title: RB silencing compromises the DNA damage-induced G2/M checkpoint and causes deregulated expression of the ECT2 oncogene.
abstract: As alterations in retinoblastoma (RB)/E2F pathway are commonly found in human cancers, the molecular mechanism underlying cell cycle deregulation caused by the mutations in the RB/E2F pathway needs to be investigated extensively. Compared with good understanding of RB/E2F functions in G1-S cell cycle progression, it is not fully understood how an abrogated RB pathway affects the G2-M phase of the cell cycle. Here, we report that disruption of RB accelerated G2-M progression in the presence of DNA damage by elevating the expression of a set of mitotic regulatory genes. We generated RB(+)- and (-)-matched cells using short hairpin RNA. In the RB(-) cells, the G2/M checkpoint mediated by a DNA-damaging agent was over-ridden. With microarray analysis, we found that the expression of key G2-M regulatory genes was upregulated in RB(-) cells. In particular, we demonstrated that the proto-oncogene ECT2 was directly regulated by E2Fs. Furthermore, suppression of ECT2 expression by small interfering RNA in RB(-) cells resulted in cytokinesis arrest, suggesting that RB(-) cells lack the regulation of E2F-mediated cytokinesis. These results indicate that aberrant ECT2 expression, observed in various human tumors, could be the direct result of RB/E2F pathway deficiency, thereby contributing to cell division in cancers.
authors.affiliation: Functional Genomics, Banyu Tsukuba Research Institute, Merck Research Laboratory, Tsukuba, Ibaraki, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Eguchi
authors.forename: T
authors.initials: T
authors.lastname: Takaki
authors.forename: H
authors.initials: H
authors.lastname: Itadani
authors.forename: H
authors.initials: H
authors.lastname: Kotani
mesh_terms: D002455:Cell Division; D002460:Cell Line; D049109:Cell Proliferation; D004249:DNA Damage; D050684:E2F Transcription Factors / Q000378:metabolism; D016195:G2 Phase; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D011401:Promoter Regions, Genetic; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D016160:Retinoblastoma Protein / Q000037:antagonists & inhibitors*
chemical_list: D050684:E2F Transcription Factors; C489850:ECT2 protein, human; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein