scholarly journals CDK4 and CDK6 Delay Senescence by Kinase-Dependent and p16INK4a-Independent Mechanisms

2007 ◽  
Vol 27 (12) ◽  
pp. 4273-4282 ◽  
Author(s):  
Margarida Ruas ◽  
Fiona Gregory ◽  
Rebecca Jones ◽  
Robert Poolman ◽  
Maria Starborg ◽  
...  
Keyword(s):  
Life Span ◽  
Replicative Senescence ◽  
Variant Form ◽  
Cdk Inhibitors ◽  
Replicative Life Span ◽  
Human Diploid Fibroblasts ◽  
Ink4 Proteins ◽  
Integrated Response ◽  
The Impact ◽  
Cdk4 Expression

ABSTRACT Replicative senescence of human diploid fibroblasts (HDFs) is largely implemented by the cyclin-dependent kinase (CDK) inhibitors p16INK4a and p21CIP1. Their accumulation results in a loss of CDK2 activity, and cells arrest with the retinoblastoma protein (pRb) in its hypophosphorylated state. It has become standard practice to bypass the effects of p16INK4a by overexpressing CDK4 or a variant form that is unable to bind to INK4 proteins. Although CDK4 and CDK6 and their INK4-insensitive variants can extend the life span of HDFs, they also cause a substantial increase in the levels of endogenous p16INK4a. Here we show that CDK4 and CDK6 can extend the life span of HDFs that have inactivating mutations in both alleles of INK4a or in which INK4a levels are repressed, indicating that overexpression of CDK4/6 is not equivalent to ablation of p16INK4a. However, catalytically inactive versions of these kinases are unable to extend the replicative life span, suggesting that the impact of ectopic CDK4/6 depends on their ability to phosphorylate as yet unidentified substrates rather than to sequester CDK inhibitors. Since p16INK4a deficiency, CDK4 expression, and p53 or p21CIP1 ablation have additive effects on replicative life span, our results underscore the idea that senescence is an integrated response to diverse signals.

Replicative senescence of human fibroblast-like cells in culture

1993 ◽  
Vol 73 (3) ◽  
pp. 617-638 ◽  
Author(s):  
V. J. Cristofalo ◽  
R. J. Pignolo
Keyword(s):  
Life History ◽  
Dna Synthesis ◽  
Life Span ◽  
Replicative Senescence ◽  
Small Sample ◽  
Cell Aging ◽  
Replicative Life Span ◽  
Cells In Culture

The life history of fibroblast and fibroblast-like cells includes an initial stage of outgrowth and establishment in culture; a period of vigorous proliferation which has a variable length, depending on the tissue of origin, age of the donor, etc.; a period of declining proliferative vigor which includes substantial cell death; and finally, the emergence of an (apparently) long-lived population which is unable to proliferate in response to growth factors. During the phase of declining proliferative vigor, the cells acquire characteristics, some of which are similar to the characteristics of cells in older individuals. Eventually the culture completely loses proliferative capacity. A comparable life history has been described for glial cells, keratinocytes, vascular smooth muscle cells, endothelial cells, and lymphocytes which suggests that this life history is characteristic of those cell types that, in vivo, retain the capacity for proliferation throughout the life span. Numerous studies have shown a correlation between the age of the tissue donor and the replicative life span of the cells in culture. In addition, for a small sample of species, there is a direct correlation between fibroblast replicative life span in vitro and maximum life span potential of the species. The period in the life history that is usually referred to as the "senescent phase" is probably more complicated than was originally thought, since studies with life span modulators suggest that there is a "conditionally" senescent state from which cells can be rescued for one or more additional rounds of DNA synthesis. Finally, the cells enter an "obligatory" arrested state in which only SV40 infection can reverse the block to DNA synthesis but not the block to mitosis. The modern era of aging research in tissue culture is just over 30 years old. The inception of the field really began with the recognition by Hayflick and Moorhead (109) that the phenomenon of senescence in vitro paralleled, in some of its characteristics, cell aging in vivo and thus provided a model that could be used to study the cellular mechanisms underlying senescence in controlled environmental conditions. The research in this area began with a detailed characterization and comparison of young versus senescent cell morphology and physiology. These studies provided the basis for a wide variety of subsequent studies that addressed possible mechanisms underlying cell senescence. These included studies on DNA repair, protein synthetic errors, chromatin structure and function, and mechanisms for modulating replicative life span.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Control of the Replicative Life Span of Human Fibroblasts by p16 and the Polycomb Protein Bmi-1

