The Biology of APOPTOSIS power point presentation

The Biology of APOPTOSIS power point presentation

1. APOPTOSIS DORCAS KIPROP EMMY KINYA

2. APOPTOSIS Apoptosis is a biological process which occurs in all multicellular organisms including plants and animals. It removes the cells from the organism that should no longer be part of it. A poptosis is a greek word meaning dropping or falling off and was first introduced by Kerr, Wyllie and Currie. Apoptosis is also called programmed cell death. It is coordinated ,energy dependent and involves activation of caspases.

3. CTD’ It occurs during development and aging and as a homeostatic process to maintain cell population in tissues. Also occurs as a defense mechanism e.g. immune reactions or when cells are damaged by disease or noxious agent. Apoptosis can also be triggered by irradiation and chemotherapeutic drugs through a P53 dependent pathway. Corticosteroids may also lead to apoptotic death in thymocytes

4. HALLMARKS OF APOPTOSIS Shrinkage of cells. Chromatin condensation. Activation of caspases which induce DNA fragmentation. Fragmentation into membrane bound apoptotic bodies. Rapid phagocytosis by neighboring cells e.g. macrophages, parenchymal cells and neoplastic cells.

5. APOPTOSIS VS NECROSIS Necrosis is uncontrolled process that affects large fields of cells while apoptosis is controlled and can affect individual or cluster of cells. Necrosis is energy independent while apoptosis is energy dependent. Necrosis is independent of caspases activation while apoptosis is caspase activation dependent.

6. CONTD’ Apoptosis Necrosis Single cells or small clusters of cells Often contiguous cells Cell shrinkage and convolution Cell swelling Pyknosis and karyorrhexis Karyolysis, pyknosis, and karyorrhexis Intact cell membrane Disrupted cell membrane Cytoplasm retained in apoptotic bodies Cytoplasm released No inflammation Inflammation usually present

7. Causes of apoptosis Divided into internal and external causes Internal causes DNA damage - cells with significant DNA damage can trigger apoptosis by P53 pathway .P53 activates genes that promote cell death to prevent propagation of mutations Oxidative stress –accumulation of ROS can lead to cellular stress prompting apoptosis as a protective mechanism against damage. Developmental signal-Apoptosis remove excess cells and shapes organs by eliminating those that are no longer needed during embryonic development

8. CONTD’ External causes Immune responses-immune system i nduces apoptosis in infected or malfunctional cells through signaling pathways that involve death receptors. Hormonal signals-hormones i.e. corticosteroids can promote apoptosis in specific cell types such thymocytes during immune regulation. Chemotherapeutic agents-cancer drugs induce apoptosis through different modes of action.

9. MECHANISM OF APOPTOSIS Intracellular signals include; DNA damage, growth factor deprivation and cytokine deprivation while most common extracellular signals are death-inducing signals produced by cytotoxic T cells from the immune system in response to cells that are damaged or infected. Once apoptosis is signaled, changes start to occur within the cell, which  include activation of caspases which cleave cellular components required for normal cellular function such cytoskeletal and nuclear proteins. Due to caspase activity, apoptotic cells begin to shrink and undergo plasma membrane changes that signal the macrophage response.

10. CONTD’ Apoptosis is carried out by caspases -a class of cysteine proteins that cleave target proteins. They’re four initiator caspases (caspase-2, -8, -9, 10) and three executioner caspases (caspase-3, -6, -7)  . E xecutioner caspases cleave the target proteins that eventually leads to the death of the cell.

11. There are three apoptotic pathways : Extrinsic or death receptor pathway. Intrinsic or mitochondrial pathway. Perforin or granzyme pathway.

12. EXTRINSIC APOPTIC PATHWAY Initiated by external signals through the activation of death receptors on the cell surface. It plays a crucial role in eliminating damaged or potentially harmful cells e.g. those infected by viruses or transformed into cancerous cells.

13. Mechanisms of extrinsic pathway. Activation of death receptors The pathway begins when TNF-alpha/ FasL binds to death receptors TNFR1/ Fas respectively. These receptors contain a cytoplasmic domain known as the death domain(DD) that is essential for signal transduction. Formation of death inducing signaling complex(DISC). The binding of FasL to Fas receptor results in the binding of the adaptor protein FADD and the binding of TNF ligand to TNFR1 leads to the binding of adaptor TRADD with recruitment of FADD and RIP. FADD then associates with procaspase-8 via dimerization of the death effector domain. This forms DISC resulting in the activation of procaspase-8 to caspase-8.

