title: Extranuclear ERα is associated with regression of T47D PKCα-overexpressing, tamoxifen-resistant breast cancer.
abstract: BACKGROUND
  Prior to the introduction of tamoxifen, high dose estradiol was used to treat breast cancer patients with similar efficacy as tamoxifen, albeit with some undesirable side effects. There is renewed interest to utilize estradiol to treat endocrine resistant breast cancers, especially since findings from several preclinical models and clinical trials indicate that estradiol may be a rational second-line therapy in patients exhibiting resistance to tamoxifen and/or aromatase inhibitors. We and others reported that breast cancer patients bearing protein kinase C alpha (PKCα)- expressing tumors exhibit endocrine resistance and tumor aggressiveness. Our T47D:A18/PKCα preclinical model is tamoxifen-resistant, hormone-independent, yet is inhibited by 17β-estradiol (E2) in vivo. We previously reported that E2-induced T47D:A18/PKCα tumor regression requires extranuclear ERα and interaction with the extracellular matrix.
  
  
  METHODS
  T47D:A18/PKCα cells were grown in vitro using two-dimensional (2D) cell culture, three-dimensional (3D) Matrigel and in vivo by establishing xenografts in athymic mice. Immunofluoresence confocal microscopy and co-localization were applied to determine estrogen receptor alpha (ERα) subcellular localization. Co-immunoprecipitation and western blot were used to examine interaction of ERα with caveolin-1.
  
  
  RESULTS
  We report that although T47D:A18/PKCα cells are cross-resistant to raloxifene in cell culture and in Matrigel, raloxifene induces regression of tamoxifen-resistant tumors. ERα rapidly translocates to extranuclear sites during T47D:A18/PKCα tumor regression in response to both raloxifene and E2, whereas ERα is primarily localized in the nucleus in proliferating tumors. E2 treatment induced complete tumor regression whereas cessation of raloxifene treatment resulted in tumor regrowth accompanied by re-localization of ERα to the nucleus. T47D:A18/neo tumors that do not overexpress PKCα maintain ERα in the nucleus during tamoxifen-mediated regression. An association between ERα and caveolin-1 increases in tumors regressing in response to E2.
  
