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Mining the Complexities of the Estrogen Signaling Pathways for Novel Therapeutics

Duke University Medical Center Durham, North Carolina 27710

Address all correspondence and requests for reprints to: Donald McDonnell, Duke University Medical Center, Box 3813, Durham, North Carolina 27710. E-mail: Donald.McDonnell{at}duke.edu.

	Introduction

Top Introduction The Findings of HERS... A Brief Primer on... Exploitation of the Complexities... References

 
Originally identified as reproductive hormones, estrogens are now generally thought to play important roles in bone, the cardiovascular system and in the central nervous system. This expanded view of estrogen action reflects the findings of a large number of clinical studies and a huge body of empirical observational data gathered on the effects of exogenous estrogen administration on the health of menopausal women. Parallel studies reporting the distribution of estrogen receptors and others describing specific estrogenic responses in functionally related tissues have led to an appreciation of the sphere of influence of this hormone. Not surprisingly, therefore, although estrogen-containing medicines were first introduced in the late 1940s as treatments for the climacteric symptoms associated with menopause, there has since been a realization that these hormones may have additional beneficial effects in nonreproductive targets. So strong were the data in support of these adjunct activities of estrogens that long-term estrogen therapy (ET) or hormone therapy (HT) ¹ evolved to be a major intervention for the treatment and prevention of osteoporosis, heart disease, and even dementia and cognitive disorders. The suspected positive effects of ET/HT were considered to dominate any negative impact these therapies had on other systems (i.e. breast), supporting the general belief that this class of medicines has a significant positive impact on mortality and morbidity in women. Indeed, until recently it would have been difficult to argue against the beneficial effects of ET/HT in menopausal women. However, this position has changed dramatically over the past 5 yr, necessitating a reevaluation of the risks and benefits associated with HT/ET in menopausal women.

The first indication of a problem with our understanding of estrogen action in the menopausal patient emerged from the Heart and Estrogen/progestin Replacement Study (HERS), in which the impact of estrogen as a secondary prevention for cardiovascular events was assessed in a randomized placebo-controlled trial (1). Previous observational studies had shown a huge (50%) reduction in the incidence of secondary heart attacks in women who received ET (2). However, in HERS, this beneficial effect was not observed, and indeed there were strong indications that estrogens may actually cause harm in these patients. It was argued at the time that the average age of the patients in this study was older than those evaluated in previous studies and that a positive effect may have been confounded by comorbid conditions or by other drugs these patients were taking. Thus, the findings of the Women’s Health Initiative (WHI), a study conducted in healthy menopausal women, were eagerly awaited to see whether, in a larger population of women, estrogens would have a primary preventive effect on cardiovascular disease and whether other positive effects, such as antiresorbtive actions in bone, would be observed in a randomized study. The interim results of the HT arm of this study were generally consistent with HERS, raising doubt as to the beneficial effects of estrogens in the primary prevention of coronary heart disease. This large study also indicated, as expected, that the incidence of invasive breast cancer was slightly elevated in patients receiving HT. Unfortunately, the negative findings of the WHI dominated discussions on ET/HT, and the important data supporting the beneficial effects of this intervention were not adequately highlighted. Significantly, this was the first large, placebo-controlled trial to demonstrate that estrogens reduce the incidence of hip fracture. In addition, there were data demonstrating that the risk of colorectal cancer among HT users was reduced by between 30 and 40%. Given the known course of this latter disease, and the fact that the harm observed in the cardiovascular system was primarily in the first year of treatment, it is likely that with continued follow-up of the participants in this study a better appreciation of the benefits of estrogens with respect to colorectal cancer will emerge. When taken together, it is clear that the WHI has changed the field of menopausal medicine and, notwithstanding the proven positive effects of ET/HT, it is clear that the next generation of medicines, which act through the estrogen signaling pathway(s), will need to have significantly improved risk/benefit ratios if they are to be used widely by menopausal women.

