S100A4 Is Involved in Stimulatory Effects Elicited by the FGF2/FGFR1 Signaling Pathway in Triple-Negative Breast Cancer (TNBC) Cells.

Triple-negative breast cancer (TNBC) is an aggressive breast tumor subtype characterized by poor clinical outcome. In recent years, numerous advancements have been made to better understand the biological landscape of TNBC, though appropriate targets still remain to be determined. In the present study, we have determined that the expression levels of FGF2 and S100A4 are higher in TNBC with respect to non-TNBC patients when analyzing "The Invasive Breast Cancer Cohort of The Cancer Genome Atlas" (TCGA) dataset. In addition, we have found that the gene expression of FGF2 is positively correlated with S100A4 in TNBC samples. Performing quantitative PCR, Western blot, CRISPR/Cas9 genome editing, promoter studies, immunofluorescence analysis, subcellular fractionation studies, and ChIP assays, we have also demonstrated that FGF2 induces in TNBC cells the upregulation and secretion of S100A4 via FGFR1, along with the ERK1/2-AKT-c-Rel transduction signaling. Using conditioned medium from TNBC cells stimulated with FGF2, we have also ascertained that the paracrine activation of the S100A4/RAGE pathway triggers angiogenic effects in vascular endothelial cells (HUVECs) and promotes the migration of cancer-associated fibroblasts (CAFs). Collectively, our data provide novel insights into the action of the FGF2/FGFR1 axis through S100A4 toward stimulatory effects elicited in TNBC cells.

c-Rel and its many roles in cancer: an old story with new twists.

When the genes encoding NF-κB subunits were first isolated, their homology to the previously identified c-Rel proto-oncogene and its viral homologue v-Rel was clear. This provided the first indication that these transcription factors also had a role in cancer. Because of its homology to v-Rel, which transforms chicken B cells together with the important role c-Rel can have as a regulator of B- and T-cell proliferation, most attention has focussed on its role in B-cell lymphomas, where the REL gene is frequently amplified. However, a growing number of reports now indicate that c-Rel has important functions in many solid tumours, although studies in mice suggest it may not always function as an oncogene. Moreover, c-Rel is a critical regulator of fibrosis, which provides an environment for tumour development in many settings. Overall, c-Rel is emerging as a complex regulator of tumorigenesis, and there is still much to learn about its functions in human malignancies and the response to cancer therapies.

The c-Rel subunit of NF-κB regulates epidermal homeostasis and promotes skin fibrosis in mice.

The five subunits of transcription factor NF-κB have distinct biological functions. NF-κB signaling is important for skin homeostasis and aging, but the contribution of individual subunits to normal skin biology and disease is unclear. Immunohistochemical analysis of the p50 and c-Rel subunits within lesional psoriatic and systemic sclerosis skin revealed abnormal epidermal expression patterns, compared with healthy skin, but RelA distribution was unaltered. The skin of Nfkb1(-/-) and c-Rel(-/-) mice is structurally normal, but epidermal thickness and proliferation are significantly reduced, compared with wild-type mice. We show that the primary defect in both Nfkb1(-/-) and c-Rel(-/-) mice is within keratinocytes that display reduced proliferation both in vitro and in vivo. However, both genotypes can respond to proliferative stress, with 12-O-tetradecanoylphorbol-13-acetate-induced epidermal hyperproliferation and closure rates of full-thickness skin wounds being equivalent to those of wild-type controls. In a model of bleomycin-induced skin fibrosis, Nfkb1(-/-) and c-Rel(-/-) mice displayed opposite phenotypes, with c-Rel(-/-) mice being protected and Nfkb1(-/-) developing more fibrosis than wild-type mice. Taken together, our data reveal a role for p50 and c-Rel in regulating epidermal proliferation and homeostasis and a profibrogenic role for c-Rel in the skin, and identify a link between epidermal c-Rel expression and systemic sclerosis. Modulating the actions of these subunits could be beneficial for treating hyperproliferative or fibrogenic diseases of the skin.

