Characterization of growth hormone (GH) in Chinese soft-shelled turtle: Molecular identification, capability in activating GH receptor and tissue distribution

Growth hormone (GH) participates in many physiological processes through the activation of its membrane-anchored receptor (GHR) in vertebrates. Because of its pivotal role in regulating growth and development, a large number of studies examining GH-GHR have been conducted in mammals, birds and fish. However, whether a functional GH-GHR pair exists in the Chinese soft-shelled turtle (st-) has not been previously studied. Here, the full-length cDNA encoding GH was cloned from Chinese soft-shelled turtle (Trionyx sinensis) pituitary. The results revealed that it consisted of 784 bp and encoded a precursor of 217 amino acids. Furthermore, recombinant stGH was prepared and purified from Escherichia coli (E. coli) strain BL21. Using the 5×STAT5-Luciferase reporter system, we found that stGHR expressed in human hepatocellular carcinoma cells could be activated in a dose-dependent manner by recombinant stGH, thereby triggering the intracellular JAK2-STAT5 signaling pathway, suggesting stGH is a functional ligand for stGHR. Quantitative real-time PCR revealed that GH mRNA was predominantly and abundantly expressed in pituitary, while GHR exhibited ubiquitous expression in all tissues examined, including pituitary and liver. Collectively, our data indicate a conserved GH-GHR pair might function in reptiles including Chinese soft-shelled turtle, as that in mammals, birds and fishes.