p 53 expression confers sensitivity to 5 ‐ fluorouracil via distinct chromatin accessibility dynamics in human colorectal cancer

One of the most commonly used drugs in chemotherapy, 5‐fluorouracil (5‐FU) has been shown to be effective in only 10‐15% of patients with colon cancer. Thus, studies of the mechanisms affecting 5‐FU sensitivity in these patients are necessary. The tumor suppressor protein p53 is a transcription factor that serves important roles in cell apoptosis by regulating the cell cycle. It has also been characterized as a key factor influencing drug sensitivity. Furthermore, accessible chromatin is a hallmark of active DNA regulatory elements and functions as a crucial epigenetic factor regulating cancer mechanisms. The present study assessed the genetic regulatory landscape in colon cancer by performing RNA sequencing and Assay for Transposase‐Accessible Chromatin sequencing, and investigated the effects of 5‐FU on chromatin accessibility and gene expression. Notably, while treatment with 5‐FU mediated global increases in chromatin accessibility, chromatin organization in several genomic regions differed depending on the expression status of p53. Since the occupancy of p53 does not overlap with accessible chromatin regions, the 5‐FU‐mediated changes in chromatin accessibility were not regulated by direct binding of p53. In the p53‐expressing condition, the 5‐FU‐mediated accessible chromatin region was primarily associated with genes encoding cell death pathways. Additionally, 5‐FU was revealed to induce open chromatin conformation at regions containing binding motifs for AP‐1 family transcription factors, which may drive expression of apoptosis pathway genes. In conclusion, expression of p53 may confer 5‐FU sensitivity by regulating chromatin accessibility of distinct genes associated with cell apoptosis in a transcription‐independent manner. Introduction Colorectal cancer ranks as the second most deadly cancer among all cancer types, and colorectal cancers are commonly treated with 5‐fluorouracil (5‐FU), anticancer drug. 5‐FU is known to interfere with DNA synthesis in cancer cells by inhibiting thymidylate synthase, as a mechanism that inhibits cell proliferation and leads to cell death (1‐3). Although 5‐FU plays a central role in the treatment of colorectal cancer, it elicits any effect in only 10-15% of colorectal cancer patients, and approximately 40-50% of treatments are successful upon combination therapy with other antitumor drugs, including oxaliplatin, leucovorin, and others. Therefore, outlining the mechanisms underlying sensitivity to 5‐FU among colorectal cancer cells would be helpful. Cancer research has shown p53 to be a tumor suppressor, and p53 dysfunction has been found to lead to the development of colorectal cancer. Moreover, p53 has been characterized a key factor influencing drug sensitivity: p53 overexpression has been shown to increase the effect of chemotherapy in patients with stage III colorectal cancer with mutant p53 (4‐6). The major biological function of p53 is to initiate cell apoptosis by regulating the cell cycle at the G1/S and the G2/M check points. Interestingly, p53 studies have indicated that active p53 exhibits both transcriptional and non‐transcriptional activity and that both can affect apoptosis. Under various cell death conditions, the non‐transcriptional activity of p53 induces mitochondrial outer membrane permeabilization (MOMP), and this triggers the release of pro-apoptotic factors from the mitochondrial inter‐membrane space (7‐9). Chromatin structure and organization influence the identity of cells by regulating cell‐specific signaling networks (10,11), and recently, various epigenetic studies have reported a link between alterations in chromatin structure and cancer progression (12‐15). Measurement of chromatin accessibility during prostate cancer progression revealed that chromatin relaxation increases the binding of oncogenic transcription factors, resulting in increased expression of tumor growth‐related genes (16,17). Another report showed that TGF‐β induces chromatin accessibility to cis‐regulatory elements of epithelial-to-mesenchymal transition-related genes, including CDH1, CDH2, and VIM. Additionally, research has shown that TGF‐β induced chromatin accessibility increases the p53 expression confers sensitivity to 5‐fluorouracil via distinct chromatin accessibility dynamics in human colorectal cancer CHUL MIN YANG1, MOO‐KOO KANG2,3, WOONG‐JAE JUNG2, JUNG‐SIK JOO2,3, YONG‐JIN KIM2,3, YEEUN CHOI2 and HYOUNG‐PYO KIM1‐3 1Severance Biomedical Science Institute; 2Department of Environmental Medical Biology, Institute of Tropical Medicine; 3Brain Korea 21 PLUS Project for Medical Science, Yonsei University College of Medicine, Seoul 120‐752, Republic of Korea Received September 18, 2020; Accepted December 3, 2020 DOI: 10.3892/ol.2021. 12487 Correspondence to: Dr Hyoung‐Pyo Kim, Department of Environmental Medical Biology, Institute of Tropical Medicine, Yonsei University College of Medicine, 50‐1 Yonsei‐ro, Seodaemun, Seoul 120‐752, Republic of Korea E‐mail: kimhp@yuhs.ac