E3 ubiquitin ligase RNF2 protects polymerase ι from destabilization.

Human DNA polymerase ι (Polι) belongs to the Y-family of specialized DNA polymerases engaged in the DNA damage tolerance pathway of translesion DNA synthesis that is crucial to the maintenance of genome integrity. The extreme infidelity of Polι and the fact that both its up- and down-regulation correlate with various cancers indicate that Polι expression and access to the replication fork should be strictly controlled. Here, we identify RNF2, an E3 ubiquitin ligase, as a new interacting partner of Polι that is responsible for Polι stabilization in vivo. Interestingly, while we report that RNF2 does not directly ubiquitinate Polι, inhibition of the E3 ubiquitin ligase activity of RNF2 affects the cellular level of Polι thereby protecting it from destabilization. Additionally, we indicate that this mechanism is more general, as DNA polymerase η, another Y-family polymerase and the closest paralogue of Polι, share similar features.

DNA polymerase ι is acetylated in response to SN2 alkylating agents.

DNA polymerase iota (Polι) belongs to the Y-family of DNA polymerases that are involved in DNA damage tolerance through their role in translesion DNA synthesis. Like all other Y-family polymerases, Polι interacts with proliferating cell nuclear antigen (PCNA), Rev1, ubiquitin and ubiquitinated-PCNA and is also ubiquitinated itself. Here, we report that Polι also interacts with the p300 acetyltransferase and is acetylated. The primary acetylation site is K550, located in the Rev1-interacting region. However, K550 amino acid substitutions have no effect on Polι's ability to interact with Rev1. Interestingly, we find that acetylation of Polι significantly and specifically increases in response to SN2 alkylating agents and to a lower extent to SN1 alkylating and oxidative agents. As we have not observed acetylation of Polι's closest paralogue, DNA polymerase eta (Polη), with which Polι shares many functional similarities, we believe that this modification might exclusively regulate yet to be determined, and separate function(s) of Polι.

Negative Correlation Between Hepatitis C Virus (HCV) and Let-7 MicroRNA Family in Transplanted Livers: The Role of rs868 Single-Nucleotide Polymorphism.

BACKGROUND Genetic alterations of TGF-ß pathway members, including its transmembrane receptor, TGFBR1, may influence the course of HCV infection. Rs868 is a single-nucleotide polymorphism of the 3'UTR region of TGFBR1, located in a binding site for the conserved let-7/miR98 microRNA family. Previously, we demonstrated a favorable course of hepatitis C recurrence after liver transplantation in rs868 AG genotype of the transplanted liver when compared to rs868 AA. The aim of the present study was to confirm the biological effect of rs868. MATERIAL AND METHODS HepG2 cell line was transfected with luciferase vectors cloned with 3'UTR of TGFBR1 gene encompassing different rs868 alleles. Post-transplant liver biopsies from 61 patients with HCV-related end-stage liver disease were evaluated histopathologically and analyzed for the expression of TGFBR1 mRNA, let-7/miR98 microRNAs, HCV RNA load, and rs868 genotype. RESULTS Luciferase expression was significantly lower in the A allele-containing vector. TGFBR1 mRNA and HCV RNA load were correlated negatively with let-7/miR98 microRNAs and this correlation was significantly stronger for rs868 AG compared to AA genotype. A strong positive correlation was demonstrated between TGFBR1 and HCV in both genotypes. In AG heterozygotes, let-7/miR98 microRNAs showed a strong negative correlation with periportal or periseptal interface hepatitis (Ishak A score). CONCLUSIONS There is a negative correlation between let-7/miR98 microRNAs and HCV viral load and TGFBR1 mRNA after liver transplantation. In the rs868 AG heterozygotes, this correlation was stronger and there was a negative correlation between let-7/miR98 and Ishak A score, which is in concordance with the previously demonstrated protective role of this genotype in post-transplant hepatitis C recurrence.

Association of 49245A>G (rs868) polymorphism in the 3'UTR of donor TGFBR1 gene with course of hepatitis C following orthotopic liver transplantation.

BACKGROUND: Terminal hepatitis C is one of the leading indications for orthotopic liver transplantation (OLT). However, hepatitis C virus (HCV) reinfection occurs in almost all recipients and usually leads to progressive fibrosis and graft failure. Transforming growth factor-b (TGF-ß) plays a part in transplanted liver cirrhosis, but nothing is known about the possible role of genetic diversity of TGF-ß receptor system. Therefore, the aim of our study was to investigate whether genetic variation in 3' untranslated region (3'UTR) of TGF-ß receptor type I (TGFBR1) gene is associated with recurrence and severity of hepatitis C and liver fibrosis following OLT in HCV-infected patients. MATERIAL AND METHODS: The study group included 95 chronic hepatitis C patients following OLT. The recipients and donors were genotyped for 49245A>G (rs868) and 51976G>A (rs334349) single nucleotide polymorphisms (SNP). RESULTS: Donor rs868 AA genotype was strongly associated with worse clinical course of recurrent hepatitis C. The rs868 AA group displayed more severe symptoms of hepatitis C during the follow-up and the fibrosis score in this group was significantly higher 3 years after OLT. CONCLUSIONS: Clinical course of hepatitis C after OLT may depend on donor rs868 SNP located in TGFBR1 3'UTR.