BCB 570 "Signal Transduction" 4/8/08

Drena Dobbs, ISU 1

for BCB 570 4/8/08 - Drena Dobbs ISU 1Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

One Biologist’s Perspective

Drena DobbsBCB & GDCB

Iowa State University

Signal Transduction

for BCB 570 4/8/08 - Drena Dobbs ISU 2Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Thanks to:

Howard Booth

BiologyEastern Michigan University

forSlides modified from his lecture

• Cell-Cell Communication

Marit Nilsen-Hamilton

BBMBIowa State University

forSlides copied from her lectures

• Small G proteins• GPCRs

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An Aging Biologist’s

Perspective

Signal Transduction

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The Perspective ofA Biologist

Signal Transduction

Who Studies Aging

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Greer, E. L. et al. J Cell Sci 2008;121:407-412 for BCB 570 4/8/08 - Drena Dobbs ISU 6Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

The Perspective ofA Biologist

Who Studies G-proteins

Signal Transduction

BCB 570 "Signal Transduction" 4/8/08

Drena Dobbs, ISU 2

for BCB 570 4/8/08 - Drena Dobbs ISU 7Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Buchsbaum, R. J. J Cell Sci 2007;120:1149-1152 for BCB 570 4/8/08 - Drena Dobbs ISU 8Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Schwartz, S. L. et al. J Cell Sci 2007;120:3905-3910

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1. Why is Signal Transduction so important?

2. What are Components of Signal Transduction Pathways?• Cytokines & Cytokine Receptors (e.g. Ig-superfamily Receptors)• Hormones & Hormone Receptors (e.g., GPCRs)• G-Proteins

• Small G-proteins (e.g., Ras, Rab, Rho)• Heterotrimeric G-proteins

• Second Messengers (e.g., Ca++, cAMP, DAG)• Kinases & Phosphatases• Transcription Regulatory Factors and Co-factors (RF&CFs)• Post-transcriptional RF&CFs• Translational RF&CFs• Post-translational RF&CFs• Metabolic RF&CFs

3. How is Signal Transduction Studied (Experimentally)?for BCB 570 4/8/08 - Drena Dobbs ISU 10

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Watch: Inner Life of a Cell

• Go to U-Tube!! - or better, HARVARD:

• http://multimedia.mcb.harvard.edu/media.html

• http://www.studiodaily.com/main/technique/tprojects/6850.html

Leukocytes = White blood cells Function in immunity

for BCB 570 4/8/08 - Drena Dobbs ISU 11Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

A few URLs: the tip of an iceberg! - p. 1

Kimballs’ Biology Pages - Glossary, Notes, etc:http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/

Cell Signaling:http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellSignaling.htmlhttp://www.biochemweb.org/signaling.shtml

Hormones in Humans:http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/Hormones.html

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A few URLs: the tip of an iceberg! - p. 2

Cytokines & Cytokine Receptors:http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellSignaling.html#Cytokine_Receptors

GPCRs:http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellSignaling.html#GPCRs

G-proteins: http://www.webbooks.com/MoBio/Free/Ch6D2.htmhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/G_Proteins.html

p53: http://www.webbooks.com/MoBio/Free/Ch4Hp53.htm

ATPases: http://multimedia.mcb.harvard.edu/media.html

BCB 570 "Signal Transduction" 4/8/08

Drena Dobbs, ISU 3

for BCB 570 4/8/08 - Drena Dobbs ISU 13Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Endocrinology = re: Hormones

3 basic types of chemical signaling:Endocrine - cell secretes “chemicals” that are carried by blood or tissue

fluids to distant cells upon which they act Ex: Release of Hormones (which can be proteins, peptides, steroids)

Paracrine - cell releases “chemical” signals that diffuse and interact withreceptors on nearby cellsEx: Release of Cytokines that cause an inflammatory response

Release of Neurotransmitters at synapses in the nervous system

Autocrine - cell signals itself with a chemical that it both synthesizes andresponds toAutocrine signaling can occur:

• Solely within the cytoplasm of the cell• By secreted chemical interacting with receptors on surface of same cell

for BCB 570 4/8/08 - Drena Dobbs ISU 14Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Cytokines

What are cytokines?• Cell signaling molecules secreted by a cell, which:

signal other cells in a paracrine fashion or

signal the secreting cell (in an autocrine fashion)

