Semaphorin 3A (Sema3A), a secreted member of the Semaphorin family, plays a role in tumour cell migration and osteoblast function. Here, we describe a previously unknown role of exogenous and tumour-derived Sema3A in the regulation of cancer cell induced osteoclastogenesis. First, we confirmed that exogenous Sema3A (100 ng/ml) reduced directed (40%, p<0.05) migration of the parental non-bony human breast cancer cells MDA-MB-231 (MDA-231-P), whereas stable knockdown by short hairpin RNAs significantly reversed these effects (66% increase in directed migration, p < 0.001). Next, we went on to demonstrate that exposure of primary bone tumour (Te85 and Saos-2 osteosarcoma cells) and highly metastatic and bone tropic breast cancer (MDA-231-BT) cell lines to exogenous Sema3A (300ng/ml) significantly inhibited the ability of these cells to enhance osteoclast formation in mouse bone marrow cell cultures (Te85, 51% reduction; Saos-2, 48% reduction; MDA-231-BT, 56% reduction; p<0.01). Sema3A (300 ng/ml) was also effective in inhibiting RANKL induced osteoclast formation (38% reduction, p<0.001), indicating direct and indirect inhibitory effects on osteoclastogenesis. Bone-tropic MDA-231-BT cells expressed significant level of pro-Sema3A, and stable knockdown of pro-Sema3A expression in these cells (40% reduction of protein level, p<0.01) enhanced the ability of these cells to stimulate osteoclast formation (70% increase, p<0.05). This result implicates tumour-derived Sema-3A in the regulation of tumour bone cell paracrine crosstalk. In conclusion, these studies suggest that both exogenous and tumour-derived Sema3A inhibit the ability of primary bone and metastatic cancer cells to enhance osteoclastogenesis in bone metastatic microenvironment. When combined with previous published work, these findings suggest that Sema3A, or novel peptides that mimics its action, may be of value in the treatment of osteolytic bone disease. In vivo studies to test the effects of Sema3A on mouse models of osteolysis are currently in progress.
Disclosure: The authors declared no competing interests.