Induction of NF-kappa B-like activity by platelet-derived growth factor in mouse fibroblasts

Elevated GRO-α and IL-18 in serum and brain implicate the NLRP3 inflammasome in frontotemporal dementia

Neuroinflammation is a hallmark of frontotemporal dementia (FTD), a heterogeneous group of proteinopathies characterized by the progressive degeneration of the frontal and temporal lobes. It is marked by microglial activation and subsequent cytokine release. Although cytokine levels in FTD brain and CSF have been examined, the number of cytokines measured in each study is limited and knowledge on cytokine concentrations in FTD serum is scarce. Here, we assessed 48 cytokines in FTD serum and brain. The aim was to determine common cytokine dysregulation pathways in serum and brain in FTD. Blood samples and brain tissue samples from the superior frontal cortex (SFC) were collected from individuals diagnosed with behavioral variant FTD (bvFTD) and healthy controls, and 48 cytokines were measured using a multiplex immunological assay. The data were evaluated by principal component factor analysis to determine the contribution from different components of the variance in the cohort. Levels of a number of cytokines were altered in serum and SFC in bvFTD compared to controls, with increases in GRO-α and IL-18 in both serum and SFC. These changes could be associated with NLRP3 inflammasome activation or the NFκB pathway, which activates NLRP3. The results suggest the possible importance of the NLRP3 inflammasome in FTD. An improved understanding of the role of inflammasomes in FTD could provide valuable insights into the pathogenesis, diagnosis and treatment of FTD.

Association of Single-Nucleotide Variants in the Human Leukocyte Antigen and Other Loci With Childhood Hodgkin Lymphoma

IMPORTANCE

Studies focusing on genetic susceptibility of childhood Hodgkin lymphoma (HL) are limited.

OBJECTIVES

To identify genetic variants associated with childhood-onset HL vs adult-onset HL.

DESIGN, SETTING, AND PARTICIPANTS

This genetic association study was performed with 3 cohorts: the St Jude Lifetime Cohort Study (SJLIFE), initiated in 2007 with ongoing follow-up, and the original and expansion cohorts of the Childhood Cancer Survivor Study (CCSS), initiated in the 1990s with ongoing follow-up. Results of these genome-wide association studies (GWASs) were combined via meta-analysis. Data were analyzed from June 2021 to June 2022.

MAIN OUTCOMES AND MEASURES

Childhood HL was the focused outcome. Single-nucleotide variant (SNV, formerly single-nucleotide polymorphism) array genotyping and imputation were conducted for the CCSS original cohort, and whole-genome sequencing was performed for the SJLIFE and CCSS expansion cohort.

RESULTS

A total of 1286 HL cases (mean diagnosis [SD] age, 14.6 [3.9] years), 6193 non-HL childhood cancer cases, and 369 noncancer controls, all of European ancestry, were included in the analysis. Using step-wise conditional logistic regression, the odds ratios (ORs) for each of the 3 independent SNVs identified in the human leukocyte antigen (HLA) locus were 1.80 (95% CI, 1.59-2.03; P = 2.14 × 10-21) for rs28383311, 1.53 (95% CI, 1.37-1.70; P = 2.05 × 10-14) for rs3129198, and 1.51 (95% CI, 1.35-1.69; P = 6.21 × 10-13) for rs3129890. Further HLA imputation revealed 9 alleles and 55 amino acid changes that potentially conferred HL susceptibility. In addition, 5 non-HLA loci were identified: (1) rs1432297 (OR, 1.29; 95% CI, 1.18-1.41; P = 2.5 × 10-8; r2 = 0.55; D' = 0.75 with previously reported rs1432295, REL); (2) rs2757647 (OR, 1.30; 95% CI, 1.18-1.42; P = 3.5 × 10-8; r2 = 0.59; D' = 0.83 with previously reported rs6928977, AHI1); (3) rs13279159 (OR, 1.33; 95% CI, 1.20-1.47; P = 1.7 × 10-8; r2 = 0.75; D' = 1.00 with previously reported rs2019960, PVT1); (4) rs3824662 (OR, 1.52; 95% CI, 1.33-1.73; P = 3.9 × 10-10; r2 = 0.91; D' = 1.00 with previously reported rs3781093, GATA3); and (5) rs117953624 (OR, 1.98; 95% CI, 1.56-2.51; P = 1.5 × 10-8; minor allele frequency, 0.02), a novel uncommon SNV mapped to PDGFD. Twelve of 18 previously reported genome-wide significant non-HLA SNVs (67%) were replicated with statistically significant results.

