Essential Cell Biology Third Edition Chapter 16 Lecture

Essential Cell Biology Third Edition Chapter 16 Lecture Outlines Cell Communication Copyright © Garland Science 2010

CHAPTER CONTENTS GENERAL PRINCIPLES OF CELL SIGNALING G-PROTEIN–COUPLED RECEPTORS ENZYME-COUPLED RECEPTORS

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

GENERAL PRINCIPLES OF CELL 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 signal is converted to another. (B) a target cell converts an extracellular signal (molecule A) into an intracellular signal (molecule B) Figure 16 -2 Essential Cell Biology (© Garland Science 2010)

GENERAL PRINCIPLES OF CELL 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 can act over long or short range. There are four types of cell communication: (A) endocrine: to long distance, (B) papacrine: to nearby neighbor Figure 16 -3 Essential Cell Biology (© Garland Science 2010)

(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 Figure 16 -4 Essential Cell Biology (© Garland Science 2010)

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 destination and function. Quiz will be given next week. You are expected to know how to spell these signal molecules.

GENERAL PRINCIPLES OF CELL 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

Each cell responds to a limited set of signals: The same signal molecule can induce different responses in different target cells. e. g. acetylcholine Figure 16 -5 Essential Cell Biology (© Garland Science 2010)

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

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

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

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

An animal cell depends on multiple extracellular signals: Figure 16 -6 Essential Cell Biology (© Garland Science 2010)

1. Every cell type displays a set of receptor proteins that enables it to respond to a specific set of signal molecules produced by other cells 2. Most cells undergo a form of cell suicide, programmed cell death, or apoptosis if there is no signal

GENERAL PRINCIPLES OF CELL 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

Extracellular signals can act slowly or rapidly Figure 16 -7 Essential Cell Biology (© Garland Science 2010)

GENERAL PRINCIPLES OF CELL 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

Extracellular signal molecules bind either to cell-surface receptors or to intracellular enzymes or receptors Figure 16 -8 Essential Cell Biology (© Garland Science 2010)

Some extracellular signal molecule is large and hydrophilic, it needs receptor on cell surface to deliver signal to cell Figure 16 -8 a Essential Cell Biology (© Garland Science 2010)

Some small, hydrophobic extracellular signal can diffuse across the membrane and binds to intracellular receptor in either the cytosol or the nucleus Figure 16 -8 b Essential Cell Biology (© Garland Science 2010)

Some small hydrophobic hormones binds to intracellular receptors that act as transcription regulators Figure 16 -9 Essential Cell Biology (© Garland Science 2010)

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 Figure 16 -10 Essential Cell Biology (© Garland Science 2010)

GENERAL PRINCIPLES OF CELL 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

Nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall: Figure 16 -11 a Essential Cell Biology (© Garland Science 2010)

1. Acetylcholine released by nerve terminal in the blood-vessel wall stimulates endothelial cells lining the blood vessel to make and release NO 2. NO diffuse from endothelial cell to adjacent smooth muscle cells causing muscle cell relaxation Figure 16 -11 b Essential Cell Biology (© Garland Science 2010)

One target protein that can be activated by NO is guanyl cyclase. The activated cyclase catalyzes the production of c. GTP from GTP Figure 16 -11 c Essential Cell Biology (© Garland Science 2010)

GENERAL PRINCIPLES OF CELL 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

Many extracellular signals act via cell-surface receptors to change the behavior of the cell. The receptor protein activates one or more intracellular signaling pathways, each mediate by a series of intracellular signaling molecules Figure 16 -12 Essential Cell Biology (© Garland Science 2010)

Intracellular signaling protein can relay, amplify, integrate and distribute the incoming signal Figure 16 -13 Essential Cell Biology (© Garland Science 2010)

GENERAL PRINCIPLES OF CELL 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

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) Figure 16 -14 Essential Cell Biology (© Garland Science 2010)

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

GENERAL PRINCIPLES OF CELL 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

Cell surface receptors fall into three basic classes: 1. An ion-channel-coupled opens or closes in response to binding of its extracellular signal molecule. These channels are also called ‘transmitter-gated ion channels Figure 16 -15 a Essential Cell Biology (© Garland Science 2010)

2. G-protein-coupled receptor: When a G-linked receptor binds its extracellular signal molecule, the signal is passed first to a GTP-binding protein (G protein) that is associated with the receptor. The activated G protein then leaves the receptor and turn on a target enzyme (or ion channel) in the membrane Figure 16 -15 b Essential Cell Biology (© Garland Science 2010)

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 Figure 16 -15 c Essential Cell Biology (© Garland Science 2010)

EGF signaling pathway

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

GENERAL PRINCIPLES OF CELL 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

Ion-channel-coupled receptors convert chemical signals into electrical ones: Fig 12. 24 the neuron-muscle junction. When the neurotransmitter binds , 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 Ca 2+ • A Ca 2+ Signal Triggers Many Biological Processes • Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability

G-protein-coupled receptors: Bind to signal molecule (ligand) Binding to G protein inside the cell Figure 16 -16 Essential Cell Biology (© Garland Science 2010)

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 Ca 2+ • A Ca 2+ Signal Triggers Many Biological Processes • Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability

Figure 16 -17 Essential Cell Biology (© Garland Science 2010)

Inactivated state Figure 16 -17 a Essential Cell Biology (© Garland Science 2010)

Binding of signal molecule to receptor causes the conformation change of this receptor, which in turn alters the conformation of the G protein 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 a βγ complex, both can regulate the activity of target proteins in the plasma membrane Figure 16 -17 b Essential Cell Biology (© Garland Science 2010)

The G-protein a subunit switches itself off by hydrolyzing its bound GTP Figure 16 -18 Essential Cell Biology (© Garland Science 2010)

Movie 16. 2

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 Ca 2+ • A Ca 2+ Signal Triggers Many Biological Processes • Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability

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 bg complex binds to and opens a K+ channel inactivation of the a subunit by hydrolysis of its bound GTP returns the G protein to its inactive state, allowing the K+ channel to close Figure 16 -19 Essential Cell Biology (© Garland Science 2010)

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 Ca 2+ • A Ca 2+ Signal Triggers Many Biological Processes • Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability

1. Some G proteins activate membrane-bound enzymes: enzyme activated by G proteins catalyze the synthesis of intracellular second-messenger molecules Figure 16 -20 Essential Cell Biology (© Garland Science 2010)

c. AMP as a second messenger http: //www. youtube. com/watch? v=MF 0 Ejhcp. Aos

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 c. AMP, IP 3 and Ca 2+

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 Ca 2+ • A Ca 2+ Signal Triggers Many Biological Processes • Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability

c-AMP pathway: c-AMP is synthesized by adenylyl cyclase and degraded by c-AMP phosphodiesterase Figure 16 -21 Essential Cell Biology (© Garland Science 2010)

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 serotonin to a G-protein-linked receptor by synthesizing c-AMP Figure 16 -22 Essential Cell Biology (© Garland Science 2010)

Table 16 -3 Essential Cell Biology (© Garland Science 2010)

c-AMP pathway: cyclic-AMP-dependent protein kinase (PKA) 1. c-AMP exerts various effects mainly by activating the enzyme PKA 2. 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 Figure 16 -23 Essential Cell Biology (© Garland Science 2010)

A rise in intracellular cyclic AMP can activate gene transcription Figure 16 -24 Essential Cell Biology (© Garland Science 2010)

Movie 16. 3

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 Ca 2+ • A Ca 2+ Signal Triggers Many Biological Processes • Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability

G-protein-linked signaling : Inositol phospholipid pathway (PIP 2): Signal molecule binds to G-protein-linked receptor PIP 2 (phosphoinositol diphosphate) phospholipase C IP 3 + DAG activates protein kinase C , IP 3 open calcium channels from ER

Phospholipase C activates two signaling pathways Figure 16 -25 Essential Cell Biology (© Garland Science 2010)

Table 16 -4 Essential Cell Biology (© Garland Science 2010)

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 Ca 2+ • A Ca 2+ Signal Triggers Many Biological Processes • Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability

G-protein-linked signaling : Inositol phospholipid pathway: 1. A Ca 2+ signal triggers many biological process Example: the fertilization of an egg by a sperm triggers an increase cytosolic Ca 2+ in the egg Figure 16 -26 Essential Cell Biology (© Garland Science 2010)

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+ /calmodulindependent protein kinase (Ca. M-kinases), and they influence other processes 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 conformational changes in Ca 2+ /calmodulin that occur when it binds to a target protein Figure 16 -27 Essential Cell Biology (© Garland Science 2010)

Movie 16. 5

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 Ca 2+ • A Ca 2+ Signal Triggers Many Biological Processes • Intracellular Signaling Cascades Can Achieve Astonishing Speed, Sensitivity, and Adaptability

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 rhodopsin molecule in the discs, through the crystal of the outer segment, to Na+ channels in the plasma membrane of the outer segment. The Na+ channels close in response to the signal, producing a change in the membrane potential of rod cell (hyper-polarization). The change of membrane potential alters the rate of neurotransmitter release from the synaptic region of the cell Figure 16 -28 Essential Cell Biology (© Garland Science 2010)

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.

the light-induced signaling cascade in rod photoreceptor cells greatly amplifies the light signal Figure 16 -29 Essential Cell Biology (© Garland Science 2010)

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 that acts as an enzyme 3. Receptor tyrosine kinases (RTKs) is the largest class of enzyme-coupled receptors in made up those with a cytoplasmic domain 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 Figure 16 -30 Essential Cell Biology (© Garland Science 2010)

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

RTKs activate Ras 1. 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 Figure 16 -31 Essential Cell Biology (© Garland Science 2010)

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 cascade 1. 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) Figure 16 -32 Essential Cell Biology (© Garland Science 2010)

