Which organelle causes apoptosis

A large calcium influx into mitochondria from the ER can promote cell death, but the magnitude and outcome of the response is modulated by the presence of various Bcl-2 family proteins on either organelle [72, 73] Fig. The cell cycle is divided into four phases, and the cellular decision to initiate mitosis or to become quiescent G0 state occurs during the G1 phase. Oncogenes have a dual role: they can induce both proliferation and apoptosis Fig.

These cells are dangerous as they can accumulate mutations and become carcinogenic. What are the stages of apoptosis? Four Stages of Apoptosis Schematic To illustrate these apoptosis events and how to detect them, Bio-Rad has created a pathway which divides apoptosis into four stages: induction, early phase, mid phase and late phase Figure 1. Can lysosomes destroy an entire cell? A lysosome is a membrane-bound cell organelle that contains digestive enzymes. Lysosomes are involved with various cell processes.

They break down excess or worn-out cell parts. If the cell is damaged beyond repair, lysosomes can help it to self-destruct in a process called programmed cell death, or apoptosis. What are some examples of apoptosis? Programmed cell death is as needed for proper development as mitosis is. Examples: The resorption of the tadpole tail at the time of its metamorphosis into a frog occurs by apoptosis.

The formation of the fingers and toes of the fetus requires the removal, by apoptosis, of the tissue between them. How is apoptosis controlled? It's sometimes referred to as programmed cell death, and indeed, the process of apoptosis follows a controlled, predictable routine. When a cell is compelled to commit suicide we'll get to the triggers for apoptosis in just a minute , proteins called caspases go into action. What gene is responsible for Apoptosis? P53 gene.

In healthy cells this lipophilic dye accumulates in the mitochondria, forming aggregates that emit a specific fluorescence. In apoptotic cells the MOM does not maintain the electrochemical gradient and the cationic dye diffuses into the cytoplasm where it emits a fluorescence that is different from the aggregated form.

Other mitochondrial dyes can be used that measure the redox potential or metabolic activity of the mitochondria in cells. However, these dyes do not address the mechanism of cell death and should be used in conjunction with other apoptosis detection methods such as a caspase assay.

Cytochrome c release from the mitochondria can also be assayed using fluorescence and electron microscopy in living or fixed cells Scorrano et al. However, cytochrome c becomes unstable once it is released into the cytoplasm Goldstein et al. Therefore a non-apoptotic control should be used to ensure that the staining conditions used are able to detect any available cytochrome c.

Apoptotic or anti-apoptotic regulator proteins such as Bax, Bid, and Bcl-2 can also be detected using fluorescence and confocal microscopy Tsien, ; Zhang et al.

However, the fluorescent protein tag may alter the interaction of the native protein with other proteins. Therefore, other apoptosis assays should be used to confirm the results. There is evidence of other forms of non-apoptotic programmed cell death that should also be considered since they may lead to new insights into cell death programs and reveal their potentially unique roles in development, homeostasis, neoplasia and degeneration. It has become increasingly apparent that cell death mechanisms include a highly diverse array of phenotypes and molecular mechanisms.

And there is evidence that modulation of one form of cell death may lead to another. There are necrotic-like phenotypes that require gene activation and protein synthesis so they are, strictly speaking, forms of programmed cell death Proskuryakov et al. By affecting the mitochondrial respiratory chain with antimycin A, Formigli and coworkers induced a type of cell death that shared dynamic, molecular, and morphological features with both apoptosis and necrosis.

Caspase-independent mechanisms of neuronal cell death have also been identified. This specific type of programmed cell death may involve specific mitochondrial factors. Oppenheim and coworkers have shown that programmed cell death occurs in developing mammalian neurons, even after the genetic deletion of caspases.

Other research has shown that inhibition of the caspase execution machinery may only temporarily rescue damaged neurons and that classical apoptotic features can still appear in caspase-inhibited neurons Volbracht et al.

It appears that caspase-dependent and caspase-independent mechanisms of neuronal cell death may depend on brain region, cell type, and age. Autophagic cell death is characterized by the sequestration of cytoplasm and organelles in double or multimembrane vesicles and delivery to the cells own lysosomes for subsequent degradation Noda et al. The mechanisms and morphology of autophagy are evolutionarily conserved with strong similarities between organisms as diverse as animals, plants and yeast.

