Fibronectin type III domain-containing protein 5, the precursor of irisin, is a protein that is encoded by the FNDC5 gene. It was reported that FNDC5 significantly decreased cell number, migration and viability through apoptosis in malignant MDA-MB-231 cells. Thus MDA-MB-231 cells were seeded overnight at a density of 5,000 cells/well, and treated with or without various concentrations of FNDC5 for 48h, then MDA-MB-231 cells were observed by inverted microscope and cell viability was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10µL of CCK-8 solution was added to each well of the plate, then measure the absorbance at 450nm using a microplate reader after incubating the plate for 1-4 hours at 37oC.<br/>Cell apoptosis of MDA-MB-231 cells after incubation with FNDC5 for 48h observed by inverted microscope was shown in Figure 1.<br/>(A) MDA-MB-231 cells cultured in DMEM, stimulated with 4nM FNDC5 for 48h; <br/>(B) Unstimulated MDA-MB-231 cells cultured in DMEM for 48h.<br/>Figure. Cell apoptosis of MDA-MB-231 cells after stimulated with FNDC5.

The dose-effect curve of FNDC5 was shown in Figure 2. It was obvious that FNDC5 significantly decreased cell viability of MDA-MB-231 cells. The ED50 for this effect is typically 1.35~12.52ug/mL.<br/>Figure. The dose-effect curve of FNDC5 on MDA-MB-231 cells.