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The Polycomb group protein enhancer of zeste homolog 2 (EZH2), which has roles during development of numerous tissues, is a critical regulator of cell type identity. Overexpression of EZH2 has been detected in invasive breast carcinoma tissue samples and is observed in human breast tissue samples of morphologically normal lobules up to 12 years before the development of breast cancer. The function of EZH2 during preneoplastic progression in the mammary gland is unknown. To investigate the role of EZH2 in the mammary gland, we targeted the expression of EZH2 to mammary epithelial cells using the mouse mammary tumor virus long terminal repeat. EZH2 overexpression resulted in aberrant terminal end bud architecture. By the age of 4 months, 100% of female mouse mammary tumor virus-EZH2 virgin mice developed intraductal epithelial hyperplasia resembling the human counterpart accompanied by premature differentiation of ductal epithelial cells and up-regulation of the luminal marker GATA-3. In addition, remodeling of the mammary gland after parturition was impaired and EZH2 overexpression caused delayed involution. Mechanistically, we found that EZH2 physically interacts with beta-catenin, inducing beta-catenin nuclear accumulation in mammary epithelial cells and activating Wnt/beta-catenin signaling. The biological significance of these data to human hyperplasias is demonstrated by EZH2 up-regulation and colocalization with beta-catenin in human intraductal epithelial hyperplasia, the earliest histologically identifiable precursor of breast carcinoma.

We have tested the hypothesis that tumor necrosis factor (TNF), by binding to and activating granulocytes, may contribute to the pathogenesis of gram-negative sepsis and the adult respiratory distress syndrome (ARDS). Buffy coat granulocytes incubated with as little as 0.5 ng/mL of recombinant TNF (rTNF) showed a dose-related increase in nitroblue tetrazolium dye reduction, in granulocyte polarization, in superoxide anion release, and in visually apparent aggregation. Purified lipopolysaccharide (1 microgram/mL) caused polymorphonuclear (PMN) aggregation and activation that was neutralized by polymyxin B. The release of superoxide was augmented by preincubation of the PMNs with gamma-interferon. The effect of TNF was neutralized by TNF-specific murine monoclonal antibodies but not by polymyxin B. Scatchard analysis of 125I-rTNF binding to granulocytes revealed about 1,200 receptors per cell with a Kd of 4.9 X 10(-10) mol/L. These results suggest that the release of TNF by mononuclear phagocytes contributes to granulocyte activation and aggregation during inflammation.