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Soldati R, Wargon V, Cerliani JP, Giulianelli S, Vanzulli SI, Gorostiaga MA, Bolado J, do Campo P, Molinolo A, Vollmer G, Lanari C. Inhibition of mammary tumor growth by estrogens: is there a specific role for estrogen receptors alpha and beta? Breast Cancer Res Treat 2010; 123:709-24. [PMID: 20012353 DOI: 10.1007/s10549-009-0659-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2009] [Accepted: 11/18/2009] [Indexed: 02/06/2023]
Abstract
To evaluate the extent to which each estrogen receptor (ER) subtype contributes to the stimulation or to the inhibition of mammary tumor growth, we evaluated the effects of specific agonists in MC4-L2 cells, which are stimulated by 17β-estradiol (E(2)), and in mammary carcinomas of the MPA mouse breast cancer model, which are inhibited by E(2). Both express ERα and ERβ. In MC4-L2 cells, 4,4',4"-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT; ERα agonist) and (4-hydroxy-phenyl)-propionitrile (DPN; ERβ agonist) stimulated cell proliferation, whereas the opposite occurred in C4-HI primary cultures. The inhibitory effect was associated with a decrease in ERα and cyclin D1 expression and an increase in progesterone receptor (PR) expression as well as in the Bax/Bcl-xl ratio. In vivo, mice carrying C4-HI or 32-2-HI tumors were treated with E(2), PPT or DPN (3 mg/kg/day) or with vehicle. PPT and DPN inhibited tumor size, as did E(2), during the first 72 h. After a few days, DPN-treated tumors started to grow again, while PPT-treated tumors remained quiescent for a longer period of time. A pronounced decrease in the mitotic index and an increase in the apoptotic index was associated with tumor regression. All treated tumors showed: (a) an increase in integrin α6 and Bax expression, (b) an increased stromal laminin redistribution, and (c) a decrease in ERα, Bcl-xl and Bcl-2 expression (P < 0.001). Apoptosis-inducing factor (Aif) expression was increased in DPN-treated tumors, while active caspase 9 was up-regulated in PPT-treated mice, demonstrating the involvement of the intrinsic apoptotic pathway in estrogen-induced regression in this model. In conclusion, our data indicate that although there may be some preferences for activation pathways by the different agonists, the stimulatory or inhibitory effects triggered by estrogens are cell-context dependent rather than ER isoform dependent.
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Affiliation(s)
- Rocío Soldati
- Laboratory of Hormonal Carcinogenesis, Institute of Experimental Biology and Medicine, National Research Council of Argentina (CONICET), 1428 Buenos Aires, Buenos Aires, Argentina
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Vanzulli S, Bolado J, Soldati R, Wargon V, Luthy I, Colombo L, Molinolo A, Lanari C. Abstract 4609: Therapeutic effects of pegylated doxorubicin liposomes in endocrine responsive and unresponsive murine mammary carcinomas. Cancer Res 2010. [DOI: 10.1158/1538-7445.am10-4609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Doxorubicin is commonly used in the treatment of several cancers, including breast and ovarian cancers. In spite of the development of modern therapeutic strategies, chemotherapy is still the treatment of choice for breast carcinomas resistant to endocrine therapy. The aim of this project was a) to evaluate the effect of doxorubicin in experimental hormone-responsive and unresponsive carcinomas, b) to evaluate if hormone resistance was associated with drug resistance and c) to test endocrine therapy in combination with doxorubicin. The tumors used were ductal metastatic mammary carcinomas expressing high levels of estrogen and progesterone receptors which show different degrees of hormone responsiveness. They have been induced in BALB/c mice by medroxyprogesterone acetate. Free doxorubicin (doxo) and commercial pegylated liposomes containing doxorubicin obtained from Schering-Plough (Cx) or Laboratorios Raffo (Dg), were used. The human ovarian carcinoma cell line SKOV-3, transplanted in nude mice was used as positive control of doxorubicin responsiveness. Eleven days after s.c. transplantation, when tumors were already palpable, mice were treated i.v. with either doxo, Cx