Feed-forward loops (FFLs) have been shown to be one of the most common and important classes of transcriptional network motifs that involved in various diseases such cancer. It enclosed in a three-node pattern, which is composed of an input element regulating another element and a jointly regulated target gene.

Enhancers are cis-regulatory elements that positively regulate protein-coding gene or microRNA by recruiting DNA-binding transcription factors (TFs).

EnhFFL is an online database to provide a data resource to browse and search typical enhancer and super-enhancer FFLs. It covers three types of FFLs, namely TF-enhancer-miRNA FFLs, enhancer-miRNA-gene FFLs, TF-enhancer-gene FFLs in 91 tissues/cell lines (in human and mouse). Additionally, TF-enhancer feed-back loops (FBLs) are also included.

At present, the database contains 16 cancer cell lines and 75 normal tissues/cell lines of human and mouse. In this study, a total number of 376,803 enhancers (332,723 typical enhancers and 44,080 super enhancers), 358 miRNAs, 164 TFs as well as 14,774 genes are included for human. And, for mouse, there are 44,676 enhancers (42,563 typical enhancers and 2,113 super enhancer), 161 miRNAs, 255 TFs and 19,183 genes. As for the four types of loops, EnhFFL contains 46,280/7,000 TF-enhancer-miRNA FFLs, 9,997/236 enhancer-miRNA-gene FFLs, 3,561,164/3,193,182 TF-enhancer-gene FFLs and 1,259/235 TF-enhancer FBLs identified for human and mouse, respectively.