Download Hormonal regulation

BIOCHEMISTRY
GENERAL MEDICINE
HORMONAL REGULATION
RNDr. Zdeněk DVOŘÁK, PhD.
Department of Medical Chemistry and Biochemistry
Faculty of Medicine, Palacky University Olomouc
HORMONAL REGULATION
Compounds involved in the co-ordination of metabolic activities of various organs
and tissues – cellular signalling; signal transduction
• HORMONES
• NEUROTRANSMITTERS
• GROWTH FACTORS
• CYTOKINES
• Extracellular signalling substances
• Synthesis in one class of cell
transmission
TARGET CELLS
HORMONES
• Synthetized by specific tissues – ENDOCRINE GLANDS
• Secreted directly into the BLOODSTREAM and carried to their sites of action
• Specifically alter METABOLIC ACTIVITIES of TARGET CELLS (remote
from secretory organ)
• Active at very low concentrations (pM – µM)
• Rapidly metabolized – SHORT-LIVED EFFECT
SIGNAL TRANSDUCTION
SIGNAL
HORMONE
RECEPTOR
TRANSDUCTOR
EFFECTOR
ULTIMATE
CELLULAR
RESPONSE
SECOND MESSENGER
Senzory inputs from the environment
INTEGRATION AND CONTROL
OF METABOLIC PROCESSES
CENTRAL NERVOUS SYSTEM
Hypothalamus
Primary target
Anterior pituitary
Thyrotropin
Corticotropin
Somatotropin
Secondary target
Thyroid
Thyroxine
Triiodothyronne
Muscles
Liver
Adrenal
cortex
Adrenal
medula
Cortisol
Corticosterone
Aldosterone
Epinephrine
Norepinephrine
Many
tissues
Liver
Muscles
Heart
Pancreatic
Islet cells
Posterior pituitary
Folicule
Luteinizing
hormone Stimulating
hormone
Ovary
Prolactin
Vasopresin
Oxytocin
Testis
Progesterone
Insulin
Testosterone
Estradiol
Glucagon
Somatostatin
Liver
Muscles
Reproductive organs Mammary Smooth Arterioles
Muscle;
glands
Mammary
glands
Ultimate target
CLASSIFICATION OF HORMONES ACCORDING TO STRUCTURE
1. Derived from aminoacids
2. Peptides and aminoacids
- epinephrine (adrenaline)
- nor-epinephrine
- thyroxine
- triiodthyronine
epinephrine
- insulin; glucagon
- liberins; oxytocin; vasopresin
- ADH; ACTH
oxytocin
3. Steroids
- cortisol; aldosterone
- progesterone; estradiol; testosterone
estradiol
4. Eicosanoids - prostaglandins; leucotrienes
- prostacyclines; thromboxanes
arachidonic acid
CLASSIFICATION OF HORMONES ACCORDING TO MODE OF ACTION
1.
