Gen Path 31 and 32: Neoplasia (apoptosis, angiogenesis, immunity, and metastasis)

Apoptotic bodies

Intact plasma membranes

Phagocytized by macrophages

Apoptosis

Tightly regulated cellular suicide

No inflammation

Physiologic or pathologic

Physiologic apoptosis

1. Embryogenesis

2. Involution with hormone withdrawal

3. Cell loss in proliferating cell populations

4. Self-reactive lymphocytes

5. Inflammatory cells

Pathologic apoptosis

1. DNA damage

2. Accumulation of misfolded proteins

3. Certain viral infections

4. Atrophy

Initiation phase, execution phase

What are the phases of apoptosis?

Intrinsic (mitochondrial) pathway, extrinsic (death receptor) pathway

Pathways of initiation phase of apoptosis

Intrinsic (mitochondrial) pathway

1. Increased mitochondrial permeability and release of pro-apoptotic molecule cytochrome c into the cytoplasm

   1. Regulated by Bcl proteins (pro- and anti-apoptotic)

      1. Bcl-2, Bim, Bid, Bad, Bax, Bak

2. Apoptosome (cytochrome c and Apaf-1)

3. Procaspase-9 → Caspase-9

Extrinsic (death receptor) pathway

1. Death receptors (TNF receptor family)

   1. FAS and FASL on cytotoxic T-lymphocytes

   2. FADD

   3. Procaspase-8 → Caspase-8

Cytochrome c, Bcl proteins, apoptosome (cytochrome c and Apaf-1), procaspase-9

What cells/molecules are involved in the intrinsic pathway of apoptosis?

Death receptors (TNF receptor family), FADD, procaspase-8

What cells/molecules are involved in the extrinsic pathway of apoptosis?

Execution phase of apoptosis

1. Mainly caspase-3, 6, and 7

2. Cleaves DNA into small pieces

3. Degrade structural components

4. Fragmentation of nucleus

5. Result: apoptotic bodies that are eventually removed by phagocytes (macrophages)

Apoptotic bodies

What does the execution phase of apoptosis result in?

Fas-associated death domain

What does FADD stand for?

Bcl-2 gene family proteins

Group of both pro- and anti- apoptotic proteins that regulate response to cell damage and mitochondrial membrane permeability

Mitochondrial outer membrane permeabilization

What does MOMP stand for?

Apoptosome

Caspase-activating complex promoted by release of cytochrome C

Death ligand external to cell

What is the extrinsic pathway of apoptosis activated by?

Fas-associated death domain (FADD)

In the extrinsic pathway of apoptosis, secondary messengers include ___, which activates caspase-8

Caspase-8, effector caspases

In the extrinsic pathway of apoptosis, sufficient levels of ___ activate ___.

Irreversible cell damage

What is the intrinsic pathway of apoptosis activated by?

Bcl-2 family proteins

What is the intrinsic apoptotic pathway regulated by?

Mitochondrial outer membrane permeabilization (MOMP) and release of cytochrome C

What does the intrinsic apoptotic pathway lead to?

Cytochrome C

Cytochrome C promotes formation of apoptosome and activation of caspase 9, then effector caspases

p53 (TP53)

1. Tumor suppressor gene

   1. “Guardian of the genome”

   2. Acts as a “molecular policeman” that prevents propagation of genetically damaged cells

   3. p53 thwarts neoplastic transformation one of three ways:

      1. Cellular quiescence, senescence, or apoptosis

Quiescence

Temporary cell cycle arrest to allow for DNA repair

Senescence

Permanent cell cycle arrest if repair fails

Think cellular arrest due to aging

Apoptosis

Programmed cell death if repair fails

Ultimate protective mechanism against neoplastic transformation

Loss of p53 activity from mutation

1. Common mutation in cancer

2. Present in approximately half of human cancers

Proto-oncogenes, tumor suppressor genes, mutations

Factors involved in controlling apoptosis

Angiogenesis

Vessel formation from existing vessels

Endothelial cells

1. Recruitment from preexisting vessels

2. Proliferation

3. Migration through ECM

Angiogenic factors

1. Up-regulation

   1. Vascular endothelial growth factor (VEGF)

      1. In mice with no VEGF, metastases does not occur

   2. Fibroblast growth factor (FGF)

Antiangiogenic factors

1. Down-regulation

   1. Thrombospondin

Angiogenic factors, antiangiogenic factors

What does angiogenesis involve a balance of?

PDFG, IL-1

What growth factors do endothelial cells produce?

