title: Cyclin E/Cdk2-dependent phosphorylation of Mcl-1 determines its stability and cellular sensitivity to BH3 mimetics.
abstract: Cyclin E/Cdk2 kinase activity is frequently deregulated in human cancers, resulting in impaired apoptosis. Here, we show that cyclin E/Cdk2 phosphorylates and stabilizes the pro-survival Bcl-2 family protein Mcl-1, a key cell death resistance determinant to the small molecule Bcl-2 family inhibitors ABT-199 and ABT-737, mimetics of the Bcl-2 homology domain 3 (BH3). Cyclin E levels were elevated and there was increased association of cyclin E/Cdk2 with Mcl-1 in ABT-737-resistant compared to parental cells. Cyclin E depletion in various human tumor cell-lines and cyclin E-/- mouse embryo fibroblasts showed decreased levels of Mcl-1 protein, with no change in Mcl-1 mRNA levels. In the absence of cyclin E, Mcl-1 ubiquitination was enhanced, leading to decreased protein stability. Studies with Mcl-1 phosphorylation mutants show that cyclin E/Cdk2-dependent phosphorylation of Mcl-1 residues on its PEST domain resulted in increased Mcl-1 stability (Thr92, and Thr163) and Bim binding (Ser64). Cyclin E knock-down restored ABT-737 sensitivity to acquired and inherently resistant Mcl-1-dependent tumor cells. CDK inhibition by dinaciclib resulted in Bim release from Mcl-1 in ABT-737-resistant cells. Dinaciclib in combination with ABT-737 and ABT-199 resulted in robust synergistic cell death in leukemic cells and primary chronic lymphocytic leukemia patient samples. Collectively, our findings identify a novel mechanism of cyclin E-mediated Mcl-1 regulation that provides a rationale for clinical use of Bcl-2 family and Cdk inhibitors for Mcl-1-dependent tumors.
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.|Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, OH, USA.
authors.forename: Gaurav S
authors.initials: GS
authors.lastname: Choudhary
authors.affiliation: Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, OH, USA.
authors.forename: Trinh T
authors.initials: TT
authors.lastname: Tat
authors.affiliation: Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Saurav
authors.initials: S
authors.lastname: Misra
authors.affiliation: Department of Hematology and Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Hill
authors.affiliation: Department of Hematology and Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Mitchell R
authors.initials: MR
authors.lastname: Smith
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.|Department of Molecular Medicine, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Almasan
authors.affiliation: Department of Immunology, Lerner Research Institute, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, USA.|Department of Molecular Medicine, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Suparna
authors.initials: S
authors.lastname: Mazumder
mesh_terms: D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism*; D051379:Mice; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000378:metabolism*; D009596:Nitrophenols / Q000494:pharmacology; D010446:Peptide Fragments; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D055550:Protein Stability; D011518:Proto-Oncogene Proteins; D060888:Real-Time Polymerase Chain Reaction; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: C501332:ABT-737; C474007:Bax protein (53-86); D001713:Biphenyl Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D019927:Cyclin E; C579095:MCL1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009596:Nitrophenols; D010446:Peptide Fragments; D010879:Piperazines; D011518:Proto-Oncogene Proteins; D013449:Sulfonamides; D051357:Cyclin-Dependent Kinase 2; C579720:venetoclax
keywords: ABT-199; CLL; Cdk2; Mcl-1; cyclin E; dinaciclib ABT-737