• Play important roles in immunity• Structurally diverse; mainly small 8-30 kDa, water-soluble

proteins & glycoproteins• Ex: various lymphokines, chemokines, interleukins

What are other types of cell signaling molecules?Hormones, Growth Factors, Neurotransmitters

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Cytokine Receptors

Dozens of cytokine receptors have been discoveredMost fall into one of several major families:

1. Receptor Tyrosine Kinases (RTKs)2. TNF (tumor necrosis factor) superfamily receptors3. TGF-β (transforming growth factor) receptors

(Ser/Thr Kinases)4. Immunoglobulin superfamily receptors (IgRs)5. Chemokine receptors (e.g., GPCRs)

6. Type I/II cytokine receptors that trigger JAK-STAT pathwaysJAK-STAT signaling mediates cellular responses to cytokines and growth factors. EmployingJanus kinases (JAKs) and Signal Transducers & Activators of Transcription (STATs), the pathwaytransduces the signal carried by these extracellular polypeptides to the cell nucleus, whereactivated STAT proteins modify gene expression <Wikipedia>

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Review a few topics:

• How cells communicate• Electrical and chemical signals• Receptor types and how they function• Local regulation of cells

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• Chemical• Autocrine & Paracrine: local signaling

• via cytokines. neurotransmitters

• Endocrine: distant targets• via hormones

• Electrical• Nervous system: fast, specific, distant target• Gap junctions: local

Types of Cell to Cell Communication:

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Gap Junctions and CAMs

• Protein channels - connexins• Direct flow to neighbor

• Electrical - ions (charge)• Chemicals/proteins

• CAMs - Cell Adhesion Molecules• Need direct surface contact• Chemicals/proteins

Figure 6-1a, b: Direct and local cell-to-cell communicationCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings

BCB 570 "Signal Transduction" 4/8/08

Drena Dobbs, ISU 4

for BCB 570 4/8/08 - Drena Dobbs ISU 19Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Paracrine & Autocrine Signaling

• Local communication• Signals diffuse to targets• Ex: Cytokines

• Autocrine– receptor onsame cell

• Paracrine – neighboringcells

Figure 6-1c: Direct and local cell-to-cell communicationCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings for BCB 570 4/8/08 - Drena Dobbs ISU 20

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

• Made in endocrine cells• Transported via blood• Receptors on target cells

Long Distance Communication: Endocrine Signaling - via Hormones

Figure 6-2a: Long distance cell-to-cell communicationCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings

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• Neurons• Electrical signal travels down axon (can be very long!!)• Change in potential causes release (in synapse) of

neurotransmitters that bind to receptors on nearby target cell

• Neurohormones• Hormones transported via blood to target• A neurohormone is any hormone produced by neurosecretory cells, usually in

the brain. Neurohormonal activity is distinguished from that of classicalneurotransmitters as it can have effects on cells distant from the source of thehormone. Examples?

• GnRH = Gonadotropin releasing hormone• CRH = Corticotropin releasing hormone• TRH = Thyrotropin-releasing hormone• Dopamine• Prolactin inhibiting hormone• Orexin (aka hypocretin) <Wikipedia>

Long Distance Communication: Neurons and Neurohormones

for BCB 570 4/8/08 - Drena Dobbs ISU 22Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Long Distance Communication: Neurons and Neurohormones

Figure 6-2b, c: Long distance cell-to-cell communicationFigure 6-2 b: Long distance cell-to-cell communication

Copyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings

for BCB 570 4/8/08 - Drena Dobbs ISU 23Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Summary: Components of Signaling Pathways

• Extracellular signaling molecule (cytokine, hormone)

• Receptor• Intracellular signaling molecule

(kinase, second messenger)

• Target protein (kinase, transcription factor)

• Response

Figure 6-3: Signal pathwaysCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings for BCB 570 4/8/08 - Drena Dobbs ISU 24

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Receptor locations?

