The modulator of retrovirus infection (MRI or CYREN) is a 30-kDa protein with a conserved N-terminal Ku-binding motif (KBM) and a C-terminal XLF-like motif (XLM). We show that MRI is intrinsically disordered and interacts with many DNA damage response (DDR) proteins, including the kinases ataxia telangiectasia mutated (ATM) and DNA-PKcs and the classical non-homologous end joining (cNHEJ) factors Ku70, Ku80, XRCC4, XLF, PAXX, and XRCC4. MRI forms large multimeric complexes that depend on its N and C termini and localizes to DNA double-strand breaks (DSBs), where it promotes the retention of DDR factors. Mice deficient in MRI and XLF exhibit embryonic lethality at a stage similar to those deficient in the core cNHEJ factors XRCC4 or DNA ligase IV. Moreover, MRI is required for cNHEJ-mediated DSB repair in XLF-deficient lymphocytes. We propose that MRI is an adaptor that, through multivalent interactions, increases the avidity of DDR factors to DSB-associated chromatin to promote cNHEJ.

N-Butylidenephthalide (BP), isolated from the chloroform extract of Angelica sinensis, has been examined for its antitumor effects on glioblastoma multiforme brain tumors; however, little is known about its antitumor effects on hepatocellular carcinoma cells. Two hepatocellular carcinoma cell lines, HepG2 and J5, were treated with either N-butylidenephthalide or a vehicle, and cell viability and apoptosis were evaluated. Apoptosis-related mRNA and proteins expressed, including orphan receptor family Nurr1, NOR-1, and Nur77, were evaluated as well as the effect of N-butylidenephthalide in an in vivo xenograft model. N-Butylidenephthalide caused growth inhibition of both the cell lines at 25 g/ml. Furthermore, N-butylidenephthalide-induced apoptosis seems to be related to Nur77 translocation from nucleus to cytosol, which leads to cytochrome c release and caspase-3-dependent apoptosis. N-Butylidenephthalide-related tumor apoptosis was associated with phosphatidylinositol 3-kinase/protein kinase B (AKT)/glycogen synthase kinase-3␤ rather than the mitogen-activated protein kinase or protein kinase C pathway. Blockade of AKT activation enhanced proliferation inhibition and the induction of phosphor-Bcl-2 and Nur77 proteins. Besides, the increasing apoptosis by BP via transfection wild-type cAMP-response element-binding protein (CREB) into tumor cell was suppressed by dominant phosphorylation site mutation of CREB. This finding suggested CREB pathway was also partly involved in tumor apoptosis caused by BP. Administration of N-butylidenephthalide showed similar antitumoral effects in both HepG2 and J5 xenograft tumors. N-Butylidenephthalide induced apoptosis in hepatocellular carcinoma cells, both in vitro and in vivo, suggesting a potential clinical use of this compound for improving the prognosis of hepatocellular carcinoma cells.Hepatocellular carcinoma (HCC) is one of the most frequent cancers worldwide. The main curative therapies for cancer are surgery and radiation, which, in general, are only successful if the cancer is diagnosed at an early stage. CurThis work was supported National Science Council of the Republic of China

Non-homologous end joining (NHEJ) is a major DNA double-strand break (DSB) repair pathway that functions in all phases of the cell cycle. NHEJ repairs genotoxic and physiological DSBs, such as those generated by ionizing radiation and during V(D)J recombination at antigen receptor loci, respectively. DNA end joining by NHEJ relies on the core factors Ku70, Ku80, XRCC4, and DNA Ligase IV. Additional proteins also play important roles in NHEJ. The XRCC4-like factor (XLF) participates in NHEJ through its interaction with XRCC4, and XLF deficiency in humans leads to immunodeficiency and increased sensitivity to ionizing radiation. However, XLF is dispensable for NHEJ-mediated DSB repair during V(D)J recombination in murine lymphocytes, where it may have redundant functions with other DSB repair factors. Paralog of XRCC4 and XLF (PAXX) is a recently identified NHEJ factor that has structural similarity to XRCC4 and XLF. Here we show that PAXX is also dispensable for NHEJ during V(D)J recombination and during the repair of genotoxic DSBs in lymphocytes. However, a combined deficiency of PAXX and XLF blocks NHEJ with a severity comparable to that observed in DNA Ligase IV-deficient cells. Similar to XLF, PAXX interacts with Ku through its C-terminal region, and mutations that disrupt Ku binding prevent PAXX from promoting NHEJ in XLF-deficient lymphocytes. Our findings suggest that the PAXX and XLF proteins may have redundant functions during NHEJ.