Identification of three NFAT binding motifs in the 5'-upstream region of the human CD3gamma gene that differentially bind NFATc1, NFATc2, and NF-kappa B p50

CRTAC1 enhances the chemosensitivity of non-small cell lung cancer to cisplatin by eliciting RyR-mediated calcium release and inhibiting Akt1 expression

Sensitivity to platinum-based combination chemotherapy is associated with a favorable prognosis in patients with non-small cell lung cancer (NSCLC). Here, our results obtained from analyses of the Gene Expression Omnibus database of NSCLC patients showed that cartilage acidic protein 1 (CRTAC1) plays a role in the response to platinum-based chemotherapy. Overexpression of CRTAC1 increased sensitivity to cisplatin in vitro, whereas knockdown of CRTAC1 decreased chemosensitivity of NSCLC cells. In vivo mouse experiments showed that CRTAC1 overexpression increased the antitumor effects of cisplatin. CRTAC1 overexpression promoted NFAT transcriptional activation by increasing intracellular Ca2+ levels, thereby inducing its regulated STUB1 mRNA transcription and protein expression, accelerating Akt1 protein degradation and, in turn, enhancing cisplatin-induced apoptosis. Taken together, the present results indicate that CRTAC1 overexpression increases the chemosensitivity of NSCLC to cisplatin treatment by inducing Ca2+-dependent Akt1 degradation and apoptosis, suggesting the potential of CRTAC1 as a biomarker for predicting cisplatin chemosensitivity. Our results further reveal that modulating the expression of CRTAC1 could be a new strategy for increasing the efficacy of cisplatin in chemotherapy of NSCLC patients.

Regulation of CD19 CAR-T cell activation based on an engineered downstream transcription factor

CAR-T cells present a highly effective therapeutic option for several malignant diseases, based on their ability to recognize the selected tumor surface marker in an MHC-independent manner. This triggers cell activation and cytokine production, resulting in the killing of the cancerous cell presenting markers recognized by the chimeric antigen receptor. CAR-T cells are highly potent serial killers that may cause serious side effects, so their activity needs to be carefully controlled. Here we designed a system to control the proliferation and activation state of CARs based on downstream NFAT transcription factors, whose activity can be regulated via chemically induced heterodimerization systems. Chemical regulators were used to either transiently trigger engineered T cell proliferation or suppress CAR-mediated activation when desired or to enhance activation of CAR-T cells upon engagement of cancer cells, shown also in vivo. Additionally, an efficient sensor to monitor activated CD19 CAR-T cells in vivo was introduced. This implementation in CAR-T cell regulation offers an efficient way for on-demand external control of CAR-T cell activity to improve their safety.

Genetic heterogeneity of liver cancer stem cells

Cancer cell heterogeneity is a serious problem in the control of tumor progression because it can cause chemoresistance and metastasis. Heterogeneity can be generated by various mechanisms, including genetic evolution of cancer cells, cancer stem cells (CSCs), and niche heterogeneity. Because the genetic heterogeneity of CSCs has been poorly characterized, the genetic mutation status of CSCs was examined using Exome-Seq and RNA-Seq data of liver cancer. Here we show that different surface markers for liver cancer stem cells (LCSCs) showed a unique propensity for genetic mutations. Cluster of differentiation 133 (CD133)-positive cells showed frequent mutations in the IRF2, BAP1, and ERBB3 genes. However, leucine-rich repeat-containing G protein-coupled receptor 5-positive cells showed frequent mutations in the CTNNB1, RELN, and ROBO1 genes. In addition, some genetic mutations were frequently observed irrespective of the surface markers for LCSCs. BAP1 mutations was frequently observed in CD133-, CD24-, CD13-, CD90-, epithelial cell adhesion molecule-, or keratin 19-positive LCSCs. ASXL2, ERBB3, IRF2, TLX3, CPS1, and NFATC2 mutations were observed in more than three types of LCSCs, suggesting that common mechanisms for the development of these LCSCs. The present study provides genetic heterogeneity depending on the surface markers for LCSCs. The genetic heterogeneity of LCSCs should be considered in the development of LCSC-targeting therapeutics.

A reporter gene assay for determining the biological activity of therapeutic antibodies targeting TIGIT

T cell immunoglobulin and ITIM domain (TIGIT) is a novel immune checkpoint that has been considered as a target in cancer immunotherapy. Current available bioassays for measuring the biological activity of therapeutic antibodies targeting TIGIT are restricted to mechanistic investigations because donor primary T cells are highly variable. Here, we designed a reporter gene assay comprising two cell lines, namely, CHO-CD112-CD3 scFv, which stably expresses CD112 (PVRL2, nectin-2) and a membrane-bound anti-CD3 single-chain fragment variable (scFv) as the target cell, and Jurkat-NFAT-TIGIT, which stably expresses TIGIT as well as the nuclear factor of activated T-cells (NFAT) response element-controlled luciferase gene, as the effector cell. The anti-CD3 scFv situated on the target cells activates Jurkat-NFAT-TIGIT cells through binding and crosslinking CD3 molecules of the effector cell, whereas interactions between CD112 and TIGIT prevent activation. The presence of anti-TIGIT mAbs disrupts their interaction, which in turn reverses the inactivation and luciferase expression. Optimization and validation studies have demonstrated that this assay is superior in terms of specificity, accuracy, linearity, and precision. In summary, this reliable and effective reporter gene assay may potentially be utilized in lot release control, stability assays, screening, and development of novel TIGIT-targeted therapeutic antibodies.

Transcriptional Regulation by the NFAT Family in Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a haematological cancer with poor outcomes due to a lack of efficacious targeted therapies. The Nuclear Factor of Activated T Cells (NFAT) family of transcription factors is well characterised as a regulator of the cell cycle and differentiation in the myeloid lineage. Recent evidence has demonstrated that NFAT family members may have roles in regulating AML leukemogenesis and resistance to targeted therapy in myeloid leukaemia. Furthermore, gene expression data from patient samples show that some NFATs are more highly expressed in poorly differentiated AML and after disease relapse, implying that the NFAT family may have roles in specific types of AML. This review outlines the evidence for the role of NFAT in healthy myeloid tissue and explores how NFAT might regulate AML pathogenesis, highlighting the potential to target specific NFAT proteins therapeutically in AML.

