The DNA binding subunit of NF-kappa B is identical to factor KBF1 and homologous to the rel oncogene product

Lipopolysaccharide-mediated transcriptional activation of the human tissue factor gene in THP-1 monocytic cells requires both activator protein 1 and nuclear factor kappa B binding sites

Lipopolysaccharide (LPS) activation of cells of monocytic lineage leads to rapid and transient expression of a set of inflammatory gene products, including tissue factor (TF). This transmembrane receptor is the major cellular initiator of the blood coagulation cascades, and induced expression of TF is postulated to play a role in inflammation. Functional studies using transfected THP-1 monocytic cells revealed the presence of a 56-bp LPS response element (LRE) within the TF promoter that conferred LPS responsiveness to a heterologous promoter. LPS stimulation of these cells activated proteins that bound to nucleotide sequences within the LRE resembling consensus binding sites for activator protein 1 (AP-1) and nuclear factor kappa B (NF-kappa B). Induction of the TF gene may represent a prototypic example of gene activation in monocytic cells by assembly of transcription factor complexes, and may clarify the role of AP-1 and NF-kappa B in the regulation of other LPS-responsive genes.

The p65 subunit is responsible for the strong transcription activating potential of NF-kappa B

The nuclear form of the NF-kappa B transcription factor binds to DNA as a heterodimer of a 50 kDa (p50) and 65 kDa (p65) polypeptide. The two polypeptides are encoded by different genes but share a long region of homology, the NRD motif, encompassing domains required for DNA binding and dimerization. In this study we have analysed the contribution of the two subunits to the strong transactivating potential of NF-kappa B. Transient expression of the p65 subunit alone resulted in a potent transactivation of a CAT reporter construct under the control of two NF-kappa B binding sites in monkey COS and mouse L cells. The strongly DNA binding p50 subunit showed only very weak, if any, induction of gene expression. Co-expression of p50 suppressed the transactivation by p65 presumably by competitive DNA binding of transcriptionally inactive p50 dimers (KBF1). Fusion of p65 sequences to DNA binding domain of the yeast GAL4 transcription factor allowed detection of the principal transactivation domain of p65 (TA1) in the C-terminal 30 amino acid sequence. TA1 is likely to adopt an amphipathic alpha-helical structure which clusters serine residues on the hydrophilic surface, a structural feature conserved between human, mouse and Xenopus p65. The unique C-terminal third of p65 contained at least one more activation domain, TA2, within a 90 amino acid sequence directly adjacent to TA1. In two mammalian cell lines, TA1 and TA2 acted separately, while in an insect cell line, the two domains were inactive after their separation. Our study suggests that the p50 subunit in NF-kappa B might only serve a helper function in DNA binding whereas the p65 subunit is responsible for initiating transcription. Homodimers of p50 seem to have the potential of down-regulating kappa B-specific gene expression.

Human T-cell leukemia virus type I Tax induces expression of the Rel-related family of kappa B enhancer-binding proteins: evidence for a pretranslational component of regulation

The Tax protein of the human T-cell leukemia virus type I (HTLV-I) serves as a potent transcriptional activator of its own long terminal repeat as well as select cellular genes, including interleukin-2 and the alpha subunit of the interleukin-2 receptor. Tax activation of these two growth-related genes appears to involve the induced nuclear expression of DNA-binding proteins that specifically engage related kappa B enhancer elements present in the 5' regulatory regions of these genes. In human T cells, kappa B enhancer-binding activity has been discerned as an unexpectedly large family of UV cross-linked nucleoprotein adducts, termed p50, p55, p75, and p85. The protein components of each of these DNA-protein adducts have been shown to share structural similarity with the v-rel oncogene product. The p55 adduct is composed of the 50-kDa subunit of NF-kappa B derived from a 105-kDa precursor polypeptide, while the p50 adduct contains a smaller protein that is closely related to NF-kappa B p50. The p75 adduct contains the 65-kDa subunit of NF-kappa B, while the p85 adduct is composed of the human c-rel proto-oncogene product. We now demonstrate that HTLV-I Tax, in the absence of other viral pX gene products, is capable of inducing the nuclear expression of all four of these kappa B-binding proteins in human T cells, with most marked effects involving c-Rel and NF-kappa B p65. Tax induction of the nuclear expression of c-Rel and NF-kappa B p50 is regulated, at least in part, at a pretranslational level involving increases in c-rel and NF-kappa B p105 mRNA expression. To study the pattern of expression of these kappa B-specific proteins in cells infected with the whole HTLV-I, seven cloned HTLV-I-infected T-cell lines were established from the peripheral blood of patients with adult T-cell leukemia. Of note, only three of these seven cell lines produced Tax, and c-rel mRNA and nuclear protein expression was confined to these three cell lines. In contrast, NF-kappa B p50 and NF-kappa B p65 were constitutively expressed in the nuclei of all seven of the HTLV-I-infected cell lines, even in the absence of detectable Tax or other viral gene expression. These findings raise the possibility of an alternate, Tax-independent pathway for the induced nuclear expression of NF-kappa B p50 and NF-kappa B p65 following HTLV-I infection.

One base pair change abolishes the T cell-restricted activity of a kB-like proto-enhancer element from the interleukin 2 promoter

The inducible, T cell-specific enhancers of murine and human Interleukin 2 (Il-2) genes contain the kB-like sequence GGGATTTCACC as an essential cis-acting enhancer motif. When cloned in multiple copies this so-called TCEd (distal T cell element) acts as an inducible proto-enhancer element in E14 T lymphoma cells, but not in HeLa cells. In extracts of induced, Il-2 secreting El4 cells three individual protein factors bind to TCEd DNA. The binding of the most prominent factor, named TCF-1 (T cell factor 1), is correlated with the proto-enhancer activity of TCEd. TCF-1 consists of two polypeptides of about 50 kD and 105 kD; the former seems to be related to the 50 kD polypeptide of NF-kB. Purified NF-kB is also able to bind to the TCEd, but TCF-1 binds stronger than NF-kB to TCEd DNA. The conversion of the TCEd to a 'perfect' NF-kB binding site leads to a tighter binding of NF-kB to TCEd DNA and, as a functional consequence, to the activity of the 'converted' TCEd motifs in HeLa cells. Thus, the substitution of the underlined A residue to a C within the GGGATTTCACC motif abolishes its T cell-restricted activity and leads to its functioning in both El4 cells and HeLa cells. These results indicate that lymphocyte-specific factors binding to the TCEd are involved in the control of T cell specific-transcription of the Il-2 gene.

