Abstract:

Objective To investigate the role of Fusobacterium nucleatum（Fn） in chemoresistance of colorectal cancer（CRC） cells. Methods A total of 87 CRC patients at Yangpu Hospital Affiliated to Tongji University from March 2015 to January 2017 were enrolled. CRC tissues from all the patients were collected to determine Fn abundance. Totally，20 cases were selected and classified into Fn group（10 cases with Fn infection） and NC group（10 cases without Fn infection） based on bacterial load. The relative expression of 15 candidate long non-coding RNA（lncRNA）was determined. Additionally，10 recurrent and 10 non-recurrent patients were independently selected from the 87 patients based on 3-year follow-up outcomes to compare target lncRNA expression levels. CRC cell lines（HCT116 and SW480）were classified according to experimental conditions. Cell viability was assessed by CCK-8 assay to calculate the half-maximal inhibitory concentration（IC₅₀）. Proliferative activity of CRC cell lines before and after lncRNA XIST knockdown was evaluated using CCK-8 assay. CCK-8 assay，flow cytometry and western blotting were used to analyze proliferation and apoptosis in chemoresistant CRC cell lines（HCT116/5-FU and SW480/5-FU）. Results Compared with 5-FU and OXA treatment groups，the E.coli/5-FU and E.coli/OXA groups showed no statistical significance in IC₅₀（P>0.05），whereas Fn/5-FU and Fn/OXA groups exhibited increased IC₅₀（P<0.01）. Among the 15 candidate lncRNA，lncRNA XIST showed the highest expression in Fn group，exceeding NC group（P<0.01）. Both Fn abundance and lncRNA XIST expression levels were higher in recurrence group than non-recurrence group（P<0.05）. Fn-infected CRC cell lines demonstrated increased lncRNA XIST expression compared with control group（P<0.01）. HCT116/5-FU and SW480/5-FU showed higher lncRNA XIST relative expression than HCT116 and SW480 cells（P<0.001）. The lncRNA XIST knockdown group showed reduced cell viability and IC₅₀（P<0.01），increased apoptosis rate（P<0.01），upregulated apoptosis protein（PARP，Caspase-3 and Bax）（P<0.01）and downregulated anti-apoptotic protein Bcl-2（P<0.01）. Conclusions Fn may promote chemoresistance in CRC cells through lncRNA XIST upregulation. Both Fn and lncRNA XIST could serve as potential biomarkers for predicting chemotherapy sensitivity in CRC patients.

Key words: Fusobacterium nucleatum, Long non-coding RNA, 5-Fluorouracil, Oxaliplatin, Colorectal cancer