The process of autophagy depends on both continuous protein synthesis and the continuous presence of ATP. The molecular mechanisms have been extensively studied in yeast and mammalian orthologues continue to be elucidated Ohsumi, ; Huang and Klionsky, This distinction of a autophagic programmed cell death was made because it was determined that some cells would undergo caspase-independent gene-activated cell death but would display few of the ultrastructural features characteristic of apoptosis Table 1 and would not exhibit DNA laddering Cohen, However these cells do require de novo gene expression with an increase in expression of the polyubiquitin gene, similar to apoptosis Ohsumi, ; Gozuacik and Kimchi, Specifically, autophagy occurs in all eukaryotic cells and involves the dynamic rearrangement of subcellular membranes to sequester cytoplasm and organelles for delivery to the lysosome or vacuole where degradation occurs.

This is considered to be the major inducible pathway for the general turnover of cytoplasmic components. A unique ubiquitin-like protein conjugation system and a protein complex that directs membrane docking and fusion at the lysosome or vacuole are important components of autophagy.

In general, the process of autophagy can be divided into 4 steps: 1 induction, 2 formation of the autophagosome, 3 fusion with the lysosome or vacuole, and 4 autophagic body breakdown and recycling. Although the molecular details are still being elucidated, the regulation of this process occurs through various kinases, phosphatases and guanosine triphosphatases GTPases.

However, the core apoptotic pathway can be diverted to induce a necrotic phenotype by alteration of the availability of intracellular ATP and the availability of caspases. A similar relationship may occur between apoptosis and autophagy. It has been suggested that mitochondria may be central organelles that integrate both apoptosis and autophagy Elmore et al.

Moreover, some of the same signals that are involved in apoptosis may also be involved in autophagy. For example, in both apoptosis and autophagy, there is the coordinated regulation of Akt protein kinase B and p70S6 kinase. Malignant transformation is another link between autophagy and apoptosis Gozuacik and Kimchi, Similarly, a correlation between reduced autophagy and cancer has also been documented.

Studies have indicated that during malignant transformation several proteins and pathways that are related to autophagy signaling are deregulated resulting in reduced autophagocytic activity. This suggests that, in some circumstances, autophagy may function as a safeguard mechanism that restricts uncontrolled cell growth. Autophagy has also been considered a protective mechanism against apoptosis.

Lemasters and coworkers observed that depolarized mitochondria, a feature of apoptosis, are rapidly eliminated by autophagy in primary hepatocytes. Eliminating damaged mitochondria prevents the release of pro-apoptotic substances from the mitochondria, thus preventing apoptosis. Autophagy is considered the major cellular mechanism for disposing of long-lived proteins and cytoplasmic organelles; however, the concept of autophagic cell death has been a matter of debate within the scientific community.

Since there is a distinct advantage of increased autophagy in various physiological and stress conditions, it has been suggested that autophagy represents an important adaptive mechanism that attempts to rescue cells from death. There are reports that apoptosis and autophagic programmed cell death are not mutually exclusive and the diverse morphologies are attributed, in part, to distinct biochemical and molecular events Gozuacik and Kimchi, In certain cells and under certain conditions the morphological features of autophagy may occur prior to apoptotic cell death, representing an early phase of apoptosis.

The controversy still remains, however interest in the field of autophagic cell death is constantly increasing with the emergence of new assays and markers for elucidating the molecular basis of autophagy and its possible implications in programmed cell death and malignant cell transformation. Apoptosis is regarded as a carefully regulated energy-dependent process, characterized by specific morphological and biochemical features in which caspase activation plays a central role.

Although many of the key apoptotic proteins that are activated or inactivated in the apoptotic pathways have been identified, the molecular mechanisms of action or activation of these proteins are not fully understood and are the focus of continued research.

The importance of understanding the mechanistic machinery of apoptosis is vital because programmed cell death is a component of both health and disease, being initiated by various physiologic and pathologic stimuli. Moreover, the widespread involvement of apoptosis in the pathophysiology of disease lends itself to therapeutic intervention at many different checkpoints. Understanding the mechanisms of apoptosis, and other variants of programmed cell death, at the molecular level provides deeper insight into various disease processes and may thus influence therapeutic strategy.

