Cloning and characterization of chicken growth hormone binding protein (cGHBP)

Growth hormone (GH) is indispensable for the growth of animals and its biological activity is mediated by binding to the growth hormone receptor (GHR) [Harvey S, Scanes CG, Daughaday WH. Growth hormone. Boca Raton: CRC Press; 1995]. GHR is a transmembrane protein responsible for signal transduction upon GH binding. GH also binds to the growth hormone binding protein (GHBP) which is the soluble form of GHR extracellular domain existing in circulation. Actions of GHBP include prolongation of GH bioavailability and prevention of GH signaling system from over-stimulation. To date, little is known about the mechanisms generating the chicken GHBP (cGHBP). Elucidating the genomic structure of cGHR will provide insights into such underlying mechanisms. Using polymerase chain reaction and library screening methods, we have characterized the genomic organization of chicken GHR (cGHR). The full-length coding region of the cGHR transcript is composed of eight exons (exons 2-10), lacking a human homolog exon 3 and spans at least 71 kb on the genome. A novel transcript of size 1.2kb was isolated from chicken liver total RNA using 5' and 3' rapid cDNA ends amplification (RACE). It was generated by utilizing a previously unknown polyadenylation signal located at the intron 6. Semi-quantitative reverse transcription polymerase chain reaction showed that this transcript is widely expressed in a variety of tissues. This transcript has an open reading frame comprising 203 amino acids. In vitro binding assay using ELISA demonstrated that Escherichia coli expressed recombinant protein encoded by this transcript was able to bind with chicken GH. Hence, this transcript is a potential candidate for cGHBP.