Analysis of hAG-2 and hAG-3 bait proteins (with their signal sequences deleted) in the same yeast two-hybrid system (Rain et al, 2001) using the same placenta-derived prey library as well as a prey library derived from a pool of four breast cancer cell lines (T47D, MCF7, BT20, MDMBA468) identified C4.4a and dystroglycan (DAG1, GenBank Accession XP_018223) as the only significant interacting partners for both proteins. Here, DAG1 is linked to breast cancer.