CONCLUSIONS AND RELEVANCE

In this genetic association study, a predominantly common and potentially unique genetic etiology was found between childhood-onset and adulthood-onset HL.

Regulation of NF-κB by the CARD proteins

Scaffold proteins play pivotal roles in the regulation of signal transduction pathways by connecting upstream receptors to downstream effector molecules. During the last decade, many scaffold proteins that contain caspase-recruitment domains (CARD) have been identified. Investigating the roles of CARD proteins has revealed that many of them play crucial roles in signaling cascades leading to activation of nuclear factor-κB (NF-κB). In this review, we discuss the contributions of CARD proteins to NF-κB activation in various signaling cascades. In particular, we share some of our personal experiences during the initial investigation of the functions of the CARMA family of CARD proteins and then summarize the roles of these proteins in signaling pathways induced by antigen receptors, G protein-coupled receptors, receptor tyrosine kinase, and C-type lectin receptors in the context of recent progress in these field.

CARMA3 is crucial for EGFR-Induced activation of NF-κB and tumor progression

EGF activates NF-κB, and constitutively activated NF-κB contributes to EGFR mutation-associated tumorigenesis, but it remains unclear precisely how EGFR signaling leads to NF-κB activation. Here we report that CARMA3, a caspase recruitment domain (CARD)-containing scaffold molecule, is required for EGF-induced NF-κB activation. CARMA3 deficiency impaired the activation of the IKK complex following EGF stimulation, resulting in a defect of EGF-induced IκBα phosphorylation and NF-κB activation. We found that CARMA3 and Bcl10 contributed to several characteristics of EGFR-associated malignancy, including proliferation, survival, migration, and invasion. Most importantly, CARMA3 contributed to tumor growth in vivo. Our findings elucidate a crucial link between EGFR-proximal signaling components and the downstream IKK complex, and they suggest a new therapeutic target for treatment of EGFR-driven cancers.

NF-κB signaling pathways regulated by CARMA family of scaffold proteins

The NF-κB family of transcription factors plays a crucial role in cell activation, survival and proliferation. Its aberrant activity results in cancer, immunodeficiency or autoimmune disorders. Over the past two decades, tremendous progress has been made in our understanding of the signals that regulate NF-κB activation, especially how scaffold proteins link different receptors to the NF-κB-activating complex, the IκB kinase complex. The growing number of these scaffolds underscores the complexity of the signaling networks in different cell types. In this review, we discuss the role of scaffold molecules in signaling cascades induced by stimulation of antigen receptors, G-protein-coupled receptors and C-type Lectin receptors, resulting in NF-κB activation. Especially, we focus on the family of Caspase recruitment domain (CARD)-containing proteins known as CARMA and their function in activation of NF-κB, as well as the link of these scaffolds to the development of various neoplastic diseases through regulation of NF-κB.

Dimethylfumarate inhibits NF-{kappa}B function at multiple levels to limit airway smooth muscle cell cytokine secretion