The NF-κB subunit c-Rel stimulates cardiac hypertrophy and fibrosis.

Cardiac remodeling and hypertrophy are the pathological consequences of cardiovascular disease and are correlated with its associated mortality. Activity of the transcription factor NF-κB is increased in the diseased heart; however, our present understanding of how the individual subunits contribute to cardiovascular disease is limited. We assign a new role for the c-Rel subunit as a stimulator of cardiac hypertrophy and fibrosis. We discovered that c-Rel-deficient mice have smaller hearts at birth, as well as during adulthood, and are protected from developing cardiac hypertrophy and fibrosis after chronic angiotensin infusion. Results of both gene expression and cross-linked chromatin immunoprecipitation assay analyses identified transcriptional activators of hypertrophy, myocyte enhancer family, Gata4, and Tbx proteins as Rel gene targets. We suggest that the p50 subunit could limit the prohypertrophic actions of c-Rel in the normal heart, because p50 overexpression in H9c2 cells repressed c-Rel levels and the absence of cardiac p50 was associated with increases in both c-Rel levels and cardiac hypertrophy. We report for the first time that c-Rel is highly expressed and confined to the nuclei of diseased adult human hearts but is restricted to the cytoplasm of normal cardiac tissues. We conclude that c-Rel-dependent signaling is critical for both cardiac remodeling and hypertrophy. Targeting its activities could offer a novel therapeutic strategy to limit the effects of cardiac disease.

The NF-κB transcription factor c-Rel is required for Th17 effector cell development in experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease involving effector Th subsets such as Th1 and Th17. In this study, we demonstrate that mice lacking the NF-κB transcription factor family member c-Rel (rel(-/-)), which are known to be resistant to EAE, show impaired Th17 development. Mixed bone marrow chimeras and EAE adoptive transfer experiments show that the deficiency of effector Th17 cells in rel(-/-) mice is T cell intrinsic. Consistent with this finding, c-Rel was activated in response to TCR signaling in the early stages of Th17 development and controlled the expression of Rorc, which encodes the Th17 transcription factor retinoic acid-related orphan receptor γt. CD28, but not IL-2, repression of Th17 development was dependent on c-Rel, implicating a dual role for c-Rel in modulating Th17 development. Adoptive transfer experiments also suggested that c-Rel control of regulatory T cell differentiation and homeostasis influences EAE development and severity by influencing the balance between Th17 and regulatory T cells. Collectively, our findings indicate that in addition to promoting Th1 differentiation, c-Rel regulates the development and severity of EAE via multiple mechanisms that impact on the generation of Th17 cells.

Three ulcerative colitis susceptibility loci are associated with primary sclerosing cholangitis and indicate a role for IL2, REL, and CARD9.

UNLABELLED: Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by inflammation and fibrosis of the bile ducts. Both environmental and genetic factors contribute to its pathogenesis. To further clarify its genetic background, we investigated susceptibility loci recently identified for ulcerative colitis (UC) in a large cohort of 1,186 PSC patients and 1,748 controls. Single nucleotide polymorphisms (SNPs) tagging 13 UC susceptibility loci were initially genotyped in 854 PSC patients and 1,491 controls from Benelux (331 cases, 735 controls), Germany (265 cases, 368 controls), and Scandinavia (258 cases, 388 controls). Subsequently, a joint analysis was performed with an independent second Scandinavian cohort (332 cases, 257 controls). SNPs at chromosomes 2p16 (P-value 4.12 × 10(-4) ), 4q27 (P-value 4.10 × 10(-5) ), and 9q34 (P-value 8.41 × 10(-4) ) were associated with PSC in the joint analysis after correcting for multiple testing. In PSC patients without inflammatory bowel disease (IBD), SNPs at 4q27 and 9q34 were nominally associated (P < 0.05). We applied additional in silico analyses to identify likely candidate genes at PSC susceptibility loci. To identify nonrandom, evidence-based links we used GRAIL (Gene Relationships Across Implicated Loci) analysis showing interconnectivity between genes in six out of in total nine PSC-associated regions. Expression quantitative trait analysis from 1,469 Dutch and UK individuals demonstrated that five out of nine SNPs had an effect on cis-gene expression. These analyses prioritized IL2, CARD9, and REL as novel candidates. CONCLUSION: We have identified three UC susceptibility loci to be associated with PSC, harboring the putative candidate genes REL, IL2, and CARD9. These results add to the scarce knowledge on the genetic background of PSC and imply an important role for both innate and adaptive immunological factors.

