Development, Evaluation and Implementation of Chief Complaint Groupings to Activate Data Collection: A Multi-Center Study of Clinical Decision Support for Children with Head Trauma.

BACKGROUND: Overuse of cranial computed tomography scans in children with blunt head trauma unnecessarily exposes them to radiation. The Pediatric Emergency Care Applied Research Network (PECARN) blunt head trauma prediction rules identify children who do not require a computed tomography scan. Electronic health record (EHR) based clinical decision support (CDS) may effectively implement these rules but must only be provided for appropriate patients in order to minimize excessive alerts. OBJECTIVES: To develop, implement and evaluate site-specific groupings of chief complaints (CC) that accurately identify children with head trauma, in order to activate data collection in an EHR. METHODS: As part of a 13 site clinical trial comparing cranial computed tomography use before and after implementation of CDS, four PECARN sites centrally developed and locally implemented CC groupings to trigger a clinical trial alert (CTA) to facilitate the completion of an emergency department head trauma data collection template. We tested and chose CC groupings to attain high sensitivity while maintaining at least moderate specificity. RESULTS: Due to variability in CCs available, identical groupings across sites were not possible. We noted substantial variability in the sensitivity and specificity of seemingly similar CC groupings between sites. The implemented CC groupings had sensitivities greater than 90% with specificities between 75-89%. During the trial, formal testing and provider feedback led to tailoring of the CC groupings at some sites. CONCLUSIONS: CC groupings can be successfully developed and implemented across multiple sites to accurately identify patients who should have a CTA triggered to facilitate EHR data collection. However, CC groupings will necessarily vary in order to attain high sensitivity and moderate-to-high specificity. In future trials, the balance between sensitivity and specificity should be considered based on the nature of the clinical condition, including prevalence and morbidity, in addition to the goals of the intervention being considered.

Antiapoptotic function of NF-kappaB in T lymphocytes is influenced by their differentiation status: roles of Fas, c-FLIP, and Bcl-xL.

Inducible protection from apoptosis in vivo controls the size of cell populations. An important question in this respect is how differentiation affects mechanisms of apoptosis regulation. Among mature T lymphocytes, the NF-kappaB/Rel transcription factors are coupled to receptors that control cell population sizes by concurrently regulating survival and multiplication. In the present study, we used a transgenic inhibitor of NF-kappaB/Rel signaling to investigate the role of this pathway in proliferation and death of mature T cells in vivo. The results indicate that NF-kappaB integrates two critical yet distinct molecular pathways preventing apoptosis affected by the death receptor Fas, coordinately regulating levels of FLIP and Bcl-x(L) in primary T cells. Surprisingly, NF-kappaB blockade preferentially impacted naive as compared to memory T cells. The Fas/FasL pathway was linked to these findings by evidence that the abnormalities imposed by NF-kappaB inhibition were ameliorated by Fas deficiency, particularly for the CD4(+) lineage. Moreover, levels of an inhibitor of Fas-mediated apoptosis, c-FLIP, were diminished in cells expressing the transgenic inhibitor. NF-kappaB was also linked to T cell survival in vivo by mediating induction of Bcl-x(L): restoration of Bcl-x(L) levels reversed the preferential deficit of naive T cells, differentially impacting the CD4 and CD8 subsets. These results show that promoting survival and effective multiplication are central roles for NF-kappaB in T lymphoid homeostasis in vivo, but this effect and its underlying mechanisms are influenced by the developmental state of the lymphocyte.

Molecular mechanisms in lymphocyte activation and growth.

Transcription factor NF-kappaB is biochemically coupled to the T cell antigen receptor (TCR) and activated transiently during an adaptive immune response. The author's laboratory is investigating the signal-dependent regulation of NF-kappaB, its downstream gene targets, and its function in lymphocyte biology. Our studies have revealed novel enzymatic checkpoints in the NF-kappaB signaling pathway and constitutive repressors of NF-kappaB that might be clinically applicable for therapeutic control of the immune system. We have also found that the Tax transforming protein encoded by human T cell leukemia virus type 1 (HTLV1) binds to and persistently activates an inducible protein kinase in the TCR/NF-kappaB axis. This viral/host interaction appears to trigger the inappropriate expression of NF-kappaB and the development of HTLV1-associated disease.

