chapter 16 lecture outlines cell communication essential cell biology third edition copyright ©...

Chapter 16 Lecture OutlinesCell Communication

EssentialCell Biology

Third Edition

Copyright © Garland Science 2010

CHAPTER CONTENTS

GENERAL PRINCIPLES OF CELL SIGNALINGG-PROTEIN–COUPLED RECEPTORSENZYME-COUPLED RECEPTORS

Figure 16-1 Essential Cell Biology (© Garland Science 2010)

Budding yeast cells are normal spherical (A) but when exposed to mating factor produced by neighboring yeast cells they extend a protrusion toward the source of the factor

GENERAL PRINCIPLES OFCELL SIGNALING

• Signals Can Act over a Long or Short Range• Each Cell Responds to a Limited Set of Signals,

Depending on Its History and Its Current State • A Cell’s Response to a Signal Can Be Fast or Slow• Some Hormones Cross the Plasma Membrane and

Bind to Intracellular Receptors• Some Dissolved Gases Cross the Plasma Membrane

and Activate Intracellular Enzymes Directly• Cell-Surface Receptors Relay Extracellular Signals

via Intracellular Signaling Pathways• Some Intracellular Signaling Proteins Act as

Molecular Switches• Cell-Surface Receptors Fall into Three Main Classes• Ion-channel–coupled Receptors Convert Chemical

Signals into Electrical Ones


Signal transduction is the process whereby one type of signalis converted to another.(B) a target cell converts an extracellular signal (molecule A) into an intracellular signal (molecule B)


Signal can act over long or short range. There are four types of cell communication: (A) endocrine: to long distance, (B) papacrine: to nearby neighbor

(C) Neuronal signaling, (D) contact-dependent: don’t need secreted molecule


Contact-dependent signaling controls nerve-cell production:Each future neuron delivers an inhibitory signal to the cells next to it to deter them from specializing as neurons too

Table 16-1 (part 1 of 2) Essential Cell Biology (© Garland Science 2010)

Table 16-1 (part 2 of 2) Essential Cell Biology (© Garland Science 2010)

Home work:List all the signal molecule, its site of origin, its destinationand function.

Quiz will be given next week.

You are expected to know how to spell these signal molecules.


Each cell responds to a limited set of signals:The same signal molecule can induce different responses in differenttarget cells. e.g. acetylcholine

Figure 16-5a Essential Cell Biology (© Garland Science 2010)

Figure 16-5b Essential Cell Biology (© Garland Science 2010)

Figure 16-5c Essential Cell Biology (© Garland Science 2010)

Figure 16-5d Essential Cell Biology (© Garland Science 2010)


An animal cell depends on multiple extracellular signals:

1. Every cell type displays a set of receptor proteins that enables it torespond to a specific set of signal molecules produced by other cells2. Most cells undergo a form of cell suicide, programmed cell death, or apoptosis if there is no signal


Extracellular signals can act slowly or rapidly


Extracellular signal molecules bind either to cell-surface receptors orto intracellular enzymes or receptors


Some extracellular signal molecule is large and hydrophilic, it needs receptor on cell surface to deliver signal to cell


Some small, hydrophobic extracellular signal can diffuseacross the membrane and binds to intracellular receptorin either the cytosol or the nucleus


Some small hydrophobic hormones binds to intracellularreceptors that act as transcription regulators


The steroid hormone cortical acts by activating a transcription regulator. Cortisol is one of the hormones produced by the adrenal glands in response to stress


Nitric oxide (NO) triggers smooth muscle relaxation in a blood-vesselwall:


1. Acetylcholine released by nerve terminal in the blood-vessel wall stimulates endothelial cells lining the blood vessel to make and release NO2. NO diffuse from endothelial cell to adjacent smooth muscle cells causing muscle cell relaxation


One target protein that can be activated by NO is guanyl cyclase.The activated cyclase catalyzes the production of cGTP from GTP