14. CONTD’ Caspase cascade The activated caspase-8 cleaves and activates downstream effector caspases that is caspase-3,6 and -7.This leads the execution phase of apoptosis marked by cellular shrinkage, nuclear fragmentation and formation of apoptic bodies. Summary: Extrinsic apoptotic pathway ensures cellular homeostasis and prevents disease progression.

15. Abbreviation Protein Name Select Alternate Nomenclature TNF- α Tumor necrosis factor alpha TNF ligand, TNFA, cachectin TNFR1 Tumor necrosis factor receptor 1 TNF receptor, TNFRSF1A, p55 TNFR, CD120a FasL Fatty acid synthetase ligand Fas ligand, TNFSF6, Apo1, apoptosis antigen ligand 1, CD95L, CD178, APT1LG1 FasR Fatty acid synthetase receptor Fas receptor, TNFRSF6, APT1, CD95 Apo3L Apo3 ligand TNFSF12, Apo3 ligand, TWEAK, DR3LG DR3 Death receptor 3 TNFRSF12, Apo3, WSL-1, TRAMP, LARD, DDR3 Apo2L Apo2 ligand TNFSF10, TRAIL, TNF-related apoptosis inducing ligand DR4 Death receptor 4 TNFRSF10A, TRAILR1, APO2 DR5 Death receptor 5 TNFRS10B, TRAIL-R2, TRICK2, KILLER, ZTNFR9 FADD Fas-associated death domain MORT1 TRADD TNF receptor-associated death domain TNFRSF1A associated via death domain RIP Receptor-interacting protein RIPK1 DED Death effector domain Apoptosis antagonizing transcription factor, CHE1 caspase-8 Cysteinyl aspartic acid-protease 8 FLICE, FADD-like Ice, Mach-1, Mch5 Extrinsic pathway proteins, abbreviations, and alternate nomenclature.

16. INTRINSIC APOPTIC PATHWAY Initiated by internal cellular stresses and is activated in response to various stressors such as DNA damage, oxidative stress, hypoxia and the absence of survival signals. MECHANISM Mitochondrial membrane permeabilization Begins with the activation of pro-apoptotic proteins from the BCL-2 family, such as BAK and BAX this induce changes in the mitochondrial membrane leading to permeabilization and the release of cytochrome C into the cytoplasm.

17. CONTD’ Formation of apoptosome Cytochrome C binds to the Apaf-1 and procaspase-9 forming a complex known as the apoptosome.This complex activates caspase-9. Caspase cascade activation Activated caspase-9 cleaves and activates effector caspases primarily caspase-3 leading to the execution phase of apoptosis.

18. Abbreviation Protein Name Select Alternate Nomenclature Smac/DIABLO Second mitochondrial activator of caspases/direct IAP binding protein with low PI None HtrA2/Omi High-temperature requirement Omi stress regulated endoprotease, serine protease Omi protein A2 IAP Inhibitor of Apoptosis Proteins XIAP, API3, ILP, HILP, HIAP2, cIAP1, API1, MIHB, NFR2-TRAF signaling complex protein Apaf-1 Apoptotic protease activating factor APAF1 Caspase-9 Cysteinyl aspartic acid-protease-9 ICE-LAP6, Mch6, Apaf-3 AIF Apoptosis Inducing Factor Programmed cell death protein 8, mitochondrial CAD Caspase-Activated DNAse CAD/CPAN/DFF40 Bcl-2 B-cell lymphoma protein 2 Apoptosis regulator Bcl-2 Bcl-x BCL2 like 1 BCL2 related protein Bcl-XL BCL2 related protein, long isoform BCL2L protein, long form of Bcl-x Bcl-XS BCL2 related protein, short isoform Bcl-w BCL2 like 2 protein Apoptosis regulator BclW BAG BCL2 associated athanogene BAG family molecular chaperone regulator Intrinsic pathway proteins, abbreviations, and alternate nomenclature.