Negative regulation of human immunodeficiency virus type 1 expression in monocytes: role of the 65-kDa plus 50-kDa NF-kappa B dimer

Although monocytic cells can provide a reservoir for viral production in vivo, their regulation of human immunodeficiency virus type 1 (HIV-1) transcription can be either latent, restricted, or productive. These differences in gene expression have not been molecularly defined. In THP-1 cells with restricted HIV expression, there is an absence of DNA-protein binding complex formation with the HIV-1 promoter-enhancer associated with markedly less viral RNA production. This absence of binding was localized to the NF-kappa B region of the HIV-1 enhancer; the 65-kDa plus 50-kDa NF-kappa B heterodimer was preferentially lost. Adding purified NF-kappa B protein to nuclear extracts from cells with restricted expression overcomes this lack of binding. In addition, treatment of these nuclear extracts with sodium deoxycholate restored their ability to form the heterodimer, suggesting the presence of an inhibitor of NF-kappa B activity. Furthermore, treatment of nuclear extracts from these cells that had restricted expression with lipopolysaccharide increased viral production and NF-kappa B activity. Antiserum specific for NF-kappa B binding proteins, but not c-rel-specific antiserum, disrupted heterodimer complex formation. Thus, both NF-kappa B-binding complexes are needed for optimal viral transcription. Binding of the 65-kDa plus 50-kDa heterodimer to the HIV-1 enhancer can be negatively regulated in monocytes, providing one mechanism restricting HIV-1 gene expression.

Induction of NF-kappa B DNA-binding activity during the G0-to-G1 transition in mouse fibroblasts

A DNA-binding factor with properties of NF-kappa B and another similar activity are rapidly induced when growth-arrested BALB/c 3T3 cells are stimulated with serum growth factors. Induction of these DNA-binding activities is not inhibited by pretreatment of quiescent cells with the protein synthesis inhibitor cycloheximide. Interestingly, the major NF-kappa B-like activity is not detected in nuclear extracts of proliferating cells, and thus its expression appears to be limited to the G0-to-G1 transition in 3T3 cells. These DNA-binding activities bind many of the expected NF-kappa B target sequences, including elements in the class I major histocompatibility complex and human immunodeficiency virus enhancers, as well as a recently identified NF-kappa B binding site upstream of the c-myc gene. Furthermore, both the class I major histocompatibility complex and c-myc NF-kappa B binding sites confer inducibility on a minimal promoter in 3T3 cells stimulated with serum growth factors. The results demonstrate that NF-kappa B-like activities are immediate-early response proteins in 3T3 cells and suggest a role for these factors in the G0-to-G1 transition.

A structural taxonomy of DNA-binding domains

The structures of several classes of DNA-binding domains reveal a variety of designs for recognizing a specific site on DNA.

Malignant transformation by mutant Rel proteins

A newly described family of transcriptional regulatory proteins, the Rel family, has recently been the subject of much interest. The Rel family includes proteins known to be important in Drosophila development, replication of HIV-1, oncogenesis and general transcriptional control. Nevertheless, there is still much to be learned about their precise mechanism of action, including the process by which the original member of this family, v-Rel, malignantly transforms cells.

Induction of NF-kappa B DNA-binding activity during the G0-to-G1 transition in mouse fibroblasts

A DNA-binding factor with properties of NF-kappa B and another similar activity are rapidly induced when growth-arrested BALB/c 3T3 cells are stimulated with serum growth factors. Induction of these DNA-binding activities is not inhibited by pretreatment of quiescent cells with the protein synthesis inhibitor cycloheximide. Interestingly, the major NF-kappa B-like activity is not detected in nuclear extracts of proliferating cells, and thus its expression appears to be limited to the G0-to-G1 transition in 3T3 cells. These DNA-binding activities bind many of the expected NF-kappa B target sequences, including elements in the class I major histocompatibility complex and human immunodeficiency virus enhancers, as well as a recently identified NF-kappa B binding site upstream of the c-myc gene. Furthermore, both the class I major histocompatibility complex and c-myc NF-kappa B binding sites confer inducibility on a minimal promoter in 3T3 cells stimulated with serum growth factors. The results demonstrate that NF-kappa B-like activities are immediate-early response proteins in 3T3 cells and suggest a role for these factors in the G0-to-G1 transition.

Functional analysis of the Drosophila twist promoter reveals a dorsal-binding ventral activator region

twist is one of the earliest expressed zygotically active genes required for dorsal-ventral pattern formation in the Drosophila embryo. Genetic studies suggest that this gene is activated in the ventral part of the blastoderm by maternally expressed dorsal gene product. Using P-element-mediated germ-line transformation, we have mapped a small (260 bp) dorsal-dependent ventral activator region (VAR) in the 5'-flanking region of the twist promoter that can direct the early ventral expression of a heterologous promoter. The VAR contains binding sites for a number of proteins present in extracts of Drosophila embryos. One of these sites bears homology to known binding sites for the dorsal transcription factor and is specifically bound by bacterially expressed dorsal protein. Furthermore, a 37-bp deletion that removes the dorsal-binding sequences abolishes the ventral-specific activity of the twist promoter constructs. Our data also show that additional sequences within the VAR are required to render the dorsal-binding sites functional. Finally, reverse genetic and biochemical data suggest that the transcription factor, encoded by the zeste gene may help control the overall level, if not the pattern, of twist expression.

The dorsal morphogen gradient regulates the mesoderm determinant twist in early Drosophila embryos

A gradient of the maternal morphogen dorsal (dl) initiates the differentiation of various tissues along the dorsal-ventral axis of early Drosophila embryos. dl is a sequence-specific DNA-binding protein that is related to the mammalian regulatory factor NF-kappa B. Previous studies suggest that dl can function as a transcriptional repressor. To determine how dl functions as an activator we have examined the promoter of the mesoderm determinant gene twist (twi). Genetic studies suggest that peak levels of dl protein in ventral regions of early embryos initiate twi expression. Using a combination of promoter fusion-P-transformation assays, and in vitro DNA-binding assays coupled with site-directed mutagenesis, we establish a direct link between dl-binding sites and twi expression in the early embryo. We also present evidence that the dorsal-ventral limits of twi expression depend on the number and affinity of dl-binding sites present in its promoter. A comparison of twi with a second dl target gene, zen, suggests a correlation between the affinities of dl-binding sites and response to different thresholds of dl morphogen.

NF-kappa B activity in T cells stably expressing the Tax protein of human T cell lymphotropic virus type I

The effect of constitutive Tax expression on the interaction of NF-kappa B with its recognition sequence and on NF-kappa B-dependent gene expression was examined in T lymphoid Jurkat cell lines (19D and 9J) stably transformed with a Tax expression vector. Tax expressing T cell lines contained a constitutive level of NF-kappa B binding activity, detectable by mobility shift assay and uv cross-linking using a palindromic NF-kappa B probe homologous to the interferon beta PRDII site. In Jurkat and NC2.10 induction with phorbol esters resulted in the appearance of new DNA binding proteins of 85, 75, and 54 kDa, whereas in Tax expressing cells the 85-kDa protein and a 92-kDa DNA binding protein were constitutively induced. Expression of Tax protein in 19D and 9J resulted in transcription of the endogenous NF-kappa B-dependent granulocyte-macrophage colony stimulating factor gene and increased basal level expression of transfected NF-kappa B-regulated promoters. Nonetheless transcription of both the endogenous and the transfected gene was inducible by PMA treatment. Tax expression in Jurkat T cells may alter the stoichiometry of NF-kappa B DNA binding proteins and thus change the expression of NF-kappa B-regulated promoters.

