Growth hormone (GH)-stimulated insulin-like growth factor I gene expression is mediated by a tyrosine phosphorylation pathway depending on C-terminal region of human GH receptor in human GH receptor-expressing Ba/F3 cells.
The signaling pathway of GH-stimulated IGF-I gene expression is still unclear, although it has been reported that the Janus kinase (JAK)-signal transducers and activators of transcription (STAT)5b pathway plays an important role in liver IGF-I expression. In this study, the GH-dependent IGF-I gene expression and its intracellular signaling mechanism have been examined in mouse pro-B, Ba/F3 cells stably expressing human GH receptor (Ba/F3-hGHR). The IGF-I gene expression was stimulated by human GH (0.01-10 nm) in a dose-dependent fashion in Ba/F3-hGHR cells. The specific inhibitors for JAK2 remarkably suppressed the GH-induced IGF-I gene expression, but MAPK or phosphatidylinositol 3 kinase-specific inhibitors failed to block the GH stimulation of the IGF-I gene expression. However, genistein, a nonspecific tyrosine kinase inhibitor that does not inhibit JAK2 and STAT5 phosphorylation, significantly suppressed the GH-induced IGF-I gene expression. Additionally, a Ba/F3-hGHR mutant that contained the truncated C-terminal hGHR up to D351 showed no IGF-I gene expression in response to human GH. The D351 form normally has the GH-induced JAK/STAT5 tyrosine phosphorylation. These results suggest that the JAK-STAT5 pathway and the novel tyrosine phosphorylation pathway, dependent on signaling from the C-terminal region of hGHR, might be involved in the GH-stimulated IGF-I gene expression in Ba/F3 cells.
Yoshizato
Hideo
H
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan. h-yoshi@ks.kyy.nitech.ac.jp
Tanaka
Minoru
M
Nakai
Naoya
N
Nakao
Nobuhiro
N
Nakashima
Kunio
K
D000818:Animals; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D013006:Growth Hormone / Q000494:pharmacology*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D053614:Janus Kinase 2; D051379:Mice; D008894:Milk Proteins; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000032:analysis; D011986:Receptors, Somatotropin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D003513:Cycloheximide; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2; D020928:Mitogen-Activated Protein Kinases