Ribosomal protein S27-like, a p53-inducible modulator of cell fate in response to genotoxic stress.

Activation of the p53 tumor suppressor upon DNA damage elicits either cell cycle arrest or apoptosis, and the precise mechanism governing cell fate after p53 response has not been well defined. Through genomic analysis, we have identified the ribosomal protein S27-like (RPS27L) as a novel p53 transcriptional target gene. Although RPS27L mRNA levels were consistently induced after diverse p53 activating signals, its change in protein level was stimuli-dependent: it was up-regulated when cells were arrested in response to DNA-damaging agents Adriamycin or VP16 but was down-regulated when cells underwent apoptosis in response to antimetabolite agent 5-fluorouracil. RPS27L is a nuclear protein that forms nuclear foci upon DNA damage. Depletion of RPS27L resulted in deficiency in DNA damage checkpoints, leading to conversion of DNA damage-induced p53 response from cell cycle arrest to apoptosis. We further show that RPS27L positively regulates p21 protein expression. Through this mechanism, RPS27L induction by p53 facilitates p21-mediated cell cycle arrest and protects against DNA damage-induced apoptosis. Thus, RPS27L modulates DNA damage response and functions as a part of the control switch to determine cell fate to DNA damage-p53 response.