N6-Methyladenine DNA Modification in Human Genome

In human cells, 5-methylcytosine (5mC) DNA modification plays an important role in gene regulation. However, N6-methyladenine (6mA) DNA modification, which is predominantly present in prokaryotes, is considered to be absent in human genomic DNA. Here, using single molecule real-time (SMRT) sequencing on human blood, we show that DNA 6mA modification is extensively present in human genome, accounting for ~0.051% of the total adenines. [G/C]AGG[C/T] was the most significant motif associated with 6mA modification. 6mA sites are enriched in the exon coding regions and are associated with transcriptional activation. DNA N6-methyladenine and N6-demethyladenine modification in human are mediated by methyltransferase N6AMT1 and demethylase ALKBH1, respectively. The 6mA abundance is significantly lower in cancer tissues compared to adjacent normal tissues, which is accompanied with decreased N6AMT1 and increased ALKBH1 levels. Decrease of 6mA modification level stimulated tumorigenesis in human. Collectively, our results demonstrate that 6mA DNA modification is present in human tissues, and we describe a potential role of the N6AMT1/ALKBH1-6mA regulatory axis in the progression of human cancer.