Rel-associated pp40: an inhibitor of the rel family of transcription factors

The Rel-associated protein pp40 is functionally related to I kappa B, an inhibitor of the transcription factor NF-kappa B. Purified pp40 inhibits the DNA binding activity of the NF-kappa B protein complex (p50:p65 heterodimers), p50:c-Rel heteromers, and c-Rel homodimers. The sequence of the complementary DNA encoding pp40 revealed similarity to the gene encoding MAD-3, a protein with mammalian I kappa B-like activity. Protein sequencing of I kappa B purified from rabbit lung confirmed that MAD-3 encodes a protein similar to I kappa B. The sequence similarity between MAD-3 and pp40 includes a casein kinase II and consensus tyrosine phosphorylation site, as well as five repeats of a sequence found in the human erythrocyte protein ankyrin. These results suggest that rel-related transcription factors, which are capable of cytosolic to nuclear translocation, may be held in the cytosol by interaction with related cytoplasmic anchor molecules.

USF-related transcription factor, HIV-TF1, stimulates transcription of human immunodeficiency virus-1

The transcription factor HIV-TF1, which binds to a region about 60 bp upstream from the enhancer of the human immunodeficiency virus-1 (HIV-1), was purified from human B cells. HIV-TF1 had a molecular weight of 39,000. Binding of HIV-TF1 to the HIV long terminal repeat (LTR) activated transcription from the HIV promoter in vitro. The HIV-TF1-binding site in HIV LTR was similar to the site recognized by upstream stimulatory factor (USF) in the adenovirus major late promoter. DNA-binding properties of HIV-TF1 suggested that HIV-TF1 might be identical or related to USF. Interestingly, treatment of purified HIV-TF1 by phosphatase greatly reduced its DNA-binding activity, suggesting that phosphorylation of HIV-TF1 was essential for DNA binding. The disruption of HIV-TF1-binding site induced a 60% decrease in the level of transcription from the HIV promoter in vivo. These results suggest that HIV-TF1 is involved in transcriptional regulation of HIV-1.

Oncogenes: a review of their clinical application

One objective of this review is to sort through and collate the recent data that suggest that human cellular oncogenes, which have been implicated as the etiologic agents in both animal and human malignancies, have also the potential to be employed as clinical tools in the struggle against cancer. For nearly 10 years, reports have been suggesting that advantage can be taken of cellular oncogenes as to their use as diagnostic and prognostic indicators of cancer and eventually as therapeutic cancer agents. It is also the purpose of this review to give an objective evaluation of these predictions. Moreover, this review will try to highlight some of the significant advances in this most rapidly evolving field of biology. Although the enormity of what has been learned about cellular oncogenes is nothing less than impressive, it is the view here that the routine implementation of oncogenes into the clinical setting will not become evident as early as the many predictions had purported.

Constitutive and NF-kappa B-like proteins in the regulation of the serum amyloid A gene by interleukin 1

Serum amyloid A (SAA) is a major acute-phase protein whose chronic production by the liver can lead to the fatal disorder of secondary amyloidosis. Control of SAA is mediated by several inflammatory cytokines, including interleukin 1 (IL-1). To study the cis-acting regulatory elements responsible for constitutive and IL-1-induced expression, DNA constructs containing varying lengths of the promoter region from the human SAA2 beta gene 5' to the bacterial reporter gene, chloramphenicol acetyltransferase (CAT), were generated and transfected into human hepatoma cells, HepG2. Both positive and negative regulatory elements were found in the 5' flanking region of the human SAA2 beta gene. The more proximal region contains an IL-1 enhancer sequence GGGACTTTCC (SAA kappa B1; between -82 and -91), the binding site for the ubiquitous transcription factor NF-kappa B. IL-1 induction of the binding of nuclear factor to this sequence is maximal between 5 min and 30 min after incubation with IL-1 and negative in cells incubated for 60 min or longer. Mutation of the SAA kappa B1 sequence to a nonbinding form of NF-kappa B (CTCACTTTCC) abolishes the IL-1 effect. The SAA 5' region also contained an upstream repressor element, shown by transfection experiments. Within this element, a second NF-kappa B binding site (SAA kappa B2; -626 to -635) was found, and mutation of SAA kappa B2 to a non-NF-kappa B-binding form results in an increase in both constitutive + IL-1 stimulated SAA transcription.(ABSTRACT TRUNCATED AT 250 WORDS)

Type I human T cell leukemia virus tax protein transforms rat fibroblasts through the cyclic adenosine monophosphate response element binding protein/activating transcription factor pathway

The Tax oncoprotein of the type I human T cell leukemia virus (HTLV-I) activates transcription of cellular and viral genes through at least two different transcription factor pathways. Tax activates transcription of the c-fos proto-oncogene by a mechanism that appears to involve members of the cAMP response element binding protein (CREB) and activating transcription factor (ATF) family of DNA-binding proteins. Tax also induces the nuclear expression of the NF-kappa B family of rel oncogene-related enhancer-binding proteins. We have investigated the potential role of these CREB/ATF and NF-kappa B/Rel transcription factors in Tax-mediated transformation by analyzing the oncogenic potential of Tax mutants that functionally segregate these two pathways of transactivation. Rat fibroblasts (Rat2) stably expressing either the wild-type Tax protein or a Tax mutant selectively deficient in the ability to induce NF-kappa B/Rel demonstrated marked changes in morphology and growth characteristics including the ability to form tumors in athymic mice. In contrast, Rat2 cells stably expressing a Tax mutant selectively deficient in the ability to activate transcription through CREB/ATF demonstrated no detectable changes in morphology or growth characteristics. These results suggest that transcriptional activation through the CREB/ATF pathway may play an important role in Tax-mediated cellular transformation.