2003 ◽  
Vol 23 (1) ◽  
pp. 389-401 ◽  
Author(s):  
Koji Itahana ◽  
Ying Zou ◽  
Yoko Itahana ◽  
Jose-Luis Martinez ◽  
Christian Beausejour ◽  
...  
Keyword(s):  
Life Span ◽  
Replicative Senescence ◽  
Human Fibroblasts ◽  
Ring Finger ◽  
Dominant Negative ◽  
Life Span Extension ◽  
Replicative Life Span ◽  
Polycomb Protein ◽  
Human Fibroblast Strains ◽  
Dominant Negative Activity

ABSTRACT The polycomb protein Bmi-1 represses the INK4a locus, which encodes the tumor suppressors p16 and p14ARF. Here we report that Bmi-1 is downregulated when WI-38 human fibroblasts undergo replicative senescence, but not quiescence, and extends replicative life span when overexpressed. Life span extension by Bmi-1 required the pRb, but not p53, tumor suppressor protein. Deletion analysis showed that the RING finger and helix-turn-helix domains of Bmi-1 were required for life span extension and suppression of p16. Furthermore, a RING finger deletion mutant exhibited dominant negative activity, inducing p16 and premature senescence. Interestingly, presenescent cultures of some, but not all, human fibroblasts contained growth-arrested cells expressing high levels of p16 and apparently arrested by a p53- and telomere-independent mechanism. Bmi-1 selectively extended the life span of these cultures. Low O2 concentrations had no effect on p16 levels or life span extension by Bmi-1 but reduced expression of the p53 target, p21. We propose that some human fibroblast strains are more sensitive to stress-induced senescence and have both p16-dependent and p53/telomere-dependent pathways of senescence. Our data suggest that Bmi-1 extends the replicative life span of human fibroblasts by suppressing the p16-dependent senescence pathway.

scholarly journals Risk factors for physical inactivity across the adult life span: the impact of depression

2006 ◽  
Vol 18 (6) ◽  
pp. 274-274
Author(s):  
J Walker ◽  
H Christensen ◽  
T Windsor ◽  
A George
Keyword(s):  
Risk Factors ◽  
Life Span ◽  
Physical Inactivity ◽  
Adult Life ◽  
Adult Life Span ◽  
The Impact

Telomerase Alone Extends the Replicative Life Span of Human Skeletal Muscle Cells Without Compromising Genomic Stability

2003 ◽  
Vol 14 (15) ◽  
pp. 1473-1487 ◽  
Author(s):  
Martha Wootton ◽  
Karen Steeghs ◽  
Diana Watt ◽  
June Munro ◽  
Katrina Gordon ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Life Span ◽  
Human Skeletal Muscle ◽  
Genomic Stability ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Replicative Life Span ◽  
Human Skeletal Muscle Cells

The Impact of Invisible Illness on Identity and Contextual Age Across the Life Span

2003 ◽  
Vol 15 (3) ◽  
pp. 331-347 ◽  
Author(s):  
Amanda L. Kundrat ◽  
Jon F. Nussbaum
Keyword(s):  
Life Span ◽  
The Impact

scholarly journals Loss of Ubp3 increases silencing, decreases unequal recombination in rDNA, and shortens the replicative life span in Saccharomyces cerevisiae

2014 ◽  
Vol 25 (12) ◽  
pp. 1916-1924 ◽  
Author(s):  
David Öling ◽  
Rehan Masoom ◽  
Kristian Kvint
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Rna Polymerase ◽  
Life Span ◽  
Rna Polymerase Ii ◽  
Ribosomal Dna ◽  
Genetic Evidence ◽  
Wild Type ◽  
Replicative Life Span ◽  
Unequal Recombination

Ubp3 is a conserved ubiquitin protease that acts as an antisilencing factor in MAT and telomeric regions. Here we show that ubp3∆ mutants also display increased silencing in ribosomal DNA (rDNA). Consistent with this, RNA polymerase II occupancy is lower in cells lacking Ubp3 than in wild-type cells in all heterochromatic regions. Moreover, in a ubp3∆ mutant, unequal recombination in rDNA is highly suppressed. We present genetic evidence that this effect on rDNA recombination, but not silencing, is entirely dependent on the silencing factor Sir2. Further, ubp3∆ sir2∆ mutants age prematurely at the same rate as sir2∆ mutants. Thus our data suggest that recombination negatively influences replicative life span more so than silencing. However, in ubp3∆ mutants, recombination is not a prerequisite for aging, since cells lacking Ubp3 have a shorter life span than isogenic wild-type cells. We discuss the data in view of different models on how silencing and unequal recombination affect replicative life span and the role of Ubp3 in these processes.

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