Conover Cheryl A, Bale Laurie K, Overgaard Michael T, Johnstone Edward W, Laursen Ulla H, Füchtbauer Ernst-Martin, Oxvig Claus, van Deursen Jan
The Division of Endocrinology, Metabolism and Nutrition, Endocrine Research Unit, Mayo Clinic and Mayo Foundation, 200 First Street SW, Rochester, MN 55905, USA.
Development. 2004 Mar;131(5):1187-94. doi: 10.1242/dev.00997.
Pregnancy-associated plasma protein A (PAPPA) is a metzincin superfamily metalloproteinase in the insulin-like growth factor (IGF) system. PAPPA increases IGF bioavailability and mitogenic effectiveness in vitro through regulated cleavage of IGF-binding protein 4 (IGFBP4). To determine its function in vivo, we generated PAPPA-null mice by gene targeting. Mice homozygous for targeted disruption of the PAPPA gene were viable but 60% the size of wild-type littermates at birth. The impact of the mutation was exerted during the early embryonic period prior to organogenesis, resulting in proportional dwarfism. PAPPA, IGF2 and IGFBP4 transcripts co-localized in wild-type embryos, and expression of IGF2 and IGFBP4 mRNA was not altered in PAPPA-deficient embryos. However, IGFBP4 proteolytic activity was completely lacking in fibroblasts derived from PAPPA-deficient embryos, and IGFBP4 effectively inhibited IGF-stimulated mitogenesis in these cells. These results provide the first direct evidence that PAPPA is an essential growth regulatory factor in vivo, and suggest a novel mechanism for regulated IGF bioavailability during early fetal development.
妊娠相关血浆蛋白A（PAPPA）是胰岛素样生长因子（IGF）系统中的一种金属锌蛋白酶超家族金属蛋白酶。PAPPA通过对胰岛素样生长因子结合蛋白4（IGFBP4）的调控性裂解，在体外提高IGF的生物利用度和促有丝分裂效力。为了确定其在体内的功能，我们通过基因打靶构建了PAPPA基因敲除小鼠。PAPPA基因靶向破坏的纯合子小鼠能够存活，但出生时大小仅为野生型同窝小鼠的60%。该突变的影响在器官发生之前的早期胚胎期就已显现，导致比例性侏儒症。PAPPA、IGF2和IGFBP4转录本在野生型胚胎中共定位，且PAPPA缺陷胚胎中IGF2和IGFBP4 mRNA的表达未发生改变。然而，来自PAPPA缺陷胚胎的成纤维细胞中完全缺乏IGFBP4蛋白水解活性，并且IGFBP4在这些细胞中有效抑制了IGF刺激的有丝分裂。这些结果提供了首个直接证据，表明PAPPA是体内一种重要的生长调节因子，并提示了胎儿早期发育过程中调控IGF生物利用度的一种新机制。