or Dg in doses of 18 or 9mg/kg body weight once a week during 1 month. Liposome vehicle was used in controls. High doses of Cx or Dg, inhibited tumor growth, but showed evident signs of toxicity (body weight loss, cardiotoxicity, skin lesions and histopathological evaluation); doxo induced a delay in tumor growth, and more severe signs of toxicity. Interestingly, the lower dose of Cx or Dg had similar therapeutic effects than the higher dose but inducing almost no toxicity. We then selected two mifepristone and 17-β-estradiol-responsive mammary carcinomas, C4-HI and CC4-3-HI, and one variant, C4-2-HI, which is unresponsive to both and we used the same experimental design as explained above. Treatments were started 4 or 11 days after tumor transplantation. The three tumors responded similarly to the chemotherapy. Doxo showed higher side effects than the liposome forms and no differences were registered between Cx or Dg-treated animals. Mice carrying C4-HI tumors of about 50 mm2, were treated with the lower dose of Dg, plus/or the antiprogestin mifepristone (12 mg/kg/day, s.c.) or 5 mg 17-β-estradiol pellets. Combined treatments induced a better therapeutic effect than single treatments (p<0.05). We can conclude that a) no differences were observed between both liposome formulations, b) the impressive therapeutic effects observed with the lower dose of Cx or Dg used, suggests that side effect can be minimized by using lower doses, c) the MPA murine breast cancer model is appropriate for chemotherapeutic drug screening either alone or in combination with endocrine therapy.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4609.
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Affiliation(s)
| | - Julieta Bolado
- 2Inst. de Biología y Medicina Experimental, Buenos Aires, Argentina
| | - Rocío Soldati
- 2Inst. de Biología y Medicina Experimental, Buenos Aires, Argentina
| | - Victoria Wargon
- 2Inst. de Biología y Medicina Experimental, Buenos Aires, Argentina
| | - Isabel Luthy
- 2Inst. de Biología y Medicina Experimental, Buenos Aires, Argentina
| | - Lucas Colombo
- 3Instituto de Oncología Angel Roffo, Buenos Aires, Argentina
| | | | - Claudia Lanari
- 2Inst. de Biología y Medicina Experimental, Buenos Aires, Argentina
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Montero Girard G, Vanzulli SI, Cerliani JP, Bottino MC, Bolado J, Vela J, Becu-Villalobos D, Benavides F, Gutkind S, Patel V, Molinolo A, Lanari C. Association of estrogen receptor-alpha and progesterone receptor A expression with hormonal mammary carcinogenesis: role of the host microenvironment. Breast Cancer Res 2007; 9:R22. [PMID: 17341305 PMCID: PMC1868922 DOI: 10.1186/bcr1660] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2006] [Revised: 02/14/2007] [Accepted: 03/06/2007] [Indexed: 11/29/2022] Open
Abstract
Introduction Medroxyprogesterone acetate (MPA) induces estrogen receptor (ER)-positive and progesterone receptor (PR)-positive ductal invasive mammary carcinomas in BALB/c mice. We sought to reproduce this MPA cancer model in C57BL/6 mice because of their widespread use in genetic engineering. Within this experimental setting, we studied the carcinogenic effects of MPA, the morphologic changes in mammary glands that are induced by MPA and progesterone, and the levels of ER and PR expression in MPA-treated and progesterone-treated mammary glands. Finally, we evaluated whether the differences found between BALB/c and C57BL/6 mouse strains were due to intrinsic differences in epithelial cells. Methods The carcinogenic effect of MPA was evaluated in C57BL/6 mice using protocols proven to be carcinogenic in BALB/c mice. In addition, BALB/c and C57BL/6 females were treated with progesterone or MPA for 1 or 2 months, and mammary glands were excised for histologic studies and for immunohistochemical and Western blot evaluation of ER and PR. Hormone levels were determined by radioimmunoassay. Isolated mammary epithelial cells were transplanted into cleared fat pads of 21-day-old female Swiss nu/nu mice or control congenic animals. Results MPA failed to induce mammary carcinomas or significant morphologic changes in the mammary glands of C57BL/6 mice. The expression of ER-α and PR isoform A in