| 1. |
- Bohm, S., et al.
(författare)
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Cooperating nonconsensus cAMP-responsive elements are mediators of adrenocorticotropin-induced VL30 transcription in steroidogenic adrenal cells
- 1993
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Ingår i: Journal of Biological Chemistry. - : American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 268:6, s. 3952-3963
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Tidskriftsartikel (refereegranskat)abstract
- Pituitary-derived trophic hormones regulate cell-type-specific expression of VL30 retrotransposons in tissues that are engaged in steroidogenesis. We show that adrenocorticotropic hormone and forskolin induced VL30 transcription in the steroidogenic adrenal cell line Y1 and that the transcriptional activation was cell type- and protein kinase A-dependent. Three novel cAMP-responsive elements (CREs), within the VL30 long terminal repeat, were identified and shown to activate transcription synergistically when templates bearing multiple sites were compared with templates bearing a single site. This type of regulation was evident only in forskolin-treated cells, and the response elements were found to be inactive as mediators of constitutive transcription. In vitro binding analyses indicated that a consensus CRE and the nonconsensus VL30 CREs differ with respect to binding affinity and specificity to a number of nuclear factors that were identified to be related to proteins within the CREB, Jun, and C/EBP families of transcription factors. The relatively low affinity and/or a restricted binding specificity of the VL30 CREs made it possible to detect forskolin-induced binding of CREB- and Jun-related proteins to these sequences. We suggest that cAMP-induced transcription, specific for steroidogenic cells, can be mediated by a novel type of nonconsensus CREs and that the mechanism for this type of gene regulation is distinct from that mediated through a consensus CRE. We also report the identification of a novel factor, distinct from previously characterized CRE-binding proteins, that constitutively binds to the identified CREs.
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| 2. |
- Castellazzi, M., et al.
(författare)
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Overexpression of c-jun, junB, or junD affects cell growth differently
- 1991
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 88:20, s. 8890-8894
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Tidskriftsartikel (refereegranskat)abstract
- The coding sequences of murine c-jun, junB, or junD, which code for proteins with practically identical dimerization and DNA binding properties, were introduced into a nondefective retroviral vector, and the phenotype of primary avian fibroblasts chronically infected with each of these viruses was studied. Cells expressing c-jun grew in low-serum medium and developed into colonies in agar, two properties characteristic of in vitro transformation. Cells expressing junB grew in agar, with a reduced efficiency as compared to c-jun, but did not grow in low-serum medium. Finally, no effect of junD expression on cell growth was observed. These different phenotypes suggest that these three closely related transcription factors play distinct roles during normal cell growth. Analysis of c-jun deletion mutants and of c-jun/junB and c-jun/junD chimeric genes showed that the N-terminal portion (amino acids 2-168) of the c-Jun protein that is involved in transcriptional activation is required for efficient transformation. On the contrary, cells expressing a truncated mouse c-Jun lacking this N-terminal domain grew slower than normal embryo fibroblasts. The reduced growth rate may be related to the finding that expression of the intact or the truncated mouse c-jun repressed the endogenous avian c-Jun homologue, suggesting that functional c-Jun product is required for normal cell growth.
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| 3. |
- Chen, J., et al.
(författare)
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Generation of normal T and B lymphocytes by c-jun deficient embryonic stem cells
- 1994
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Ingår i: Immunity. - : Cell Press. - 1074-7613 .- 1097-4180. ; 1:1, s. 65-72
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Tidskriftsartikel (refereegranskat)abstract
- To determine the potential roles of c-jun in lymphocyte development, we generated somatic chimeric mice by injecting homozygous c-jun mutant embryonic stem (ES) cells into blastocysts from recombination activating gene-2 (RAG-2)-deficient mice. Chimeric mice had poor restoration of thymocytes, but contained substantial numbers of mature T and B lymphocytes in the periphery. Stimulation of c-jun-/- B cells resulted in normal levels of proliferation and immunoglobulin secretion. Likewise, stimulation of c-jun-/- T cells resulted in essentially normal levels of IL-2R alpha expression, IL-2 secretion, and proliferation. We further showed that the relatively normal activation responses of the c-jun-/- T cells probably results from the fact that other members of the Jun family contribute to the bulk of the activator protein-1 (AP-1) complexes in normal T cells and, as a result, AP-1 complexes are found at relatively normal levels in c-jun-/- T cells.
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| 4. |
- Doucas, V., et al.