3D-QSAR and docking studies on ursolic acid derivatives for anticancer activity based on bladder cell line T24 targeting NF-kB pathway inhibition

Bladder cancer is the common reason for mortality worldwide, and its increasing rate announces as a significant area of research in drug designing. The side effects and toxicity of existing drugs and the consequence of gradual cancer cell resistance against the available therapy make the treatment poor. Globally, there is a continuous high demand to develop new, more potent, and easily affordable drugs against cancer. The current research article illustrates the application of developed three-dimensional quantitative structure-activity relationship (3D-QSAR) based on human bladder cancer cell line T24 in vitro anticancer activity. The derived QSAR model has been used for prediction of natural compounds and analogs with 80% similarity of the most active compound of the dataset. The developed model describes the structure-activity relationship for terpenes and their derivatives at the molecular level. The developed comparative molecular field analysis (CoMFA) model shows a satisfactory cross-validation correlation coefficient (q2) of 0.54 and a regression correlation coefficient (r2) of 0.86. In order to evaluate the compliance with electronic pharmacokinetic parameters, Lipinski's rule of five filter, absorption, distribution, metabolism, and excretion (ADME) and toxicity of predicted compounds have been calculated. Furthermore, molecular-docking study has been performed to prioritize these predicted compounds based on their docking score and binding pocket similarity through the identified potential anticancer targets. Finally, two compounds T9 and B42 have been identified as the best hit because these two fall within the standard limits of all filters and show a good binding affinity. Conclusively, all satisfactory results strongly suggest that the derived 3D-QSAR model and obtained candidate's binding structures are reasonable in the prediction of a new antagonist's activity. The strategy adopted in the present research is expected to be of immense importance and a great support in the identification and optimization of lead in the early and advance drug discovery.

NFAT1 protects articular cartilage against osteoarthritic degradation by directly regulating transcription of specific anabolic and catabolic genes

Objectives

Adult mice lacking the transcription factor NFAT1 exhibit osteoarthritis (OA). The precise molecular mechanism for NFAT1 deficiency-induced osteoarthritic cartilage degradation remains to be clarified. This study aimed to investigate if NFAT1 protects articular cartilage (AC) against OA by directly regulating the transcription of specific catabolic and anabolic genes in articular chondrocytes.

Methods

Through a combined approach of gene expression analysis and web-based searching of NFAT1 binding sequences, 25 candidate target genes that displayed aberrant expression in Nfat1 ^-/- AC at the initiation stage of OA, and possessed at least four NFAT1 binding sites in the promoter of each gene, were selected and tested for NFAT1 transcriptional activities by chromatin immunoprecipitation (ChIP) and promoter luciferase reporter assays using chondrocytes isolated from the AC of three- to four-month-old wild-type mice or Nfat1 ^-/- mice with early OA phenotype.

Results

Chromatin immunoprecipitation assays revealed that NFAT1 bound directly to the promoter of 21 of the 25 tested genes encoding cartilage-matrix proteins, growth factors, inflammatory cytokines, matrix-degrading proteinases, and specific transcription factors. Promoter luciferase reporter assays of representative anabolic and catabolic genes demonstrated that NFAT1-DNA binding functionally regulated the luciferase activity of specific target genes in wild-type chondrocytes, but not in Nfat1 ^-/- chondrocytes or in wild-type chondrocytes transfected with plasmids containing mutated NFAT1 binding sequences.

Conclusion

NFAT1 protects AC against degradation by directly regulating the transcription of target genes in articular chondrocytes. NFAT1 deficiency causes defective transcription of specific anabolic and catabolic genes in articular chondrocytes, leading to increased matrix catabolism and osteoarthritic cartilage degradation.Cite this article: M. Zhang, Q. Lu, T. Budden, J. Wang. NFAT1 protects articular cartilage against osteoarthritic degradation by directly regulating transcription of specific anabolic and catabolic genes. Bone Joint Res 2019;8:90-100. DOI: 10.1302/2046-3758.82.BJR-2018-0114.R1.

Involvement of JNK signaling pathway in lipopolysaccharide-induced complement C3 transcriptional activation from amphioxus Branchiostoma belcheri

Complement C3 is a pivotal component of three cascades of complement activation. C3 in circulation is mainly provided by the hepatic cecum. The expression and secretion of C3 by hepatocytes is increased during acute inflammation. The detailed information on the regulationary mechanism underlying C3 transcriptional activation is limited. Here, we characterized the 5'-flanking region of the amphioxus C3 gene. To functionally analyze the upstream regulatory region of the C3 gene, a series of luciferase reporter gene constructs containing deleted or mutant regulatory elements were prepared. Using luciferase assay, we revealed that a potential C-JUN-1 binding sites within the proximal promoter region were necessary for full activation of the C3 promoter, whereas NF-κB, AP-1, C-JUN-2 and NFAT transcription factor binding sites played roles in governing the promoter activity at a homeostatic level. Our data also indicated that sp600125, a c-Jun N-terminal kinase (JNK) inhibitor, decreased lipopolysaccharide (LPS)-stimulated C3 promoter activity, mRNA expression and protein secretion using western blotting and quantitative real-time PCR analysis. These findings demonstrated that JNK signaling pathway is involved in the regulation of C3 gene transcription by targeting C-JUN transcription factor binding sites in the 5'-flanking promoter region, leading to LPS-induced C3 activation and therefore providing a potential target for regulating C3 expression.

NFAT1 and NFAT2 Differentially Regulate CTL Differentiation Upon Acute Viral Infection

CD8+ T cell differentiation orchestrated by transcription regulators is critical for balancing pathogen eradication and long-term immunity by effector and memory CTLs, respectively. The transcription factor Nuclear Factor of Activated T cells (NFAT) family members are known for their roles in T cell development and activation but still largely undetermined in CD8+ T cell differentiation in vivo. Here, we interrogated the role of two NFAT family members, NFAT1 and NFAT2, in the effector and memory phase of CD8+ T cell differentiation using LCMVArm acute infection model. We found that NFAT1 is critical for effector population generation whereas NFAT2 is required for promoting memory CTLs in a cell intrinsic manner. Moreover, we found that mice lacking both NFAT1 and NFAT2 in T cells display a significant increase in KLRG1hi CD127hi population and are unable to clear an acute viral infection. NFAT-deficient CTLs showed different degrees of impaired IFN-γ and TNF-α expression with NFAT1 being mainly responsible for IFN-γ production upon ex-vivo stimulation as well as for antigen-specific cytotoxicity. Our results suggest that NFAT1 and NFAT2 have distinct roles in mediating CD8+ T cell differentiation and function.