19. Summary: Intrinsic pathway maintains cellular homeostasis and eliminates damaged cells making it a critical target for cancer therapies aimed at inducing apoptosis in malignant cells.

20. PERFORIN/GRANZYME APOPTOTIC PATHWAY Is a variant of type IV hypersensitivity where sensitized CD8 cells kill antigen variant cells . CTLs are able to kill target via; The extrinsic pathway and FasL/ FasR interaction. Secretion of perforin (Transmembrane pore forming molecule) with the release of cytoplasmic granules composed of granzyme A and B.These granules are released through the pore and into the target cell.

21. Granzyme A and B Granzyme B will cleave proteins and activate procaspase-10.It can also cleave factors like ICADD(inhibitor of caspase activated DNase). It can utilize the mitochondrial pathway for amplification of the death signal by specific cleavage of Bid and induction of cytochrome C release. Granzyme B can also directly activate caspase-3 therefore the upstream signaling pathways are bypassed and there's direct induction of the apoptotic execution phase.

22. CONTD’ Granzyme A is important in CTLs induced apoptosis and activates caspase independent pathways. Once in the cell granzyme A activates DNA nicking via DNAse NM23-H1, which is a tumor suppressor gene. The nucleosome assembly protein SET inhibits the NM23-H1 gene. Granzyme A cleaves the SET complex thus releasing the inhibition of the NM23-H1 gene resulting in apoptotic DNA degradation. The SET complex has important functions in chromatid structure and DNA repair. Thus inactivation of this complex by granzyme A likely contributes to a poptosis by blocking the maintenance of DNA and chromatin structure integrity.

23. APOPTOSIS IN CANCER Delayed or inhibited apoptosis is associated with cancer. Prevention of cancer is one of the main functions of apoptosis. The loss of apoptotic control allows cancer cells to survive longer and gives more time for the accumulation of mutations which can increase invasiveness during tumor progression, stimulate angiogenesis, deregulate cell proliferation and interfere with differentiation  .

24. CONTD’ A hallmark of cancer includes apoptotic evasion which occurs via; Caspase function inhibition. Disabling apoptosis triggers. Upregulation of anti-apoptotic BCL2 proteins. Loss of BAX and BAK. BCL2 mutations . Overexpression of BCL2 proteins which result in tumor cells that are resistant to any intrinsic apoptotic stimuli which includes some anticancer drugs.

25. APOPTOSIS AND CANCER THERAPY Using the cell’s own mechanism for death is a highly effective method for cancer treatment and is the most successful non surgical treatment mode. Targeting apoptosis is also effective for all types of cancer, as apoptosis evasion is a hallmark of cancer and is nonspecific to the cause or type of the cancer .   Common strategies for therapeutic targeting are stimulation of pro-apoptotic molecules and inhibition of anti-apoptotic molecules.

26. CONTD’ Some of the targets that have been researched include ligands for death-receptors , inhibitors for BCL-2 , XIAP inhibition and alkylphospholipid analogs (APL) which act as apoptotic signals.

27. REFERENCES Saraste A, Pulkki K. Morphologic and biochemical hallmarks of apoptosis. Cardiovasc Res. 2000 Feb;45(3):528-37. doi: 10.1016/s0008-6363(99)00384-3. PMID: 10728374. Pfeffer CM, Singh ATK. Apoptosis: A Target for Anticancer Therapy. Int J Mol Sci. 2018 Feb 2;19(2):448. doi: 10.3390/ijms19020448. PMID: 29393886; PMCID: PMC5855670. O'Brien MA, Kirby R. Apoptosis: A review of pro‐apoptotic and anti‐apoptotic pathways and dysregulation in disease. J Vet Emerg Crit Care (San Antonio). 2008 Dec;18(6):572–85. doi: 10.1111/j.1476-4431.2008.00363.x. Epub 2008 Dec 18. PMCID: PMC7169302.

28. CONTD’ Sec. Pharmacology of Anti-Cancer Drugs.Volume 14 - 2023 |  https://doi.org/10.3389/fphar.2023.1338633 Mol Cancer Ther . 2016 September ; 15(9): 2011–2017. doi:10.1158/1535-7163.MCT-16-0031