Nuclear receptors YT

Introduction to Nuclear Receptors

• Overview of nuclear receptors in cellular biology.
• Focus on glucocorticoid signaling for illustration.

Location of Nuclear Receptors

• Intracellular Location:
    - Nuclear receptors are located inside the cell, unlike membrane-bound receptors.
• Ligand Characteristics:
    - Ligands are lipid-soluble, allowing them to cross the cell membrane and bind to intracellular receptors.

Function of Nuclear Receptors

• Transcription Factors:
    - Function as transcription factors, regulating gene expression and protein synthesis.

Subfamilies of Nuclear Receptors

• Steroid Hormone Receptors:
    - Includes receptors for glucocorticoids, mineralocorticoids, androgens, estrogens.
• Other Hormone Receptors:
    - Receptors for vitamin D, thyroid hormones, and retinoic acid.
• Xenobiotic and Metabolite Receptors:
    - Recognize a wide range of xenobiotics and metabolites.

Locations of Different Nuclear Receptors Under Inactive State

• Glucocorticoid and Mineralocorticoid Receptors:
    - Located in the cytoplasm under resting conditions.
• Estrogen and Progesterone Receptors:
    - Found in the nucleus even in the inactive state.
• Thyroid Hormone and Retinoic Acid Receptors:
    - Attached to DNA and remain bound, regardless of activity state.

Structure of Nuclear Receptors

• Main Domains:
    - Ligand-Binding Domain:
      - Site where the ligand binds.   - DNA Binding Domain:
      - Binds to DNA.   - Transactivation Domain:
      - Modifies DNA conformation to initiate transcription.

Signaling Pathway of Glucocorticoid Receptors

• Location:
    - Glucocorticoid receptors are located in the cytoplasm under resting conditions.
• Resting State Interaction:
    - Activity is inhibited by chaperone proteins, specifically heat shock proteins (HSP-90).
• Activation Steps:
    - Binding of glucocorticoid ligand to the ligand-binding domain leads to the release of HSP-90.   - Dimerization of two activated receptor proteins.   - Entry into the nucleus.   - Binding with a coregulator (can be a co-activator or co-repressor).
• Target Site on DNA:
    - Complex binds to glucocorticoid responsive elements (GRE) on genes.
• Modulation of Gene Expression:
    - This binding leads to facilitation or repression of gene expression.   - In facilitation, mRNA is produced and moves into the cytoplasm for protein synthesis.   - New proteins enact changes in cellular activity.

Time Frame of Nuclear Receptor Effects

• Slow Activation and Duration:
    - Effects of nuclear receptor activity develop slowly compared to other signaling pathways.   - Once effects manifest, they tend to last longer.   - Duration is due to the persistence of synthesized proteins even after the removal of the stimulus; proteins remain active until degraded.

Summary of Key Points

• Nuclear Receptors:
    - Located inside cells, binding to lipophilic ligand molecules.
• Transcription Factors:
    - Structure includes ligand-binding domain, DNA binding domain, and transactivation domain.
• Resting State of Glucocorticoid Receptors:
    - Found in the cytoplasm, bound to HSP-90 which inhibits activity.
• Process Overview:
    - Ligand binding leads to the release of chaperone proteins, dimerization, nuclear entry, coregulator binding, DNA binding, and transcription modulation.
• Onset and Longevity of Effects:
    - Slow to appear, slow to disappear due to involvement of protein synthesis.