Functional modularity in the SP6 kappa promoter

The requirements of the SP6 kappa promoter for transcriptional activation were studied in nontransformed murine B lymphocytes stimulated with lipopolysaccharide. Three different DNA motifs, besides the TATA-box, were needed for restoration of transcriptional activation to the same magnitude as seen with the native SP6 kappa promoter. The decamer motif (TNCTTTGCAT) was found to induce transcription alone and point-mutation of this element reduced transcription to negligible levels, although the other two required elements were present. The penta-decamer element (TGCAG/CCTGTGNCCAG) did not stimulate transcription alone, but activated transcription synergistically in conjunction with the decamer motif. This synergism required the presence of a third pyrimidine rich element (CCCT) in the decamer 3' flanking sequence. The pyrimidine rich element could partly be substituted for by an E-box core motif (CANNTG) 3' of, but not by the kappa Y motif (CTTCCTTA) 5' of, the decamer. Proteins interacting specifically with the penta-decamer element were detected by band-shift assay. The decamer 3' flanking sequence of the SP6 kappa promoter was found to modify the binding of endogenous Oct2 isoforms to the decamer motif i B lymphocytes, but not in CHO cells transfected with various Oct2 isoforms. Thus, complex protein/DNA interactions can be observed in the SP6 kappa promoter which correlate functionally with a synergism in transcriptional activation.

Cloning of an NF-kappa B subunit which stimulates HIV transcription in synergy with p65

The transcription factor NF-kappa B is a protein complex which comprises a DNA-binding subunit and an associated transactivation protein (of relative molecular masses 50,000 (50K) and 65K, respectively). Both the 50K and 65K subunits have similarity with the rel oncogene and the Drosophila maternal effect gene dorsal. The 50K DNA-binding subunit was previously thought to be a unique protein, derived from the 105K gene product (p105). We now report the isolation of a complementary DNA that encodes an alternative DNA-binding subunit of NF-kappa B. It is more similar to p105 NF-kappa B than other family members and defines a new subset of rel-related genes. It is synthesized as approximately 100K protein (p100) that is expressed in different cell types, contains cell cycle motifs and, like p105, must be processed to generate a 50K form. A 49K product (p49) can be generated independently from an alternatively spliced transcript; it has specific kappa B DNA-binding activity and can form heterodimers with other rel proteins. In contrast to the approximately 50K protein derived from p105, p49 acts in synergy with p65 to stimulate the human immunodeficiency virus (HIV) enhancer in transiently transfected Jurkat cells. p49/p100 NF-kappa B could therefore be important in the regulation of HIV and other kappa B-containing genes.

A complex regulatory DNA element associated with a major histocompatibility complex class I gene consists of both a silencer and an enhancer

A novel regulatory element which contributes to the regulation of quantitative, tissue-specific differences in gene expression has been found between -771 and -676 bp upstream of the major histocompatibility complex (MHC) class I gene, PD1. Molecular dissection of this element reveals the presence of two overlapping functional activities: an enhancer and a silencer. Distinct nuclear factors bind to the overlapping enhancer and silencer DNA sequence elements within the regulatory domain. The levels of factors binding the silencer DNA sequence in different cell types are inversely related to levels of class I expression; in contrast, factors binding the enhancer DNA sequence can be detected in all cells. In cultured cell lines, inhibition of protein synthesis leads to the rapid loss of silencer complexes, with a concomitant increase in both enhancer complexes and MHC class I RNA. From these data, we conclude that a labile silencer factor competes with a constitutively expressed, stable enhancer factor for overlapping DNA-binding sites; the relative abundance of the silencer factor contributes to establishing steady-state levels of MHC class I gene expression.

Convergence of Ets- and notch-related structural motifs in a heteromeric DNA binding complex

Analysis of the heteromeric DNA binding protein GABP has revealed the interaction of two distinct peptide sequence motifs normally associated with proteins located in different cellular compartments. The alpha subunit of GABP contains an 85-amino acid segment related to the Ets family of DNA binding proteins. The ETS domain of GABP alpha facilitates weak binding to DNA and, together with an adjacent segment of 37 amino acids, mediates stable interaction with GABP beta. The beta subunit of GABP contains four imperfect repeats of a sequence present in several transmembrane proteins including the product of the Notch gene of Drosophila melanogaster. These amino-terminal repeats of GABP beta mediate stable interaction with GABP alpha and, when complexed with GABP alpha, directly contact DNA. These observations provide evidence for a distinct biochemical role for the 33-amino acid repeats, and suggest that they may serve as a module for the generation of specific dimerization interfaces.

Identification of Ets- and notch-related subunits in GA binding protein

Recombinant cDNA clones that encode two distinct subunits of the transcription factor GA binding protein (GABP) have been isolated. The predicted amino acid sequence of one subunit, GABP alpha, exhibits similarity to the sequence of the product of the ets-1 protooncogene in a region known to encompass the Ets DNA binding domain. The sequence of the second subunit, GABP beta, contains four 33-amino acid repeats located close to the NH2-terminus of the subunit. The sequences of these repeats are similar to repeats in several transmembrane proteins, including Notch from Drosophila melanogaster and Glp-1 and Lin-12 from Caenorhabditis elegans. Avid, sequence-specific binding to DNA required the presence of both polypeptides, revealing a conceptual convergence of nuclear transforming proteins and membrane-anchored proteins implicated in developmentally regulated signal transduction processes.

A complex regulatory DNA element associated with a major histocompatibility complex class I gene consists of both a silencer and an enhancer

A novel regulatory element which contributes to the regulation of quantitative, tissue-specific differences in gene expression has been found between -771 and -676 bp upstream of the major histocompatibility complex (MHC) class I gene, PD1. Molecular dissection of this element reveals the presence of two overlapping functional activities: an enhancer and a silencer. Distinct nuclear factors bind to the overlapping enhancer and silencer DNA sequence elements within the regulatory domain. The levels of factors binding the silencer DNA sequence in different cell types are inversely related to levels of class I expression; in contrast, factors binding the enhancer DNA sequence can be detected in all cells. In cultured cell lines, inhibition of protein synthesis leads to the rapid loss of silencer complexes, with a concomitant increase in both enhancer complexes and MHC class I RNA. From these data, we conclude that a labile silencer factor competes with a constitutively expressed, stable enhancer factor for overlapping DNA-binding sites; the relative abundance of the silencer factor contributes to establishing steady-state levels of MHC class I gene expression.

Mechanisms of complex transcriptional regulation: implications for brain development

The large number of transcription factors, their diverse sequence-specific interactions with DNA sites and with other transcription factors, and their ability to be modified in response to a variety of environmental cues and intracellular signals provide combinatorial codes for highly complex and yet highly organized patterns of gene expression likely to underlie the determination of diversity of neuronal phenotypes. Subtle differences in the combinations of transcription factors are likely to have profound consequences for cell phenotype, similar to the mechanism involved in the specification of cell types in yeast (reviewed in Herskowitz, 1989). Although our current understanding of transcriptional regulation in the brain comes largely from phenomenological studies, recent technical progress on two fronts promises a bright future. Homologous recombination technology in embryonic stem cells (reviewed in Capecchi, 1989; Rossant, 1990) allows the disruption of particular genes in transgenic mice and definition of the roles of identified transcription factors in mammalian neurogenesis. A second technological advance, targeted tumorigenesis, has provided neuronal model cell lines (Mellon et al., 1990; reviewed in Cepko, 1988; McKay et al., 1988) that mimic certain neuronal differentiation pathways. These combined genetic, cell biological, and biochemical approaches will greatly facilitate the study of neural development and function.

