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T Curran

Publications and source records attributed to T Curran.

At least 109 records · Page 6Linked to original sources
PubMed1994

Targeted disruption of NMDA receptor 1 gene abolishes NMDA response and results in neonatal death.

In vitro studies have suggested that the NMDA receptor consists of an essential subunit, NR1, and various modulatory NR2 subunits. To test this hypothesis directly in vivo, we generated mice carrying a disrupted NR1 allele. NMDA-inducible increases in intracellular calcium and membrane currents were abolished in neurons from homozygous null mutants (NR1-/-). Thus, NR1 has a unique role, which cannot be substituted by any other subunit, in determining the activity of the endogenous NMDA receptor. A concomitant reduction in levels of NR2B but not NR2A occurred in NR1-/- mice, demonstrating that there is an interdependence of subunit expression. NR1-/- mice died 8-15 hr after birth, indicating a vital neonatal function for the NMDA receptor. Although the NMDA receptor has been implicated in several aspects of neurodevelopment, overall neuroanatomy of NR1-/- mice appeared normal. Pathological evidence suggested that respiratory failure was the ultimate cause of death.

Animals↗
PubMed1994

Striatonigral degeneration: iron deposition in putamen correlates with the slit-like void signal of magnetic resonance imaging.

We report three patients with striatonigral degeneration highlighting the correlation between magnetic resonance imaging (MRI) and the pathological changes. The "slit-like void signal" observed in the putamen is typical of striatonigral degeneration and can be used to assist diagnosis during life. Our histochemical studies support the concept that increased iron deposition in the putamen is responsible for this MRI picture.

Adult↗
PubMed1994

Fos and Jun repress transcription activation by NF-IL6 through association at the basic zipper region.

NF-IL6 and AP-1 family transcription factors are coordinately induced by interleukin-6 (IL-6) in a cell-type-specific manner, suggesting that they mediate IL-6 signals in the nucleus. We show that the basic leucine zipper (bZIP) region of NF-IL6 mediates a direct association with the bZIP regions of Fos and Jun in vitro. This interaction does not depend on the presence of their cognate recognition DNA elements or the posttranslational modification of either partner. NF-IL6 homodimers can bind to both NF-IL6 and AP-1 sites, whereas Fos and Jun cannot bind to most NF-IL6 sites. Cross-family association with Fos or with Jun alters the DNA binding specificity of NF-IL6 and reduced its binding to NF-IL6 sites. NF-IL6 isoforms that differ in the site of translation initiation have distinct transcriptional activities. Activation of a reporter gene linked to the NF-IL6 site by NF-IL6 is repressed by Fos and by Jun in transient transfection assays. Thus, association with AP-1 results in repression of transcription activation by NF-IL6. The repression is NF-IL6 site dependent and may have a role in determining the promoter and cell type specificity in IL-6 signaling.

Base Sequence↗
PubMed1994

A central role for Fos in human B- and T-cell NFAT (nuclear factor of activated T cells): an acidic region is required for in vitro assembly.

Nuclear factor of activated T cells (NFAT) is a multicomponent transcription factor that contains Fos and Jun family proteins in addition to a constitutively expressed factor(s). It is important for the production of interleukin 2 (IL-2) by T cells and is also expressed in B cells. Here we show that NFAT complexes in B- and T-cell nuclear extracts can be supershifted prominently with Fos antibodies and to a variable extent with Jun family protein antibodies. Fos and Jun proteins appear to participate in NFAT complexes as heterodimers, since efficient in vitro reconstitution of NFAT in unstimulated B- or T-cell nuclear extracts required both Fos and Jun. Using Fos and Jun deletion derivatives, we found that an acidic Fos region (amino acids 118 to 138), outside the DNA binding and dimerization domains, was necessary for the in vitro reconstitution of the NFAT complex in both B- and T-lymphocyte extracts although it was not required for binding to an AP-1 site. Fos-Jun heterodimers exhibited low-affinity direct binding to the NFAT site in the absence of nuclear extracts. This binding also required the Fos acidic region, amino acids 118 to 138. Mutating a variant AP-1 site in the NFAT oligonucleotide abolished both direct binding of Fos-Jun heterodimers and in vitro reconstitution of NFAT. These results demonstrate a central role of Fos in NFAT complex formation in both B and T lymphocytes and show that NFAT assembly involves direct binding of Fos-Jun heterodimers to a variant AP-1 site within the human NFAT recognition site.