The antipsoriatic dimethylfumarate (DMF) has been anecdotically reported to reduce asthma symptoms and to improve quality of life of asthma patients. DMF decreases the expression of proinflammatory mediators by inhibiting the transcription factor NF-kappaB and might therefore be of interest for the therapy of inflammatory lung diseases. In this study, we determined the effect of DMF on platelet-derived growth factor (PDGF)-BB- and TNFalpha-induced asthma-relevant cytokines and NF-kappaB activation by primary human asthmatic and nonasthmatic airway smooth muscle cells (ASMC). Confluent nonasthmatic and asthmatic ASMC were incubated with DMF (0.1-100 microM) and/or dexamethasone (0.0001-0.1 microM), NF-kappaB p65 siRNA (100 nM), the NF-kappaB inhibitor helenalin (1 microM) before stimulation with PDGF-BB or TNFalpha (10 ng/ml). Cytokine release was measured by ELISA. NF-kappaB, mitogen and stress-activated kinase (MSK-1), and CREB activation was determined by immunoblotting and EMSA. TNFalpha-induced eotaxin, RANTES, and IL-6 as well as PDGF-BB-induced IL-6 expression was inhibited by DMF and by dexamethasone from asthmatic and nonasthmatic ASMC, but the combination of both drugs showed no glucocorticoid sparing effect in either of the two groups. NF-kappaB p65 siRNA and/or the NF-kappaB inhibitor helenalin reduced PDGF-BB- and TNFalpha-induced cytokine expression, suggesting the involvement of NF-kappaB signaling. DMF inhibited TNFalpha-induced NF-kappaB p65 phosphorylation, NF-kappaB nuclear entry, and NF-kappaB-DNA complex formation, whereas PDGF-BB appeared not to activate NF-kappaB within 60 min. Both stimuli induced the phosphorylation of MSK-1, NF-kappaB p65 at Ser276, and CREB, and all were inhibited by DMF. These data suggest that DMF downregulates cytokine secretion not only by inhibiting NF-kappaB but a wider range of NF-kappaB-linked signaling proteins, which may explain its potential beneficial effect in asthma.

Altered transcriptional regulators in response to serum in immortalized lymphocytes from Alzheimer's disease patients

Cell cycle disturbances may precede neuronal death in Alzheimer's disease (AD). We described alterations, in lymphocytes from AD patients, on the activity of two transcription factors, E2F and NF-kappaB, involved in cell proliferation and survival regulation, demonstrating that cell cycle dysfunction also occurs in peripheral cells. The analysis of E2F-DNA binding activity revealed lower signal intensity of protein-DNA complexes in AD cells, which correlated with increased phosphorylation of retinoblastoma (pRb) related proteins and enhanced proliferation. The calmodulin (CaM) antagonist calmidazolium (CMZ) abrogated the increased activity of AD cells by partially dephosphorylating pRb and p130. The NF-kappaB-DNA binding activity increased as cell progress through the cell cycle. The reduced NF-kappaB activation observed in AD cells appears not to be related to the increased phosphorylation of the pRb family proteins nor with the enhanced proliferative activity of AD cells, but seems to protect them from death induced by the loss of trophic support. Ca2+/CaM antagonists rescue NF-kappaB-DNA binding activity and sensitize AD cells to serum withdrawal. These observations suggest that disruption of Ca2+/CaM signaling pathway could be linked mechanistically to its pro cell survival actions, promoting enhanced proliferation or decreased cell death depending on the presence of growth-stimulatory signals.

Activation of NF-kappaB is required for PDGF-B chain to transform NIH3T3 cells

Elucidating the secondary signaling molecules that are necessary for platelet-derived growth factor (PDGF) to stimulate tumor development will be crucial to the understanding and treatment of a variety of cancers. Several lines of evidence have indicated that the transcription factor NF-kappaB plays a central role in transformation induced by Ha-ras and Bcr-abl, but nothing is known concerning its role in transformation by PDGF. Here we demonstrate that transcription from a promoter containing NF-kappaB binding sequences as well as the DNA binding activity of NF-kappaB were increased in PDGF-B-chain-transformed mouse fibroblast cells. Focus formation of PDGF-B-chain-transformed mouse fibroblasts was suppressed by treatment with acetylsalicylic acid (ASA) and salicylic acid, which are known inhibitors of NF-kappaB activation, but other nonsteroidal anti-inflammatory drugs that do not have an effect on NF-kappaB activity did not affect focus formation in these cells. Furthermore, expression of a dominant negative mutant of IkappaBalpha, pMEIkappaBalpha67CJ, and a dominant negative mutant of p65, p65DeltaC, resulted in decreased focus formation and NF-kappaB activity. Therefore, the transcription factor NF-kappaB plays a vital role in PDGF-B chain transformation of mouse fibroblast cells, and the NF-kappaB activity is sensitive to treatment with ASA.

