IDENTIFICATION AND CHARACTERIZATION OF A RAT DECIDUAL INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN COMPLEMENTARY-DNA

A partial cDNA which encodes the rat homolog of human placental protein-12, the low mol wt insulinlike growth factor-binding protein (IGFBP-1), has been isolated from a rat decidual cDNA library using low stringency hybridization with a human IGFBP-1 cDNA probe. The incomplete cDNA obtained from this library was used to screen a rat liver cDNA library from which a full-length cDNA was obtained. The predicted amino acid sequence of rat IGFBP-1 showed 66%, 29%, and 34% sequence identity with the human IGFBP-1, the human GH-dependent binding protein IGFBP-3, and rat IGFBP-2, the BP secreted by buffalo rat liver cells, respectively. The rat IGFBP-1 cDNA hybridized with a 1.6-kilobase transcript which was easily detected in uterine RNA from the pseudopregnant rat and RNA from the liver and kidney of adult rats. A low level of expression was apparent in the brain and the diestrous uterus. Of the tissues examined the order of abundance of IGFBP-1 mRNA was deciduoma tissue ≥ liver >> kidney >> uterus > brain. The 1.6-kb mRNA was more abundant in RNA from neonatal rat liver than in that from maternal liver, but was not detected in total RNA (50 µg) from other neonatal rat tissues (kidney, lung, brain, and heart). Under stringent conditions, rat IGFBP-1 did not hybridize with RNA from the BRL-3A rat liver cell line. In food-deprived rats, hepatic IGFBP-1 mRNA was increased 10.0 ± 2.2-fold compared to that in control rats. Ligand blotting with [125I]IGF-I was used to detect the BP in conditioned medium from COS-1 cells transfected with rat IGFBP-1 cDNA driven by the SV40 promoter. From these studies we conclude that the rat IGFBP-1 is expressed in some nonhepatic tissues, is more highly expressed in the neonatal rat, and is up-regulated after food deprivation. The availability of a rat cDNA probe should provide a useful tool to examine the regulation of IGFBP-1 expression. © 1990 by The Endocrine Society.