Growth Factors, Receptors, and Signal Transduction II Tumor Biology: Cellular and Molecular Aspects of the Transformed Cell Growth Factors, Receptors, and Signal Transduction II Rebecca Riggins 202.687.7451 rbr7@georgetown.edu

Overview Intracellular signaling “downstream” of receptors - key pathways: Ras/MAPK, Src, PI3K Intracellular signaling defects in cancer Targeted therapies to intracellular signaling molecules TNF and TRAIL

Brief Review – Growth Factors and Receptors most growth factors are secreted receptors are transmembrane proteins 3 major features: extracellular domain transmembrane region intracellular domain where, when, and how they are expressed determines their biological function

Brief Review – Receptor Activity intracellular, or catalytic, domain has kinase activity kinases add phosphate groups to (phosphorylate) specific amino acids ATP-binding Phospho-transferase ATP P Amino Acid P ADP

Consequences of RTK activation GROWTH FACTOR PIP3 PIP3 RTK SOS Grb2 RAS RAS P P P PI3K p85 p110 Akt PDK1 Raf P MEK P P GSK3 P P P P BAD NF-ĸB MDM2 p70S6K FKHR P ERK PROLIFERATION CELL SURVIVAL PROTEIN SYNTHESIS . Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).

Intracellular Signaling begins with autophosphorylated or transphosphorylated amino acids on the receptor Phosphorylation recruits other proteins to the receptor Amino acids surrounding the phosphorylation site determine which proteins are bound… 4 major protein interaction domains: SH2, PTB, SH3, PH Membrane -Tyr P Kinase Domain -Tyr P

Basics of Amino Acid Structure

Basics of Protein Structure Primary Structure = “beads on a string” Quaternary Structure = specific folding creates domains, or “units” of the protein

SH2 domains SH2 = src homology 2 was first identified as a 100 amino acid region of homology (“sameness”) in the src tyrosine kinase specifically recognizes phosphorylated Tyrosine 2 classes of SH2 domain-containing proteins… - have enzymatic activity (like Src) - don’t have enzymatic activity Those with no enzymatic activity bind other proteins to the receptor…adaptor molecules

SH2 domain specificity specificity is determined by the amino acids C-terminal to the phospho-Tyr in most cases, it is the amino acid at position +3 that determines specificity Hydrophobic amino acid Science, Vol 278, Issue 5346, 2075-2080 , 19 December 1997

PTB domains phosphotyrosine binding domains recognize amino acids N-terminal to the phospho-Tyr PTB-containing proteins also participate in hormone signaling any amino acid Science, Vol 278, Issue 5346, 2075-2080 , 19 December 1997

SH3 domains src homology 3 domains recognize amino acid sequences rich in Proline (Pro-rich) Is a more general protein-protein interaction motif… many cytoskeletal proteins contain it any amino acid Science, Vol 278, Issue 5346, 2075-2080 , 19 December 1997

PH domains pleckstrin homology domains recognize phospholipids (components of the plasma membrane) Science, Vol 278, Issue 5346, 2075-2080 , 19 December 1997

Protein-Protein Interactions and Receptors Proteins with many different interaction domains can bind to growth factor receptor family members Protein-protein interactions connect receptors to their intracellular signaling networks Figure 6.9 The Biology of Cancer (© Garland Science 2007)

Receptors bind other Kinases, and Adaptor Proteins Figure 6.10a The Biology of Cancer (© Garland Science 2007)

EGFR and the Ras Pathway SOS Grb2 RAS P P Raf P MEK Grb2: adaptor protein that binds to phosphorylated Tyr on EGFR using its SH2 domain P ERK PROLIFERATION CELL SURVIVAL . Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).

Grb2 has multiple protein interaction domains Cell. 2004 Jan 23;116(2):191-203.

EGFR and the Ras pathway, cont’d. SOS Grb2 RAS P P Raf P MEK SOS binds to the Grb2 SH3 domain P ERK PROLIFERATION CELL SURVIVAL . Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).

