Target identification and physiological analyses of bovine prolactin-related proteins.

牛胎盘产生一系列与垂体催乳素（PRL）结构相似的蛋白质。牛胎盘PRL家族中至少有10个基因，包括牛胎盘乳原（bPL）和10个牛胎盘PRL相关蛋白bPRP-I - to- xi)，编码激素/细胞因子，预计参与妊娠的建立和维持。牛PRL家族大多数成员的靶标和生物学作用尚未明确。对牛PRL家族的3个成员bPL、bPRP-I和bPRP-VI进行了研究。使用碱性磷酸酶（AP）标记策略来监测配体与靶标的相互作用。AP-bPRP-I和APbPRP-VI特异性结合到牛胎盘组织切片上。AP-bPRP-I和AP-bPRP-VI在胎盘组内的结合模拟了细胞外基质（ECM）的分布。因此，评估AP融合蛋白与单个细胞外基质成分（肝素、层粘连蛋白、纤维连接蛋白、I型胶原和IV型胶原）的结合。AP-bPRP-I与IV型胶原特异性结合，但不与其他ECM成分结合。AP- bprp - vi与ECM成分表现出弱相互作用，而AP- bpl和AP与ECM成分均无明显结合。AP-bPRP-I与IV型胶原的结合是浓度依赖性的，受盐浓度的影响，并且特异性于IV型胶原的n端交联结构域（7S），而不是其三螺旋结构域。bPRP-I与IV型胶原的相互作用表明，bPRP-I在细胞外基质中积累，可能在细胞中作用于穿过牛胎盘组的细胞。

The bovine placenta produces an array of proteins structurally similar to pituitary prolactin (PRL). At least ten genes of the bovine placental PRL family, including bovine placental lactogen (bPL) and ten bovine PRL-related proteins bPRP-I to-XI), encode hormones/cytokines predicted to be involved in the establishment and maintenance of pregnancy. Targets and biological roles for most members of the bovine PRL family have yet to be specified. This study focused on three members of bovine PRL family, bPL, bPRP-I and bPRP-VI. An alkaline phosphatase (AP) tagging strategy was used to monitor interactions of the ligands with their targets. AP-bPRP-I and APbPRP-VI specifically bound to tissue sections of the bovine placentome. AP-bPRP-I and AP-bPRP-VI binding within the placentome mimicked the distribution of the extracellular matrix (ECM). Consequently, AP fusion protein binding to individual extracellular matrix components (heparin, laminin, fibronectin, type I collagen and type IV collagen) was evaluated. AP-bPRP-I specifically bound to type IV collagen, but not to the other ECM components. AP-bPRP-VI exhibited weak interactions with ECM components, while AP-bPL and AP did not show significant binding to any of the ECM components. Binding of AP-bPRP-I to type IV collagen was concentration dependent, influenced by salt concentrations, and specific to the N-terminal cross-linking domain (7S) of type IV collagen but not its triple-helical domain. The interaction of bPRP-I with type IV collagen suggests that bPRP-I accumulates in the extracellular matrix where it likely acts on cells traversing the bovine placentome.