OXPHOS-dependent metabolic reprogramming prompts metastatic potential of breast cancer cells under osteogenic differentiation

Background Microcalcification is one of the most reliable clinical features of the malignancy risk of breast cancer, and it is associated with enhanced tumour aggressiveness and poor prognosis. However, its underlying molecular mechanism remains unclear. Methods Clinical data were retrieved to analyse the association between calcification and bone metastasis in patients with breast cancer. Using multiple human breast cancer cell lines, the osteogenic cocktail model was established in vitro to demonstrate calcification-exacerbated metastasis. Migration and invasion characteristics were determined by wound healing and transwell migration. mRNA and protein expression were identified by quantitative PCR and western blotting. Metabolic alterations in breast cancer cells were evaluated using Seahorse Analyser. Results The osteogenic differentiation of human breast cancer cells activated the classical TGF-β/Smad signalling pathway and the non-canonical MAPK pathway, which, in turn, exacerbated the progression of epithelial–mesenchymal transition (EMT). The metabolic programme switched to enhancing mitochondrial oxidative phosphorylation (OXPHOS) upon osteogenic differentiation. Rotenone was used to inhibit the OXPHOS complex during osteogenesis to block mitochondrial function, consequently reversing the EMT phenotype. Conclusions This study provides important insights into the mechanisms involved in breast cancer bone metastasis, and outlines a possible strategy to intervene in OXPHOS for the treatment of breast tumours. This manuscript provides a simplified overview of the involvement of mitochondrial activity and OXPHOS in the metastasis of breast cancer with calcification. We propose that massive accumulation of calcified granules due to breast cancer necrosis or deposition of spontaneous secretions around the glands lead to reprogramming of tumour metabolism, particularly enhancement of mitochondrial metabolism. Upregulation of the OXPHOS complex and subsequent activation of TGFβ-SMAD and MAPK (e.g., JNK, ERK, P38) signalling pathways facilitate the EMT process of breast cancer cells. Interestingly, the OXPHOS inhibitor rotenone could block the EMT process due to cell calcification.