Persistent activation of NF-kappa B by the tax transforming protein involves chronic phosphorylation of IkappaB kinase subunits IKKbeta and IKKgamma.

The Tax transforming protein encoded by human T-cell leukemia virus type 1 (HTLV1) persistently activates transcription factor NF-kappaB and deregulates the expression of downstream genes that mediate cell cycle entry. We recently found that Tax binds to and chronically stimulates the catalytic function of IkappaB kinase (IKK), a cellular enzyme complex that phosphorylates and inactivates the IkappaB inhibitory subunit of NF-kappaB. We now demonstrate that the IKKbeta catalytic subunit and IKKgamma regulatory subunit of IKK are chronically phosphorylated in HTLV1-infected and Tax-transfected cells. Alanine substitutions at Ser-177 and Ser-181 in the T loop of IKKbeta protect both of these IKK subunits from Tax-directed phosphorylation and prevent the induction of IkappaB kinase activity. Each of these inhibitory effects is recapitulated in Tax transfectants expressing the bacterial protein YopJ, a potent in vivo agonist of T loop phosphorylation. Moreover, ectopically expressed forms of IKKbeta that contain glutamic acid substitutions at Ser-177 and Ser-181 have the capacity to phosphorylate a recombinant IKKgamma substrate in vitro. We conclude that Tax-induced phosphorylation of IKKbeta is required for IKKbeta activation, phosphoryl group transfer to IKKgamma, and acquisition of the deregulated IKK phenotype.

Bruton's tyrosine kinase is required for activation of IkappaB kinase and nuclear factor kappaB in response to B cell receptor engagement.

Mutations in the gene encoding Bruton's tyrosine kinase (btk) cause the B cell deficiency diseases X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (xid) in mice. In vivo and in vitro studies indicate that the BTK protein is essential for B cell survival, cell cycle progression, and proliferation in response to B cell antigen receptor (BCR) stimulation. BCR stimulation leads to the activation of transcription factor nuclear factor (NF)-kappaB, which in turn regulates genes controlling B cell growth. We now demonstrate that a null mutation in btk known to cause the xid phenotype prevents BCR-induced activation of NF-kappaB. This defect can be rescued by reconstitution with wild-type BTK. This mutation also interferes with BCR-directed activation of IkappaB kinase (IKK), which normally targets the NF-kappaB inhibitor IkappaBalpha for degradation. Taken together, these findings indicate that BTK couples IKK and NF-kappaB to the BCR. Interference with this coupling mechanism may contribute to the B cell deficiencies observed in XLA and xid.

NF-kappa B is required for H-ras oncogene induced abnormal cell proliferation and tumorigenesis.

Oncogenic mutations in ras lead to constitutive activation of downstream signaling pathways that modulate the activities of transcription factors. In turn, these factors control the expression of a subset of genes responsible for neoplastic cell transformation. Recent studies suggest that transcription factor NF-kappa B contributes to cell transformation by inhibiting the cell death signal activated by oncogenic Ras. In this study, inhibition of NF-kappa B activity by forced expression of a super-repressor form of I kappa B alpha, the major inhibitor of NF-kappa B, markedly decreased the growth rate, saturation density and tumorigenicity of oncogenic H-Ras transformed rat embryo fibroblasts. Such clonally isolated cells overexpressing I kappa B alpha super-repressor not only were viable but also exhibited no sign of spontaneous apoptosis. Inhibition of NF-kappa B in these cells was functionally demonstrated by both the loss of cytokine induced DNA binding activity and a profoundly increased sensitivity to cell death in response to TNF-alpha treatment. In contrast, inhibition of NF-kappa B activity in non-transformed fibroblasts had minimal effect on growth, but rendered the cells resistant to a subsequent transformation by H-ras oncogene. Similar results were also obtained with rat intestinal epithelial cells harboring an inducible ras oncogene. Taken together, these findings suggest that NF-kappa B activity is essential for abnormal cell proliferation and tumorigenicity activated by the ras oncogene and highlight an alternative functional role for NF-kappa B in oncogenic Ras-mediated cell transformation that is distinct from its anti-apoptotic activity. Oncogene (2000) 19, 841 - 849.

