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.