City of Hope Irell & Manella Graduate School of Biological Sciences, Duarte, CA, 91010, USA.
Department of Pathology, University of California San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0612, USA.
Breast Cancer Res. 2018 Oct 22;20(1):127. 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.
骨是晚期乳腺癌最常见的转移部位之一。目前的治疗药物旨在抑制破骨细胞介导的骨质吸收，但仅具有姑息作用。在正常骨重塑过程中，骨吸收和成骨细胞介导的骨形成之间的平衡对于骨稳态至关重要。成骨细胞在骨形成过程中的主要功能之一是分泌 I 型前胶原，然后在前胶原交联和沉积到骨基质之前进行处理。
使用小 RNA 测序和定量实时 PCR 检测患者血液样本以及亲本和骨趋向性 MDA-MB-231 乳腺癌细胞的细胞裂解物和细胞外囊泡中的 miRNA 水平。通过定量实时 PCR、Western blot 分析和 P1NP 骨形成标志物分析，检测通过超速离心分离并携带不同水平 miR-218 的癌细胞衍生的细胞外囊泡对成骨细胞的影响。通过 RNA 测序进行转录组谱分析，检测过表达 miR-218 的癌细胞，以鉴定受 miR-218 影响的内在基因和途径。
我们表明，循环 miR-218 与乳腺癌骨转移有关。癌细胞分泌的 miR-218 直接下调成骨细胞中的 I 型胶原，而乳腺癌细胞中的细胞内 miR-218 调节抑制素β亚基的表达。癌细胞分泌的抑制素β A 增加导致成骨细胞中 Timp3 表达升高，随后抑制成骨细胞分化过程中前胶原的加工。
在这里，我们确定了源自癌症的 miR-218 的双重功能，其在血液中的水平与乳腺癌转移到骨骼有关，调节成骨细胞中 I 型胶原的沉积。由 miR-218 介导的骨基质的适应性可能进一步使平衡向溶骨倾斜，从而促进其他促进骨转移的机制。
