| Breast cancer, the leading cause of death among women with an onset frequency of one in eight, is the most common type of cancer among women. However, despite the advancement in therapy, the mortality rate in breast cancer patients still remains high. The proactive, complex and dynamic tumor microenvironment of breast cancer adds to the grim scenario of the disease by accumulating inflammatory and angiogenic growth factors and creating a niche for the growth and metastasis of breast cancer cells. Osteoprotegerin (OPG), a soluble decoy receptor for tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL), and belongs to the tumor necrosis factor receptor superfamily (TNFRSF), was initially found to contribute to homeostasis of bone turnover due to its capability of binding to receptor activator of nuclear factor kappa beta (RANKL). However, apart from bone turnover, OPG is associated with several organ pathologies, multiple myeloma and cancers of bladder, stomach, prostate, and breast.;In the first half of the study we show that SUM149PT and SUM1315MO2 cells secrete high levels of the cytokine OPG compared to primary human mammary epithelial cells (HMEC). High expression of OPG was also detected in human breast cancer tissue samples compared to the uninvolved tissue from the same patient. OPG induced proliferation of control HMEC spheres and triggered the onset of aneuploidy in HMEC sphere cultures. OPG induced the expression of aneuploidy related kinases Aurora-A Kinase (AURKA or IAK-1), Bub1 and BubR1 probably through the receptor activator of nuclear factor kappa-B ligand (RANKL) and syndecan-1 receptors via the Erk, AKT and GSK3beta signaling pathway. OPG induced gene copy numbers for oncogenic pathway regulators such as AKT1, Aurora-A Kinase (AURKA or IAK-1), epidermal growth factor receptor (EGFR) and MYC but reduced the copy numbers of cyclin dependent kinase inhibitor 2A (CDKN2A), PTEN and DNA topoisomerase 2 alpha (TOP2A).;The second part of the study highlights OPG's interaction with fatty acid synthase (FASN), which is a key enzyme of the fatty acid biosynthetic pathway in breast cancer cells. We reasoned that there might be crosstalk between OPG, FASN, and COX-2 that sustains the inflammatory pathways in breast cancer. Interestingly, knocking down OPG by CRISPR/Cas9 gene editing in the breast cancer cells decreased FASN expression at protein level. Here, we identified cis-acting elements involved in the transcriptional regulation of COX-2 and FASN by recombinant human OPG (rhOPG). Treatment with FASN inhibitor C75 and COX-2 inhibitor celecoxib individually decreased the number of lipid body/cell, downregulated phosphorylation of ERK, GSK3beta, and induced apoptosis by caspase-3/7 and caspapse-9 activation. But a more efficient and effective decrease in lipid body/cell and survival kinase signaling was observed combining the drug treatment for the aggressive cancer cells.;Overall our studies highlight the role of OPG in reprogramming normal mammary epithelial cells to a tumorigenic state and suggest promising avenues for treating inflammatory breast cancer as well as highly invasive breast cancer with new therapeutic targets. Our results also established a novel biological crosstalk between OPG, FASN, and COX-2 advocating for combinatorial drug treatment to block these players of carcinogenesis as a promising therapeutic to target highly invasive and inflammatory breast cancer. (Abstract shortened by ProQuest.). |