virgin mice was surprisingly much higher in BALB/c than in C57BL/6 mammary glands, and both receptors were downregulated in progestin-treated BALB/c mice (P < 0.05). PR isoform B levels were low in virgin control mice and increased after progestin treatment in both strains. ER-β expression followed a similar trend. No differences in hormone levels were found between strains. Surprisingly, the transplantation of the epithelial mammary gland cells of both strains into the cleared fat pads of Swiss (nu/nu) mice abolished the mammary gland morphologic differences and the ER and PR differences between strains. Conclusion C57BL/6 mammary glands are resistant to MPA-induced carcinogenesis and to hormone action. MPA and progesterone have different effects on mammary glands. Low ER-α and PR-A levels in untreated mammary glands may be associated with a low-risk breast cancer profile. Although we cannot at this time rule out the participation of other, untested factors, our findings implicate the stroma as playing a crucial role in the strain-specific differential hormone receptor expression and hormone responsiveness.
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Affiliation(s)
- Guadalupe Montero Girard
- Instituto de Investigaciones Oncológicas, Academia Nacional de Medicina, 3092 Las Heras, Buenos Aires 1425, Argentina
| | - Silvia I Vanzulli
- Instituto de Investigaciones Oncológicas, Academia Nacional de Medicina, 3092 Las Heras, Buenos Aires 1425, Argentina
| | - Juan Pablo Cerliani
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, 2490 V de Obligado, Buenos Aires 1428, Argentina
| | - María Cecilia Bottino
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, 2490 V de Obligado, Buenos Aires 1428, Argentina
| | - Julieta Bolado
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, 2490 V de Obligado, Buenos Aires 1428, Argentina
| | - Jorge Vela
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, 2490 V de Obligado, Buenos Aires 1428, Argentina
| | - Damasia Becu-Villalobos
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, 2490 V de Obligado, Buenos Aires 1428, Argentina
| | - Fernando Benavides
- Department of Carcinogenesis, Science Park Research Division, The University of Texas MD Anderson Cancer Center, Park Road 1C, Science Park, Smithville, Texas 78957, USA
| | - Silvio Gutkind
- Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Rockville Pike, Bethesda, Maryland 20892, USA
| | - Vyomesh Patel
- Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Rockville Pike, Bethesda, Maryland 20892, USA
| | - Alfredo Molinolo
- Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Rockville Pike, Bethesda, Maryland 20892, USA
| | - Claudia Lanari
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, 2490 V de Obligado, Buenos Aires 1428, Argentina
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Abstract
An important requirement for physiologic homeostasis is the detoxification and removal of endogenous hormones and xenobiotic compounds with biological activity. Much of the detoxification is performed by cytochrome P-450 enzymes, many of which have broad substrate specificity and are inducible by hundreds of different compounds, including steroids. The ingestion of dietary steroids and lipids induces the same enzymes; therefore, they would appear to be integrated into a coordinated metabolic pathway. Instead of possessing hundreds of receptors, one for each inducing compound, we propose the existence of a few broad specificity, low-affinity sensing receptors that would monitor aggregate levels of inducers to trigger production of metabolizing enzymes. In support of this model, we have isolated a novel nuclear receptor, termed the steroid and xenobiotic receptor (SXR), which activates transcription in response to a diversity of natural and synthetic compounds. SXR forms a heterodimer with RXR that can bind to and induce transcription from response elements present in steroid-inducible cytochrome P-450 genes and is expressed in tissues in which these catabolic enzymes are expressed. These results strongly support the steroid sensor hypothesis and suggest that broad specificity sensing receptors may represent a novel branch of the nuclear receptor superfamily.
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Affiliation(s)
- B Blumberg
- Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
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Blumberg B, Kang H, Bolado J, Chen H, Craig AG, Moreno TA, Umesono K, Perlmann T, De Robertis EM, Evans RM. BXR, an embryonic orphan nuclear receptor activated by a novel class of endogenous benzoate metabolites. Genes Dev 1998; 12:1269-77. [PMID: 9573044 PMCID: PMC316771 DOI: 10.1101/gad.12.9.1269] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Nuclear receptors are ligand-modulated transcription factors that respond to steroids, retinoids, and thyroid hormones to control development and body physiology. Orphan nuclear receptors, which lack identified ligands, provide a unique, and largely untapped, resource to discover new principles of physiologic homeostasis. We describe the isolation and characterization of the vertebrate orphan receptor, BXR, which heterodimerizes with RXR and binds high-affinity DNA sites composed of a variant thyroid hormone response element. A bioactivity-guided screen of embryonic extracts revealed that BXR is activatable by low-molecular-weight molecules with spectral patterns distinct from known nuclear receptor ligands. Mass spectrometry and 1H NMR analysis identified alkyl esters of amino and hydroxy benzoic acids as potent, stereoselective activators. In vitro cofactor association studies, along with competable binding of radiolabeled compounds, establish these molecules as bona fide ligands. Benzoates comprise a new molecular class of nuclear receptor ligand and their activity suggests that BXR may control a previously unsuspected vertebrate signaling pathway.
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Affiliation(s)
- B Blumberg
- Gene Expression Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037, USA.
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Abstract
The vertebrate central nervous system (CNS) is induced by signals emanating from the dorsal mesoderm, or organizer, that divert the ectoderm away from an epidermal and towards a neural fate. Additional signals from the organizer pattern the neural ectoderm along the anteroposterior axis. We devised highly specific methods utilizing constitutively active or dominant negative receptors to evaluate the role of retinoids in neural patterning. Microinjection of these reagents either augments or reduces retinoid signaling in specific regions of the embryo. We show that increased receptor activity suppresses anterior neural structures while dominant negative receptors lead to anterior enhancement. Similarly, microinjection of the dominant negative receptor leads to the loss of posterior marker genes. We demonstrate that retinoid receptors comprise a critical component in neural posteriorization and are required for proper neuronal differentiation. These results support a quantitative role for retinoid signaling in regionalization of the CNS.
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Affiliation(s)
- B Blumberg
- Gene Expression Laboratory, Salk Institute, La Jolla, CA 92037, USA.
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Achkar CC, Derguini F, Blumberg B, Langston A, Levin AA, Speck J, Evans RM, Bolado J, Nakanishi K, Buck J, Gudas LJ. 4-Oxoretinol, a new natural ligand and transactivator of the retinoic acid receptors. Proc Natl Acad Sci U S A 1996; 93:4879-84. [PMID: 8643497 PMCID: PMC39373 DOI: 10.1073/pnas.93.10.4879] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
All-trans-retinoic acid (at-RA) induces cell differentiation in a wide variety of cell types, including F9 embryonic teratocarcinoma cells, and can influence axial pattern formation during embryonic development. We now identify a novel retinoid synthetic pathway in differentiating F9 cells that results in the intracellular production of 4-oxoretinol (4-oxo-ROL) from retinol (vitamin A). Approximately 10-15% of the total retinol in the culture is metabolized to 4-hydroxyretinol and 4-oxo-ROL by the at-RA-treated, differentiating F9 cells over an 18-hr period, but no detectable metabolism of all-trans-retinol to at-RA or 9-cis-retinoic acid is observed in these cells. Remarkably, we show that 4-oxo-ROL can bind and activate transcription of the retinoic acid receptors whereas all-trans-retinol shows neither activity. Low doses of 4-oxo-ROL (e.g., 10(-9) or 10(-10 M) can activate the retinoic acid receptors even though, unlike at-RA, 4-oxo-ROL does not contain an acid moiety at the carbon 15 position. 4-oxo-ROL does not bind or transcriptionally activate the retinoid X receptors. Treatment of F9 cells with 4-oxo-ROL induces differentiation without conversion to the acid and 4-oxo-ROL is active in causing axial truncation when administered to Xenopus embryos at the blastula stage. Thus, 4-oxo-ROL is a natural, biologically active retinoid that is present in differentiated F9 cells. Our data suggest that 4-oxo-ROL may be a novel signaling molecule and regulator of cell differentiation.
