Journal Article

p27 allosterically activates cyclin-dependent kinase 4 and antagonizes palbociclib inhibition

Rubin, Seth M., Barkovich, Krister J., Knudsen, Erik S., Witkiewicz, Agnieszka K., Guiley, Keelan Z., Tripathi, Sarvind, Wijeratne, Tilini U., Kumarasamy, Vishnu, Stevenson, Jack W., Lou, Kevin, Bunch, Katharine L., Shokat, Kevan M.

2019

Overview

A crystal structure of the active form of cyclin-dependent kinase 4 (CDK4) provides insight into regulation of the cell cycle and the mechanism of action of a drug used for breast cancer therapy. The protein p27 has been thought to act as a CDK inhibitor. Guiley et al. performed a structural analysis of active complexes of CDK4 with cyclin D1 (CycD1) and p27 (see the Perspective by Sherr). The results showed that p27 actually remodels the active site of CDK4 to allow full activation when p27 is phosphorylated on tyrosine (phosp27). Furthermore, they found that the breast cancer drug palbociclib, a CDK4 inhibitor, doesn't actually interact with active phosp27-CDK4-CycD1 trimers. Instead, it appears that the drug, which shows promise in the clinic, binds to inactive CDK4 monomers and prevents interaction with p27. Science , this issue p. eaaw2106 ; see also p. 1315 Crystal structures clarify the regulation mechanism of a kinase complex linked to cancer. The p27 protein is a canonical negative regulator of cell proliferation and acts primarily by inhibiting cyclin-dependent kinases (CDKs). Under some circumstances, p27 is associated with active CDK4, but no mechanism for activation has been described. We found that p27, when phosphorylated by tyrosine kinases, allosterically activated CDK4 in complex with cyclin D1 (CDK4-CycD1). Structural and biochemical data revealed that binding of phosphorylated p27 (phosp27) to CDK4 altered the kinase adenosine triphosphate site to promote phosphorylation of the retinoblastoma tumor suppressor protein (Rb) and other substrates. Surprisingly, purified and endogenous phosp27-CDK4-CycD1 complexes were insensitive to the CDK4-targeting drug palbociclib. Palbociclib instead primarily targeted monomeric CDK4 and CDK6 (CDK4/6) in breast tumor cells. Our data characterize phosp27-CDK4-CycD1 as an active Rb kinase that is refractory to clinically relevant CDK4/6 inhibitors.

• Publisher: American Association for the Advancement of Science,The American Association for the Advancement of Science
• Subject: Activation / Adenosine kinase / Adenosine triphosphate / Allosteric Regulation / Antiestrogens / Antineoplastic Agents - pharmacology / Assembly / ATP / Binding sites / Biocatalysis / Breast cancer / Cancer / Cell cycle / Cell Line, Tumor / Cell proliferation / Clinical trials / Crystal structure / Crystallography, X-Ray / Cyclin D / Cyclin D1 / Cyclin D1 - chemistry / Cyclin-dependent kinase 2 / Cyclin-dependent kinase 4 / Cyclin-Dependent Kinase 4 - antagonists & inhibitors / Cyclin-Dependent Kinase 4 - chemistry / Cyclin-Dependent Kinase 4 - metabolism / Cyclin-dependent kinase inhibitor p21 / Cyclin-dependent kinase inhibitor p27 / Cyclin-Dependent Kinase Inhibitor p27 - chemistry / Cyclin-Dependent Kinase Inhibitor p27 - metabolism / Cyclin-dependent kinases / Deactivation / Enzyme Activation / ErbB-2 protein / Humans / Inactivation / Inhibition / Inhibitors / Kinases / Low concentrations / Monomers / Organic chemistry / Phosphorylation / Piperazines - pharmacology / Protein Conformation / Protein Kinase Inhibitors - pharmacology / Proteins / Pyridines - pharmacology / RESEARCH ARTICLE SUMMARY / Retina / Retinoblastoma / Retinoblastoma protein / Retinoblastoma Protein - metabolism / Structural analysis / Structural Analysis (Linguistics) / Structural Analysis (Science) / Substrates / Trimers / Tumor cells / Tumor suppressor genes / Tumors / Tyrosine