Glutathione-redox balance regulates c-rel-driven IL-12 production in macrophages: possible implications in antituberculosis immunotherapy.

The glutathione-redox balance, expressed as the ratio of intracellular reduced glutathione (GSH) and oxidized glutathione, plays an important role in regulating cellular immune responses. In the current study, we demonstrate that alteration of glutathione-redox balance in macrophages by GSH donors like cell-permeable glutathione ethyl ester reduced or N-acetyl-L-cysteine (NAC) can differentially regulate production of IL-12 cytokine in macrophages. A low concentration of NAC increased IL-12 p40/p70 production, whereas at high concentration, IL-12 production was inhibited due to increased calmodulin expression that binds and sequesters c-rel in the cytoplasm. Although NAC treatment increased the IkappaBalpha phosphorylation, it failed to increase TNF-alpha levels due to enhanced expression of suppressor of cytokine signaling 1, which specifically prevented nuclear translocation of p65 NF-kappaB. We demonstrate that NAC at 3 mM concentration could increase bacillus Calmette-Guérin-induced IFN-gamma production by PBMCs from patients with active tuberculosis and shifts the anti-bacillus Calmette-Guérin immune response toward the protective Th1 type. Our results indicate that redox balance of glutathione plays a critical role in regulating IL-12 induction in native macrophages, and NAC can be used in tailoring macrophages to induce enhanced Th1 response that may be helpful to control tuberculosis and other pathophysiological disorders.

Cutting edge: CD28 and c-Rel-dependent pathways initiate regulatory T cell development.

Regulatory T cell (Treg) development proceeds via a two-step process in which naive CD4(+) thymocytes are first converted into CD4(+)CD25(+)CD122(+)GITR(+)Foxp3(-) Treg progenitors, followed by a second step in which IL-2 converts these Treg progenitors into CD4(+)Foxp3(+) Tregs. The costimulatory molecule CD28 is required for efficient Treg development. However, the stage at which CD28 affects Treg development remains undefined. In this article, we demonstrate that Cd28(-/-) mice lack Treg progenitors. Furthermore, the P(187)YAP motif in the cytoplasmic tail of CD28, which links CD28 to Lck activation, is required for this process. In contrast, the Y(170)MNM motif, which links CD28 to PI3K activation, is not required for Treg progenitor development. Finally, the CD28/Lck pathway was shown to activate the NF-kappaB family of transcription factors. We demonstrate that c-Rel, but not NF-kappaB1, promotes the development of Treg progenitors. Thus, a CD28/c-Rel-dependent pathway is involved in initiating Treg development.

Divergent roles of RelA and c-Rel in establishing chromosomal loops upon activation of the Igkappa gene.

Precise regulation of eukaryotic gene expression requires interactions between distal cis-acting regulatory sequences with the looping out of the intervening DNA, but how trans-acting regulatory proteins work to establish and maintain DNA loops during gene activation remains largely unexplored. LPS-induced transcription of the mouse Igkappa gene in B lymphocytes utilizes three distal enhancers and requires the transcription factor NF-kappaB, whose family members include RelA and c-Rel. Using chromosome conformation capture technology in combination with chromatin immunoprecipitation, here we demonstrate that LPS-induced Igkappa gene activation creates chromosomal loops by bridging together all three pairwise interactions between the distal enhancers and RNA polymerase II, the apparent molecular tie for the bases of these loops. RelA and actin polymerization are essential for triggering these processes, which do not require new transcription, protein synthesis, or c-Rel. We have thus identified both essential and nonessential events that establish higher order chromatin reorganization during Igkappa gene activation.

