Circular RNA circXPO1 Promotes Multiple Myeloma Progression by Regulating miR-495-3p/DNA Damage-Induced Transcription 4 Axis.

Multiple myeloma (MM) is a hematologic malignancy that results from uncontrolled plasma cell proliferation. Circular RNAs are versatile regulators that influence cancer aggression. The pathogenic mechanism of circXPO1 in MM is still unknown. In this study, the expression of circXPO1, miR-495-3p, and DNA damage-induced transcription 4 (DDIT4) was detected. Knockdown and overexpression assays were used to evaluate the effect of circXPO1 on MM. Specifically, 5-ethynyl-2'-deoxyuridine and cell counting kit-8 assay were used to investigate cell proliferation. Meanwhile, flow cytometry was adopted to detect cell apoptosis and cell cycle. Apoptosis-associated and cell cycle-related proteins were detected by Western blot. Mechanistically, biotin RNA pull-down assay and dual-luciferase assay were implemented to verify the combination among miR495-3p and circXPO1 or DDIT4. The function of circXPO1 in vivo was explored in xenograft experiments. The results showed that circXPO1 was up-regulated in both MM samples and MM cell lines and miR-495-3p was down-regulated in MM patients. Silencing circXPO1 inhibited cell proliferation, increased apoptosis rates, and caused the G1 phase arrest. Overexpression of circXPO1 yielded opposite results. In addition, RNA pull-down experiment demonstrated the interaction between circXPO1 and miR-495-3p. Silencing miR-495-3p rescued the inhibitory function caused by the knockdown of circXPO1. DDIT4 was the target of miR-495-3p. Finally, silencing circXPO1 inhibited the growth of subcutaneous tumors in vivo. In conclusion, our findings showed that circXPO1 could promote MM progression via the miR-495-3p/DDIT4 axis.

MRE11-RAD50-NBS1 Complex Is Sufficient to Promote Transcription by RNA Polymerase II at Double-Strand Breaks by Melting DNA Ends.

The MRE11-RAD50-NBS1 (MRN) complex supports the synthesis of damage-induced long non-coding RNA (dilncRNA) by RNA polymerase II (RNAPII) from DNA double-strand breaks (DSBs) by an unknown mechanism. Here, we show that recombinant human MRN and native RNAPII are sufficient to reconstitute a minimal functional transcriptional apparatus at DSBs. MRN recruits and stabilizes RNAPII at DSBs. Unexpectedly, transcription is promoted independently from MRN nuclease activities. Rather, transcription depends on the ability of MRN to melt DNA ends, as shown by the use of MRN mutants and specific allosteric inhibitors. Single-molecule FRET assays with wild-type and mutant MRN show a tight correlation between the ability to melt DNA ends and to promote transcription. The addition of RPA enhances MRN-mediated transcription, and unpaired DNA ends allow MRN-independent transcription by RNAPII. These results support a model in which MRN generates single-strand DNA ends that favor the initiation of transcription by RNAPII.