Background: Tumor metastasis of colorectal cancer (CRC) is the main cause of death in most patients and the major difficulty in comprehensive CRC treatment. Circular RNAs (circRNAs) affect many biological functions in solid tumors. However, their mechanisms in CRC metastasis remain unclear. Methods: RNA sequencing (RNA-seq) and quantitative real-time PCR were performed to screen differentially expressed circRNAs between CRC tissues and adjacent normal tissues. CCK-8, cell migration and wound healing assays were performed to determine the functions of circRHOBTB3 in cell proliferation and metastasis. RNA pulldown and RNA immunoprecipitation assays were performed to verify the interaction between circRHOBTB3 and the HuR (ELAVL1) protein. Further RNA-seq and rescue experiments were applied to search for the downstream target. We also conducted a mouse xenograft model to elucidate the effect of circRHOBTB3 on cancer metastasis in vivo . Results: We identified circRHOBTB3 which is markedly downregulated in CRC tissues and cell lines. Furthermore, lower circRHOBTB3 levels were significantly associated with advanced clinical stages and greater risk of metastases. Overexpression of circRHOBTB3 suppresses tumor metastasis in CRC cells. Mechanistically, circRHOBTB3 binds to HuR, which is a ubiquitously expressed and functional RNA-binding protein (RBP) in CRC development, and promotes β-Trcp1-mediated ubiquitination of HuR. Normally, HuR binds to the 3'UTR of target mRNAs to facilitate their stabilization, whereas the interaction between circRHOBTB3 and HuR degrades HuR to reduce the expression level of the downstream target PTBP1. Furthermore, overexpressed circRHOBTB3 suppresses lung metastases in vivo , and this effect can be partly reversed by PTBP1 overexpression. In addition, the transcription of circRHOBTB3 can be improved by both FUS and ADARB2 in CRC cells. Conclusions: Our findings indicate that circRHOBTB3 exerts suppressive effects on CRC aggressiveness through the HuR/PTBP1 axis.

Purpose5-Fluorouracil (5-Fu) is used as a conventional chemotherapy drug in chemotherapy for patients with advanced colorectal cancer, but many patients still suffer from treatment failure due to 5-Fu resistance. Emerging observations revealed the important role of chemokine (C-X-C motif) ligand 13 (CXCL-13) in tumor microenvironment and its relationship with prognosis in patients with colorectal cancer. This study is designed to reveal the important role of CXCL-13 in causing colorectal cancer resistance to 5-Fu.Materials and MethodsCXCL-13 levels of patient's serum or cell culture supernatants were measured separately by enzyme-linked immunosorbent assay. In cell assays, cell viability is detected by Cell Counting Kit-8. Therefore, the recombinant human CXCL-13 was used to simulate its high expression in cells while its antibody and siRNA were used to reduce CXCL-13 expression in cells.ResultsIn this study, we demonstrated that CXCL-13 is associated with 5-Fu resistance by culture medium exchange experiments and cytokine arrays of colorectal cancer resistant and nonresistant cells. Clinical studies showed that CXCL-13 is highly expressed in the serum of 5-Fu–resistant patients. High levels of serum CXCL-13 also predict a worse clinical outcome. The addition of recombinant CXCL-13 cytokine resulted in 5-Fu resistance, while its antibody overcame 5-Fu resistance, and knockdown of CXCL-13 expression by siRNA also reduced 5-Fu resistance, which can be saved by added recombination CXCL-13.ConclusionThese results not only identify a CXCL-13 mediated 5-Fu resistance mechanism but also provide a novel target for 5-Fu–resistant colorectal cancer in prevention and treatment strategies.

At present, anterior resection of the rectum or transabdominal rectal resection is the most common surgical technique for rectal cancer. Laparoscopic techniques are popular, and the efficacy and safety of laparoscopic rectal surgery have been confirmed. However, postoperative anastomotic leakage is a common, severe complication that leads to high mortality. Thus, early diagnosis of anastomotic leakage is important for reducing clinical consequences. The aim of this study was to determine whether C-reactive protein (CRP) is a good predictor of anastomotic leakage in laparoscopic transabdominal rectal resection. Our retrospective study involved a series of 196 rectal cancer patients who underwent laparoscopic transabdominal rectal resection without ileostomy between May 2013 and April 2015 at the Sir Run Run Shaw Hospital, Zhejiang University College of Medicine. The following patient data were collected: demographic data, manifestations of the complication, CRP levels and neutrophil percentage during the first 7 postoperative days. Anastomotic leakage was detected in 11 patients (5.6%). Each group showed significant differences ( P < .05) in CRP levels on postoperative days 3 to 7; compared with other groups, the anastomotic leakage group showed significant differences in CRP levels ( P < .05) on postoperative day 6. When patients were divided into groups with or without anastomotic leakage, CRP was a reliable predictor on postoperative days 4 to 7 ( P < .05, area under the curve > 0.800). The best combination was CRP on postoperative day 6 (area under the curve = 0.932) with a cut-off of 76.6 mg/L, resulting in a sensitivity of 83.3%, a specificity of 94.6% and a negative predictive value of 99%. CRP is a reliable predictor of anastomotic leakage after laparoscopic transabdominal rectal resection surgery. High CRP levels on postoperative days 4 to 7 indicate the need for a more careful patient evaluation.