IP3R-mediated Ca2+ signals govern hematopoietic and cardiac divergence of Flk1+ cells via the calcineurin-NFATc3-Etv2 pathway

Ca2+ signals participate in various cellular processes with spatial and temporal dynamics, among which, inositol 1,4,5-trisphosphate receptors (IP3Rs)-mediated Ca2+ signals are essential for early development. However, the underlying mechanisms of IP3R-regulated cell fate decision remain largely unknown. Here we report that IP3Rs are required for the hematopoietic and cardiac fate divergence of mouse embryonic stem cells (mESCs). Deletion of IP3Rs (IP3R-tKO) reduced Flk1+/PDGFRα- hematopoietic mesoderm, c-Kit+/CD41+ hematopoietic progenitor cell population, and the colony-forming unit activity, but increased cardiac progenitor markers as well as cardiomyocytes. Concomitantly, the expression of a key regulator of hematopoiesis, Etv2, was reduced in IP3R-tKO cells, which could be rescued by the activation of Ca2+ signals and calcineurin or overexpression of constitutively active form of NFATc3. Furthermore, IP3R-tKO impaired specific targeting of Etv2 by NFATc3 via its evolutionarily conserved cis-element in differentiating ESCs. Importantly, the activation of Ca2+-calcineurin-NFAT pathway reversed the phenotype of IP3R-tKO cells. These findings reveal an unrecognized governing role of IP3Rs in hematopoietic and cardiac fate commitment via IP3Rs-Ca2+-calcineurin-NFATc3-Etv2 pathway.

Acetyl-CoA promotes glioblastoma cell adhesion and migration through Ca2+-NFAT signaling

Here, Lee et al. investigated the molecular mechanisms by which acetyl-CoA production impacts gene expression and how acetyl-CoA promotes malignant phenotypes. Their findings show that acetyl-CoA can enhance H3K27ac in a locus-specific manner and that expression of cell adhesion genes is driven by acetyl-CoA in part through activation of Ca²⁺–NFAT signaling.

The metabolite acetyl-coenzyme A (acetyl-CoA) is the required acetyl donor for lysine acetylation and thereby links metabolism, signaling, and epigenetics. Nutrient availability alters acetyl-CoA levels in cancer cells, correlating with changes in global histone acetylation and gene expression. However, the specific molecular mechanisms through which acetyl-CoA production impacts gene expression and its functional roles in promoting malignant phenotypes are poorly understood. Here, using histone H3 Lys27 acetylation (H3K27ac) ChIP-seq (chromatin immunoprecipitation [ChIP] coupled with next-generation sequencing) with normalization to an exogenous reference genome (ChIP-Rx), we found that changes in acetyl-CoA abundance trigger site-specific regulation of H3K27ac, correlating with gene expression as opposed to uniformly modulating this mark at all genes. Genes involved in integrin signaling and cell adhesion were identified as acetyl-CoA-responsive in glioblastoma cells, and we demonstrate that ATP citrate lyase (ACLY)-dependent acetyl-CoA production promotes cell migration and adhesion to the extracellular matrix. Mechanistically, the transcription factor NFAT1 (nuclear factor of activated T cells 1) was found to mediate acetyl-CoA-dependent gene regulation and cell adhesion. This occurs through modulation of Ca²⁺ signals, triggering NFAT1 nuclear translocation when acetyl-CoA is abundant. The findings of this study thus establish that acetyl-CoA impacts H3K27ac at specific loci, correlating with gene expression, and that expression of cell adhesion genes are driven by acetyl-CoA in part through activation of Ca²⁺–NFAT signaling.

Functional Incompatibility between the Generic NF-κB Motif and a Subtype-Specific Sp1III Element Drives the Formation of the HIV-1 Subtype C Viral Promoter

Of the various genetic subtypes of human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) and simian immunodeficiency virus (SIV), only in subtype C of HIV-1 is a genetically variant NF-κB binding site found at the core of the viral promoter in association with a subtype-specific Sp1III motif. How the subtype-associated variations in the core transcription factor binding sites (TFBS) influence gene expression from the viral promoter has not been examined previously. Using panels of infectious viral molecular clones, we demonstrate that subtype-specific NF-κB and Sp1III motifs have evolved for optimal gene expression, and neither of the motifs can be replaced by a corresponding TFBS variant. The variant NF-κB motif binds NF-κB with an affinity 2-fold higher than that of the generic NF-κB site. Importantly, in the context of an infectious virus, the subtype-specific Sp1III motif demonstrates a profound loss of function in association with the generic NF-κB motif. An additional substitution of the Sp1III motif fully restores viral replication, suggesting that the subtype C-specific Sp1III has evolved to function with the variant, but not generic, NF-κB motif. A change of only two base pairs in the central NF-κB motif completely suppresses viral transcription from the provirus and converts the promoter into heterochromatin refractory to tumor necrosis factor alpha (TNF-α) induction. The present work represents the first demonstration of functional incompatibility between an otherwise functional NF-κB motif and a unique Sp1 site in the context of an HIV-1 promoter. Our work provides important leads as to the evolution of the HIV-1 subtype C viral promoter with relevance for gene expression regulation and viral latency.

IMPORTANCE

Subtype-specific genetic variations provide a powerful tool to examine how these variations offer a replication advantage to specific viral subtypes, if any. Only in subtype C of HIV-1 are two genetically distinct transcription factor binding sites positioned at the most critical location of the viral promoter. Since a single promoter regulates viral gene expression, the promoter variations can play a critical role in determining the replication fitness of the viral strains. Our work for the first time provides a scientific explanation for the presence of a unique NF-κB binding motif in subtype C, a major HIV-1 genetic family responsible for half of the global HIV-1 infections. The results offer compelling evidence that the subtype C viral promoter not only is stronger but also is endowed with a qualitative gain-of-function advantage. The genetically variant NF-κB and the Sp1III motifs may be respond differently to specific cell signal pathways, and these mechanisms must be examined.

NFAT1 and NFAT3 cooperate with HDAC4 during regulation of alternative splicing of PMCA isoforms in PC12 cells

Background

The bulk of human genes undergo alternative splicing (AS) upon response to physiological stimuli. AS is a great source of protein diversity and biological processes and is associated with the development of many diseases. Pheochromocytoma is a neuroendocrine tumor, characterized by an excessive Ca²⁺-dependent secretion of catecholamines. This underlines the importance of balanced control of calcium transport via regulation of gene expression pattern, including different calcium transport systems, such as plasma membrane Ca²⁺-ATPases (PMCAs), abundantly expressed in pheochromocytoma chromaffin cells (PC12 cells). PMCAs are encoded by four genes (Atp2b1, Atp2b2, Atp2b3, Atp2b4), whose transcript products undergo alternative splicing giving almost 30 variants.