Reovirus-induced apoptosis requires activation of transcription factor NF-kappaB.

Reovirus infection induces apoptosis in cultured cells and in vivo. To identify host cell factors that mediate this response, we investigated whether reovirus infection alters the activation state of the transcription factor nuclear factor kappa B (NF-kappaB). As determined in electrophoretic mobility shift assays, reovirus infection of HeLa cells leads to nuclear translocation of NF-kappaB complexes containing Rel family members p50 and p65. Reovirus-induced activation of NF-kappaB DNA-binding activity correlated with the onset of NF-kappaB-directed transcription in reporter gene assays. Three independent lines of evidence indicate that this functional form of NF-kappaB is required for reovirus-induced apoptosis. First, treatment of reovirus-infected HeLa cells with a proteasome inhibitor prevents NF-kappaB activation following infection and substantially diminishes reovirus-induced apoptosis. Second, transient expression of a dominant-negative form of IkappaB that constitutively represses NF-kappaB activation significantly reduces levels of apoptosis triggered by reovirus infection. Third, mutant cell lines deficient for either the p50 or p65 subunits of NF-kappaB are resistant to reovirus-induced apoptosis compared with cells expressing an intact NF-kappaB signaling pathway. These findings indicate that NF-kappaB plays a significant role in the mechanism by which reovirus induces apoptosis in susceptible host cells.

Transcription factor NF-kappaB regulates inducible CD83 gene expression in activated T lymphocytes.

The immunoglobulin superfamily member CD83 is expressed on the surface of mature dendritic cells that present processed antigens to T lymphocytes. In addition, T cells acquire CD83 expression following mitogenic stimulation in vitro. Here we report two lines of evidence demonstrating that this inducible lymphocyte response is genetically programmed by transcription factor NF-kappaB and contingent upon proteolytic breakdown of its cytoplasmic inhibitor IkappaBalpha. First, signal-dependent induction of CD83 mRNA expression is blocked in both transformed and primary T cells harboring a degradation-resistant mutant of IkappaBalpha that constitutively represses NF-kappaB. Second, as revealed in gel retardation assays, the IkappaBalpha constitutive repressor prevents the inducible interaction of NF-kappaB with consensus recognition sites identified in the CD83 promoter. Given that IkappaBalpha is functionally coupled to the T-cell antigen receptor, these findings suggest that the downstream transcription unit for CD83 is triggered by NF-kappaB during an adaptive immune response.

Persistent activation of NF-kappaB by the tax transforming protein of HTLV-1: hijacking cellular IkappaB kinases.

Biochemical coupling of transcription factor NF-kappaB to antigen and co-stimulatory receptors is required for the temporal control of T-cell proliferation. In contrast to its transitory activation during normal growth-signal transduction, NF-kappaB is constitutively deployed in T-cells transformed by the type 1 human T-cell leukemia virus (HTLV-1). This viral/host interaction is mediated by the HTLV-1-encoded Tax protein, which has potent oncogenic properties. As reviewed here, Tax activates NF-kappaB primarily via a pathway leading to the chronic phosphorylation and degradation of IkappaBalpha, a cytoplasmic inhibitor of NF-kappaB. To access this pathway, Tax associates stably with a cytokine-inducible IkappaB kinase (IKK), which contains both catalytic (IKKalpha and IKKbeta) and noncatalytic (IKKgamma) subunits. Unlike their transiently induced counterparts in cytokine-treated cells, Tax-associated forms of IKKalpha and IKKbeta are persistently activated in HTLV-1-infected T cells. Acquisition of the deregulated IKK phenotype is contingent on the presence of IKKgamma, which functions as a molecular adaptor in the assembly of pathologic Tax/IkappaB kinase complexes. These findings highlight a key mechanistic role for IKK in the Tax/NF-kappaB signaling axis and define new intracellular targets for the therapeutic control of HTLV-1-associated disease.

IkappaB kinase complex is an intracellular target for endotoxic lipopolysaccharide in human monocytic cells.

