SFRP1 and lung cancer: Our current data indicate that miR-31 directly inhibits expression of Dkk-1 and DACT3 in lung cancer cells as well as normal respiratory epithelia; furthermore, miR-31 over-expression in these cells depletes several other antagonists of Wnt signaling with potential miR-31 binding motifs including SFRP1, SFRP4, and WIF-1, which are frequently silenced in human lung cancers [53].