Regulation of Estrogen Response by Corepressors
Abstracts
Initial Award Abstract |
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The development and function of the normal breast is under the regulation of an interacting series of hormones and growth factors. Estrogens play particularly important roles in the growth and differentiation (maturation) of the normal breast by binding to estrogen receptors, which operate primarily as hormone-regulated transcription factors. The ability of estrogen receptors to turn on or off different target genes depends on the interaction of the receptor with auxiliary proteins, called coactivators and corepressors. Notably, breast cancer cells often display abnormal responses to estrogens, and these aberrant responses have important consequences for the growth and clinical treatment of mammary cancers; mammary tumors that retain a normal response to estrogens can be treated with anti-estrogens, whereas non-responsive tumors cannot.
Corepressors play important roles in regulating the ability of estrogen receptors to respond to positive and to negative-acting hormones. We have recently demonstrated that corepressors are phosphorylated (chemically altered) by, and inhibited by, other proteins called kinases that operate in response to important peptide growth factor receptors, such as the epidermal growth factor receptor (EGF-R) and HER2. We propose that this phosphorylation of corepressors alters the response of the mammary cell to estrogen; thus linking the actions of peptide growth factors to the actions of estrogen receptors and altering the proliferation and differentiation of mammary cells. Changes in this growth factor/kinase signaling appear to play a role in mammary cancers that develop resistance to anti-estrogen chemotherapy.
We will test our hypothesis by using a series of molecular and biochemical techniques. We will test the ability of growth factor receptors to induce phosphorylation of corepressor in cultured mammary cells. Associated alterations in the interaction of corepressor with estrogen receptor will be examined using protein-protein binding assays. The effects of corepressor phosphorylation on regulation of estrogen target genes will be determined by experimentally manipulating the levels of corepressor phosphorylation and measuring the ability of estrogen receptor to turn on and off an appropriate reporter gene construct. We will also assay the effect of corepressor phosphorylation on mammary tumor cell replication -/+ tamoxifen.
Much of the prior work on the estrogen response in the normal and cancerous breast has focused on estrogen hormones, anti-estrogens, and phosphorylation events that modify the estrogen receptor itself. Our results suggest that phosphorylation of corepressors is likely to be an additional, physiologically-relevant, and relatively unexplored regulatory pathway by which the estrogen response is regulated and modified in both normal and cancerous mammary cells. The work proposed here will help elucidate the role of corepressor phosphorylation in the normal breast, will provide new information as to how certain breast tumors acquire resistance to anti-estrogen chemotherapy, and may indicate new treatments for these drug-resistant neoplasia that are among the most lethal forms of breast cancer. |
Final Report |
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Introduction: Estrogens play particularly important roles in the growth and differentiation of the normal breast by binding to estrogen receptors, which operate primarily as hormone-regulated transcription factors. Additional auxiliary proteins, denoted corepressors, help regulate this ability of estrogen receptors to respond to positive and to negative-acting hormones. Notably, breast cancer cells often display abnormal responses to estrogens, and these aberrant responses have important consequences for the growth and clinical treatment of mammary cancers. The development and function of the normal breast is also under the regulation of polypeptide growth factors, and changes in growth factor/kinase signaling appear to play a role in mammary cancers that develop resistance to anti-estrogen chemotherapy.
Topic addressed: We previously demonstrated that growth factor signaling can influence the actions of corepressors through a kinase cascade. We propose that this phosphorylation of corepressors alters the response of the mammary cell to estrogen; thus linking the actions of peptide growth factors to the actions of estrogen receptors and altering the proliferation and differentiation of mammary cells.
Progress made: We have been able to establish that growth factor signaling does influence the function of estrogen receptors and alters their ability to interact with corepressors. For example, two different growth factors, epidermal growth factor signaling and heregulin- induced a relocalization of the SMRT corepressor out of the nucleus in to a cytoplasmic compartment. Notably, the N-CoR corepressor, a close relative of SMRT, responded quite differently to growth factor signaling, and was generally unaffected by the same kinase cascades that lead to inactivation and relocalization of the SMRT corepressor. We are investigating the basis and implications of these differences between SMRT and N-CoR. We have recently expanded our studies to an investigation of the abilities of estrogen and thyroid hormone receptors to cross-recognize target genes to better understand how these receptors specify their DNA targets, and the aberrations of gene expression involved in the mammary tumor phenotype.
Future directions and impact: The work proposed here will help elucidate the role of corepressor phosphorylation in the normal breast, will provide new information as to how certain breast tumors acquire resistance to anti-estrogen chemotherapy, and may indicate new treatments for these drug-resistant neoplasia that are among the most lethal forms of breast cancer. |
Initial Award Abstract |
|
The development and function of the normal breast is under the regulation of an interacting series of hormones and growth factors. Estrogens play particularly important roles in the growth and differentiation (maturation) of the normal breast by binding to estrogen receptors, which operate primarily as hormone-regulated transcription factors. The ability of estrogen receptors to turn on or off different target genes depends on the interaction of the receptor with auxiliary proteins, called coactivators and corepressors. Notably, breast cancer cells often display abnormal responses to estrogens, and these aberrant responses have important consequences for the growth and clinical treatment of mammary cancers; mammary tumors that retain a normal response to estrogens can be treated with anti-estrogens, whereas non-responsive tumors cannot.
Corepressors play important roles in regulating the ability of estrogen receptors to respond to positive and to negative-acting hormones. We have recently demonstrated that corepressors are phosphorylated (chemically altered) by, and inhibited by, other proteins called kinases that operate in response to important peptide growth factor receptors, such as the epidermal growth factor receptor (EGF-R) and HER2. We propose that this phosphorylation of corepressors alters the response of the mammary cell to estrogen; thus linking the actions of peptide growth factors to the actions of estrogen receptors and altering the proliferation and differentiation of mammary cells. Changes in this growth factor/kinase signaling appear to play a role in mammary cancers that develop resistance to anti-estrogen chemotherapy.
We will test our hypothesis by using a series of molecular and biochemical techniques. We will test the ability of growth factor receptors to induce phosphorylation of corepressor in cultured mammary cells. Associated alterations in the interaction of corepressor with estrogen receptor will be examined using protein-protein binding assays. The effects of corepressor phosphorylation on regulation of estrogen target genes will be determined by experimentally manipulating the levels of corepressor phosphorylation and measuring the ability of estrogen receptor to turn on and off an appropriate reporter gene construct. We will also assay the effect of corepressor phosphorylation on mammary tumor cell replication -/+ tamoxifen.
Much of the prior work on the estrogen response in the normal and cancerous breast has focused on estrogen hormones, anti-estrogens, and phosphorylation events that modify the estrogen receptor itself. Our results suggest that phosphorylation of corepressors is likely to be an additional, physiologically-relevant, and relatively unexplored regulatory pathway by which the estrogen response is regulated and modified in both normal and cancerous mammary cells. The work proposed here will help elucidate the role of corepressor phosphorylation in the normal breast, will provide new information as to how certain breast tumors acquire resistance to anti-estrogen chemotherapy, and may indicate new treatments for these drug-resistant neoplasia that are among the most lethal forms of breast cancer. |
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