Minireview: Genomic Organization of the Human ER{alpha} Gene Promoter Region

Martin Kos, George Reid, Stefanie Denger and Frank Gannon

European Molecular Biology Laboratory, D-69117 Heidelberg, Germany

Address all correspondence and requests for reprints to: Dr. Martin Kos, European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117, Heidelberg, Germany. E-mail: kos{at}embl-heidelberg.de

ABSTRACT

The ER{alpha} gene has been intensively studied for more than a decade. During this long time, multiple promoters used in ER{alpha} expression have been discovered in several species. Although an already large body of literature describing various aspects of the regulation of ER{alpha} expression and utilization of different promoters is constantly growing, the inconsistent terminology used by individual authors makes the interpretation and comparison of data very difficult. Furthermore, completion of the human genome project now allows all known human ER{alpha} promoters to be placed on a physical map. This review describes promoters used in the generation of ER{alpha} transcripts in human and in other species and suggests a consistent nomenclature. The possible role of multiple promoters in the differential expression of ER{alpha} in tissues and during development is also discussed.

ESTROGENS PLAY A crucial role in sexual development and reproduction as well as in many physiological processes in various tissues. They are also known to be involved in many pathological processes such as breast and endometrial cancer (1) and osteoporosis (2). The effects of estrogens are mediated by their intracellular receptors (3, 4). To date, two nuclear ERs have been described—ER{alpha} (NR3A1) (5) and ERß (NR3A2; Refs. 6 and 7). Both belong to the superfamily of nuclear receptors and family of steroid receptors that act as ligand-inducible transcription factors (8, 9). For a detailed overview of the nuclear receptor superfamily, their structural features, and interactions with cofactors, see Refs. 10, 11, 12, 13, 14 .

The human ER{alpha} cDNA was cloned in 1986 (5, 15) and the genomic organization was described 2 yr later (16). Everything seemed to be clear—the gene consists of 8 exons spanning 140 kb of the chromosome 6q25.1 locus (17, 18). A comparison of ER{alpha} cDNA sequence from human with those of chicken (19), rat (20), and mouse (21) showed a high level of conservation between species with the exception of the 5'- end. However, evidence from the analysis of other nuclear receptor family members indicated that multiple promoters might be a common feature of steroid hormone receptors (22, 23). To date, several exons encoding 5'-untranslated regions (UTRs) of ER{alpha} mRNAs have been identified. Unfortunately, different terminology has been used by individual researchers and has resulted in confusion regarding the different promoters used in ER{alpha} expression.

The aim of this review is to describe chronologically the discoveries of all human ER{alpha} exons upstream of the translational start site, which is in exon 1 (16). Various names for each of these exons are listed and a unified nomenclature is suggested. Furthermore, the genomic organization of the promoter region of the human ER{alpha} gene is elucidated using sequences of two overlapping genomic contigs sequenced and assembled by Sanger centre. Multiple promoters and upstream exons of the human ER{alpha} gene are compared with known exons and promoters in ER{alpha} genes from other species. Finally, some possible functions of multiple promoters in regulation of ER{alpha} expression are discussed.

PROMOTER REGION OF THE HUMAN ER{alpha} GENE

In the following paragraphs we will try to clearly describe the discovery of human ER{alpha} upstream exons, and we ask readers to refer to Fig. 1Go whenever they feel confused.



View larger version (18K):
[in this window]
[in a new window]
 
Figure 1. Genomic Organization of the Promoter Region of the Human ER{alpha} Gene

In the upper part of the figure the exons and the names used for them by individual research groups are depicted in chronological order from the top. On the bottom the genomic location of multiple promoters and upstream exons described to date is shown. Two genomic contigs covering the region are outlined below. Colored boxes represent upstream exons with names according to the suggested nomenclature. Promoters are depicted as broken arrows. Numbers below exons correspond to the distance from the originally described transcription start site +1 in base pairs. Numbers between exons show the size of major introns in kilobase pairs. Broken lines symbolize observed splicing, and the common acceptor splice site in exon 1 is represented by an open triangle. *, These exons were described incorrectly as contiguous.

