Localization of large foci was investigated by Immuno FISH research that mixed immunofluorescent detection of H2AX phosphorylation with telomere angiogenesis pathway. In as shown in Figure 1, nevertheless, they were discovered much later compared with the cells cultured in normoxic condition. hypoxic condition, big foci development was equally observed. Consequently, these information demonstrated that large foci were produced by endogenous oxidative stress, and the forming of large foci was highly correlated with senescence induction. 3. 3. Activation of ATM p53 Path in the Big Foci of Phosphorylated H2AX. We next examined whether ATM p53 pathway is associated with persistent activation of cell cycle arrest in senescent cells. In replicative senescence of HE49, accumulation of p53 accompanied with phosphorylation at Ser15 and transactivation of p21 was observed on the culture time. Specially, p53 p21 path was routinely up-regulated when p16 was also induced.. p53 was then visualized by immunofluorescence staining following Cellular differentiation formalin fixation at mentioned PDLs.. Roughly 200-meter of cells at PDL 21 weakly expressed p53 in nuclear, and the others were under detection level of p53. Boost of p53 expressing cells was seen at PDL 61 as detected in western blotting, and p53 highly accumulated in one month at PDL 61.. Curiously, accumulated p53 shaped colocalized foci with phosphorylated ATM foci.. p53 was also visualized in the cells receiving preextraction therapy accompanied by formalin fixation.. Preextraction eliminated accumulating p53 and chromatinfree nuclear protein in nuclear disappeared, while aggregated p53 was still detected at the internet sites produced significant foci of phosphorylated ATM. Moreover, ubiquitin conjugation Ser15 phosphorylation type of p53 was also recognized in the significant foci of phosphorylated ATM following preextraction.. More over, the consequence of ATM kinase inhibition on p53 phosphorylation at Ser15 in senescent cells revealed suppression of phosphorylation stage specially at lower doses, suggesting ATM is involved in p53 activation in replicative senescence. These data suggest ATM p53 pathway continually activated at the site of significant foci in senescent cells. 4. Discussion The current study shows that prolonged audio of DNA damage signal is involved with replicative senescence. It has been generally speaking considered that prolonged activation of DNA damage response at structural telomere results in permanent cell cycle arrest in replicative senescence. Certainly, foci creation at telomeres is noticed in senescent cells. Our current research provides such observation and adds the data that DNA damage signals at structural telomeres are mostly amplified. We also demonstrated that increase in size was needed for amplification of DNA damage signals.