Mouse DAM1 regulates pro-apoptotic activity of BLK in mammary epithelial cells

Mouse mammary gland cDNA library was screened to search for BLK-interacting protein using yeast two-hybrid system, and a mouse DNA amplified in mammary carcinoma 1 (mDAM1) was obtained. mDAM1 cDNA contained a full coding region of 678bp encoding 225 amino acids with the predicted molecular mass of 26kDa. Comparison of the mouse to human DAM1 revealed 90 and 100% identities at the nucleotide and protein levels, respectively. A single 1.5kb transcript for mDAM1 was expressed in NMuMG mouse mammary epithelial cells. Through in vitro protein binding assay, interaction between mDAM1 and BLK was also confirmed. NMuMG cells, stably transfected and expressing mDAM1, promoted cell death under serum starvation condition. Transient coexpression of mDAM1 and BLK showed increased cell death compared to BLK expression alone in NMuMG cells. These results indicate that mDAM1 promotes mammary epithelial cell death and pro-apoptotic function of BLK.