title: Cell type- and estrogen receptor-subtype specific regulation of selective estrogen receptor modulator regulatory elements.
abstract: Selective estrogen receptor modulators (SERMs), such as tamoxifen and raloxifene can act as estrogen receptor (ER) antagonists or agonists depending on the cell type. The antagonistic action of tamoxifen has been invaluable for treating breast cancer, whereas the agonist activity of SERMs also has important clinical applications as demonstrated by the use of raloxifene for osteoporosis. Whereas the mechanism whereby SERMs function as antagonists has been studied extensively very little is known about how SERMs produce agonist effects in different tissues with the two ER types; ERalpha and ERbeta. We examined the regulation of 32 SERM-responsive regions with ERalpha and ERbeta in transiently transfected MCF-7 breast, Ishikawa endometrial, HeLa cervical and WAR-5 prostate cancer cells. The regions were regulated by tamoxifen and raloxifene in some cell types, but not in all cell lines. Tamoxifen activated similar number of regions with ERalpha and ERbeta in the cell lines, whereas raloxifene activated over twice as many regions with ERbeta compared to ERalpha. In Ishikawa endometrial cancer cells, tamoxifen activated 17 regions with ERalpha, whereas raloxifene activated only 2 regions, which might explain their different effects on the endometrium. Microarray studies also found that raloxifene regulated fewer genes than tamoxifen in U2OS bone cancer cells expressing ERalpha, whereas tamoxifen was equally effective at regulating genes with ERalpha and ERbeta. Our studies indicate that tamoxifen is a non-selective agonist, whereas raloxifene is a relative ERbeta-selective agonist, and suggest that ERbeta-selective SERMs might be safer for treating clinical conditions that are dependent on the agonist property of SERMs.
authors.affiliation: Departments of Obstetrics, Gynecology and Reproductive Sciences, Cellular and Molecular Pharmacology, Center for Reproductive Sciences, University of California, San Francisco, CA 94143, USA.
authors.forename: Lonnele J
authors.initials: LJ
authors.lastname: Ball
authors.forename: Nitzan
authors.initials: N
authors.lastname: Levy
authors.forename: Xiaoyue
authors.initials: X
authors.lastname: Zhao
authors.forename: Chandi
authors.initials: C
authors.lastname: Griffin
authors.forename: Mary
authors.initials: M
authors.lastname: Tagliaferri
authors.forename: Isaac
authors.initials: I
authors.lastname: Cohen
authors.forename: William A
authors.initials: WA
authors.lastname: Ricke
authors.forename: Terence P
authors.initials: TP
authors.lastname: Speed
authors.forename: Gary L
authors.initials: GL
authors.lastname: Firestone
authors.forename: Dale C
authors.initials: DC
authors.lastname: Leitman
mesh_terms: D045744:Cell Line, Tumor; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D009928:Organ Specificity / Q000187:drug effects*; D020849:Raloxifene Hydrochloride / Q000494:pharmacology; D011960:Receptors, Estrogen / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D020845:Selective Estrogen Receptor Modulators / Q000494:pharmacology*; D013629:Tamoxifen / Q000494:pharmacology
chemical_list: D047628:Estrogen Receptor alpha; D011960:Receptors, Estrogen; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen; D020849:Raloxifene Hydrochloride; D004958:Estradiol