1. Endo. 4 Detecting and signalling Cell surface receptors: G protein linked and tyrosine kinase receptors: second messengers, phosphorylating kinases, activation of transcription Intracellular steroid receptors; transcription factors Receptor regulation Hormone receptors and disease

2. Hormone receptors Peptide and protein hormones Steroid hormones
Water soluble cell surface receptors
Activate second messengers and/or enzymes
Cytoplasmic and nuclear effects
Steroid hormones
Lipophilic intracellular receptors in cytoplasm or nucleus. Cell surface receptors?
Receptors are transcription factors

3. General types of cell surface receptors

4. Protein and peptide hormone receptors
G-protein linked
Gs, Gi, Gq, G12
Open ion channels
Activate enzymes
second messengers
activation of tyrosine kinases
activation of serine/ threonine kinases
Enzyme linked or associated
Tyrosine kinase on receptor or on molecule associated with receptor
activation of serine/
threonine kinases

5. G-protein linked receptors
Receptors with or associated with tyrosine kinase domains

6. G-protein linked receptors
I and E loops

7. Activity of trimeric G proteins after hormone binding to a G-protein linked receptor

8. Second messengers in G-protein linked receptors
Adenyl cyclase cAMP Protein kinase A
DAG Protein kinase C
Phospholipase C IP2
IP Ca2+
Calcium Calmodulin Ca-CAM
protein kinase

9. Signalling at the TSH receptor

10. cAMP signalling system

11. The phosphinositide signalling system

12. Signalling at the vasopressin receptor

13. A CASCADE OF KINASES G-protein receptors
cAMP. Phospholipase C, Ca2+/calmodulin
Protein kinase A, C, or CaCM
cytoplasm
Serine/threonine kinases
MEK MAP pathway nucleus

14. Tyrosine kinases in intracellular signalling

15. G-protein linked receptors
Receptors with or associated with tyrosine kinase domains

16. Signalling at a receptor with tyrosine kinase activity

17. Increased glycogen synthase
Insulin
Insulin signaling
in muscle P P
SHC P P P
IRS
1,2,3 P P
PI3K
GRB/SHP P
GLUT-4
vesicles
Endosome
PDK1
SOS
RAS
PKB
RAF, MEK, MAPK
Increased glycogen synthase
FOS, ELK--> gene transcription

18. JAK-STAT signalling pathway - receptor with tyrosine kinase associated molecule

19. Signalling pathways at G-protein linked and tyrosine kinase receptors

20. STEROID RECEPTORS Intracellular Membrane receptors
Type I - in cytoplasm combined with hsp e.g sex steroids, glucocorticoids. Form homodimers
Type II - in nucleus, often bound to DNA e.g. thyroid hormones,vitamin D
Form homo- and hetero-dimers
Membrane receptors

21. STEROID HORMONE RECEPTORS
Steroid hormone receptors are a family of transcrtiption factors
Different functional regions of the receptor are defined as domains - A-F
The C domain is the DNA binding region and is highly conserved
Both the A/B domains and E/F domains have transcriptional activity
Different steroid receptors are continually being discovered

22. Hormone crosses cell membrane
Heat shock protein dissociates from receptor
Hormone binds to receptor and dimerization occurs
Dimerized receptors translocate to the nucleus
Binds to the hormone response element on the DNA
Along with other transcription factors transcription is initiated

23. Steroid hormone binding to its receptor
hsp

24. The C domain The DNA binding region is made up of 2 zinc fingers
Each finger contains 3 helical regions, I, II and III
The first helix contains the P box which recognizes specific base sequences on the DNA - the HRE
The amino acids indicated in brown are those concerned with dimerization of two receptors

25. Cartoon showing two dimerized receptors linking into the DNA helix
Cartoon showing two dimerized receptors linking into the DNA helix. The base sequences of the estrogen and glucocorticoid response elements are shown below

26. Activation of transcription by steroid hormone receptors
Binding of steroid hormone receptors (transcription factors) to the hormone response element on the DNA induces chromatin remodelling
There is binding of additional transcription factors and acetylation of histones
RNA polymerase is activated and transcription is stimulated
When histones are deacetylated transcription is repressed
DNA
Histones

28. Homologous and heterologous regulation
RECEPTOR REGULATION
Affinity of receptors - postitive and negative co-operativity
Number of receptors - up and down regulation
Desensitization of receptors - receptor phosphorylation, uncoupling
Homologous and heterologous regulation

29. Receptor regulation Phosphorylation of receptor Binding of arrestin
complete desensitization
Phosphatases remove phosphate and may reactivate receptor
Receptor regulation

30. Hormone receptors and disease
Genetic mutations of receptors - vitamin D resistant rickets.
Auto-antibodies against membrane receptors - Graves’ disease.
Inability to couple receptors with signal transduction pathways - pseudohypoparathyroidism
Receptor regulation in excess deficiency - obesity and insulin resistance
Inappropriate receptor interaction (specificity) - LH/TSH, prolactin/GH

31. Grave’s disease