•
•
•
•
•
•
Hormone DOES NOT TRAVERSE plasma membrane of a target cell
amino acids; peptides
hydrophylic compounds
binding of hormone to the RECEPTOR at the CELL SURFACE
hormonal response inside the cell – changes in AFFINITY of key proteins/enzymes
ACTION THROUGH: - second messengers
- activation of enzyme activity of cytosolic receptor domain
- opening ion channels
SHORT-TERM action; ULTRA-RAPID response
2. Hormone TRAVERSES plasma membrane of a target cell
• steroid and thyroid hormones
• lipophylic compounds
• binding of hormone to the INTRACELLULAR RECEPTOR
• HORMONE-RECEPTOR complex binds to DNA and triggers TRASCRIPTION of
specific genes – changes in LEVEL of key proteins/enzymes
• LONGTERM action; SLOW response
RECEPTORS
• proteins
• located in plasma membrane or in interior of the cell
• 2 binding sites - hormone binding site
- a component of signal transduction system
Peptides, AA
HORMONE BINDING
(saturable; M.-M. kinetics)
P
P
GR GR
GRE
TR
Extensive conformation
change of receptor
RAR
thyroid
GR
GR
retinoids
steroids
ACTIVATION OF SECOND
BINDING SITE
HORMONE
Several classes
of receptor
Identical hormone
binding site
ADRENERGIC RECEPTORS
α1 – coupled to phosphatidyl inositol cascade
α2, β1, β2 – coupled to adenylate cyclase cascade
α1 – salivary gland
α2 – pancreatic β−cells
- muscle
β1 – heart
- adipocyte
β2 – liver
↑ K+; ↑ H2O secretion
↓ secretion
↑ glycogenolysis
↑ rate; contraction force
↑ lipolysis
↑ glycogenolysis
Different second
binding site
Various physiological effects
(different tissue)
• increase in receptor density in the cell = increased cellular response
GTP- binding proteins = G - proteins
• guanyl-nucleotides proteins
• TRANSDUCTORS = carriers of excitation signal from RECEPTOR to EFFECTOR
within plasma membrane
• peripheral membrane proteins (located on cytosolic side)
• TRIMER = it consists of α, β and γ subunits
• α subunit is binding site for GDP/GDP; GTPase activity
• large extracellular ligand binding domain
• formation of hormone-receptor complex
• conformation change of the receptor
• transduction of signal inside the cell
• receptor interacts with G-protein
• exchange of GDP for GTP in α-subunit
• release of α-(GTP) subunit
• hydrolysis of GTP to GDP
• activation of effector
• release of α-GDP from effector
• re-association with β and γ subunits
G - protein signalling
GS - stimulatory
Interaction with
different receptors
G - proteins
Gi - inhibitory
• Inhibition of GTPase activity of α-GTP subunit results in irreversibile inactivation
of effector and consequently in uncontrolled cellular response
• Example: Vibrio cholerae toxin inhibits GTPase activity in enterocytes that in
turn leads to permanent activation of the effector (adenylate cyclase). As the
result; the secretion of Na+ and H2O is uncontrolled and severe dehydratation of
organism is developed.
Stimulus
Receptor
G-prot.
Effector
Epinephrine
Serotonin
Light
IgE-antigen complex
f-Met peptide
Acetylcholine
β-adrenergic r.
Serotonin r.
Rhodopsin
Mast cell IgE r.
Chemotactic r.
Muscarinic r.
Gs
Adenylate cyclase
Gs
Adenylate cyclase
Transducin cGMP phosphodiest.
Phospholipase C
GPLC
GPLC
Phospholipase C
Gk
Potassium channel
Response
Glycogen breakdown
Behavioral sensitization
Visual excitation
Secretion
Chemotaxis
Slowing pacemaker activity
SECOND MESSENGERS
• amplified intracellular signals – products of activated effector action
• small molecules or ions – allosteric effectors
• cAMP - cyclic adenosine monophosphate
• cGMP - cyclic guanosine monophosphate
• DAG - 1,2-diacylglycerol
• IP3 - inositol-1,4,5-triphosphate
• Ca2+ - calcium (free or bound to calmodulin)
SIGNAL TRANSDUCTION SYSTEMS
• ADENYLATE CYCLASE system
• PHOSPHATIDYLINOSITOL system