(författare)
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Unregulated expression of c-Jun or c-Fos proteins but not Jun D inhibits oestrogen receptor activity in human breast cancer derived cells
- 1991
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Ingår i: EMBO Journal. - : Wiley-Blackwell. - 0261-4189 .- 1460-2075. ; 10:8, s. 2237-2245
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Tidskriftsartikel (refereegranskat)abstract
- We present evidence that oestrogen receptor activity in human MCF-7 breast cancer cells is reduced by over-expression of c-Jun or c-Fos proteins and to a lesser extent by Jun B overexpression. In contrast, overexpression of Jun D protein does not affect the activity of the oestrogen receptor. A region of c-Jun found to be required for repression of oestrogen receptor activity is located outside the DNA binding domain and is not conserved among the three Jun proteins. Finally, we suggest that c-Jun and c-Fos act independently to inactivate the oestrogen receptor.
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| 5. |
- Pfarr, C. M., et al.
(författare)
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Mouse JunD negatively regulates fibroblast growth and antagonizes transformation by ras
- 1994
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Ingår i: Cell. - : Cell Press. - 0092-8674 .- 1097-4172. ; 76:4, s. 747-760
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Tidskriftsartikel (refereegranskat)abstract
- As NIH 3T3 fibroblasts become quiescent, the level of c-Jun protein decreases while JunD accumulates. When resting cells are stimulated with fresh serum, nuclear-localized JunD is rapidly degraded, followed by resynthesis of both c-Jun and JunD later in G1. Overexpression of JunD results in slower growth and an increase in the percentage of cells in G0/G1 while c-Jun overexpression produces larger S/G2 and M phase populations. In addition, JunD partially suppresses transformation by an activated ras gene whereas c-Jun cooperates with ras to transform cells. These data indicate that two closely related transcription factors can function in an opposing manner.
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| 6. |
- Spyrou, Giannis, et al.
(författare)
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Characterization of the flavin reductase gene (fre) of Escherichia coli and construction of a plasmid for overproduction of the enzyme
- 1991
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Ingår i: Journal of Bacteriology. - : American Society for Microbiology. - 0021-9193 .- 1098-5530. ; 173:12, s. 3673-3679
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Tidskriftsartikel (refereegranskat)abstract
- The enzyme NAD(P)H:flavin oxidoreductase (flavin reductase) catalyzes the reduction of soluble flavins by reduced pyridine nucleotides. In Escherichia coli it is part of a multienzyme system that reduces the Fe(III) center of ribonucleotide reductase to Fe(II) and thereby sets the stage for the generation by dioxygen of a free tyrosyl radical required for enzyme activity. Similar enzymes are known in other organisms and may more generally be involved in iron metabolism. We have now isolated the gene for the E. coli flavin reductase from a lambda gt11 library. After DNA sequencing we found an open reading frame coding for a polypeptide of 233 amino acids, with a molecular weight of 26,212 and with an N-terminal segment identical to that determined by direct Edman degradation. The coding sequence is preceded by a weak ribosome binding site centered 8 nucleotides from the start codon and by a promoterlike sequence centered at a distance of 83 nucleotides. In a Kohara library the gene hybridized to position 3680 on the physical map of E. coli. A bacterial strain that overproduced the enzyme approximately 100-fold was constructed. The translated amino acid sequence contained a potential pyridine nucleotide-binding site and showed 25% identity with the C-terminal part of one subunit (protein C) of methane monooxygenase from methanotropic bacteria that reduces the iron center of a second subunit (protein A) of the oxygenase by pyridine nucleotides.
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| 7. |
- Thierry, F., et al.
(författare)
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Two AP1 sites binding JunB are essential for human papillomavirus type 18 transcription in keratinocytes
- 1992
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Ingår i: Journal of Virology. - : American Society for Microbiology. - 0022-538X .- 1098-5514. ; 66:6, s. 3740-3748
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Tidskriftsartikel (refereegranskat)abstract
- The activity and epithelial tropism of the human papillomavirus type 18 P105 early promoter, which directs the synthesis of the E6 and E7 transforming genes, are controlled by cis elements included in the viral long control region. To identify potential cellular regulators of this promoter, we mutagenized one or both of the 5'-TGACTAA-3' cis elements capable of interacting with the AP1 transcription factor, which is composed either of homodimers or heterodimers of the Jun products or of heterodimers of Jun and Fos. Mutation of both elements completely abolished P105 promoter activity in human keratinocytes. We show that either AP1 site can interact efficiently in vitro with any of the three different Jun products as heterodimers with c-Fos. However, in nuclear extracts prepared from human keratinocytes, JunB was the predominant Jun component bound to the DNA probe containing this cis element. These results implicate JunB as an important factor in human papillomavirus type 18 transcription in keratinocytes and strongly suggest a potential role of this Jun gene product in the tissue-specific transcription of the genital papillomaviruses.
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