Establishment of dorsal-ventral and terminal pattern in the Drosophila embryo

Dorsal-ventral and terminal pattern formation in the Drosophila embryo is mediated via inductive signals originating during oogenesis from the somatic follicle cells that ensheath the developing oocyte. This somatically expressed spatial information controls dorsal-ventral development by defining the polarity of a signal transduction pathway that results in the graded nuclear concentration of the dorsal gene product, a transcription factor.

The rel-associated pp40 protein prevents DNA binding of Rel and NF-kappa B: relationship with I kappa B beta and regulation by phosphorylation

The product of proto-oncogene Rel associates with a number of cellular proteins. We have studied the effect of one of them, a phosphoprotein of 40 kD (pp40), on the DNA-binding activity of the Rel protein. We demonstrate that purified pp40 not only inhibits the binding of Rel, but also NF-kappa B (p50-p65) heterocomplex to DNA. Additionally, I kappa B beta, but not I kappa B alpha, also prevented the binding of Rel to the kappa B site. I kappa B beta and pp40 are related proteins because (1) they share a number of common tryptic peptides, (2) their inhibitory effect on DNA binding can be abolished by preincubation with pp40-specific antiserum, and (3) labeled I kappa B beta can be immunoprecipitated with pp40 antibodies. pp40 is part of the Rel complex present in the cytoplasm and nuclear extracts of WEHI-231 cells. The activity of pp40 to inhibit the DNA binding of Rel and NF-kappa B is modulated by phosphorylation.

The v-rel oncogene of avian reticuloendotheliosis virus transforms immature and mature lymphoid cells of the B cell lineage in vitro

Heavy chain gene rearrangements were analyzed in 67 independently derived reticuloendotheliosis virus (REV-T) transformed avian lymphoid cell lines. The status of the heavy chain genes in these REV-T transformed cell lines was determined, in part, by the age of the chicken whose spleen cells were transformed. Cell lines derived by the in vitro transformation of splenic lymphocytes obtained from embryos did not contain heavy chain gene Ig rearrangements. By contrast, splenic lymphocytes transformed by REV-T obtained from birds 1 week or older generally exhibited heavy chain gene rearrangements. The REV-T transformed lymphoid cell lines with heavy chain rearrangements also had light chain gene rearrangements. The Ig gene rearrangements in REV-T transformed cells were functional. The majority of the cells which had heavy chain rearrangements expressed a 2.2-kb mu transcript and synthesized and secreted IgM. An REV-T transformant was also identified which produced IgG, suggesting that v-rel can transform a terminally differentiated cell. Irrespective of their Ig chain gene status the REV-T transformed cell lines expressed variable amounts of some but not all normal B cell-specific markers and failed to express T cell markers. All the cell lines analyzed expressed the B-L (Ia-like) antigen as well as a common leukocyte antigen. Based on the expression of these surface molecules, the transformants with or without Ig gene rearrangements all appear to be committed to the B cell pathway.

Ionizing radiation induces expression and binding activity of the nuclear factor kappa B

Recent studies have demonstrated that treatment of mammalian cells with ionizing radiation is associated with activation of gene expression. Although the signal transduction pathways stimulated by ionizing radiation remain unclear, our previous findings indicate that radiation induces specific genes at the transcriptional level. The present work has examined the effects of ionizing radiation on the transcription factor NF-kappa B. The results demonstrate that ionizing radiation activates DNA binding of nuclear factor (NF)kappa B. This effect was detectable at 2 grays (Gy) and reached a maximum at 5-20 Gy. At a dose of 20 Gy, the increase in NF-kappa B binding activity was maximal at 2-4 h and then declined to pretreatment levels. The results also demonstrate that ionizing radiation transiently increases NF-kappa B mRNA levels. However, the finding that induction of NF-kappa B binding to DNA occurs in the presence of cycloheximide indicates that ionizing radiation activates preexisting NF-kappa B protein. NF-kappa B exists as a cytoplasmic protein before activation. Thus, our results suggest that ionizing radiation induces transduction pathways which include cytoplasmic signaling events.

Identification of cis sequences controlling efficient position-independent tissue-specific expression of human major histocompatibility complex class I genes in transgenic mice

We previously reported that genomic major histocompatibility complex class I human leukocyte antigen (HLA)-B7 gene constructs with as little as 0.66 kb of 5'- and 2.0 kb of 3'-flanking DNA were expressed efficiently and appropriately in transgenic mice. To identify and characterize the relevant cis-acting regulatory elements in more detail, we have generated and analyzed a series of transgenic mice carrying native HLA-B7 genes with further 5' truncations or intronic deletions and hybrid constructs linking the 5'-flanking region of B7 to a reporter gene. We were unable to detect a specific requirement for sequence information within introns 2 to 7 for either appropriate constitutive or inducible class I expression in adult animals. The results revealed the presence of cis-acting regulatory sequences between -0.075 kb and -0.66 kb involved in driving efficient copy number-dependent constitutive and gamma interferon-enhanced tissue-specific expression. The region from -0.11 to -0.66 kb is also sufficient to prevent integration site-specific "position effects," because in its absence HLA-B7 expression is frequently detected at significant levels at inappropriate sites. Conserved sequence elements homologous to the H-2 class I regulatory element, or enhancer A, and the interferon response sequence are located between about -151 and -228 bp of the B7 gene. Our results also indicate the existence of sequences downstream of -0.11 kb which can influence the pattern of tissue-specific expression of the HLA-B7 gene and the ability of this gene to respond to gamma interferon.

Formation of several specific nucleoprotein complexes on the human cytomegalovirus immediate early enhancer

The major immediate early enhancer of the human cytomegalovirus (HCMV) is composed of unique and repeated sequence motifs, which interact with different nuclear proteins, thus forming a large nucleoprotein complex. Using DNAase I protection analysis, we determined at the nucleotide level the interactions of B cell and HeLa cell nuclear proteins with transcription factor binding sites in the enhancer/promoter. In agreement with in vivo activity, protein binding to the 18 bp repeats (kappa B element) was found predominantly with B cell extract. Competition for proteins with individual transcription factor binding sites allowed us to define boundaries of closely spaced and overlapping binding sites, and to group binding proteins into several classes. Using gel mobility shift assays, we could show that proteins, which bind to the 17 bp repeat, also bind to a classical NF1 site. In addition, several novel binding sites were identified. The presence of overlapping binding sites, together with differences in the occupation of the 18 bp repeats in the two cell types, suggest that the HCMV major IE enhancer has several possibilities of forming nucleoprotein complexes.

