Stimulation of Cyclooxygenase-2 Expression by Bone-Derived Transforming Growth Factor-β Enhances Bone Metastases in Breast Cancer

Abstract

Cyclooxygenase-2 (COX-2), the rate-limiting enzyme of prostaglandin synthesis, has been implicated in invasiveness and distant metastases of cancer. Bone is one of the most common target sites of cancer metastasis. However, the role of COX-2 in bone metastasis is unclear. We examined the surgical specimens of bone metastases from patients with various types of cancers by using immunohistochemistry and observed evident COX-2 expression in these bone metastases. In a nude mouse model of bone metastasis, the MDA-MB-231 human breast cancer cells showed no COX-2 expression at orthotopic sites, whereas these cells, when metastasized to bone, intensely expressed COX-2, suggesting that the bone microenvironment induced COX-2 expression. Consistent with this notion, inhibition of bone resorption by the bisphosphonate ibandronate reduced COX-2 expression in MDA-MB-231 cells in bone. Transforming growth factor-B (TGFB), one of the most abundant growth factors stored in bone, increased COX-2 expression and prostaglandin E 2 production in MDA-MB-231 cells in culture. MDA-MB-231 cells overexpressing dominantnegative TGFB type II receptors showed decreased bone metastases and reduced osteoclastic bone resorption with impaired COX-2 expression. The COX-2 inhibitors, NS-398 and nimesulide, significantly suppressed bone metastases with decreased osteoclast number and increased apoptosis in MDA-MB-231 cells. These results suggest that bone-derived TGFB up-regulates COX-2 expression in breast cancer cells, thereby increasing prostaglandin E 2 production, which in turn, stimulates osteoclastic bone destruction, leading to the progression of bone metastases. Our results also suggest that COX-2 is a potential therapeutic target for bone metastases in breast cancer. (Cancer Res 2006; 66(4): 2067-73)

Nuclear co-localization and functional interaction of COX-2 and HIF-1α characterize bone metastasis of human breast carcinoma

“…The 1833 cells (8 x 10 4 ) on coverslips were exposed to (i) 24-h hypoxia [15], in the presence or the absence of 1 M NS398 (COX-2 inhibitor) (4-h inhibitor pre-treatment and 20-h hypoxia plus the inhibitor) [16]; (ii) 100 g/ml cycloheximide for 2 or 4 h after 12-hypoxia exposure [27]; (iii) 10 M clasto-lactacystin--lactone (LLnL) 4 h before HGF-treatment (24 h) [15]. The antibodies used were: anti-COX-2 (1:30) and anti-HIF-1α (1:50).…”

“…The expression vector (200 ng) for HIF-1α or HIF-1β (L. Poellinger, Karolinska Institute, Stockholm, Sweden) was co-transfected with the genereporters. After overnight starvation (0.1% fetal bovine serum, FBS), 24-h treatment with 200 ng/ml HGF [2] or 5 ng/ml TGF-1 [16], also under hypoxia, was performed. Cells exposed to hypoxia alone were not starved.…”

“…In addition, HIF-1α seems to be a promising target for controlling organotropic metastatization of breast cancer [30], and inhibitors of HIF-1α and TGF-β may improve treatment of bone metastases obtained with MDA-MB231 cells increasing patient survival [6,16,31]. TGF-β and HGF regulate COX-2 expression in breast and colon carcinoma cells, respectively, and hypoxia potentiates HGFdependent PGE 2 release in colorectal cancer [16,32]. PGE 2 participates in nuclear translocation of exogenously expressed HIF-1α in prostate carcinoma cells [33].…”

“…PGE 2 participates in nuclear translocation of exogenously expressed HIF-1α in prostate carcinoma cells [33]. COX-2 inhibition largely prevents MDA-MB231 bone metastasis by decreasing osteoclast number and increasing apoptosis [16].…”

“…In animal models obtained with mouse (TM40D-MB or 4T1.2) and human (MDA-MB231) cells, COX-2/PGE2 system participates in osteolysis [6,[16][17][18] but the distinct functions contributing to breast-carcinoma metastasis remain largely unknown. HGF/Met couple is important for the cross-talk between metastasis and microenvironment [2], and its activation by hypoxia might be hypothesized based on data from normal and neoplastic cell types [19,20].…”