Differential role for c-Rel and C/EBPbeta/delta in TLR-mediated induction of proinflammatory cytokines.

TLR stimulation triggers a signaling pathway via MyD88 and IL-1R-associated kinase 4 that is essential for proinflammatory cytokine induction. Although NF-kappaB has been shown to be one of the key transcriptional regulators of these cytokines, evidence suggests that other factors may also be important. In this study, we showed that MyD88-deficient macrophages have defective c-Rel activation, which has been linked to IL-12p40 induction, but not IL-6 or TNF-alpha. We also investigated other transcription factors and showed that C/EBPbeta and C/EBPdelta expression was limited in MyD88- or IL-1R-associated kinase 4-deficient macrophages treated with LPS. Importantly, the absence of both C/EBPbeta and C/EBPdelta resulted in the impaired induction of proinflammatory cytokines stimulated by several TLR ligands. Our results identify c-Rel and C/EBPbeta/delta as important transcription factors in a MyD88-dependent pathway that regulate the induction of proinflammatory cytokines.

c-Rel regulates interleukin 12 p70 expression in CD8(+) dendritic cells by specifically inducing p35 gene transcription.

Interleukin 12 (IL-12) is a 70-kD proinflammatory cytokine produced by antigen presenting cells that is essential for the induction of T helper type 1 development. It comprises 35-kD (p35) and 40-kD (p40) polypeptides encoded by separate genes that are induced by a range of stimuli that include lipopolysaccharide (LPS), DNA, and CD40 ligand. To date, the regulation of IL-12 expression at the transcriptional level has mainly been examined in macrophages and restricted almost exclusively to the p40 gene. Here we show that in CD8(+) dendritic cells, major producers of IL-12 p70, the Rel/nuclear factor (NF)-kappaB signaling pathway is necessary for the induction of IL-12 in response to microbial stimuli. In contrast to macrophages which require c-Rel for p40 transcription, in CD8(+) dendritic cells, the induced expression of p35 rather than p40 by inactivated Staphylococcus aureus, DNA, or LPS is c-Rel dependent and regulated directly by c-Rel complexes binding to the p35 promoter. This data establishes the IL-12 p35 gene as a new target of c-Rel and shows that the regulation of IL-12 p70 expression at the transcriptional level by Rel/NF-kappaB is controlled through both the p35 and p40 genes in a cell type-specific fashion.

Combined deficiency of p50 and cRel in CD4+ T cells reveals an essential requirement for nuclear factor kappaB in regulating mature T cell survival and in vivo function.

Signaling pathways involved in regulating T cell proliferation and survival are not well understood. Here we have investigated a possible role of the nuclear factor (NF)-kappaB pathway in regulating mature T cell function by using CD4+ T cells from p50-/- cRel-/- mice, which exhibit virtually no inducible kappaB site binding activity. Studies with these mice indicate an essential role of T cell receptor (TCR)-induced NF-kappaB in regulating interleukin (IL)-2 expression, cell cycle entry, and survival of T cells. Our results further indicate that NF-kappaB regulates TCR-induced expression of antiapoptotic Bcl-2 family members. Strikingly, retroviral transduction of CD4+ T cells with the NF-kappaB-inducing IkappaB kinase beta showed that NF-kappaB activation is not only necessary but also sufficient for T cell survival. In contrast, our results indicate a lack of involvement of NF-kappaB in both IL-2 and Akt-induced survival pathways. In vivo, p50-/- cRel-/- mice showed impaired superantigen-induced T cell responses as well as decreased numbers of effector/memory and regulatory CD4+ T cells. These findings provide the first demonstration of a role for NF-kappaB proteins in regulating T cell function in vivo and establish a critically important function of NF-kappaB in TCR-induced regulation of survival.

