Mechanism of action-1

Transcription

1 Mechanism of action-1 receptors: mediators of hormone action, membrane associated vs. intracellular receptors: measurements of receptor - ligand interaction, mechanism surface-receptors: kinases, phosphatases, GC activities, ligand-gated ion channels intracellular receptors:, thyroid, retinoid and arylhydrocarbon receptors 02 mechanism of thyroid, gonad and adrenal hormone action: gene by T3, P4,T, E2, ALD, COT and their receptors in addition, neuros mechanism of action : actions, actions at cell surface through their membrane receptors genetic control of hormone biosynthesis permissive action, / thyroid hormone endocrine pathologies, action mechanism a review using expression of a polypeptide hormone controlled by a liposoluble hormone Today s lecture afferent story line integrator center a reflex arc a base for a control model efferent story line S diagram for a control system as that present in a refrigerator E sensor negative feedback story line effector S E if story lines are linked through an integrator, then you have control Page 1

2 Today s lecture story line I suggest you put this information into a table YOU design!!! Membrane What does a cell membrane look like? What does a receptor look like? What does a receptor in a membrane look like? What does an enzyme look like? What does an enzyme in a membrane look like? What does an ion channel look like? What does an ion channel in a membrane look like? Page 2

3 All eceptors bound hormone ( H ) binding capacity How do hormones and receptors interact? What is affinity and what is specificity? What is a conformation change? What is the relation between binding and biological effect? What are spare receptors? k1 H + <------> H H * H = Scatchard plot bound / free H / H k2 k1 k2 = kd single binding slope = - 1 / kd capacity half saturation affinity = kd free hormone ( H ) double binding What is the life cycle of a hormone receptor? bound hormone ( H ) high affinity / low capacity low affinity / high capacity All eceptors number of occupied receptors per cell x Specific hormone binding % reduction in the number of receptors biological response as % of maximum Biological response hormone concentration (M) number of receptors occupied for maximal biological response (100%) Page 3

4 Membrane eceptors surface - receptors: kinases, phosphatases and GC activities, ligandgated ion channels, transport next lecture Transducer, comparator, amplifier, crosstalk Gs AC ---> camp ----> PKA ----> intermediaries pump channel enzyme Gi AC ---> camp ----> PKA ----> intermediaries nucleus Membrane eceptors E mna Golgi recycled or destroyed Lysosomes surface - receptors: kinases, phosphatases and GC activities, ligandgated ion channels, transport next lecture next lecture c e l l m e m b r a n e Transducer, comparator, amplifier, crosstalk Gs AC ---> camp ----> PKA ----> intermediaries pump channel enzyme Gi AC ---> camp ----> PKA ----> intermediaries Page 4

5 Nuclear eceptors gene, exons, introns cis - acting, trans - acting transcription, translation splicing NA cap polya tail Hormonal action can be regulated at the level of transcription, translation, NA turnover, protein turnover, and post - translational modification. Nuclear eceptor Structure NH 2 DNA binding region Hormone binding region COOH E P COT T T Vit D Page 5

6 Zinc Fingers Structure Transcription Factors Structure Page 6

7 Transcription and Acetylation Transcription and Methylation DNMT, DNA methyl! transferase! DNMT and a TF,! transcription factor! TGS, transcriptional! gene silencing! DNA methylation is a phenomenon occurring on the DNA known to consist of four bases. One of them, cytosine, exists in a "normal" and in a methylated version, ie with a methyl group attached, but only when directly followed by the base guanine. The consequences of methylation lie in the of gene expression: methylated cytosines in the promotor region of a gene lead to inactivation, thus acting as an "on" and "off" switch for genes. This is a naturally occurring mechanism to prevent all genes in a tissue/cell to be expressed at a time. As all cytosines in a CG context (ie in front of a guanine) are known, it is possible to analyze the patterns of methylated and unmethylated cytosines in the genome and to identify the pattern that is typical for a specific tissue and type of disease. Once differentially methylated cytosines for a certain disease are known, their detection enables an exact diagnosis at a very early stage, molecular classification and the likely reaction of a patient to treatment. Epis can obtain this information based on its robust proprietary technology.#! Page 7

