Apoptosis is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, DNA fragmentation, and mRNA decay. The average adult human loses between 50 and 70 billion cells each day due to apoptosis. For an average human child between eight and fourteen years old, approximately twenty to thirty billion cells die per day.
In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen. Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen.
Fas ligand is a type-II transmembrane protein expressed on cytotoxic T lymphocytes and natural killer (NK) cells. Its binding with Fas receptor (FasR) induces programmed cell death in the FasR-carrying target cell. Fas ligand/receptor interactions play an important role in the regulation of the immune system and the progression of cancer.
Casein kinase 2 (CK2/CSNK2) is a serine/threonine-selective protein kinase that has been implicated in cell cycle control, DNA repair, regulation of the circadian rhythm, and other cellular processes. De-regulation of CK2 has been linked to tumorigenesis as a potential protection mechanism for mutated cells. Proper CK2 function is necessary for survival of cells as no knockout models have been successfully generated.
The Fas receptor, also known as Fas, FasR, apoptosis antigen 1, cluster of differentiation 95 (CD95) or tumor necrosis factor receptor superfamily member 6 (TNFRSF6), is a protein that in humans is encoded by the FAS gene. Fas was first identified using a monoclonal antibody generated by immunizing mice with the FS-7 cell line. Thus, the name Fas is derived from FS-7-associated surface antigen.
Caspase-9 is an enzyme that in humans is encoded by the CASP9 gene. It is an initiator caspase, critical to the apoptotic pathway found in many tissues. Caspase-9 homologs have been identified in all mammals for which they are known to exist, such as Mus musculus and Pan troglodytes.
The PHLPP isoforms are a pair of protein phosphatases, PHLPP1 and PHLPP2, that are important regulators of Akt serine-threonine kinases and conventional/novel protein kinase C (PKC) isoforms. PHLPP may act as a tumor suppressor in several types of cancer due to its ability to block growth factor-induced signaling in cancer cells.
X-linked inhibitor of apoptosis protein (XIAP), also known as inhibitor of apoptosis protein 3 (IAP3) and baculoviral IAP repeat-containing protein 4 (BIRC4), is a protein that stops apoptotic cell death. In humans, this protein (XIAP) is produced by a gene named XIAP gene located on the X chromosome.
Caspase-3 is a caspase protein that interacts with caspase-8 and caspase-9. It is encoded by the CASP3 gene. CASP3 orthologs have been identified in numerous mammals for which complete genome data are available. Unique orthologs are also present in birds, lizards, lissamphibians, and teleosts.
Serine/threonine-protein kinase PAK 2 is an enzyme that in humans is encoded by the PAK2 gene.
Caspase-6 is an enzyme that in humans is encoded by the CASP6 gene. CASP6 orthologs have been identified in numerous mammals for which complete genome data are available. Unique orthologs are also present in birds, lizards, lissamphibians, and teleosts. Caspase-6 has known functions in apoptosis, early immune response and neurodegeneration in Huntington's and Alzheimer's disease.
Diablo homolog (DIABLO) is a mitochondrial protein that in humans is encoded by the DIABLO gene on chromosome 12. DIABLO is also referred to as second mitochondria-derived activator of caspases or SMAC. This protein binds inhibitor of apoptosis proteins (IAPs), thus freeing caspases to activate apoptosis. Due to its proapoptotic function, SMAC is implicated in a broad spectrum of tumors, and small molecule SMAC mimetics have been developed to enhance current cancer treatments.
Deleted in Liver Cancer 1 also known as DLC1 and StAR-related lipid transfer protein 12 (STARD12) is a protein which in humans is encoded by the DLC1 gene.
Baculoviral IAP repeat-containing protein 7 is a protein that in humans is encoded by the BIRC7 gene.
Ischemic cell death, or oncosis, is a form of accidental cell death. The process is characterized by an ATP depletion within the cell leading to impairment of ionic pumps, cell swelling, clearing of the cytosol, dilation of the endoplasmic reticulum and golgi apparatus, mitochondrial condensation, chromatin clumping, and cytoplasmic bleb formation. Oncosis refers to a series of cellular reactions following injury that precedes cell death. The process of oncosis is divided into three stages. First, the cell becomes committed to oncosis as a result of damage incurred to the plasma membrane through toxicity or ischemia, resulting in the leak of ions and water due to ATP depletion. The ionic imbalance that occurs subsequently causes the cell to swell without a concurrent change in membrane permeability to reverse the swelling. In stage two, the reversibility threshold for the cell is passed and the cell becomes committed to cell death. During this stage the membrane becomes abnormally permeable to trypan blue and propidium iodide, indicating membrane compromise. The final stage is cell death and removal of the cell via phagocytosis mediated by an inflammatory response.
David Cheresh is a Michigan-born scientist who studies angiogenesis and cancer metastasis. His early research focused on the function of integrins, cellular receptors for the extracellular matrix, in cell migration and survival. His current work is on signaling aspects of cell invasion by vascular cells and tumor cells, with a focus on preventing tumor metastasis.
Necroptosis is a programmed form of necrosis, or inflammatory cell death. Conventionally, necrosis is associated with unprogrammed cell death resulting from cellular damage or infiltration by pathogens, in contrast to orderly, programmed cell death via apoptosis. The discovery of necroptosis showed that cells can execute necrosis in a programmed fashion and that apoptosis is not always the preferred form of cell death. Furthermore, the immunogenic nature of necroptosis favors its participation in certain circumstances, such as aiding in defence against pathogens by the immune system. Necroptosis is well defined as a viral defense mechanism, allowing the cell to undergo "cellular suicide" in a caspase-independent fashion in the presence of viral caspase inhibitors to restrict virus replication. In addition to being a response to disease, necroptosis has also been characterized as a component of inflammatory diseases such as Crohn's disease, pancreatitis, and myocardial infarction.
In cellular biology, dependence receptors are proteins that mediate programmed cell death by monitoring the absence of certain trophic factors that otherwise serve as ligands (interactors) for the dependence receptors. A trophic ligand is a molecule whose protein binding stimulates cell growth, differentiation, and/or survival. Cells depend for their survival on stimulation that is mediated by various receptors and sensors, and integrated via signaling within the cell and between cells. The withdrawal of such trophic support leads to a form of cellular suicide.
Paraptosis is a type of programmed cell death, morphologically distinct from apoptosis and necrosis. The defining features of paraptosis are cytoplasmic vacuolation, independent of caspase activation and inhibition, and lack of apoptotic morphology. Paraptosis lacks several of the hallmark characteristics of apoptosis, such as membrane blebbing, chromatin condensation, and nuclear fragmentation. Like apoptosis and other types of programmed cell death, the cell is involved in causing its own death, and gene expression is required. This is in contrast to necrosis, which is non-programmed cell death that results from injury to the cell.
Human growth and transformation-dependent protein (HGTD-P), also called E2-induced gene 5 protein (E2IG5), is a protein that in humans is encoded by the FAM162A gene on chromosome 3. This protein promotes intrinsic apoptosis in response to hypoxia via interactions with hypoxia-inducible factor-1α (HIF-1α). As a result, it has been associated with cerebral ischemia, myocardial infarction, and various cancers.