 
In 1991, Keaveney et al. (24) analyzed sequences of genomic clones containing 5'-flanking regions of the human ER{alpha} gene. A region with high homology to the first exon of the mouse ER{alpha} gene (21) and the 5'-end of the rat ER{alpha} cDNA (20) was found approximately 2 kb upstream of the transcription start site identified by Green et al. (5). Moreover, a potential acceptor splice site located in exon 1 of human ER{alpha} at position +163 was found to be conserved between species. It was proposed that the identified region, called at that time "exon 1'," was spliced to this acceptor splice site +163. This transcript was indeed isolated from human uterus (24). Other laboratories subsequently confirmed this finding (25, 26). Piva et al. (27) then described an ER{alpha} transcript containing the 1' exon found by Keaveney et al. but extending approximately 1.1 kb upstream. It was suggested that a putative promoter exists further upstream of the one proposed by Keaveney et al. (based by then on the homology with mouse ER{alpha} gene) and that two major transcription start sites are used to transcribe these two mRNAs (27). However, the longer mRNA variant suggested by Piva et al. (27) has not been detected in experiments designed to map the 5'-ends of various ER{alpha} mRNAs performed by others (28, 29, 30). These results indicated that the human ER{alpha} gene is transcribed from at least two promoters and the resulting transcripts differ in their 5'-UTR. The corresponding promoters were referred to originally as proximal and distal or simply as P0 or P1. This was not the end of the story. Grandien (28) screened various human cell lines and tissues and isolated from liver a new ER{alpha} mRNA variant that had a distinct 5'-UTR. This established that another promoter and 5'-exon exist in the human ER{alpha} gene. This exon is also spliced to the acceptor splice site at position +163. As this was the third exon to be identified, it was called "C" and the previously identified exons were renamed "A" and "B." However, 1 yr later three new 5'-exons were isolated from a cDNA library prepared from MCF7 cells (29). Screening of the cDNA library yielded clones with two new transcripts that varied in their 5'-end from the previously described human ER{alpha} mRNA variants. These were named by Thompson et al. (29) as "E" and "H." Sequence searches in databases that are now available show that exon E is located in the intronic region between exons 1' and 1, respectively, which had been sequenced previously (24, 25). Part of the H transcript turned out to be identical to the 3'-part of exon C described by Grandien (28), but both sequences varied in their 5'-ends. Further analysis of a genomic library revealed that the 5'-end of the H transcript is encoded by two separate exons called "Ha" and "Hb" by Thompson et al., and these were separated by an intronic sequence of more than 9 kb. Exon Hb is common to two separate transcripts that result from the splicing of exon C (the 5'-unique part) or Ha to exon Hb, which is then spliced to the splice acceptor site +163 in exon 1 of the human ER{alpha} gene (29). Only one year later another 5'-exon of the human ER{alpha} was reported (30). Using the rapid amplification of cDNA ends technique, a new exon D was cloned from MCF7 cells and localized to approximately 3.7 kb upstream of exon 1. The other previously identified mRNA variants were also isolated and their 5'-ends mapped confirming the promoter and exon structure reported previously. Authors tried to simplify the nomenclature and renamed all the 5'-upstream exons using capital letters starting from the originally identified exon as exon 1A and going upstream in alphabetical order to 1F. This order has been recently again disrupted by two new exons isolated from testis total RNA (Brand, H., M. Kos, S. Denger, G. Flouriot, F. Gannon, and G. Reid, manuscript submitted). Sequence search shows that T1 and T2 exons are separated by 101-bp intron and are located approximately 15 kb upstream of exon 1. Exon T1 can splice to exon T2 or directly to the acceptor splice site +163 (Brand et al., submitted).

In summary, the human ER{alpha} gene is transcribed from at least seven promoters into multiple transcripts that all vary in their 5'-UTRs. All upstream exons are spliced to the acceptor splice site at position +163 in coding exon 1. The scheme of the genomic organization of the human ER{alpha} promoter region with all reported alternative splicing is shown in Fig. 1Go. This was constructed using the sequence of two genomic contigs, available from the Sanger centre, that we found overlapped with each other by 100 bp. We have confirmed this overlap by PCR using primers that amplified a genomic region of 800 bp spanning the contig junction (data not shown). A similar, but less complete, genomic organization has been recently reported (31). The human ER{alpha} gene is a large genetic unit that spans approximately 300 kb of chromosome 6 [including the 140 kb containing the 8 protein coding exons (16)]. It is likely that other promoters and exons exist that are perhaps used in only a selected range of cell types or tissues and which have remained undiscovered to date. The description of the testis transcript is perhaps a foretaste of such a proliferation. Any nomenclature system will be inevitably affected by future discoveries of new upstream exons. Although we are aware that an "ideal" nomenclature is an impossible task, we would like to suggest that the nomenclature shown in Fig. 1Go is used in the future and that any new exon is named using capital letters fitting into an alphabetical order if possible, or a letter referring to the tissue to which an expression of such exon is restricted (e.g. T1 and T2 for testis). It is hoped that this will alleviate some of the existing confusion.