Targeting the NF-kappaB pathway in asthma and chronic obstructive pulmonary disease.

Asthma and chronic obstructive pulmonary disease are inflammatory lung disorders responsible for significant morbidity and mortality worldwide. While the importance of allergic responses in asthma is well known, respiratory viral and bacterial infections and pollutants especially cigarette smoke are important factors in the pathogenesis of both diseases. Corticosteroid treatment remains the first preference of treatment in either disease, however these therapies are not always completely effective, and are associated with side effects and steroid resistance. Due to such limitations, development of new treatments represents a major goal for both the pharmaceutical industry and academic researchers. There are now excellent reasons to promote NF-kappaB signalling intermediates and Rel family proteins as potential therapeutic targets for both asthma and chronic obstructive pulmonary disease. This notion is supported by the fact that much of the underlying inflammation of both diseases independent of stimuli, is mediated at least in part, by NF-kappaB mediated signalling events in several cell types. Also, a range of inhibitors of NF-kappaB signalling intermediates are now available, including DNA oligonucleotides and DNA-peptide molecules that act as NF-kappaB decoy sequences, small molecule inhibitors such as IKK-beta inhibitors, and proteasome inhibitors affecting NF-kappaB signalling, that have either shown promise in animal models or have begun clinical trials in other disorders. This review will focus on the role of NF-kappaB in both diseases, will discuss its suitability as a target, and will highlight recent key studies that support the potential of NF-kappaB as a therapeutic target in these two important inflammatory lung diseases.

NF-kappaB1 and c-Rel cooperate to promote the survival of TLR4-activated B cells by neutralizing Bim via distinct mechanisms.

The nuclear factor-kappaB (NF-kappaB) pathway is crucial for the survival of B cells stimulated through Toll-like receptors (TLRs). Here, we show that the heightened death of TLR4-activated nfkb1(-/-) B cells is the result of a failure of the Tpl(2)/MEK/ERK pathway to phosphorylate the proapo-ptotic BH3-only protein Bim and target it for degradation. ERK inactivation of Bim after TLR4 stimulation is accompanied by an increase in A1/Bim and Bcl-x(L)/Bim complexes that we propose represents a c-Rel-dependent mechanism for neutralizing Bim. Together these findings establish that optimal survival of TLR4-activated B cells depends on the NF-kappaB pathway neutralizing Bim through a combination of Bcl-2 prosurvival protein induction and Tpl2/ERK-dependent Bim phosphorylation and degradation.

NF-kappaB p50/RelA and c-Rel-containing dimers: opposite regulators of neuron vulnerability to ischaemia.

Diverse nuclear factor-kappaB subunits mediate opposite effects of extracellular signals on neuron survival. While RelA is activated by neurotoxic agents, c-Rel drives neuroprotective effects. In brain ischaemia RelA and p50 factors rapidly activate, but how they associate with c-Rel to form active dimers and contribute to the changes in diverse dimer activation for neuron susceptibility is unknown. We show that in both cortical neurons exposed to oxygen glucose deprivation (OGD) and mice subjected to brain ischaemia, activation of p50/RelA was associated with inhibition of c-Rel/RelA dimer and no change p50/c-Rel. Targeting c-Rel and RelA expression revealed that c-Rel dimers reduced while p50/RelA enhanced neuronal susceptibility to anoxia. Activation of p50/RelA complex is known to induce the pro-apoptotic Bim and Noxa genes. We now show that c-Rel-containing dimers, p50/c-Rel and RelA/c-Rel, but not p50/RelA, promoted Bcl-xL transcription. Accordingly, the OGD exposure induced Bim, but reduced Bcl-xL promoter activity and decreased the content of endogenous Bcl-xL protein. These findings demonstrate that within the same neuronal cell, the balance between activation of p50/RelA and c-Rel-containing complexes fine tunes the threshold of neuron vulnerability to the ischaemic insult. Selective targeting of different dimers will unravel new approaches to limit ischaemia-associated apoptosis.

