Abstract A10: A Cdk4-dependent phosphorylation threshold regulates the cell cycle entry decision

Abstract

Abstract Cyclin-dependent kinases (Cdk's) are major cell cycle regulators and uncontrolled cell cycle entry is a hallmark of cancer. Cyclin D, the regulatory subunit of Cdk4, is misregulated in about 75% of human malignancies, leading to hyperactive Cdk4 and uncontrolled cell cycle entry. In sharp contrast, the total loss of Cyclin D-mediated activity results in permanent cell cycle arrest. Several functions of Cdk4 during cell cycle entry have been identified; however, the underlying mechanism for cell cycle arrest upon its inactivation remains unanswered. Here we employed CRISPR/Cas9 and rAAV-mediated gene editing to visualize Restriction Point passage in highly synchronized single cells and find that cyclin D:Cdk4/6 complexes perform a critical switch-like function that results in activation of cyclin E:Cdk2 complexes. Taken together, our data indicate that while cyclin E:Cdk2 is the rate-limiting step for transition across the Restriction Point, it is dependent on cyclin D:Cdk4/6 phosphorylation of an as of yet unknown molecule. Citation Format: Manuel Kaulich, Steven Dowdy. A Cdk4-dependent phosphorylation threshold regulates the cell cycle entry decision. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Cancer Cell Cycle - Tumor Progression and Therapeutic Response; Feb 28-Mar 2, 2016; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(11_Suppl):Abstract nr A10.