Results

In this scientific report, we propose a novel mechanism of regulation of PMCA alternative splicing in PC12 cells through cooperation of the nuclear factor of activated T-cells (NFAT) and histone deacetylases (HDACs). Luciferase assays showed increased activity of NFAT in PC12 cells, which was associated with altered expression of PMCA. RT-PCR experiments suggested that inhibition of the transcriptional activity of NFAT might result in the rearrangement of PMCA splicing variants in PC12 cells. NFAT inhibition led to dominant expression of 2x/c, 3x/a and 4x/a PMCA variants, while in untreated cells the 2w,z/b, 3z,x/b,c,e,f, and 4x/b variants were found as well. Furthermore, chromatin immunoprecipitation experiments showed that NFAT1-HDAC4 or NFAT3-HDAC4 complexes might be involved in regulation of PMCA2x splicing variant generation.

Conclusions

We suggest that the influence of NFAT/HDAC on PMCA isoform composition might be important for altered dopamine secretion by PC12 cells.

15-Deoxy-Δ¹²,¹⁴-prostaglandin J₂-glycerol, a putative metabolite of 2-arachidonyl glycerol and a peroxisome proliferator-activated receptor γ ligand, modulates nuclear factor of activated T cells

2-Arachidonyl glycerol (2-AG) is an endogenous arachidonic acid derivative released on demand from membrane precursors. 2-AG-mediated suppression of interleukin (IL)-2 depends on cyclooxygenase 2 (COX-2) metabolism and peroxisome proliferator-activated receptor γ (PPARγ) activation. 15-Deoxy-Δ¹²,¹⁴-prostaglandin J₂-glycerol ester (15d-PGJ₂-G), a putative COX-2 metabolite of 2-AG, acts as a PPARγ ligand and produces IL-2 suppression in activated Jurkat T cells, in part, by decreasing nuclear factor of activated T cells (NFAT) transcriptional activity. The objective of the present studies was to investigate the mechanism by which 15d-PGJ₂-G modulates NFAT activity to suppress IL-2. 15d-PGJ₂-G treatment decreased phorbol 12-myristate 13-acetate (PMA)/calcium ionophore (I₀)-induced NFAT DNA binding to the human IL-2 promoter and nuclear NFAT2 accumulation. It is noteworthy that 15d-PGJ₂-G treatment increased active nuclear HDM2 (human homolog of the oncoprotein and E3 ubiquitin ligase murine double minute 2) expression, whereas there was no change in the expression of glycogen synthase kinase 3β, both of which regulate NFAT. 15d-PGJ₂-G and other PPARγ agonists, such as rosiglitazone and ciglitazone, decreased PMA/I₀-mediated elevation in intracellular calcium concentration ([Ca²⁺](i)) in activated Jurkat cells. We were surprised to find that the PPARγ antagonists 2-chloro-5-nitro-N-4-pyridinylbenzamide (T0070907) and 2-chloro-5-nitrobenzanilide (GW9662) also decreased the PMA/I₀-mediated elevation in [Ca²⁺](i) in activated T cells. In addition, the presence of T0070907 plus 15d-PGJ₂-G produced an additive decrease in PMA/I₀-mediated elevation of [Ca²⁺](i), suggesting that the 15d-PGJ₂-G effects on calcium might be either PPARγ-independent or -dependent on occupation of the PPARγ ligand binding domain. Collectively, our findings suggest that 15d-PGJ₂-G increases active nuclear HDM2, which could lead to a decrease in NFAT2 and IL-2 suppression.

Activation of alpha(1) -adrenergic receptors stimulate the growth of small mouse cholangiocytes via calcium-dependent activation of nuclear factor of activated T cells 2 and specificity protein 1

Small cholangiocytes proliferate via activation of calcium (Ca(2+) )-dependent signaling in response to pathological conditions that trigger the damage of large cyclic adenosine monophosphate-dependent cholangiocytes. Although our previous studies suggest that small cholangiocyte proliferation is regulated by the activation of Ca(2+) -dependent signaling, the intracellular mechanisms regulating small cholangiocyte proliferation are undefined. Therefore, we sought to address the role and mechanisms of action by which phenylephrine, an α(1) -adrenergic agonist stimulating intracellular D-myo-inositol-1,4,5-triphosphate (IP(3) )/Ca(2+) levels, regulates small cholangiocyte proliferation. Small and large bile ducts and cholangiocytes expressed all AR receptor subtypes. Small (but not large) cholangiocytes respond to phenylephrine with increased proliferation via the activation of IP(3) /Ca(2+) -dependent signaling. Phenylephrine stimulated the production of intracellular IP(3) . The Ca(2+) -dependent transcription factors, nuclear factor of activated T cells 2 (NFAT2) and NFAT4, were predominantly expressed by small bile ducts and small cholangiocytes. Phenylephrine stimulated the Ca(2+) -dependent DNA-binding activities of NFAT2, NFAT4, and Sp1 (but not Sp3) and the nuclear translocation of NFAT2 and NFAT4 in small cholangiocytes. To determine the relative roles of NFAT2, NFAT4, or Sp1, we knocked down the expression of these transcription factors with small hairpin RNA. We observed an inhibition of phenylephrine-induced proliferation in small cholangiocytes lacking the expression of NFAT2 or Sp1. Phenylephrine stimulated small cholangiocyte proliferation is regulated by Ca(2+) -dependent activation of NFAT2 and Sp1.

CONCLUSION

Selective stimulation of Ca(2+) -dependent small cholangiocyte proliferation may be key to promote the repopulation of the biliary epithelium when large bile ducts are damaged during cholestasis or by toxins.

