title: Polo-like kinase 1 activated by the hepatitis B virus X protein attenuates both the DNA damage checkpoint and DNA repair resulting in partial polyploidy.
abstract: Hepatitis B virus X protein (pX), implicated in hepatocarcinogenesis, induces DNA damage because of re-replication and allows propagation of damaged DNA, resulting in partial polyploidy and oncogenic transformation. The mechanism by which pX allows cells with DNA damage to continue proliferating is unknown. Herein, we show pX activates Polo-like kinase 1 (Plk1) in the G(2) phase, thereby attenuating the DNA damage checkpoint. Specifically, in the G(2) phase of pX-expressing cells, the checkpoint kinase Chk1 was inactive despite DNA damage, and protein levels of claspin, an adaptor of ataxia telangiectasia-mutated and Rad3-related protein-mediated Chk1 phosphorylation, were reduced. Pharmacologic inhibition or knockdown of Plk1 restored claspin protein levels, Chk1 activation, and p53 stabilization. Also, protein levels of DNA repair protein Mre11 were decreased in the G(2) phase of pX-expressing cells but not with Plk1 knockdown. Interestingly, in pX-expressing cells, Mre11 co-immunoprecipitated with transfected Plk1 Polo-box domain, and inhibition of Plk1 increased Mre11 stability in cycloheximide-treated cells. These results suggest that pX-activated Plk1 by down-regulating Mre11 attenuates DNA repair. Importantly, concurrent inhibition of Plk1, p53, and Mre11 increased the number of pX-expressing cells with DNA damage entering mitosis, relative to Plk1 inhibition alone. By contrast, inhibition or knockdown of Plk1 reduced pX-induced polyploidy while increasing apoptosis. We conclude Plk1, activated by pX, allows propagation of DNA damage by concurrently attenuating the DNA damage checkpoint and DNA repair, resulting in polyploidy. We propose this novel Plk1 mechanism initiates pX-mediated hepatocyte transformation.
authors.affiliation: Department of Basic Medical Sciences, Purdue University Center for Cancer Research, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Leo
authors.initials: L
authors.lastname: Studach
authors.forename: Wen-Horng
authors.initials: WH
authors.lastname: Wang
authors.forename: Gregory
authors.initials: G
authors.lastname: Weber
authors.forename: Jiabin
authors.initials: J
authors.lastname: Tang
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Hullinger
authors.forename: Raphael
authors.initials: R
authors.lastname: Malbrue
authors.forename: Xiaoqi
authors.initials: X
authors.lastname: Liu
authors.forename: Ourania
authors.initials: O
authors.lastname: Andrisani
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002472:Cell Transformation, Viral; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D016195:G2 Phase / Q000235:genetics; D006515:Hepatitis B virus / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism / Q000821:virology; D006801:Humans; D000076228:MRE11 Homologue Protein; D010766:Phosphorylation / Q000235:genetics; D011123:Polyploidy; D011485:Protein Binding / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D055550:Protein Stability; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins; D000097869:Polo-Like Kinase 1
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D000071877:Checkpoint Kinase 1; D004268:DNA-Binding Proteins; D000076228:MRE11 Homologue Protein; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D016159:Tumor Suppressor Protein p53; D054334:Viral Regulatory and Accessory Proteins; D000097869:Polo-Like Kinase 1; C488158:CLSPN protein, human; C121766:MRE11 protein, human; C495901:TP53 protein, human; C057628:hepatitis B virus X protein; C000605867:CHEK1 protein, human