Isolation and characterization of cDNAs encoding human brain ankyrins reveal a family of alternatively spliced genes

Ankyrins are a family of membrane-associated proteins that can be divided into two immunologically distinct groups: (a) erythrocyte-related isoforms (ankyrinR) that have polarized distributions in particular cell types; and (b) brain-related isoforms (ankyrinB) that display a broader distribution. In this paper, we report the isolation and sequences of cDNAs related to two ankyrinB isoforms, human brain ankyrin 1 and 2, and show that these isoforms are produced from alternatively spliced mRNAs of a single gene. Human brain ankyrin 1 and 2 share a common NH2-terminus that is similar to human erythrocyte ankyrins, with the most striking conservation occurring between areas composed of a repeated 33-amino acid motif and between areas corresponding to the central portion of the spectrin-binding domain. In contrast, COOH-terminal sequences of brain ankyrin 1 and 2 are distinct from one another and from human erythrocyte ankyrins, and thus are candidates to mediate protein interactions that distinguish these isoforms. The brain ankyrin 2 cDNA sequence includes a stop codon and encodes a polypeptide with a predicted molecular mass of 202 kD, which is similar to the Mr of the major form of ankyrin in adult bovine brain membranes. Moreover, an antibody raised against the conserved NH2-terminal domain of brain ankyrin cross-reacts with a single Mr = 220 kD polypeptide in adult human brain. These results strongly suggest that the amino acid sequence of brain ankyrin 2 determined in this report represents the complete coding sequence of the major form of ankyrin in adult human brain. In contrast, the brain ankyrin 1 cDNAs encode only part of a larger isoform. An immunoreactive polypeptide of Mr = 440 kD, which is evident in brain tissue of young rats, is a candidate to be encoded by brain ankyrin 1 mRNA. The COOH-terminal portion of brain ankyrin 1 includes 15 contiguous copies of a novel 12-amino acid repeat. Analysis of DNA from a panel of human/rodent cell hybrids linked this human brain ankyrin gene to chromosome 4. This result, coupled with previous reports assigning the human erythrocyte ankyrin gene to chromosome 8, demonstrates that human brain and erythrocyte ankyrins are encoded by distinct members of a multigene family.

Identification of cis sequences controlling efficient position-independent tissue-specific expression of human major histocompatibility complex class I genes in transgenic mice

We previously reported that genomic major histocompatibility complex class I human leukocyte antigen (HLA)-B7 gene constructs with as little as 0.66 kb of 5'- and 2.0 kb of 3'-flanking DNA were expressed efficiently and appropriately in transgenic mice. To identify and characterize the relevant cis-acting regulatory elements in more detail, we have generated and analyzed a series of transgenic mice carrying native HLA-B7 genes with further 5' truncations or intronic deletions and hybrid constructs linking the 5'-flanking region of B7 to a reporter gene. We were unable to detect a specific requirement for sequence information within introns 2 to 7 for either appropriate constitutive or inducible class I expression in adult animals. The results revealed the presence of cis-acting regulatory sequences between -0.075 kb and -0.66 kb involved in driving efficient copy number-dependent constitutive and gamma interferon-enhanced tissue-specific expression. The region from -0.11 to -0.66 kb is also sufficient to prevent integration site-specific "position effects," because in its absence HLA-B7 expression is frequently detected at significant levels at inappropriate sites. Conserved sequence elements homologous to the H-2 class I regulatory element, or enhancer A, and the interferon response sequence are located between about -151 and -228 bp of the B7 gene. Our results also indicate the existence of sequences downstream of -0.11 kb which can influence the pattern of tissue-specific expression of the HLA-B7 gene and the ability of this gene to respond to gamma interferon.

Developmental and tissue-specific expression of the Q5k gene

Expression of the Q5k gene was examined by northern blot analysis and polymerase chain reaction (PCR) in the AKR mouse and various cell lines, each of the H-2k haplotype. Our results show that Q5k mRNA is present during the whole postimplantational development of the AKR embryo/fetus (gestation day 6 to 15). In the juvenile mouse (week 2 to 4) transcription of the Q5k gene persisted in all organs examined. In contrast, in the adult animal expression of the Q5k gene was limited to the thymus and uterus of the pregnant mouse. Upon malignant transformation, the amount of Q5k-specific mRNA increased dramatically in thymus and could also be observed in the spleen of thymoma bearing animals. Expression of the Q5k gene was also detectable in several transformed mouse cell lines. Mitogen stimulation or treatment with cytokines induced Q5k expression in primary spleen cell cultures. A possible explanation for the tissue-restricted expression in the adult AKR mouse is discussed.

NF-kappa B contacts DNA by a heterodimer of the p50 and p65 subunit

We recently reported that the apparently non-DNA-binding 65 kd subunit (p65) of the NF-kappa B transcription factor can modulate the DNA-binding specificity of the 50 kd subunit (p50) of NF-kappa B. In this study we provide an explanation for this property of p65. In electrophoretic mobility shift assays and upon UV cross-linking to DNA, gel-purified p65 is shown to be a kappa B-specific DNA-binding protein on its own. The binding activity was only detectable if high amounts of p65 were used for the analyses and after the application of a modified renaturation protocol. DNA-binding of the p65 dimer, in contrast to that of p50, was inhibited by I kappa B-alpha and -beta. This finding is consistent with a receptor function of p65 for both inhibitory subunits. Direct UV cross-linking of NF-kappa B to DNA probes which were photoreactive within only one half-site and a binding competition analysis with p65 showed that p65 has a strong preference for binding to the less conserved half site of kappa B motifs whereas p50 has a moderate preference for the more highly conserved half site. In electrophoretic mobility shift assays and upon sedimentation through glycerol gradients, NF-kappa B appears to exist as a heterodimer composed of one p50 and one p65 subunit whereas data from gel filtration suggest a higher order complex.

Inhibition of transcription factors belonging to the rel/NF-kappa B family by a transdominant negative mutant

The KBF1 factor, which binds to the enhancer A located in the promoter of the mouse MHC class I gene H-2Kb, is indistinguishable from the p50 DNA binding subunit of the transcription factor NF-kappa B, which regulates a series of genes involved in immune and inflammatory responses. The KBF1/p50 factor binds as a homodimer but can also form heterodimers with the products of other members of the same family, like the c-rel and v-rel (proto)oncogenes. The dimerization domain of KBF1/p50 is contained between amino acids 201 and 367. A mutant of KBF1/p50 (delta SP), unable to bind to DNA but able to form homo- or heterodimers, has been constructed. This protein reduces or abolishes in vitro the DNA binding activity of wild-type proteins of the same family (KBF1/p50, c- and v-rel). This mutant also functions in vivo as a trans-acting dominant negative regulator: the transcriptional inducibility of the HIV long terminal repeat (which contains two potential NF-kappa B binding sites) by phorbol ester (PMA) is inhibited when it is co-transfected into CD4+ T cells with the delta SP mutant. Similarly the basal as well as TNF or IL1-induced activity of the MHC class I H-2Kb promoter can be inhibited by this mutant in two different cell lines. These results constitute the first formal demonstration that these genes are regulated by members of the rel/NF-kappa B family.

