Estrogen receptors are intracellular nuclear hormone receptors that activate messenger RNA transcription and regulate cell proliferation. They are found in cells that target estrogen and play a role in bone growth, cholesterol regulation, and breast and uterine preparation for pregnancy. However, they may also increase the risk of breast and uterine cancer.
An estrogen receptor is one of a group of hormone receptor proteins that are activated by the steroid hormone estrogen. These receptors are intracellular nuclear hormone receptors, which means they are found within the nucleus of a cell and specialize in sensing steroid hormones. Only estrogen or a molecule with a similar structure can bind to an estrogen receptor, and the receptors themselves are found only in cells that target estrogen, such as cells in the liver, uterus, and breasts. The main function of estrogen receptors is to act as deoxyribonucleic acid (DNA) transcription factor proteins, which are proteins that activate the transcription of messenger ribonucleic acid (mRNA). Estrogen receptors also play an important role in the process of cell proliferation and regulate bone growth and breakdown.
When no estrogen is present in the nucleus of a cell, an estrogen receptor remains inactive. As soon as an estrogen hormone enters the cell nucleus, it binds to the estrogen receptor. The receptor changes shape when the hormone is bound to it and becomes known as an estrogen-receptor complex. The estrogen receptor complexes then bind to DNA sequences that are also present in the nucleus and are known as estrogen response elements. Once bound to DNA, the estrogen-receptor complexes activate nearby gene sequences, which begin transcribing mRNA, a type of molecule that provides a genetic blueprint for protein synthesis.
Guided by the mRNA, the cell starts producing specific protein sequences. These proteins have a direct effect on the activity of the cell. For example, liver cells are directly affected by the activity of estrogen receptors. The estrogen receptor triggers the production of proteins that regulate cholesterol levels in liver cells. In this way, estrogen receptors reduce the risk of contracting heart disease.
Cell proliferation, or the process of cell growth and division, is also influenced by estrogen receptors. The mammary gland cells are stimulated by estrogen receptors, thus preparing the breasts to start producing milk in case of pregnancy. The endometrium, or inner lining of the uterus, is also stimulated by estrogen receptors, which prepare the uterus for a potential pregnancy.
Due to their role in cell proliferation, estrogen receptors may also increase the risk of breast cancer and uterine cancer. If cells in the breast or uterine lining have begun to change due to environmental or genetic causes, the estrogen receptor can cause the changed cells to proliferate. These mutated cells are more likely to become cancerous. Normal breast and uterine lining cells exposed to estrogen are also more vulnerable to spontaneous DNA mutation, which can also lead to an increased risk of cancer.
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