Modification of gene expression after internalization of Growth Hormone into the cell nucleus

Growth hormone (GH) and many other hormones or growth factors have been shown to be rapidly internalized and translocated into the nucleus. The first event of peptide action is binding to its receptor which initiates both signal transduction pathways and internalization. The latter process involves the nucleus and probably gene transcription. In order to analyze the consequences of internalization of GH on gene expression, we used different populations of CHO cells, transfected with either full length GH receptor, or with defective receptor unable to trigger either signal transduction (deletion of box1) or the internalization of GH (Phe346 mutation in Ala). In addition, functional isolated nuclei were incubated 10 and 30 min with 50 nM GH in order to analyze the direct effect of GH on gene expression without surrounding cytoplasmic structures. The genes involved in signal transduction pathways were not revealed if GH internalization is the only functional activity in the whole cell as well as with isolated nuclei. In intact cell, internalization increased expression of 297 genes and decreased fewer than 10% of those known to be influenced by GH. Variations of expression in purified nuclei showed large variations with time. If cell signaling was not modified, cellular growth and proliferation, nucleic acid metabolism, cellular development, cell cycle and gene expression showed many variations with time. GH internalization shows direct effects on gene expression, different from those stimulated by signal transduction.