Study On The Mechanism Of Promoting ATM Expression By Antisense Transcript L1-ATM-AS

Breast cancer is one of the most common malignant tumors in women and the incidence of breast cancer is increasing year by year.It is known that the reduction or loss of function of tumor suppressor genes is one of the important pathological mechanisms of breast cancer.ATM(Ataxia Telangiectasia Mutated gene)is a critical tumor suppressor gene.It encodes ATM protein that play an important role in DNA repair.The ATM gene is located in human chromosome 11(11q22-23),about 150 kb in length and contains 63 exons.Abnormal decrease in expression of the ATM gene has been functionally connected breast carcinogenesis.However,it is unclear how the ATM gene expression is abnormally reduced.There are about 500000 copies of Long Interspersed Elements-1(LINE-1)in human genome,accounting for about 20% of the genome.The full length of LINE-1is 6kb that harbors two open reading frames(ORF1 and ORF2).The promoter of LINE-1 is a bi-directional promoter,which can drive an antisense chimeric RNA to regulate expression of adjacent genes in addition to driving a sense RNA.Using bioinformatics analysis we found that the 61 st intron of ATM gene contained a complete LINE-1.The previous work in our laboratory confirmed that the LINE-1antisense promoter(L1-ASP)could drive an antisense RNA named L1-ATM-AS with a length larger than 200nt(nucleotide);L1-ATM-AS could significantly up-regulate the expression of ATM.However,the regulatory mechanism is unclear.It has been known that antisense lncRNA generally regulates activity of the target genes by altering histone modifications of the promoter regions.Therefore,weassumed that L1-ATM-AS might bind to certain histone-modifying enzyme to form a complex,by increasing histone modifications of the ATM promoter to keep chromatin in open and active state,thus to activate expression of the ATM gene.To verify this assumption we performed a series of molecular,cellular and epigenetic experiments using DNA binding protein purification,Mass spectrometry analysis,ChIP and RIP technology.Our results showed that L1-ATM-AS interacted with histone acetylase KAT5 and formed a RNA-Protein complex to induce histone acetylation(H3K14ac)of the ATM promoter.As a result,the ATM gene expression was up-regulated.Our work indicated that LINE-1 antisense RNA was an important regulator of ATM gene activity,which revealed a new regulatory mechanism of ATM gene expression and provided a enlightening clue for understanding mechanism of breast carcinogenesis.