Date on Master's Thesis/Doctoral Dissertation

5-2013

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biochemistry and Molecular Biology

Committee Chair

Klinge, Carolyn Muriel

Author's Keywords

Breast cancer; Tamoxifen; COUP-TFII; Endocrine resistance; NFKB; Retinoic acid receptor B

Subject

Breast--Cancer

Abstract

Chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an orphan nuclear receptor that functions as either a transcriptional activator or repressor. COUP-TFII expression is reduced in endocrine-resistant breast cancer cells and overexpression of COUP-TFII restores the ability of antiestrogens to inhibit cell proliferation. In this study, I tested the hypothesis that the activity of COUP-TFII in maintenance of endocrine sensitivity and cell differentiation is dependent on its interacting proteins. A direct interaction was identified between COUP-TFII and the phosphoprotein nucleolin, which was found to function as a coregulator for COUP-TFIImediated transcription. COUP-TFII increased the expression of the tumor suppressor retinoic acid receptor B2 (RARB2) in a nucleolin-dependent manner. COUP-TFII and nucleolin expression were correlated in estrogen receptor a (ERa)+ invasive ductal carcinomas. COUP-TFII expression was inversely correlated with patient tumor grade. Aberrant activation of the NFKB pathway has also been implicated in endocrine resistance. COUP-TFII trans feet ion suppressed NFKB activity in endocrine-resistant breast cancer cells. COUP-TFII overexpression also reduced the expression of NFKB target genes (IL6, ICAMl, TNFAIP3, and CCL2) and subunits (NFKBl, REL, RELA, and RELB) through a mechanism involving interaction of COUP-TFII with NFK13 subunits RelB and NFK131 to inhibit NFK13 DNA-binding. COUP-TFII also reduced the ability of coactivators SRC-l, SRC-3, and CBP to enhance NFK13 activity. An inverse correlation between COUP-TFII and IL6, ICAMl, TNFAIP3, NFKB2, REL, RELA, and RELB was observed in breast tumors from tamoxifen-treated breast cancer patients. The combination of COUP-TFII overexpression, NFK13 inhibition, and tamoxifen treatment inhibited the growth of endocrine-resistant breast cancer cells. Endocrine-resistant breast cancer cells were more sensitive to treatment with an NFK13 inhibitor than endocrine-sensitive cells, reflecting their reliance on the NFK13 pathway for survival. To further explore the role of COUP-TFII-interacting proteins III endocrine sensitivity, mass spectrometry was used to identify proteins that interacted with COUPTFII specifically when breast cancer cells were treated with tamoxifen versus vehicle control. HSP27 was selected for follow-up from the proteins identified as interacting specifically with COUP-TFII in cells treated with tamoxifen. HSP27 expression was reduced in an endocrine-resistant breast cancer cell line that has undergone epithelial to mesenchymal transition, L Y2, as well as in a trastuzumab-resistant breast cancer cell line, JIMT -1. A concomitant reduction in COUP-TFII expression was also observed in these cells. Future studies will explore the role of COUP-TFII-HSP27 interaction in resistance to tamoxifen and trastuzumab. COUP-TFII may be both a useful biomarker to predict tamoxifen and/or trastuzurnab sensitivity as well as a target to restore sensitivity to resistant cells.

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