DKK1 and breast cancer: Finally, to explore the possibility that DKK1 might modulate the expression of NK cell activating and/or inhibitory ligands on the tumor cells, we stimulated the MDA-MD-231 breast cancer line with rhDKK1 but noted no changes in activating and inhibitory NK ligand levels via flow cytometry (Supp Fig. 7B, C) and qRT-PCR (Supp Fig. 7D).