Endotoxic lipopolysaccharide (LPS) is a proinflammatory agonist produced by gram-negative bacteria and a contributor to the majority of the 400,000 septic shock cases recorded annually in US hospitals. The primary target cells for LPS are monocytes and macrophages. Their response consists of massive production of proinflammatory cytokines, reactive oxygen- and nitrogen-intermediates, procoagulants, and cell adhesion molecules. In turn, expression of these LPS-responsive factors contributes to collapse of the circulatory system, to disseminated intravascular coagulation, and to a 30% mortality rate. A common intracellular mechanism responsible for the expression of septic shock genes in monocytes and macrophages involves the activation of NF-kappaB. This transcription factor is regulated by a family of structurally related inhibitors including IkappaBalpha, IkappaBbeta, and IkappaBepsilon, which trap NF-kappaB in the cytoplasm. In this report, the investigators show that LPS derived from different gram-negative bacteria activates cytokine-responsive IkappaB kinases containing catalytic subunits termed IKKalpha (IKK1) and IKKbeta (IKK2). The kinetics of IKKalpha and IKKbeta activation in LPS-stimulated human monocytic cells differ from that recorded on their stimulation with tumor necrosis factor-alpha, thereby implying a distinct activation mechanism. LPS-activated IKK complexes phosphorylate all 3 inhibitors of NF-kappaB: IkappaBalpha, IkappaBbeta, and IkappaBepsilon. Moreover, LPS activates IKKbeta preferentially, relative to IKKalpha. Thus, IKK complex constitutes the main intracellular target for LPS-induced NF-kappaB signaling to the nucleus in human monocytic cells to activate genes responsible for septic shock.

An intact NF-kappa B signaling pathway is required for maintenance of mature B cell subsets.

Members of the NF-kappaB/Rel transcription factor family are expressed constitutively during B cell development and are further induced by mitogen activation. Mice harboring germline disruptions in individual NF-kappaB subunits exhibit distinct defects in B lymphocyte activation and survival. However, the role of NF-kappaB in the production and maintenance of B cell subsets has been difficult to dissect in these knockout animals due to functional impairment of other immune cells. To directly address the cell autonomous requirements for NF-kappaB in humoral immune compartments, transgenic mice were generated that express a transdominant form of Ikappa-Balpha in B lineage cells. Whereas expression of the inhibitor had only modest effects on basal or LPS-induced levels of NF-kappaB, transgenic B cells were significantly impaired for cellular proliferation and NF-kappaB induction in response to B cell receptor (BCR) crosslinking. Furthermore, the trans-dominant inhibitor produced a dose-dependent reduction in the population of mature splenic B cells. This cellular defect was more pronounced in long-lived B lymphocyte subsets that recirculate to the adult bone marrow. Together, these results indicate that BCR-mediated signaling must maintain NF-kappaB levels above a stringent threshold for proper regulation of B cell homeostasis.

Fibroblast growth factor-1 (FGF-1) enhances IL-2 production and nuclear translocation of NF-kappaB in FGF receptor-bearing Jurkat T cells.

Fibroblast growth factors (FGFs) are heparin-binding proteins crucial to embryogenesis, angiogenesis, and wound healing. FGF-1 is abundantly expressed in the synovium in rheumatoid arthritis and in rejecting allografts, sites of chronic immune-mediated inflammation. The frequency of FGF-1-responsive T cells is increased in the peripheral blood of these disorders, and a high percentage of infiltrating T cells in rheumatoid arthritis synovium express receptors for FGF-1. To understand the action of FGF-1 in T cells, studies were initiated in Jurkat T cells that express the signaling isoform of FGF receptor-1. These experiments show that FGF-1 stimulation of Jurkat T cells provides a second signal that augments TCR-mediated IL-2 production. Analogous to costimulation via CD28, this activity is mediated through activation of Rel/kappaB, a family of transcription factors known to regulate IL-2 and other activation-inducible proteins. FGF-1 alone induces modest nuclear translocation of kappaB-binding proteins, and this translocation is enhanced by the combination of anti-CD3 and FGF-1. This NF-kappaB binding complex is composed of transcriptionally active p65(RelA)/p50 heterodimers and results primarily from the targeted degradation of IkappaB-alpha, an inhibitor that sequesters Rel/kappaB in the cytoplasm. These data are the first to show a connection between FGF-1 signaling and NF-kappaB activation outside of embryonic development. The signaling events that link FGF receptor-1 engagement and NF-kappaB activation in Jurkat are probably distinct from the CD28 costimulation pathway, since FGF-1-induced Rel/kappaB binding proteins do not contain significant levels of c-Rel and are not identical with the CD28 response complex.

