Growth hormone-regulated intracellular signaling in UMR 106 osteosarcoma cells

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are important growth factors for postnatal longitudinal bone growth, Although many effect s of GH on bone growth are mediated by IGF-1, GH can directly influence bon e cells, Limited knowledge exists regarding specific intracellular signalin g pathways and genes activated by GH in bone cells. GH is known to activate several intracellular signaling pathways, among them the Janus kinase (JAR )/signal transducers and activators of transcription (STAT) pathway, GN mai nly activates JAK2 and both isoforms of STAT5, A and B, STAT5 gene deletion experiments have shown the importance of these transcription factors for g rowth, To understand the molecular mechanism(s) behind this, different expe rimental models are needed. The UMR 106 cell line is a rat clonal osteosarc oma cell line with osteoblast-like phenotypic properties, one is the endoge nous expression of GH receptor (GHR), The present study focused on whether these cells express a functional GH-responsive JAM2/STAT5 pathway. Analysis of cell extracts by immunoprecipitation and Western blot showed that physi ological concentrations of GH activated JAK2, Western blot analysis of nucl ear extracts from GH-stimulated UMR 106 cells shelved that physiological co ncentrations of GIP induced nuclear translocation of both. STAT5 isoforms, but with STAT5A being predominant. Both isoforms displayed similar nuclear turnover after GH stimulation of cells, Gel electrophoretic mobility shift assay (GEMSA) of nuclear extract revealed that both STAT5A and STAT5B obtai ned DNA-binding capacity after GH stimulation. Thus, me have shown, for the first time, the expression and GH-induced activation of JAK2 and STAT5A/B in UMR 106 osteoblast-like cells. This study also shows that this cell line is a suitable experimental model to study unique GH effects in osteoblasts mediated by STAT5.