Sequence-specific transactivation of the Drosophila twist gene by the dorsal gene product

The maternal gene dorsal encodes a nuclear protein acting as a morphogen that determines the size and fate of regions along the dorsal-ventral axis of the Drosophila embryo. From previous genetic and biochemical studies it was hypothesized that dorsal might be responsible for the activation of the zygotic gene twist. In this report, regulatory sequences required for correct spatial and quantitative expression of twist are defined, by using phenotypic rescue and studying twist-beta-galactosidase expression. In addition, by transient cotransfection assays, we show that the dorsal protein specifically activates expression from the twist promoter. We demonstrate that dorsal is a sequence-specific DNA-binding protein that recognizes a motif similar to that recognized by the mammalian transcriptional activator NF-kappa B.

Characterization of an immediate-early gene induced in adherent monocytes that encodes I kappa B-like activity

We have cloned a group of cDNAs representing mRNAs that are rapidly induced following adherence of human monocytes. One of the induced transcripts (MAD-3) encodes a protein of 317 amino acids with one domain containing five tandem repeats of the cdc10/ankyrin motif, which is 60% similar (46% identical) to the ankyrin repeat region of the precursor of NF-kappa B/KBF1 p50. The C-terminus has a putative protein kinase C phosphorylation site. In vitro translated MAD-3 protein was found to specifically inhibit the DNA-binding activity of the p50/p65 NF-kappa B complex but not that of the p50/p50 KBF1 factor or of other DNA-binding proteins. The MAD-3 cDNA encodes an I kappa B-like protein that is likely to be involved in regulation of transcriptional responses to NF-kappa B, including adhesion-dependent pathways of monocyte activation.

A labile repressor acts through the NFkB-like binding sites of the human urokinase gene

Transcription of the human urokinase type plasminogen activator (uPA) gene in HeLa cells is induced by phorbol myristate acetate (PMA), interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha). The response to these factors is rapid, independent of new protein synthesis and amplified in the presence of an inhibitor of protein synthesis, indicating the presence of a labile repressor. A DNA element, similar to the binding site for the transcription factor NFkB, is located around--1865 with respect to the start site of transcription in the uPA promoter and confers superinducibility by these agents in the presence of cycloheximide (CHX). A synthetic copy of this element confers superinducibility on a minimal uPA gene promoter and on the thymidine kinase (TK) gene promoter linked to the chloramphenicol acetyl transferase (CAT) gene. CHX alone does not increase transcription from these constructs in HeLa cells, although it superinduces the effects of PMA, IL-1 and TNF alpha. A second NFkB-like binding site located at around--1835 is not capable of conferring transcriptional activation under the same conditions. Our results suggest that maximal transcriptional activation of the uPA gene by PMA, IL-1 and TNF alpha requires the induction of NFkB activity and the decay of a short lived repressor protein, possibly IkB.

vRel is an inactive member of the Rel family of transcriptional activating proteins

The vRel oncoprotein is member of a family of related proteins that also includes cRel, NF-kappa B, and Dorsal. We investigated the transcriptional regulatory properties of several Rel proteins in cotransfection assays with chicken embryo fibroblasts (CEF). Retroviral vectors expressing hybrid proteins that contain the DNA-binding domain of LexA fused to portions of the viral oncoprotein vRel or chicken, mouse, human, or Drosophila melanogaster (Dorsal) cRel proteins were cotransfected with a reporter plasmid that contains the DNA sequence recognized by LexA, a promoter, and the assayable gene for chloramphenicol acetyltransferase. In transient assays, a LexA-vRel protein did not activate transcription in CEF. Full-length chicken cRel, mouse cRel, and Dorsal fusion proteins all activated transcription weakly; however, deletion of N-terminal Rel sequences from each of these proto-oncogene encoded proteins resulted in strong activation by LexA fusion proteins containing only C-terminal sequences. Inhibition of the C-terminal chicken cRel gene activation domain by N-terminal sequences was seen in CEF and mouse and monkey fibroblasts. These results show that cRel proteins from different species have the same general organization: an N-terminal inhibitory domain and a C-terminal activation domain. Sequence comparison suggests that the inhibitory domain is conserved but the activation domain is species specific. In contrast, vRel lacks a strong C-terminal gene activation function, since a LexA fusion protein containing C-terminal vRel sequences alone only weakly activated transcription. In addition, the wild-type vRel protein (lacking LexA sequences) repressed transcription from reporter plasmids containing NF-kappa B target sequences; nontransforming vRel mutants did not repress transcription from these plasmids. Our results suggest that vRel transforms cells by interfering with transcriptional activation by cellular Rel proteins.

Nuclear oncogenes

Ample evidence has accumulated in recent years to establish that most, if not all, nuclear proto-oncogenes are in fact sequence-specific DNA-binding proteins that modulate gene expression. Their synthesis or activity is modulated by extracellular signals or by cross talk between different classes of transcription factors.

Signal transduction and gene control

Extracellular signals regulate gene expression by triggering signal transduction cascades that result in the modulation of transcription factor activity. This is most commonly achieved by changes in the phosphorylation state of these nuclear proteins. Phosphorylation affects transcription factor activity at several distinct levels. It can modulate their intracellular localization by controlling the association with other proteins, have both negative and positive effects on their DNA-binding activity, and modulate the activity of their transcriptional activation domains. In addition to phosphorylation, protein-protein interactions also have an important role in mediating a crosstalk at the nuclear level between different signalling pathways.

The polarity of the dorsoventral axis in the Drosophila embryo is defined by an extracellular signal

Twelve maternal effect loci are required for the production of Drosophila embryos with a correct dorsoventral axis. Analysis of mosaic females indicates that the expression of the genes nudel, pipe, and windbeutel is required in the somatic tissue, presumably in the follicle cells that surround the oocyte. Thus, information coming from outside the egg cell influences dorsoventral pattern formation during embryogenesis. In transplantation experiments, the perivitelline fluid from the compartment surrounding the embryo can restore dorsoventral pattern to embryos from females mutant for nudel, pipe, or windbeutel. The positioning of the transplanted pervitelline fluid also determines the polarity of the restored dorsoventral axis. We propose that the polarizing activity, normally present at the ventral side of the egg, is a ligand for the Toll receptor. Presumably, local activation of the Toll protein by the ligand initiates the formation of the nuclear concentration gradient of the dorsal protein, thereby determining dorsoventral pattern.

