Recombinant Human Growth Hormone R (GHR) Fc Chimera, CF

Growth hormone (GH), also known as somatotropin, is a member of a family of growth factors that includes prolactin, placental lactogens, proliferins and somatolactin (1, 2). It is synthesized primarily by somatotropes in the anterior pituitary and is released as an endocrine hormone. Other cells and tissues, including lymphoid tissues, can also produce GH (3). GH is a pleiotropic molecule which can act directly or indirectly via IGF-I, to regulate growth and metabolism as well as enhance T cell survival and thymic functions (1, 2, 4). GH exerts its biological actions by binding to the GH receptor (GHR) that is present in many cell types (1, 2). Human GHR cDNA encodes a 638 amino acid (aa) residue type I transmembrane protein with an 18 aa putative signal peptide, a 246 aa extracellular domain, a 24 aa transmembrane domain and a 350 aa cytoplasmic domain (5). At least two alternatively spliced isoforms of human GHR, lacking the sequence encoded by exon 3, or lacking most of the cytoplasmic domain, also exist (6, 7). Soluble GH-binding proteins corresponding to extracellular domain of the transmembrane proteins can be generated from the membrane proteins (8). Ligation of GHR by GH has been shown to result in receptor dimerization and activation of the JAK/STAT signaling cascade (9). The soluble GHBP has been shown to interfere with GH signaling by competing with the transmembrane receptor of GH. Alternatively, the GHBP has also been shown to enhance GH action by slowing GH clearance (8, 10).