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Affiliation(s)
- C C Achkar
- Department of Pharmacology, Cornell University Medical College, New York, NY 10021, USA
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8
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Blumberg B, Bolado J, Derguini F, Craig AG, Moreno TA, Chakravarti D, Heyman RA, Buck J, Evans RM. Novel retinoic acid receptor ligands in Xenopus embryos. Proc Natl Acad Sci U S A 1996; 93:4873-8. [PMID: 8643496 PMCID: PMC39372 DOI: 10.1073/pnas.93.10.4873] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Retinoids are a large family of natural and synthetic compounds related to vitamin A that have pleiotropic effects on body physiology, reproduction, immunity, and embryonic development. The diverse activities of retinoids are primarily mediated by two families of nuclear retinoic acid receptors, the RARs and RXRs. Retinoic acids are thought to be the only natural ligands for these receptors and are widely assumed to be the active principle of vitamin A. However, during an unbiased, bioactivity-guided fractionation of Xenopus embryos, we were unable to detect significant levels of all-trans or 9-cis retinoic acids. Instead, we found that the major bioactive retinoid in the Xenopus egg and early embryo is 4-oxoretinaldehyde, which is capable of binding to and transactivating RARs. In addition to its inherent activity, 4-oxoretinaldehyde appears to be a metabolic precursor of two other RAR ligands, 4-oxoretinoic acid and 4-oxoretinol. The remarkable increase in activity of retinaldehyde and retinol as a consequence of 4-oxo derivatization suggests that this metabolic step could serve a critical regulatory function during embryogenesis.
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Affiliation(s)
- B Blumberg
- Gene Expression Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA
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Kakizuka A, Sebastian B, Borgmeyer U, Hermans-Borgmeyer I, Bolado J, Hunter T, Hoekstra MF, Evans RM. A mouse cdc25 homolog is differentially and developmentally expressed. Genes Dev 1992; 6:578-90. [PMID: 1313771 DOI: 10.1101/gad.6.4.578] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The timing and activation of the p34cdc2 kinase in mammals is associated with dephosphorylation of phosphotyrosine and phosphothreonine residues on the p34cdc2 kinase. For fission yeast, the timing of mitosis is regulated by cyclic accumulation of cdc25, which promotes dephosphorylation of p34cdc2 and concomitant protein kinase activation. We report the identification and characterization of a structural and functional mouse homolog, Cdc25M2, of the cdc25 phosphatase. Cdc25M2 shows high sequence identity to the previously reported human homolog cdc25Hu2. Cdc25M2 can functionally complement for a Schizosaccharomyces pombe cdc25ts mutation, and when expressed in Escherichia coli and purified, Cdc25M2 is an active phosphatase. cdc25M2 mRNA shows variation in expression in different tissues in the mouse embryo and is expressed in a developmental and cell-cycle-dependent fashion. We suggest that the expression and accumulation of the cdc25 mitotic inducer may play a critical role in the regulation of mouse development.
