KDM4B and breast cancer: It has been shown that the histone demethylase KDM4B, a novel regulator of LINE-1, activates the reverse transcriptional activity of LINE-1 by catalyzing the demethylation reaction of the repressive histone H3K9me3 leading to DNA damage, and exhibits increased LINE-1 expression and copy number in breast cancers expressing high levels of KDM4B (86).