Expression of osteoprotegerin and receptor activator of nuclear factor-kappaB ligand (RANKL) in HCC70 breast cancer cells and effects of treatment with gonadotropin-releasing hormone on RANKL expression.

BACKGROUND: The majority of human breast cancers and in addition most breast-cancer cell lines express gonadotropin-releasing hormone (GnRH) receptors. Their proliferation and in addition their bone-directed invasion is time- and dose-dependently reduced by GnRH. Osteolytic metastases are characteristic for breast cancer-derived metastasis. Since the osteolytic activity depends on the receptor activator of nuclear factor-kappaB (NFkappaB) ligand (RANKL)/osteoprotegerin (OPG) ratio, we analyzed RANKL and OPG expression in different breast-cancer cell lines.

METHODS: Different human breast-cancer cell lines were tested for expression of GnRH receptor, OPG and RANKL. Using a co-culture system of breast-cancer cell lines and human primary osteoblasts (hOB), we analyzed the expression of OPG and RANKL in the GnRH receptor-positive breast-cancer cell line HCC70 co-cultured with or without hOB. In addition, we assessed the effects of GnRH analog treatment on OPG and RANKL mRNA and protein levels.

RESULTS: All tested breast-cancer cell lines were GnRH receptor-positive. The majority of these cell lines expressed OPG but not RANKL. The HCC70 breast-cancer cell line derived from an invasive ductal carcinoma with metastases was positive for both OPG and RANKL. The expression of RANKL by HCC70 cells was increased when co-cultured with hOB. Treatment with GnRH analogs reduced the expression of RANKL by HCC70 cells co-cultured with hOB. No effects were observed on breast cancer OPG expression.

CONCLUSIONS: These data show that the majority of human breast-cancer cell lines express OPG but not RANKL. The HCC70 breast-cancer cell line is RANKL-positive. Co-culture of HCC70 breast cancer cells with hOB increases RANKL expression. Activation of tumor GnRH receptors reduces RANKL expression. These experiments demonstrate that HCC70 breast cancer cells are able to activate osteoclasts directly via RANKL. The interaction between HCC70 breast cancer cells and osteoblasts induces osteoclastogenesis through an increase of RANKL expression. GnRH seems to play an important role by modulating the RANKL expression in HCC70 breast cancer cells.