Apoptosis 1 PDF

Apoptosis 1. Judit Bátor 2024. Types of cell death Not regulated: necrosis The damaging effect cannot be survived ( = pathological circumstances) E.g. heat, mechanical stress, irradiation, chemicals, anoxia Regulated: The damaging effect could be survived (...

Apoptosis 1. Judit Bátor 2024. Types of cell death Not regulated: necrosis The damaging effect cannot be survived ( = pathological circumstances) E.g. heat, mechanical stress, irradiation, chemicals, anoxia Regulated: The damaging effect could be survived (heat, irradiation, chemicals, hypoxia, growth factor withdrawal, etc.), but the cell kills itself for the good of the organism/other cells Active cell death, signal transduction, ATP are required More types exist (more, than 10) Autophagy: role of lysosomes; pathological stimuli activate it Apoptosis: may be activated under physiological conditions (healthy cell is not any more needed), or under pathological circumstances (see also: physiological and pathological role of apoptosis) This type of cell death should be induced during chemo- and radiotherapy of tumor cells Morphological features of apoptosis and necrosis Necrosis Apoptosis Stimuli always pathological Physiological or pathological Appearance Group of cells Single cells or groups of cells Involved cells swell shrink, later apoptotic bodies are formed Cell nucleus Karyolysis Karyopyknosis Karyorrhexis DNA Random cleavage internucleosomal DNA cleavage Cell membrane Early damaged Remains intact Externalisation of phosphatidyl- serine organelles Damaged Remain intact Result Content of cells will Apoptotic bodies be released to their environment Inflammation yes no Phagocytosis no yes Molecular Cell Biology Syllabus Alterations of nucleus (see Syllabus, ”The pathology of cell nucleus” chapter) Apoptosis: Necrosis: Karyolysis Karyopyknosis (lysis of nucleus) (shrinkage of nucleus, chromatin condensation), followed by Karyorrhexis (fragmentation of nucleus) Molecular Cell Biology Syllabus Signal transduction of apoptosis Intrinsic pathway: mitochondrial pathway Cell detects inside the damaging effect E.g. DNA damaging effect of irradiation, chemotherapeutical agents, free radicals Extrinsic pathway: receptor-mediated apoptosis So-called death ligands bind to their receptors Intrinsic pathway: p53 protein plays an important role transcription factor (but it has probably also functions independent of transcription) Always synthesized - but also broken down (by ubiquitin- proteasome system) in healthy cells It is activated and stabilized for DNA damage It’s function: Lesser DNA-damage: stops cell cycle, induces repair enzymes Larger DNA-damage: induces apoptosis Induces proapoptotic proteins, among them proapoptotic BH3-only Bcl2 family members Molecular Cell Biology Syllabus Intrinsic pathway: proteins of Bcl2 family play an important role Name: abbreviation of ‚B-cell lymphoma’ Members: Antiapoptotic or Proapoptotic role Antiapoptotic Bcl2 family members Contain BH1, BH2, BH3, BH4 domains (BH is abbreviation of ‚Bcl-2 homologous’) Are always present and active In healthy cells they bind to proapoptotic multidomain family members thereby inactivating them In apoptotic cells they prefer the binding to the newly synthesized/activated ”BH3- only” family members E.g. Bcl-2, Bcl-xL Molecular Cell Biology Syllabus Bcl2 family (2) Proapoptotic family members Proapoptotic multidomain family members Contain BH1,BH2, BH3 domains Always present, but in healthy cells inactivated by binding of antiapoptotic Bcl-2 family members to them Activation: released by antiapoptotic family members, they bind with each other to form pores in the outer membrane of mitochondria. Certain proteins are released to the cytosol through these pores (e.g. cytochrome c). E.g. Bax Molecular Cell Biology Syllabus  Bcl2 family (3) Proapoptotic family members Proapoptotic ”BH3-only” proteins Contain only BH3 domain (BH1,2,4 not) Are synthesized or activated as a result of apoptotic stimuli Bind antiapoptotic Bcl-2 family members (are preferred by them) E.g. Bad, Puma Molecular Cell Biology Syllabus, Caspases: important in the effector phase of apoptosis Protein family Name: cysteinyl-aspartases (Cysteine containing proteases, which cleave after an aspartic acid residue) Always present, also in healthy cells in inactive form: called procaspases Activation happens by cleavage as a result of apoptotic signal transduction procaspase → caspase Autocleavage or cleaved by a different caspase Caspase-cascade Active form: cleaves target proteins (very specific cleavage, does not chop into small pieces, but activates/inactivates them) Initiator caspases: cleave the effector caspases (e.g. caspase 8 and caspase 9) Effector caspases: cleave many different target proteins (e.g. caspase 3)  Intrinsic pathway 1. e.g. DNA damage Activation of p53→ Induction of „BH3-only” Bcl2 family members, which bind to the antiapoptotic Bcl2 family members Multidomain-proapoptotich family members are released (from antiapoptotic members), form pores in mitochondrial outer membrane Through these pores cytochrom C is released to cytosol Cytochrom C forms a complex with Apaf1 (apoptosis-activating factor 1) and procaspase 9 (name of the complex: apoptosome) Molecular Cell Biology Syllabus, modified  Intrinsic pathway 2. Procaspase 9 (initiator caspase) in the apoptosome cleaves itself to active caspase 9 Cleaves effector caspases, e.g. procaspase 3 caspase 3 cleaves different target proteins: Signal transduction proteins (may be activated or inactivated, depending on the cleaved protein) Repair proteins are inactivated Nuclease is activated Proteins of cytoskelett (cell shape changes) Lamin proteins (shrinkage of nucleus, condensation of chromatin ”death by thousands of cuts” Apoptotic bodies are formed (membrane bounded vesicles containing fragments of cytoplasm and cell nucleus) Which are phagocyted by neighboring cells. Molecular Cell Biology Syllabus, modified Thank you for your attention!