Meeting Abstract

92.8  Wednesday, Jan. 7  Ligand Binding, Agonist-Induced Regulation, and Signaling Characteristics of Trout Growth Hormone Receptors in Transfected Cells REINDL, K.M.; KITTILSON, J.D.; SHERIDAN, M.A.*; North Dakota St. Univ., Fargo mark.sheridan@ndsu.edu

Previously, we isolated and characterized two distinct growth hormone receptor (GHR)-encoding mRNAs, GHR1 and GHR2, from rainbow trout. In this study, CHO-K1 cells, which do not endogenously express GHRs, were individually transfected with plasmids that contained GHR1- or GHR2-encoding cDNAs. High affinity binding of ¹²⁵I-salmonid GH by expressed receptors was saturable, displaceable, and ligand selective. Whole-cell binding analysis revealed a single class of binding site; for GHR1 Kd=13 nM, for GHR2 Kd=21 nM. While salmonid prolactin (PRL) displaced ¹²⁵I-GH from both GHR1 and GHR2, the affinity of either receptor subtype for PRL was substantially less than that for GH; salmonid somatolactin, another member of the GH-PRL family, did not displace labeled GH except at pharmacological concentrations. ¹²⁵I-GH was internalized by GHR1- and GHR2-expressing cells in a time-dependent manner; maximum internalization reached 57% for GHR1 and 42% for GHR2. GH activated the JAK/STAT and extracellular signal-regulated kinase (ERK) subfamily of MAP kinases in both GHR1 and GHR2-transfected cells; however, greater phosphorylation of JAK and STAT was observed in GHR1 cells than in GHR2 cells and greater phosphorylation of ERK was observed in GHR2 cells than in GHR1 cells. These results indicate that trout GHRs display both overlapping and distinct characteristics that may be important for ligand selection and differential action in target organs. (Supported by NSF IOB 0444860 to M.A.S.)