ER{alpha} GENE IN OTHER SPECIES

Are ER{alpha} genes of other species as complex as the human gene? Although ER{alpha} cDNA from many species is known, only the genomic structure of ER{alpha} from chicken, mouse, rat, and rainbow trout has been extensively studied. The genomic organization of the 5'-region of the ER{alpha} gene of these species compared with human is shown in Fig. 2Go.



View larger version (25K):
[in this window]
[in a new window]
 
Figure 2. Comparison of Promoter Regions of ER{alpha} Genes of Human and Other Species

All symbols are as in Fig. 1Go. Exons conserved between human and other species are depicted in the same color, and their homology to human sequence in percentages of identity is shown above each exon. Exons that don’t have a known counterpart in human are shown in light gray. Dark gray represents exons conserved between species but not known in the human. The genomic location of most exons in other species is arbitrary, as their genomic organization is not known and is indicated by question marks instead of the size of introns. The originally described transcription start sites in all species are represented by +1. The first coding exon is depicted as exon 1 (except trout).

 
Two species with relatively well characterized ER{alpha} genomic organization are the closely related rat and mouse. The first exon of the mouse corresponds to exon C of the human and is also located approximately 2 kb upstream of the second exon, which contains the translation start site. Thus, exon 2 of the mouse is equal to exon 1 of the human, etc. For simplicity we number the exons according to the human gene: exon 1 is the exon that contains the translation start site. The same applies to the rat ER{alpha} gene. At least six upstream exons (A, B, C, F1, F2, and H) exist in the ER{alpha} gene of the mouse (32) and four upstream exons (called 0 or B, 0S, 0N, and liver-specific C) in the rat (33, 34, 35). Mouse promoters and exons A and B are equivalent to human A and B; however, their expression is very low in all tissues tested so far (32). There is no functional A promoter in the rat (35). Human and mouse exon C and rat exon 0/B share a high homology. Also the sequences of the exons F of the human, F1 of the mouse, and part of exon 0S of the rat are highly conserved between these species. Although exons H of the mouse and C of the rat are more than 95% homologous and they are both expressed specifically in liver, no known counterpart to them has been identified in humans to date.

The chicken ER{alpha} gene is transcribed from at least five different promoters known as A1, A2, B, C, and D (36, 37). Exons A1 and B are homologous to exons A and B of the human ER{alpha} gene. Exon C is not homologous directly to human C but to a region of human ER{alpha} located in the intron between exons B and C. The A2 promoter is located in the region of the translational start site of the main open reading frame, and the transcribed mRNA encodes a protein variant missing 41 amino acids at the N terminus. The smaller ER{alpha} protein is predominantly expressed in liver (37).

Finally, it has been known for several years that two ER{alpha} protein isoforms exist in rainbow trout (38). However, the origin of these two isoforms has been elucidated only recently. The rainbow trout ER{alpha} gene is transcribed from two different promoters, and the resulting mRNAs encode ER{alpha} proteins of 65 kDa and 71 kDa; the latter isoform possesses an additional 45 amino acids at its N terminus (39).

We can conclude that chicken, mouse, rat, and rainbow trout ER{alpha} genes are also complex transcription units with multiple promoters and upstream exons. All upstream exons are again spliced to an acceptor splice site located in the first translated exon. This splice site is highly conserved between species, although the sequences of upstream exons are less homologous.

