NOG and breast cancer: To further investigate whether the BMP/SMAD signaling pathway mediates the FOXF2-regulated osteotropism of breast cancer metastasis, we added the BMP antagonist Noggin to the culture medium of MCF-7 or MDA-MB-231 cells transfected with FOXF2-expression plasmid or vector control, and added BMP4 to the culture medium of MDA-MB-231 cells transfected with small interfering RNAs (siRNAs) targeting FOXF2 (siFOXF2) or non-targeting siRNA (siControl).