Insulin-Like Growth Factor Binding Proteins in Maternal Serum Throughout Gestation and in the Puerperium: Effects of a Pregnancy-Associated Serum Protease Activity*

Abstract

The cDNAs encoding three major insulin-like growth factor-binding proteins (IGFBPs) have been cloned and sequenced. We have examined, by Western ligand blotting, the profiles of these binding proteins in human female serum in the normal menstrual cycle, throughout pregnancy, and during the postpartum period. There was no change in the serum profile of any of the binding proteins in early pregnancy compared to that in the secretory phase of the menstrual cycle. However, there was a marked decrease in circulating levels of the main serum IGFBP, IGFBP-3, after 6 weeks of gestation, continuing progressively to term and returning to nonpregnant levels by 5 days postpartum. IGFBP-2 decreased steadily throughout gestation. In contrast, IGFBP-1 levels were found to rise by the second trimester. Endoglycosidase-F digestion did not enhance detection of IGFBP-3 by ligand blotting. Immunoprecipitations with two separate antibodies against IGFBP-3 and IGFBP-2, followed by Western ligand blotting, confirmed the marked decrease in IGFBP-3 levels after 6 weeks of gestation and the more gradual decrease in IGFBP-2. In contrast, immunoprecipitations with IGFBP-1 monoclonal antibodies confirmed the increase in IGFBP-1 during gestation. Endogenous serum IGFs were separated from serum IGFBPs by acid chromatography, and an 80% decrease in total IGF-binding activity in the IGFBP fraction of chromatographed pregnancy vs. nonpregnancy serum was detected by charcoal absorption assay. Furthermore, immunoprecipitations of IGF affinity cross-linked IGFBP fractions with IGFBP-3-specific antiserum confirmed a marked diminution of IGFBP-3 in pregnancy compared to nonpregnancy serum, and revealed, only in pregnancy serum, the concomitant appearance of a band with a mol wt of 34K and three less intense bands with mol wt between 20-26K on sodium dodecyl sulfate gels. Incubation of nonpregnancy serum with 6-week pregnancy serum at 37 C for 5 h, followed by Western ligand blotting, showed only a slight reduction in the amount of IGFBP-3 in the mixture compared to that in controls. However, incubation of term pregnancy with nonpregnancy serum at 37 C for 5 h revealed a marked reduction of IGFBP-3 in the mixture. When iodinated recombinant IGFBP-3 was incubated with term pregnancy serum under the same conditions, the appearance of a 29K protein was identified by gel electrophoresis and autoradiography, along with three less intense bands with mol wt between 17-22K.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin-Like Growth Factors (IGFs) and IGF-Binding Proteins (IGFBP-1, -2 and -3) in Diabetic Pregnancy: Relationship to Macrosomia.

“…Other studies have shown that the serum concentrations of IGFBP-1, unlike IGFBP-3, increase during pregnancy [25,[32][33][34], and are high in the fetus and newborn [35,36], which was consistent with our results obtained in both normal and diabetic subjects. In addition, we found that they were significantly higher in IDDM mothers and their infants.…”

“…4), due to the increased protease activity for IGFBP-3 in pregnant serum [24][25][26]. There was also no difference among the three groups in the amount of 30 KDa species (data not shown).…”

“…IGFBP-3 is the main serum IGFBP which plays a major role in determining the free concentration of IGFs, which decreases during pregnancy because of proteinase activity [24,25]. Actually, there was no 38/41 KSa species of IGFBP-3 in the maternal serum obtained at the time of delivery from the normal and diabetic women.…”

Insulin-like growth factors and their binding proteins in human colonocytes: preferential degradation of insulin-like growth factor binding protein 2 in colonic cancers

“…A serine protease that specifically degrades IGFBP-5 in fibroblasts has been reported (Nam et al, 1994). In pregnancy, a serum protease exists that degrades IGFBP-3 (Giudice et al, 1990). In all of these conditions, IGFBP degradation, specific or general, resulted in enhanced IGF activity, and dysregulation of this process may promote autonomous growth.…”

Maternal serum insulin-like growth factor-binding protein-3 (IGFBP-3) at 11–13 weeks in preeclampsia

“…16,17 In the circulation, IGFBP-3 binds to approximately 95% of IGF-I and IGF-II and this complex prolongs the half-life of IGFs and protects them from degradation. [16][17][18][19] An endogenous pregnancy-related IGFBP-3 proteolytic activity is considered a fundamental mechanism to increase the bioavailability of IGF-I, [20][21][22] which is a mitogenic polypeptide that stimulates cellular proliferation and differentiation and is involved in the regulation of trophoblast invasion and placental development. [23][24][25] In addition, IGFBP-3 can inhibit cell proliferation and stimulate apoptosis via non-IGFdependent pathways.…”