Thyroid hormone receptors

Definition

Thyroid hormone receptors (TRs) are a group of proteins found in the nucleus of cells that mediate the effects of thyroid hormones, specifically thyroxine (T4) and triiodothyronine (T3). They play a crucial role in regulating gene expression and influencing various physiological processes such as metabolism, growth, and development. TRs belong to the nuclear receptor superfamily, which functions as transcription factors that respond to signaling molecules like thyroid hormones.

5 Must Know Facts For Your Next Test

1. Thyroid hormone receptors exist in two main isoforms: TRα and TRβ, which have different tissue distributions and functions.
2. When thyroid hormones bind to TRs, they undergo a conformational change that allows them to interact with DNA and regulate gene expression.
3. TRs can also function as repressors when thyroid hormones are absent, inhibiting gene expression until activated by hormone binding.
4. Dysregulation of TR function can lead to various disorders, including hypothyroidism, hyperthyroidism, and resistance to thyroid hormone.
5. TRs are involved in a variety of biological processes, including thermogenesis, heart rate regulation, and neuronal development.

Review Questions

• How do thyroid hormone receptors influence gene expression in target cells?
  • Thyroid hormone receptors influence gene expression by binding to thyroid hormones like T3 and T4. Once bound, these receptors change shape and attach to specific DNA sequences, promoting or inhibiting the transcription of target genes. This process leads to changes in protein synthesis, which impacts various cellular functions such as metabolism and growth.
• What roles do the different isoforms of thyroid hormone receptors play in physiological processes?
  • The two main isoforms of thyroid hormone receptors, TRα and TRβ, have distinct roles in different tissues. TRα is primarily involved in regulating heart rate and thermogenesis, while TRβ is more prominent in regulating cholesterol metabolism and brain development. This specialization allows for a nuanced response to thyroid hormones across various physiological contexts.
• Evaluate the potential consequences of thyroid hormone receptor dysfunction on human health.
  • Dysfunction of thyroid hormone receptors can lead to serious health issues such as hypothyroidism or hyperthyroidism, both of which can disrupt normal metabolic processes. Additionally, resistance to thyroid hormone can occur, where target tissues become less responsive to these hormones despite their normal levels. Such conditions can result in symptoms like weight gain or loss, fatigue, and developmental issues, highlighting the critical role of TRs in maintaining overall health.

Related terms

Thyroid hormones: Hormones produced by the thyroid gland, mainly thyroxine (T4) and triiodothyronine (T3), that regulate metabolism and other bodily functions.

Nuclear receptors: A class of proteins that regulate gene expression in response to hormones and other signaling molecules, including thyroid hormones.

Transcription factors:

Proteins that help initiate or regulate the transcription of specific genes by binding to nearby DNA.