Histone methyltransferases and demethylases reversibly modulate histone lysine methylation, which is considered a key epigenetic mark associated with gene regulation. Recently, aberrant regulation of gene expression by histone methylation modifiers has emerged as an important mechanism for tumorigenesis. However, it remains largely unknown how histone methyltransferases and demethylases coregulate transcriptional profiles for cancer cell characteristics. Here, we show that in breast cancer cells, the histone H3 lysine 27 (H3K27) demethylase UTX (also known as KDM6A) positively regulates gene expression programs associated with cell proliferation and invasion. The majority of UTX-controlled genes, including a cohort of oncogenes and prometastatic genes, are coregulated by the H3K4 methyltransferase mixed lineage leukemia 4 (MLL4, also called ALR, KMT2D, and MLL2). UTX interacted with a C-terminal region of MLL4. UTX knockdown resulted in significant decreases in the proliferation and invasiveness of breast cancer cells in vitro and in a mouse xenograft model. Such defective cellular characteristics of UTX-depleted cells were phenocopied by MLL4 knockdown cells. UTX-catalyzed demethylation of trimethylated H3K27 and MLL4-mediated trimethylation at H3K4 occurred interdependently at cotarget genes of UTX and MLL4. Clinically, high levels of UTX or MLL4 were associated with poor prognosis in patients with breast cancer. Taken together, these findings uncover that coordinated regulation of gene expression programs by a histone methyltransferase and a histone demethylase is coupled to the proliferation and invasion of breast cancer cells. Cancer Res; 74(6); 1705–17. ©2014 AACR.