Cell cycle checkpoints work as a double-edged sword. On the one hand, they facilitate DNA repair thus promoting the survival of normal tissues; on the other hand, they might reduce the effectiveness of many cancer treatments. Recent clinical trials on CHK1 and WEE1 inhibitors explored the potential of increasing the toxicity of chemo-and radio-therapy by targeting the DNA damage checkpoints. However, the detailed molecular mechanism of the checkpoint abrogation is not fully elucidated. One of the mysteries in the field is the roles of cyclin A2 (cycA2) in G₂/M checkpoint. In mammalian cells, cycA2 starts accumulating at S phase and is degraded in prometaphase. Although the function of cycA2 in S phase progression is well known, whether it is either an M-phase promoting factor (M...[ Read more ]

Cell cycle checkpoints work as a double-edged sword. On the one hand, they facilitate DNA repair thus promoting the survival of normal tissues; on the other hand, they might reduce the effectiveness of many cancer treatments. Recent clinical trials on CHK1 and WEE1 inhibitors explored the potential of increasing the toxicity of chemo-and radio-therapy by targeting the DNA damage checkpoints. However, the detailed molecular mechanism of the checkpoint abrogation is not fully elucidated. One of the mysteries in the field is the roles of cyclin A2 (cycA2) in G₂/M checkpoint. In mammalian cells, cycA2 starts accumulating at S phase and is degraded in prometaphase. Although the function of cycA2 in S phase progression is well known, whether it is either an M-phase promoting factor (MPF) or an activator of MPF or both in G2/M transition is still controversial. RNA interference was widely used to downregulate cycA2 gene expression, but the caveat of its slow responses limits the accuracy of many previous studies since cycA2 plays several roles at different phases in cell cycle. Here, we developed a method combining tetracycline-controlled transcriptional repression and auxin inducible degron-mediated degradation for rapid conditional cycA2 gene inactivation. As a result, we are able to turn off the cycA2 after passing through the S phase. Data suggest that cycA2 functions as both MPF and activator of MPF in G₂/M checkpoint abrogation. The preliminary data also propose that PLK1 may be the upstream regulator of cyclin A2. These results suggest a potential therapeutic strategy in patients bearing tumors with high cycA2 expression.