Treatment of cells with n-alpha-tosyl-L-phenylalanine-chloromethyl ketone induces the proteolytic loss of STAT6 transcription factor.

The implication of the STAT6 transcription factor in several human diseases makes the regulation of its activity a topic of great biological interest. The activation of this transcription factor is tightly regulated by kinases, phosphatases, and proteases. The initial aim of this study was to investigate the utility of protease inhibitors in controlling STAT6 activation. Among all inhibitors analyzed, n-alpha-tosyl-L-phenylalanine-chloromethyl ketone (TPCK) was found to inhibit the IL-4-induced STAT6 activation. Unexpectedly, this inhibition was accompanied by a loss of STAT6 protein. Thus, TPCK promoted the loss of STAT6 by a mechanism sensitive to the serine-protease inhibitor 4-(2-aminoetyl)-benzenesulfonyl fluoride. However, the effects of TPCK seemed not to be mediated by its protease inhibitory activity since multiple protease inhibitors tested had no effect on STAT6 expression. The results found suggest that the effect of TPCK was mediated by its alkylating activity. Thus, cysteine reactive and thiol antioxidant compounds prevented the loss of STAT6 induced by TPCK. The reactivity of thiol groups on STAT6 was moreover demonstrated with biotinylated sulfhydryl-reactive compounds. Analysis of other signaling molecules indicated that STAT5, but not other STATs, Shc, or c-Rel, was also affected by TPCK, suggesting a common downregulatory mechanism for STAT6 and STAT5. These results reveal a novel mechanism of action of TPCK in inducing a selective loss of STAT proteins. These findings may have implications for diseases in which STAT proteins are involved.

Nitric oxide inhibits interleukin-12 p40 through p38 MAPK-mediated regulation of calmodulin and c-rel.

In activated macrophages, the rel/NF-kappaB transcription factors are known to play important roles in interleukin-12 (IL-12) p40 regulation by nitric oxide (NO). However, the relative contributions of these factors are not well understood. Here, we describe a dominant role for c-rel involving p38 mitogen-activated protein kinase (p38 MAPK) and calmodulin (CaM) protein in NO-mediated IL-12 p40 inhibition in activated macrophages. Inhibition of NO production by aminoguanidine increased, whereas sodium nitroprusside (SNP; an exogenous NO generator) reduced, nuclear c-rel levels in LPS + IFN-gamma-activated RAW 264.7 macrophages. Overexpression of c-rel but not p65 NF-kappaB increased IL-12 p40 during NO treatment. The p38 MAPK phosphorylation is increased by NO, and inhibition of p38 MAPK in SNP-treated macrophages by SB203580 or transient expression of a dominant-negative mutant of p38 MAPK upregulated both nuclear c-rel and IL-12 p40 levels, indicating that NO targeted the p38 MAPK pathway to inhibit c-rel and IL-12 p40. Cytoplasmic CaM level was increased by NO, and SB203580 decreased the CaM level in NO-exposed macrophages. Inhibition of CaM activity by trifluoperazine rescued the inhibitory effect of NO on c-rel and IL-12 p40. Our findings indicate that c-rel plays an important role in NO-mediated inhibition of IL-12 p40 and is regulated by p38 MAPK through CaM protein.

Characterization of a Rel\NF-kappaB homologue in a gastropod abalone, Haliotis diversicolor supertexta.

