CCNE1是致癌基因，CCNE1（cyclin E1，细胞周期蛋白E1）编码蛋白是在细胞周期G1/S转化过程中的调节细胞周期蛋白依赖性激酶2（CDK2）活化。细胞周期蛋白E1-CDK2复合物使P27（KIP1）和P21磷酸化，这是细胞周期蛋白D降解的信号，并促进细胞周期蛋白A的表达，导致细胞周期S期的进展。细胞周期蛋白E1-CDK2被SCF-FBW7降解，泛素连接酶E3在癌症中普遍突变。细胞系中的细胞周期蛋白E表达的增加导致G1/S期的快速传代，但细胞周期蛋白E或CDK2在小鼠中的缺失不会导致G1/S缺陷。细胞周期蛋白E1的扩增和过表达与许多癌症中密切相关，包括乳腺癌，并且可以预示不良预后。

CCNE1 (cyclin E1) is a protein that regulates the activation of cyclin-dependent kinase 2 (CDK2) during the G1/S transition of the cell cycle. The cyclin E1-CDK2 complex phosphorylates p27(Kip1) and p21, which signals for the degradation of cyclin D and promotes the expression of cyclin A, leading to progression through S phase of the cell cycle. Cyclin E1-CDK2 phosphorylates and inactivates retinoblastoma protein (RB), thus leading to the induction of a gene expression program regulated by the E2F family of transcription factors that is important in the transition from G1 to S phase in the cell cycle. Cyclin E1-CDK2 is degraded by SCF-Fbw7, an E3 ubiquitin ligase that is commonly mutated in cancer. Increased cyclin E expression in cell lines leads to quicker passage through the G1/S phase, but deletion of cyclin E or CDK2 in mice does not result in a G1/S defect. Amplification and overexpression of cyclin E1 has been implicated in many cancers, including breast cancer, and can be indicative of poor prognosis.

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