Transient suppression of nuclear Cdc2 activity in response to ionizing radiation

Abstract

Abstract. Suppression of Cdc2 activity is essential for DNA damage-induced G2 arrest. In the present study, we elucidated regulatory mechanism of Cdc2 activity during radiation-induced transient G2 arrest. Exposure of the cells to γ-radiation (4 Gy) led to a transient increase of cells in G2 at 12 h rather than M phase and then the cells resumed cell cycle progression from the G2 arrest. However, the levels of cyclin B1 and Cdc2 activity were increased in the whole cell extracts at 12 h. Despite cyclin B1 induction and increased level of Cdc2 activity after irradiation the activities in the nuclear fractions were transiently decreased at 12 h and returned to control levels by 24-48 h, demonstrating transient inhibition of nuclear translocation of cyclin B1 in response to radiation. Moreover, inhibitory phosphorylation of the Cdc2 on Tyr15 and the Cdc25C on Ser216 were increased concomitant with transient G2 arrest. The level of phosphorylated Wee1 and its activity were also markedly increased at 12 h after irradiation. In addition, radiation caused nuclear accumulation of p21 CIP1/WAF1 at 12 h, resulting in increased-binding of p21 CIP1/WAF1 to Cdc2. Nuclear p21protein level and its binding to Cdc2 gradually returned to control level when the cells resumed cell cycle progression. However, total protein level of p21 CIP1/WAF1 continued to increase until 48 h after irradiation. Collectively, these results indicate that the suppression of nuclear import of cyclin B1, the induction of Wee1 kinase activity, and the transient nuclear accumulation of p21 CIP1/WAF1 may play important roles in the transient cell cycle delay in response to ionizing radiation.

5-Aza-2′-deoxycytidine sensitizes busulfan-resistant myeloid leukemia cells by regulating expression of genes involved in cell cycle checkpoint and apoptosis

“…The up-regulation of p21 WAF1/CIP1 in the presence of DAC is likely related to the observed phosphorylation of p53 at Ser15 as previously reported [26, 27] and discussed further below. Although p21 WAF1/CIP1 is known to be capable of triggering G1-arrest, it also causes G2-arrest by interacting with CDK1/CDC2 [28, 29]. The DAC-induced increase in p21 WAF1/CIP1 correlates with the observed accumulation of P-CDC2 (Figure 3A), a known hallmark of G2-M checkpoint activation [30].…”

Selective Radiosensitization of Human Cervical Cancer Cells and Normal Cells by Artemisinin Through the Abrogation of Radiation-Induced G2 Block

“…18 Inhibition of Wee1 activity could result in sensitization of tumor cells to a DNA damage agent like radiation. 18,21 On the other hand, the association of Cdc2 with cyclin B1 is necessary for G2/M transition. The kinase activity of Cdc2 during the cell cycle is controlled by both its association with cyclin B1 and phosphorylation/dephosphorylation of the inhibitory phosphorylation sites, Thr-14 and Tyr-15.…”

“…The kinase activity of Cdc2 during the cell cycle is controlled by both its association with cyclin B1 and phosphorylation/dephosphorylation of the inhibitory phosphorylation sites, Thr-14 and Tyr-15. 20,21 Depressing the expression of cyclin B1 by radiation in HeLa cells of patients with cervical cancer was related to radiationinduced G2 arrest. 19,22 Some studies show that the addition of methylxanthines, such as pentoxifylline and caffeine, induces cyclin B1 expression and restores the cyclin B1/ Cdc2 ratios, which decline after radiation and result in sensitizing HeLa cells to radiation.…”

Mechanisms of therapy resistance in osteosarcoma: a review

“…In the absence of functional p53, the G1 cell cycle checkpoint is often surpassed and the other cell cycle checkpoints become of more importance to the tumour cell for DNA damage management and survival [14,[46][47][48]50,55,56]. Both the S-phase and the G2/M-phase checkpoint have been described in drug response in OS and arrest of the cell cycle in G2/M-phase is commonly observed upon DNA damage in malignant cells of various types, including OS [47,48,[57][58][59][60]. In the case of damage, DNA double strand breaks are detected by ATM, which relays a signal (mostly) to Chk2, which in turn phosphorylates Cdc25C.…”

“…Cdc2 (also known as Cdk1) is a Cyclin-Dependent Kinase that plays a pivotal role in the onset of mitosis or the induction of a G2/M arrest. Abrogation of its inhibitory phosphorylation can abrogate the G2 arrest, initiate an unwanted acceleration of the cell cycle and force DNA damaged cells into mitosis, ultimately leading to enhanced apoptotic cell death [48,56,[59][60][61]67,68]. Another way to intervene in cell cycle regulation is to manipulate CDK-regulatory pathways, rather than targeting the CDKs directly.…”