NF-kappaB (p65/RelA) as a regulator of TNFalpha-mediated ML-1 cell differentiation

ML-1 human myeloblastic leukemia cells, suspended in serum-depleted medium, proliferate when the insulin-like growth factor-1 (IGF-1) and transferrin (Tf) are supplied, but differentiate to monocytes when these factors are replaced by the tumor necrosis factor-alpha (TNF-alpha). Induction of differentiation, but not of proliferation, involved the selective activation of diverse members of the NF-kappaB family of proteins. In differentiation-induced cells, NF-kappaB (p65) was translocated from the cytoplasm to the nucleus, whereas NF-kappaB (p75) remained localized to the cytoplasm. In contrast, NF-kappaB (p52) was present in the nuclei of proliferation- as well as of differentiation-induced ML-1 cells. The differentiation-specific translocation of NF-kappaB (p65) from the cytoplasm to the nucleus was mediated by an increase in the level of NIK, the NF-kappaB-inducing kinase which, through phosphorylation of IkappaB kinase alpha (Ikappakalpha), causes a decrease in the level of IkappaBalpha, allowing p65 to move from the cytoplasm to the nucleus. The p52/p65 heterodimer formed in the nucleus, bound specifically to the promoter of the tumor suppressor protein p53, effecting a 25 to 30-fold increase in the level of this protein. As we reported previously (Li et al, Cancer Res 1998; 58: 4282-4287), that increase led to the decreased expression of proliferating cell nuclear antigen (PCNA) and to the loss of proliferation-associated DNA synthesis. The ensuing uncoupling of growth from differentiation was followed by the initiation of the monocyte-specific differentiation program.

NF-kappaB and cell-cycle regulation: the cyclin connection

The cyclins are a family of proteins that are centrally involved in cell cycle regulation and which are structurally identified by conserved "cyclin box" regions. They are regulatory subunits of holoenzyme cyclin-dependent kinase (CDK) complexes controlling progression through cell cycle checkpoints by phosphorylating and inactivating target substrates. CDK activity is controlled by cyclin abundance and subcellular location and by the activity of two families of inhibitors, the cyclin-dependent kinase inhibitors (CKI). Many hormones and growth factors influence cell growth through signal transduction pathways that modify the activity of the cyclins. Dysregulated cyclin activity in transformed cells contributes to accelerated cell cycle progression and may arise because of dysregulated activity in pathways that control the abundance of a cyclin or because of loss-of-function mutations in inhibitory proteins.Analysis of transformed cells and cells undergoing mitogen-stimulated growth implicate proteins of the NF-kappaB family in cell cycle regulation, through actions on the CDK/CKI system. The mammalian members of this family are Rel-A (p65), NF-kappaB(1) (p50; p105), NF-kappaB(2) (p52; p100), c-Rel and Rel-B. These proteins are structurally identified by an amino-terminal region of about 300 amino acids, known as the Rel-homology domain. They exist in cytoplasmic complexes with inhibitory proteins of the IkappaB family, and translocate to the nucleus to act as transcription factors when activated. NF-kappaB pathway activation occurs during transformation induced by a number of classical oncogenes, including Bcr/Abl, Ras and Rac, and is necessary for full transforming potential. The avian viral oncogene, v-Rel is an NF-kappaB protein. The best explored link between NF-kappaB activation and cell cycle progression involves cyclin D(1), a cyclin which is expressed relatively early in the cell cycle and which is crucial to commitment to DNA synthesis. This review examines the interactions between NF-kappaB signaling and the CDK/CKI system in cell cycle progression in normal and transformed cells. The growth-promoting actions of NF-kappaB factors are accompanied, in some instances, by inhibition of cellular differentiation and by inhibition of programmed cell death, which involve related response pathways and which contribute to the overall increase in mass of undifferentiated tissue.

