title: The CDK4/CDK6 inhibitor PD0332991 paradoxically stabilizes activated cyclin D3-CDK4/6 complexes.
abstract: CDK4 and CDK6 bound to D-type cyclins are master integrators of G1 phase cell cycle regulations by initiating the inactivating phosphorylation of the central oncosuppressor pRb. Because of their frequent deregulation in cancer, cyclin D-CDK4/6 complexes are emerging as especially promising therapeutic targets. The specific CDK4/6 inhibitor PD0332991 is currently tested in a growing number of phase II/III clinical trials against a variety of pRb-proficient chemotherapy-resistant cancers. We have previously shown that PD0332991 inhibits not only CDK4/6 activity but also the activation by phosphorylation of the bulk of cyclin D-CDK4 complexes stabilized by p21 binding. Here we show that PD0332991 has either a positive or a negative impact on the activation of cyclin D-CDK4/6 complexes, depending on their binding to p21. Indeed, whereas PD0332991 inhibits the phosphorylation and activity of p21-bound CDK4/6, it specifically stabilized activated cyclin D3-CDK4/6 complexes devoid of p21 and p27. After elimination of PD0332991, these activated cyclin D3-CDK4/6 complexes persisted for at least 24 h, resulting in paradoxical cell cycle entry in the absence of a mitogenic stimulation. This unsuspected positive effect of PD0332991 on cyclin D3-CDK4/6 activation should be carefully assessed in the clinical evaluation of PD0332991, which until now only involves discontinuous administration protocols.
authors.affiliation: a WELBIO and Institute of Interdisciplinary Research (IRIBHM) ; Université Libre de Bruxelles ; Campus Erasme; Brussels , Belgium.
authors.forename: Sabine
authors.initials: S
authors.lastname: Paternot
authors.forename: Bianca
authors.initials: B
authors.lastname: Colleoni
authors.forename: Xavier
authors.initials: X
authors.lastname: Bisteau
authors.forename: Pierre P
authors.initials: PP
authors.lastname: Roger
mesh_terms: D000818:Animals; D016466:CHO Cells; D045744:Cell Line, Tumor; D006224:Cricetinae; D003412:Cricetulus; D016895:Culture Media, Serum-Free; D056743:Cyclin D3 / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D006801:Humans; D046912:Multiprotein Complexes / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D055550:Protein Stability / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology*; D016160:Retinoblastoma Protein / Q000378:metabolism
chemical_list: D016895:Culture Media, Serum-Free; D056743:Cyclin D3; D050759:Cyclin-Dependent Kinase Inhibitor p21; D046912:Multiprotein Complexes; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D016160:Retinoblastoma Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004247:DNA; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; C500026:palbociclib
keywords: 2D, 2-dimensional; BrdU, bromodeoxyuridine; CAK, CDK-activating kinase; CDK, cyclin-dependent kinase; CDK4; CDK6; FBS, fetal bovine serum; IP, immunoprecipitation; PAGE, polyacrylamide gel electrophoresis; PBS, phosphate buffer saline; PD033, PD0332991; PD0332991; Palbociclib; SDS, sodium dodecyl sulfate; SEM, standard error of the mean; cell cycle-based tumor therapeutics; cyclin D3; p21; pRb, retinoblastoma susceptibility protein