National Center for Biotechnology Information , U. Toxicol Pathol. Author manuscript; available in PMC Dec 6. Susan Elmore. Author information Copyright and License information Disclaimer.

Copyright notice. The publisher's final edited version of this article is available at Toxicol Pathol. See other articles in PMC that cite the published article. Abstract The process of programmed cell death, or apoptosis, is generally characterized by distinct morphological characteristics and energy-dependent biochemical mechanisms.

Introduction The term apoptosis a-po-toe-sis was first used in a now-classic paper by Kerr, Wyllie, and Currie in to describe a morphologically distinct form of cell death, although certain components of the apoptosis concept had been explicitly described many years previously Kerr et al. Morphology of Apoptosis Light and electron microscopy have identified the various morphological changes that occur during apoptosis Hacker, Open in a separate window. Figure 1. Figure 2. Distinguishing Apoptosis from Necrosis The alternative to apoptotic cell death is necrosis, which is considered to be a toxic process where the cell is a passive victim and follows an energy-independent mode of death.

Table 1 Comparison of morphological features of apoptosis and necrosis. 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.

Is Apoptosis an Irreversible Process? Mechanisms of Apoptosis The mechanisms of apoptosis are highly complex and sophisticated, involving an energy-dependent cascade of molecular events Figure 3.

Figure 3. Biochemical Features Apoptotic cells exhibit several biochemical modifications such as protein cleavage, protein cross-linking, DNA breakdown, and phagocytic recognition that together result in the distinctive structural pathology described previously Hengartner, Extrinsic Pathway The extrinsic signaling pathways that initiate apoptosis involve transmembrane receptor-mediated interactions. Table 2 Extrinsic pathway proteins, abbreviations, and alternate nomenclature.

Intrinsic Pathway The intrinsic signaling pathways that initiate apoptosis involve a diverse array of non-receptor-mediated stimuli that produce intracellular signals that act directly on targets within the cell and are mitochondrial-initiated events. Table 3 Intrinsic pathway proteins, abbreviations, and alternate nomenclature.

Execution Pathway The extrinsic and intrinsic pathways both end at the point of the execution phase, considered the final pathway of apoptosis. Table 4 Execution pathway proteins, abbreviations, and alternate nomenclature. Physiologic Apoptosis The role of apoptosis in normal physiology is as significant as that of its counterpart, mitosis. Inhibition of Apoptosis There are many pathological conditions that feature excessive apoptosis neurodegenerative diseases, AIDS, ischemia, etc.

Assays for Apoptosis Since apoptosis occurs via a complex signaling cascade that is tightly regulated at multiple points, there are many opportunities to evaluate the activity of the proteins involved. Apoptosis assays, based on methodology, can be classified into six major groups and a subset of the available assays in each group is indicated and briefly discussed: Cytomorphological alterations DNA fragmentation Detection of caspases, cleaved substrates, regulators and inhibitors Membrane alterations Detection of apoptosis in whole mounts 6.

Mitochondrial assays. Cytomorphological Alterations The evaluation of hematoxylin and eosin-stained tissue sections with light microscopy does allow the visualization of apoptotic cells. Figure 4. Detection of Caspases, Cleaved Substrates, Regulators, and Inhibitors There are more than 13 known caspases procaspases or active cysteine caspases that can be detected using various types of caspase activity assays Gurtu et al.

Figure 5. Membrane Alterations Externalization of phosphatidylserine residues on the outer plasma membrane of apoptotic cells allows detection via An-nexin V in tissues, embryos or cultured cells Bossy-Wetzel and Green, Mitochondrial Assays Mitochondrial assays and cytochrome c release allow the detection of changes in the early phase of the intrinsic pathway.

Other Forms of Programmed Cell Death There is evidence of other forms of non-apoptotic programmed cell death that should also be considered since they may lead to new insights into cell death programs and reveal their potentially unique roles in development, homeostasis, neoplasia and degeneration.

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Cancer Res. Fluorometric and colorimetric detection of caspase activity associated with apoptosis. Anal Biochem. Which protozoan organelle is responsible for digestion? What organelle is responsible for information storage?

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