title: The human oncoprotein MDM2 induces replication stress eliciting early intra-S-phase checkpoint response and inhibition of DNA replication origin firing.
abstract: Conventional paradigm ascribes the cell proliferative function of the human oncoprotein mouse double minute2 (MDM2) primarily to its ability to degrade p53. Here we report that in the absence of p53, MDM2 induces replication stress eliciting an early S-phase checkpoint response to inhibit further firing of DNA replication origins. Partially synchronized lung cells cultured from p53-/-:MDM2 transgenic mice enter S phase and induce S-phase checkpoint response earlier than lung cells from p53-/- mice and inhibit firing of DNA replication origins. MDM2 activates chk1 phosphorylation, elevates mixed lineage lymphoma histone methyl transferase levels and promotes checkpoint-dependent tri-methylation of histone H3 at lysine 4, known to prevent firing of late replication origins at the early S phase. In the absence of p53, a condition that disables inhibition of cyclin A expression by MDM2, MDM2 increases expression of cyclin D2 and A and hastens S-phase entry of cells. Consistently, inhibition of cyclin-dependent kinases, known to activate DNA replication origins during firing, inhibits MDM2-mediated induction of chk1 phosphorylation indicating the requirement of this activity in MDM2-mediated chk1 phosphorylation. Our data reveal a novel pathway, defended by the intra-S-phase checkpoint, by which MDM2 induces unscheduled origin firing and accelerates S-phase entry of cells in the absence of p53.
authors.affiliation: Division of Hematology, Oncology and Palliative Care, Department of Medicine, The Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA, Department of Biochemistry and Molecular Biology, The Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA, Department of Biostatistics, The Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA and Department of Medicinal Chemistry, The Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Frum
authors.forename: Shilpa
authors.initials: S
authors.lastname: Singh
authors.forename: Catherine
authors.initials: C
authors.lastname: Vaughan
authors.forename: Nitai D
authors.initials: ND
authors.lastname: Mukhopadhyay
authors.forename: Steven R
authors.initials: SR
authors.lastname: Grossman
authors.forename: Brad
authors.initials: B
authors.lastname: Windle
authors.forename: Sumitra
authors.initials: S
authors.lastname: Deb
authors.forename: Swati Palit
authors.initials: SP
authors.lastname: Deb
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D019925:Cyclin A / Q000378:metabolism; D056742:Cyclin D2 / Q000378:metabolism; D004261:DNA Replication; D016158:Genes, p53; D011495:Histone-Lysine N-Methyltransferase / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics / Q000378:metabolism*; D018741:Replication Origin / Q000187:drug effects; D059807:S Phase Cell Cycle Checkpoints / Q000235:genetics*; D013312:Stress, Physiological / Q000235:genetics
chemical_list: D019925:Cyclin A; D056742:Cyclin D2; D006657:Histones; D047428:Protein Kinase Inhibitors; D002110:Caffeine; D011495:Histone-Lysine N-Methyltransferase; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse