Search

This study examines the role of LEF1, a component of the Wnt signaling pathway, in human breast and murine mammary carcinoma and its relationship to ErbB2 (her-2/neu) expression. Mammary tissue and tumors from 5 different Wnt pathway-activated transgenic mouse strains and 5 different ErbB2 pathway-activated transgenic mouse strains were studied for the amount and distribution of expression of beta-catenin and LEF1. Fourteen samples of human infiltrating ductal breast cancer arising from a background of ductal carcinoma in situ (DCIS) were analyzed for LEF1, estrogen and progesterone receptor (ER and PR) and her-2/neu expression. in vitro, the effect of estradiol on LEF1 protein expression was examined in several breast cancer cell lines. The functional role of LEF1 was analyzed by a Matrigel invasion assay following transfection of breast cancer cell lines with either an LEF1 expression construct or a dominant-negative LEF1 construct. A significant (p=0.023) negative correlation between the expression of LEF1 and her-2/neu was observed in human breast cancer. LEF1 was strongly expressed, and beta-catenin had nuclear localization, in mammary tumors derived from Wnt pathway transgenic mice but not in ErbB2 pathway transgenic mice. In estrogen-receptor-positive breast cancer cell lines, LEF1 protein expression increased significantly following estradiol incubation (>200% of baseline). Following transient transfection, overexpression of LEF1 promoted and dominant-negative LEF1 inhibited tumor cell invasion. LEF1, a downstream component of the Wnt signaling pathway, defines a distinct, her-2/neu negative (non-overexpressing) subset of breast/mammary cancers in both humans and mice, mediates breast cancer cell invasion, and may be regulated in part by estradiol.

The Wnt genes encode a family of related, secreted proteins which initiate a signal cascade upon binding to cell surface receptor molecules. The signaling pathway has been shown to be critical for normal growth and development in model organisms and is implicated in the genesis of numerous human cancers. Wnt proteins regulate mammary development in the mouse but their precise role in normal breast development and malignant transformation in humans remains poorly defined. In this study, we have examined the expression of several Wnt ligands by in sing anti-sense RNA hybridization in normal and malignant human breast tissue, as well as in several estrogen-responsive and estrogen-independent human breast cancer cell lines. The specific Wnt genes tested included Wntl, Wnt2, Wnt4, Wnt5a, Wnt5b, Wnt6, Wnt7b and Wnt10b. We have also studied the expression of frizzled receptors 1 and 2 by immunohistochemistry in these tissues. Our results indicate that several of the Wnt ligands, especially Wnt1 and Wnt6, are strongly expressed in both normal and malignant breast tissue and that Wnt7b is down-regulated in breast cancer, compared to normal breast epithelium. The expression of frizzled 1 and 2 receptors was found to be up-regulated in breast cancer. These studies provide additional support to the hypothesis that the Wnt signaling pathway is involved in human breast cancer.