PDGF-induced Akt phosphorylation does not activate NF-kappa B in human vascular smooth muscle cells and fibroblasts

A recent report suggested that platelet-derived growth factor (PDGF) activates nuclear factor-kappa B (NF-kappa B) by phosphorylation of the protein kinase Akt [Romashkova and Makarov, Nature 401 (1999) 86-90]. The present study investigates the role of Akt in the activation of NF-kappa B by tumor necrosis factor-alpha (TNF alpha, 10 ng/ml) and PDGF-BB (20 ng/ml) in human vascular smooth muscle cells (SMC), skin and foreskin fibroblasts. TNF alpha stimulated serine phosphorylation and degradation of the inhibitory protein I kappa B alpha and strongly induced nuclear NF-kappa B translocation and binding activity. PDGF did not induce serine phosphorylation or degradation of I kappa B alpha and did not enhance binding activity of NF-kappa B. In contrast, stimulation with PDGF resulted in a marked phosphorylation of Akt, but no Akt phosphorylation occurred after stimulation with TNF alpha. These data suggest that Akt phosphorylation is not involved in NF-kappa B activation in human SMC and fibroblasts.

Consequences of Stat6 deletion on Sis/PDGF- and IL-4-induced proliferation and transcriptional activation in murine fibroblasts

Aberrant communication among growth factors and cytokines that regulate tissue homeostasis often results in malignancy. Among the many cell types that participate in this process, stromal fibroblasts communicate in a paracrine and juxtracrine manner with cells of epithelial, endothelial, and hematopoietic origin. For fibroblasts, platelet-derived growth factor (PDGF) is a major proliferative and differentiation agent. Interleukin-4 (IL-4), however, possesses only modulating functions in this cell type. Here, we investigated the consequences of deleting Stat6 on PDGF and IL-4 signaling, proliferation, and transcriptional activation by establishing and characterizing early passage fibroblasts from wild-type and Stat6 null mice. Both wild-type and Stat6-/- fibroblasts showed nearly identical PDGFR and IL-4R activation, gross substrate tyrosine phosphorylation, PI 3-kinase activation, as well as Stat1, 3 and 5 DNA binding activities. Unexpectedly, IL-4's enhancement of PDGF-induced [3H]thymidine incorporation was greatly diminished in Stat6-/-, but not wild-type fibroblasts. PDGF-induced [3H]thymidine uptake was largely unaffected. Strikingly, IL-4, but not PDGF induction of the proinflammatory gene products, IL-6 and MCP-1 was markedly reduced in Stat6-/- fibroblasts. Thus, Stat6 is an important and specific mediator of IL-4-enhanced PDGF-induced proliferation as well as IL-4's transcriptional activation of IL-6 and MCP-1.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.

NF-kappaB is a target of AKT in anti-apoptotic PDGF signalling

The mechanisms of cell proliferation and transformation are intrinsically linked to the process of apoptosis: the default of proliferating cells is to die unless specific survival signals are provided. Platelet-derived growth factor (PDGF) is a principal survival factor that inhibits apoptosis and promotes proliferation, but the mechanisms mediating its anti-apoptotic properties are not completely understood. Here we show that the transcription factor NF-kappaB is important in PDGF signalling. NF-kappaB transmits two signals: one is required for the induction of proto-oncogene c-myc and proliferation, and the second, an anti-apoptotic signal, counterbalances c-Myc cytotoxicity. We have traced a putative pathway whereby PDGF activates NF-kappaB through Ras and phospatidylinositol-3-kinase (PI(3)K) to the PKB/Akt protein kinase and the IkappaB kinase (IKK); NF-kappaB thus appears to be a target of the anti-apoptotic Ras/PI(3)K/Akt pathway. We show that, upon PDGF stimulation, Akt transiently associates in vivo with IKK and induces IKK activation. These findings establish a role for NF-kappaB in growth factor signalling and define an anti-apoptotic Ras/PI(3)K/Akt/IKK/NF-kappaB pathway, thus linking anti-apoptotic signalling with transcription machinery.