Rel/NF-kappaB can trigger the Notch signaling pathway by inducing the expression of Jagged1, a ligand for Notch receptors.

Jagged1 belongs to the DSL family of ligands for Notch receptors that control the proliferation and differentiation of various cell lineages. However, little is known about the transcription factors that regulate its expression. Here, we show that Jagged1 is a Rel/NF-kappaB-responsive gene. Both c-Rel and RelA induced jagged1 gene expression, whereas a mutant defective for transactivation did not. Importantly, jagged1 transcripts were also upregulated by endogenous NF-kappaB activation and this effect was inhibited by a dominant mutant of IkappaBalpha, a physiological inhibitor of NF-kappaB. Cell surface expression of Jagged1 in c-Rel-expressing cell monolayers led to a functional interaction with lymphocytes expressing the Notch1/TAN-1 receptor. This correlated with the initiation of signaling downstream of Notch, as evidenced by increased levels of HES-1 transcripts in co-cultivated T cells and of CD23 transcripts in co-cultivated B cells. Consistent with its Rel/NF-kappaB-dependent induction, Jagged1 was found to be highly expressed in splenic B cells where c-Rel is expressed constitutively. These results demonstrate that c-Rel can trigger the Notch signaling pathway in neighboring cells by inducing jagged1 gene expression, and suggest a role for Jagged1 in B-cell activation, differentiation or function. These findings also highlight the potential for an interplay between the Notch and NF-kappaB signaling pathways in the immune system.

IKKgamma mediates the interaction of cellular IkappaB kinases with the tax transforming protein of human T cell leukemia virus type 1.

The Tax oncoprotein of human T cell leukemia virus type 1 constitutively activates transcription factor NF-kappaB by a mechanism involving Tax-induced phosphorylation of IkappaBalpha, a labile cytoplasmic inhibitor of NF-kappaB. To trigger this signaling cascade, Tax associates stably with and persistently activates a cellular IkappaB kinase (IKK) containing both catalytic (IKKalpha and IKKbeta) and noncatalytic (IKKgamma) subunits. We now demonstrate that IKKgamma enables Tax to dock with the IKKbeta catalytic subunit, resulting in chronic IkappaB kinase activation. Mutations in either IKKgamma or Tax that prevent formation of these higher order Tax.IKK complexes also interfere with the ability of Tax to induce IKKbeta catalytic function in vivo. Deletion mapping studies indicate that amino acids 1-100 of IKKgamma are required for this Tax targeting function. Together, these findings identify IKKgamma as an adaptor protein that directs the stable formation of pathologic Tax.IKK complexes in virally infected T cells.

Elevated constitutive IkappaB kinase activity and IkappaB-alpha phosphorylation in Hs294T melanoma cells lead to increased basal MGSA/GRO-alpha transcription.