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Affiliation(s)
- A Kakizuka
- Gene Expression Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037
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Schüle R, Rangarajan P, Yang N, Kliewer S, Ransone LJ, Bolado J, Verma IM, Evans RM. Retinoic acid is a negative regulator of AP-1-responsive genes. Proc Natl Acad Sci U S A 1991; 88:6092-6. [PMID: 1648728 PMCID: PMC52028 DOI: 10.1073/pnas.88.14.6092] [Citation(s) in RCA: 424] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
We present evidence that retinoic acid can down-regulate transcriptional activation by the nuclear protooncogene c-jun. All three members of the retinoic acid receptor (RAR) subfamily (RAR alpha, RAR beta, and RAR gamma) can repress transcriptional induction of the human collagenase gene or a heterologous promoter that contains the collagenase promoter AP-1-binding site. In contrast, the retinoid X receptor fails to repress Jun/AP-1 activity, demonstrating a significant difference between the two regulatory systems through which retinoids exert their transcriptional control. Analysis of RAR alpha mutants in transfection studies reveals that the DNA-binding domain is important for the inhibition of Jun/AP-1 activity, even though the RAR does not bind the collagenase AP-1 site. Rather, gel-retardation assays reveal that bacterially expressed full-length RAR alpha inhibits binding of Jun protein to target DNA. These data suggest that the RAR alpha may form a nonproductive complex with c-Jun and provides a simple mechanisms by which retinoic acid may limit cell growth and possibly malignant progression.
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Affiliation(s)
- R Schüle
- Howard Hughes Medical Institute, La Jolla, CA
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Schüle R, Rangarajan P, Kliewer S, Ransone LJ, Bolado J, Yang N, Verma IM, Evans RM. Functional antagonism between oncoprotein c-Jun and the glucocorticoid receptor. Cell 1990; 62:1217-26. [PMID: 2169353 DOI: 10.1016/0092-8674(90)90397-w] [Citation(s) in RCA: 990] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We present evidence that the glucocorticoid receptor (GR) and transcription factor Jun/AP-1 can reciprocally repress one another's transcriptional activation by a novel mechanism that is independent of DNA binding. Overexpression of c-Jun prevents the glucocorticoid-induced activation of genes carrying a functional glucocorticoid response element (GRE). Conversely, GR is able to repress AP-1-mediated transcriptional activation. Mutant analysis reveals that the ligand binding and DNA binding domains of GR and the region including the leucine zipper of c-Jun are required for repression. Gel retardation analysis demonstrates that bacterially expressed c-Jun disrupts GR-GRE complexes. These data indicate that members of two distinct classes of transcription factors can oppose one another's activity through a mechanism likely involving protein-protein interactions.
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Affiliation(s)
- R Schüle
- Howard Hughes Medical Institute, Salk Institute for Biological Studies, La Jolla, California 92037
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12
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Schüle R, Umesono K, Mangelsdorf DJ, Bolado J, Pike JW, Evans RM. Jun-Fos and receptors for vitamins A and D recognize a common response element in the human osteocalcin gene. Cell 1990; 61:497-504. [PMID: 2159384 DOI: 10.1016/0092-8674(90)90531-i] [Citation(s) in RCA: 408] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We present evidence that the vitamin D response element in the human osteocalcin gene confers responsiveness to the vitamin A metabolite, retinoic acid. Retinoic acid receptor (RAR) expressed in E. coli binds to this sequence in vitro. Transfection of RAR expression vectors in cultured cells activates heterologous promoters containing this sequence in vivo. This response element contains a consensus AP-1 site TGACTCA and in vitro is bound by the Jun-Fos complex. Unexpectedly, cotransfection of Jun and Fos expression vectors suppresses basal level transcription of the osteocalcin gene and suppresses induction by both retinoic acid and vitamin D3. Additional studies delimit an 11 nucleotide segment as a minimal hormone response element containing the AP-1 site as its core. These results indicate that two distinct classes of transcription factors can recognize common regulatory sequences, a phenomenon we refer to as cross-coupling.
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Affiliation(s)
- R Schüle
- Howard Hughes Medical Institute, Salk Institute, La Jolla, California 92037
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