Characterization of a Rac1 signaling pathway to cyclin D(1) expression in airway smooth muscle cells

We examined the importance of the Rho family GTPase Rac1 for cyclin D(1) promoter transcriptional activation in bovine tracheal myocytes. Overexpression of active Rac1 induced transcription from the cyclin D(1) promoter, whereas platelet-derived growth factor (PDGF)-induced transcription was inhibited by a dominant-negative allele of Rac1, suggesting that Rac1 functions as an upstream activator of cyclin D(1) in this system. Rac1 forms part of the NADPH oxidase complex that generates reactive oxygen species such as H(2)O(2). PDGF stimulated a substantial increase in intracellular reactive oxygen species, as measured by the fluorescence of dichlorofluorescein-loaded cells, and this was blocked by the glutathione peroxidase mimetic ebselen. Pretreatment with ebselen, catalase, and the flavoprotein inhibitor diphenylene iodonium each attenuated PDGF- and Rac1-mediated cyclin D(1) promoter activation, while having no effect on the induction of cyclin D(1) by mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase-1 (MEK1), the upstream activator of ERKs. Antioxidant treatment also inhibited PDGF-induced cyclin D(1) protein expression and DNA synthesis. Overexpression of an N-terminal fragment of p67(phox), a component of NADPH oxidase which interacts with Rac1, attenuated PDGF-induced cyclin D(1) promoter activity, whereas overexpression of the wild-type p67 did not. Finally, Rac1 was neither required nor sufficient for ERK activation. Taken together, these data suggest a model by which two distinct signaling pathways, the ERK and Rac1 pathways, positively regulate cyclin D(1) and smooth muscle growth.

Biological effects of c-Mer receptor tyrosine kinase in hematopoietic cells depend on the Grb2 binding site in the receptor and activation of NF-kappaB

The c-Mer receptor tyrosine kinase (RTK) is most closely related to chicken c-Eyk and belongs to the Axl RTK subfamily. Although not detected in normal lymphocytes, c-Mer is expressed in B- and T-cell leukemia cell lines, suggesting an association with lymphoid malignancies. To gain an understanding of the role of this receptor in lymphoid cells, we expressed in murine interleukin-3 (IL-3)-dependent Ba/F3 pro-B-lymphocyte cells a constitutively active receptor, CDMer, formed from the CD8 extracellular domain and the c-Mer intracellular domain. Cells transfected with a plasmid encoding the CDMer receptor became IL-3 independent. When tyrosine (Y)-to-phenylalanine (F) mutations were introduced into c-Mer, only the Y867 change significantly reduced the IL-3-independent cell proliferation. The Y867 residue in the CDMer receptor mediated the binding of Grb2, which recruited the p85 phosphatidylinositol 3-kinase (PI 3-kinase). Despite the difference in promotion of proliferation, both the CDMer and mutant F867 receptors activated Erk in transfected cells. On the other hand, we found that both transcriptional activation of NF-kappaB and activation of PI 3-kinase were significantly suppressed with the F867 mutant receptor, suggesting that the activation of antiapoptotic pathways is the major mechanism for the observed phenotypic difference. Consistent with this notion, apoptosis induced by IL-3 withdrawal was strongly prevented by CDMer but not by the F867 mutant receptor.

Transactivation by expression of the hepatitis B virus X protein with an inducible system

We describe here the conditional expression of the hepatitis B virus X protein using the inducible system controlled by a tet-responsive promoter. Induction of the X protein in Rat-2 fibroblasts activated transcription from a heterologous gene promoter and stimulated the DNA-binding activity of NFkB. The ability to produce this biologically active X protein in a stable cell line will accelerate the elucidation of the function and mechanisms of X and eventually help us understand the role of X in natural viral infection and carcinogenesis.

c-Rel arrests the proliferation of HeLa cells and affects critical regulators of the G1/S-phase transition

A tetracycline-regulated system was used to characterize the effects of c-Rel on cell proliferation. The expression of c-Rel in HeLa cells led to growth arrest at the G1/S-phase transition, which correlated with its nuclear localization and the induction of endogenous IkappaB alpha expression. These changes were accompanied by a decrease in E2F DNA binding and the accumulation of the hypophosphorylated form of Rb. In vitro kinase assays showed a reduction in Cdk2 kinase activity that correlated with elevated levels of p21WAF1 Cdk inhibitor and p53 tumor suppressor protein. While the steady-state levels of WAF1 transcripts were increased, pulse-chase analysis revealed a sharp increase in p53 protein stability. Importantly, the deletion of the C-terminal transactivation domains of c-Rel abolished these effects. Together, these studies demonstrate that c-Rel can affect cell cycle control and suggest the involvement of the p21WAF1 and p53 cell cycle regulators.