The basal transcription of the CXC chemokine, melanocyte growth stimulatory activity (MGSA)/growth-regulated protein (GRO)-alpha, is up-regulated in Hs294T melanoma cells compared with the normal retinal pigment epithelial (RPE) cells. Previous studies characterized a cytokine-inducible, functional nuclear factor (NF)-kappaB consensus element in the immediate 5' regulatory region of the MGSA/GRO-alpha gene at -78 bp. Although the cytokine-inducible mechanisms for transcription of this gene are fairly well delineated, the mechanisms involved in its basal up-regulation of transcription in Hs294T melanoma cells are poorly understood. Recently, we demonstrated an increased rate of IkappaB-alpha degradation in Hs294T cells, which leads to an increased nuclear localization of NF-kappaB (R. L. Shattuck-Brandt and A. Richmond. Cancer Res., 57: 3032-3039, 1997). Here we demonstrate that Hs294T melanoma cells have elevated basal IkappaB kinase (IKK) activity relative to RPE cells, causing an increased constitutive IkappaB-alpha phosphorylation and degradation. We also show here that the resultant elevated nuclear NF-kappaB (p50/p65) in these cells is responsible for the increased basal transcription of MGSA/GRO-alpha. Pretreatment of Hs294T or RPE cells with proteasome inhibitors MG115 or MG132 captures the slower migrating, constitutively phosphorylated form of IkappaB-alpha in Hs294T melanoma cells, but not in RPE cells. In addition, a phospho-specific antibody that specifically recognizes the inhibitory form of IkappaB that is phosphorylated at Ser-32 reacted with IkappaB-alpha in Hs294T cell, but not in unstimulated RPE cells. Although the basal level of protein expression of IKK-alpha or IKK-beta are the same in both Hs294T and RPE cells, immunoprecipitation with IKK-alpha antibody combined with activity assay reveal a constitutively active IKK complex in Hs294T melanoma cells. Cotransfection of a 350-bp MGSA/GRO-alpha promoter-luciferase reporter construct with either the dominant negative IKK-alpha or the repressors of NF-kappaB, the IkappaB-alpha wild type or mutants lacking the inducible phosphorylation sites, demonstrates that the increased basal MGSA/GRO-alpha transcription in the Hs294T cells is due to the enhanced nuclear activation of NF-kappaB.

Constitutive activation of NF-kappaB in primary adult T-cell leukemia cells.

Human T-cell leukemia virus type I (HTLV-I) is an etiologic agent of adult T-cell leukemia (ATL). The viral protein Tax induces the activation and nuclear translocalization of transcription factor NF-kappaB, which is proposed to play a crucial role in the transformation of T cells by HTLV-I. However, the HTLV-I genes including Tax are not expressed significantly in primary leukemic cells from ATL patients. In this study, we examined the basis for NF-kappaB activation in freshly isolated leukemic cells from ATL patients. We found that leukemic cells from ATL patients, like HTLV-I-infected T-cell lines, display constitutive NF-kappaB DNA binding activity and increased degradation of IkappaBalpha (an inhibitor of NF-kappaB). Whereas the NF-kappaB binding activity in Tax-expressing T-cell lines consisted mostly of p50/c-Rel, fresh ATL samples contained p50/p50 and p50/p65 heterodimers. One T-cell line derived from ATL leukemic cells, TL-Om1, displayed constitutive NF-kappaB activity, as well as enhanced degradation of IkappaBalpha, despite the lack of detectable Tax expression. Interestingly, the NF-kappaB in TL-Om1 consists of p50/p50 and p50/p65 like that in fresh primary leukemic cells. Our results suggest that activation of NF-kappaB occurs through a Tax-independent mechanism in leukemic cells of ATL patients, possibly due to differential NF-kappaB subunit activation.

Human T-cell leukemia virus type I Tax transactivates human interleukin 8 gene through acting concurrently on AP-1 and nuclear factor-kappaB-like sites.

The transactivator protein, Tax, from the human T-cell leukemia virus type I (HTLV-I) transactivates both viral and cellular genes. Previously, we had shown that interleukin 8 (IL-8) is constitutively expressed in HTLV-I-infected cells and in cells transiently expressing Tax. We show here that the IL-8 promoter is Tax responsive in Jurkat T cells. Furthermore, using several deletion and mutated plasmids of the 5'-flanking regulatory region of the IL-8 gene linked to the luciferase gene as a reporter and mutant tax gene expression vectors, we have established that both AP-1 at -126 to -120 and nuclear factor (NF)-kappaB-like cis-element at -80 to -71 are essential and sufficient for the induction of the IL-8 gene by HTLV-I Tax. In addition, overexpression of the dominant-negative mutants of NF-kappaB inhibitor molecules, IkappaBalpha and IkappaBbeta, abolished the Tax-induced activation of IL-8 gene. Gel mobility shift assays detected proteins specifically binding to the AP-1 and NF-kappaB-like sites in Tax-expressing T-cell lines infected with HTLV-I. Similarly, the nuclear translocation of proteins specifically bound to these two motifs was shown in JPX-9 cells, a subclone of Jurkat cells, carrying the Tax sequences under the control of an inducible promoter. Taken together, these results suggest that the cooperation of transcription factors NF-kappaB and AP-1 is essential for transactivation of IL-8 gene by HTLV-I Tax.

