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リエゾンラボ研究会
発表内容

Title:
Maintenance of Genome Stability by TLS DNA polymerases

 

Speaker:
Takeshi Todo, PhD. Radioisotope Research Center, Osaka University

 

Abstract:
Genomic DNA undergoes constant modifications mediated by endogenous and environmental genotoxic agents. If these modifications are not repaired, they block DNA replication by the high-fidelity DNA polymerases Polδ and Polε. The resultant stalled replication forks have deleterious consequences on genome stability, including replication fork collapse and subsequent induction of DNA double strand break (DSB). This unusual situation lead to chromosome instability and ultimately triggers carcinogenesis. To circumvent this catastrophic scenario, cells possess specialized translesion synthesis (TLS) DNA polymerases that replace stalled replicative DNA polymerases and resolve replication blocks by inserting a nucleotide opposite the modified base on the template. However, TLS DNA polymerases frequently incorporate incorrect nucleotides, leading to point mutations. Thus, TLS polymerases protect the genome from the dangerous consequences of blocked replication at the expense of introducing point mutations. Several TLS enzymes have been identified in vertebrates, including Y-family DNA polymerases Rev1, Polη, Polι, and Polκ and the B-family DNA polymerase Polζ. TLS reaction is performed via a two-step process. In the first step, an “inserter” polymerase incorporates a nucleotide across the lesion. This step is catalyzed by Y-family DNA polymerases and Rev1 plays an essential role. In the second step, an “extender” polymerase extends the aberrant DNA primer terminus. This step is catalyzed by the B-family DNA polymerase Pol. To investigate the role of TLS polymerases on tumorigenesis, we generated knockout mutants for rev1 and rev3l, a core catalytic subunit of Polζ, in the small laboratory fish medaka, and examined the effects of deficiency in these polymerases on spontaneous and carcinogen-induced tumorigenesis. We found rev1 mutant exhibited a higher tumorigenic rate than wild-type fish after exposure with alkylating agent. Interestingly, loss of heterozygosity (LOH) occurred frequently in the mutant cells depending on the alkylating agent-treatment. On the other hand, in the rev3l mutant intestinal tumor developed spontaneously at high rate, whereas no tumor was observed in wild-type fish. In the rev3l deficient cell, DSBs were detected at higher rate than wild-type cell, and spontaneous chromosomal aberrations occurred frequently. These results demonstrate an involvement of the TLS pathway in maintaining genome integrity and its ability to suppress tumorigenesis.