However, some unrepaired DNA lesions can remain at replication because of limited capacity of DNA repair systems. These lesions induce gaps in the newly synthesized strand. The gaps are filled by postreplication repair (PRR) system and this repair system is conserved from yeast to mammalian cells [3, 4]. In the yeast Saccharomyces cerevisiae, genes belonging to the Rad6 Selonsertib molecular weight epistasis group play an important role in the PRR pathway . In this pathway, Rad6 and Rad18 are the most important genes. Rad6 is an ubiquitin-conjugating enzyme (E2) and Rad18 is a single-stranded DNA binding protein and has ubiquitin-ligase
(E3) activity. Rad18 forms a specific complex with Rad6 [6, 7]. Human homolog of yeast Rad18 gene is mapped on chromosome 3p24-25 and it has been shown that human Rad18 protein interacts with the human homologs check details selleck kinase inhibitor of the Rad6 protein (HHR6A and HHR6B) and is involved in PRR [8, 9]. Rad18 or Rad6 mutations cause higher sensitivity to various mutagens . Inactivation of Rad18 in mouse embryonic stem cells leads to increasing sensitivity to various DNA-damaging agents and to increasing sister-chromatic exchange.
Rad18 contributes to maintenance of genomic stability through PRR . However, the status of Rad18 in human cancers is still unknown. In the present study, we analyzed the expression and the mutation of Rad18 in human cancer cell lines and NSCLC tissues and also assessed whether there is some functional difference due to the SNP of Rad18. Methods Cell lines and cell culture Twenty-nine digestive carcinoma cell lines and five lung carcinoma cell lines were used in this study. They comprised: 7 esophageal carcinoma cell lines (KYSE30, KYSE140, TE1, TE9, TE10, TE12, TE13), 6 gastric carcinoma crotamiton cell lines (AGS, MKN1, MKN28, MKN45, NUGC3, NUGC4), 9 colon carcinoma cell lines (Caco2, Colo201, Colo205, DLD-1, HCT116, HT29, SW480, SW620, WiDr), 7 pancreatic carcinoma cell lines (AsPC-1, Capan1, Capan2, Panc1, SUIT-2, MiaPaCa2, Hs700T) and 5 lung carcinoma cell lines (A549, EBC1, LU99, PC3,
LCOK). Cell lines were cultured in recommended medium supplemented with 10% fetal bovine serum (Invitrogen) at 37°C in a humidified atmosphere of 5% CO2 to 95% air. Tissue samples Non-small cell lung cancer samples were all surgically resected in Kumamoto University Hospital (Kumamoto, Japan) between 2005 and 2006. Informed consent was performed to all patients. Only the samples with agreement were used for further analysis. This study was approved by the ethical committees of Kumamoto University Hospital. The following features were looked at: sex, age, and pathological status (size, histological type, T stage, lymph node metastasis, pStage). UICC Tumor-Node-Metastasis Classification of Malignant Tumors  was used to classify pathological status. For the controls, peripheral white blood cells of 26 healthy volunteers were collected.