BCOR 103 1st Edition Lecture 18 Outline of Last Lecture I PKA Activation II Second Messengers III Kinases and Signaling Proteins Outline of Current Lecture I Apoptosis II Caspases III Intrinsic and Extrinsic Pathways IV Cell Cycle Current Lecture Apoptosis programmed cell death o Balances cell division and cell death to maintain constant cell numbers in tissueshomeostasis o Defense mechanisms in response to pathogen infections cell damage and DNA damage o Elimination of unwanted cells during development Cellular Effects of Apoptosis o DNA fragmentation occurs chromatin condenses fragmentation of the nucleus then fragmentation of the cell Apoptosis in C elegans requires Ced 3 o During development 131 cells die through apoptosis o Results in exactly 959 somatic cells in adult worms o In mutant worms that have Ced 1 There is no engulfment of apoptotic dead cells Ced 1 is required for signaling to engulf apoptotic cells receptors Caspases Function in Apoptotic Protein Degradation These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Caspases proteases with cysteine C resides at their active sites that cleave after aspartic acid residues in substrate proteins o At least seven caspases in mammalian cells only 1 Ced 3 in C elegans o 100 target proteins are destroyed Functions of Caspases o Inhibitor of DNase ICAD DNA fragmentation o Nuclear lamins fragmentation of nucleus o Cytoskeletal proteins actin myosin actinin tubulin vimentin cytoskeletal disruption cell fragmentation membrane bubbling o Golgi Matrix Proteins fragmentation of Golgi Caspases are activated by Proteolytic Caspase Cascades o All caspases are activated by proteolytic cleavage which is catalyzed by other caspases o Caspases can be either initiator or effector caspases o Initiator caspases activated in response to primary apoptotic signal o Effector caspases activated by initiator caspases they cleave target proteins Intrinsic Pathway of Apoptosis o Two major pathways by which signals can trigger apoptosis o Intrinsic pathway cell damage leads to release of cytochrome c from mitochondria a k a activated T cell autonomous death ACAD o IAPs inhibitor of Apoptosis proteins Suppress apoptosis by inhibiting caspase activity Extrinsic Pathway of Apoptosis o Extrinsic pathway secreted polypeptides activate cell death receptors a k a activation induced cell death AICD o Polypeptides belong to tumor necrosis factor TNF family o TNFs bind to TNF receptors Leads to activation of initiator caspases e g caspase 8 Ex Fas receptor functions in immune cell death Apoptosis and Bacterial Pathogens o Bacterial pathogens and HIV can either inhibit or induce apoptosis through either intrinsic or extrinsic apoptosis pathways Cell Survival Signaling requires PIP3 o PIP2 PI 3 Kinase PIP3 o PIP3 PTEN PIP2 Cell Survival Signaling Anti Apoptosis o PI 3 Kinase and Akt human oncogenes o PTEN human tumor suppressor gene Eukaryotic Cell Cycle and its Regulators o Cell division cycle process by which eukaryotic cells grow and divide Cell Division Cycle must occur with High Fidelity o DNA must be duplicated without errors o Chromosomes must segregate equally to daughter cells o Centrioles centrosomes must be duplicated and distributed to daughter cells during mitosis o Transcriptional programming must be maintained or reprogrammed in response to environmental cues o Mitochondria and other cellular organelles must be distributed to daughter cells o Cell division must be carefully controlled during development and in tissues o Cell division must be integrated with apoptosis Phases of Eukaryotic Cell Cycle o Mitosis M phase nuclear division separation of daughter chromosomes o Interphase period between mitoses growth and DNA replication occurs G1 phase gap between mitosis and DNA replication cells are metabolically active S phase DNA replication G2 phase gap between DNA replication and mitosis cells continue to synthesize proteins G0 phase quiescent stage Cells are metabolically active but do not proliferate Extracellular signals can induce cells to re enter G1 phase Embryonic Cell Cycles o Very rapid cell divisions o No G1 or G2 phases cells do not grow o Only M and S phases very short S phase Dependency Mechanisms vs Clock Mechanism o Cells integrate duplication of cell material with growth o Stage specific events vs continuous processes Events depend on previous event being completed o Progress monitored at checkpoints o DNA replication occurs immediately after mitosis and doesn t depend on mitosis being completed o Suggest a clock mechanism for control Techniques used to study Cell cycle o Biochemical approaches Examine enzyme activities or protein levels that fluctuate during the cell cycle Determine cellular DNA content using fluorescent dye propidium iodide that binds to DNA o Cytological approaches Morphology of yeast cells can distinguish stages of cell cycle Fluorescent dyes stain actin tubulin etc o Genetic approaches Isolate mutants with defects in cell cycle cell division cycle cdc mutants Most cdc mutants affect essential cell cycle events and are lethal events must use conditional lethal mutants Comparison of Yeast and Mammalian Cell Cycles o Genetic yeast and biochemical mammal approaches converged to show that cell cycle regulation is fundamentally the same for all eukaryotes Transit though the cell cycle is regulated by phosphorylation dephosphorylation and proteolysis