TISSUE-SPECIFIC PROMOTER UTILIZATION

The purpose and function of multiple promoters in the ER{alpha} gene has been questioned since the discovery of the first alternative promoter. Probably one of the most obvious implications is a potential for a tissue-specific regulation of particular promoters and thus regulation of expression of mRNA variants in tissues. Indeed, Grandien et al. (26) showed that both human ER{alpha} promoters A and C are used in MCF7 cells but only promoter A is used in ZR-75-1 cells. Another report from the same laboratory describes an increased utilization of the promoter A in comparison to decreased transcription from the promoter B in tumor-derived cell lines as opposed to normal breast and uterine tissue (40). Differential use of promoter C in normal and cancerous breast tissue was also demonstrated (41). Later, Grandien also described the liver-specific mRNA variant "E2-E1" (28) (originally called "C" by the author) showing the existence of the promoter E, which is used predominantly in liver as confirmed by others (30). However, as we have already mentioned, rat exon C and mouse exon H are exclusively expressed in the liver of rat and mouse and are highly conserved between both species (32, 35), and yet these are not homologous to the human liver-specific exon E. Several other publications show tissue- specific expression of ER{alpha} mRNA variants in the human, mouse, chicken, rat, rainbow trout, and even Japanese monkey (30, 32, 33, 34, 36, 37, 39, 42, 43, 44).

MULTIPLE PROMOTERS AND REGULATION OF ER{alpha} EXPRESSION

Several attempts to characterize promoters of ER{alpha} yielded a handful of enhancer elements and transcription factors involved in regulation of promoters in several cell lines (31, 45, 46, 47, 48, 49, 50, 51). Also auto-regulation of some ER{alpha} promoters by estrogen has been observed (36, 43, 52, 53, 54). Most ER{alpha} promoters have no TATA, CCAAT box, or GC box sequences or, if present, these do not match consensus sequences very well. Consequently, multiple transcription start sites have been identified for most upstream exons. Furthermore, ER{alpha} promoters are rather weak when compared with other promoters, e.g. human A, F, and T promoters are 100- to 1,000-fold weaker than the human glyceraldehyde-3-phosphate dehydrogenase promoter in transient transfection assays (our unpublished data). The low transcriptional activity of the ER{alpha} promoters ensures that only low levels of protein are expressed in the cell. This raises the question of why there are multiple promoters rather than one that would be tightly regulated? Several explanations are possible: 1) different tissues use different promoters and/or 2) different promoters are used in different stages of development and/or 3) transcripts produced from various promoters undergo different alternative splicing resulting in transcripts encoding various protein isoforms. We should also note that if we consider a hypothetical system with only one promoter, then the levels of various transcription activators and/or repressors need to be regulated in a tissue-specific or developmental stage-specific manner to ensure appropriate spatiotemporal expression of the target protein. This could be achieved, for example, by control of transcription by other factor and/or by regulating differential stabilities of mRNAs encoding these factors or by the various stabilities of the factors themselves. Such a system is perhaps even more complicated than the reality found in nature with multiple promoters for ER{alpha} gene. An increasing number of genes for which multiple promoters are being described might support this view. Another interesting feature of the ER{alpha} gene is its size. Large distances between promoters might be needed to allow epigenetic regulation of promoters, as gene silencing usually involves large genomic regions (for review see e.g. Ref. 55).

The tissue-specific utilization of ER{alpha} promoters has been well demonstrated as we have described. However, the relative quantification of levels of ER{alpha} mRNA variants (28, 30, 32, 36, 37) shows that some promoters are used, albeit to different extents, in all the tissues tested and perhaps, surprisingly, also in tissues for which a specific promoter had been described. We can speculate that the promoters that are active in all tissues result in basal levels of ER{alpha} mRNA and the tissue-specific promoters refine the level of ER{alpha} expression according to the requirements of the cell. This would presume that ubiquitously active promoters might share the same regulatory elements; however no data supporting or rejecting this hypothesis are available today. Perhaps a genetic approach using conditional and selective knockout technology might help to elucidate the role of individual promoters in development and differentiation.

A lack of data also accompanies the question of the developmental regulation of ER{alpha} promoters. Kato et al. (42) reported that levels of mRNA variants in rat brain change during embryonic development. However, no more data addressing the regulation of different promoters during development have been published. The recent characterization of multiple ER{alpha} variants in the mouse (32) renders this issue more amenable to investigation.