SOS activates Ras SOS is an exchange factor (it exchanges one nucleotide for another) Proline-rich DH PH CDC25 Dbl-Homology Catalytic Domain SH3-Binding Membrane- targeting Grb2 EGFR Rho GTPases (Rac) A. Chan, Ras-MAPK Pathways. Sci. STKE 2005, tr5 (2005).

What is Ras? Ras is an oncogene Ras is a small GTP-binding protein…it binds guanine triphosphate Ras bound to GTP is active…Ras bound to GDP is inactive Ras mutation is implicated in many kinds of cancer…

A. Chan, Ras-MAPK Pathways. Sci. STKE 2005, tr5 (2005).

Ras Mutations display Tumor Specificity Pancreatic Carcinoma K-Ras codon 12 (GGTgly) >GTTval Lung carcinoma K-Ras codon 12 (GGTgly) >AGTser Bladder Carcinoma H-Ras codon 12 (GGCgly) >GTCval Melanoma N-Ras codon 61 (CAAgln)>CGAarg A. Chan, Ras-MAPK Pathways. Sci. STKE 2005, tr5 (2005).

How is Ras activated? Figure 5.30 The Biology of Cancer (© Garland Science 2007)

What does active Ras do? Autocrine growth factor signaling Figure 5.32a The Biology of Cancer (© Garland Science 2007)

What else does active Ras do? EGF EGFR SOS Grb2 RAS P P Raf P MEK Ras activates Raf and the Erk/MAPK pathway P ERK PROLIFERATION CELL SURVIVAL . Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).

The Erk/MAPK pathway Erk = extracellular signal regulated kinase MAPK = mitogen activated protein kinase MAPK promotes cell growth and survival by phosphorylating other proteins An immediate consequence of MAPK activation is transcription (DNA → RNA) MAPK activation is a major event following EGF stimulation… Nature Reviews Cancer 4, 937-947 (2004)

Inhibitors of the MAPK Pathway Nature Reviews Cancer 4, 937-947 (2004)

Mechanisms of Ras/MAPK inhibitors inhibit Ras binding to the plasma membrane inhibit Raf inhibit MEK some of these have entered clinical studies… EGF EGFR SOS Grb2 RAS P P Raf P MEK P ERK . Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).

EGFR and the PI3K pathway GROWTH FACTOR PIP3 PIP3 RTK P P P PI3K p85 p110 Akt PDK1 GSK3 P P P P P BAD NF-ĸB MDM2 FKHR CELL SURVIVAL . Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).

What is PI3K? PI3K = phosphatidyl inositol 3-kinase phosphatidyl inositol is a lipid, part of the plasma membrane so, PI3K phosphorylates lipids (fats) instead of other proteins There are 2 subunits of PI3K… Kinase Domain -Tyr P p85 = regulatory subunit p85 has an SH2 domain that binds phospho-Tyrosine on the EGFR PI3K p85 p110 p110 = catalytic subunit that phosphorylates lipids

PI3K Target(s) PI3K phosphorylates PIP2 to make PIP3 PIP3 is now a binding site for Akt… Figure 6.19a The Biology of Cancer (© Garland Science 2007)

Akt – the real master regulator GROWTH FACTOR Akt is a Serine/Threonine kinase Akt has targets in the cytoplasm as well as the nucleus Akt inhibits the cell cycle inhibitors inhibitor + inhibitor = GROWTH, and SURVIVAL PIP3 RTK P P P PI3K p85 p110 Akt GSK3 P P P P P S M G1 G2 Cyclins, Cyclin-dependent kinases, and inhibitors BAD NF-ĸB MDM2 FKHR CELL SURVIVAL . Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).

Table 6.3 The Biology of Cancer (© Garland Science 2007)

PI3K/Akt Defects in Cancer RTK GF Cancer Syndromes PIP3 p PI3-K Lipid Kinase GI, Br, Ov Akt1/2 Ser/Thr Kinase PANC Hamartin Tuberin (Tuberous Sclerosis Complex) TSC1 TSC2 (Ras-homology enriched in brain) RheB Inhibitors to PI3K and/or Akt are being developed for patient use (Target of rapamycin) mTOR S6K 4EBP-1 Protein synthesis Cell growth/size/survival Kovich & Cohen (2004) Dematology Online Journal 10: 3. Perelman (2004) Dematology Online Journal 10: 17.

pp60 c-Src “normal,” cellular Src is another protooncogene viral Src (v-src) is the transforming gene of the avian Rous sarcoma virus Src is a tyrosine kinase, but NOT a receptor Cooperation/synergy with the EGFR in promoting proliferation and tumorigenesis in breast cancer cells Kinase Domain -Tyr P Phosphorylation of transcription factors Src MAPK and PI3K pathways P Cell Growth

c-Src phosphorylates many cellular proteins Isolate protein and load onto poly-acrylamide gel; detect phospho-Tyrosine with specific antibodies Figure 5.7a The Biology of Cancer (© Garland Science 2007)

c-Src and Cancer 30-70% of breast cancers overexpress Src, show elevated activity…many of these also overexpress EGFR Other cancers Src may contribute to are: colon, lung, skin, endometrial, head/neck Src is usually not mutated…how is it activated?

Regulation of Src Activity Kinase Kinase domain has no access to target proteins SH3 “Inactive” Kinase N SH2 pY527 C Viral Src has lost this Tyrosine “Active” N C Kinase (p)Y527 SH2 SH3 X Y Kinase domain is now accessible

How does Src become activated? Src can bind to EGFR or PDGFR, and the active configuration is stabilized However, are other proteins that can bind to and activate Src besides RTKs… “Active” N C Kinase (p)Y527 SH2 SH3 X Y Adaptor proteins with the right binding sites for SH2 and SH3 domains could activate Src

The adaptor protein Cas can activate Src “Active” SH3 Kinase Kinase (p)Y527 N SH2 RP640LPSPP pY668DYV C Cas Cas is important for cell proliferation, cell migration, and transformation by oncogenes (including viral Src)

Cas, Src, and Breast Cancer Cas, like Src, can also be overexpressed in breast cancer Cas and Src bind to each other in breast cancer cells Cas and Src are localized to the same areas of breast cancer cells Cas overexpression in breast cancer is associated with resistance to a particular kind of drug (Tamoxifen)…this involves Src activation Cas Src Cas + Src

Inhibitors of Src in Cancer Therapy Inhibit protein-protein interactions (like those with Cas) Inhibit kinase activity (preclinical/phase I trials) Inhibit protein stability (accelerate Src degradation) These will likely be used in combination with other chemotherapy drugs, EGFR inhibitors, etc.

Adhesion Receptors

Integrins Figure 5.28b The Biology of Cancer (© Garland Science 2007)

Tyrosine Kinases and Adhesion Receptors: Overlap in Cytoplasmic Signaling Figure 6.24b The Biology of Cancer (© Garland Science 2007)

G protein-coupled receptors: More overlap Figure 6.28 The Biology of Cancer (© Garland Science 2007)

Tumor Necrosis Factor (TNF) Review in some cells, TNF is mitogenic, but in most it promotes cell death, or apoptosis this growth factor is not soluble, but is inserted into the plasma membrane TNF receptors have no catalytic domain…rely on intracellular proteins to signal Juxtacrine Intracrine

TNF family of growth factors Schulze-Osthoff, Trends Cell Biol. 1994 Dec;4(12):421-426.

TNFR Signaling to Death DD = death domain, another protein interaction motif DD and DED form dimers DED = death effector domain CELL DEATH Sci STKE. 2004 Jun 22;2004(239)

TNFR Signaling to Survival Other proteins CELL SURVIVAL TNF Signaling and cancer therapy: Will this work? Sci STKE. 2004 Jun 22;2004(239)

TRAIL Signaling to Survival and Death TRAIL = TNF-related apoptosis-inducing ligand