NFAT and IRF proteins regulate transcription of the anti-HIV gene, APOBEC3G

The human cytidine deaminase APOBEC3G (A3G) is an innate restriction factor that inhibits human immunodeficiency virus, type 1 (HIV-1) replication. Regulation of A3G gene expression plays an important role in this suppression. Currently, an understanding of the mechanism of this gene regulation is largely unknown. Here, we have identified and characterized a TATA-less core promoter with an NFAT/IRF-4 composite binding site that confers cell type-specific transcriptional regulation. We found that A3G expression is critically dependent on NFATc1/NFATc2 and IRF-4. When either NFATc1 or NFATc2 and IRF-4 were co-expressed, A3G promoter activity was observed in cells that normally lack A3G expression and expression was not detected in the presence of the individual factors. This induced A3G expression allowed normally permissive CEMss cells to adopt a nonpermissive state, able to resist an HIV-1Δvif challenge. This represents the first reporting of manipulating the restrictive state of a cell type via gene regulation. Identification of NFAT and IRF family members as critical regulators of A3G expression offers important insight into the transcriptional control mechanisms that regulate innate immune responses and identifies specific targets for therapeutic intervention aimed at effectively boosting our natural immunity, in the form of a host defensive factor, against HIV-1.

NF-kappaB regulates thrombin-induced ICAM-1 gene expression in cooperation with NFAT by binding to the intronic NF-kappaB site in the ICAM-1 gene

Activation of NF-kappaB is essential for protease-activated receptor-1 (PAR-1)-mediated ICAM-1 expression in endothelial cells. Here we show that PAR-1 activation induces binding of both p65/RelA and NFATc1 to the NF-kappaB binding site localized in intron-1 of the ICAM-1 gene to initiate transcription in endothelial cells. We discovered the presence of two NF-kappaB binding sites in intron-1 (+70, NF-kappaB site 1; +611, NF-kappaB site 2) of the human ICAM-1 gene. Chromatin immunoprecipitation results showed that thrombin induced binding of p65/RelA and of NFATc1 specifically to intronic NF-kappaB site 1 of the ICAM-1 gene. Electrophoretic mobility shift and supershift assays confirmed the binding of p65/RelA and NFATc1 to the intronic NF-kappaB site 1 in thrombin-stimulated cells. Thrombin increased the expression of ICAM-1-promoter-intron 1-reporter (-1,385 to +234) construct approximately 25-fold and mutation of intronic NF-kappaB site 1 markedly reduced thrombin-induced reporter expression. Moreover, inhibition of calcineurin, knockdown of either NFATc1 or p65/RelA with siRNA significantly reduced thrombin-induced ICAM-1 expression and polymorphonuclear leukocyte adhesion to endothelial cells. In contrast, NFATc1 knockdown had no effect on TNF-alpha-induced ICAM-1 expression. Thus these results suggest that p65/RelA and NFATc1 bind to the intronic NF-kappaB site 1 sequence to induce optimal transcription of the ICAM-1 gene in response to thrombin in endothelial cells.

Up-regulation of cathepsin B expression and enhanced secretion in mitochondrial DNA-depleted osteosarcoma cells

BACKGROUND INFORMATION

mtDNA (mitochondrial DNA) mutations that impair oxidative phosphorylation can contribute to carcinogenesis through the increased production of reactive oxygen species and through the release of proteins involved in cell motility and invasion. On the other hand, many human cancers are associated with both the up-regulation and the increased secretion of several proteases and heparanase. In the present study, we tried to determine whether the depletion in mtDNA could modulate the expression and/or the secretion of some lysosomal hydrolases in the 143B osteosarcoma cells, as these mtDNA-depleted cells are characterized by a higher degree of invasiveness than the parental cells.

RESULTS

In comparison with the parental cells, we measured a higher amount of procathepsin B in the conditioned culture medium of the 143B cells lacking mtDNA (rho(0) 143B cells), as well as a rise in the specific activity of intracellular cathepsin B. In addition, we observed an activation of the transcription factor NF-kappaB (nuclear factor kappaB) in the cells devoid of functional mitochondria. Finally, we demonstrated that the down-regulation of the NF-kappaB p65 subunit by RNA interference led to a reduction in cathepsin B expression in rho(0) 143B cells.

CONCLUSIONS

The up-regulation of cathepsin B by NF-kappaB, followed by its secretion into the extracellular environment, might be partly responsible for the previously reported invasiveness of the mtDNA-depleted 143B osteosarcoma cells.

The neuropeptide pituitary adenylate cyclase activating polypeptide modulates Ca2+ and pro-inflammatory functions in human monocytes through the G protein-coupled receptors VPAC-1 and formyl peptide receptor-like 1

In human neutrophils, the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) acting via the G protein-coupled receptors vasoactive intestinal peptide/PACAP receptor 1 (VPAC-1) and formyl peptide receptor-like 1 (FPRL1) modulates Ca2+ and pro-inflammatory activities. We evaluated in human monocytes the importance of the Ca2+ signal and the participation of FPRL1 in PACAP-associated signaling pathways and pro-inflammatory activities. PACAP-evoked Ca2+ transient involved both Ca2+ influx and intracytoplasmic Ca2+ mobilisation. This was pertussis toxin, protein kinase A and adenylate cyclase dependent indicating the participation of Galphai and Galphas with mobilisation of both InsP3 sensitive and insensitive stores. Intra- or extracellular Ca2+ depletion resulted in the inhibition of PACAP-induced, Akt, ERK, p38 and NF-kappaB activations as well as a decrease in PACAP-associated reactive oxygen species (ROS) production and integrin CD11b membrane upregulation. The FPRL1 antagonist, Trp-Arg-Trp-Trp-Trp (WRW4), decreased PACAP-evoked Ca2+ signal, Akt, ERK phosphorylation, ROS and CD11b upregulation without affecting p38 phosphorylation. NF-kappaB inhibitors prevented PACAP-induced Ca2+ mobilisation. Monocytes pre-treatment with fMLP but not with LPS desensitised cells to the pro-inflammatory effects of PACAP. Thus, both intra- and extracellular Ca2+ play a role in controlling pro-inflammatory functions stimulated by PACAP which acts through a VPAC-1, FPRL1/Galphai/PI3K/ERK pathway and a VPAC-1/Galphas/PKA/p38 pathway to fully activate monocytes.

