Histone deacetylase inhibitors induce a senescence-like state in human cells by a p16-dependent mechanism that is independent of a mitotic clock.

We show here that histone deacetylase inhibitors (HDACIs) sodium dibutyrate (SDB) and trichostatin A (TSA) induce a phenotype that has similarities to replicative senescence in human fibroblasts. There was no evidence that SDB accelerated a constitutive cell division counting mechanism as previously suggested because cells pretreated with SDB for three mean population doublings (MPDs) exhibited a similar overall proliferative life span to controls once SDB was withdrawn. SDB-treated cells upregulated the cell cycle inhibitors p21(WAF1) and p16(INK4A), but not p14(ARF), in the same sequential order as in senescence and the cells developed biochemical markers of senescence.

Telomerase alone extends the replicative life span of human skeletal muscle cells without compromising genomic stability.

Continuous cycles of muscle fiber necrosis and regeneration are characteristic of the muscular dystrophies, and in some cases this leads to premature replicative senescence of myoblasts in vitro. The molecular mechanism of senescence in human myoblasts is poorly understood but there is evidence to suggest that telomeric attrition may be one of the ways by which this is achieved. We report here, for the first time, the extension of normal human skeletal muscle cell replicative life span by the reconstitution of telomerase activity.

A mortality gene(s) for the human adenocarcinoma line HeLa maps to a 130-kb region of human chromosome 4q22-q23.

Human chromosome 4 was previously shown to elicit features of senescence when introduced into cell lines that map to complementation group B for senescence, including HeLa cells. Subsequently, a DNA segment encoding the pseudogene Mortality Factor 4 (MORF4) was shown to reproduce some of the effects of the intact chromosome 4 and was suggested to be a candidate mortality gene. We have identified multiple MORF4 alleles in several cell lines and tissues by sequencing and have failed to detect any cancer-specific mutations in three of the complementation group B lines (HeLa, T98G, and J82).

Functional evidence for a squamous cell carcinoma mortality gene(s) on human chromosome 4.

Squamous cell carcinoma (SCC) immortality is associated with p53 and INK4A dysfunction, high levels of telomerase and loss of heterozygosity (LOH) of other chromosomes, including chromosome 4. To test for a functional cancer mortality gene on human chromosome 4 we introduced a complete or fragmented copy of the chromosome into SCC lines by microcell-mediated chromosome transfer (MMCT). Human chromosome 4 caused a delayed crisis, specifically in SCC lines with LOH on chromosome 4, but chromosomes 3, 6, 11 and 15 were without effect.