Regulation of Rapid Signal Transducer and Activator of Transcription-5 Phosphorylation in the Resting Cells of the Growth Plate and in the Liver by Growth Hormone and Feeding

• Published in: Endocrinology (Philadelphia) 2009-08, Vol.150 (8), p.3627-3636
• Main Authors: Gevers, Evelien F, Hannah, Matthew J, Waters, Michael J, Robinson, Iain C. A. F
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Blotting, Western; Cell differentiation; Cell Line, Tumor; Chondrocytes; Chondrogenesis; Chronic exposure; Fundamental and applied biological sciences. Psychology; Gene Expression - drug effects; Gene regulation; Grooves; Growth Hormone - pharmacology; Growth hormones; Growth plate; Growth Plate - drug effects; Growth Plate - metabolism; Hepatocytes; Humans; Immunohistochemistry; Insulin-Like Growth Factor I - pharmacology; Janus kinase; Kinases; Liver - drug effects; Liver - metabolism; Nutritional status; Phosphorylation; Phosphorylation - drug effects; Physiological effects; Prolactin; Prolactin - pharmacology; Rats; Receptors; Receptors, Somatotropin - metabolism; Stat5 protein; STAT5 Transcription Factor - metabolism; Transducers; Vertebrates: endocrinology
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2008-0985

GH has physiological functions in many tissues, but the cellular targets for direct effects of GH remain ill defined in complex tissues such as the growth plate in which the contribution of direct vs. indirect actions of GH remains controversial. The Janus kinase (Jak)-signal transducer and activator of transcription (STAT)-5 pathway is activated by GH, so we developed a method to visualize nuclear Stat5b and phosphorylated Stat5 in single cells in response to a pulse of GH. Hep2 cells did not show a Stat5 phosphorylation (pY-Stat5) response to GH except in cells transfected to express GH receptors. ATDC5 cells express GH receptors and showed GH-induced pY-Stat5 responses, which varied with their state of chondrocyte differentiation. In vivo, Stat5b+ve nuclei were seen in the resting and prehypertrophic chondrocytes of the growth plate. After a single ip pulse of human GH or mouse GH, but not prolactin, pY-Stat5 responses were visible in cells in the resting zone and groove of Ranvier, 10–45 min later. Prehypertrophic chondrocytes showed no pY-Stat5 response to GH. GH target cells were also identified in other tissues, and a marked variability in spatiotemporal pY-Stat5 responses was evident. Endogenous hepatic pY-Stat5 was detected in mice with intact GH secretion but only during a GH pulse. Fasting and chronic exposure to GH attenuated the pY-Stat5 response to an acute GH injection. In conclusion, pY-Stat5 responses to GH vary in time and space, are sensitive to nutritional status, and may be inhibited by prior GH exposure. In the growth plate, our data provide direct in vivo support for an early role of GH to regulate the fate of immature chondrocytes. With 10 minutes of an in vivo GH-injection in mice, the GH-responsive JAK2-STAT5 signaling pathway is activated specifically in the most immature chondrocytes of the growth plate, suggesting that GH acts directly on the growth plate.