OX40 gene expression is up-regulated by chromatin remodeling in its promoter region containing Sp1/Sp3, YY1, and NF-kappa B binding sites

OX40 is a member of the TNFR superfamily (CD134; TNFRSF4) that is expressed on activated T cells and regulates T cell-mediated immune responses. In this study, we have examined the regulation of OX40 gene expression in T cells. Low-level OX40 mRNA expression was detected in both resting T cells and the nonactivated EL4 T cell line, and was up-regulated in both types of T cells upon activation with anti-CD3 Ab. We have shown in this study that basal OX40 promoter activity is regulated by constitutively expressed Sp1/Sp3 and YY1 transcription factors. NF-kappaB (p50 and p65) also binds to the OX40 promoter region, but the level of direct enhancement of the OX40 promoter activity by this transcription factor is not sufficient to account for the observed up-regulation of OX40 mRNA expression associated with activation. We have detected by chromatin immunoprecipitation that histone H4 molecules in the OX40 promoter region are highly acetylated by activation and NF-kappaB binds to the OX40 promoter in vivo. These findings suggest that OX40 gene expression is regulated by chromatin remodeling, and that NF-kappaB might be involved in initiation of chromatin remodeling in the OX40 promoter region in activated T cells. CD4(+)CD25(+) regulatory T (Treg) cells also express OX40 at high levels, and signaling through this receptor can neutralize suppressive activity of this Treg cell. In CD4(+)CD25(+) Treg cells, histone H4 molecules in the OX40 promoter region are also highly acetylated, even in the absence of in vitro activation.

Progressive loss of CD3 expression after HTLV-I infection results from chromatin remodeling affecting all the CD3 genes and persists despite early viral genes silencing

Background

HTLV-I infected CD4⁺ T-cells lines usually progress towards a CD3^- or CD3^low phenotype. In this paper, we studied expression, kinetics, chromatin remodeling of the CD3 gene at different time-points post HTLV-I infection.

Results

The onset of this phenomenon coincided with a decrease of CD3γ followed by the subsequent progressive reduction in CD3δ, then CD3ε and CD3ζ mRNA. Transient transfection experiments showed that the CD3γ promoter was still active in CD3^- HTLV-I infected cells demonstrating that adequate amounts of the required transcription factors were available. We next looked at whether epigenetic mechanisms could be responsible for this progressive decrease in CD3 expression using DNase I hypersensitivity (DHS) experiments examining the CD3γ and CD3δ promoters and the CD3δ enhancer. In uninfected and cells immediately post-infection all three DHS sites were open, then the CD3γ promoter became non accessible, and this was followed by a sequential closure of all the DHS sites corresponding to all three transcriptional control regions. Furthermore, a continuous decrease of in vivo bound transcription initiation factors to the CD3γ promoter was observed after silencing of the viral genome. Coincidently, cells with a lower expression of CD3 grew more rapidly.

Conclusion

We conclude that HTLV-I infection initiates a process leading to a complete loss of CD3 membrane expression by an epigenetic mechanism which continues along time, despite an early silencing of the viral genome. Whether CD3 progressive loss is an epiphenomenon or a causal event in the process of eventual malignant transformation remains to be investigated.

Two conserved regions within the tissue-type plasminogen activator gene promoter mediate regulation by brain-derived neurotrophic factor

Tissue-type plasminogen activator (t-PA) has recently been identified as a modulator of neuronal plasticity and can initiate conversion of the pro-form of brain-derived neurotrophic factor (BDNF) into its mature form. BDNF also increases t-PA gene expression implicating t-PA as a downstream effector of BDNF function. Here we demonstrate that BDNF-mediated induction of t-PA mRNA requires an increase in t-PA gene transcription. Reporter constructs harboring 9.5 kb of the human t-PA promoter conferred BDNF-responsiveness in transfected mouse primary cortical neurons. This regulation was recapitulated in HEK 293 cells coexpressing the TrkB neurotrophin receptor. t-PA promoter-deletion analysis revealed the presence of two BDNF-responsive domains, one located between -3.07 and -2.5 kb and the other within the proximal promoter. The upstream region was shown to confer BDNF responsiveness in a TrkB-dependent manner when attached to a heterologous promoter. We also identify homologous regions within the murine and bovine t-PA gene promoters and demonstrate that the equivalent upstream murine sequence functions as a BDNF-responsive enhancer when inserted 5' of the human proximal t-PA promoter. Hence, BDNF-mediated induction of t-PA transcription relies on conserved modular promoter elements including a novel upstream BDNF-responsive domain and the proximal t-PA gene promoter.

HTLV-I infection of WE17/10 CD4+ cell line leads to progressive alteration of Ca2+ influx that eventually results in loss of CD7 expression and activation of an antiapoptotic pathway involving AKT and BAD which paves the way for malignant transformation

Adult T-cell leukemia/lymphoma (ATLL) is a malignancy slowly emerging from human T-cell leukemia virus type 1 (HTLV-I)-infected mature CD4(+) T-cells. To characterize the molecular modifications induced by HTLV-I infection, we compared HTLV-I-infected WE17/10 cells with control cells, using micro-arrays. Many calcium-related genes were progressively downmodulated over a period of 2 years. Infected cells acquired a profound decrease of intracellular calcium levels in response to ionomycin, timely correlated with decreased CD7 expression. Focusing on apoptosis-related genes and their relationship with CD7, we observed an underexpression of most antiapoptotic genes. Western blotting revealed increasing Akt and Bad phosphorylation, timely correlated with CD7 loss. This was shown to be phosphatidylinositol 3-kinase (PI3K)-dependent. Activation of PI3K/Akt induced resistance to the apoptotic effect of interleukin-2 deprivation. We thus propose the following model: HTLV-I infection induces a progressive decrease in CD3 genes expression, which eventually abrogates CD3 expression; loss of CD3 is known to perturb calcium transport. This perturbation correlates with loss of CD7 expression and induction of Akt and Bad phosphorylation via activation of PI3K. The activation of the Akt/Bad pathway generates a progressive resistance to apoptosis, at a time HTLV-I genes expression is silenced, thus avoiding immune surveillance. This could be a major event in the process of the malignant transformation into ATLL.

Promoter analysis of human CC chemokine CCL23 gene in U937 monocytoid cells

Expression of CCL23 is induced by external stimuli including PMA in monocytes, but its transcriptional regulation has not been studied to date. Serial deletion analysis of its 5' flanking region revealed that the region -293 to +31 was important for induction by PMA. Cis-acting elements at the -269/-264 (NFAT site), -167/-159 (NF-kappaB site), and -51/-43 (AP-1 site) positions were identified as the critical sites for the CCL23 expression in U937 cells. We demonstrated the binding of the transcription factors to the consensus sites. Specific inhibitors for signal pathways reduced PMA-induced expression of CCL23, confirming involvement of these transcription factors.