Rapid activation of PDGF-A and -B expression at sites of lung injury in asbestos-exposed rats

The development of interstitial pulmonary fibrosis is associated with a variety of inflammatory mediators, including peptide growth factors and cytokines. In the work presented here, we have asked whether or not platelet-derived growth factor (PDGF)-A and -B genes and proteins are expressed in anatomic and temporal patterns consistent with this factor playing a role in the disease process. Using an established rat model of asbestos-induced fibroproliferative lung disease, we demonstrate elevated levels of PDGF-A and -B mRNAs in total lung RNA immediately after a single 5-h exposure to approximately 1,000 fibers/ml of chrysotile asbestos. In situ hybridization revealed the PDGF-A and -B in RNAs primarily in macrophages and bronchiolar-alveolar epithelial cells at sites of initial fiber deposition and lung injury. There was clear evidence of PDGF-A and -B mRNAs in interstitial cells as well. The pattern of in situ hybridization was entirely consistent with the appearance (established by immunohistochemistry) of PDGF-A and -B proteins by 24 h post-exposure in the same cell types. Both mRNAs and proteins remained detectable at the fiber deposition sites for almost 2 wk post-exposures. These findings are consistent with our previous studies showing increased mesenchymal cell proliferation and fibroproliferative lesions that progress at the sites where PDGF-A and -B are expressed. Although it is clear that multiple growth factors are produced simultaneously at sites of initial injury, we suggest that the PDGF isoforms could be playing a central role in the disease process based upon their potent mitogenic effects upon mesenchymal cells.

Insulin activates nuclear factor kappa B in mammalian cells through a Raf-1-mediated pathway

We examined the effect of insulin on nuclear factor kappa B (NF-kappa B) activity in Chinese ovary (CHO) cells overexpressing wild-type (CHO-R cells) or -defective insulin receptors mutated at Tyr1162 and Tyr1163 autophosphorylation sites (CHO-Y2 cells). In CHO-R cells, insulin caused a specific, time-, and concentration-dependent activation of NF-kappa B. The insulin-induced DNA-binding complex was identified as the p50/p65 heterodimer. Insulin activation of NF-kappa B: 1) was related to insulin receptor number and tyrosine kinase activity since it was markedly reduced in parental CHO cells which proved to respond to insulin growth factor-1 and phorbol 12-myristate 13-acetate (PMA) activation, and was dramatically decreased in CHO-Y2 cells; 2) persisted in the presence of cycloheximide and was blocked by pyrrolidine dithiocarbamate, aspirin and sodium salicylate, three compounds interfering with I kappa B degradation and/or NF-kappa B.I kappa B complex dissociation; 3) was independent of both PMA-sensitive and atypical (zeta) protein kinases C; and 4) was dependent on Raf-1 kinase activity since insulin-stimulated NF-kappa B DNA binding activity was inhibited by 8-bromo-cAMP, a Raf-1 kinase inhibitor. Moreover, insulin activation of NF-kappa B-driven luciferase reporter gene expression was blocked in CHO-R cells expressing a Raf-1 dominant negative mutant. This is the first evidence that insulin activates NF-kappa B in mammalian cells through a post-translational mechanism requiring both insulin receptor tyrosine kinase and Raf-1 kinase activities.