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 Kinase http: //www. youtube. com/watch? v=b. Yio. Sv. T 33 c. A Cancer parthway (Ras pathway) http: //www. youtube. com/watch? v=L 9 dsg 0 w. JRR 8&feature= related The MAP-Kinase (MAPK) signalling pathway (5 min) http: //www. youtube. com/watch? v=r 7 Go. Z 9 v. FCY 8

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

RTKs can activate the PI-3 -Akt signaling pathway 1. An extracellular survival signal, such as IGF (insulin-like growth factor) family, activate an RTK, which recruits and activates PI-3 kinase pathway to promote cell growth and survival Figure 16 -33 Essential Cell Biology (© Garland Science 2010)

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

The PI 3 K/AKT signalling pathway http: //www. youtube. com/watch? v=ewg. Ld 9 N 3 s-4&NR=1 PI 3 K/AKT Pathway and Cancer http: //www. youtube. com/watch? v=Jq 4 ZOu 2 Ubq. A&featu re=related

Activated Akt promotes cell survival : 1. One of the relocated signaling proteins in the PI-3 -kinase pathway is the serine/threonine protein kinase Akt (also called protein kinase B (PKB)). This pathway called PI-3 -kinase-Akt singaling pathway 2. Akt promotes the growth and survival of may cell types often by inactivating the signaling proteins it phosphorylates. It also stimulate cells to grow in size Figure 16 -34 Essential Cell Biology (© Garland Science 2010)

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 RTK activates the PI-3 -kinase-Akt signaling pathway 2. Akt then indirectly activate Tor (by phosphorylating and inhibiting a protein that helps to keep Tor shut down) 3. Tor, a serine/threonine kinase, stimulates protein synthesis and inhibits protein degradation Figure 16 -35 Essential Cell Biology (© Garland Science 2010)

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, PKA PIP 2, DAG & IP 3 2. RTK: Ras, MAPK Ras, PI-3 -kinase-Akt signaling

How we know: untangling cell signaling pathways 1. Cannot reveal the whole signaling pathway in a single exp. 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 response to and extracellular signal such as insulin Exp: 1. Check the ‘stimulated phosphorylation’ : Stimulate cells, separate all cellular proteins by gel, use antibody to detect phosphorylated proteins

2. Close encounters: Once the activated proteins have been identified, one can determine which proteins interact with them using ‘co-immunoprecipitation’. If two proteins are dragged down at the same time, very likely they 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 intracellular signaling molecule binds

Mutant proteins can help to determine exactly where an intracellular signaling molecule binds Figure 16 -36 Essential Cell Biology (© Garland Science 2010)

3. ‘Jamming the pathway’: To test the function: use the recombinant DNA technology to insert the gene in the form of constantly active form, to see if this mimics the effect of the extracellular signal e. g. A constitutively active form of Ras transmits a signal even in the absence of an extracellular signal molecule Figure 16 -37 Essential Cell Biology (© Garland Science 2010)

On the contratory, scientist also needs to inactive the protein or its gene and see weather the signaling pathway is affected. e. g. to induce a ‘dominant-negtive’ mutant form of Ras, i. e. Ras binds to GTP too tightly to be 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 not functioning properly

Genetic analysis reveals the order in which intracellular signaling proteins act in a pathway Figure 16 -38 a Essential Cell Biology (© Garland Science 2010)

Figure 16 -38 b Essential Cell Biology (© Garland Science 2010)

Figure 16 -38 c Essential Cell Biology (© Garland Science 2010)

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

Some Enzyme-linked receptors activate a fast track to the nucleus 1. Some receptors use a more direct route to control gene expression 2. Cytokines binds to receptor, which activates a type of regulatory proteins called STATS (signal transducers and activators of transcription) Figure 16 -39 Essential Cell Biology (© Garland Science 2010)

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 the phosphotyrosine site of the receptor to be activated STATs dissociate from the receptor, dimerize, migrate to the nucleus activate the transcription of specific target genes 5. example: hormone prolactin which stimulates breast cell to make milk

The notch receptor itself is a transcription regulator 1. Notch receptor generate an even more direct signaling pathway which controls the development of neural cells in Drosophila Figure 16 -40 Essential Cell Biology (© Garland Science 2010)

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

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

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 their serine/threonine kinase receptor is very different to animal’s 3. Plant receptors trigger a large variety of cell signaling prosess involves 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 mediates the response of cells to ethylene- a gaseous hormone that regulates a diverse array of development processes, including seed germination and fruit ripening

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

Signaling pathways can be highly interconnected (cross-talk) Protein kinases in both pathways phosphorylate many proteins, including proteins belonging to the other pathway Figure 16 -42 Essential Cell Biology (© Garland Science 2010)

Movie 16. 7

Movie 16. 8

Movie 16. 9

Some intracellular signaling proteins serve to integrate incoming signals Figure 16 -43 Essential Cell Biology (© Garland Science 2010)