An NF kappa B-like factor is essential but not sufficient for cytokine induction of endothelial leukocyte adhesion molecule 1 (ELAM-1) gene transcription

The endothelial leukocyte adhesion molecule 1 (ELAM-1) is transiently expressed specifically on the surface of cytokine-induced endothelial cells. We demonstrate that the transient expression of the protein is paralleled by an increase and decrease in transcription of the ELAM-1 gene. To identify the cis-acting transcription control regions within the ELAM-1 gene that are responsible for this cytokine-induced expression, we isolated and analyzed an ELAM-1 genomic clone containing sequences upstream of the transcription start site. We constructed a series of ELAM-1 deletion mutants linked to a reporter gene and analyzed their expression in both endothelial and non-endothelial cells. Results show that a fragment of 233 bp upstream of the transcription start site is sufficient to confer cytokine inducibility upon the reporter gene in both endothelial and non-endothelial cells. Further analysis defined two elements within this region that are involved in the cytokine inducibility of the ELAM-1 gene. One element lies within the -233 to -117 region, the other element represents an NF kappa B consensus binding site between nucleotides -94 to -85. Gel shift analysis reveals increased binding of an NF kappa B-like factor to this consensus sequence in extracts prepared from IL-1-induced endothelial cells. The results suggest that cytokine induction of ELAM-1 gene transcription is imparted by a combination of positive factors, one being an NF kappa B-like transcription factor, interacting with cis-acting elements within the enhancer/promoter of the gene.

Angiotensinogen gene-inducible enhancer-binding protein 1, a member of a new family of large nuclear proteins that recognize nuclear factor kappa B-binding sites through a zinc finger motif

Transcriptional activation of the rat angiotensinogen gene during the acute-phase response is dependent on a previously characterized acute-phase response element (APRE) that binds at least two types of nuclear proteins: a cytokine-inducible activity indistinguishable from nuclear factor kappa-B (NF kappa B) and a family of C/EBP-like proteins. We screened a rat liver cDNA expression library with a labeled APRE DNA probe and isolated a single clone that encodes a sequence-specific APRE-binding protein. This new protein, the angiotensinogen gene-inducible enhancer-binding protein 1 (AGIE-BP1), is encoded by a large continuous open reading frame and contains a zinc finger motif virtually identical to the DNA-binding domain of a recently described human protein, MBP-1/PRDII-BF1, and a homologous mouse protein, alpha A-CRYBP1. Outside the binding domain, the sequences diverged considerably. Southern blot analysis indicated that AGIE-BP1 and alpha A-CRYBP1 are encoded by separate genes, thus defining a new family of DNA-binding proteins. Electrophoretic mobility shift assays, methylation interference, and DNase I footprint protection assays with the bacterially expressed DNA-binding domain of AGIE-BP1 demonstrated a binding specificity indistinguishable from that of purified NF kappa B. Antiserum raised against the bacterially expressed DNA-binding domain of AGIE-BP1 detected on immunoblots of cellular proteins a large (greater than 250-kDa) nuclear protein. Northern (RNA) blot analysis of RNAs from different rat tissues and cell lines indicated different levels of expression of the large (greater than 10-kb) AGIE-BP1 transcript in different tissues. The potential role of AGIE-BP1 in the regulation of gene expression is discussed.

Modulation of transcription factor NF-kappa B binding activity by oxidation-reduction in vitro

NF-kappa B is a widely used regulator of inducible and tissue-specific gene control. In the cytosol, when complexed to an inhibitory molecule, I kappa B, NF-kappa B is in an inactive form and cannot bind DNA. Activation of cells with appropriate stimuli results in the dissociation of NF-kappa B from I kappa B and its translocation to the nucleus as an active binding protein. We now demonstrate that NF-kappa B binding in vitro can be inhibited by agents that modify free sulfhydryls. Binding is eliminated after treatment with N-ethylmaleimide, an alkylating agent, and diamide, an oxidizing agent. The diamide effect can be reversed by 2-mercaptoethanol. Further, 2-mercaptoethanol acts synergistically with deoxycholate plus Nonidet P-40 in converting inactive cytosolic NF-kappa B to an active DNA-binding form. It is therefore possible that modulation of the redox state of NF-kappa B could represent a post-translational control mechanism for this factor.

Dominant and recessive mutations define functional domains of Toll, a transmembrane protein required for dorsal-ventral polarity in the Drosophila embryo

The asymmetry of the dorsal-ventral pattern of the Drosophila embryo appears to depend on the ventral activation of the transmembrane Toll protein. The Toll protein is found around the entire dorsal-ventral circumference of the embryo, and it appears to act as a receptor for a ventral, extracellular signal and to then relay that signal to the cytoplasm in ventral regions of the embryo. Three of five recessive loss-of-function alleles of Toll are caused by point mutations in the region of the cytoplasmic domain of Toll that is similar to the mammalian interleukin-1 receptor, supporting the hypothesis that Toll acts as a signal-transducing receptor. Nine dominant gain-of-function alleles that cause Toll to be active in dorsal, as well as ventral, regions of the embryo are caused by mutations in the extracellular domain. Three of the dominant alleles appear to cause the protein to be constitutively active and are caused by cysteine-to-tyrosine changes immediately outside the transmembrane domain. All six of the remaining dominant alleles require the presence of a wild-type transmembrane Toll protein for their ventralizing effect and all encode truncated proteins that lack the transmembrane and cytoplasmic domains.

NF-kappa B activation by tumor necrosis factor alpha in the Jurkat T cell line is independent of protein kinase A, protein kinase C, and Ca(2+)-regulated kinases

NF-kappa B is a DNA-binding regulatory factor able to control transcription of a number of genes, including human immunodeficiency virus (HIV) genes. In T cells, NF-kappa B is activated upon cellular treatment by phorbol esters and the cytokine tumor necrosis factor alpha (TNF alpha). In the present work, we investigated the molecular events leading to NF-kappa B activation by TNF alpha in a human T cell line (Jurkat) and its subclone JCT6, which presents a deficiency in the PKA transduction pathway. We found that in both cell lines, both phorbol ester and TNF alpha were able to activate NF-kappa B. Phorbol activation was positively modulated by Ca2+ influx while TNF alpha activation was not. Furthermore, while PMA activation was inhibited by the PKC inhibitor staurosporin, the TNF alpha effect was unchanged. TNF alpha did not activate cAMP production and its signal was not modulated by cAMP activators. Moreover, cAMP activators did not activate NF-kappa B in Jurkat cells. Thus, TNF alpha-induced NF-kappa B activation was found to be mediated by none of the major signal-mediating kinases such as protein kinase C (PKC), protein kinase A, or Ca(2+)-regulated kinases. Furthermore, we found that cytoplasmic acidification facilitated NF-kappa B activation by both TNF alpha and PKC, by a mechanism that increases NF-kappa B/I kappa B dissociation without affecting the NF-kappa B translocation step.