Many extracellular signals act via cell-surface receptors to change the behavior of the cell. The receptor protein activates one or moreintracellular signaling pathways, each mediate by a series of intracellular signaling molecules


Intracellular signaling protein can relay, amplify, integrate and distribute the incoming signal


Many intracellular signaling proteins act as molecular switches(A)Signaling by phosphorylation : signaling proteins are activated by the addition of a phosphate group by protein kinase, and inactivated by removal of the phosphate by protein phosphatase. Protein kinase phosphates serine/threonine (called ser/thr kinase) or tyrosine (called tyrosine kinase)

(B) Signaling by GTP-binding protein: a GTP-binding signaling protein is induced to exchange its bound GDT for GTP (i.e. adds aphosphate to the protein). The hydrolysis of the bound GTP to GDP Then switches the protein off


Cell surface receptors fall into three basic classes:1. An ion-channel-coupled opens or closes in response to binding ofits extracellular signal molecule. These channels are also called‘transmitter-gated ion channels


2. G-protein-coupled receptor: When a G-linked receptor binds its extracellular signal molecule, the signal is passed first to aGTP-binding protein (G protein) that is associated with the receptor. The activated G protein then leaves the receptor and turn on a targetenzyme (or ion channel) in the membrane


3. Enzyme-coupled receptors: An enzyme-linked receptor binds its extracellular signal molecule, switching on an enzyme activity, either at the other end of the enzyme or other associated enzyme

EGF signaling pathway

Table 16-2 Essential Cell Biology (© Garland Science 2010)

Ion-channel-coupled receptors convert chemical signals intoelectrical ones:Fig 12.24 the neuron-muscle junction. When the neurotransmitterbinds , this type of receptor alters its conformation so as to open an ion channel in the plasma membrane

Movie 16.1

G-PROTEIN–COUPLED RECEPTORS

• Stimulation of GPCRs Activates G-Protein Subunits

• Some G Proteins Directly Regulate Ion Channels

• Some G Proteins Activate Membrane-bound Enzymes

• The Cyclic AMP Pathway Can Activate Enzymes and Turn On Genes

• The Inositol Phospholipid Pathway Triggers a Rise in Intracellular Ca2+

• A Ca2+ Signal Triggers Many Biological Processes

• Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability


Bind to signal molecule (ligand)

Binding to G protein inside the cell

G-protein-coupled receptors:


Inactivated state


The alteration of the α subunit of G protein allows it to exchange its GDP to GTP. This causes the G protein to break up into two activate components- α subunit and aβγ complex, both can regulate the activity of target proteins in the plasma membrane

Binding of signal molecule to receptor causes the conformation change of this receptor, which in turn alters the conformation of the G protein


The G-protein subunit switches itself off by hydrolyzing its bound GTP

Movie 16.2


G-protein-linked signaling :Some G-protein regulate ion channels: e.g. G protein couple receptor activation to opening of K+ channels in the plasma membrane of heart muscle cells

activated complex binds toand opens a K+ channel

inactivation of the a subunit byhydrolysis of its bound GTP returns the G protein to itsinactive state, allowing the K+ channel to close


1. Some G proteins activate membrane-bound enzymes: enzyme activated by G proteins catalyze the synthesis of intracellular second-messenger molecules

cAMP as a second messenger

http://www.youtube.com/watch?v=MF0EjhcpAos

http://www.youtube.com/watch?v=MF0EjhcpAos

Second messenger: small molecule formed in or released into the cytosol in response to an extracellular signal (first messenger) that helps to relay the signal to the interior of the cell. Examples include cAMP, IP3 and Ca 2+


c-AMP pathway: c-AMP is synthesized by adenylyl cyclase and degraded byc-AMP phosphodiesterase


Example of c-AMP pathway: c-AMP (second messenger) concentration rises rapidly in response to an extracellular signal (first messenger)

