BMP4 and neoplasm: Next, we examined by qRT-PCR if FOXC2 knockdown in U2OS cells affects the expression of several genes known to be enriched in tumor-propagating cells, such as the cell surface marker CD133, multidrug resistance pump ABCG2, Notch signaling receptor ligands JAG1 and BMP4, and chemokine receptor CXCR4 [28–30].