Role of Irisin/FNDC5 (rs3480) Single Nucleotide Polymorphism in Breast Cancer

Breast cancer is the most frequent cancer in women worldwide. Its incidence is increasing but mortality has decreased in a considerable way due to the combined effect of early detection and improvement in treatment .

Irisin is encoded by the FNDC5 gene, whose expression is controlled by the peroxi- some proliferator activated receptor gamma coactivator 1 alpha (PGC-1α). PGC-1α is a transcriptional co-activator which does not bind directly to DNA. Studies indicated that the estrogen-related receptor alpha (ERRα) could be a factor that plays a role in PGC-1α binding to DNA. ERRα is encoded by the ESRRA gene and is an orphan nuclear receptor, which has two domains. One of them allows the interaction with DNA, and the second one with a ligand. The ERRα structure is similar to that of the estrogen receptor alpha (ERα), but this receptor does not bind to natural estrogens. ERRα interacts with a canonical sequence of the estrogen response elements (ERRE). ERRα and ERα could compete with each other to bind to similar DNA elements. Together, ERRα binds to DNA, in complex with PGC-1α, to regulate the activity of genes such as FNDC5 .

CA15-3, a high molecular weight glycoprotein (300-450 kDa), is produced by the epithelial ducts and acinic breast cells and is then secreted in milk normally. It has been widely used for the prediction of bone metastases in patients with breast cancer .