A nerve cell in culture responds to the binding of the neurotransmitter serotoninto a G-protein-linked receptor by synthesizing c-AMP

c-AMP pathway: cyclic-AMP-dependent protein kinase (PKA)

1.c-AMP exerts various effects mainly by activating the enzyme PKA2.The binding of c-AMP causes the conformation change and activate PKA. The activated PKA then phosphorates certain intracellular proteins on its serine or threonine sites, thus altering their activity


Example of cell using c-AMP pathway:Adrenaline stimulates glycogen breakdown in skeletal muscle cells


A rise in intracellular cyclic AMP can activate gene transcription

Movie 16.3

G-protein-linked signaling : Inositol phospholipid pathway (PIP2):

Signal molecule binds to G-protein-linked receptor

PIP2 (phosphoinositol diphosphate) phospholipase C

IP3 + DAG

DAG activates protein kinase C , IP3 open calcium channels from ER


Phospholipase C activates two signaling pathways


G-protein-linked signaling :Inositol phospholipid pathway:

1. A Ca 2+ signal triggers many biological processExample: the fertilization of an egg by a sperm triggers an increase cytosolic Ca 2+ in the egg

2. The effect of Ca 2+ in the cytosol are largely indirect, they are mediated through the interaction of Ca 2+ + with various transducer protein, known collectively as Ca 2+ binding proteins, such as calmodulin.

3. Once Ca 2+ binds with calmodulin, it forms Ca 2+ /calmodulin-dependent protein kinase (CaM-kinases), and they influence otherprocesses in the cell by phosphorylating selected proteins

Movie 16.4


Structure of Ca 2+ /calmodulin: (A) Calmodulin molecule has a dumbbell shape with two globular ends connected by a long, flexible a helix, each end has two Ca 2+ binding domains, (B) The confor-mational changes in Ca 2+ /calmodulin that occur when it binds to atarget protein

Movie 16.5


Intracellular signaling cascades can achieve astonishing speed,sensitivity, and adaptability:

e.g. photoreceptor in the eye:When the rod cell is stimulated by light,a signal is relayed from the rhodopsinmolecule in the discs, through the crystalof the outer segment, to Na+ channels in the plasma membrane of the outer segment.The Na+ channels close in response to thesignal, producing a change in the membranepotential of rod cell (hyper-polarization).The change of membrane potential altersthe rate of neurotransmitter release fromthe synaptic region of the cell

Light reception by eye and signal transduction to SCN (suprachiasmatic nuclei). Rods and cones, photoreceptor cells located in the inner retina, mediate the perception of light.

http://molinterv.aspetjournals.org/content/2/8/484/F2.large.jpg


the light-induced signaling cascade in rod photoreceptorcells greatly amplifies thelight signal

ENZYME-COUPLED RECEPTORS

• Activated RTKs Recruit a Complex of Intracellular Signaling Proteins

• Most RTKs Activate the Monomeric GTPase Ras

• RTKs Activate PI 3-Kinase to Produce Lipid Docking Sites in the Plasma Membrane

• Some Receptors Activate a Fast Track to the Nucleus

• Multicellularity and Cell Communication Evolved Independently in Plants and Animals

• Protein Kinase Networks Integrate Information to Control Complex Cell Behaviors

Enzyme-coupled receptors

1. Enzyme-coupled receptors are transmembrane proteins that display their ligand-binding domain on the outer surface of the plasma membrane

2. The cytoplasmic domain of the receptor either acts as an enzyme itself or forms a complex with another protein thatacts as an enzyme

3. Receptor tyrosine kinases (RTKs) is the largest class of enzyme-coupled receptors in made up those with a cytoplasmicdomain that functions as a tyrosine protein kinase, phosphorylating specific tyrosine on selected intracellular proteins


Activated receptor tyrosine kinase assemble a complex of intracellular signaling proteins


RTKs activate Ras1.Ras: a small protein that is bound by a lipid tail to the cytoplasmic face of the plasma membrane. The binding of Ras-activating protein makes Ras exchange its bound GDP to GTP. The activated Ras then stimulates the next steps in the signling pathway

2. Adaptor: protein for helping to build a large signaling aggregate by coupling the receptor to other proteins. Here the adaptor recruits and stimulates Ras-activating protein


Ras activates a MAP-kinase Phosphorylation cascade1.MAP kinase: protein kinase that performs a crucial step in relaying signals from cell-surface receptors to the nucleus. It is the final kinase in a 3-kinase sequence (mitogen-activated protein kinase)

2. MAP kinase phosphorylates various downstream target proteins. These target can include other protein kinase, and most important, gene regulatory proteins that control gene expression. Changes in gene expression and protein activity result in complex changes in cell behaviors such as proliferation and differentiation

MAP Kinasehttp://www.youtube.com/watch?v=bYioSvT33cA

Cancer parthway (Ras pathway)http://www.youtube.com/watch?v=L9dsg0wJRR8&feature=related

The MAP-Kinase (MAPK) signalling pathway (5 min)http://www.youtube.com/watch?v=r7GoZ9vFCY8

http://www.youtube.com/watch?v=bYioSvT33cA

http://www.youtube.com/watch?v=L9dsg0wJRR8&feature=related

http://www.youtube.com/watch?v=L9dsg0wJRR8&feature=related

http://www.youtube.com/watch?v=r7GoZ9vFCY8


RTKs can activate the PI-3-Akt signaling pathway1.An extracellular survival signal, such as IGF (insulin-like growthfactor) family, activate an RTK, which recruits and activates PI-3-kinase pathway to promote cell growth and survival

2. PI3-kinase (phosphoinositide 3-kinase) is an enzyme which can phoshphorylate inositol phospholipid in the plasma membrane3. These phosphorylated lipids become docking sites for specificintracellular signaling proteins, which relocate from cytosol to membrane, where they can activate one another

The PI3K/AKT signalling pathwayhttp://www.youtube.com/watch?v=ewgLd9N3s-4&NR=1

PI3K/AKT Pathway and Cancerhttp://www.youtube.com/watch?v=Jq4ZOu2UbqA&feature=related

http://www.youtube.com/watch?v=ewgLd9N3s-4&NR=1

http://www.youtube.com/watch?v=Jq4ZOu2UbqA&feature=related

http://www.youtube.com/watch?v=Jq4ZOu2UbqA&feature=related


Activated Akt promotes cell survival : 1. One of the relocated signaling proteins in the PI-3-kinase pathwayis the serine/threonine protein kinase Akt (also called protein kinase B (PKB)). This pathway called PI-3-kinase-Akt singaling pathway2. Akt promotes the growth and survival of may cell types often byinactivating the signaling proteins it phosphorylates. It also stimulatecells to grow in size

3. Mechanism of PI-3-kinase-Akt singaling to promote cell survival:Akt phosphorylates and inactivates a cytosolic protein, Bad, to inhibits apoptosis in cells


Akt also stimulates cells to grow in size by ativating Tor:

1.The binding of growth factor to and RTKactivates the PI-3-kinase-Akt signaling pathway

2.Akt then indirectly activate Tor (by phos-phorylating and inhibiting a protein that helpsto keep Tor shut down)

3. Tor, a serine/threonine kinase, stimulatesprotein synthesis and inhibits protein degradation

Pop-up quiz:1.Give two expalmes of G-protein-coupled singaling pathway

2.Give two examples of enzyme-coupled signaling pathway

Answere:1.G-protein-coupled: adenyl cyclase, C-AMP, PKAPIP2, DAG & IP3

2.RTK:Ras, MAPKRas, PI-3-kinase-Akt signaling

How we know: untangling cell signaling pathways1. Cannot reveal the whole signaling pathway in a singleexp.2. Needs to figure out piece by piece of how all the links in the chain fit together, and how each contributes to the cell’s responseto and extracellular signal such as insulin

