Endocrinology, lecture on Mechanisms of Action for Nuclear Receptors
USD Department of Biology
Endocrine Glands
2nd Messengers
Nuclear Receptors
Genetic Regulation
Hormone Synthesis
Receptor Regulation
Hypothalamo-Hypophysial Communication
Tropic Hormones
Neurohypophysial Nonapeptides
Thyroid Axis
Adrenal Axis
Adrenal Medulla
Osmotic-Pressure Balance
Reproductive Endocrinology
Somatic Axis
Growth Factors
Immune Factors
Ca++, PO4 Homeostasis
Pancreatic Hormones
GI Hormones
Guts 'n Brains
Brain Hormones
Endocrine Evolution
Figures for Endocrionology
text:Vertebrate Endocrinology5th Edition - David O. Norris:
Read pages 61-72, 86-93 for this lecture
acronyms    end
VI. Nuclear Receptors and Mechanisms of Action  	

	A. Nuclear and Cytosolic receptors interact directly with DNA

	B. Receptor Translocation

		1. in the absence of hormone (steroids and thyroid hormones) all or
		   part of the receptors are weakly bound in the nucleus

			a. receptors for E, P, and T3 are "always" found
			    in the nucleus
				i. may be found at plasma membrane

		2. after hormone binding their affininty for nuclear
		   constituents (DNA) increases

			a. receptor-chaperone complex (transportosome)
				i. chaperones (like heat-shock proteins) maintain 3-D shape (before binding)
				   influence affinity for the nucleus, influence translocation, 
				   affect folding after translocation

		3. if binding occurs in the cytoplasm receptors move to the nucleus

			a. this translocation is not a limiting step
				i. involves chaperones

	C. Affinity Activation

		1. the unbound steroid receptor has a molecular weight of ~300,000 d (daltons)

			a. d = 1.000 atomic mass ~H

		2. a hetero-oligomer - the 8S receptor						

			a. includes 1 - 2 receptors and up to 4 heat-shock protein molecules
				i. hsp 56; 56,000 d
				   hsp 70; 70,000 d
				2x hsp 90; 90,000 d; non-steroid binding

				ii. production of hsp's increase with heat or other injury

		3. hormone binding releases 2x hsp 90, exposing a positively charged
		   DNA binding site on the receptor

			a. receptor is activated - 4S receptor

			b. affinity for the hormone is also increased

	D. Structure

		1. DNA binding domain  ~70aa						

			a. 300aa away from the C (carboxy)-terminal extremity

				i. 100 - 600aa away from N-terminal

			b. 2 fingers, each stabilized by a Zn++			

				i. binds to HRE
					(1) helped by nuclear adaptor proteins, transcription factors

			c. highly conserved - 40-90% homology between receptors for different hormones

				i. 100% conservation between species for the same hormone

			d. belong to a family of transcriptional regulatory factors

				i. related DNA-binding proteins characterized by metal fingers

		2. Ligand Binding Domain = Hormone Binding

			a. C-terminal portion ~250aa

			b. hydrophobic pocket - steroid binding

			c. also highly conserved

		3. N-terminal region

			a. less well conserved - variations in size

			b. interaction with other regulatory proteins

				i. transcription factors

		4. No intrisic protein kinase activity

VII. Mechanisms of Action/Genetic Regulation