University of Louisville

The Role of COUP-TF in Tamoxifen Resistant Breast Cancer Proliferation

Institution

University of Louisville

Abstract

Lifetime exposure to estrogens is an established risk factor for developing breast cancer. Estradiol (E2) binds to estrogen receptors alpha and beta (ERalpha and ERbeta) in the cell nucleus. ER then binds to regions of DNA called Estrogen Response Elements (EREs) to increase the expression of genes that stimulate tumor growth. Drugs called antiestrogens, i.e., Tamoxifen (TAM), compete with E2 for binding ER and prevent tumor recurrence. Unfortunately, breast cancer cells become resistant to TAM. The nuclear receptor COUPTF (Chicken Ovalbumin Upstream Promoter Transcription-Factor) interacts with TAMoccupied ERalpha and inhibits its activity. My hypothesis is the loss of COUP-TF expression plays a role in breast cancer progression and TAM-resistance. TAM-resistant LCC2 cells grew in charcoal-stripped serum whereas the parental TAM-sensitive MCF-7 cells failed to grow under the same conditions. These results indicate that the cell lines used in this study are good models of TAM-resistant tumor growth. The expression of COUP-TFI and COUP-TFII as well as the cell signaling proteins ERK1/ERK2 (MAPK) was determined in TAM-sensitive and -resistant human breast cancer cell lines. RNA was isolated and purified for use in real-time RT-PCR to examine COUP-TFI and COUP-TFII expression. Western Blots showed that TAM-resistant cell lines showed elevated basal MAPK activity. E2-induced MAPK activation in TAM-sensitive MCF-7 cells and was inhibited by the antiestrogen ICI 182,780 demonstrating that the non-genomic E2 activity is mediated by ER. Understanding the role of COUP-TF may lead to more effective antiestrogen and gene therapies to prevent and treat breast cancer.

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The Role of COUP-TF in Tamoxifen Resistant Breast Cancer Proliferation

Lifetime exposure to estrogens is an established risk factor for developing breast cancer. Estradiol (E2) binds to estrogen receptors alpha and beta (ERalpha and ERbeta) in the cell nucleus. ER then binds to regions of DNA called Estrogen Response Elements (EREs) to increase the expression of genes that stimulate tumor growth. Drugs called antiestrogens, i.e., Tamoxifen (TAM), compete with E2 for binding ER and prevent tumor recurrence. Unfortunately, breast cancer cells become resistant to TAM. The nuclear receptor COUPTF (Chicken Ovalbumin Upstream Promoter Transcription-Factor) interacts with TAMoccupied ERalpha and inhibits its activity. My hypothesis is the loss of COUP-TF expression plays a role in breast cancer progression and TAM-resistance. TAM-resistant LCC2 cells grew in charcoal-stripped serum whereas the parental TAM-sensitive MCF-7 cells failed to grow under the same conditions. These results indicate that the cell lines used in this study are good models of TAM-resistant tumor growth. The expression of COUP-TFI and COUP-TFII as well as the cell signaling proteins ERK1/ERK2 (MAPK) was determined in TAM-sensitive and -resistant human breast cancer cell lines. RNA was isolated and purified for use in real-time RT-PCR to examine COUP-TFI and COUP-TFII expression. Western Blots showed that TAM-resistant cell lines showed elevated basal MAPK activity. E2-induced MAPK activation in TAM-sensitive MCF-7 cells and was inhibited by the antiestrogen ICI 182,780 demonstrating that the non-genomic E2 activity is mediated by ER. Understanding the role of COUP-TF may lead to more effective antiestrogen and gene therapies to prevent and treat breast cancer.