The structures of a plurality of peptide ligands, each having a minimum activity unit which is believed to activate BRS-3, are predicted from the human genome sequence. Next, some peptides each having the minimum activity unit are chemically synthesized based on the predicted peptide structures, and the BRS-3 activation ability of the synthesized peptides are then examined. As a result, it is found that a peptide having the following amino acid sequence: Leu-Trp-Ala-Cys-Gly-Ser-Phe-Met (SEQ ID NO:3) can activate BRS-3 in a selective manner.