• Intracellular:• Cytosolic or Nuclear• Lipophilic ligand enters cell• Often activates transcription

of gene(s)• Relatively slow response

• Cell surface:• Transmembrane• Lipophobic ligand can't enter

cell• Often activates protein

kinase cascade• Relatively fast response

Figure 6-4: Target cell receptorsCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings

BCB 570 "Signal Transduction" 4/8/08

Drena Dobbs, ISU 5

for BCB 570 4/8/08 - Drena Dobbs ISU 25Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

• Integrins (in Inner Life of Cell)• Ligand-gated channels

• Receptor enzymes• RTKs & other “single pass” transmembrane (TM) domain receptors

• G-protein coupled• GPCRs & other 7 TM domain receptors)

Membrane Receptor Classes

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Membrane Receptor Classes

Figure 6-5: Four classes of membrane receptors

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Receptor Enzyme: ReceptorTyrosine Kinase• Transmembrane (TM)

proteins• Transduce signal across

membrane• Binding of ligand to

extracellular receptordomain

• Somehow transducessignal through TMdomain

• Resulting in activationof intracellular kinasedomain

Figure 6-10: Tyrosine kinase, an example of a receptor-enzymeCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings for BCB 570 4/8/08 - Drena Dobbs ISU 28

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

G Protein-Coupled Receptors = GPCRs

Figure 6-11: The G protein-coupled adenylyl cyclase-cAMP systemCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings

for BCB 570 4/8/08 - Drena Dobbs ISU 29Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

G Protein-Coupled Receptors

• Hundreds of types• Main signal transducers in eukaryotic cells

• Activate enzymes• Open ion channels (e.g., to allow influx of Ca++)• Amplify signals:

• Adenyl cyclase >>> cAMP• Activate downstream effectors

• Effector? Protein/enzyme “activated” by another protein

But - What is a G-protein???

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Summary: Steps in Signal Transduction

• Signal = ligand (small molecule)• Binds Receptor, which activates:• Protein kinases

• Tyr or Ser/Thr• & Second messengers

• cAMP, Ca++, DAG, which result inactivation of “downstream”proteins or enzymes via:

• Phosphorylation cascades or otherpost-translational modifications(PTMs) or Ca++ binding

• Resulting in Cellular Response

Figure 6-8: Biological signal transductionCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings

BCB 570 "Signal Transduction" 4/8/08

Drena Dobbs, ISU 6

for BCB 570 4/8/08 - Drena Dobbs ISU 31Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Ca++ - Mediated Signaling?

Figure 6-15: Calcium as an intracellular messenger

In neurons:

• Electrical signal causes: Ca++ release from intracellular stores (endoplasmic reticulum, ER)

or Influx of Ca++ through

voltage-gated Ca++ channels

• Activates Ca++ binding proteins• Causing conformational changes that• Activate downstream effectors

Copyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings for BCB 570 4/8/08 - Drena Dobbs ISU 32Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Critical Aspect: Signal Amplification

• Small signal produceslarge cellular response

• via amplification enzymes• Ex: “phosphorylation” or

“kinase” cascade( MAP kinase cascade)

Figure 6-7: Signal amplificationCopyright © 2004 Pearson Education, Inc., pub as Benjamin Cummings

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Signal Transduction: the Big Picture

Copyright © 2004 Pearson Education, Inc., pub as Benjamin CummingsFig 6-14: Summary of signal transduction systems

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Take home messages:1. Signal Transduction involves transfer of signal

information, often from outside a cell (environmentalstimulus) to inside, evoking a response

Extracellular Signal >>> Cellular Response2. Amplification of signal occurs via activation of kinases

(“kinase cascades”) or release of Ca++ (Ca++ -mediatedsignaling)

3. In eukaryotic cells, membranes and membranouscompartments (nucleus, ER, Golgi apparatus, plasmamembrane) play critical roles in signal transduction

4. Cross-talk occurs between components of differentsignal transduction pathways/networks

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Signal Transduction & Cancer:

1. Cancer is a genetic disease (although only a few raretypes of cancer are known to be inherited)

2. Most of what we know about cancer - and about normaldevelopment - was built on results of basic biologicalresearch on rare cancer-causing viruses

3. Such studies have shown that:• All known cancers result from mutations in

components of signal transduction networks (& genes that control cell division or DNA repair)

• Viral oncogenes are variants of “normal” cellulargenes that have been “picked up” by viruses

for BCB 570 4/8/08 - Drena Dobbs ISU 36Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

HPV, Vaccines & Cancer1. Cervical cancer (a deadly cancer in women) is caused by

certain strains of Human Papilloma Virus (HPV), forwhich a vaccine is now available

2. Many health insurance policies do not cover the cost ofGardasil (but do cover the cost of Viagra…)

3. HPV is sexually-transmitted4. Both men & women can be infected with no obvious

symptoms5. ~75% of US reproductive-age population has been

infected with one or more types of genital HPV6. HPV also causes certain cancers in men (~10% as

frequent as cervical cancer in women)http://www.cdc.gov/std/HPV/default.htm#fact