The Course of Etoposide-induced Apoptosis from Damage to DNA and p53 Activation to Mitochondrial Release of Cytochromec

Abstract

Apoptosis is a process that removes unwanted or damaged cells. The biochemical events that mediate apoptotic cell death are generally initiated in one of two ways. In the first instance, death signals are generated at the cell surface. Activation of such cell surface proteins as the tumor necrosis factor-␣ or Fas receptors initiate an apoptotic cascade. Alternatively, the deprivation of many trophic growth factors that act through an interaction with a plasma membrane receptor can similarly result in apoptotic cell death. Our current understanding of the events that follow activation of either the tumor necrosis factor-␣ or Fas receptor envisions an initial premitochondrial phase that involves the Bcl-2 family of pro-and anti-apoptotic proteins and that may or may not require the participation of caspases (1). The mitochondrial phase that follows eventuates in the release of cytochrome c and the consequent activation of caspases, enzymes in which action leads to the variety of phenotypic alterations characteristic of apoptotic cell death. The apoptosis consequent to growth factor deprivation is also held to involve an initial phase mediated by the Bcl-2 family of proteins that again results in cytochrome c release from the mitochondria followed by a caspase-mediated effector phase (2, 3). Signals that result in apoptotic cell death are also generated from within the cell. Staurosporine and taxol are two well known examples of chemicals that induce apoptosis as a result of an interaction with an intracellular target. In most cases, however, the specific target and the earliest events that ensue upon the interaction with the inducing chemical are poorly understood.The best known intracellular target for the induction of apoptosis is, of course, DNA. Physical and chemical agents can damage DNA in a variety of ways and with distinct functional consequences, both immediate and delayed. A number of effects on the integrity of the DNA result in the induction of apoptosis, a response that removes cells that can no longer replicate or that have potentially mutagenic damage. The details as to the mechanism whereby the cell recognizes lesions in the DNA that are not readily repairable and then sets in motion events that result in apoptotic cell death are the subject of considerable research efforts. The most dominant current paradigm places p53 at the center of a process that couples DNA damage to the transcriptional regulation of much of the same pro-and antiapoptotic machinery that is activated by signals originating from the cell surface.The topoisomerase II inhibitor etoposide is an antineoplastic drug that has been widely used to couple DNA damage to apoptosis (4). Topoisomerase II is a nuclear enzyme that functions during both DNA replication and transcription (5). Topoisomerase II prevents "knots" from forming in DNA by allowing the passage of an intact segment of the helical DNA through a transient double strand break (6). Topoisomerase II inhibitors such as etoposide stabilize the complex formed by topoisomerase I...

Smac/DIABLO is not released from mitochondria during apoptotic signalling in cells deficient in cytochrome c

“…11 Reference cell lines 143B and NIH3T3 treated with 50 mM etoposide release both cyt c and Smac/DIABLO from the mitochondria as early as 12 h after treatment (Figure 4b). In contrast, the cyt cÀ/À cells show no detectable release of Smac/DIABLO into the cytosolic fraction even after 48 h treatment with etoposide.…”

Gene network analysis of oxidative stress-mediated drug sensitivity in resistant ovarian carcinoma cells

“…40,41 However, interaction of DNA-PKc with p53 is observed in both the nucleus and the cytoplasm of Cbl cos cells, but only in the nucleus of Cbltreated cells. Although both are predominantly nuclear proteins, it is possible that both are extruded from the nucleus in response to COS treatment and will move to the cytoplasm or more precisely to the mitochondria.…”

Novel substituted methylenedioxy lignan suppresses proliferation of cancer cells by inhibiting telomerase and activation of c-myc and caspases leading to apoptosis

“…Hence, it is thought that targeting such molecules in a cancer may provide a new therapeutic strategy. Traditional medicinal practices of several countries provided valuable leads from which new molecules have been derived and used successfully for the treatment of cancers like etoposide (Karpinich et al, 2002). Many of the current chemotherapeutic agents have been obtained from plant sources (Cragg and Newman, 1999).…”