It has been recognized that the remarkable decline in infant mortality and the extension in human lifespan involving both developing and developed countries alike, has been influenced by social and economic developments and public health orientated measures (such as clean water and sewerage) rather more than by developments in medical research. However, the identification of important disease risk factors for a number of common conditions such as smoking, solar exposure, dietary fat and alcohol has led to further reductions in disease prevalence and mortality, at least in some countries.
Normal human breast epithelial cells were transfected with expression vectors containing the p53 gene mutated at either codon 143, 175, 248 or 273, or by infection with a recombinant retroviral vector containing the p53 gene mutated at codons 143, 175, 248, or 273. The breast epithelial cells were monitored for extension of in vitro lifespan and immortalization. Expression of some, but not all, p53 mutants resulted in an extension of in vitro lifespan.
BACKGROUND: Among patients with well differentiated papillary thyroid carcinoma who generally have an excellent prognosis and a near-normal lifespan, there exist subsets of patients who have significant risk for morbidity and mortality from this disease. It is important to define the patterns of disease progression and the clinical outcome of such patients to develop effective surveillance and treatment strategies.
This study addresses the question of whether loss of p16INK4 expression contributes to the immortalization of human cells. In vitro immortalization usually proceeds through two phases. In the first phase (lifespan extension), cells continue proliferating and their telomeres continue shortening beyond the point at which normal cells become senescent. In the second phase (immortalization), the cells activate a telomere maintenance mechanism and acquire an unlimited proliferative potential.
European Journal of Cancer (Oxford, England: 1990)
This article reviews the current understanding of the involvement of telomerase in in vitro immortalisation of human cells. In vitro immortalisation with DNA tumour viruses or chemicals usually occurs in two phases. The first stage is an extension of lifespan beyond that at which cells would normally senescence, after which the culture enters a period of crisis. The second stage involves the escape from crisis of a rare cell in the culture, which goes on to proliferate indefinitely.
Telomere loss has been proposed as a mechanism for counting cell divisions during aging in normal somatic cells. How such a mitotic clock initiates the intracellular signalling events that culminate in G1 cell cycle arrest and senescence to restrict the lifespan of normal human cells is not known. We investigated the possibility that critically short telomere length activates a DNA damage response pathway involving p53 and p21(WAF1) in aging cells.
Cell cycle checkpoints and tumor suppressor gene functions appear to be required for the maintenance of a stable genome in proliferating cells. In this study chromosomal destabilization was monitored in relation to telomere structure, lifespan control and G2 checkpoint function. Replicative senescence was inactivated in secondary cultures of human skin fibroblasts by expressing the human papillomavirus type 16 (HPV-16) E6 oncoprotein to inactivate p53. Chromosome aberrations were enumerated during in vitro aging of isogenic control (F5neo) and HPV-16E6-expressing (F5E6) fibroblasts.
Reactive oxygen (RO) has been identified as an important effector in ageing and lifespan determination. The specific cell types, however, in which oxidative damage acts to limit lifespan of the whole organism have not been explicitly identified. The association between mutations in the gene encoding the oxygen radical metabolizing enzyme CuZn superoxide dismutase (SOD1) and loss of motorneurons in the brain and spinal cord that occurs in the life-shortening paralytic disease, Familial Amyotrophic Lateral Sclerosis (FALS; ref.
Accessible and readily utilized software, tables and approximation formulae have been developed to estimate power and sample size for studies of time to event (survival times) when the survival times are assumed to be exponential. These methods can markedly misestimate power when the distribution is Weibull and not exponential. The Weibull distribution with increasing hazard is common in aging research, especially when the whole life span of the subjects is of interest.
Transfection of nearly senesced human fibroblasts with plasmids encoding HPV16 E6 protein or dominant-negative p53 mutants greatly increased their colony-forming ability. Isolated colonies with these plasmids showed extension of lifespan compared to those with a control plasmid. These data demonstrate that p53 plays a major role in senescence in normal human fibroblasts.