As indicated above, another possible explanation for multiple promoters is that it permits the variation of the alternative splicing of transcripts produced from different promoters. Splicing of upstream exons to the acceptor splice site in the first coding exon results in multiple transcripts encoding the same full-length protein. These mRNA variants differ only in their 5'-UTRs. It is known that regulatory elements and short open reading frames in the 5'-UTR can control the translation of mRNA (for review see Ref. 56). Most upstream exons contain short open reading frames. Our data show that these can significantly reduce translation of the mRNA (our unpublished data). ER{alpha} 5'-UTRs may further tighten the regulation of ER{alpha} expression achieved by selective promoter usage. However, it has been recently demonstrated that human exon F can be spliced directly to the second coding exon in approximately 10% of transcripts from F promoter in MCF7 cells. The resulting mRNA encodes an ER{alpha} protein variant that lacks the N-terminal domain containing the trans-activation function 1 (AF-1). This protein isoform was detected in MCF7 cells (57). The same transcript is also present in human osteoblasts; however, in this case it is expressed to the same level as the full-length ER{alpha} protein (58). The different relative levels of the F-exon1 and F-exon2 transcripts indicate that this alternative splicing might be regulated in a tissue-specific manner. It is thus possible that utilization of some promoters can lead to the alternative splicing of upstream exons to different coding exons downstream of translational start sites and thereby lead to the expression of ER{alpha} protein variants lacking various amounts of the N terminus. We have also observed that most upstream exons in mouse ER{alpha} can be spliced to the second or even third coding exon, but the putative shorter protein isoforms encoded by these transcripts have not been detected (our unpublished data). Also, many alternatively spliced mRNA transcripts with a deletion of one or more coding exons or truncation in the coding region have been observed, especially in breast cancer tissue (for review see Refs. 59 and 60). However, a correlation between the particular promoter usage and splicing pattern has not been clearly demonstrated (61). Further investigation addressing the question of possible tissue-specific regulation of this alternative splicing and its consequences on a protein level is necessary.

We have shown in this review that ER{alpha} is a large and complex transcription unit. Although a significant amount of data on the function and regulation of ER{alpha} in various species has been generated, many questions, especially regarding the function of multiple promoters, remain unanswered. We hope that this review will help to stimulate new thoughts and ideas to clarify these issues.

Sources of used sequences are listed in Table 1Go.


View this table:
[in this window]
[in a new window]
 
Table 1. Accession Numbers of Sequences Used in This Publication

 

ACKNOWLEDGMENTS

We would like to thank members of our laboratory for helpful comments and discussions.

FOOTNOTES

This work was partially supported by European Community Grant QLK6-1999-02108.

Abbreviations: UTR, Untranslated region.

Received for publication July 9, 2001. Accepted for publication August 3, 2001.