B-Lymphocytes↗
PubMed1994

Cell transformation by c-fos requires an extended period of expression and is independent of the cell cycle.

The proto-oncogene transcription factors Fos and Jun form a heterodimeric complex that binds to DNA and regulates expression of specific target genes. Continuous expression of c-fos causes transformation of cultured fibroblasts and induces osteogenic sarcoma in mice. To investigate the molecular basis of fos-mediated oncogenesis, we developed a conditional cell transformation system in which Fos expression was regulated by isopropyl-beta-D-thiogalactopyranoside (IPTG). Synthesis or repression of Fos in L1-3c-fos cells occurred rapidly, within 30 min, after the removal or addition of IPTG to the culture medium. However, there was a significant delay between the induction of Fos expression and the appearance of morphological transformation. No effect was observed after 12 h of Fos expression, partial transformation was detected after 24 h, and full transformation required approximately 3 days of continuous Fos expression. Similarly, the transformed cell morphology persisted for at least 2 days after repression of Fos, and a normal phenotype was observed only after 3 days. Fos-Jun complexes, capable of binding to AP-1 sequences, were present continuously during the delay in morphological transformation. Furthermore, increased expression of several candidate Fos target genes, including those encoding Fra-1, transin (stromelysin), collagenase, and ornithine decarboxylase, was detected shortly after Fos induction. The induction of morphological transformation was not dependent on the cell cycle, as it occurred in both cycling and noncycling cells. Thus, the Fos-Jun complexes present before L1-3c-fos cells become fully transformed are transcriptionally active. These complexes disappeared, and the Fos target genes were repressed at least 2 days prior to reversion. Our results suggest that cell transformation by Fos requires increased expression of a target gene(s) with a long-lived product(s) that must reach a critical level.

Animals↗
PubMed1994

Activation of AP-1 and of a nuclear redox factor, Ref-1, in the response of HT29 colon cancer cells to hypoxia.

Many solid tumors contain substantial fractions of hypoxic cells which are relatively resistant to both radiation therapy and certain cytotoxic drugs. We have previously shown that exposure of human HT29 cells to hypoxic conditions results in the overexpression of certain enzymes involved in the detoxication of xenobiotics, including NAD(P)H:(quinone acceptor) oxidoreductase (DT)-diaphorase, and gamma-glutamylcysteine synthetase, the rate-limiting enzyme in glutathione synthesis. This hypoxic effect on DT-diaphorase was shown to involve both transcriptional induction and altered message stability. We have investigated the effects of hypoxia on elements in the promoter region of DT-diaphorase. Electrophoretic mobility shift assays demonstrate the induction of a binding activity to the AP-1 response element of DT-diaphorase. Supershift assays suggest that this binding is due to AP-1 nuclear factors and that members of the jun family are induced to a greater degree than fos by hypoxia. Analysis of the kinetics of transcription factor expression indicates that the expression of c-jun and junD is induced during hypoxic exposure; mRNA levels fall during reoxygenation. Induction of fos on the other hand is not as florid during hypoxia (5-fold) and is most pronounced (17-fold) 24 h after the restoration of an oxic environment. Thus, the hypoxic response of DT-diaphorase expression is mediated in part through AP-1, initially by a jun-related mechanism and then by the involvement of fos. The affinity of transcription factors for the AP-1 binding site depends on the redox state of a cysteine residue located close to the DNA-binding region of both Fos and Jun. A nuclear protein, Ref-1, maintains the reduced state of Fos and Jun and promotes binding to AP-1. Nuclear extracts of HT29 cells exposed to hypoxia show markedly increased Ref-1 protein content. Elevation of ref-1 steady-state mRNA levels occurs as an early event following induction of hypoxia and persists when cells are restored to a normally oxygenated environment. Nuclear run-on analysis demonstrates that induction of transcription is the mechanism of ref-1 mRNA elevation. Electrophoretic mobility shift assays and immunodepletion assays were used to further define the interaction of Ref-1 with specific AP-1-binding proteins under hypoxic conditions. These data demonstrate that the induction of detoxicating enzyme expression in HT29 cells exposed to hypoxia results from the induction of both transactivating factors that bind to the AP-1 element and of redox proteins that enhance their affinity for this element.

