Medical Biotechnology Master’s Programmes
at the University of Pécs and at the University of Debrecen
Identification number: TÁMOP-4.1.2-08/1/A-2009-0011
SECOND MESSENGERS
Tímea Berki and Ferenc Boldizsár Signal transduction
Medical Biotechnology Master’s Programmes
at the University of Pécs and at the University of Debrecen
Identification number: TÁMOP-4.1.2-08/1/A-2009-0011
Second messengers
• Hydrophylic molecules: cAMP, cGMP, IP3, Ca2+
• Hydrophobic molecules (lipids): diacylglycerol (DAG), phosphatidylinositols
• Gases: NO,CO, (H2S)
General scheme of intracellular signaling
Second messengers activates intercellular
process
G-protein is activated and produces effector
Effector stimulates second messenger
synthesis Agonist activates
membrane bound receptor
Discovery of second messengers - cAMP
• E. W. Sutherland
• Adrenaline effect of the liver is mediated through cyclic-AMP
• 1971. Nobel Prize in Physiology and Medicine
Synthesis of cAMP
O
OH OH
ATP cAMP
AMP
H H H CH2
NH2
N N N
N O
O O
O P
O O
O P
O O O
P
Adenylyl cyclase
PPi
O
OH OH H H H CH2
NH2 N N N
N O
O O
P H H
cAMP phosphodiesterase
H2O H
O
OH OH H H H CH2
NH2
N N N
N O
H O
O P
O
cAMP activates Protein kinase A
Inactive PKA Activated PKA
R R
C C cAMP
cAMP cAMP
cAMP R
R
C C
C C R
R cAMP cAMP
cAMP cAMP
Regulatory subunit
Catalytic subunit
PKA targets
• Enzymes
• Stucture proteins
• Transcription factors: CREB
• CREB: dimeric form binds to cAMP-responsive elements (CRE)
CREB
CRE
Phospholipase C
Hormone
Receptor Plasma membrane
Cytoplasm
IP3 opens Ca2+ channel
Lumen of smooth endoplasmatic reticulum
IP3R
DAG PKC
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
IP3 IP3
GTP
b g a
G protein
PIP2
GTP
a PLC
IP3 receptor pathway
Hormone
Receptor
Plasma membrane
Cytoplasm
IP3R DAG
GTP
a PLC
PIP2
IP3 IP3
Ca2+
Lumen of smooth endoplasmatic reticulum
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Pump Pump Ca2+
channel
+ -
GTP
b g a
G protein
Ca2+
Ca2+
Gases as second messengers:
NO way!
• “Endothelium-derived relaxation factor” (EDRF):
mediator(s) produced by endothelial cells causing vasodilatation
• 1980s: NO!! [Nature 1983 Nov 10- 16;306(5939):174-6.]
• 1992: NO:“molecule of the year” (Science); “Nitric Oxide Society” established
• 1998: Nobel Prize in Physiology or Medicine – F.
Murad, R.F. Furchgott, L. Ignarro, S. Moncada
• ~3000 papers/year published about NO!
NO synthesis
NO synthase (NOS):
1 eNOS: endothelial
2 iNOS: inducible (eg. macrophages) 3 nNOS: neuronal
2 major domains:
1 N-term. Oxygenase (Heme-thiolate proteins)
2 C-term. Reductase (~NADPH-cytochromeP450 reductase) 3 Linker: calmodulin-binding sequence
L-Arg
H2N+ NH2 NH
NH+ 3 H O O
–
NADPH + O2 NADP+ + H2O
R NOHLA
1/2 NADPH + O2 1/2 NADP+ + H2O N
NH2 NH
NH+ 3 H O O
– HO
L-Citrulline
H2N + NO
NH
NH+ 3 H O O
– O
NO-cGMP pathway
Vascular lumen
Endothelial cell Smooth muscle cell
Acetylcholine
Shear stress
Bradykinin
L-arginine
L-citrulline
NO• NO•
GTP
cGMP
eNos GC Ca2+↑
Vasodilatation Platelet aggregation ↓ Smooth muscle growth ↓
Neutrophil adhesion ↓ NO• inactivation
Oxidative stress
ONOO- .OH M
B2
cGMP
Protein kinase G
• Ser/Thr protein kinase activated by cGMP
• Expressed by vascular smooth muscle cells,
platelets, endothel, heart muscle, fibroblasts, renal cells, leukocytes, nervous system
• Regulates smooth muscle relaxation, platelet function, sperm metabolism, cell division and nucleic acid synthesis
Functions of NO
• Vascular effect: vasodilatation
– e.g. Nitroglycerin: treatment of coronary disease (Angina pectoris)
– e.g.Viagra: erection
• Heart: contractility and heart rate ↓
• Immune system: macrophages produce NO to kill bacteria BUT in severe systemic infection (Sepsis) this leads to
generalised vasodilatation and SHOCK (Septic shock)
