Defective DNA damage response is a threat to genome stability and a proven cause of tumorigenesis. C21ORF2 (chromosome 21 open reading frame 2) is a novel gene on chromosome 21, and the C21ORF2 protein is found to interact with NEK1. Earlier studies showed that C21ORF2 might be associated with some human genetic diseases including Down syndrome. However, the cellular functions of C21ORF2 remain unknown. In the present study, we reported that C21ORF2 affected cell proliferation after DNA damage induced by ionizing radiation, and DNA repair was less efficient in C21ORF2-depleted cells compared with control cells. However, C21ORF2-knockdown cells did not show defects in the activation of the G2-phase DNA damage checkpoint. Furthermore, homologous recombination, but not non-homologous end joining repair, was found to be impaired after C21ORF2 attenuation, which could be rescued by the overexpression of NEK1, indicating that C21ORF2 functions in the same pathway as NEK1 in DNA damage repair.

bCdc14 is a phosphatase that controls mitotic exit and cytokinesis in budding yeast. In mammals, the two Cdc14 homologues, Cdc14A and Cdc14B, have been proposed to regulate DNA damage repair, whereas the mitotic exit and cytokinesis rely on another phosphatase, PP2A-B55␣. It is unclear if the two Cdc14s work redundantly in DNA repair and which repair pathways they participate in. More importantly, their target(s) in DNA repair remains elusive. Here we report that Cdc14B knockout (Cdc14B ؊/؊ ) mouse embryonic fibroblasts (MEFs) showed defects in repairing ionizing radiation (IR)-induced DNA doublestrand breaks (DSBs), which occurred only at late passages when Cdc14A levels were low. This repair defect could occur at early passages if Cdc14A levels were also compromised. These results indicate redundancy between Cdc14B and Cdc14A in DSB repair. Further, we found that Cdc14B deficiency impaired both homologous recombination (HR) and nonhomologous end joining (NHEJ), the two major DSB repair pathways. We also provide evidence that Cdh1 is a downstream target of Cdc14B in DSB repair.

The REGγ-proteasome serves as a short-cut for the destruction of certain intact mammalian proteins in the absence of ubiquitin-and ATP. The biological roles of the proteasome activator REGγ are not completely understood. Here we demonstrate that REGγ controls degradation of protein kinase A catalytic subunit-α (PKAca) both in primary human umbilical vein endothelial cells (HUVECs) and mouse embryonic fibroblast cells (MEFs). Accumulation of PKAca in REGγ-deficient HUVECs or MEFs results in phosphorylation and nuclear exclusion of the transcription factor FoxO1, indicating that REGγ is involved in preserving FoxO1 transcriptional activity. Consequently, VEGF-induced expression of the FoxO1 responsive genes, VCAM-1 and E-Selectin, was tightly controlled by REGγ in a PKA dependent manner. Functionally, REGγ is crucial for the migration of HUVECs. REGγ−/− mice display compromised VEGF-instigated neovascularization in cornea and aortic ring models. Implanted matrigel plugs containing VEGF in REGγ−/− mice induced fewer capillaries than in REGγ+/+ littermates. Taken together, our study identifies REGγ as a novel angiogenic factor that plays an important role in VEGF-induced expression of VCAM-1 and E-Selectin by antagonizing PKA signaling. Identification of the REGγ–PKA–FoxO1 pathway in endothelial cells (ECs) provides another potential target for therapeutic intervention in vascular diseases.

No abstract