Biology of Cancer - Tunghai University

Transcript Biology of Cancer - Tunghai University

Chapter 5 Growth Factors, Receptors and Cancer

- 5. 2 ~ 5.9 Mar 27 & 29, 2007

Decisions about growth versus no-growth must be made for the welfare of the entire tissue and whole organism, not for the benefit of its individual component cells.

5.2 the Src protein functions as a tyrosine kinase

protein kinase

is a kinase enzyme that modifies other proteins by chemically adding phosphate groups to them (phosphorylation).

Figure 5.5a

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- Most of the kinases in the cell are serine /threonine kinases (add phosphate group on serine/threonine).

- More than 99% of the phosphoamino acids in normal cells are phosphothreonine or phosphoserine; phosphotyrosine constitutes as little as 0.05 to 0.1% of these cells’ total phosphoamino acids.

Electrophoresis can be used to resolve 3 types of phosphoamino acids – phosphotyrosine, phosphothreonine and phosphoserine almost no phosphotyrosine increased level of phosphotyrosine Figure 5.8

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Src can phosphorylate more than 50 distinct proteins (substrate) in the cell

32 P-labeled ATP was added into the cell lysates Figure 5.7a

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A protein kinase usually phosphorylates and modifies the functional state of a number of distinct substrate proteins

Akt: AK R mouse T -cell lymphoma (v-Akt) PKB: p rotein k inase B GSK: g lycogen s ynthase k inase Figure 5.7b

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5.3 The epidermal growth factor receptor (EGF-R) functions as a tyrosine kinase

- A variety of proteins involved in cell-to-cell signaling were found and sequenced.

- The 1 st of the growth factors to be discovered was epidermal growth factor (EGF).

- EGF has mitogenic effects when applied to a variety of epithelial cell types.

- EGF (ligand) is able to bind to a surface protein (receptor) of the cells whose growth it stimulates.

Structure of the epidermis growth factor (EGF) receptor

Figure 5.9a

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Structure of tyrosine kinase receptors

IGF-1: i nsulin-like g rowth f actor 1 , NGF: n erve g rowth f actor, PDGF: p latelet d erived g rowth f actor, FGF: f ibroblast g rowth f actor, VEGF: v ascular e ndothelial g rowth f actor, Eph: eph rin Figure 5.10

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Growth factors and their tyrosine kinase receptors HGF: h epatocyte g rowth f actor, SF: s catter f actor GDNF: g lial cell d erived n eurotrophic f actor Ret: Re arranged during t ransfection, SCF: s tem c ell f actor Table 5.1

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5.4 An altered growth factor receptor can function as an oncoprotein -

In 1984, the sequence of the EGF receptor was recognized to be closely related to the sequence of a known oncogene product v-ErbB from avian erythroblastosis virus.

Figure 5.11

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Mutations in growth factor receptor gene can cause ligand-independent activation

Figure 5.12a

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Tumor cells may synthesize growth factor and creates an autocrine signaling invasive human breast carcinoma

receptor: EGF-R ligand: TGF-α super imposed Figure 5.12b

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4.6 - In about 1/3 of glioblastomas examined, the EGF-R has been found to be decapitated, lacking most of its extracellular domain.

- In many lung cancers, the EGF-R mRNA lacks the coding sequences carried by exons 2 through 7.

Table 5.2

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5.5 A growth factor gene can become an oncogene: the case of

sis

- In 1983, the B chain of platelet-derived growth factor (PDGF) was found to be closely related in sequence to the oncoprotein encoded by the v-

sis

oncogenes of si mian s arcoma virus.

A B PDGF can also be AA or BB

- PDGF stimulates growth of mesenchymal cells, such as fibroblasts, adipocytes, smooth muscle cells, and endothelial cells.

Growth factors can act on cells via three ways

(SCLC)

IL-6: i nter l eukin-6, NRG: n eu r e g ulin, PRL: pr o l actin, TGF: t ransforming g rowth f actor, GRP: g astrin r eleasing p eptide Table 5.3

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Certain lung cancers produce 3 distinct growth factors and express their receptors: 1. transforming growth factor (TGF) - α / EGF-R 2. stem cell factor (SCF) / Kit 3. insulin-like growth factor (IGF) - 1 / IGF-1-R - Kaposi’s sarcomas produce PDGF, TGF-β, IGF-1, angiogenin 2 ( Ang2), CCL8, CXCL11, endothelin and express their receptors. At the same time, the causal agent of this disease, the human herpesvirus-8 (HHV-8) produces vIL-6 and macrophage inflammatory protein (vMIP).

5.6 Transphosphorylation underlies the operations of r eceptor t yrosine k inases (RTK)

How do growth factor receptors use their tyrosine kinase domains to emit signals in response to ligand binding?

Receptor dimerization following ligand binding

Figure 5.15

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Transphosphorylation of the EGF receptor -

EGF + EGF A431 human vulve epidermoid carcinoma cell line (overexpress EGF-R) in 32 PO 4 -containing medium Figure 5.14

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Why does overexpression of growth factor receptors participate in the formation of cancers ?

1. When the receptor molecules are overexpressed, their high numbers cause them to collide frequently, and these encounters, like the dimerization events triggered by ligand binding, can result in trans-phosphorylation, receptor activation, and signal emission.

2. Alternatively, excessive receptor expression may make some cancer cells hyper-responsive to the low levels of growth factors that may be present in their surroundings.