	The Findings of HERS and the WHI Have Framed Several Important Research Questions and Driven the Search for New Drugs

Top Introduction The Findings of HERS... A Brief Primer on... Exploitation of the Complexities... References

 
Aside from the important clinical implications of HERS and the WHI study, there have emerged several important scientific questions, the resolution of which will lead to improved medicines. The surprising finding that HT protects against colon cancer will surely have a bearing on decisions by women about whether or not to take ET/HT. Likewise, as we begin to identify additional systems in which estrogens have either positive or negative effects, the overall understanding of who will benefit most from this therapy will become clearer. Thus, there is an urgent need to clearly map and define the target tissues of estrogens and how they respond to estrogens and antiestrogens. More understanding in this regard may help to separate specific groups of patients contraindicated for ET/HT therapy from those who are most likely to benefit. A second related direction research will take is in the application of pharmacogenetics to identify patients who have a likelihood to positively or negatively respond to ET/HT. In the era of the completed human genome, the use of genetic approaches to stratify patients in terms of likely risk and potential benefits is now beginning. Indeed, in an elegant study published last year, Herrington et al. (3) linked the occurrence of specific alleles within the human estrogen receptor (ER) gene to the magnitude of high-density lipoprotein regulation in response to estrogens. Similar associations were shown to exist with E-selectin but not C-reactive protein, two important estrogen responsive genes (4). It is anticipated that, as the molecular components of the estrogen signaling pathway(s) are identified, similar associations between genetic variations and clinical outcome will emerge. Finally, given the known and proven effects of ET/HT in humans, it is clear there is an unmet medial need for agents that manifest their activity in a process- or tissue-selective manner. A drug that lacks the negative impact of estrogens in the cardiovascular system and breast, while retaining the positive effects in other systems, would appear to be a major and urgent goal of researchers working in this area. However, in the interim, any improvements in selectivity over those drugs currently used for ET/HT will clearly have a positive impact on the treatment of conditions associated with estrogen deprivation. It is within the context of these framed questions that Harris and colleagues (5, 6) embarked on a search for ER subtype-specific agonists. In this issue of Endocrinology, they report the identification of ERB-041, a highly specific agonist of the ß-isoform of ER, and its use in defining new estrogen responsive targets (5). This work follows previous studies that have been published in collaboration with the Katzenellenbogen laboratories that describe the activities of propyl pyrazole triol (PPT), an ER-specific agonist (6). The identification of these ER subtype-specific compounds marks an important milestone in this field, enabling studies that will allow the definition of the individual roles of each of the two ER isoforms in estrogen action.

	A Brief Primer on the Molecular Pharmacology of the and ß Subtypes of the ER

Top Introduction The Findings of HERS... A Brief Primer on... Exploitation of the Complexities... References

 
A short discussion of what is known about estrogen action will help to put in context the significance of the identification of ER subtype-selective ligands. Although there is some debate as to the specifics, a coherent model of ER action is emerging that helps to explain the action of estrogens and antiestrogens in different target tissues. Estrogens manifest their actions in cells that contain a specific high-affinity nuclear receptor (7). Until recently, it was believed that a single ER existed; however, the discovery of a second ER in 1996 suggested that our previous understanding of ER action was incomplete (8). It is now known that these two receptors, ER and ERß, have distinct functions in cells (9, 10, 11, 12, 13). Both receptors possess identical DNA binding preferences and predictably, due to the high conservation in their ligand-binding domains, have overlapping ligand-binding properties (10). In the absence of ligand, these receptors reside in an inactive form within target cell nuclei. The binding of an agonist facilitates an activating conformational change that permits the receptor to form either /, /ß, or ß/ß dimers, the relative abundance of which appears to be determined solely by relative expression level (13). In established models of ER action, it was assumed that the activated ER-dimer manifests all of its activities by interacting directly with specific estrogen responsive elements, DNA sequences within target genes. However, there is an accumulating amount of information that indicates that ER-regulated gene transcription can occur through 1) direct estrogen responsive element binding, 2) indirect interaction of the receptor with transcription factors such as activator protein-1 residing on target promoters, and 3) physical interaction between the receptor and factors such as nuclear factor-B, where it functions as a ligand-dependent inhibitor of transcription in a manner that does not require DNA binding (14). With respect to its ability to activate transcription, it is now established that the agonist-activated receptor is responsible for recruiting multiprotein complexes to target gene promoters that enable transcriptional regulation by 1) modifying and remodeling chromatin structure, 2) stabilizing the preinitiation complex, and 3) facilitating recruitment of RNA PolII. These activities occur secondary to the initial recruitment of specific coactivator proteins that interact with a specific domain on agonist-activated ER and provide a platform upon which the additional factors required for ER action are assembled (15). The demonstration that there are multiple coactivators, each of which has distinct functional activities and whose relative and absolute expression level varies between cells, provides a molecular explanation as to why the same receptor does not function in an identical manner in all cells (15, 16, 17, 18). In addition to direct actions as a transcription factor, there is also a substantial body of evidence that indicates that ligand-activated ERs may directly regulate the activity of enzymes involved in cell signaling cascades, i.e. MAPK and AKT (19, 20). There is even some suggestion that a subpopulation of "nuclear ERs" may reside in the plasma membrane and or caveolae and may facilitate rapid actions of estradiol that do not involve gene transcription (20, 21). The demonstration, primarily in vitro, that ER can participate as a regulator of nongenomic events is intriguing, although the physiological significance of these alternate pathways remains to be determined. The extent to which each ER subtype can participate in each of these activities is slowly being unraveled. When all these activities are considered, it is clear that ER and ERß are not components of redundant regulatory systems but rather that each receptor has a distinct role to play in estrogen signaling.

