signal transduction and the related disorders department of pathophysiology shanghai jiao-tong...

Signal Transduction and thSignal Transduction and the Related Disorderse Related Disorders

Department of PathophysiologyDepartment of Pathophysiology

Shanghai Jiao-Tong University School of MedicineShanghai Jiao-Tong University School of Medicine

CHAPTER 1CHAPTER 1

General Introduction of Cell Signal TransductiGeneral Introduction of Cell Signal Transductionon

Concept of Cell Signaling

The process in which cells sense the extracellular stimuli through membranous or intracellular receptors, transduce the signals via intracellular molecules, and thus regulate the biological function of the cells

Signal molecules

Physical signals Light, electronic, mechanic, UV, heat, volume or osmotic, etc

Chemical signals Hormones, neurotransmitters, Growthe factors, cytokines, odor molecules, ATP, active oxygen, drugs, toxins, etc

Endocrine: Act on a far away organ via blood circulation Paracrine: Act on a nearby target Autocrine: Act on itself after secreted Synaptic: Presynaptic to postsynaptic,

Autocrine

Endocrine Paracrine

Synaptic

Modes for the function of endogenous signals

The primary pathways of cell signalling

G-protein-mediated pathway Adenylate cyclase mediated pathway

Phospholipase mediated pathway

Small G-protein-mediated pathway

Non-G-protein-mediated pathway Receptor tyrosine kinase mediated pathway

Receptor serine/threonine kinase mediated pathway

Receptor guanilate cyclase mediated pathway

Intracellular (unclear) receptor mediated pathway

G-protein-mediated pathway

High moleular weight G-protein (trimeric GTP-binding regulatory protein）

Low moleular weight G-protein Ras

Classification of G-protein

G-proteins, coupled with members of the seven transmembrane domain of the receptor superfamily, are regulatory proteins that act as molecular switches. They control a wide range of biological processes

Regulation of G-Protein Activity

G protein-coupled receptors exhibit a common structural motif consisting of seven membrane spanning regions. Receptor occupation promotes interaction between the receptor and the G protein on the interior surface of the membrane. This induces an exchange of GDP for GTP on the G protein subunit and dissociation of the subunit from the heterodimer. Depending on its isoform, the GTP- subunit complex mediates intracellular signaling either indirectly by acting on effector molecules such as adenylyl cyclase (AC) or phospholipase C (PLC), or directly by regulating ion channel or kinase function.

Regulation of G-Protein Activity


Adenylate cyclase mediated pathway

Phospholipase mediated pathway

Small G-protein-mediated pathway


cAMP can activate protein kinase A(PKA), which can phosphorylate CREB （ bi

nding protein of cAMP-respones element） and initiate gene transcription.CRE is cAMP response element in DNA.

Adenylate cyclase mediated pathway

Phospholipase C mediated pathway


Non-G-protein-mediated pathway

Receptor tyrosine kinase mediated pathway

Receptor tyrosine kinases transmit signals across the plasma membrane, from the cell exterior to the cytoplasm.

The interaction of the external domain of a receptor tyrosine kinase with the ligand, often a growth factor, up-regulates the enzymatic activity of the intracellular catalytic domain, which causes tyrosine phosphorylation of cytoplasmic signaling molecules.



Receptor guanilate cyclase mediated pathway

Intracellular (unclear) receptor mediated pathway

Receptor tyrosine kinases transmit signals across the plasma membrane, from the cell exterior to the cytoplasm.

The interaction of the external domain of a receptor tyrosine kinase with the ligand, often a growth factor, up-regulates the enzymatic activity of the intracellular catalytic domain, which causes tyrosine phosphorylation of cytoplasmic signaling molecules.


Mechanism of Tyrosine Kinase Receptors

When hormone binds to the extracellular domain the receptors aggregate

When the receptors aggregate, the tyrosine kinase domains phosphorylate

the C terminal tyrosine residues


This phosphorylation produces binding sites for proteins with SH2 domains. GRB2 is one of these proteins. GRB2, with SOS bound to it, then binds to the receptor complex. This causes the activation of SOS.


SOS is a guanyl nucleotide-release protein (GNRP). When this is activated, it causes certain G proteins to release GDP and exchange it for GTP. Ras is one of these proteins. When ras has GTP bound to it, it becomes active.