The neuropeptide pituitary adenylate cyclase activating protein stimulates human monocytes by transactivation of the Trk/NGF pathway

Transactivation is a process whereby stimulation of G-protein-coupled receptors (GPCR) activates signaling from receptors tyrosine kinase (RTK). In neuronal cells, the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) acting through the GPCR VPAC-1 exerts trophic effects by transactivating the RTK TrkA receptor for the nerve growth factor (NGF). Both PACAP and NGF have pro-inflammatory activities on monocytes. We have tested the possibility that in monocytes, PACAP, as reported in neuronal cells, uses NGF/TrkA signaling pathway. In these cells, PACAP increases TrkA tyrosine phosphorylations through a PI-3kinase dependent but phospholipase C independent pathway. K252a, an inhibitor of TrkA decreases PACAP-induced Akt and ERK phosphorylation and calcium mobilisation resulting in decreases in intracellular H2O2 production and membrane upregulation of CD11b expression, both functions being inhibited after anti-NGF or anti-TrkA antibody treatment. K252a also inhibits PACAP-associated NF-KB activity. Monocytes increase in NGF production is seen after micromolar PACAP exposure while nanomolar treatment which desensitizes cells to high dose of PACAP prevents PACAP-induced TrkA phosphorylation, H2O2 production and CD11b expression. Finally, NGF-dependent ERK activation and H2O2 production is pertussis toxin sensitive. Altogether these data indicate that in PACAP-activated monocytes some pro-inflammatory activities occur through transactivation mechanisms involving VPAC-1, NGF and TrkA-associated tyrosine kinase activity.

Bortezomib (PS-341, Velcade) increases the efficacy of trastuzumab (Herceptin) in HER-2-positive breast cancer cells in a synergistic manner

BACKGROUND

Preclinical and clinical studies have shown that the proteasome inhibitor bortezomib (PS341, Velcade) is highly effective when combined with chemotherapeutic agents. The value of trastuzumab (Herceptin) in HER-2-positive (3+ score by immunohistochemistry or fluorescence in situ hybridization positive) breast cancer is also known; however, the response rate is <40% for metastatic breast cancer. These two pharmacologic agents prevent nuclear factor-kappaB (NF-kappaB) activation and induce nuclear accumulation of the cyclin-dependent kinase inhibitor p27(kip1), suggesting that combining bortezomib with trastuzumab could increase trastuzumab efficacy.

METHODS

Drug cytotoxicity, both individually and together, and drug effects on p27 localization and NF-kappaB activation were investigated on four breast cancer cell lines: SKBR-3 (HER-2+++), MDA-MB-453 (HER-2++), HER-2-transfected MCF-7 (HER-2+++), and MCF-7 (HER-2-).

RESULTS

Bortezomib induced apoptosis in HER-2-positive and HER-2-negative breast cancer cells in a dose- and time-dependent manner. Together, these drugs induced apoptosis of HER-2++/+++ cells at low concentrations, which had no effect when used alone, indicating there was a synergistic effect. Sequential treatment (trastuzumab then bortezomib) induced either necrosis or apoptosis, depending on the trastuzumab preincubation time. Susceptibility to bortezomib alone and the drug combination correlated with NF-kappaB activity and p27 localization.

CONCLUSIONS

The addition of bortezomib to trastuzumab increases the effect of trastuzumab in HER-2+++/++ cell lines in a synergistic way. This effect likely results from the ability of these two drugs to target the NF-kappaB and p27 pathways. The potential clinical application of this drug combination is under current evaluation by our group in a phase 1 clinical trial.

Pertussis toxin activates adult and neonatal naive human CD4+ T lymphocytes

Pertussis toxin (PTX) is known to be mitogenic for T lymphocytes, but its direct action on naive human T cells has not been specified. Herein, we show that PTX induces the proliferation of purified adult CD45RA(+)CD4(+) T cells independently of its ADP-ribosyltransferase activity. PTX directly induces TNF-alpha and IL-2 mRNA expression, modulates the level of several cell surface receptors and induces Forkhead box p3 (Foxp3) protein accumulation in naive CD4(+) T cells. Addition of autologous dendritic cells was found to be required for the production of high levels of IFN-gamma by PTX-stimulated naive T cells. These effects of PTX occurred in conjunction with activation of NF-kappaB and NFAT transcription factors. Overall, responses of neonatal CD4(+) T cells to PTX were similar to those of adult CD45RA(+)CD4(+) naive T cells except for their blunted CD40 ligand up-regulation. We suggest that the adjuvant properties of PTX during primary cell-mediated immune responses involve a direct action on naive T lymphocytes in addition to activation of antigen-presenting cells.

HIV-1 gp120 induces NFAT nuclear translocation in resting CD4+ T-cells

The replication of human immunodeficiency virus (HIV) in CD4+ T-cells is strongly dependent upon the state of activation of infected cells. Infection of sub-optimally activated cells is believed to play a critical role in both the transmission of virus and the persistence of CD4+ T-cell reservoirs. There is accumulating evidence that HIV can modulate signal-transduction pathways in a manner that may facilitate replication in such cells. We previously demonstrated that HIV gp120 induces virus replication in resting CD4+ T cells isolated from HIV-infected individuals. Here, we show that in resting CD4+ T-cells, gp120 activates NFATs and induces their translocation into the nucleus. The HIV LTR encodes NFAT recognition sites, and NFATs may play a critical role in promoting viral replication in sub-optimally activated cells. These observations provide insight into a potential mechanism by which HIV is able to establish infection in resting cells, which may have implications for both transmission of HIV and the persistence of viral reservoirs.

Defective CD3γ gene transcription is associated with NFATc2 overexpression in the lymphocytic variant of hypereosinophilic syndrome

OBJECTIVE

Determine the molecular defects underlying the CD3(-)CD4(+) T-cell phenotype and persistence of this clonal population in patients with hypereosinophilic syndrome.

PATIENTS AND METHODS

Patients in this study suffer from the lymphocytic variant of hypereosinophilic syndrome distinguished by a CD3(-)CD4(+) T-cell clone that overexpresses Th2 cytokines upon activation and thereby provokes the eosinophilia. Interleukin-2-dependent CD3(-)CD4(+) T-cell lines were derived from patient blood at various disease stages and used to investigate the molecular modifications correlated with their abnormal phenotype.

RESULTS

We demonstrate that the CD3(-)CD4(+) T cells, characterized by a clonal TCRbeta gene rearrangement, maintained the same immunophenotype over the 6-year period of our study, during which one patient progressed from premalignant disease to CD3(-)CD4(+) T-cell lymphoma. We show that a specific loss of CD3gamma gene transcripts is responsible for the defect in TCR/CD3 surface expression. In addition, the level of NFATc2 binding to NFAT motifs in the CD3gamma gene promoter was greatly increased in the abnormal T cells. Our studies indicate that CD3gamma promoter activity can be positively influenced by NFATc1 plus NF-kappaB p50 and negatively regulated by NFATc2 containing complexes. We show that in patients' CD3(-)CD4(+) T cells, an increase in nuclear NFATc2 occurs in parallel with a decrease in NFATc1 and NF-kappaB gene expression.

