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. Author manuscript; available in PMC: 2020 Oct 1.
Published in final edited form as: Curr Opin Cell Biol. 2019 Jun 25;60:106–113. doi: 10.1016/j.ceb.2019.05.005

Figure 2: Model for Integration of Cell-Cycle Inputs.

Figure 2:

External and internal signals regulate the core cell-cycle machinery, including cyclins and CDK inhibitors. While mitogenic signals are known to regulate cyclin D expression, recent work has shown that endogenous DNA damage leads to the upregulation of p21. Additionally, extrinsic and intrinsic growth signals contribute to cell-cycle decisions. We propose a model in which the cell cycle decisions rely on the combined effects of pro-and anti-growth signals and their integration by their combined effects on the expression of CDKs, cyclins, and CDK inhibitors. This model is consistent with an ultrasensitive activation of CDKs.