Carbon-Oxygen Lyases↗
PubMed1994

A conserved region adjacent to the basic domain is required for recognition of an extended DNA binding site by Maf/Nrl family proteins.

The c-maf proto-oncogene and the neural retina specific gene nrl encode members of a subfamily of bZIP proteins that form heterodimers with Fos and Jun. We have determined the DNA binding specificities of various homo- and heterodimeric combinations among Nrl, Maf, Fos and Jun. Fos-Jun heterodimers and Jun homodimers bound to a palindromic TGAC(G)TCA recognition sequence as previously demonstrated. Maf and Nrl homodimers also bound to palindromic recognition sites with the consensus sequence TGC(N)6-7GCA. Fos-Nrl, Jun-Nrl and Fos-Maf heterodimers bound to nonpalindromic recognition sequences with the consensus sequence TGAC(N)3-4GCA. These results indicate that Nrl and Maf have a DNA binding specificity distinct from that of Fos and Jun, and that each subunit in the dimer independently recognizes one half of the recognition sequence. This allows combinatorial determination of target gene specificity. Specific recognition of the extended DNA binding sequence by Maf requires an ancillary DNA binding region on the amino terminal side of the basic domain that is conserved among Maf/Nrl family members. Thus, heterodimer formation among distantly related bZIP family members can generate novel DNA binding specificities and the addition of an auxiliary DNA binding domain to the simple bZIP motif can facilitate the recognition of extended binding sites.

Amino Acid Sequence↗
PubMed1994

Maf and Nrl can bind to AP-1 sites and form heterodimers with Fos and Jun.

The c-maf proto-oncogene and the neural retina specific gene nrl encode members of a new bZIP protein subfamily. We have examined the dimerization and DNA binding properties of this new protein family using polypeptides encompassing the leucine zipper and basic regions. Purified polypeptides bound specifically to the AP-1 and CRE sites as well as to variants of the AP-1 site. Maf and Nrl were also able to form heterodimers with Fos and Jun in vitro. All pairwise combinations of Maf, Nrl, Fos and Jun could be co-immunoprecipitated by antisera directed against either subunit. Heterodimers among these proteins bound to the AP-1 site, although with different affinities. Mutations in the leucine zipper dimerization interface or in the basic DNA contact region inhibited heterodimer formation and binding to the AP-1 site. These results indicate that Maf and Nrl together with Fos and Jun family proteins form a bZIP protein superfamily whose members can form an array of heterodimers that have overlapping DNA binding specificities.

Amino Acid Sequence↗
PubMed1993

Differential roles for Fos and Jun in DNA-binding: redox-dependent and independent functions.

The Fos and Jun family of transcription factors contain an invariant sequence motif lysine-cysteine-arginine (KCR) in the highly conserved DNA-binding region. Reduction of the cysteine residue is necessary to facilitate DNA-binding. Here, we examined the potential dual roles of the flanking lysine and arginine residues in influencing the redox reactivity of the cysteine and the DNA-binding activity of Fos and Jun. Two sets of Fos and Jun mutants were generated: the KCR and KSR series representing proteins capable of redox-dependent and redox-independent DNA-binding activity, respectively. Mutation of the lysine in Fos-Jun heterodimers had no obvious effect on the redox reactivity of the cysteine, suggesting that lysine is not essential in this respect. However, mutation of the arginine but not lysine, in both the KCR and the KSR series abolished DNA-binding activity. Thus, the arginine but not the lysine residue in the KCR motif is critical for both redox-dependent and redox-independent functions in DNA-binding. Surprisingly, the triple substitution, ISI, exhibited high levels of DNA-binding activity. This demonstrates that the effects of amino acid substitutions can be highly dependent on context and that non-basic amino acids can function efficiently in DNA-binding. Analysis of combinations of wild-type and mutant Fos and Jun proteins indicated that Fos was dominant in dictating the DNA-binding ability of Fos-Jun heterodimers. This suggests that the lysine and arginine residues in the KCR region of Fos are not equivalent to those in Jun and that they interact with DNA differently.

Animals↗
PubMed1993

Isolation of the cyclosporin-sensitive T cell transcription factor NFATp.

