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Replicative senescence and oxidant-induced premature senescence. Beyond the control of cell cycle checkpoints
1Department of Pharmacology, University of Arizona, Tucson 85721, USA. chen@pharmacy.arizona.edu
Abstract:
Normal human diploid fibroblasts (HDFs) undergo replicative senescence inevitably in tissue culture after a certain number of cell divisions. A number of molecular changes observed in replicative senescent cells occur in somatic cells during the process of aging. Genetic studies on replicative senescence indicate the control of tumor suppression mechanisms. Despite the significance of replicative senescence in aging and cancer, little is known about the central cause of the complex changes observed in replicative senescent cells. The interest in the phenomenon has intensified in recent years, since damaging agents, certain oncogenes and tumor suppressor genes have been found to induce features of senescence in early passage young HDFs or in immortalized tumor cells. The reported features of senescence are summarized here in order to clarify the concept of replicative senescence or premature senescence. The experimental results of extending the replicative life span by reducing ambient oxygen tension or by N-tert-butyl-alpha-phenylnitrone (PBN) argue a role of oxidative damage in replicative senescence. By inducing premature senescence with a pulse treatment of H2O2, we can study the role of the cell cycle checkpoint proteins p53, p21, p16 and Rb in gaining each feature of senescence. Although p53 and Rb control G1 arrest and Rb appears to control cell enlargement, activation of the senescent associate beta-galactosidase, loss of cell replication and multiple molecular changes observed in premature senescent or replicative senescent cells are likely controlled by mechanisms beyond the cell cycle checkpoints.
Insights
Replicative senescence, a key aspect of aging and cancer, involves complex molecular changes. Oxidative damage and factors beyond cell cycle checkpoints likely drive these alterations in aging cells.
Area of Science:
- Cell Biology
- Aging Research
- Cancer Biology
Background:
- Normal human diploid fibroblasts (HDFs) exhibit replicative senescence, a process mirroring molecular changes in somatic aging.
- Senescence is linked to tumor suppression, but its underlying causes remain unclear.
- Recent research shows that damaging agents, oncogenes, and tumor suppressors can induce senescence features.
Purpose of the Study:
- To summarize features of replicative and premature senescence.
- To investigate the role of oxidative damage in replicative senescence.
- To explore the involvement of cell cycle checkpoint proteins in senescence.
Main Methods:
- Reviewing reported features of senescence.
- Analyzing experimental data on extending replicative lifespan by reducing oxygen or using N-tert-butyl-alpha-phenylnitrone (PBN).
- Inducing premature senescence with hydrogen peroxide (H2O2) to study cell cycle proteins (p53, p21, p16, Rb).
Main Results:
- Reduced oxygen or PBN treatment extended cell lifespan, suggesting oxidative damage involvement.
- p53 and Rb control G1 arrest and cell enlargement.
- Senescence-associated beta-galactosidase activation, loss of replication, and molecular changes occur independently of cell cycle checkpoints.
Conclusions:
- Oxidative damage plays a role in replicative senescence.
- Cell cycle checkpoints (p53, Rb) regulate specific senescence features like G1 arrest and cell enlargement.
- Key senescence characteristics are controlled by mechanisms distinct from canonical cell cycle checkpoints.