Cleavage of CDK Inhibitor p21Cip1/Waf1 by Caspases Is an Early Event during DNA Damage-induced Apoptosis

Abstract

Activation of the p53-mediated DNA damage response induces either G 1 cell cycle arrest or apoptosis. The G 1 cell cycle arrest is in part caused by the p53-dependent transcriptional activation of the CDK inhibitor, p21 Cip1/ Waf1. We report here that human p21 protein is rapidly induced but selectively cleaved during the apoptotic response to ␥-irradiation. Such an event occurred early, well before the morphological appearance of apoptosis. Ectopical expression of p53 in tumor cells alone could induce p21 expression, followed by p21 cleavage and apoptosis. The cleavage of p21 could be reproduced in extracts prepared from irradiated cells or by recombinant caspase-3, suggesting that a caspase-like activity is responsible for this cleavage. p21 binds independently to both CDK2 and proliferation cell nuclear antigen (PCNA). Our studies indicated that p21 cleavage by the caspase-like activity specifically abolished its interaction with PCNA, suggesting that p21 cleavage may interfere with normal PCNA-dependent repair. Our data suggest that p21 may serve as a critical checkpoint regulator for both cell cycle arrest and apoptosis during the p53-mediated DNA damage response. Manipulation of the checkpoint regulators involved in cell cycle arrest and apoptosis may thus provide a novel strategy to cancer therapy.

Induction of apoptosis in U937 human leukemia cells by suberoylanilide hydroxamic acid (SAHA) proceeds through pathways that are regulated by Bcl-2/Bcl-XL, c-Jun, and p21CIP1, but independent of p53

“…A similar phenomenon has been reported in Saos-2 osteosarcoma cells (Tang et al, 1998). Nevertheless, increases in expression of p21 CIP1 over basal levels were most prominent in HMBA-treated cells, which also displayed evidence of a cross-reactive *17-kDa species, possibly representing a p21 CIP1 cleavage product (Gervais et al, 1998).…”

Low p21Waf1/Cip1 protein level sensitizes testicular germ cell tumor cells to Fas-mediated apoptosis

“…As depicted in Figure 1a, Tera and A2780 cells revealed similar cisplatin-induced p53 protein accumulation, but only a marginal induction of p21 protein was observed in Tera cells in comparison to A2780 cells. p21 protein level can be regulated by proteasomal degradation or caspase-mediated cleavage (Gervais et al, 1998;Levkau et al, 1998;Zhang et al, 1999;Naujokat and Hoffmann, 2002;Xiang et al, 2002). As shown in Figure 1b, p21 protein levels in A2780 cells increased considerably upon exposure to the proteasome inhibitor MG-132.…”

“…In addition, most TGCTs lack p21 protein expression (Guillou et al, 1996;Bartkova et al, 2000;Datta et al, 2001). Several studies have shown that p21 is not only an important mediator of p53-induced cell cycle arrest (El-Deiry et al, 1993 but also of apoptosis suppression following DNA-damaging agents exposure (Gorospe et al, 1997;Gervais et al, 1998;Levkau et al, 1998;Asada et al, 1999;Zhang et al, 1999). The reduced p21 expression in TGCT cells may thus not only result in a less efficient inhibition of cell cycle progression but also fail to prevent rapid apoptosis induction upon DNA damage.…”

Mn‐SOD antisense upregulates in vivo apoptosis of squamous cell carcinoma cells by anticancer drugs and γ‐rays regulating expression of the BCL‐2 family proteins, COX‐2 and p21

“…54 The roles of both families in G 1 phase arrest and induction of differentiation and apoptosis have been thoroughly studied. [55][56][57][58] In SCC cells, the CIP1/KIP1 family appears to play a more important role than the INK4 family because p21 waf1/cip1 is strongly expressed but p16 INK4a is weakly expressed. 59,60 In the present study, p16 INK4a expression was not increased in the Mn-SOD antisense-transfected SCC cells, while p21 waf1/cip1 expression was increased and coordinated with the upregulation of Bax and downregulation of Bcl-2 expression.…”