Monoclonal antibodies (mAb) were raised against human sperm components.  One of the mAb possessing sperm agglutinating activity was selected and designated as YWK-II. The target antigens were identified in human sperm as 60 and 72 kDa proteins and in rat sperm as 88 and 115 kDa proteins. Using the YWK-II mAb, a cDNA insert was isolated from a rat testis λgt11 expression library. The cDNA consisted of 1837 bp with an open reading frame of 573 bp, coding a polypeptide composed of 91 amino acids and assigned the accession number M31322. The C-terminus of the YWK-II polypeptide has high similarity (70.6%) to the transmembrane-cytoplasmic domain of βA4-amyloid precursor protein (APP) found in brain plaques of Alzheimer’s disease subjects. The YWK-II protein is structurally related to the human placenta amyloid protein precursor homologue (APPH) and to the rat amyloid precursor-like protein2 (APLP2).

Our recent studies show that the YWK-II component interacts with G(o) GTP binding protein, hDIA1, a diaphanous protein, and the Mullerian inhibiting substance (MIS). Its action is mediated by being coupled to an intracellular signal transducing system. In male germ cells it plays a role in their differentiation to spermatozoa. Dietary treatment of rat bearing mammary carcinoma with the monoterpene, limonene, caused regression of the cancer, associated with a marked expression of the YWK-II gene in the tumor cells. In conclusion, the YWK-II component should be considered a cancer/testis antigen because of its involvement in the differentiation and apoptosis of germ and cancer cells.