215P 53BP1 loss induces the chemoresistance of colorectal cancer cells to 5-fluorouracil by inhibiting ATM-CHK2-P53 pathway

Abstract

Background P53bindingprotein1(53BP1)isakeycomponentinDNArepairto maintain genetic stability and preventing tumors. Our previous studyindicated that 53BP1 lossisanadverseprognosticfactorofcolorectalcancer,butitseffectonthe sensitivityofcolorectalcancerto5-fluorouracil(5-FU) isunknown.Thisstudyaimedto examine the effect of 53BP1 expression on the sensitivity of colorectal cancer to 5-FU. Methods Immunohistochemical analysis of was performed in 30 metastatic colorectal cancer (mCRC) samples to investigate the association of 53BP1 expression level with clinical therapeutic effect and prognosis. IC50 values for 5-FU and 53BP1 expression were determined by MTT assay and Western blotting in 5 colorectal cancer cell lines. 53BP1 knockdown was also performed in HCT116 and HT29 cells with relativelyhigh 5BP1 expression, and the effects on cell proliferation, apoptosis and cell cycle were evaluated. Inaddition, theproteinexpressionsof ATM-CHK2-P53 pathway componentsandBcl-2familyweremeasuredbyWesternblotting.Finally,theeffectof 53BP1 knockdownontumorgrowthand5-FUchemoresistancewasinvestigatedin vivo. Results 53BP1 expression was closely related to time to progress (TTP) after the first- linechemotherapybasedondownregulationof53BP1resultinginareductionofTTP. Invitro,downregulated53BP1inducedS-phasearrestofHCT116andHT29cells, increasedtheproliferation, inhibitedapoptosisafter5-FUtreatment, andinhibiting relativeproteinsexpressioninATM-CHK2-P53apoptoticpathway,aswellasapoptotic proteinscapase9,capase3andupregulatingBcl-2expression.Inaddition,theinvivo study further confirmed that 53BP1 downregulation accelerated the proliferation of implanted tumor cells in nude mice and enhanced resistance to 5-FU. Conclusions Our studies showed the 53BP1 loss served as a negative factor to affecting chemotherapy efficacy, and could promote cell proliferation and inhibit apoptosis throughinhibitionofthepathwayofATM-CHK2-P53toinduce5-FUresistance.Our study provides a new prospect for the research in this field. Clinical trial indentification The tumor tissues from 30 mCRC patients who have receivedfirst-linechemotherapywerecollectedfromMarch2012toDecember 2014.ThestudywasapprovedbytheHumanEthicsReviewBoardfromtheUnion Hospital of Tongji Medical College of Huazhong University of Science and Technology (Hubei, China). Legal entity responsible for the study N/A Funding SupportedbyNatural Science Foundation of Hubei Province of China, No2015CFB659 Disclosure All authors have declared no conflicts of interest.