Molecular Brain Research 112 (2003) 170–176 www.elsevier.com / locate / molbrainres Research report Estrogen receptor alpha forms estrogen-dependent multimolecular complexes with insulin-like growth factor receptor and phosphatidylinositol 3-kinase in the adult rat brain a b a, * ˜ Pablo Mendez , Inigo Azcoitia , Luis M. Garcia-Segura a Instituto Cajal, C.S.I.C., Av. Dr. Arce 37, 28002, Madrid, Spain b Departamento de Biologia Celular, Facultad de Biologia, Universidad Complutense de Madrid, 28040, Madrid, Spain Accepted 13 February 2003 Abstract Estradiol and insulin-like growth factor-I (IGF-I) have numerous functional interactions in the brain, including the regulation of neuroendocrine events, the control of reproductive behavior and the promotion of synaptic plasticity and neuronal survival. To explore the mechanisms involved in these interdependent actions of estradiol and IGF-I in the adult brain, the potential interactions of estrogen receptors with components of the IGF-I signaling system were assessed in this study. Systemic estradiol administration resulted in a transient immunocoprecipitation of the IGF-I receptor with the estrogen receptor a and in a transient increase in tyrosine phosphorylation of the IGF-I receptor in the hypothalamus of adult ovariectomized Wistar rats. Both effects were coincident in time, with a peak between 1 and 3 h after systemic estradiol administration. Three hours after estradiol treatment, there was an enhanced immunocoprecipitation of estrogen receptor a with p85 subunit of phosphatidylinositol 3-kinase, as well as an enhanced immunocoprecipitation of p85 with insulin receptor substrate-1. The interaction with the IGF-I receptor was specific for the a form of the estrogen receptor and was also induced by intracerebroventricular injection of IGF-I. These hormonal actions may be part of the mechanism by which estradiol activates IGF-I receptor signaling pathways in the brain and may explain the interdependence of estrogen receptors and the IGF-I receptor in synaptic plasticity, neuroprotection and other neural events.  2003 Elsevier Science B.V. All rights reserved. Theme: Endocrine and autonomic regulation Topic: Hypothalamic–pituitary–gonadal regulation Keywords: Phosphatidylinositol 3-kinase; Estradiol; Akt; Hypothalamus; Synaptic plasticity; Neuroendocrine regulation; Neuroprotection 1. Introduction different cell types in the central nervous system [11,16,37,39]. In addition, rapid membrane effects of Estradiol exerts a great variety of effects in the brain, estrogen in the brain have been recognized for a long time regulating neuronal and glial differentiation, neuronal [21,30,45]. Membrane and cytoplasmic effects of estrogen survival, synaptic plasticity, mood, cognitive function, are linked to the activation of different kinases and second 21 memory and behavior [2,5,7,22,31,48]. These diverse messenger systems, such as cAMP [9], intracellular Ca effects of estradiol are mediated by a comparable multip- [8,32] and activation of other transcriptional regulators licity of mechanisms of action. The classical mechanism of such as the cAMP response element binding protein action of estradiol in the brain is the regulation of (CREB) [50]. transcription by the activation of nuclear estrogen receptors As in other tissues, some of the effects of estradiol in the (ERs), members of the steroid receptor superfamily of nervous tissue may be mediated by the activation of transcription factors [4] that are widely distributed within growth factor signaling. One growth factor that interacts with estradiol in the brain is insulin-like growth factor-I (IGF-I). An interdependence between estrogen and IGF-I *Corresponding author. Tel.: 134-91-5854729; fax: 134-91-5854754. E-mail address: lmgs@cajal.csic.es (L.M. Garcia-Segura). has been widely documented for different events, such as 0169-328X / 03 / $ – see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016 / S0169-328X(03)00088-3