REFERENCES

  1. Henderson BE, Ross R, Bernstein L 1988 Estrogen as a cause of human cancer: The Richard and Linda Rosenthal Foundation Award Lecture. Cancer Res 48:246–253[Medline]
  2. Horowitz MC 1993 Cytokines and estrogen in bone: anti-osteoporotic effects. Science 260:626–627[Medline]
  3. Jensen EV, Jacobson HI 1962 Basic guides to the mechanism of estrogen action. Recent Prog Horm Res 18:387–414
  4. Jensen EV, DeSombre ER 1972 Mechanism of action of the female sex hormones. Annu Rev Biochem 41:203–230[CrossRef][Medline]
  5. Green S, Walter P, Kumar V, Krust A, Bornert JM, Argos P, Chambon P 1986 Human estrogen receptor cDNA: sequence, expression and homology to v-erbA. Nature 320:134–139[Medline]
  6. Nuclear Receptors Nomenclature Committee 1999 A unified nomenclature system for the nuclear receptor superfamily. Cell 97:161–163[Medline]
  7. Kuiper GG, Enmark E, Pelto-Huikko M, Nilsson S, Gustafsson JA 1996 Cloning of a novel receptor expressed in rat prostate and ovary. Proc Natl Acad Sci USA 93:5925–5930[Abstract/Free Full Text]
  8. Evans RM 1988 The steroid and thyroid hormone receptor superfamily. Science 240:889–895[Medline]
  9. Beato M 1989 Gene regulation by steroid hormones. Cell 56:335–344[Medline]
  10. Mangelsdorf DJ, Thummel C, Beato M, Herrlich P, Schütz G, Umesono K, Blumberg B, Kastner P, Mark M, Chambon P, Evans RM 1995 The nuclear receptor superfamily: the second decade. Cell 83:835–839[Medline]
  11. Beato M, Herrlich P, Schütz G 1995 Steroid hormone receptors: many actors in search of a plot. Cell 83:851–857[Medline]
  12. Bourguet W, Germain P, Gronemeyer H 2000 Nuclear receptor ligand-binding domains: three-dimensional structures, molecular interactions and pharmacological implications. Trends Pharmacol Sci 21:381–388[CrossRef][Medline]
  13. Glass CK, Rosenfeld MG 2000 The coregulator exchange in transcriptional functions of nuclear receptors. Genes Dev 14:121–141[Free Full Text]
  14. Aranda A, Pascual A 2001 Nuclear hormone receptors and gene expression. Physiol Rev 81:1269–1304[Abstract/Free Full Text]
  15. Greene GL, Gilna P, Waterfield M, Baker A, Hort Y, Shine J 1986 Sequence and expression of human estrogen receptor complementary DNA. Science 231:1150–1154[Medline]
  16. Ponglikitmongkol M, Green S, Chambon P 1988 Genomic organization of the human oestrogen receptor gene. EMBO J 7:3385–3388[Abstract]
  17. Walter P, Green S, Greene G, Krust A, Bornert JM, Jeltsch JM, Staub A, Jensen E, Scrace G, Waterfield M, 1985 Cloning of the human estrogen receptor cDNA. Proc Natl Acad Sci USA 82:7889–7893[Abstract]
  18. Gosden JR, Middleton PG, Rout D 1986 Localization of the human oestrogen receptor gene to chromosome 6q24–q27 by in situ hybridization. Cytogenet Cell Genet 43:218–220[Medline]
  19. Krust A, Green S, Argos P, Kumar V, Walter P, Bornert JM, Chambon P 1986 The chicken oestrogen receptor sequence: homology with v-erbA and the human oestrogen and glucocorticoid receptors. EMBO J 5:891–897[Abstract]
  20. Koike S, Sakai M, Muramatsu M 1987 Molecular cloning and characterization of rat estrogen receptor cDNA. Nucleic Acids Res 15:2499–2513[Abstract]
  21. White R, Lees JA, Needham M, Ham J, Parker MG 1987 Structural organization and expression of the mouse estrogen receptor. Mol Endocrinol 1:735–744[Abstract]
  22. Hodin RA, Lazar MA, Wintman BI, Darling DS, Koenig RJ, Larsen PR, Moore DD, Chin WW 1989 Identification of a thyroid hormone receptor that is pituitary-specific. Science 244:76–79[Medline]
  23. Kastner P, Krust A, Turcotte B, Stropp U, Tora L, Gronemeyer H, Chambon P 1990 Two distinct estrogen-regulated promoters generate transcripts encoding the two functionally different human progesterone receptor forms A and B. EMBO J 9:1603–1614[Abstract]
  24. Keaveney M, Klug J, Dawson MT, Nestor PV, Neilan JG, Forde RC, Gannon F 1991 Evidence for a previously unidentified upstream exon in the human oestrogen receptor gene. J Mol Endocrinol 6:111–115[Abstract]
