Histone Methyltransferase EHMT2 Promotes the Progression of Breast Ductal Carcinoma by Regulating the Hippo Pathway

Invasive ductal carcinoma (IDC) is a major type of breast cancer. The utilization of inhibitors targeting histone methyltransferases introduces novel therapeutic avenues for the treatment of cancer. Immunohistochemistry, Western blot, and reverse transcription quantitative polymerase chain reaction experiments were applied to assess the levels of EHMT2 in IDC and adjacent tissues. HCC70 cells were treated with EHMT2 inhibitors (UNC0646 and BIX-01294), and assessed using Cell Counting Kit-8 (CCK-8), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, and transwell assays to evaluate cell viability, apoptosis, and migratory capacity, respectively. The reactive oxygen species (ROS) levels were assessed using the 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescent probe. The expressions of Hippo pathway were analyzed via Western blot assay. Immunofluorescence staining was employed to detect the subcellular localization changes in YAP expression. A xenograft tumor model of HCC70 cells was applied to validate the tumor-suppressive influences of EHMT2 inhibitors in vivo. We observed significant upregulation of EHMT2 in both IDC clinical samples and IDC cell lines, with high EHMT2 expression correlating with poor prognosis. After treatment with EHMT2 inhibitors UNC0646 or BIX-01294, HCC70 cells exhibited inhibition of proliferation and migratory capacity, alongside an increase in apoptosis rate and ROS production levels. UNC064 or BIX-01294 promoted the phosphorylation levels of MST1, LATS1, MOB1A, and YAP, indicating the activation of the Hippo pathway by EHMT2 inhibitors. Moreover, UNC0646 and BIX-01294 enhanced the cytoplasmic expression of YAP while inhibiting its nuclear localization, preventing its nuclear activation. EHMT2 was upregulated in IDC, and EHMT2 inhibitors suppressed IDC progression by modulating the Hippo signaling pathway.