Supply oxygen and nutrients to tumor, growth factors produced by endothelial cells, allow for metastasis

Functions of angiogenesis in neoplasia

Vascular endothelial growth factor (VEGF)

In mice without ___, metastasis does not occur.

Abnormal vascular network

Unstable, disorganized, leaky

Normal vascular network

Stable, organized, limited permeability

Immunosurveillance

Identifying and destroying tumor cells

Proteins, glycoproteins, glycolipids, carbohydrates on surface of tumor cells

What tumor antigens exist?

Tumor-specific antigens, tumor-specific shared antigens, tissue-specific antigens

Types of tumor antigens

Tumor-specific antigens

Which type of tumor antigen?:

Tumor cells only

Tumor-specific shared antigens

Which type of tumor antigen?:

Many types of tumors

Tissue-specific antigens

Which type of tumor antigen?:

Shared by tumors and the normal tissue they arise from

Differentiation antigens

Both normal and tumor tissues but occur at specific point in differentiation in normal tissues

Antigens derived from oncogenic viruses (e.g., proteins produced by papillomaviruses)

What are examples of tumor-specific antigens?

Cell products that are absent/rare in normal adult tissue but common in many different types of neoplasia (e.g., MAGE family proteins)

What are examples of tumor-specific shared antigens?

Some B lymphocyte receptors, CD20

What are examples of differentiation antigens?

Liquid biopsy

Detection of neoplastic cells and/or tumor antigens in blood allowing for earlier detection of cancer

Innate immune system

First line of defense

No antigen-specific priming

No lasting immunity

Cells:

• NK cells

• Macrophages

Natural killer (NK) cells

Lymphocytes

Recognize MHC molecules and stress-induced ligands

Kill cells that lack MHC class I

Immunologic synapse leads to cytolysis

Perforin, granzymes

What proteins/enzymes are released by NK cells?

Macrophages

Kills by releasing reactive oxygen intermediates, lysosomal enzymes, nitric oxide, tumor necrosis factor (TNF)

Stimulated by interferon-gamma (IFN-gamma) released by lymphocytes and NK cells

Independent of MHC

Direct contact required

However, can promote angiogenesis, tumor invasion, and metastasis

Blocking these cells may be useful in cancer therapy

Adaptive immune system

Antigen-specific

Cells must be primed

MHC class I and II

• Types:

  • Cell mediated

  • Humoral

Cytotoxic T lymphocytes (CTL), T helper lymphocytes, regulatory T cells (Treg)

Types of T lymphocytes

Cytotoxic T lymphocytes (CTL)

Primary effector cells of adaptive antitumor immune response

CD8, MHC class I

Kill by cytolysis

Most effective antitumor immune defense in an organism

Cytotoxic T lymphocytes

What is the most effective antitumor immune defense in an organism?

T helper lymphocytes

CD4, MHC class II

Secrete IL2 and IFN-gamma to stimulate CTLs

Regulatory T cells (Treg)

Protect tumors by inducing tolerance

B lymphocytes

Humoral immune response

Antibodies bind to tumor cells, activate complement cascade and membrane attack complex (MAC)

Antibody-dependent cell-mediated cytotoxicity (ADCC)

Altered MHC expression

Downregulation of MHC

However, cells with no MHC class 1 susceptible to NK cell killing

Antigen masking

Antigens complexed with other molecules, fibrin, etc.

Tolerance

Tumor antigens that are shared with normal tissue

Treg cells

Immunosuppression

TGF-alpha production by tumor cells

FAS ligand expression by tumor cells— induces apoptosis of lymphocytes

Meta

Beyond, after

Stasis

Still, inactivity

Metastasis

Malignant tumors only

Inefficient

90% of human cancer deaths

Adhesion, migration, stromal invasion, intravasation, tumor emboli, extravasation

Mechanisms of metastasis

Adhesion

1. Loss of intracellular adhesion structures

   1. Desmosomes, adhesion junctions, cadherins

2. Interaction with ECM

   1. Integrins, other receptors

Migration

Autocrine growth factors (HGF, scatter factor)

Stromal invasion

1. Basement membrane degradation

   1. Increased protease activity (neoplastic or surrounding cells)

Intravasation

Chemotactic factors, tumor-associated macrophages

Extravasation

1. Adhesion molecules on endothelium

2. Suitable microenvironment is necessary

Lymphatic, hematogenous, transcoelomic

Pathways of metastasis

Lymphatic

Which metastasis pathway?:

Carcinomas

Regional lymph node

Widespread

Hematogenous

Which metastasis pathway?:

Sarcomas

Veins

First capillary bed