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Studies on regulation of IGF (insulin-like growth factor)-binding protein (IGFBP) 4 proteolysis by pregnancy-associated plasma protein-A (PAPP-A) in cells treated with phorbol ester.

ABSTRACT: PAPP-A (pregnancy-associated plasma protein-A) is produced by hSFs (human skin fibroblasts) and hOBs (human osteoblasts) and enhances the mitogenic activity of IGFs (insulin-like growth factors) by degradation of IGFBP-4 (insulin-like growth factor-binding protein 4). PKC (protein kinase C) activation in these cells led to reduction in IGFBP-4 proteolysis. This study was undertaken to determine the mechanism by which activation of PKC suppresses IGFBP-4 proteolysis. Treatment of hSFs/hOBs with TPA (PMA; 100 nM) reduced IGFBP-4 proteolysis without significantly decreasing the PAPP-A level in the CM (conditioned medium). Immunodepletion of the proform of eosinophil major basic protein (proMBP), a known PAPP-A inhibitor, from CM of TPA-treated cells (TPA CM) failed to increase IGFBP-4 proteolytic activity. Transduction of hSFs with proMBP retrovirus increased the concentration of proMBP up to 30 ng/ml and led to a moderate reduction in IGFBP-4 proteolysis. In contrast, TPA treatment blocked IGFBP-4 proteolysis but failed to induce a detectable amount of proMBP in the CM. While proMBP overexpression led to the formation of a covalent proMBP-PAPP-A complex and reduced the migration of PAPP-A on SDS/PAGE, TPA treatment dose- and time-dependently increased the conversion of a approximately 470 kDa PAPP-A form (PAPP-A470) to a approximately 400 kDa PAPP-A form (PAPP-A400). Since unreduced PAPP-A400 co-migrated with the 400 kDa recombinant PAPP-A homodimer and since PAPP-A monomers from reduced PAPP-A470 and PAPP-A400 co-migrated on SDS/PAGE, conversion of PAPP-A470 to PAPP-A400 is unlikely to be caused by proteolytic cleavage of PAPP-A. Consistent with the data showing that the increase in the ratio of PAPP-A400/PAPP-A470 is correlated with the extent of reduction in IGFBP-4 proteolysis, partially purified PAPP-A400 exhibited a 4-fold reduction in IGFBP-4 proteolytic activity compared with PAPP-A470. These data suggest that a novel mechanism, namely conversion of PAPP-A470 to the less-active PAPP-A400, could account for the TPA-induced suppression of PAPP-A activity.

SUBMITTER: Sivanandam AS

PROVIDER: S-EPMC1224057 | biostudies-other | 2004 Apr

REPOSITORIES: biostudies-other

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Project description:The insulin-like growth factor (IGF) family plays key roles in growth and development. In the cornea, IGF family members have been implicated in proliferation, differentiation, and migration, critical events that maintain a smooth refracting surface that is essential for vision. The IGF family is composed of multiple ligands, receptors, and ligand binding proteins. Expression of IGF type 1 receptor (IGF-1R), IGF type 2 receptor (IGF-2R), and insulin receptor (INSR) in the cornea has been well characterized, including the presence of the IGF-1R and INSR hybrid (Hybrid-R) in the corneal epithelium. Recent data also indicates that each of these receptors display unique intracellular localization. Thus, in addition to canonical ligand binding at the plasma membrane and the initiation of downstream signaling cascades, IGF-1R, INSR, and Hybrid-R also function to regulate mitochondrial stability and nuclear gene expression. IGF-1 and IGF-2, two of three principal ligands, are polypeptide growth factors that function in all cellular layers of the cornea. Unlike IGF-1 and IGF-2, the hormone insulin plays a unique role in the cornea, different from many other tissues in the body. In the corneal epithelium, insulin is not required for glucose uptake, due to constitutive activation of the glucose transporter, GLUT1. However, insulin is needed for the regulation of metabolism, circadian rhythm, autophagy, proliferation, and migration after wounding. There is conflicting evidence regarding expression of the six IGF-binding proteins (IGFBPs), which function primarily to sequester IGF ligands. Within the cornea, IGFBP-2 and IGFBP-3 have identified roles in tissue homeostasis. While IGFBP-3 regulates growth control and intracellular receptor localization in the corneal epithelium, both IGFBP-2 and IGFBP-3 function in corneal fibroblast differentiation and myofibroblast proliferation, key events in stromal wound healing. IGFBP-2 has also been linked to cellular overgrowth in pterygium. There is a clear role for IGF family members in regulating tissue homeostasis in the cornea. This review summarizes what is known regarding the function of IGF and related proteins in corneal development, during wound healing, and in the pathophysiology of disease. Finally, we highlight key areas of research that are in need of future study.

Project description:Background: Prenatal exposure to dietary protein may program growth-regulating hormones, consequently influencing early-life growth patterns and later risk of associated chronic diseases. The insulin-like growth factor (IGF) axis is of particular interest in this context given its influence on pre- and postnatal growth and its sensitivity to the early nutritional environment.Objective: Our objective was to examine associations of maternal protein intake during pregnancy with cord blood concentrations of IGF-I, IGF-II, IGF binding protein-3 (IGFBP-3), and insulin.Methods: We studied 938 mother-child pairs from early pregnancy through delivery in the Project Viva cohort. Using multivariable linear regression models adjusted for maternal race/ethnicity, education, income, smoking, parity, height, and gestational weight gain and for child sex, we examined associations of second-trimester maternal protein intake [grams per kilogram (weight before pregnancy) per day], as reported on a food frequency questionnaire, with IGF-I, IGF-II, IGFBP-3, and insulin concentrations in cord blood. We also examined how these associations may differ by child sex and parity.Results: Mothers were predominantly white (71%), college-educated (64%), and nonsmokers (67%). Mean ± SD protein intake was 1.35 ± 0.35 g ⋅ kg-1 ⋅ d-1 Each 1-SD increment in second-trimester protein intake corresponded to a change of -0.50 ng/mL (95% CI: -2.26, 1.26 ng/mL) in IGF-I and -0.91 μU/mL (95% CI: -1.45, -0.37 μU/mL) in insulin. Child sex and parity modified associations of maternal protein intake with IGF-II and IGFBP-3: protein intake was inversely associated with IGF-II in girls (P-interaction = 0.04) and multiparous mothers (P-interaction = 0.05), and with IGFBP-3 in multiparous mothers (P-interaction = 0.04).Conclusions: In a cohort of pregnant women with relatively high mean protein intakes, higher intake was associated with lower concentrations of growth-promoting hormones in cord blood, suggesting a pathway that may link higher protein intake to lower fetal growth. This trial was registered at clinicaltrials.gov as NCT02820402.

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Studies on regulation of IGF (insulin-like growth factor)-binding protein (IGFBP) 4 proteolysis by pregnancy-associated plasma protein-A (PAPP-A) in cells treated with phorbol ester.

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