Epigenetic Mechanisms Underlying OST? Repression In Colorectal Cancer

Background and purpose:Colorectal cancer(CRC)is the third most common cancer and the fourth-leading cause of cancer-related deaths worldwide.Recently,many researches have revealed that bile acid especially deoxycholic acid(DCA)and lithocholic acid(LCA)play important roles during carcinogenesis and development of colorectal cancer.In our experiment,we found OST?(Organic solute transporter ?),an important bile acid export transporter,was significantly down-regulated in CRC.That is interesting because this may be related to reduced DCA and LCA export.In our research,we try to expalin mechanisms underlying OST? repression in CRC using epigenetic methods.Experimental approach:The repression of OST? was identified using Western blot and RT-qPCR.The histone acetylation state at the OST? promoter region was then evaluated with chromatin immunoprecipitation(ChIP)and trichostation A(TSA)treatment in CRC cell lines HT29 and HCT15.The histone acetylation state was further identified in CRC tissues using ChIP.To find which HAT or HDAC was responsible for reducedH3K27Ac at OST? promoter region,RT-qPCR,siRNA knock-down,ChIP,dual-luciferase reporter gene assay were used.Key results:OST? was significantly down-regulated in CRC compared with adjacent normal tissues.After TSAtreatment,OST? expression incresed a lot due to up-regulated H3K27Ac at OST? promoter region.We also treated HT29 cell line with CTB(an activator of p300),C646(an inhibitor of p300)as well as siRNAfor p300,and found p300 regulates H3K27Ac state at OST? promoter region to control its expressionConclusions and implications:In CRC,p300 expression is reduced,which leadto lower H3K27Ac at OST? promoter region,so OST? transcription is inhibited,finally,OST?expression is significantly down-regulated.In our experiment,we revealed mechanisms underlying OST? repression in CRC,hoping this mechanism would help us to understand carcinogenesis and development of CRC.