dr.s.chakravarty, md list the various types of receptors in the cells differentiate the features of...
TRANSCRIPT
SIGNAL TRANSDUCTION AND MECHANISM OF HORMONE
ACTION
Dr.S.Chakravarty, MD
Learning objectives • List the various types of receptors in the cells
• Differentiate the features of water and fat soluble hormones
• List the various second messengers involved in signal transduction
• Describe the G protein and its coupled receptor in detail
• Differentiate intrinsic and extrinsic tyrosine kinase mediated pathways of signal transduction
• Describe the mechanism of insulin release and the structure of insulin receptor
Types of signalling
Receptors for various hormones
• Intracellular (transcription factors) – type 1 hormones
• Cell surface – type 2 hormones
Types of hormones based on solubility
Effect Days Minutes to hours
Type -1 hormones –intracellular receptors
Type 2 hormones- have membrane receptors
Growth factors!
G protein coupled receptor:
• Primary receptor for most of type 2 hormones.
• Link receptors to second messengers
• Serpentine -7 channel transmembrane receptor
• Coupled to G proteins.
• 4 types of G proteins – Gs, Gi, Gq and G12
• 3 heterotrimers of G proteins – αβγ subunits.
GPCR – Plasma membrane coupled receptor
G-α β
γ ATP
C -AMPProtein Kinase A
Enzyme Enzyme
P
CREB
CREB
P
CRE
GDP(Inactive)
Adenylate Cyclase
Cell membrane
Cytosol
Plasma
G – protein coupled Receptor cAMP mediated pathway
GTP(active)
cAMP response element binding protein
cAMP response element
Second messenger is cAMP
c-AMP pathway cont..
PKA is also known as cAMP-dependent protein kinase
Mechanism of action of c-AMP on protein kinase-A
PKA is also known as cAMP-dependent protein kinase
Hydrolysis of c-AMP by Phosphodiesterase
c-AMP 5’-AMP
Active Inactive
H2O
Phosphodiesterase
(-)
Methyl Xanthines(Caffeine, Theophylline,
Theobromine)
Various types of G-proteins
Classes and Functions of Selected G Proteins1
Class or Type Stimulus Effector Effect
Gs
αs
αOlf
Glucagon, α-adrenergics
Odorant
Adenylyl cyclaseCardiac Ca2+, Cl–, and Na+ channelsAdenylyl cyclase
Glyconeogenesis, lipolysis, glycogenolysis
Olfaction
Gi
αi-1,2,3
α0
αt
Acetylcholine, α2-adrenergicsM2 cholinergicsOpioids, endorphins
Light
Adenylyl cyclasePotassium channelsCalcium channelsPotassium channelscGMP phosphodiesterase
Slowed heart rateNeuronal electrical activity
Vision
Gq
αq
α11
M1 cholinergicsα1-Adrenergicsα1-Adrenergics
Phospholipase C-β1
Phospholipase C-β2
Decreased Muscle contractionand decreased Blood pressure
G12
α12Thrombin Rho Cell shape changes
Table 42–2. Subclassification of Group II.A Hormones
HORMONES THAT STIMULATE ADENYLYL CYCLASE
HORMONES THAT INHIBIT ADENYLYL CYCLASE
ACTH Acetylcholine
ADH α2-Adrenergics
α1-Adrenergics Angiotensin II
Calcitonin Somatostatin
CRHFSH
GlucagonhCGLH
LPHMSHPTHTSH
Protein Phosphorylation by protein kinases
• Serine / threonine phosphorylation:
• Protein kinase A and C and G attach phosphate groups to hydroxyl groups of serine and threonine – to phosphorylate proteins
Type- 3 Second messenger as Calcium and phosphatidyl inositol
Calcium is required for : • Skeletal muscle contraction
• Blood clotting
• Secretion of various hormones and enzymes
• Membrane excitability
• Enzymatic activity.
IMP
Action of phospholipase C
Important aspect in Metabolic regulation
Enzyme Enzyme P
Protein kinase
Phosphatases
ATP ADP
H2O
GlucagonEpinephrine
Insulin P
ADP RIBOSYLATION OF PROTEINS
ADP-ribosyltransferase
ADP-ribosyltransferases
ADP RIBOSYLATION OF PROTEINS
• Cholera toxin – causes ADP ribosylation of GαS
& subunit and inhibits intrinsic GTPase activity – prolonged action of adenylate cyclase – watery diarrhea
• Pertussis toxin – causes ADP ribosylation of G α i-2 and prevents dissociation of α i-2 from βγ subunit .Gαs activity in such cells unopposed.
Usmle!
Two more toxins for USMLE !
• Diphtheria toxin – causes ADP ribosylation of eEF-2 and inhibits protein synthesis by inhibiting translocation of ribosomes
• Tetrodotoxin – is a neurotoxin which acts on fast sodium channels in the neuronal membrane and inhibit action potential in the neurons.(pufferfish, porcupinefish, ocean sunfish or mola, and
triggerfish, )Usmle!
membrane bound Guanyl
cyclase
GTP C-GMP GTP
Protein kinase G
Vasodilation (smooth muscle)
NO ANF Cyclic GMP pathway
Soluble Guanyl cyclase
5’-GMP
Phosphodiesterase
Anti anginal Drugs
+
Guanyl cyclase – cGMP (class II)
• Membrane bound Guanyl cyclase – Atrial natriuretic peptide (ANP).
• Soluble Guanyl cyclase – nitrates, nitroprusside, NO.
• Sildenafil (Viagra) – phosphodiesterase V inhibitor
• Remember :-Theophylline, caffeine – phosphodiesterase inhibitors.
Drugs acting through NO pathway
• Sodium nitroprusside – arterial and venodilator
• Nitroglycerine – veins • Hydralazine – arterial
• Artery – decreased TPR and BP• Vein – decreased preload and cardiac output
Receptor tyrosine kinase Insulin and growth factors
Tyrosine kinases – phosphorylate proteins at hydroxyl groups of tyrosine amino acid
With intrinsic tyrosine kinase activity
• Insulin receptor• IGF -1 • EGF, PDGF, FGF
• MAP kinase RAS protein
Without intrinsic tyrosine kinase
• GH, Prolactin • Erythropoietin • Cytokines
• Janus kinase STAT (signal transducers and
activators of transcription)
I
Cell membrane
Beta subunit
Alpha subunit
GLUT-4
G
GG
GI
Phosphorylation of Insulin Receptor substrates
GLUT-4
G
G
G
PHOSPHORYLATION OF TYROSINE RESIDUES
DIFFERENT PATHWAYS
One Cause for insulin resistance
Serine phosphorylation instead of tyrosine phosphorylation of insulin receptor– mediated by inflammatory mediators like TNF-alpha, interleukins, free fatty acids etc.
Translocation of GLUT-4 receptor
• Insulin dependent translocation
• Well fed state/abundant glucose in blood
• PI-3 kinase pathway
• Exercise induced translocation:
• During exercise – no insulin
• AMPK pathway
Pathway G-protein Enzyme Second messenger
Protein kinase
C-AMP Gs or Gi Adenylate cyclase
C-AMP PK –A
C-GMP Single channel Guanyl cyclase C-GMP PK - G
PIP-2 Gq Phospholipase C IP-3, Ca2+ and DAG
PK - C
Insulin and GFs IRS and SH2 domains
•Tyrosine kinase •Protein phosphatase
Mechanism of action of steroid hormones
SRESteroid receptor
HSP 90Steroid hormone( Cortisol)
In the absence of the steroid hormone cortisol, Glucocorticoid receptor resides in the cytosol complexed with several chaperone proteins including Hsp90
Foye’s Medicinal Chemistry, 7th Edition by Lemke
Nf-kb pathway
p50 p65
Ikb
Cytokines, TNF a, free radicals, viruses
IKKcomplex
P +
Nucleus
Ubiquitin proteosome pathway
Steroids inhibit this pathway and act as potent anti-inflammatory agents
(Inhibitor of Κb)
IκB kinase
Very large family of Nuclear receptor proteins
DBD – DNA BINDING DOMAINLBD – LIGAND BINDING DOMAIN HINGE REGION - Highly variable region that provides flexibility to the receptor, so it can assume different DNA-binding conformationsAF-1 transactivation domain referred
Convergence of pathways
CREB binding protein & p300 coactivator
Function of CBP/P300 protein
• Histone acetyl transferase activity
• Recruitment of RNA pol II to the promoter region of the gene of interest
• Helps in transcription and translation of proteins.
MCQ 1
MCQ 2
The phosphorylase kinase-associated regulatory protein identified by the letter A in Figure 3-4 is a calcium-binding protein. Which of the following proteins represents this regulatory subunit?
MCQ 3
Thank you