CONCLUSION

Hypereosinophilic syndrome joins the growing number of pathological conditions where a defect in surface expression and/or function of the TCR/CD3 complex results from altered regulation of CD3gamma gene expression.

Transcriptional Regulation of the HumanCD3γ Gene: The TATA-LessCD3γ Promoter Functions via an Initiator and Contiguous Sp-Binding Elements

Growing evidence that the CD3gamma gene is specifically targeted in some T cell diseases focused our attention on the need to identify and characterize the elusive elements involved in CD3gamma transcriptional control. In this study, we show that while the human CD3gamma and CD3delta genes are oriented head-to-head and separated by only 1.6 kb, the CD3gamma gene is transcribed from an independent but weak, lymphoid-specific TATA-less proximal promoter. Using RNA ligase-mediated rapid amplification of cDNA ends, we demonstrate that a cluster of transcription initiation sites is present in the vicinity of the primary core promoter, and the major start site is situated in a classical initiator sequence. A GT box immediately upstream of the initiator binds Sp family proteins and the general transcription machinery, with the activity of these adjacent elements enhanced by the presence of a second GC box 10 nt further upstream. The primary core promoter is limited to a sequence that extends upstream to -15 and contains the initiator and GT box. An identical GT box located approximately 50 nt from the initiator functions as a weak secondary core promoter and likely generates transcripts originating upstream from the +1. Finally, we show that two previously identified NFAT motifs in the proximal promoter positively (NFATgamma(1)) or negatively (NFATgamma(1) and NFATgamma(2)) regulate expression of the human CD3gamma gene by their differential binding of NFATc1 plus NF-kappaB p50 or NFATc2 containing complexes, respectively. These data elucidate some of the mechanisms controlling expression of the CD3gamma gene as a step toward furthering our understanding of how its transcription is targeted in human disease.

Reciprocal regulation of the nuclear factor of activated T cells and HIV-1

The human immunodeficiency virus type 1 (HIV-1) has evolved to coordinate its replication with the activation state of the host CD4T cell. To this end, it taps into major host cell signaling pathways and their associated transcription factors. Of these, T-cell activation and the transcription factor NF-kappaB, respectively, have become the best-studied examples. The past several years have revealed compelling evidence that another transcription factor family involved in T-cell activation, the nuclear factor of activated T cells (NFAT), plays an important role in the regulation of HIV-1. Major advances have been made in our understanding of the interaction of HIV-1 with this intriguing transcription factor. The duplicated NF-kappaB binding sites in the HIV-1 enhancer surprisingly also bind NFAT proteins and appear to be the most important targets for NFAT transactivation of the HIV-1 long terminal repeat. The crystal structure of NFAT1 bound to one of these duplicated sites was solved recently. Interestingly, it showed that NFAT1 binds to this site as a homodimer and occupies the core of the NF-kappaB site, suggesting mutually exclusive binding and alternate transactivation by these two factors. NFAT also regulates HIV-1 infection indirectly, as it can relieve a block to reverse transcription in quiescent T cells. In turn, HIV-1, and particularly its Tat and Nef gene products, can upregulate NFAT expression and activity. This reciprocal regulation between virus and transcription factor potentially creates a positive feedback loop, which may facilitate the establishment of early HIV-1 infection and, later, the transition from latent to productive infection. The immunosuppressive drug cyclosporin A (CsA) inhibits NFAT activity and thus represents a potential treatment for HIV-1 infection. Recent small-scale clinical trials have yielded optimistic results, suggesting roles for CsA after organ transplantation in HIV-1+ individuals and as adjunct treatment in stable early HIV-1 infection.

Quinolone Alkaloids with Inhibitory Activity against Nuclear Factor of Activated T Cells from the Fruits of Evodia rutaecarpa

Nine quinolone alkaloids (1-9) from the fruits of Evodia rutaecarpa were investigated for their inhibitory activity on nuclear factor of activated T cells (NFAT)-dependent transcription in comparison with nuclear factor (NF)-kappa B-dependent transcription using a reporter gene assay. These alkaloids showed inhibitory effects against NFAT activity, with IC(50) values between 0.91 microM and 15.91 microM. Of the N-methylated quinolones, the longer aliphatic side chain at the quinolone ring showed stronger inhibition of NFAT activity. These N-methylated compounds showed comparable inhibitory effects against NF-kappa B activity. However, quinolone alkaloids without the N-methyl group showed a more selective inhibition of NFAT activity.

Disruption of B-cell homeostatic control mediated by the BLV-Tax oncoprotein: association with the upregulation of Bcl-2 and signaling through NF-kappaB

Transactivating proteins associated with complex onco-retroviruses including human T-cell leukemia virus-1 (HTLV-1) and bovine leukemia virus (BLV) mediate transformation using poorly understood mechanisms. To gain insight into the processes that govern tumor onset and progression, we have examined the impact of BLV-Tax expression on ovine B-cells, the targets of BLV in experimentally infected sheep, using B-cell clones that are dependent on CD154 and gammac-common cytokines. Tax was capable of mediating progression of B-cells from cytokine dependence to cytokine independence, indicating that the transactivator can over-ride signaling pathways typically controlled by cytokine receptor activation in B-cells. When examined in the presence of both CD154 and interleukin-4, Tax had a clear supportive role on B-cell growth, with an impact on B-cell proliferation, cell cycle phase distribution, and survival. Apoptotic B-cell death mediated by growth factor withdrawal, physical insult, and NF-kappaB inhibition was dramatically reduced in the presence of Tax. Furthermore, the expression of Tax was associated with higher Bcl-2 protein levels, providing rationale for the rescue signals mediated by the transactivator. Finally, Tax expression in B-cells led to a dramatic increase of nuclear RelB/p50 and p50/p50 NF-kappaB dimers, indicating that cellular signaling through NF-kappaB is a major contributory mechanism in the disruption of B-cell homeostasis. Although Tax is involved in aspects of pathogenesis that are unique to complex retroviruses, the viral strategies associated with this transactivating oncoprotein may have wide-ranging effects that are relevant to other B-cell malignancies.