Dose-dependent insulin regulation of insulin-like growth factor binding protein-1 in human endometrial stromal cells is mediated by distinct signaling pathways

R B Lathi, Ruth B. Lathi, AP Hess, A P Hess, Suzana Tulač, S Tulac, Nihar R. Nayak, N. R. Nayak, Marco Conti, M. Conti, Linda C. Giudice, L C Giudice
The Journal of clinical endocrinology and metabolism · 2005 · vol. 90(3) , pp. 1599–1606 · doi:10.1210/jc.2004-1676 · PMID:15613433 · W2060712358
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Insulin inhibits IGFBP-1 in human endometrial cells via PI3-kinase at low doses and additionally MAPK at higher doses.

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Abstract

IGF binding protein-1 (IGFBP-1) is a major product of decidualized human endometrial stromal cells and decidua, and as a modulator of IGF action and/or by independent mechanisms, it regulates cell growth and differentiation and embryonic implantation in these tissues. IGFBP-1 secretion is primarily stimulated by progesterone and cAMP and is inhibited by insulin and IGFs. The signaling pathways mediating the latter are not well defined, and the current study was conducted to determine which pathways mediate the effects of insulin on IGFBP-1 mRNA and protein expression by human endometrial stromal cells decidualized in vitro by progesterone. Cells were cultured and treated with different combinations of insulin; wortmannin, an inhibitor of the phosphatidylinositide-3-kinase (PI3-kinase) pathway; and PD98059, an inhibitor of the MAPK pathway. IGFBP-1 mRNA was determined by real-time PCR, and protein secretion in the conditioned medium was measured by ELISA. Activation of the PI3-kinase and the MAPK pathways was assessed by the detection of phosphorylated AKT and ERK in Western blots, respectively. Insulin inhibited IGFBP-1 mRNA and protein secretion in a dose-dependent fashion, with an ED(50) for the latter 0.127 ng/ml (21.6 pm). Inhibitor studies revealed that at low doses, insulin acts through the PI3-kinase pathway, whereas at higher levels it also activates the MAPK pathway in the inhibition of IGFBP-1. The data demonstrate that human endometrium is a target for insulin action in the regulation of IGFBP-1. At physiological levels insulin likely plays a homeostatic role for energy metabolism in the endometrium, and in hyperinsulinemic states, insulin action on the endometrium may activate cellular mitosis via the MAPK pathway and perhaps predispose this tissue to hyperplasia and/or cancer.

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MeSH descriptors

Endometrium Hypoglycemic Agents Insulin Insulin-Like Growth Factor Binding Protein 1 MAP Kinase Signaling System Stromal Cells Adult Cells, Cultured Dose-Response Relationship, Drug Endometrium Endometrium Enzyme Inhibitors Enzyme Inhibitors Extracellular Signal-Regulated MAP Kinases Extracellular Signal-Regulated MAP Kinases Extracellular Signal-Regulated MAP Kinases Female Humans Hypoglycemic Agents Hypoglycemic Agents

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