Identification of a rel-related protein in the nucleus during the S phase of the cell cycle

The c-rel proto-oncogene encodes a 75-kDa protein (p75c-rel) which is present in the cytosol of chick embryo fibroblasts (CEF) associated with a distinct set of cellular proteins with molecular masses of 40, 115, and 124 kDa. CEF cultures arrested in S phase of the cell cycle, or enriched for G2 or mitotic cells, were examined to determine whether the expression of c-rel was altered during the cell cycle. Levels of p75c-rel remained constant in all portions of the cell cycle examined; however, a Rel-related protein with an apparent molecular mass of 64 kDa was detected in nuclei of S-phase cells. As cells enter G2, the level of this protein in the nucleus decreases. This protein reacts with antiserum generated against the carboxy terminus of p75c-rel in radioimmunoprecipitations and Western immunoblot experiments and was also detected in a Western immunoblot with antiserum generated against the first 161 amino acids of pp59v-rel. Thus, unlike other Rel/NF-kappa B family members, p64 has carboxy-terminal homology with c-Rel. The majority of peptides generated by partial proteolytic cleavage of p64 are shared with peptides generated by digestion of p75c-rel and/or pp59v-rel. We suggest that this protein represents a new member of the Rel family of transcription factors and is located in the nucleus of avian fibroblasts during S phase of the cell cycle.

Identification of a rel-related protein in the nucleus during the S phase of the cell cycle

The c-rel proto-oncogene encodes a 75-kDa protein (p75c-rel) which is present in the cytosol of chick embryo fibroblasts (CEF) associated with a distinct set of cellular proteins with molecular masses of 40, 115, and 124 kDa. CEF cultures arrested in S phase of the cell cycle, or enriched for G2 or mitotic cells, were examined to determine whether the expression of c-rel was altered during the cell cycle. Levels of p75c-rel remained constant in all portions of the cell cycle examined; however, a Rel-related protein with an apparent molecular mass of 64 kDa was detected in nuclei of S-phase cells. As cells enter G2, the level of this protein in the nucleus decreases. This protein reacts with antiserum generated against the carboxy terminus of p75c-rel in radioimmunoprecipitations and Western immunoblot experiments and was also detected in a Western immunoblot with antiserum generated against the first 161 amino acids of pp59v-rel. Thus, unlike other Rel/NF-kappa B family members, p64 has carboxy-terminal homology with c-Rel. The majority of peptides generated by partial proteolytic cleavage of p64 are shared with peptides generated by digestion of p75c-rel and/or pp59v-rel. We suggest that this protein represents a new member of the Rel family of transcription factors and is located in the nucleus of avian fibroblasts during S phase of the cell cycle.

Multiple mechanisms are implicated in the regulation of NF-kappa B activity during human cytomegalovirus infection

Infection-induced activation of the human cytomegalovirus major immediate early enhancer/promoter has been shown to be regulated primarily by transcription factor NF-kappa B cis elements. However, the mechanism(s) by which human cytomegalovirus induces NF-kappa B activity is unknown. A study was therefore undertaken to determine how this virus would affect normal NF-kappa B regulation. Viral infection of fibroblasts resulted in the specific stimulation of promoters containing major histocompatibility complex NF-kappa B cis elements fused upstream of the chloramphenicol acetyltransferase reporter gene. Electrophoretic mobility shift assays of nuclear extracts derived from mock- and virus-infected cells showed dramatic and sustained increases in DNA-binding proteins specific for these NF-kappa B sequences. Experiments using MAD-3 I kappa B, a specific inhibitor of NF-kappa B, and antibodies directed against rel family members demonstrated that the induced binding activities contained p50 and p65 proteins but not c-rel. Northern analysis indicated maximal levels of p50 mRNA by 4 h postinfection, whereas p65 and MAD-3 I kappa B mRNA accumulation peaked at 48-72 h postinfection, suggesting different regulatory mechanisms for p50 and p65/I kappa B genes. Electrophoretic mobility shift assays with deoxycholate-treated cytoplasmic extracts demonstrated a 3- to 4-fold decrease in the cytosolic stores of NF-kappa B binding activity by 4 h postinfection. Western blots probed with antibodies directed against MAD-3 I kappa B or pp40 (a protein isolated from chicken with sequence and biochemical properties similar to those of MAD-3 I kappa B) indicated that a cross-reactive peptide of 39 kDa was no longer detectable after 24 h postinfection. These results demonstrate that the activation and maintenance of nuclear NF-kappa B DNA binding and enhancer activities upon human cytomegalovirus infection occurs by multiple mechanisms.