Metastatic breast cancer cells overexpress and secrete miR-218 to regulate type I collagen deposition by osteoblasts

• Published in: Breast cancer research : BCR Vol. 20; no. 1; p. 127
• Main Authors: Liu, Xuxiang, Cao, Minghui, Palomares, Melanie, Wu, Xiwei, Li, Arthur, Yan, Wei, Fong, Miranda Y, Chan, Wing-Chung, Wang, Shizhen Emily
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 22-10-2018; BioMed Central; BMC
• Subjects: Adult; Animals; Bone cancer; Bone growth; Bone Marrow Cells; Bone matrix; Bone metastasis; Bone Neoplasms - blood; Bone Neoplasms - genetics; Bone Neoplasms - secondary; Bone remodeling; Bone resorption; Bone turnover; Bones; Breast cancer; Breast Neoplasms - blood; Breast Neoplasms - genetics; Breast Neoplasms - pathology; Cancer cells; Care and treatment; Cell adhesion & migration; Cell cycle; Cell Differentiation - genetics; Cell Line, Tumor; Circulating MicroRNA - metabolism; Cloning; Collagen; Collagen (type I); Collagen Type I - metabolism; Complications and side effects; Cytokines; Down-Regulation; Female; Fibroblasts; Gene expression; Genetic aspects; Health aspects; Homeostasis; Humans; Inhibin; Inhibin-beta Subunits - metabolism; Kinases; Ligands; Lysates; Metastases; Metastasis; Mice; Mice, Inbred C57BL; MicroRNAs; MicroRNAs - metabolism; Middle Aged; miRNA; Osteoblastogenesis; Osteoblasts; Osteoblasts - metabolism; Osteoclasts - physiology; Osteogenesis; Osteogenesis - genetics; Osteolysis; Primary Cell Culture; Procollagen; Proteins; RNA sequencing; Secretion; Stem cells; Tissue inhibitor of metalloproteinase 3; Type I collagen; Ultracentrifugation; Vesicles; miRNA; Bone metastasis; Breast cancer; Cytokines; Type I collagen; Osteoblasts
• ISSN: 1465-542X; 1465-5411; 1465-542X
• DOI: 10.1186/s13058-018-1059-y

Bone is one of the most frequent metastatic sites of advanced breast cancer. Current therapeutic agents aim to inhibit osteoclast-mediated bone resorption but only have palliative effects. During normal bone remodeling, the balance between bone resorption and osteoblast-mediated bone formation is essential for bone homeostasis. One major function of osteoblast during bone formation is to secrete type I procollagen, which will then be processed before being crosslinked and deposited into the bone matrix.
Small RNA sequencing and quantitative real-time PCR were used to detect miRNA levels in patient blood samples and in the cell lysates as well as extracellular vesicles of parental and bone-tropic MDA-MB-231 breast cancer cells. The effects of cancer cell-derived extracellular vesicles isolated by ultracentrifugation and carrying varying levels of miR-218 were examined in osteoblasts by quantitative real-time PCR, Western blot analysis, and P1NP bone formation marker analysis. Cancer cells overexpressing miR-218 were examined by transcriptome profiling through RNA sequencing to identify intrinsic genes and pathways influenced by miR-218.
We show that circulating miR-218 is associated with breast cancer bone metastasis. Cancer-secreted miR-218 directly downregulates type I collagen in osteoblasts, whereas intracellular miR-218 in breast cancer cells regulates the expression of inhibin β subunits. Increased cancer secretion of inhibin βA results in elevated Timp3 expression in osteoblasts and the subsequent repression of procollagen processing during osteoblast differentiation.
Here we identify a twofold function of cancer-derived miR-218, whose levels in the blood are associated with breast cancer metastasis to the bone, in the regulation of type I collagen deposition by osteoblasts. The adaptation of the bone niche mediated by miR-218 might further tilt the balance towards osteolysis, thereby facilitating other mechanisms to promote bone metastasis.