Biological activities of ovine and bovine placental prolactin family proteins

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Bovine prolactin-related protein-I (PRP1) is a non-classical member of prolactin (PRL) family proteins. However, its function is still unknown. PRL, when cleaved by cathepsin D and matrix metalloproteinases (MMPs), resulted in N-terminal 16 kDa fragments (16K-PRL) that have antiangiogenetic properties in human and rodents. We examined the possibility of similar activity of bovine PRP1. PRP1 (normally 33 kDa) was cleaved by cathepsins (CTSs), MMPs, and bovine cotyledonary-conditioned medium (BCCM), and generated mainly 26 kDa N-terminal fragments. Two specific enzyme families, CTSs and MMPs cleaved intact PRP1, and BCCM also contained PRP1 cleavage activity. Bioactivity of cleaved PRP1 was examined in a cell proliferation assay using bovine brain vascular endothelial cells. The cleaved PRP1 stimulated the proliferation of endothelial cells in vitro. The endothelial cell proliferation activity of cleaved PRP1 may be shared in specific bovine placentomal angiogenesis.