Level of reactive oxygen species induced by p21^{WAF(1)/CIP(1)} is critical for the determination of cell fate

Abstract

p21WAF(1)/CIP(1) is a well-known cell cycle regulatory protein which is overexpressed in several cancer cell lines, and known to determine cell fate. We generated three recombinant adenovirus vectors that expressed either the full-length p21 (Ad-p21F), a p21 mutant with a deletion of the C-terminal proliferative cell nuclear antigen (PCNA) binding domain (Ad-p21N), or a p21 mutant with a deletion of the N-terminal cyclindependent kinase binding domain (Ad-p21C). We transfected these vectors into five cancer cell lines. Premature senescence was induced in all of the lines only following transfection with Ad-p21N and Ad-p21F. In addition, apoptosis was also induced in LoVo and HCT116 cells that harbored wild-type p53 and the reactive oxygen species (ROS) level was higher than in senescent cells. Finally, the induction of apoptosis was inhibited by using siRNA to downregulate p53. This observation implies that there is a feedback signaling loop involving p21/ROS/p53 in apoptotic responses. It appears to be, at least in part, driven by high levels of p21 protein. Next, we investigated the cell death effect of endogenous p21 protein on cell fate using sodium butyrate (NaB). Treatment with 1 mM NaB or 2 to 5 mM NaB induced senescence or apoptosis, respectively. The level of intracellular ROS in 5 mM NaB treated cells was 2-fold higher, compared with that in 1 mM NaB treated cells. We also demonstrated that DNA damage response signals including ataxia telangiectasia mutated, gH2AX, and p38 MAPK were involved in NaB-induced cell death. The magnitude of intracellular ROS levels in response to p21 elicited either senescence or apoptosis in the cancer cell lines. (Cancer Sci 2009; 100: 1275-1283)

Reactive Oxygen Species and Mitochondrial Sensitivity to Oxidative Stress Determine Induction of Cancer Cell Death by p21

“…p53 induction has been observed after p21 has been highly overexpressed (25). On the other hand, previous reports have shown that p21 can negatively regulate p53 stability in different cell types in the context of a normal DNA damage response (34).…”

“…Depending on the context, p21 can induce proapoptotic effectors such as Bax or members of the TNF family (24), as well as p53 (25). Also, p21-mediated depletion of proteins that control cell division can lead to abnormal mitosis and genetic destabilization when arrested cells attempt to re-enter cell cycle after p21 down-regulation, causing death by mitotic catastrophe independently of p53 or the apoptotic pathway (26).…”

“…Further adding to its complex pleiotropic functions, it has been recently shown that p21 can also trigger cell death (24,25), although the mechanisms involved in these processes have not been fully elucidated. Depending on the context, p21 can induce proapoptotic effectors such as Bax or members of the TNF family (24), as well as p53 (25).…”

Sodium Butyrate Inhibits the Self-Renewal Capacity of Endometrial Tumor Side-Population Cells by Inducing a DNA Damage Response

“…We have previously shown that NaB induced p21 expression, resulting in growth arrest and cell death (34). Recently, we have also shown that DNA damage signals were involved in NaB-induced cell death (35). In this study, NaB inhibited primary colony-forming potential and regeneration of SP cells, indicating suppression of self-renewal capacity.…”

“…Recently, we reported that treatment with NaB induced cell death in several cancer cell lines mediated by enhanced ROS levels, DNA damage response signals, and upregulation of p21 (35). Thus, we examined the change of these signal levels in RK12V-SP cells and RK12V-NSP cells.…”