Abstract

Bone-resorbing osteoclast activation facilitates breast and prostate carcinoma bone metastasis. We have identified peroxiredoxin-4 (PRDX4) as a mediator of osteoclast genesis that is released by cancer cells through proteomics methods. Using immunoblotting and mass spectrometry, we now report the characterization of L-plastin in MDA-MB-231 human breast cancer cells’ conditioned media (CM). With L-plastin silenced by siRNA, the osteoclastogenic potential of MDA-MB-231 CM was significantly diminished. L-plastin was found in cancer-derived exosomes, and MDA-MB- 231 CM’s osteoclastogenic capacity was significantly diminished when exosomal release was inhibited. Recombinant L-plastin induced calcium/NFATc1-mediated osteoclastogenesis to levels comparable to continuous RANKL treatment when added to osteoclast precursors primed with RANKL for two days. We used ssRNA to generate MDA-MB-231 cells devoid of PRDX4, L-plastin, or both, and injected these cell populations into CD-1 immunodeficient mice via the tibia. When MDA-MB-231 cells lacking both L-plastin and PRDX4 were injected, micro-CT and histomorphometric analysis revealed a complete loss of osteolysis. Multiple human cancers, including breast and prostate carcinomas, showed an increase in L-plastin and PRDX4 mRNA expression, according to a meta-analysis. This study demonstrates that human breast cancer cells activate osteoclasts through the secretion of L-plastin and PRDX4.