A computational approach on studying the regulation of TGF-β1-stimulated Runx2 expression by MicroRNAs in human breast cancer cells

BACKGROUND

Transforming growth factor-beta1 (TGF-β1) acts as a most effective growth inhibitor for normal epithelial cells. Loss of this anti-proliferative factor in breast tissues favors invasion and development of osteolytic metastases, aided by a master transcription factor, runt-related transcription factor 2 (Runx2). Several reports identified Runx2 regulation with the help of non-coding RNAs such as microRNAs (miRNAs) under physiological and pathological conditions.

METHODS

Using bioinformatics tools such as miRDB, STarMir, Venny, TarBase, a unique list of miRNAs that putatively target the 3' UTR Runx2 was identified. Further, the expression patterns of those miRNAs at the precursor and mature levels were studied by RT-qPCR analyses. Following this, computational analyses using software like TransmiR and bc-GenExMiner v4.6 were done to speculate the miRNA's other target genes that indirectly regulate Runx2 activity in breast cancer.

RESULTS

There were 13 miRNAs that putatively target Runx2 identified using bioinformatics tools. Among these miRNAs, miR-5703 expression was significantly downregulated at both precursor and mature levels upon TGF-β1-treatment in human breast cancer cells. Computational analyses speculated an indirect targeting of Runx2 by miR-5703 by influencing multiple Runx2 regulatory signaling pathways including Jak/Stat, MAPK, Wnt/β-Catenin, Notch, BMP, and PKA pathways. Furthermore, a correlation of the expression profiles of the speculated genes and Runx2 with miR-5703 was depicted in triple-negative breast cancer patients.

CONCLUSION

Identification of miR-5703 and its network for Runx2 regulation directly or indirectly in breast cancer cells could significantly advance our understanding of breast cancer-mediated bone metastasis. In addition, it would potentially pave the way for miRNAs to be used as biomarkers and therapeutic agents in cancer research.

Inhibitory effects of low intensity pulsed ultrasound on osteoclastogenesis induced in vitro by breast cancer cells

Background

Bone tissue is one of the main sites for breast metastasis; patients diagnosed with advanced breast cancer mostly develop bone metastasis characterized by severe osteolytic lesions, which heavily influence their life quality. Low Intensity Pulsed Ultrasound (LIPUS) is a form of mechanical energy able to modulate various molecular pathways both in cancer and in health cells.

The purpose of the present study was to evaluate for the first time, the ability of LIPUS to modulate osteolytic capability of breast cancer cells.

Methods

Two different approaches were employed: a) Indirect method -conditioned medium obtained by MDA-MB-231 cell line treated or untreated with LIPUS was used to induce osteoclast differentiation of murine macrophage Raw264.7 cell line; and b) Direct method -MDA-MB-231 were co-cultured with Raw264.7 cells and treated or untreated with LIPUS.

Results

LIPUS treatment impaired MDA-MB-231 cell dependentosteoclast differentiation and produced a reduction of osteoclast markers such as Cathepsin K, Matrix Metalloproteinase 9 and Tartrate Resistant Acid Phosphatase, suggesting its role as an effective and safe adjuvant in bone metastasis management.

Conclusion

LIPUS treatment could be a good and safety therapeutic adjuvant in osteolyitic bone metastasis not only for the induction properties of bone regeneration, but also for the reduction of osteolysis.

NDRG2 Expression Decreases Tumor-Induced Osteoclast Differentiation by Down-regulating ICAM1 in Breast Cancer Cells

Bone matrix is properly maintained by osteoclasts and osteoblasts. In the tumor microenvironment, osteoclasts are increasingly differentiated by the various ligands and cytokines secreted from the metastasized cancer cells at the bone metastasis niche. The activated osteoclasts generate osteolytic lesions. For this reason, studies focusing on the differentiation of osteoclasts are important to reduce bone destruction by tumor metastasis. The N-myc downstream-regulated gene 2 (NDRG2) has been known to contribute to the suppression of tumor growth and metastasis, but the precise role of NDRG2 in osteoclast differentiation induced by cancer cells has not been elucidated. In this study, we demonstrate that NDRG2 expression in breast cancer cells has an inhibitory effect on osteoclast differentiation. RAW 264.7 cells, which are monocytic preosteoclast cells, treated with the conditioned media (CM) of murine breast cancer cells (4T1) expressing NDRG2 are less differentiated into the multinucleated osteoclast-like cells than those treated with the CM of 4T1-WT or 4T1-mock cells. Interestingly, 4T1 cells stably expressing NDRG2 showed a decreased mRNA and protein level of intercellular adhesion molecule 1 (ICAM1), which is known to enhance osteoclast maturation. Osteoclast differentiation was also reduced by ICAM1 knockdown in 4T1 cells. In addition, blocking the interaction between soluble ICAM1 and ICAM1 receptors significantly decreased osteoclastogenesis of RAW 264.7 cells in the tumor environment. Collectively, these results suggest that the reduction of ICAM1 expression by NDRG2 in breast cancer cells decreases osteoclast differentiation, and demonstrate that excessive bone resorption could be inhibited via ICAM1 down-regulation by NDRG2 expression.