Table 5.2

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Sidebar 5.7 Mutant forms of a single tyrosine kinase-R may play a causal role in very different types of cancer

c-Kit is the receptor for s tem c ell f actor (SCF) SCF stimulates the formation of various types of cells in the blood (hematopoiesis), as well as the development of a variety of nonhematopoietic cell types, including melanocytes and the cells mediating gut motility.

a.a. substitutions or deletions GIST:

gastrointestinal stromal tumor

AML:

acute myelogenous leukemia Figure 5.18a

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5.7 Yet other types of receptors enable mammalian cells to communicate with their environment - O

ther types of receptors which contain no kinase domains also contribute to cancer formation. (1) When the receptors dimerize in response to ligand binding, the associated other.

Ja nus k inases (Jaks) phosphorylate and activate each The activated Jaks then proceed to phosphorylate the C-terminal tails of the receptor molecules, thereby activating the receptors to emit signals.

Janus : Roman god of gates and doors 兩面神

Receptors with Jaks as associated tyrosine kinases

erythropoietin (EPO) receptor – regulates the development of erythrocytes.

thromboietin (TPO) receptor – controls the development of the precursors of blood platelets, megakaryocytes.

interferon (IFN) receptor – delivers anti-viral signals.

Jak family:

Jak1, Jak2, Jak3, Tyk2 Ty rosine k inase 2 Figure 5.20

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(2) Transforming growth factor β (TGF-β) receptors are heterodimers and their kinas domains phosphorylate serine and threonine rather than tyrosine residues.

→

suppress the proli feration of normal epithelial cells and promote the acquisition of invasive properties by transformed cells Figure 5.21

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(3) Notch receptor: After binding ligands (NotchL, Delta, Jagged),

cytoplasm

Notch is cleaved successively by two proteases.

One of the resulting proteolytic Notch fragments, derived from its cytoplasmic domain, migrates to the nucleus, where it functions as part of a complex of transcription factors that activate expression of responder genes.

act as a transcription factor contribute to Ras-mediated cell transformation and morphogenetic processes.

Figure 5.22

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(4) Patched (Ptc) receptor: When the ligand Hedgehog (Hh) binds, Ptc moves away from a 2 nd membrane-spanning protein called Smoothened (Smo). (functionally inert)

of transcription

Smoothened then signals to a cytoplasmic complex that releases a transcription factor, and translocates to the nucleus. Mutant alleles of both

Ptc

and

Smo

have been found in the common basal cell carcinoma of the skin.

Figure 5.23

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(5) Wnt (growth factor) can activate Frizzled (Frz, the receptor) and trigger a cascade of steps that shut down g lycogen s ynthase k inase 3β (GSK-3β) firing, allowing its downstream substrate  -catenin to escape degradation and to promote cell proliferation.

( a denomatous p olyposis c oli) Figure 5.24

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Signaling through G proteins by serpentine receptors

seven-membrane-spanning - signaling through G proteins ( g uanine nucleotide-binding proteins) - also called G-protein-coupled receptors (GPCRs) - contribute to the pathogenesis of a small number of human cancers Figure 5.25

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5.8 Integrin receptors sense association between the cell and the extracellular matrix anchorage-independent growth

In the absence of attachment, many types of normal cells will activate a death program (apoptosis) that is called

anoikis

Figure 3.12

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- Cells are not anchored directly to the glass or plastic surface of the dishes. - Instead, they attach to a complex network of molecules, called e xtra c ellular m atrix (ECM), which is usually found in the spaces between cells within most tissues.

- ECM is composed of glycoproteins, including collagens, laminins, proteoglycans, and fibronectin.

- Cells are able to sense whether or not they attach to the ECM.

- Such sensing depends on

integrin

receptors.

extracellular matrix Figure 5.26

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- Integrins constitute a large family of

heterodimeric

transmembrane cell surface receptors composed of

and

subunits.

- At least 18 α and 8 β subunits have been identified, with a total of 24 distinct integrins.

Figure 5.27

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Table 5.4

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Integrin clustering connects ECM to cytoskeleton (focal adhesions) and activate signaling pathways

- cell migration, proliferation and survival (anti-apoptosis)

focal adhesion

(clustered integrins, cytoskeletons, associated proteins)

actin fiber

Figure 5.28a

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Organization of ECM-integrin-cytoskeleton

signals outside-in signals inside-out Figure 5.28b

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5.9 The Ras protein functions as a G protein

- The

ras

changes in cells which are transformed by

erbB

oncogene triggers many of the same (truncated EGF-R) or

sis

(PDGF-B). - Could Ras be found somewhere downstream of

erbB and sis

- Do the signals emitted by EGF-R and PDGF-R converge on some common molecule ?

EGF/EGFR-mediated Ras activation SH2, SH3: S rc h omolog GRB2: g rowth factor r eceptor b ound protein 2 Sos: s on o f s evenless

Sos is a g uanosine e xchange f actor (GEF)

G uanosine d i p hosphate G uanosine t ri p hosphate

EGF/EGFR-mediated Ras activation

Regulation of Ras (a GTPase) activity GEF: g uanine nucleotide e xchange f actor Sos is a GEF, which catalyzes conversion of inactive GDP-bound Ras to the active GTP-bound form.

GAP: G TPase a ctivating (or a ccelerating) p rotein

Mammalian Ras proteins have been studied in great detail because mutants Ras proteins are associated with many types of human cancer . These mutant proteins, which bind but cannot hydrolyze GTP , are permanently in the “on” state and contribute to neoplastic transformation.

Most oncogenic, constitutively active Ras protein contain a mutation at position 12. Replacement of the normal glycine-12 with other amino acid blocks the functional binding of GAP, and in essence “lock” Ras in the active GTP-bound state.

The structure of the Ras protein

Figure 5.31

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Alternative mechanisms of transformation by Ras

Figure 5.32a

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Biology of Cancer - Tunghai University

Transcript Biology of Cancer - Tunghai University

Chapter 5 Growth Factors, Receptors and Cancer

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