Lecture 19 Homework Review Apoptosis and Cancer Next Two Lectures: Cell-Cell Interactions/Tissues Early Development and Stem Cells For Exam III- You are not responsible for any material in assigned chapters relating to Plants! Office Hours This Week: Today ~ 5:30- 7:30pm

Apoptosis: Regulated Cell Death Role in Killing of Unneeded, Damaged, or Potentially Deleterious Cells Occurs in Embryonic and Adult Tissues Proteins Involved are Always Present in Cells- Needs to Be Activated by Stimuli Can Result From: Developmental Cues Withdrawl of Essential Growth Factors DNA Damage Various Cell Stresses

Programmed Cell Death Cell Death Occurring at a Defined Point in Development Usually proceeds by Apoptosis Mouse Paws

Not All Cell Death is Apoptotic Apoptosis: An Active Regulated Process DNA Fragmentation Chromatin Condensation Fragmentation of Nucleus Cell Shrinks Formation of Membrane Enclosed Fragments called Apoptotic Bodies Recognition and Engulfment by Phagocytic Cells or Neighboring Cells Oncosis and Necrosis: Unregulated Cell Death Due to Injury Cell Swells (Oncosis) Nucleus Swells Disruption of Organelles and Rupture/Release of Contents Contents Released into Extracellular Space

The Morphological Changes of Apoptosis Are Orchestrated by Caspases Cysteine Proteases that cleave at Aspartic Acid Residues Activate Apoptosis by Cleaving Specific Substrates Present but inactive in cells Two Main Types of Caspases: 1) Initiators- Need to dimerize to become active “induced proximity” 2) Executioner (Effector) - Need to be proteolytically cleaved to become active - Cleavage is usually Mediated by Initiator Caspases Zymogens

Once Executioners are Activated their Key Targets of Proteolysis Include: 1)An Inhibitor of a DNAse- Leads to Fragmentation of DNA 2)Nuclear Lamins- Leads to Fragmentation of Nucleus 3)Other Cytoskeletal Associated Proteins- Leads to Disruption of Cytoskeleton and Cell Fragmentation 4)Additional Caspases Caspase Activation Amplification Cascade

Main Pathways Regulating Caspase Activation During Apoptosis Intrinsic Pathway- Mitochondrial Mediated Major Pathway in Mammalian Cells –Outer Mitochondrial Membrane Permeabilization (MOMP) –Release of Cytochrome C from Mitochondrial Intermembrane Space into Cytosol –Apoptosome Formation- Activation of Initiator Caspase –Effector Caspases Activated Extrinsic Pathway- Signaling through Death Receptors –Ligand Bound Death Receptors –Adaptor Protein Association –Initiator Caspase Recruitment and Activation –Effector Caspases Activated

Intrinsic Pathway of Apoptosis Activation Association of Adaptor with Procaspase allows Procaspase self cleavage MOMPs cytochrome c Release Apoptosome Formation: Adaptor (Apaf1), dATP cytochrome c and procaspase complex Active Initiator Caspase Cleaves Effector Caspases Which now Cleave Targets

Critical Regulators of Cell Death Bcl-2 Family – Regulate whether MOMPs Occurs Anti-Apoptotic Factors - Death Inhibitors A) Function to Inhibit MOMPs by Pro Apoptotic Factors Pro-Apoptotic Factors- Death Activators A) Bind and inhibit Death Inhibitors B) Directly cause Permeabilization of MOM to Stimulate Release of Cytochrome C ( BAX AND BAK) IAP Family (Inhibitor of Apoptosis) Bind Procaspases prevent activation Bind Caspases and inhibit Activity

Survival Factor Signaling is Required to Prevent Apoptosis

Programmed Cell Death in Neuronal Development

Survival Factors Signaling Can Function to Keep Anti-Apoptotic Factor Bcl-2 Active No Survival Signal Bcl-2 Complexes with Bad Can’t prevent BAK and BAX Mediated MOMPs

Extrinsic Pathway of Apoptosis Activation: Signaling through the Death Receptors Ligand Bound Death Receptors Adaptor Protein and Procaspase Recruitment Initiator Caspase Activation Effector Caspases Activated Target cells : Viral Infected Cells or Cancer Cells Removal of Excess Lymphocytes after Infection

Cancer Cancer is a Disease of Cells that Proliferate at Inappropriate Times and Locations in the Body. Tumors (Neoplasms) - Masses of cells derived from a single abnormally proliferating cell. Tumors are Clonal 1. Benign- Noninvasive, Do not affect other tissues 2. Malignant- Cancerous, Locally Invasive and May Spread Tumors are classified by cell type from which they arise. 1. Carcinoma- 90% of human cancers- Malignacy of Epithelial Cells 2. Sarcomas – Rare, Solid tumors of connective tissue, such as bone, muscle, cartilage, and fibrous tissue. 3. Leukemias and Lymphomas- 7% of cancers, Blood forming cells and cells of immune system 4. Neuroectodermal- Cells of central or peripheral nervous system

The Development of Cancer is a Multistep Process Typically requires four to six different mutations Tumorigenesis Occurs by Clonal Expansion: Yields Population of Cells More Abnormal and More Adapted Proliferate, Survive, Invade and Metastasize Intravasation: Malignant cells gain access to blood vessels and lymphatic system and spread Metastasis: Malignant cells Establish in distant organs Initial Cell Proliferating Abnormally

Key Characteristic Normal Cell Cancer Cell Contact Inhibition of Growth Present Absent Growth Factor Requirements High Low Anchorage Dependence Present Absent Cell Cycle Checkpoints Intact Absent Karyotypic Profile Normal Abnormal Proliferative Life Span Finite Indefinite Cancer cells are also: Defective in Differentiation Fail to Undergo Apoptosis Cancer Cells are Characterized by Several Distinct Properties when Grown in vitro

Cancer Cells Are Created when Certain Genes are Mutated Mutations can be Inherited, Introduced by Viruses, or Result of DNA Damage (exposure to a mutagen) 1. Oncogenes - Gene whose presence can trigger inappropriate cell proliferation. Example: ras, bcl-2 (Normal version of gene: Proto-oncogene) 2. Tumor Suppressors- Gene whose absence or inactivation can lead to cancer Usually Function to Block Cell Cycle Progression Example: p53, Rb DNA Repair Genes- Increase Rate of Mutation, provide opportunity for mutation in growth controlling genes, increase rate of tumor progression

Cancer Cells Are Created When Certain Genes are Mutated Activation of Oncogene Can Also Occur By: Overexpression of Proto- oncogene Translocations that create hybrid proteins Inhibition of Tumor Suppressor Genes

Oncogenes are Found in Mitogen and Growth Factor Signal Transduction Pathways Mutation of Proto-oncogene- Constitutively Active Downstream Signal Transduction Pathway

Inactivation of Tumor Suppressor Rb Common Target for Viruses that Cause Tumors (along with p53)

Cancer Cells Exhibit Unlimited Proliferative Ability Cancer cells avoid senescence by inactivating tumor suppressor genes, p53 and Rb. Cancer Cells will continue to divide for a period of time Crisis Point – Large number of Cancer Cells Die- Result of catastrophic rearrangements- due to lack of telomerase Rare Occasion A Cell Survives- It is Immortalized. At some point- derepressed telomerase expression ~ 90% of cancer cells express significant levels of telomerase