Figure 7.

A Friction Model of Cell Apoptosis Response to DNA Damage Signaling

(A) A simple scheme for Chk1, Chk2, p53, and p21 protein interactions.

(B) A cartoon of the “friction model.” A cyan-to-orange gradient indicates the balance between survival (cyan region) and apoptosis (orange region). Cellular outcome to DNA damage is determined by the balance of the driving force (caused by p53) and the friction force (induced by p21). To move cells to the apoptotic state, the driving force should be larger than the friction force. The size of arrows depicts the relative strength of the driving and friction forces in breast and lung cells in response to cisplatin or doxorubicin treatment. p-Chk1 and p-Chk2 contribute to p53 phosphorylation, and both p-p53 and Chk2 can induce p21 transcription. However, whether p21 expression increases also depends on the nature of the stress.