  25. Piva R, Gambari R, Zorzato F, Kumar L, del Senno L 1992 Analysis of upstream sequences of the human estrogen receptor gene. Biochem Biophys Res Commun 183:996–1002[Medline]
  26. Grandien KF, Berkenstam A, Nilsson S, Gustafsson JA 1993 Localization of DNase I hypersensitive sites in the human oestrogen receptor gene correlates with the transcriptional activity of two differentially used promoters. J Mol Endocrinol 10:269–277[Abstract]
  27. Piva R, Bianchi N, Aguiari GL, Gambari R, del Senno L 1993 Sequencing of an RNA transcript of the human estrogen receptor gene: evidence for a new transcriptional event. J Steroid Biochem Mol Biol 46:531–538[CrossRef][Medline]
  28. Grandien K 1996 Determination of transcription start sites in the human estrogen receptor gene and identification of a novel, tissue-specific, estrogen receptor-mRNA isoform. Mol Cell Endocrinol 116:207–212[CrossRef][Medline]
  29. Thompson DA, McPherson LA, Carmeci C, deConinck EC, Weigel RJ 1997 Identification of two estrogen receptor transcripts with novel 5' exons isolated from a MCF7 cDNA library. J Steroid Biochem Mol Biol 62:143–153[CrossRef][Medline]
  30. Flouriot G, Griffin C, Kenealy M-R, Sonntag-Buck V, Gannon F 1998 Differentially expressed messenger RNA isoforms of the human estrogen receptor-{alpha} gene are generated by alternative splicing and promoter usage. Mol Endocrinol 12:1939–1954[Abstract/Free Full Text]
  31. Schuur ER, McPherson LA, Yang GP, Weigel RJ 2001 Genomic structure of the promoters of the human estrogen receptor-{alpha} gene demonstrate changes in chromatin structure induced by AP2 {gamma}. J Biol Chem 276:15519–15526[Abstract/Free Full Text]
  32. Kos M, O’Brien S, Flouriot G, Gannon F 2000 Tissue-specific expression of multiple mRNA variants of the mouse estrogen receptor {alpha} gene. FEBS Lett 477:15–20[CrossRef][Medline]
  33. Hirata S, Koh H, Yamada-Mouri N, Hoshi K, Kato J 1996 The untranslated exon "exon 0S" of the rat estrogen receptor (ER) gene. FEBS Lett 394:371–373[CrossRef][Medline]
  34. Hirata S, Koh H, Yamada-Mouri N, Kato J 1996 The novel untranslated first "exon 0N" of the rat estrogen receptor gene. Biochem Biophys Res Commun 225:849–854[CrossRef][Medline]
  35. Freyschuss B, Grandien K 1996 The 5' flank of the rat estrogen receptor gene: structural characterization and evidence for tissue- and species-specific promoter utilization. J Mol Endocrinol 17:197–206[Abstract]
  36. Griffin C, Flouriot G, Sonntag-Buck V, Nestor PV, Gannon F 1998 Identification of novel chicken estrogen receptor-{alpha} messenger ribonucleic acid isoforms generated by alternative splicing and promoter usage. Endocrinology 139:4614–4625[Abstract/Free Full Text]
  37. Griffin C, Flouriot G, Sonntag-Buck V, Gannon F 1999 Two functionally different protein isoforms are produced from the chicken estrogen receptor-{alpha} gene. Mol Endocrinol 13:1571–1587[Abstract/Free Full Text]
  38. Pakdel F, Petit F, Anglade I, Kah O, Delaunay F, Bailhache T, Valotaire Y 1994 Overexpression of rainbow trout estrogen receptor domains in Escherichia coli: characterization and utilization in the production of antibodies for immunoblotting and immunocytochemistry. Mol Cell Endocrinol 104:81–93[CrossRef][Medline]
  39. Pakdel F, Metivier R, Flouriot G, Valotaire Y 2000 Two estrogen receptor (ER) isoforms with different estrogen dependencies are generated from the trout ER gene. Endocrinology 141:571–580[Abstract/Free Full Text]
  40. Grandien K, Backdahl M, Ljunggren O, Gustafsson JA, Berkenstam A 1995 Estrogen target tissue determines alternative promoter utilization of the human estrogen receptor gene in osteoblasts and tumor cell lines. Endocrinology 136:2223–2229[Abstract]
  41. Weigel RJ, Crooks DL, Iglehart JD, deConinck EC 1995 Quantitative analysis of the transcritional start sites of estrogen receptor in breast carcinoma. Cell Growth Differ 6:707–711[Abstract]
  42. Kato J, Hirata S, Koh T, Yamada-Mouri N, Hoshi K, Okinaga S 1998 The multiple untranslated first exons and promoters system of the oestrogen receptor gene in the brain and peripheral tissues of the rat and monkey and the developing rat cerebral cortex. J Steroid Biochem Mol Biol 65:281–293[CrossRef][Medline]
