Characterization ofgenes involved in genomic stability using an experinental model organism.

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Many human cancers originate from defects in the DNA damage response and the cell cycle control. These defects cause instability of chromosomes. To identify and characterize novel genes of DNA damage response and the cell cycle control, we used an experimental model organism the nematode Caenorthabditis elegans.In eukaryotic cells, members of the ataxia telangiectasia mutated gene (ATM) family play important roles in conserved signal transduction pathways for the DNA damage response. We have identified an ATM-like Ce-atl-1 in the C. elegans genome. Depletion of its gene product by RNA-mediated interference (RNA1) caused pronounced defects in chromosomal segregation and DNA damage responses such as repair, apoptosis, and G1 arrest From the results of yeast two-hybrid analysis, its N-terminal half physically interacted with PCNA and its C-terminal half interacted with several gene products related to transport of ER, endocytosis, transcriptional factor, single strand binding protein SSB. … More Some of them were essential for apoptosis, but dispensable for DNA repair process.We also analyzed the Ring-H2 finger protein RBX1 that is a common subunit of SKP1-CDC53/CUL1-F box (SCF), other Cullins and von Hippel-Lindau (VHL) tumour suppressor E3 ubiquitin ligase complexes. The RBX1 RNAi experiment suggested that the RBX1 protein participates in diverse functions relevant to mitotic chromosomal condensation and segregation, G1/S progression and cytokinesis. All these defects of RB×1 RNAi were consistent with those found after either depletion of CUL2, Elongin B (ELB1) or Elongin C (ELC1). In addition, direct interactions between ELC1 and CUL2, and ELC1 and ELC2, respectively, were revealed by bacterial two-hybrid analysis. Thus, the RB×1/CUL2/ELC1/ELB1 complex acts as an E3 ubiquitin ligase in C. elegans and is essential for diverse functions relevant to chromosomal dynamics and cell cycle control. These phenomena are probably ubiquitous in human cancer, because all these genes identified in this study are highly conserved in mammals. Less