Purpose: Neoadjuvant chemoradiotherapy (neoCRT) is a standard treatment for locally advanced rectal cancer (LARC); however, resistance to chemoradiotherapy is one of the main obstacles to improving treatment outcomes. The goal of this study was to identify factors involved in the radioresistance of colorectal cancer and to clarify the underlying mechanisms.Experimental Design: A genome-wide RNAi screen was used to search for candidate radioresistance genes. After RFC4 knockdown or overexpression, colorectal cancer cells exposed to X-rays both in vitro and in a mouse model were assayed for DNA damage, cytotoxicity, and apoptosis. Moreover, the regulatory effects and mechanisms of RFC4 in DNA repair were investigated in vitro. Finally, the relationships between RFC4 expression and clinical parameters and outcomes were investigated in 145 patients with LARC receiving neoCRT.Results: RFC4, NCAPH, SYNE3, LDLRAD2, NHP2, and FICD were identified as potential candidate radioresistance genes. RFC4 protected colorectal cancer cells from X-rayinduced DNA damage and apoptosis in vitro and in vivo. Mechanistically, RFC4 promoted nonhomologous end joining (NHEJ)-mediated DNA repair by interacting with Ku70/ Ku80 but did not affect homologous recombination-mediated repair. Higher RFC4 expression in cancer tissue was associated with weaker tumor regression and poorer prognosis in patients with LARC treated with neoCRT, which likely resulted from the effect of RFC4 on radioresistance, not chemoresistance.Conclusions: RFC4 was identified as a radioresistance factor that promotes NHEJ-mediated DNA repair in colorectal cancer cells. In addition, the expression level of RFC4 predicted radiotherapy responsiveness and the outcome of neoadjuvant radiotherapy in patients with LARC.

There was an error published in J. Cell Sci. 126, 4995-5004.One source of funding was accidentally omitted. The correct funding section is as shown below. FundingThis work was supported by the National Institutes of Health [grant number Summary Cytokinesis involves temporally and spatially coordinated action of the cell cycle, cytoskeletal and membrane systems to achieve separation of daughter cells. The septation initiation network (SIN) and mitotic exit network (MEN) signaling pathways regulate cytokinesis and mitotic exit in the yeasts Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively. Previously, we have shown that in fission yeast, the nucleolar protein Dnt1 negatively regulates the SIN pathway in a manner that is independent of the Cdc14-family phosphatase Clp1/Flp1, but how Dnt1 modulates this pathway has remained elusive. By contrast, it is clear that its budding yeast relative, Net1/Cfi1, regulates the homologous MEN signaling pathway by sequestering Cdc14 phosphatase in the nucleolus before mitotic exit. In this study, we show that dnt1 + positively regulates G2/M transition during the cell cycle. By conducting epistasis analyses to measure cell length at septation in double mutant (for dnt1 and genes involved in G2/M control) cells, we found a link between dnt1 + and wee1 + . Furthermore, we showed that elevated protein levels of the mitotic inhibitor Wee1 kinase and the corresponding attenuation in Cdk1 activity is responsible for the rescuing effect of dnt1D on SIN mutants. Finally, our data also suggest that Dnt1 modulates Wee1 activity in parallel with SCF-mediated Wee1 degradation. Therefore, this study reveals an unexpected missing link between the nucleolar protein Dnt1 and the SIN signaling pathway, which is mediated by the Cdk1 regulator Wee1 kinase. Our findings also define a novel mode of regulation of Wee1 and Cdk1, which is important for integration of the signals controlling the SIN pathway in fission yeast.

There was an error published in J. Cell Sci. 126, 4995-5004.One source of funding was accidentally omitted. The correct funding section is as shown below.