	Exploitation of the Complexities of Estrogen Signaling for the Discovery of New Drugs

Top Introduction The Findings of HERS... A Brief Primer on... Exploitation of the Complexities... References

 
Given the diversity of the processes that are regulated by estrogens, it is likely that compounds whose estrogenic action are manifest in a cell-selective manner are likely to have clinical utility. The discovery and development of selective ER modulators (SERMs), compounds that can function as cell-selective ER agonists and antagonists, was a significant step toward selectivity. One currently marketed compound of this class, raloxifene, manifests estrogenic activity in bone and in the cardiovascular systems while opposing estrogen action in the uterus and breast (22, 23). The mechanism for this selectivity appears to rely on the fact that raloxifene induces a unique conformational change in ER structure, favoring its interaction with a specific subset of coactivators (18, 24, 25, 26, 27, 28). Fortunately, the shape that ER adopts in the presence of raloxifene enables the engagement of cofactors that enable it to manifest positive actions in bone but not in the breast or the uterus, where it functions as an antagonist. Additional drugs of this class are emerging that display unique tissue selectivity (28, 29). Although not proven directly, it appears that the differential effects of these compounds on ER structure influence specific coactivator recruitment and subsequently transcriptional activity (25). It is likely that more selective drugs of this class will be developed by designing screens for compounds that facilitate specific receptor-cofactor interactions, a goal that will be realized in the not-too-distant future.

The discovery of a second ER provided an additional drug discovery target and suggested that functional selectivity could be achieved using subtype-specific agonists and antagonists. SERMs such as raloxifene do exhibit some binding selectivity for ER over ERß, although it is unlikely at the doses used that this selectivity is clinically important (30). However, a major breakthrough in this regard was made in 1999 with the discovery of PPT, a compound that displays 400-fold binding selectivity for ER over ERß (31). These latter studies were important in that they demonstrated, despite the close similarity in the ligand-binding domain for the two ERs, that selectivity was possible. Analysis of the in vivo activities of PPT indicated that most of the reproductive, skeletal, and cardiovascular activities previously attributed to classical agonists such as estradiol could be duplicated by this selective compound (6). This finding generally supports the results observed in animals bearing genetic disruptions of either ER or ERß (9). However, the lack of consensus in the interpretation of the phenotypes in ERß-knockout mice and the lack of a specific agonist of this receptor subtype have made it difficult to define the targets of ERß. This outstanding issue in estrogen action has been addressed in the landmark study by Harris et al. (5), which details the identification and characterization of a compound (ERB-041) demonstrating 200-fold binding selectivity for ERß over ER. The selectivity observed in receptor binding studies in vitro holds also in cell-based models of ER action and, more importantly, in vivo. It is fortunate that the selectivity of ERB-041 is maintained from the human to the rodent receptors, allowing its use as a tool to study ER action in animal models while also serving possibly as a novel therapeutic agent. The comprehensive analysis performed by the investigators in this study revealed that, although most ER-containing tissues also express ERß, ERB-041 was unable to evoke an estrogenic response. At first glance, these results appear disappointing, as, although this compound does not manifest agonist activity in the breast and uterus, neither does it appear to protect against ovariectomy-induced bone loss or be effective in animal models of vasomotor instability. However, the studies did find an unexpected role of ERB-041 as an effective suppressor of the inflammatory bowel phenotype in the HLA-B27 transgenic rat model. Indeed, its antiinflammatory action in this model system is comparable to that reported previously for the glucocorticoid prednisone (Harris, H., personal communication). Similarly, in the Lewis rat model of adjuvant-induced arthritis, this ERß-selective agonist effectively reverses the inflammatory phenotype. Given that the systemic inflammatory phenotypes manifest in both of these models appear to result from autoimmune disorders, the observed positive activity of ERB-041 in these systems implicates ERß as an important regulator of immune function. It is important to note that the action of ERB-041 in the HLA-B27 transgenic rat is blocked by the pure antiestrogen, ICI-182780. Considering the results presented in this study, those of the WHI, and the findings of an early American Cancer Society observational study demonstrating that estrogens protect against colorectal cancer, it is clear that the colon is a target of estrogen action (32, 33). Whether these activities result from a direct action through ERß expressed in the enterocytes, or as a consequence of an activity at a distal target site, remains to be determined. Regardless, these data provide hard functional evidence supporting a specific role for ERß in mammalian biology and reveal a therapeutic target for estrogen that until now has not been considered. It should be readily appreciated that these new functions of estrogens, if borne out to be significant in the clinic, will also cause a reevaluation of the relative risks and benefits of currently available ET/HT regimens.

The discovery of the ER subtype-selective ligands PPT and ERB-041 provide investigators with the tools needed to dissect the biology of ER and ERß. Furthermore, it is likely that "new" estrogen biology will be discovered in studies using these compounds to isolate ER- and ERß-mediated signaling pathways, actions that may have been masked by the simultaneous activation of both receptors by classical agonists. Whereas most attention has focused on studying ER action in females, it is clear that ERß is expressed and functional in the prostate (34). The availability of ER subtype-selective agonists should provide the impetus to reevaluate the estrogen signal transduction pathway(s) in males for new therapeutic indications. Clearly, the universe of estrogen will change significantly over the next few years as a consequence of both preclinical and clinical studies with SERMs and the new subtype-selective agonists. Thus, although the results of HERS and the WHI were initially met with disappointment, their important findings have set the bar for new therapeutics. Fortunately, a path toward the discovery and development of drugs with improved therapeutic profiles is becoming clearer.

	Footnotes

 
Abbreviations: ER, Estrogen receptor; ET, estrogen therapy; HERS, Heart and Estrogen/progestin Replacement Study; HT, hormone therapy; PPT, propyl pyrazole triol; SERM, selective ER modulator; WHI, Women’s Health Initiative.

¹ HT describes regimens in which a progestin is administered in a continuous or sequential manner with an estrogen.

Received July 18, 2003.

Accepted for publication July 21, 2003.

	References

Top Introduction The Findings of HERS... A Brief Primer on... Exploitation of the Complexities... References

 

