title: Camptothecin-induced downregulation of MLL5 contributes to the activation of tumor suppressor p53.
abstract: Mixed lineage leukemia 5 (MLL5) has been implicated in multiple aspects of cell physiology, such as hematopoiesis, cell cycle control and chromatin regulatory network. In this study, we present evidence that MLL5 is involved in the camptothecin (CPT)-induced p53 activation. CPT promoted the degradation of MLL5 protein in a time- and dose-dependent manner in actively replicating cells. The downregulation of MLL5 led to phosphorylation of p53 at Ser392, which was abrogated by exogenous overexpression of MLL5. In MLL5-knockdown cells, p53 protein was stabilized and bound to DNA with higher affinity, leading to activation of downstream genes. Co-immunoprecipitation showed that MLL5 preferentially interacted with the tetramerized form of p53, and knockdown of MLL5 promoted chromatin accumulation of p53 tetramers, suggesting that the association of MLL5 with p53 may prevent the p53 tetramers from binding to the chromatin target sites. The role of MLL5 in CPT-induced p53 activation was conserved in developing zebrafish, where CPT downregulated zebrafish Mll5 protein, and the microinjection of zebrafish mll5 mRNA substantially blocked the CPT-induced apoptosis. In summary, our study proposed MLL5 as a novel component in the regulation of p53 homeostasis and a new cellular determinant of CPT.
authors.affiliation: Department of Biochemistry, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore.
authors.forename: F
authors.initials: F
authors.lastname: Cheng
authors.forename: J
authors.initials: J
authors.lastname: Liu
authors.forename: C
authors.initials: C
authors.lastname: Teh
authors.forename: S-W
authors.initials: SW
authors.lastname: Chong
authors.forename: V
authors.initials: V
authors.lastname: Korzh
authors.forename: Y-J
authors.initials: YJ
authors.lastname: Jiang
authors.forename: L-W
authors.initials: LW
authors.lastname: Deng
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D064007:Ataxia Telangiectasia Mutated Proteins; D002166:Camptothecin / Q000494:pharmacology*; D018797:Cell Cycle Proteins / Q000502:physiology; D002843:Chromatin / Q000378:metabolism; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D015536:Down-Regulation / Q000187:drug effects*; D045325:HCT116 Cells; D057809:HEK293 Cells; D006801:Humans; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000502:physiology; D015027:Zebrafish
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D018797:Cell Cycle Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; C460660:KMT2E protein, human; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D002166:Camptothecin