  
  CONCLUSIONS
  Extranuclear ERα plays a role in the regression of PKCα-overexpressing tamoxifen-resistant tumors. These studies underline the unique role of extranuclear ERα in E2- and raloxifene-induced tumor regression that may have implications for treatment of endocrine-resistant PKCα-expressing tumors encountered in the clinic.
authors: Department of Biopharmaceutical Sciences, College of Pharmacy, University of Illinois at Chicago, 833 S, Wood Street, Chicago, IL 60611, USA.
authors: Bethany
authors: B
authors: Perez White
authors: Mary Ellen
authors: ME
authors: Molloy
authors: Huiping
authors: H
authors: Zhao
authors: Yiyun
authors: Y
authors: Zhang
authors: Debra A
authors: DA
authors: Tonetti
mesh_terms: D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000008:administration & dosage / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D051242:Caveolin 1 / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D003593:Cytoplasm / Q000378:metabolism; D004195:Disease Models, Animal; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D005260:Female; D015870:Gene Expression; D006801:Humans; D051379:Mice; D011485:Protein Binding; D051571:Protein Kinase C-alpha / Q000235:genetics*; D021381:Protein Transport / Q000187:drug effects; D020849:Raloxifene Hydrochloride / Q000008:administration & dosage / Q000494:pharmacology; D013629:Tamoxifen / Q000008:administration & dosage / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D018931:Antineoplastic Agents, Hormonal; D051242:Caveolin 1; D047628:Estrogen Receptor alpha; D013629:Tamoxifen; D020849:Raloxifene Hydrochloride; D004958:Estradiol; D051571:Protein Kinase C-alpha
references: J Steroid Biochem Mol Biol. 2010 Feb 28;118(4-5):219-30
references: 19815064
references: J Histochem Cytochem. 2004 Mar;52(3):419-22
references: 14966210
references: JAMA. 2009 Aug 19;302(7):774-80
references: 19690310
references: Oncology. 2004;67(1):1-10
references: 15459489
references: J Natl Cancer Inst. 2002 Feb 20;94(4):274-83
references: 11854389
references: Am J Physiol Endocrinol Metab. 2010 Mar;298(3):E395-402
references: 19934406
references: Br J Cancer. 2003 May 6;88(9):1400-2
references: 12778068
references: Clin Cancer Res. 2012 Jan 1;18(1):118-26
references: 21980134
references: Cancer Res. 1989 Jun 15;49(12):3215-7
references: 2720675
references: Mol Endocrinol. 2002 Jan;16(1):116-27
references: 11773443
references: Clin Cancer Res. 2004 Jun 1;10(11):3621-8
references: 15173068
references: Nature. 2000 Sep 28;407(6803):538-41
references: 11029009
references: Int J Cancer. 1998 Dec 9;78(6):760-5
references: 9833770
references: Eur J Cancer. 2004 Oct;40(15):2269-73
references: 15454252
references: Cancer Res. 2007 Feb 1;67(3):1352-60
references: 17283173
references: Proc Soc Exp Biol Med. 1999 Jan;220(1):9-19
references: 9893163
references: Clin Cancer Res. 2012 Jan 1;18(1):6-8
references: 22215901
references: Oncogene. 2001 Sep 6;20(39):5420-30
references: 11571639
references: Oncogene. 2003 Sep 11;22(39):7998-8011
references: 12970748
references: Mol Cell Biol. 2003 Mar;23(5):1633-46
references: 12588983
references: Biochem Biophys Res Commun. 2004 Apr 9;316(3):878-83
references: 15033483
references: Biochem Biophys Res Commun. 1998 Jul 30;248(3):443-9
references: 9703943
references: Mol Cell Endocrinol. 2012 May 15;355(1):169-79
references: 22366173
references: Clin Cancer Res. 2001 Oct;7(10):3156-65
references: 11595710
references: Mol Cell. 2003 Mar;11(3):695-707
references: 12667452
references: Mol Endocrinol. 2003 May;17(5):818-30
references: 12554767
references: Int J Breast Cancer. 2012;2012:740353
references: 22500240
references: Endocrinology. 1986 Nov;119(5):2038-46
references: 3533520
references: Annu Rev Med. 2011;62:233-47
references: 20887199
references: J Clin Pathol. 2007 Nov;60(11):1216-21
references: 17965220
references: Breast Cancer Res Treat. 2008 Apr;108(3):351-61
references: 17592774
references: J Biol Chem. 2007 Aug 3;282(31):22278-88
references: 17535799
references: Proc Natl Acad Sci U S A. 2004 Feb 17;101(7):2076-81
references: 14764897
references: Clin Cancer Res. 2000 May;6(5):2028-36
references: 10815929
references: Trends Endocrinol Metab. 2001 May-Jun;12(4):152-6
references: 11295570
references: Oncogene. 2006 Jun 1;25(23):3286-95
references: 16407820
references: Mol Cancer. 2010 Apr 14;9:76
references: 20398285
references: Carcinogenesis. 2006 Aug;27(8):1538-46
references: 16513679
references: Br J Cancer. 2000 Sep;83(6):782-91
references: 10952784
references: EMBO J. 2001 Nov 1;20(21):6050-9
references: 11689445
references: Breast Cancer Res Treat. 2005;93 Suppl 1:S3-10
references: 16247594
references: J Biol Chem. 2001 Sep 21;276(38):35684-92
references: 11473106
references: Life Sci. 2009 May 22;84(21-22):766-71
references: 19324060
references: Cancer Res. 2010 May 15;70(10):4092-101
references: 20460518
references: Bone. 2004 Jan;34(1):100-11
references: 14751567
references: PLoS One. 2008 May 21;3(5):e2238
references: 18493596
references: Breast Cancer Res Treat. 2001 May;67(2):111-6
references: 11519859
references: Cell. 2001 Mar 9;104(5):719-30
references: 11257226
references: Cancer Chemother Pharmacol. 2005 Nov;56 Suppl 1:10-20
references: 16273359
references: Nature. 2002 Aug 8;418(6898):654-7
references: 12167865
references: J Biol Chem. 2000 Apr 28;275(17):12565-71
references: 10777546
references: EMBO J. 1996 Mar 15;15(6):1292-300
references: 8635462
references: Mol Cancer Res. 2009 Apr;7(4):498-510
references: 19372579
references: Mol Biol Cell. 2005 Jan;16(1):231-7
references: 15496458
references: Biochemistry. 1999 Oct 26;38(43):14146-56
references: 10571988