1. Hulley S, Grady D, Bush T, Furberg C, Herrington D, Riggs B, Vittinghoff E 1998 Randomized trial of estrogen plus progestin for secondary prevention of coronary heart disease in postmenopausal women. JAMA 280:605–613[Abstract/Free Full Text]
2. Sullivan JM, Zwaag RV, Hughes JP, Maddock V, Kroetz FW, Ramanathan KB 1990 Estrogen replacement and coronary artery disease. Effect on survival in postmenopausal women. Arch Intern Med 150:2557–2562[Abstract]
3. Herrington DM, Howard TD, Hawkins GA, Reboussin DM, Xu J, Zheng SL, Brosnihan KB, Meyers DA, Bleecker ER 2002 Estrogen-receptor polymorphisms and effects of estrogen replacement on high-density lipoprotein cholesterol in women with coronary disease. N Engl J Med 346:967–974[Abstract/Free Full Text]
4. Herrington DM, Howard TD, Brosnihan B, McDonnell DP, Li X, Hawkins GA, Reboussin DM, Xu J, Zheng SL, Meyers DA, Bleecker ER 2002 Common estrogen receptor polymorphism augments effects of hormone replacement therapy on E-selectin but not C-reactive protein. Circulation 105:1879–1882[Abstract/Free Full Text]
5. Harris HA, Albert LM, Leathurby Y, Malamas MS, Mewshaw RE, Miller CP, Kharode YP, Marzolf J, Komm BS, Winneker RC, Frail DE, Henderson RA, Zhu Y, JC Keith J 2003 Evaluation of an estrogen receptor-ß agonist in animal models of human disease. Endocrinology 144:4241–4249[Abstract/Free Full Text]
6. Harris HA, Katzenellenbogen JA, Katzenellenbogen BS 2002 Characterization of the biological roles of the estrogen receptors, ER and ERß, in estrogen target tissues in vivo through the use of an ER-selective ligand. Endocrinology 143:4172–4177[Abstract/Free Full Text]
7. Jensen EV, Jacobson HI 1962 Basic guides to the mechanism of estrogen action. Recent Prog Horm Res 18:387–414
8. Kuiper GGJM, Enmark E, Pelto-Huikko M, Nilsson S, Gustafsson J-A 1996 Cloning of a novel estrogen receptor expressed in rat prostate and ovary. Proc Natl Acad Sci USA 93:5925–5930[Abstract/Free Full Text]
9. Couse JF, Korach KS 1999 Estrogen receptor null mice: what have we learned and where will they lead us? Endocr Rev 20:358–417[Abstract/Free Full Text]
10. Kuiper GGJM, Carlsson B, Grandien K, Enmark E, Häggblad J, Nilsson S, Gustafsson J-A 1997 Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors and ß. Endocrinology 138:863–870[Abstract/Free Full Text]
11. Paech K, Webb P, Kuiper GGJM, Nilsson S, Gustafsson J-A, Kushner PJ, Scanlan TS 1997 Differential ligand activation of estrogen receptors ER and ERß at AP1 sites. Science 277:1508–1510[Abstract/Free Full Text]
12. Weihua Z, Saji S, Mäkinen S, Cheng G, Jensen EV, Warner M, Gustafsson JA 2000 Estrogen receptor (ER) ß, a modulator of ER in the uterus. Proc Natl Acad Sci USA 97:5936–5941[Abstract/Free Full Text]
13. Hall JM, McDonnell DP 1999 The estrogen receptor ß-isoform (ERß) of the human estrogen receptor modulates ER transcriptional activity and is a key regulator of the cellular response to estrogens and antiestrogens. Endocrinology 140:5566–5578[Abstract/Free Full Text]
14. McDonnell DP 1999 The molecular pharmacology of SERMs. Trends Endocrinol Metab 10:301–311[CrossRef][Medline]
15. McKenna NJ, O’Malley BW 2000 An issue of tissues: divining the split personalities of selective estrogen receptor modulators. Nat Med 6:960–962[CrossRef][Medline]
16. McDonnell DP, Norris JD 2002 Connections and regulation of the human estrogen receptor. Science 296:1642–1644[Abstract/Free Full Text]
17. McKenna NJ, Lanz RB, O’Malley BW 1999 Nuclear receptor coregulators: Cellular and molecular biology. Endocr Rev 20:321–344[Abstract/Free Full Text]
18. Kraichely DM, Sun J, Katzenellenbogen JA, Katzenellenbogen BS 2000 Conformational changes and coactivator recruitment by novel ligands for estrogen receptor- and estrogen receptor-ß: correlations with biological character and distinct differences among SRC coactivator family members. Endocrinology 141:3534–3545[Abstract/Free Full Text]
19. Improta-Brears T, Whorton AR, Codazzi F, York JD, Meyer T 1999 Estrogen-induced activation of mitogen-activated protein kinase requires mobilization of intracellular calcium. Proc Natl Acad Sci USA 96:4686–4691[Abstract/Free Full Text]
