P53-response CircRNA_0006420 Aggravates Lung Cancer Radiotherapy Resistance by Promoting Formation of HUR/PTBP1 Complex

Background: p53 wild-type lung cancer cells can develop radiation resistance. Circular RNA (circRNA) consists of a family of transcripts with exclusive structures. circRNA is critical in tumorigenesis and is a potential biomarker or therapeutic target. It is uncertain how circRNA expression and functions are regulated post-radiation in p53 wild-type cancer cells.

Methods: A549 or H1299 cells were divided into p53 and p53 groups by CRISPR/Cas9; both groups were subjected to 4 Gy ionizing radiation (IR: p53-IR and p53-IR). RNA-seq, CCK8, cell cycle, and other functional and mechanism experiments were performed in vivo. p53 gene knockout mice were generated to test the cell results in vitro.

Results: circRNAs were found in differential groups. circRNA_0006420 (IRSense) was upregulated in p53 cells but had the same expression level as p53 cells after radiation, indicating that p53 silencing prevents its upregulation after IR. In the presence of p53, upregulated IRSense post-radiation induces G2/M arrest by regulating DNA damage repair (DDR) pathway-related proteins. Meanwhile, upregulated IRSense post-radiation aggravates the radiation-induced epithelial-mesenchymal transition (EMT). Interestingly, in the presence of p53, it promotes IRSense/HUR/PTBP1 complex formation resulting in the promotion of the radiation-induced EMT. Moreover, c-Jun regulates the upregulation of p53 transcription after radiation treatment. For these lung cancer cells with p53, upregulated IRSense aggravates lung cancer cell proliferation and increases radiation resistance by interacting with HUR (ElAV-like protein 1) and PTBP1 (polypyrimidine tract-binding protein 1) in the nucleus.

Conclusions: Lung cancer cells retaining p53 may upregulate circRNA_0006420 (IRSense) expression post radiation to form an IRSense/HUR/PTBP1 complex leading to radiotherapy resistance. This study furthers our understanding of the roles of circRNA in regulating the effect of radiotherapy and provides novel therapeutic avenues for effective clinical lung cancer therapies.