Exp: 1.Check the ‘stimulated phosphorylation’ :Stimulate cells, separate all cellular proteins by gel, use antibodyto detect phosphorylated proteins

2. Close encounters:Once the activated proteins have been identified, one can determinewhich proteins interact with them using ‘co-immunoprecipitation’.If two proteins are dragged down at the same time, very likelythey are interact with each other. In this way, researchers can identify which proteins interact when an extracellular signal molecule stimulates cells

Mutant proteins can help to determine exactly where an intracellularsignaling molecule binds


Mutant proteins can help to determine exactly where an intracellularsignaling molecule binds


3. ‘Jamming the pathway’:To test the function: use the recombinant DNA technology toinsert the gene in the form of constantly active form, to see ifthis mimics the effect of the extracellular signale.g. A constitutively active form of Ras transmits a signal even in the absence of an extracellular signal molecule

On the contratory, scientist also needs to inactivethe protein or its gene and see weather the signalingpathway is affected. e.g. to induce a ‘dominant-negtive’mutant form of Ras, i.e. Ras binds to GTP too tightly tobe activated

4. ‘Ordering the pathway’:Treat animals (fruit flies or nematode worms) with mutagen and then looking for mutants in which a signaling pathway is notfunctioning properly


Genetic analysis reveals the order in which intracellular signalingproteins act in a pathway


Some Enzyme-linked receptors activate a fast track to the nucleus1.Some receptors use a more direct route to control gene expression2.Cytokines binds to receptor, which activates a type of regulatoryproteins called STATS (signal transducers and activators of transcription)

3. The signaling pathway of the cytokines: Binding of a cytokine to its receptor causes associated tyrosine kinase (called janus kinases, or JAKs) to cross phosphorylate and activate one another they phosphorylate the receptor protein on tyrosine

4. gene regulatory proteins, called STATs, attach to thephosphotyrosine site of the receptor to be activated STATs dissociate from the receptor, dimerize, migrate to the nucleus activate the transcription of specific target genes5. example: hormone prolactin which stimulates breast cell to makemilk


The notch receptor itself is a transcription regulator1.Notch receptor generate an even more direct signaling pathway which controls the development of neural cells in Drosophila

2. In this pathway, the receptor itself acts as a transcription regulator

3. Mechanism: when activated by the binding of Delta ,the Norch receptor is cleaved. The released cytosolic tail of the receptor heads to the nucleus to activate the appropriate set of Notch-responsive genes

1. Plants and animals have been evolving independently for more than a billion years

2. Like animals, plants make extensive use of transmembrane cell-surface receptors, especially enzyme-coupled receptors.e.g. the spindly weed Arabidopsis Thaliana (Fig 1-33) has hundreds of genes encoding receptor serine/threonine kinase, but theirserine/threonine kinase receptor is very different to animal’s

3. Plant receptors trigger a large variety of cell signaling prosessinvolves in plant growth, development and disease resistance

4. Plant don’t use RTKs, steroid-hormone-type nuclear receptors,or c-AMP, they seem to use few GPCRs

5. One of the best-studied signaling pathways in plant mediatesthe response of cells to ethylene- a gaseous hormone that regulatesa diverse array of development processes, including seed germination and fruit ripening


Signaling pathways can be highly interconnected (cross-talk)Protein kinases in both pathways phosphorylate many proteins, including proteins belonging to the other pathway

Movie 16.7

Movie 16.8

Movie 16.9


Some intracellular signaling proteins serve to integrate incoming signals

chapter 16 lecture outlines cell communication essential cell biology third edition copyright ©...

Documents

target cell

receptors slide

intracellular receptors

types of cell communication

controls nervecell production

chemical signals

extracellular signal

secreted molecule slide