The tax oncoprotein of human T-cell leukemia virus type 1 associates with and persistently activates IkappaB kinases containing IKKalpha and IKKbeta.

The Tax oncoprotein of human T-cell leukemia virus type 1 (HTLV1) chronically activates transcription factor NF-kappaB by a mechanism involving degradation of IkappaBalpha, an NF-kappaB-associated cytoplasmic inhibitor. Tax-induced breakdown of IkappaBalpha requires phosphorylation of the inhibitor at Ser-32 and Ser-36, which is also a prerequisite for the transient activation of NF-kappaB in cytokine-treated T lymphocytes. However, it remained unclear how Tax interfaces with the cellular NF-kappaB/IkappaB signaling machinery to generate a chronic rather than a transient NF-kappaB response. We now demonstrate that Tax associates with cytokine-inducible IkappaB kinase (IKK) complexes containing catalytic subunits IKKalpha and IKKbeta, which mediate phosphorylation of IkappaBalpha at Ser-32 and Ser-36. Unlike their transiently activated counterparts in cytokine-treated cells, Tax-associated forms of IKK are constitutively active in either Tax transfectants or HTLV1-infected T lymphocytes. Moreover, point mutations in Tax that ablate its IKK-binding function also prevent Tax-mediated activation of IKK and NF-kappaB. Together, these findings suggest that the persistent activation of NF-kappaB in HTLV1-infected T-cells is mediated by a direct Tax/IKK coupling mechanism.

Transcription factor NF-kappaB regulates inducible Oct-2 gene expression in precursor B lymphocytes.

The POU transcription factors Oct-1 and Oct-2 regulate the activity of octamer-dependent promoters, including those that direct transcription from rearranged immunoglobulin genes. Unlike Oct-1, which is constitutively expressed in many cell types, Oct-2 expression is restricted primarily to B lymphocytes and can be induced in precursor B cells by stimulation with bacterial lipopolysaccharide (LPS). However, the precise factors that mediate this induction mechanism remain unknown. In the present study, we monitored Oct-2 expression in cells arrested for the activation of NF-kappaB, an LPS-responsive member of the Rel transcription factor family. Despite stimulation with LPS, disruption of the NF-kappaB signaling pathway in precursor B cells led to the loss of inducible Oct-2 DNA binding activity in vitro and the suppression of Oct-2-directed transcription in vivo. This biochemical defect correlated with a specific block to Oct-2 gene expression at the level of transcription, whereas the expression of Oct-1 was unaffected. The finding that Oct-2 is under NF-kappaB control highlights an important cross-talk mechanism involving two distinct transcription factor families that regulate B lymphocyte function.

Phosphorylation of the PEST domain of IkappaBbeta regulates the function of NF-kappaB/IkappaBbeta complexes.

Activation of transcription factor NF-kappaB involves the signal-dependent degradation of basally phosphorylated inhibitors such as IkappaBalpha and IkappaBbeta. The gene encoding IkappaBalpha is under NF-kappaB control, which provides a negative feedback loop to terminate the induced NF-kappaB response. However, recent studies have identified a hypophosphorylated pool of IkappaBbeta that shields nuclear NF-kappaB from inhibition by newly synthesized IkappaBalpha. In the present work, we provide three lines of evidence indicating that this protection mechanism is regulated by the C-terminal PEST domain of IkappaBbeta. First, disruption of two basal phosphoacceptors present in the IkappaBbeta PEST domain (Ser-313 and Ser-315) yields a mutant that forms ternary complexes with NF-kappaB and its target DNA-binding site. Second, based on in vitro mixing experiments, these ternary complexes are resistant to the inhibitory action of IkappaBalpha. Third, mutants of IkappaBbeta that are defective for phosphorylation at Ser-313 and Ser-315 fail to efficiently block NF-kappaB-directed transcription in vivo, whereas replacement of these two IkappaBbeta residues with a phosphoserine mimetic generates a fully functional repressor. Taken together, our findings suggest that the functional fate of NF-kappaB when bound to IkappaBbeta is critically dependent on the phosphorylation status of the IkappaBbeta PEST domain.