Rel\NF-kappaB signal transduction pathway is evolutionarily conserved and involved in numerous biological processes. We report here, for the first time that a homologue of Rel\NF-kappaB transcription factor, Ab-Rel, was identified and functionally characterized in a gastropod abalone, H. diversicolor supertexta. The full-length Ab-Rel cDNA consists of 1943 bp with an ORF encoding a 584 amino acids protein. Amino acid sequence analysis revealed that Ab-Rel shares conserved signature motifs with other Rel proteins, including the Rel homology domain (RHD), nuclear localization signal (NLS) and phosphorylation site, RRPS. Northern hybridization and real-time PCR indicated that Ab-Rel was ubiquitously and constitutively expressed in abalone. The recombinant Ab-Rel RHD protein was confirmed to specifically bind the consensus NF-kappaB binding site. Furthermore, EMSA showed that NF-kappaB activity was induced in abalone hemocytes by stimulation with LPS. These results strongly suggest that Ab-Rel is a Rel homologue, which plays a conserved role in the immune response of the ancient invertebrate, abalone, allowing us to study the Rel\NF-kappaB signaling pathway in an evolutionary context.

Interferon regulatory factor 4 contributes to transformation of v-Rel-expressing fibroblasts.

The avian homologue of the interferon regulatory factor 4 (IRF-4) and a novel splice variant lacking exon 6, IRF-4DeltaE6, were isolated and characterized. Chicken IRF-4 is expressed in lymphoid organs, less in small intestine, and lungs. IRF-4DeltaE6 mRNA, though less abundant than full-length IRF-4, was detected in lymphoid tissues, with the highest levels observed in thymic cells. IRF-4 is highly expressed in v-Rel-transformed lymphocytes, and the expression of IRF-4 is increased in v-Rel- and c-Rel-transformed fibroblasts relative to control cells. The expression of IRF-4 from retrovirus vectors morphologically transformed primary fibroblasts, increased their saturation density, proliferation, and life span, and promoted their growth in soft agar. IRF-4 and v-Rel cooperated synergistically to transform fibroblasts. The expression of IRF-4 antisense RNA eliminated formation of soft agar colonies by v-Rel and reduced the proliferation of v-Rel-transformed cells. v-Rel-transformed fibroblasts produced interferon 1 (IFN1), which inhibits fibroblast proliferation. Infection of fibroblasts with retroviruses expressing v-Rel resulted in an increase in the mRNA levels of IFN1, the IFN receptor, STAT1, JAK1, and 2',5'-oligo(A) synthetase. The exogenous expression of IRF-4 in v-Rel-transformed fibroblasts decreased the production of IFN1 and suppressed the expression of several genes in the IFN transduction pathway. These results suggest that induction of IRF-4 expression by v-Rel likely facilitates transformation of fibroblasts by decreasing the induction of this antiproliferative pathway.

The transcription factors c-rel and RelA control epidermal development and homeostasis in embryonic and adult skin via distinct mechanisms.

Determining the roles of Rel/NF-kappaB transcription factors in mouse skin development with loss-of-function mutants has been limited by redundancy among these proteins and by embryonic lethality associated with the absence of RelA. Using mice lacking RelA and c-rel, which survive throughout embryogenesis on a tumor necrosis factor alpha (TNF-alpha)-deficient background (rela(-/-) c-rel(-/-) tnfalpha(-/-)), we show that c-rel and RelA are required for normal epidermal development. Although mutant fetuses fail to form tylotrich hair and have a thinner epidermis, mutant keratinocyte progenitors undergo terminal differentiation to form an outer cornified layer. Mutant basal keratinocytes are abnormally small, exhibit a delay in G(1) progression, and fail to form keratinocyte colonies in culture. In contrast to the reduced proliferation of mutant keratinocytes during embryogenesis, skin grafting experiments revealed that the mutant epidermis develops a TNF-alpha-dependent hyperproliferative condition. Collectively, our findings indicate that RelA and c-rel control the development of the epidermis and associated appendages during embryogenesis and regulate epidermal homeostasis in a postnatal environment through the suppression of innate immune-mediated inflammation.