Activated ras then causes the activation of a cellular kinase called raf-1


Raf-1 kinase then phosphorylates another cellular kinase called MEK. This cause the activation of MEK


Activated MEK then phosphorylates another protein kinase called MAPK causing its activation. This series of phosphylating activations is called a kinase cascade. It results in amplification of the signal


Among the final targets of the kinase cascade are transcriptions factors (fos and jun showed here). Phosphorylation of these proteins causes them to become active and bind to the DNA, causing changes in gene transcription


Signal Transduction Through Receptor Tyrosine Kinases

(1) Type I and type II receptors for TGF(beta) in a cell prior to binding of the growth factor.

(2) Binding of growth factor results in clustering of type I and type II receptors, and phosphorylation of type I receptors by type II receptors.

(3) The activated type I receptors then phosphorylate particular receptor-mediated Smads.

(4) These Smads then bind to other Smads (co-Smads), and together they enter the nucleus.


Intracellular (nuclear) receptor mediated pathway

Basic Structure of nuclear receptor

Hormone-bindind domain

DNA-binding domain

Transcription-activating domain

The signal pathway by steroid hormones

nuclear receptor mediated pathway

The signal pathway by steroid hormones

Networks of Signal Transduction

600 G protein-coupled receptors

Multiple gene families and combinations

of G protein subunits

20G isoforms

6 G isoforms

12 G isoforms

Multiple gene families for selected effector proteins

Adenylyl cyclases

Phospholipases

Ion channels

+

+

The magnitude of amplification within this cellular cascade structure often exceeds 10+4. That is, the binding of one molecule of ligand to a cell-surface receptor leads a change of 10,000-fold in the intracellular concentration of a metabolic product.

Cascade structure of cellular signal pathways

CHAPTER CHAPTER 22

Dysfunction of cellular signal

transduction in diseases

Aberrant Signal in cell signaling

Aberrant Receptor in cell signaling

Aberrant G-protein in cell signaling

Aberrant Intracellular Signaling

Multiple Abnormalities in cell signaling

Aberrant Signal in cell signaling

ischemia, epilepsy, neurodegenerative diseases

extracellular glutamate/aspartic acid

NMDAR activation

Ca2+ influx

[Ca2+]i , activation of enzymes

excitatory intoxication

Receptor-based diseases

Alterations in number, structure or function of receptors will lead to disorder in cellular signal transdution

Up-regulation/hypersensitivity

Down-regulation/desensitization

Receptor Gene Mutation

Aberrant Receptor in cell signaling

Myasthenia Gravis is an autoimmune receptor disorder in which antibodies form against acetylcholine(Ach) nicotinic postsynaptic receptors at the neuromuscular junction

Myasthenia Gravis

Ach

The Neuromuscular Junction

AchR

anti n-AchR

influx of Na

Contraction of muscle fiber

mechanism

manifestations

Drooping of the eyelidsDouble visionDifficulty smiling, speaking, swallowingDifficulty raising the armsDifficulty walkingDifficulty breathing if chest muscle are affected

Autoimmune Thyroid Diseases

hyperthyroidism (Grave's disease)

hypothyroidism (Hashimoto's thyroiditis)

DG

hyperthyroidism

Stimulatory Ab

TSH-R

Gs Gq

AC

cAMP

Thyroid proliferation & secretion

PLC

IP3

Ca2+ PKC

hypothyroidism

Blocking Ab

TSH-R 295~302

385~395

AA residues

Binding of TSH to R↓

mechanism

manifestations

Grave's disease

Stimulatory antibodies mimic the function of TSH Stimulating thyroid hormone synthesis, secretion, a

nd thyroid growth female:male incidence -- 5:1 to 10:1diffusely enlarged goiter

Hashimoto's thyroiditis

manifestations

Inhibitory antibodies antaonize the function of TSH Inhibiting thyroid hormone synthesis, secretion, and thy

roid growth Thyroid gland is gradually destroyed Myxedema

Receptor Gene Mutation--Genetic insulin-resistant diabetes

NIDDM is a chronic metabolic syndrome defined by resistance to the hormone insulin. This leads to inappropriate hyperglycaemia (increased blood sugar levels) and deranged metabolism of carbohydrate, fats and proteins.

Diabetes Mellitus Type 1


Non-Insulin dependent diabetes mellitus, NIDDM

The cause of Diabetes Mellitus Type 2 is not known, but it may involve a defect or change in the insulin receptor (IR).

mechanism

Disturbances in

synthesis

transfer to the membrane

affinity to insulin

RPTK activation

proteolysis

Genetic insulin-resistant diabetes

IR gene mutations


G protein-based disease

pituitary tumor

GHRH--Growth-hormone-releasing hormone

GH--Growth-hormone

GHRHGHRH

Pituitary

GHRH Receptor

GsαGsα(+)cAMPcAMP GH secretionGH secretion(-)

somatostatinsomatostatin

GiGi

mechanism

Gs gene mutation

GTPase activity

Persistent activation of Gs

Persistent activation of AC

cAMP

Acromegaly or Gigantism

Pituitary proliferation and secretion

manifestations

G-protein modification——cholera

lumen of intestine

GsCTCTAC

cAMP ↑ ↑ ↑

Cl-H2O Na+

CT--Cholera toxin Gs ribosylation at Arg201

manifestations

Diarrhea

Dehydration

Circulation failure

Aberrant Intracellular Signaling

The intracellular signaling involves various messengers, transducers and transcription factors. Disorders can occur in any of these settings.

WNT sinal pathway

Wnt-1 was found as an oncogene activated by the Mouse Mammary Tumor Virus in murine breast cancer. APC was first isolated as a tumor suppressor gene in human colon cancer. After establishing that APC and beta-catenin bind to each other activating mutations in the human beta-catenin gene were found in human colon cancer and melanomas .These mutations alter specific beta-catenin residues important for GSK3 phosphorylation and stability .The role for Frat/GBP in cancer is illustrated by its activation by proviral insertion in mouse lymphomas. Interestingly, mutations in the human AXIN1 gene were reported in human hepatocellular carcinomas. TCF1 can also act as a tumor suppressor gene , as Tcf1 mutant mice develop adenomas in the gut and mammary glands

Cancer

Multiple Abnormalities in Signaling Pathway

In the development of diseases, the aberrant cellular signal transduction usually involves multiple molecules or pathways. Such diseases include type-2 diabetes mellitus, cancers, hypertension, and so on

Multifactor Aberrancies and Cancer (Enhancement of proliferating signals)

Ligands (GFs)

Receptors (overexpression, activation of TPK)

Intracellular transducers：

Ras mutation Ras-GTPase Ras activation Raf MEK ERK Proliferation

Cancer

Multifactor Aberrancies and Cancer (Deficits in proliferation-inhibiting signal)

Smad2 SARA

Smad2

Smad2Smad4

Smad4

P300

Fast2P300

Smad4 Smad2

Fast2

-P

-P

-P

P15、P21

Smad6,7

Cell memberane

Cytosal

Nuclear membrane

Ⅱ Ⅰ Ⅱ Ⅰ

GS

（TGF-β ）2

（—）

Principles for Treatment

To regulate the level of extracellular molecules

To regulate the structure and the function of receptors

To regulate the level and modifications of intracellular

messenger molecules and transducers

To regulate the level of nuclear transcription factors

Target Therapy

Chr.9

abl

bcr

Chr.22

Chr.9+

bcr-abl

Ph

FUSION PROTEINWITH TYROSINEKINASE ACTIVITY

The Philadelphia Chromosome: t(9;22) Translocation

Structure of BCR-ABL Fusion Proteins

p210Bcr-Abl Fusion Protein Tyrosine Kinase

Extracellular space

Y177

BAP-1 GRB2

Cytoplasm

SH3 SH2 SH1

CBL SHC CRKL

Extracellular space

Y177

BAP-1 GRB2

Cytoplasm

SH3 SH2 SH1

CBL SHC CRKL

Gleevec®-Tyrosine Kinase Inhibitor

Bcr-Abl

ATP

Substrate

STI571

Y = TyrosineP = Phosphate

Bcr-Abl

Substrate

PPP

P

Bcr-Abl

ATP

Substrate

STI571

Y = TyrosineP = Phosphate

Bcr-Abl

Substrate

PPP

P

Goldman JM. Lancet. 2000;355:1031-1032.

signal transduction and the related disorders department of pathophysiology shanghai jiao-tong...

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