林光輝 (KH Lin): 生物醫學研究所 教授兼副院長 醫學大樓 Room 0861 Tel: 5177, 5975 e-mail:khlin@mail.cgu.tw

1. 林光輝(KH Lin): 生物醫學研究所 教授兼副院長 醫學大樓 Room 0861 Tel: 5177, 5975 e-mail:khlin@mail.cgu.edu.tw

2. Nuclear Hormone Receptor is a ligand-dependent transcriptional factor • Classes of hormones • General properties of nuclear hormone receptorssuperfamily • Functional characterization of nuclear hormone receptors • Thyroid hormonesand thyroid hormone receptors • Hormone response elements:palindromic (inverted repeat), directed repeat, everted repeat. • Mechanism of nuclear hormone actionCofactors in two steps dimerization pathway—Coactivators (CoA)-SRC, Corepressor (CoR)-SMRT

3. Mechanism of transcriptional repressioncompetition for overlapping binding sites • 8. Resistance to thyroid hormone (RTH) • 9. Transgenic model to study the receptor functions. • Dominant negative activity • 10. Thyroid hormone coactivator, corepressor. • 11. Mutant nuclear hormone has oncogenic potential

4. Binding of extracellular signal molecules Hydrophilic molecules bind to cell-surface receptors Hydrophobic molecules bind to intracellular receptors *

6. Small molecule coactivators of transcription Steroids

7. Small molecule coactivators of transcription Lipid-Soluble Vitamins & Thyroid Hormone Vitamin A Thyroid Hormone

8. Thyroid hormone receptors

9. Nuclear Receptor Family • is Large but not ubiquitous: • mammals have ~50-60 genes • flies 21 • worms 270 (!!!) • plants 0 • yeast 0 • Only a handful of physiological ligands have been identified, • (despite many genes, worms lack any known lipid based endocrine system)

10. For a steroid hormone to turn gene transcription on, its receptor must: • bind to the hormone • bind to a second copy of itself to form a homodimer • be in the nucleus, moving from the cytosol if necessary • bind to its response element • activate other transcription factors to start transcription.

11. Nuclear receptor family (steroid) • Steroid hormone receptors are part of the superfamily of nuclear receptors that contains over 30 members. • All members have conserved regions of high homology • Hormone binding domain 90% homologous • 10% difference accounts for specificity • DNA binding domain which contains zinc fingers • Receptors are found complexed with heat shock proteins (HSP) • Unoccupied receptor held in inactive conformation by HSP • Ligand binding releases HSP and exposes DNA binding domain • Hormone receptor complex then binds to response elements on gene and allows transcription to occur

12. Structure of Intracellular Receptors Steroid and thyroid hormone receptors are members of a large group ("superfamily") of transcription factors. All of these receptors are composed of a single polypeptide chain that has, in the simplest analysis, three distinct domains: A/B, C, E.

13. Thyroid hormone receptors

15. Thyroid • Thyroid • just below the larynx. • Follicular cells secrete T3, T4 (which are “assembled” in colloid). • Parafollicular cells secrete calcitonin, which regulates blood calcium levels.

16. Thyroid

17. EFFECTS • T3: • - Stimulates protein synthesis. • - Stimulates rate of cellular respiration. • - Increases metabolic rate.

18. Diseases of the Thyroid • Hypothyroid • Decreased metabolic rate. • Weight gain. • Decreased ability to adapt to cold. • Lethargy. • Hyperthyroid: • weight loss. • Nervousness, irritability (易怒). • Intolerance to heat. • Bulging eyes.

19. CTE: JBC:277(28),25115–25124, 2002

20. TR isoforms

22. Nuclear hormone receptor: domain structure Zinc finger DNA binding domain… inserts into major groove of DNA

24. Steroid hormone receptors family

28. Hormone response elements (HRE)

30. DNA Sequence half-sites are arranged as direct repeats

31. Interaction of Thyroid Hormone Receptors with DNA Thyroid hormone receptors bind to short, repeated sequences of DNA called thyroid or T3 response elements (TREs), a type of hormone response element. A TRE is composed of twoAGGTCA "half sites" separated by four nucleotides. The half sites of a TRE can be arranged as direct repeats, palindromes or inverted repeats.

32. Half site 5‘-AGGTCA-3’ n IR: inverted repeat n DR: directed repeat n ER: everted repeat

33. In the absence of hormone, some intracellular receptors do bind their hormone response elements loosely and silence transcription, when complexed to hormone, become activated and strongly stimulate transcription.

34. “3– 4–5” rule: VDR: DR3 TR: DR4 RAR: DR5 Endocr Rew: 15:391, 1994.

35. The updated hormone action-Two steps model

36. Ligand-bound state: Binding of T3 to its receptor induces a conformational change in the receptor that makes it incompetent to bind the corepressor complex, but competent to bind a group of coactivator proteins. The coactivator complex contains histone transacetylase (HAT) activity, which imposes an open configuration on adjacent chromatin. The coactivator complex associated with the T3-bound receptor functions to activate transcription from linked genes.

37. Thyroid hormone action Deiodinase T4 T4 T3

38. Thyroid hormone action Transcription machinery T3 Pol II TR RXR Transcriptional start site Thyroid responsive element (TRE)

39. A two-step model for TR/RXR heterodimer receptor activation

40. CoactivatorAnnu. Rev. Physiol. 2004. 66:315–60

41. Corepressor Annu. Rev. Physiol. 2004. 66:315–60

42. Nuclear receptor function -Ligand +Ligand

44. Transcriptional Repression Mechanisms

45. Mechanisms of Transcriptional Repression

46. Histone acetylation is reversible HDACs (histone deacetylase complexes) remove acetyl groups from N-terminal lysines, restoring their positive charge Histone deacetylation correlates with transcriptional inactivation.

47. Key repression step: Deacetylation of N-terminal lysines Acetyl group no positive charge transcriptional inactivation

49. Resistance to thyroid hormone (RTH) TRb1 mutation Autosomal dominant disorder Elevated free thyroid hormones in the serum TSH elevated or inappropriated normal

50. Mutation sites for TRb1