Control of cell cycle commitment by APC-C-Cdh1

Division Of Basic Sciences - Nci

Investigators

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Abstract

The overall goal of this project is to investigate how stress signaling pathways induce a return to quiescence during G1 phase of the cell cycle and to investigate the source of single-cell variability in this fate choice. It has been proposed that the decision to enter the cell cycle is made at a discreet point during G1 phase called the restriction point. However, we recently showed that if cells encounter genotoxic stress even after they have passed the restriction point, they can still exit the cell cycle and return to quiescence, indicating cells have not yet committed to the cell cycle at the restriction point. Furthermore, there is considerable single-cell variability with the majority of cells failing to trigger the G1/S checkpoint and exiting to quiescence after DNA damage is induced. These results call into question the concept that cells make the decision to divide at a single point in the cell cycle and also demonstrate that the DNA damage-regulated G1/S checkpoint is highly ineffective. To investigate the mechanisms underlying cell cycle de-commitment we are using using time-lapse microscopy and fluorescent biosensors for CDK2 and APC/C activity that we developed as well as automated single-cell tracking algorithms to follow single-cells as they enter and exit the cell cycle. We are currently dissecting the effects of DNA damage signaling on key cell cycle regulators including Cyclin D and p21 to understand why some cells are sensitive to DNA damage while others are not. Furthermore, we are analyzing the behavior of genetically-identical sister cells to identify deterministic factors that can predict what fate a cell will choose. In addition, we are tracking cells over multiple generations to understand the consequences of failing to return to quiescence after DNA damage is induced.