New roles of osteocytes in proliferation, migration and invasion of breast and prostate cancer cells

BACKGROUND: Most cases of prostate and breast cancer metastasis occur to the bone, and are responsible for the majority of cancer-related deaths. Osteocytes constitute over 90% of adult bone cells. They orchestrate bone remodelling through determining osteoclast activity and affecting osteoblasts. The osteocyte lacuno-canalicular network is also intimately associated with the blood vessel network in the bone matrix. However, the roles of osteocytes in cancer cell invasion and metastasis remain unknown. MATERIALS AND METHODS: In this study, we investigated the effects of early osteocytes on the behaviour of breast and prostate cancer cells. The proliferation of cultured cells was assessed using the AlamarBlue assay. The electric cell-substrate impedance sensing (ECIS) system was used to measure spreading, attachment and migratory behaviour of cancer cells in response to conditioned medium (CM) from mouse osteocytes. Other cell assays, including in vitro wound healing and transwell migration/invasion assays, were also applied to evaluate the effect of osteocytes on cancer cells. RESULTS: We found that CM from osteocytes from both monolayer and three-dimensional (3D) cultures, stimulated proliferation of DU145 and PC3 prostate cancer cells but not LNCaP cells compared to control medium. Osteocyte CM also stimulated proliferation of MDA-MB-231 and MCF-7 breast cancer cells. However, osteocyte CM promoted the migration and adhesion of PC3 and DU145 in prostate cancer cells but had the reverse effect on PZHPV7, a normal prostate epithelial cell line. In the breast cancer cells studied, osteocyte CM inhibited post-wound migration of MCF-7 and ZR-75.1 cells but not MDA-MB-231 cells. Moreover, osteocyte CM stimulated transwell chemotactic migration of MDA-MB-231 cells but not of MCF-7 and ZR-75.1 cells. CONCLUSION: Osteocytes play diverse roles in the proliferative and migratory potential of breast and prostate cancer cells that may be associated with cancer-specific bone metastasis and requires further investigation