosophila Na(+)-Ca2+ exchanger by Ca2+

The Na(+)-Ca2+ exchanger from Drosophila was expressed in Xenopus and characterized electrophysiologically using the giant excised patch technique. This protein, termed Calx, shares 49% amino acid identity to the canine cardiac Na(+)-Ca2+ exchanger, NCX1. Calx exhibits properties similar to previously characterized Na(+)-Ca2+ exchangers including intracellular Na+ affinities, current-voltage relationships, and sensitivity to the peptide inhibitor, XIP. However, the Drosophila Na(+)-Ca2+ exchanger shows a completely opposite response to cytoplasmic Ca2+. Previously cloned Na(+)-Ca2+ exchangers (NCX1 and NCX2) are stimulated by cytoplasmic Ca2+ in the micromolar range (0.1-10 microM). This stimulation of exchange current is mediated by occupancy of a regulatory Ca2+ binding site separate from the Ca2+ transport site. In contrast, Calx is inhibited by cytoplasmic Ca2+ over this same concentration range. The inhibition of exchange current is evident for both forward and reverse modes of transport. The characteristics of the inhibition are consistent with the binding of Ca2+ at a regulatory site distinct from the transport site. These data provide a rational basis for subsequent structure-function studies targeting the intracellular Ca2+ regulatory mechanism.

Constitutive phosphorylation of IkappaBalpha by casein kinase II occurs preferentially at serine 293: requirement for degradation of free IkappaBalpha

IkappaBalpha is a phosphoprotein that sequesters the NF-kappaB/Rel transcription factors in the cytoplasm by physical association. Following induction by a wide variety of agents, IkappaBalpha is further phosphorylated and degraded, allowing NF-kappaB/Rel proteins to translocate to the nucleus and induce transcription. We have previously reported that the constitutive phosphorylation site resides in the C-terminal PEST region of IkappaBalpha and is phosphorylated by casein kinase II (CKII). Here we show that serine 293 is the preferred CKII phosphorylation site. Additionally, we show compensatory phosphorylation by CKII at neighboring serine and threonine residues. Thus, only when all five of the serine and threonine residues in the C-terminal region of IkappaBalpha are converted to alanine (MutF), is constitutive phosphorylation abolished. Finally, we show that constitutive phosphorylation is required for efficient degradation of free IkappaBalpha, in that unassociated Mutf has a half-life two times longer than wild-type IkappaBalpha. A serine residue alone at position 293, as well as aspartic acid at this position, can revert the Mutf phenotype. Therefore, the constitutive CKII phosphorylation site is an integral part of the PEST region of IkappaBalpha, and this phosphorylation is required for rapid proteolysis of the unassociated protein.

Constitutive phosphorylation of I kappa B alpha by casein kinase II

The NF-kappa B/Rel proteins are sequestered in the cytoplasm in association with the phosphorylated form of I kappa B alpha. Upon induction with a wide variety of agents, the activity of NF-kappa B/Rel proteins is preceded by the rapid degradation of I kappa B alpha protein. We report the identification and partial purification of a cellular kinase from unstimulated or stimulated murine cells, which specifically phosphorylates the C terminus of I kappa B alpha. There are several consensus sites for casein kinase II (CKII) in the C-terminal region of I kappa B alpha. Additionally, the activity of the cellular kinase is blocked by antibodies against the alpha subunit of CKII. No phosphorylation of the C-terminal region of I kappa B alpha can be detected if the five possible serine and threonine residues that can be phosphorylated by CKII are mutated to alanine. A two-dimensional tryptic phosphopeptide map of I kappa B alpha from unstimulated cells was identical to that obtained by in vitro phosphorylation of I kappa B alpha with the partially purified cellular kinase. We propose that constitutive phosphorylation of I kappa B alpha is carried out by CKII.

Cellular and humoral immune responses to adenoviral vectors containing factor IX gene: tolerization of factor IX and vector antigens allows for long-term expression

Recombinant adenoviruses containing the canine factor IX (FIX) cDNA were directly introduced in the hind leg muscle of mice. We show that (i) in nude mice, high expression (1-5 micrograms/ml in plasma) of FIX protein can be detected for > 300 days; (ii) in contrast, expression of FIX protein was transient (7-10 days) in normal mice; (iii) CD8+ lymphocytes could be detected within 3 days in the infected muscle tissue; (iv) use of beta 2-microglobulin and immunoglobulin M heavy chain "knockout" mice showed that lack of sustained expression of FIX protein is due to cell-mediated and humoral immune responses; (v) normal mice, once infected with recombinant adenovirus, could not be reinfected efficiently for at least 30 days due to neutralizing viral antibodies; and, finally, (vi) using immunosuppressive drugs, some normal mice can be tolerized to produce and secrete FIX protein for > 5 months. We conclude that currently available adenoviral vectors have serious limitations for use for long-term gene therapy.

Molecular regulation of human interleukin 2 and T-cell function by interleukin 4

Distinct functional T-cell subsets, differing in the patterns of lymphokines produced, regulate cell-mediated and humoral immune responses. The two major types and their principal products, interleukin 4 and interferon gamma (IL-4 and IFN-gamma), are reciprocally negatively interactive. To analyze the molecular mechanism of IL-4-mediated suppression of cell-mediated immunity we studied its effects on expression of interleukin 2 (IL-2) and IFN-gamma. IL-4 pretreatment of Jurkat cells prior to stimulation resulted in a decrease in transcription of the IL2 gene. IL-4 suppressed IL-2 and IFN-gamma mRNA levels in primary human T cells, and addition of anti-CD28 antibodies relieved this suppression. Using enhancer-reporter constructs, IL-4 specifically down-regulated the NFIL-2B element. Electrophoretic mobility shift assays using a DNA oligomer containing the NFIL-2B binding site indicated that IL-4 inhibited the NFIL-2B complex and that the NFIL-2B DNA binding factor is distinct from AP-1. These results suggest that IL-4 may regulate development and function of T-cell subsets involved in cell-mediated immunity in part by inhibiting factors required for transcription of the IL2 gene.