Neuroscience Letters 390 (2005) 21–24 Differential distributions of peptides in the epidermal growth factor family and phosphorylation of ErbB1 receptor in adult rat brain Ying-shan Piao, Yuriko Iwakura, Nobuyuki Takei, Hiroyuki Nawa ∗ Division of Molecular Neurobiology, Brain Research Institute, Niigata University, Asahimachi-dori 1-757, Niigata 951-8585, Japan Received 15 June 2005; received in revised form 25 July 2005; accepted 25 July 2005 Abstract Using two-site enzyme immunoassays, we measured protein levels of epidermal growth factor (EGF), transforming growth factor alpha (TGF), and heparin-binding epidermal growth factor (HB-EGF) in adult rat brain, and compared them with the phosphorylation levels of their receptor (ErbB1). There were significant variations in the brain distributions of each ErbB1 ligand. Among these ErbB1 ligands, HB-EGF protein levels were higher than those of TGF and those of EGF were the lowest. TGF protein was relatively enriched in the midbrain regions, while HB-EGF levels were most abundant in the cerebellum. Protein distributions of the EGF family members were discordant with previously reported mRNA distributions. In addition, there was significant basal ErbB1 phosphorylation detected with the largest amount of activation in the midbrain. These observations suggest that the activation of brain ErbB1 involves post-translational regulation of multiple EGF family members in a region-specific manner. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: EGF; TGF; HB-EGF; ErbB1; Her1; EIA; Schizophrenia; Parkinson’s disease Epidermal growth factor (EGF) and structurally related pep- tides such as transforming growth factor (TGF)  and heparin-binding (HB)-EGF are mitogenic peptides for var- ious types of cells and all bind to ErbB1 (Her1) receptors [4,15]. The spatial and temporal aspects of EGF concen- tration gradients are thought to regulate many cellular and molecular processes in both developing and mature central nervous system (CNS) [16]. These peptides are implicated in the proliferation and maintenance of multipotent neural stem cells in embryonic as well as adult rat brain [3]. The EGF family also has neurotrophic and protective effects on various types of neurons such as dopaminergic and GABAer- gic neurons [1,8,11]. In situ hybridization techniques reveal that mRNA for TGF and HB-EGF is relatively abundant in almost all brain regions [5,14]. In contrast, EGF mRNA lev- els are much lower than those of TGF or HB-EGF mRNA, while mRNA for the EGF precursor is detectable in the rat brain [7]. Previous reports indicate that EGF can cross the ∗ Corresponding author. Fax: +81 25 227 0815. E-mail address: hnawa@bri.niigata-u.ac.jp (H. Nawa). blood–brain barrier; therefore, EGF protein circulating in blood might have a direct influence on brain development and function [13]. Peptides in the EGF family are all produced as membrane-anchored precursor proteins and released as a soluble molecule through proteolytic processing, so-called ectodomain shedding. A disintegrin and metalloprotease (ADAM)-type metalloproteinases are involved in this pro- cess and cleaves the precursor protein at the region located between the growth-factor domain and the transmembrane- anchoring domain [10]. Accordingly, EGF family members are under distinct regulation at an mRNA level as well as by ectodomain shedding of the precursors. Few studies have assessed protein expression of the EGF family and activa- tion of ErbB1 receptors in the brain, however. In present study, we used two-site enzyme immunoassays (EIAs) to measure EGF, TGF, and HB-EGF protein levels in the same brain preparations. Moreover, to evaluate the basal activity of the endogenous ErbB1 ligands, total ErbB1 protein and its tyrosine phosphorylation levels were quantified by Western blotting and EIA in adult rat brain, respectively. 0304-3940/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2005.07.048