KIP1 (cyclin-dependent kinase inhibitor 1B) is a kinesin-related motor protein required for mitotic spindle assembly and chromosome segregation. Many tumorigenic processes modulate cell-cycle progression by regulating the levels of the cyclin-dependent kinase inhibitor KIP1. KIP1 binds to and inhibits cyclinE-Cdk2 complex, cyclinA-CDK2 and cyclinD1-CDK4. The phosphorylation- and ubiquitination-dependent proteolysis of KIP1 is implicated in control of the G1-S transition in the cell cycle. KIP1 is critical for retinoblastoma protein (Rb)-induced cellular proliferative senescence.