The cyclin-dependent kinases Cdk4 and Cdk6 form complexes with D-type cyclins to drive cell proliferation. A well-known target of cyclin D-Cdk4,6 is the retinoblastoma protein Rb, which inhibits cell-cycle progression until its inactivation by phosphorylation. However, the role of Rb phosphorylation by cyclin D-Cdk4,6 in cell-cycle progression is unclear because Rb can be phosphorylated by other cyclin-Cdks, and cyclin D-Cdk4,6 has other targets involved in cell division. Here, we show that cyclin D-Cdk4,6 docks one side of an alpha-helix in the Rb C terminus, which is not recognized by cyclins E, A, and B. This helix-based docking mechanism is shared by the p107 and p130 Rb-family members across metazoans. Mutation of the Rb C-terminal helix prevents its phosphorylation, promotes G1 arrest, and enhances Rb’s tumor suppressive function. Our work conclusively demonstrates that the cyclin D-Rb interaction drives cell division and expands the diversity of known cyclin-based protein docking mechanisms.

细胞周期蛋白依赖性激酶Cdk4和Cdk6与D型细胞周期蛋白形成复合物以驱动细胞增殖。细胞周期蛋白D-Cdk4,6的一个众所周知的靶标是成视网膜细胞瘤蛋白Rb，它抑制细胞周期进程，直到其被磷酸化灭活为止。然而，细胞周期蛋白D-Cdk4,6在细胞周期进程中Rb磷酸化的作用尚不清楚，因为Rb可以被其他细胞周期蛋白-Cdks磷酸化，而细胞周期蛋白D-Cdk4,6还有其他参与细胞分裂的靶标。在这里，我们显示出细胞周期蛋白D-Cdk4,6停靠在Rb C末端的一个α螺旋的一侧，而细胞周期蛋白E，A和B无法识别该螺旋。p107和p130后生动物的Rb家族成员。Rb C末端螺旋的突变阻止其磷酸化，促进G1阻滞，并增强Rb的肿瘤抑制功能。