8 Nuclear eceptor for Steroids H Intracellular receptors for s are transcription factors. Their Zn fingers are binding regions which attach to the promotor segment of DNA H H H HSP 90 HSP 90 Zn Zn H E Zn TATA box NA Pol II HSP 90 HSP 90 D N A Nuclear eceptor for T3 Hormone inactive transcription T3 empty binding site H E T3 co-repressor NH2 COOH TFIIB TATA box NA- Pol II D N A co-repressor active transcription T3 T3 H E T3 COOH NH2 TFIIB TATA box NA- Pol II D N A Page 8

9 Nuclear eceptor for T3 Hormone In its free state T3 binds to its HE as homo-dimer, or as a hetero-dimer with retinoid-x (e.g. Vit A). The carboxy-terminus of T3 interacts with TFIIB preventing the formation of a stable preinitiation complex and, together with a co-repressor, silences transcription. Upon T3 binding, its receptor undergoes a conformational change ( magic ), dissociation of the co-repressor, a decreased interaction of the T3 with the carboxy-terminus TFIIB and an increase interaction of the T3 amino-terminus with TFIIB. These changes facilitate TFIIB binding an assembly of a stable pre-initiation complex, the binding of NA polymerase II and the activation of transcription initiation. Efficiency, permissiveness Na / K pump camp ----> PKA ----> channel / enzyme AC Protein synthesis XX1 HE 5 3 E1 mna Cellular response S Steroid S > S DNA additional transcription factor Page 9

10 Permissive Action Action on specific mna synthesis could cause an increase in the number of membrane receptors, which might increase the production of cyclic nucleotides, thus leading to an increase cellular response to hormones acting on the plasmalemma. Thyroid or hormones could increase or decrease the amount of cyclic nucleotide - dependent protein kinases PK or amount of substrate available for phosphorylation by camp or cgmp - dependent PK. Thyroid and hormones could enhance the synthesis of a protein that could act as an inhibitor of another protein (e.g.. phosphoprotein phosphatase) whose action is antagonistic to cyclic nucleotide action. Pathologies Theoretically, genetic pathologies can be associated with each step of the biosynthetic pathway leading to the production of a particular enzyme or protein. congenital adrenal hyperplasia due to gene deletion or to point mutation of the 21 - hydroxylase enzyme ( beard lady ). testicular feminization due to point mutations scattered throughout the androgen receptor gene, cause decrease amounts of functional androgen receptors, altered sexual differentiation &feed-back ( beware of single bars ). Vit D - dependent rickets due to a single point mutation in tip of one of thedna - Zn fingers binding domain of Vit D receptor, thus making it unable to interact and transcriptionally regulate Vit D - responsive genes ( link to rickets and osteoporosis ). Page 10

11 eview of the mechanism of action of intracellular receptors in For example, lecture) peptide out Consensus gene encoding a prototypical peptide hormone Consensus gene encoding a prototypical peptide hormone For example, in lecture) Consensus gene encoding a prototypical peptide hormone Page 11

12 Consensus gene encoding a prototypical peptide hormone For example, in lecture) Consensus gene encoding a prototypical peptide hormone Consensus gene encoding a prototypical peptide hormone For example, in lecture) Consensus gene encoding a prototypical peptide hormone Page 12

13 Consensus gene encoding a prototypical peptide hormone For example, in lecture) Consensus gene encoding a prototypical peptide hormone Consensus gene encoding a prototypical peptide hormone For example, in lecture) Consensus gene encoding a prototypical peptide hormone Page 13

14 Consensus gene encoding a prototypical peptide hormone For example, in lecture) peptide out Consensus gene encoding a prototypical peptide hormone Consensus gene encoding a prototypical peptide hormone For example, in lecture) peptide out Consensus gene encoding a prototypical peptide hormone Page 14

15 Consensus gene encoding a prototypical peptide hormone For example, in lecture) peptide out Consensus gene encoding a prototypical peptide hormone Consensus gene encoding a prototypical peptide hormone For example, in lecture) peptide out Consensus gene encoding a prototypical peptide hormone Page 15

16 Endocrine Physiology levels of organization! structure! - function! homeostatic!! Potential control points for of gene expression in hormone production effector hormone Page 16

17 Models for activation of gene expression Cis model consensus gene Trans model Mechanisms of transcriptional repression Competition Sequestration Quenching / tethering Active ( or fat Albert and the buck - buck game ) Page 17

18 Activation of specific transcription factors by s Cell-surface receptor coupled signal transduction pathways involved in activation of nuclear transcription factors Page 18

19 Cell-surface receptor coupled signal transduction pathways involved in activation of nuclear transcription factors Page 19