Nuclear factor of activated T cells (NFAT) is a transcription factor that regulates expression of the cytokine interleukin-2 (IL-2) in activated T cells. The DNA-binding specificity of NFAT is conferred by NFATp, a phosphoprotein that is a target for the immunosuppressive compounds cyclosporin A and FK506. Here, the purification of NFATp from murine T cells and the isolation of a complementary DNA clone encoding NFATp are reported. A truncated form of NFATp, expressed as a recombinant protein in bacteria, binds specifically to the NFAT site of the murine IL-2 promoter and forms a transcriptionally active complex with recombinant protein fragment react with T cell NFATp. The molecular cloning of NFATp should allow detailed analysis of a T cell transcription factor that is central to initiation of the immune response.

Amino Acid Sequence↗
PubMed1993

The T-cell transcription factor NFATp is a substrate for calcineurin and interacts with Fos and Jun.

Transcription of lymphokine genes in activated T cells is inhibited by the immunosuppressive agents cyclosporin A and FK506, which act by blocking the phosphatase activity of calcineurin. NFAT, a DNA-binding protein required for interleukin-2 gene transcription, is a potential target for calcineurin, cyclosporin A and FK506. NFAT contains a subunit (NFATp) which is present in unstimulated T cells and which forms a complex with Fos and Jun proteins in the nucleus of activated T cells. Here we report that NFATp is a DNA-binding phosphoprotein of relative molecular mass approximately 120,000 and is a substrate for calcineurin in vitro. Purified NFATp forms DNA-protein complexes with recombinant Jun homodimers or Jun-Fos heterodimers; the DNA-binding domains of Fos and Jun are essential for the formation of the NFATp-Fos-Jun-DNA complex. The interaction between the lymphoid-specific factor NFATp and the ubiquitous transcription factors Fos and Jun provides a novel mechanism for combinatorial regulation of interleukin-2 gene transcription, which integrates the calcium-dependent and the protein-kinase C-dependent pathways of T-cell activation.

Animals↗
PubMed1993

Dimerization and DNA binding alter phosphorylation of Fos and Jun.

Fos and Jun form dimeric complexes that bind to activator protein 1 (AP-1) DNA sequences and regulate gene expression. The levels of expression and activities of these proteins are regulated by a variety of extracellular stimuli. They are thought to function in nuclear signal transduction processes in many different cell types. The role of Fos and Jun in gene transcription is complex and may be regulated in several ways including association with different dimerization partners, interactions with other transcriptional factors, effects on DNA topology, and reduction/oxidation of a conserved cysteine residue in the DNA-binding domain. In addition, phosphorylation has been suggested to control the activity of Fos and Jun. Here we show that phosphorylation of Fos and Jun by several protein kinases is affected by dimerization and binding to DNA. Jun homodimers are phosphorylated efficiently by casein kinase II, whereas Fos-Jun heterodimers are not. DNA binding also reduces phosphorylation of Jun by casein kinase II, p34cdc2 (cdc2) kinase, and protein kinase C. Phosphorylation of Fos by cAMP-dependent protein kinase and cdc2 is relatively insensitive to dimerization and DNA binding, whereas phosphorylation of Fos and Jun by DNA-dependent protein kinase is dramatically stimulated by binding to the AP-1 site. These results imply that different protein kinases can distinguish among Fos and Jun proteins in the form of monomers, homodimers, and heterodimers and between DNA-bound and non-DNA-bound proteins. Thus, potentially, these different states of Fos and Jun can be recognized and regulated independently by phosphorylation.

Animals↗
PubMed1993

Continuous c-fos expression precedes programmed cell death in vivo.

The development of a multicellular organism involves a delicate balance among the processes of proliferation, differentiation and death. Naturally occurring cell death aids tissue remodelling, eliminates supernumerary cell populations and provides structural elements such as hair and skin. In the nervous system, selective cell death contributes to the formation and organization of the spinal cord and sympathetic ganglia, retina and corpus callosum. But cell death also occurs in several neuropathological conditions, such as amyelotrophic lateral sclerosis and Alzheimer's disease. Therefore an elucidation of the mechanisms responsible for cell death is critical for an appreciation of both normal development and neuropathological disorders. Using a fos-lacZ transgenic mouse, we provide evidence showing that the continuous expression of Fos, beginning hours or days before the morphological demise of the cell, appears to be a hallmark of terminal differentiation and a harbinger of death.

