p27/Kip1 Proteins and Enzymes

The cyclin-dependent kinase (cdk) inhibitor p27/Kip1 is a tumor suppressor protein that acts in the nucleus to enforce cell cycle checkpoints. p27/Kip1 binds to and inhibits many cyclin/cdk complexes, including cyclin D/cdk4, cyclin E/cdk2, and cyclin A/cdk2. This inhibition can subsequently block progression through different phases of the cell cycle. p27/Kip1 is phosphorylated at T198 in cells treated with the AMP-dependent protein kinase (AMPK) activator AICAR (5-amino-4-imidazolecarboxamide riboside) or glucose withdrawal.