1. Hormones and Signal Transduction III
Dr. Kevin Ahern

2. RTKs - Epidermal Growth Factor
Epidermal Growth Factor Receptor (EGFR)
EGFR Signaling, Part 1
EGFR Dimer
Autophosphorylated
Tyrosines in
Cytoplasmic Domain
Signaling Complex
Assembled on
Phosphotyrosines
GTP
GTP
GDP
Prepares Cell for Division

3. RTKs - Epidermal Growth Factor
RAS Activates RAF Kinase
RAF/RAS Activates MEK Kinase
MEK Activates
MAP Kinase Cascade
Transcription Factor
Phosphorylation
Activates Gene Expression

4. Human r-RAS Bound GDP RAS RAS is a Family of Related Proteins
Each is Monomeric and like the α-subunit of G-Proteins
RAS Proteins Bind Guanine Nucleotides
RAS Swaps GDP for GTP on Activation
RAS Slowly Cleaves GTP to GDP
Human r-RAS
Bound GDP

5. RTKs Summary Dimerization is Important for RTK Activation
RTKs Play Important Roles in Regulating Cell Proliferation
Binding of Ligand Causes Dimerization for Most RTKs
Dimerization Causes Cytoplasmic Tails to Autophosphorylate and Activate
A Signaling Complex Binds to Phosphotyrosines and Communicates Message to
Cell (usually by phosphorylation)
The Insulin Receptor is a RTK that Stimulates Movement of GLUT4 to Membranes
Insulin Signaling Stimulates Phosphoprotein Phosphatase
Phosphoprotein Phosphatase Reverses Effects of Epinephrine
Insulin Signaling Favors Reduced Blood Glucose and Glycogen Synthesis
Epinephrine Signaling Favors Increased Blood Glucose and Glycogen Breakdown
EGFR Dimerizes and Activates on Binding EGF
EGF Signaling Activates Transcription and Favors Cell Division
RAS is Like a G-Protein and Activates Cell Division When Bound to GTP
Turning off EGFR Signaling Involves GTPase (Ras), Phosphatases, and Endocytosis of
Receptors

6. Steroid Hormone Signaling
Steroid Hormones Control Metabolism, Inflammation, Immune Functions, Water/salt Balance,
Sexual Characteristics, and Response to Illness/Injury
Steroid Signaling Uses Intracellular, Non-membrane Receptors
Five Classes of Steroid Hormones in Two Groups - Corticosteroids and Sex Hormones
Signaling Mostly Affects Gene Expression so Tends to be Slower in its Effects

7. Steroid Hormone Signaling
Steroid Hormone Released into Blood
Crosses Lipid Bilayer of Target Cell
Binds to Internal Receptor
Internal Receptor Changes Shape,
Becoming Transcription Factor
Transcription Factor Alters Cell’s
Gene Expression

8. Steroid Hormone Signaling
5. Transcription
5. Hormone-bound
Receptor Binds DNA,
Initiates Transcription 3
3. Hormone Binds
Receptor, Hsp70
Released 2
2. Movement Across Lipid Bilayer 4
4. Movement of
Hormone-bound
Receptor to Nucleus 1
1. Hormone Arrives in Blood
Receptor Bound to Hsp70
Nucleus
Lipid Bilayer
Cell

9. Steroid Hormone Signaling
HSP Release
Hormone Entry
Dimerization
Movement
to Nucleus
Steroid Hormone Signaling
Transcription
Activation
Glucocorticoid Hormone Signaling

10. Hormones and Signal Transduction
Non-Hormone Signaling
Cells Communicate in Other Ways Than With Hormones
Nerve Transmission
Relies on Ion Gradients and Neurotransmitter Molecules to Transmit Signal
Blocked by Ion Channel Blocking Molecules
Prostanoids
Derived from Arachidonic Acid and Exert Effects Near Where They are Released - Prostaglandins, Prostacyclin and Thromboxanes
Synthesis Inhibited by Steroids and NSAIDs - Aspirin, Ibuprofen
Prostaglandin H2
Thromboxane A2

11. Signaling Gone Wild
Signaling Gone Wild
Signaling Proteins Play Important Roles in Growth and Division
Oncogene - A Mutated Gene Whose Activity Can Cause Uncontrolled Growth
Proto-Oncogene - Unmutated Form of an Oncogene
Mutations in Signaling Systems Can Lead to Tumor Formation
Mutations Affecting Protein Structure/Function
Mutations Affecting Expression of Protein
Other Mutations