  43. Donaghue C, Westley BR, May FE 1999 Selective promoter usage of the human estrogen receptor-{alpha} gene and its regulation by estrogen. Mol Endocrinol 13:1934–1950[Abstract/Free Full Text]
  44. Osterlund MK, Grandien K, Keller E, Hurd YL 2000 The human brain has distinct regional expression patterns of estrogen receptor {alpha} mRNA isoforms derived from alternative promoters. J Neurochem 75:1390–1397[CrossRef][Medline]
  45. deConinck EC, McPherson LA, Weigel RJ 1995 Transcriptional regulation of estrogen receptor in breast carcinomas. Mol Cell Biol 15:2191–2196[Abstract]
  46. McPherson LA, Baichwal VR, Weigel RJ 1997 Identification of ERF-1 as a member of the AP2 transcription factor family. Proc Natl Acad Sci USA 94:4342–4347[Abstract/Free Full Text]
  47. Tang Z, Treilleux I, Brown M 1997 A transcriptional enhancer required for the differential expression of the human estrogen receptor in breast cancers. Mol Cell Biol 17:1274–1280[Abstract]
  48. Cohn CS, Sullivan JA, Kiefer T, Hill SM 1999 Identification of an enhancer element in the estrogen receptor upstream region: implications for regulation of ER transcription in breast cancer. Mol Cell Endocrinol 158:25–36[CrossRef][Medline]
  49. McPherson LA, Weigel RJ 1999 AP2{alpha} and AP2{gamma}: a comparison of binding site specificity and trans-activation of the estrogen receptor promoter and single site promoter constructs. Nucleic Acids Res 27:4040–4049[Abstract/Free Full Text]
  50. Tanimoto K, Eguchi H, Yoshida T, Hajiro-Nakanishi K, Hayashi S 1999 Regulation of estrogen receptor {alpha} gene mediated by promoter B responsible for its enhanced expression in human breast cancer. Nucleic Acids Res 27:903–909[Abstract/Free Full Text]
  51. Penolazzi L, Lambertini E, Aguiari G, del Senno L, Piva R 2000 Cis element "decoy" against the upstream promoter of the human estrogen receptor gene. Biochim Biophys Acta 1492:560–567[Medline]
  52. Castles CG, Oesterreich S, Hansen R, Fuqua SAW 1997 Auto-regulation of the estrogen receptor promoter. J Steroid Biochem Mol Biol 62:155–163[CrossRef][Medline]
  53. Pakdel F, Le Guellec C, Vaillant C, Le Roux MG, Valotaire Y 1989 Identification and estrogen induction of two estrogen receptors (ER) messenger ribonucleic acids in the rainbow trout liver: sequence homology with other ERs. Mol Endocrinol 3:44–51[Abstract]
  54. Treilleux I, Peloux N, Brown M, Sergeant A 1997 Human estrogen receptor (ER) gene promoter-P1: estradiol independent activity and estradiol inducibility in ER+ and ER- cells. Mol Endocrinol 11:1319–1331[Abstract/Free Full Text]
  55. Wolffe AP, Matzke MA 1999 Epigenetics: regulation through repression. Science 286:481–486[Abstract/Free Full Text]
  56. Gray NK, Wickens M 1998 Control of translation initiation in animals. Annu Rev Cell Dev Biol 14:399–458[CrossRef][Medline]
  57. Flouriot G, Brand H, Denger S, Metivier R, Kos M, Reid G, Sonntag-Buck V, Gannon F 2000 Identification of a new isoform of the human estrogen receptor-{alpha} (hER-{alpha}) that is encoded by distinct transcripts and that is able to repress hER-{alpha} activation function 1. EMBO J 19:4688–4700[Abstract/Free Full Text]
  58. Denger S, Reid G, Kos M, Flouriot G, Parsch D, Brand H, Korach KS, Sonntag-Buck V, Gannon F 2001 ER{alpha} gene expression in human primary osteoblasts: evidence for the expression of two receptor proteins. Mol Endocrinol 15:2064–2077[Abstract/Free Full Text]
  59. Pfeffer U 1996 Estrogen receptor mRNA variants. Do they have a physiological role? Ann NY Acad Sci 784:304–312[Medline]
  60. Zhang QX, Hilsenbeck SG, Fuqua SA, Borg A 1996 Multiple splicing variants of the estrogen receptor are present in individual human breast tumors. J Steroid Biochem Mol Biol 59:251–260[CrossRef][Medline]
  61. Fasco MJ 1998 Estrogen receptor mRNA splice variants produced from the distal and proximal promoter transcripts. Mol Cell Endocrinol 138:51–59[CrossRef][Medline]