20. Chambliss KL, Yuhanna IS, Anderson RGW, Mendelsohn ME, Shaul PW 2002 ERß has nongenomic action in caveolae. Mol Endocrinol 16:938–946[Abstract/Free Full Text]
21. Norfleet AM, Thomas ML, Gametchu B, Watson CS 1999 Estrogen receptor- detected on the plasma membrane of aldehyde-fixed GH₃/B6/F10 rat pituitary tumor cells by enzyme-linked immunocytochemistry. Endocrinology 140:3805–3814[Abstract/Free Full Text]
22. Delmas PD, Bjarnason NH, Mitlak BH, Ravoux AC, Shah AS, Huster WJ, Draper M, Christiansen C 1997 Effects of raloxifene on bone mineral density, serum cholesterol concentrations, and uterine endometrium in postmenopausal women. N Engl J Med 337:1641–1647[Abstract/Free Full Text]
23. Ettinger B, Black DM, Mitlak BH, Knickerbocker RK, Nickelsen T, Genant HK, Christiansen C, Delmas PD, Zanchetta JR, Stakkestad J, Gluer CC, Krueger K, Cohen FJ, Eckert S, Ensrud KE, Avioli LV, Lips P, Cummings SR 1999 Reduction of vertebral risk in postmenopausal women with osteoporosis treated with raloxifene: results from a 3-year randomized clinical trial. Multiple Outcomes of Raloxifene Evaluation (MORE) Investigators. JAMA 282:637–645[Abstract/Free Full Text]
24. Clemm DL, Macy BL, Santiso-Mere D, McDonnell DP 1995 Definition of the critical cellular components which distinguish between hormone and antihormone activated progesterone receptor. J Steroid Biochem Mol Biol 53:487–495[CrossRef][Medline]
25. Paige LA, Christensen DJ, Grøn H, Norris JD, Gottlin EB, Padilla KM, Chang C-Y, Ballas LM, Hamilton PT, McDonnell DP 1999 Estrogen receptor (ER) modulators each induce distinct conformational changes in ER and ERß. Proc Natl Acad Sci USA 96:3999–4004[Abstract/Free Full Text]
26. Norris JD, Paige LA, Christensen DJ, Chang C-Y, Huacani MR, Fan D, Hamilton PT, Fowlkes DM, McDonnell DP 1999 Peptide antagonists of the human estrogen receptor. Science 285:744–746[Abstract/Free Full Text]
27. Brzozowski AM, Pike AC, Dauter Z, Hubbard RE, Bonn T, Engstrom O, Ohman L, Greene GL, Gustafsson JA, Carlquist M 1997 Molecular basis of agonism and antagonism in the oestrogen receptor. Nature 389:753–758[CrossRef][Medline]
28. Miller CP, Harris HA, Komm BS 2002 Bazedoxifene acetate. Selective estrogen receptor modulator. Treatment and prevention of osteoporosis. Drugs Future 27:117–121
29. Ke HZ, Paralkar VM, Grasser WA, Crawford DT, Qi H, Simmons HA, Pirie CM, Chidsey-Frink KL, Owen TA, Smock SL, Chen HK, Jee WS, Cameron KO, Rosati RL, Brown TA, Dasilva-Jardine P, Thompson DD 1998 Effects of CP-336, 156, a new, nonsteroidal estrogen agonist/antagonist, on bone, serum cholesterol, uterus and body composition in rat models. Endocrinology 139:2068–2076[Abstract/Free Full Text]
30. Zou A, Marschke KB, Arnold KE, Berger EM, Fitzgerald P, Mais DE, Allegretto EA 1999 Estrogen receptor b activates the human retinoic acid receptor -1 promoter in response to tamoxifen and other estrogen receptor antagonists, but not in response to estrogen. Mol Endocrinol 13:418–430[Abstract/Free Full Text]
31. Stauffer SR, Coletta CJ, Tedesco R, Nishiguchi G, Carlson K, Sun J, Katzenellenbogen BS, Katzenellenbogen JA 2000 Pyrazole ligands: structure-affinity/activity relationships and estrogen receptor--selective agonists. J Med Chem 43:4934–4947[CrossRef][Medline]
32. Rossouw JE, Anderson GL, Prentice RL, LaCroix AZ, Kooperberg C, Stefanick ML, Jackson RD, Beresford SA, Howard BV, Johnson KC, Kotchen JM, Ockene J, Writing Group for the Women’s Health Initiative Investigators 2002 Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women’s Health Initiative Randomized Controlled Trial. JAMA 288:321–333[Abstract/Free Full Text]
33. Willis DB, Calle EE, Miracle-McMahill HL, Heath CW 1996 Estrogen replacement therapy and risk of fatal breast cancer in a prospective cohort of postmenopausal women in the United States. Cancer Causes Control 7:449–457[CrossRef][Medline]
34. Weihua Z, Lathe R, Warner M, Gustafsson J-A 2002 An endocrine pathway in the prostate, ERß, AR, 5-androstane-3ß, 17ß-diol, and CYP7B1, regulates prostate growth. Proc Natl Acad Sci USA 99:13589–13594[Abstract/Free Full Text]

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