12. Hormones and Signal Transduction
Signaling Gone Wild
Mutations Affecting Protein Structure/Function
RAS
Mutated RAS Most Common
Point Mutation in Cancer
1. GDP Bound
RAS Inactive
2. GTP Binding
Activates
Mutated RAS in 90% of
Pancreatic Cancer and
20% of all Cancers
3. GTPase Converts
GTP to GDP, Inactivating
4. Mutations of Amino Acids
11/12 or 61 Inhibit GTPase &
Activate RAS
5. Activated RAS Stimulates Cell Division

13. Hormones and Signal Transduction
Signaling Gone Wild
Src
Not All Tyrosine Kinases are RTKs
Src Proteins are Tyrosine Kinases Found in Various
Cell Locations
Dephosphorylated Src Acts to Stimulate Cell Division
Phosphorylation of Src’s Tyrosines Turns it OFF
Mutations that Affect Src’s Phosphorylation Convert
it to an Oncogene

14. Hormones and Signal Transduction
Signaling Gone Wild
Mutations Affecting Protein Structure/Function
Src
Phosphorylated Tyrosines
Block Access to its SH2 Domain and
Prevent it From Participating in Signaling
Leaving it Inactive
Src
Mutations Changing These Tyrosines
Leave the Protein Always Activated,
Stimulating Uncontrolled Cell Division

15. Hormones and Signal Transduction
Introduction
Mutations Affecting Expression of Protein
HER2-Herceptin Complex
HER2 Doesn’t Require EGF Binding for Dimerization/Activation
Is Always Signaling Cell to Divide When Dimerized
Mutations Increasing Levels of HER2 Found in Several Cancers
Breast Cancer (15-30%)
Ovarian Cancer
Stomach Cancer
Uterine Cancer
Treated with Monoclonal Antibody - Herceptin
Herceptin Binds HER2’s Extracellular Domain to Prevent Dimerization

16. Hormones and Signal Transduction
Introduction
Other Mutations
Bcr-Abl Fusion
The bcr-abl fusion links the
tyrosine kinase of abl
with the N-terminus
and transcription control of bcr
abl
bcr 22 9
Fusion Chromosomes
9/22
22/9
bcr-abl fusion
Crossover
All regulation of abl is lost
in the fusion, so the
bcr-abl fusion is signaling
‘division’ all the time
Chromosomes 9 & 22

17. Hormones and Signal Transduction
Introduction
Bcr-Abl Fusion
Also Known as Philadelphia Translocation
Present in 95% of people with CML (Chronic Myelogenous Leukemia)
Treated with Tyrosine Kinase Inhibitor - Gleevec (Imatinib)
Gleevec has Almost Doubled the Five Year Survival Rate of CML Patients

18. Other Signaling Considerations
Steroid Hormone Signaling Uses Intracellular, Non-membrane Receptors
Steroid Hormone Receptors Act as Transcription Factors When Bound to Hormone
Non-hormone Signaling Includes Nerve Transmission and Prostanoid Signaling Src Proteins
are Tyrosine Kinases Found in Various Cell Locations
Nerve Transmission Involves Action Potentials Generated by Ion Gradient Changes
Oncogenes Cause Cancer and are Mutated Proto-Oncogenes
Mutations in Signaling Systems Can Lead to Tumor Formation
RAS Mutations that Inhibit GTPase Can Cause Cancer
Mutated RAS Most Common Point Mutation in Cancer
Phosphorylation of Src’s Tyrosines Turns it OFF
Phosphorylated Tyrosines Block Access to Src’s SH2 Domain
Src’s SH2 Domain Controls Access to Other Signaling Proteins
Mutations Changing Src’s Tyrosines Leave the Protein Always Activated
Human EGFR (HER2) HER2 Doesn’t Require EGF Binding for Dimerization/Activation
Overexpression of HER2 Linked to Many Cancers
HER2 Cancers Treated with Herceptin
bcr-abl Fusion links the Tyrosine Kinase of abl with N-terminus & Transcription Control of bcr
bcr-abl Fusions Implicated in Many CMLs
bcr-abl Tumors Fought with Tyrosine Kinase Inhibitor - Gleevec

19. Student Nightmares Metabolic Melody I answered 3 ‘b’.
(To the tune of “Norwegian Wood”)
Copyright © Kevin Ahern
Metabolic Melody
I answered 3 ‘b’.  
But then I thought.  It might be ‘c’
Or was the false true?  
I can’t undo. It makes me blue
It asked me to list all the enzymes that regulate fat
As I wrote them down I discovered I didn’t know Jack
I ought to give thanks, 
Scoring some points, filling in blanks
I squirmed in my seat
Feeling the heat, shuffling my feet
Professor then told me there wasn’t a chance I would pass
So I started crying and fell through a big pane of glass
I suffered no harm, 
'Cuz I awoke, to my alarm
Oh nothing compares
To deadly scares, of student nightmares