3T3 Cells↗
PubMed1993

Flunarizine in essential tremor.

We studied the effects of flunarizine (Fz) in 10 patients with moderate to severe essential tremor. Tremor was evaluated after 6 weeks of treatment using patient and physician assessment as well as blinded video analysis. Only one patient had mild subjective transient improvement and three experienced worsening of tremor. No patient elected to remain on Fz. We conclude that Fz is ineffective for moderate to severe essential tremor and may actually worsen the symptoms in some patients.

Adult↗
PubMed1993

Regulation of proto-oncogene expression in adult and developing lungs.

Activation of immediate-early gene expression has been associated with mitogenesis, differentiation, nerve cell depolarization, and recently, terminal differentiation processes and programmed cell death. Previous evidence also suggested that immediate-early genes play a role in the physiology of the lungs (J. I. Morgan, D. R. Cohen, J. L. Hempstead, and T. Curran, Science 237:192-197, 1987). Therefore, we analyzed c-fos expression in adult and developing lung tissues. Seizures elicited by chemoconvulsants induced expression of mRNA for c-fos, c-jun, and junB and Fos-like immunoreactivity in lung tissue. The use of pharmacological antagonists and adrenalectomy indicated that this increased expression was neurogenic. Interestingly, by using a fos-lacZ transgenic mouse, it was shown that Fos-LacZ expression in response to seizure occurred preferentially in clusters of epithelial cells at the poles of the bronchioles. This was the same location of Fos-LacZ expression detected during early lung development. These data imply that pharmacological induction of immediate-early gene expression in adult mice recapitulates an embryological program of gene expression.

Adrenalectomy↗
PubMed1993

Fos is a preferential target of glucocorticoid receptor inhibition of AP-1 activity in vitro.

Several regulatory interactions between the AP-1 and the nuclear hormone receptor families of transcription factors have been reported. However, the molecular mechanisms that underlie these interactions remain unknown, and models derived from transient-transfection experiments are contradictory. We have investigated the effect of the purified glucocorticoid receptor (GR) DNA-binding domain (GR residues 440 to 533 [GR440-533]) on DNA binding and transcription activation by Fos-Jun heterodimers and Jun homodimers. GR440-533 differentially inhibited DNA binding and transcription activation by Fos-Jun heterodimers. Inhibition of Jun homodimers required a 10-fold-higher concentration of GR440-533. An excess of Fos monomers protected Fos-Jun heterodimers from inhibition by GR440-533. Surprisingly, regions outside the leucine zipper and basic region were required for GR inhibition of Fos and Jun DNA binding. The region of GR440-533 required for inhibition of Fos-Jun DNA binding was localized to the zinc finger DNA-binding domain. However, inhibition of Fos-Jun DNA binding was independent of DNA binding by GR440-533. GR440-533 also differentially inhibited Fos-Jun heterodimer binding to the proliferin plfG element. Differential inhibition of DNA binding by different AP-1 family complexes provides a potential mechanism for the diverse interactions between nuclear hormone receptors and AP-1 family proteins at different promoters and in different cell types.

Amino Acid Sequence↗
PubMed1993

Selective DNA bending by a variety of bZIP proteins.

We have investigated DNA bending by bZIP family proteins that can bind to the AP-1 site. DNA bending is widespread, although not universal, among members of this family. Different bZIP protein dimers induced distinct DNA bends. The DNA bend angles ranged from virtually 0 to greater than 40 degrees as measured by phasing analysis and were oriented toward both the major and the minor grooves at the center of the AP-1 site. The DNA bends induced by the various heterodimeric complexes suggested that each component of the complex induced an independent DNA bend as previously shown for Fos and Jun. The Fos-related proteins Fra1 and Fra2 bent DNA in the same orientation as Fos but induced smaller DNA bend angles. ATF2 also bent DNA toward the minor groove in heterodimers formed with Fos, Fra2, and Jun. CREB and ATF1, which favor binding to the CRE site, did not induce significant DNA bending. Zta, which is a divergent member of the bZIP family, bent DNA toward the major groove. A variety of DNA structures can therefore be induced at the AP-1 site through combinatorial interactions between different bZIP family proteins. This diversity of DNA structures may contribute to regulatory specificity among the plethora of proteins that can bind to the AP-1 site.

Activating Transcription Factors↗