Involvement of Rev1 in alkylating agent-induced loss of heterozygosity in Oryzias latipes

Rev1 overexpression accelerates N-methyl-N-nitrosourea (MNU)-induced thymic lymphoma by increasing mutagenesis

Rev1 has two important functions in the translesion synthesis pathway, including dCMP transferase activity, and acts as a scaffolding protein for other polymerases involved in translesion synthesis. However, the role of Rev1 in mutagenesis and tumorigenesis in vivo remains unclear. We previously generated Rev1-overexpressing (Rev1-Tg) mice and reported that they exhibited a significantly increased incidence of intestinal adenoma and thymic lymphoma (TL) after N-methyl-N-nitrosourea (MNU) treatment. In this study, we investigated mutagenesis of MNU-induced TL tumorigenesis in wild-type (WT) and Rev1-Tg mice using diverse approaches, including whole-exome sequencing (WES). In Rev1-Tg TLs, the mutation frequency was higher than that in WT TL in most cases. However, no difference in the number of nonsynonymous mutations in the Catalogue of Somatic Mutations in Cancer (COSMIC) genes was observed, and mutations involved in Notch1 and MAPK signaling were similarly detected in both TLs. Mutational signature analysis of WT and Rev1-Tg TLs revealed cosine similarity with COSMIC mutational SBS5 (aging-related) and SBS11 (alkylation-related). Interestingly, the total number of mutations, but not the genotypes of WT and Rev1-Tg, was positively correlated with the relative contribution of SBS5 in individual TLs, suggesting that genetic instability could be accelerated in Rev1-Tg TLs. Finally, we demonstrated that preleukemic cells could be detected earlier in Rev1-Tg mice than in WT mice, following MNU treatment. In conclusion, Rev1 overexpression accelerates mutagenesis and increases the incidence of MNU-induced TL by shortening the latency period, which may be associated with more frequent DNA damage-induced genetic instability.

Carcinogenesis Models Using Small Fish

Experimental animals are indispensable in life science-related research, including cancer studies. After rats and mice, small fishes, such as zebrafish and medaka, are the second most frequently used model species. Fish models have some advantageous physical characteristics that make them suitable for research, including their small size, some transparency, genetic manipulability, ease of handling, and highly ortholog correspondence with humans. This review introduces technological advances in carcinogenesis model production using small fish. Carcinogenesis model production begins with chemical carcinogenesis, followed by mutagenesis. Gene transfer technology has made it possible to incorporate various mechanisms that act on cancer-related genes in individuals. For example, scientists may now spatiotemporally control gene expression in a single fish through methods including the localization of an expression site via a tissue-specific promoter and expression control using light, heat, or a chemical substance. In addition, genome editing technology is realizing more specific and more efficient gene disruption than conventional mutagenesis, in which the disruption of the gene of interest depends on chance. These technological advances have improved animal models and will soon create carcinogenesis models that better mimic human pathology. We conclude by discussing future expectations for cancer research using small fish.

Targeting translesion synthesis (TLS) to expose replication gaps, a unique cancer vulnerability

Introduction: Translesion synthesis (TLS) is a DNA damage tolerance (DDT) mechanism that employs error-prone polymerases to bypass replication blocking DNA lesions, contributing to a gain in mutagenesis and chemo-resistance. However, recent findings illustrate an emerging role for TLS in replication gap suppression (RGS), distinct from its role in post-replication gap filling. Here, TLS protects cells from replication stress (RS)-induced toxic single-stranded DNA (ssDNA) gaps that accumulate in the wake of active replication. Intriguingly, TLS-mediated RGS is specifically observed in several cancer cell lines and contributes to their survival. Thus, targeting TLS has the potential to uniquely eradicate tumors without harming non-cancer tissues. Areas Covered: This review provides an innovative perspective on the role of TLS beyond its canonical function of lesion bypass or post-replicative gap filling. We provide a comprehensive analysis that underscores the emerging role of TLS as a cancer adaptation necessary to overcome the replication stress response (RSR), an anti-cancer barrier. Expert Opinion: TLS RGS is critical for tumorigenesis and is a new hallmark of cancer. Although the exact mechanism and extent of TLS dependency in cancer is still emerging, TLS inhibitors have shown promise as an anti-cancer therapy in selectively targeting this unique cancer vulnerability.

Involvement of Rev1 in alkylating agent-induced loss of heterozygosity in Oryzias latipes

Translesion synthesis (TLS) polymerases mediate DNA damage bypass during replication. The TLS polymerase Rev1 has two important functions in the TLS pathway, including dCMP transferase activity and acting as a scaffolding protein for other TLS polymerases at the C‐terminus. Because of the former activity, Rev1 bypasses apurinic/apyrimidinic sites by incorporating dCMP, whereas the latter activity mediates assembly of multipolymerase complexes at the DNA lesions. We generated rev1 mutants lacking each of these two activities in Oryzias latipes (medaka) fish and analyzed cytotoxicity and mutagenicity in response to the alkylating agent diethylnitrosamine (DENA). Mutant lacking the C‐terminus was highly sensitive to DENA cytotoxicity, whereas mutant with reduced dCMP transferase activity was slightly sensitive to DENA cytotoxicity, but exhibited a higher tumorigenic rate than wild‐type fish. There was no significant difference in the frequency of DENA‐induced mutations between mutant with reduced dCMP transferase activity and wild‐type cultured cell. However, loss of heterozygosity (LOH) occurred frequently in cells with reduced dCMP transferase activity. LOH is a common genetic event in many cancer types and plays an important role on carcinogenesis. To our knowledge, this is the first report to identify the involvement of the catalytic activity of Rev1 in suppression of LOH.