• TYROSINE KINASE system
• GUANYLATE CYCLASE system
• STEROID/THYROID/RETINOID SIGNALLING
ADENYLATE CYCLASE (AC) SYSTEM
• AC is activated via G-protein
• effector = membrane AC
• AC converts ATP to cAMP
• elevation of cytosolic cAMP
• cAMP is second messenger
cAMP action
• cAMP is allosteric activator of proteinkinases
• activated proteinkinases phosphorylate target proteins
• phosphorylated proteins (enzymes) have altered functions – cellular response
• ↑ degradation of storage fuels
• ↑ HCl secretion by gastric mucosa
• ↓ aggregation of blood platelets
Obrázek IX/5
ACTIVATION OF PROTEIN KINASE A (PKA) BY cAMP
• PKA - 2 catalytic and 2 regulatory subunits
• cAMP binds to regulatory subunits
• PKA phosphorylates cytosolic proteins
• PKA may enter nucleus and phosphorylate TFs
• heterotetramer dissociates
• active catalytic subunits of PKA are released
• phosphorylated TFs recruit co-activators
• gene expression is triggered
cAMP signalling
Hormones using cAMP as second messenger
• Calcitonin
• Chorionic gonadotropin
• Corticotropin
• Epinephrine
• Follicle-stimulating hormone
• Glucagon
• Luteinizing hormone
• Nor-epinephrine
• Lipotropin
• Melanocyte-stimulating hormone
• Parathyroid hormone
• Thyroid-stimulating hormone
• Vasopressin
Extracellular
side
GUANYLATE CYCLASE SYSTEM
Peptide hormone
(natriuretic factor)
Cytosolic
side
P
P
P
P
P
P
GTP
P
P
hydrolysis by
phosphodiesterases
• inactivation
• loss of cellular response
cGMP
• inhibited by VIAGRA
• prolonged cell response
• cellular response
• e.g. NO synthesis
P
PHOSPHATIDYL INOSITOL PHOSPHATE (PIP) SYSTEM
• principal molecule in the signalling is
phosphatidyl inositol-4,5-bis-phosphate (PIP2)
• PI3K phosphorylates PIP2 to PIP3
• membrane receptor trasmits signal
and activate effector – PI3 kinase
• phosphatidyl inositol-3,4,5-tris-phosphate (PIP3)
• PIP3 recruits tyrosin kinase (BTK) and
phospholipase C (PLC)
• activated PLC cleaves PIP2 to 2 fragments
• 2 second messengers!!!
• BTK phosphorylates PLC
• IP3 = inositol-1,4,5-triphophate
• DAG = 1,2-diacylglycerol
• IP3 binds calcium channel in ER
•Ca2+ binds protein kinase C (PKC)
• PKC then goes to plasma membrane
• channels open and releases Ca2+ in cytosol
•PKC is activated when both, i.e.
calcium and DAG are bound
• PKC phosporylates its target proteins
PIP
Important role in control
of cell division and proliferation
Protein Kinase C
Phosphorylates variety of target
proteins; e.g.: insulin receptor;
glucose carrier; CYP P450;
tyrosine hydroxylase etc.
• PIP system is activated via variety of stimuli; e.g. ACTH, epinephrine,
Neurotransmitters, growth factors, antigens
• Inactivation of PIP system: IP3
IP2
• PIP system mediates variety of effects; e.g. Glycogenolysis in liver cells;
Histamine secretion by mast cells; Serotonine release by blood platelets;
Insulin secretion by pancreatic islet cells; Smoth muscle contraction;
Epinephrine secretion by adrenal chromaffin cells; visual transduction
Ca2+ is released from ER
in response to hormones
or neurotransmitters
Ca2+
Endoplasmic Ca2+
reticulum
Ca2+
Calmodulin-Ca2+ complex
is an essential component
of many Ca2+ dependent
enzymes
calmodulin
Ca2+
Transinet increase of
intracellular Ca2+ favors
formation of complex
Ca2+
Ca2+
Ca2+
calmodulin
calmodulin
Ca2+
Ca2+
Ca2+
Ca2+
Complex
Calmodulin-Ca2+
active
enzyme
Ca2+
inactive
enzyme
substrate
product
TYROSINE KINASE (TK) SYSTEM
• membrane receptor – contains effector domain
• effector = tyrosine kinase (TK); protein kinase specific for phosphorylation
of tyrosine residue
• second messenger = O ? x IRS
• extracellular signals – insulin, nerve growth factor; epidermal growth factor
insulin
ATP
ADP
autophosphorylation
P
• catalytic activity of TK switched on
by insuline binding
P
P
• enhanced activity independent
of insuline binding
TYROSINE KINASE (TK) SYSTEM
• hormone binds TK = H-R complex = TK activation
• TK phosphorylates target proteins (e.g. phosphatases; amino acid
transporter; glucose transporter etc.) = CELLULAR RESPONSE
• autophosphorylation of TK ensures that TK activity is switched on even in
absence of hormone = long term effect of insulin
• insulin has general growth-promoting properties – it acts as metabolic activator
and growth factor almost in all cells in the body it acts
• SHORT-TERM effects = polysaccharide and fat synthesis
• LONG-TERM effects = nucleic acud and protein synthesis
OUTSIDE CELL
membrane
INSIDE
CELL
Nitric
oxide
1
2
3
4
5
1
2
3
4
5
G-prot
G-prot
G-prot
G-prot
second
messengers
Cyclic AMP
Cyclic GMP
Ca2+
DAG
PKA
PKG
Calmodulin
PKC
Multifunctional Dedicated
kinases
kinases
Protein substrates
receptors
Tyrosin
kinase
IP3
Protein substrates
Hormonal
signals
Proteins
Ser/Thr kinases
Protein substrates
Other phospholipases
STEROID AND THYROID HORMONES ACTION
• steroid/thyroid receptors – intracellular localization
• cytosolic - glucocorticoid; estrogen; androgen; progesterone; mineralocorticoid
(undergo nucle-cytosolic traslocation)
• nuclear – retinoid (RARs, RXRs), vitamine D, thyroid
• no second messenger
• DNA is the effector
• binding to DNA – triggering gene expression = cellular response
• enhanced synthesis of specific proteins
Hormone
travers
plasma
membrane
Hormone
Outside
of cell
cytosol or
nucleus
+
Receptor
Nuclear
translocation
HR complex
binding to DNA
cellular response
Free steroid hormone
Plasma-bound
steroid hormone
Biological response
hsp
NEW PROTEIN
HR
HR
HR
Protein
synthesis
HR
HR
translation
HR
mRNA
mRNA
transcription
HR
DNA
ligand
Transcription
Iniciation
komplex
Co-repressor
HR
RNA transcription
HR
Co-activator
DNA
PROMOTER REGION
Hormone response element
TR, VDR and RARs regulation of transcription: Hormone receptor (HR) is dimerized
and bound to DNA at hormone response element site. Without the ligand, transcription
is inactive due to the interaction of HR with co-repressor. When hormone binds to HR,
the bound co-repressor dissociates leading to an interaction between co-activator and
HR. These regulatory changes result in increased transcription.
Target organs and genes for steroid and thyroid hormones
Hormone class
Target organ
Target gene
Glucocorticoids
Liver
Liver, Retina
Kidney
Oviduct
Pituitary
tyrosine aminotransferase
tryptophan oxygenase
α-fetoprotein (down-regulation)
metallothionein
glutamine synthetase
Phophoenolpyruvate carboxykinase (PEPCK)
Ovalbumin
Pro-opiomelanocortin
Estrogens
Oviduct
Ovalbumin; Lysozyme
Progesterone
Oviduct
Uterus
Ovalbumin; Ovidin
Uteroglobine
Androgens
Prostate
Kidney
Oviduct
Aldolase
β-glucuronidase
Albumin
1,25-dihydroxyvimin D3
Intestine
Calcium-binding protein
Thyroid hormones
Liver
Pituitary
Carbamoyl phosphyte synthetase; Malic enzyme
Growth hormone; Prolactin (down-regulation)
HORMONE ACTION AND CARCINOGENESIS
Alteration of structure of any component in signal transduction system
Loss of metabolic control in a cell
Transformation of normal cell
• G-proteins
• insulin receptor
• thyroid/steroid hormone receptors
• DAG
Analogs encoded by specific VIRAL
ONCOGENES = proteins which bind
hormone (HR complex) but LACK
SWITCH OFF mechanism (lack of GTPase
activity; permanent TK activity; tight
binding of hormone
Analogs (PHORBOL ESTERS) = cause
activation of protein kinase C = stimulation
of tumor formation (mainly in presence
of carcinogen)
• Loss of metabolic control; uncontrolled cell growth; transformation
of a normal cell to a cancer cell