A NOVEL IN-VITRO MODEL FOR STUDYING SIGNAL-TRANSDUCTION AND GENE-REGULATION VIA THE GROWTH-HORMONE RECEPTOR

Buffalo rat liver cells were stably transfected with an expression vector containing rat GH (rGH) receptor cDNA. Transfected cells expressed rGH receptor mRNA and specifically bound GH with high affinity. When transfected cells were stimulated with GH, levels of lipoprotein lipase (LPL) mRNA were increased in a time- and dose-dependent fashion, while glyceraldehyde-3-phosphate-dehydrogenase mRNA levels were unaffected. No GH binding or LPL mRNA could be detected in untransfected cells. Treatment of transfected cells with actinomycin D inhibited the GH-stimulated increase in LPL mRNA, indicating that GH acts at a transcriptional level. When protein synthesis was inhibited using cycloheximide, basal levels of LPL mRNA were increased, and there was no GH stimulation. This suggests that LPL gene expression is constantly repressed by a labile protein. Chloramphenicol acetyltransferase constructs containing the human LPL promoter could be regulated by GH. In conclusion, stimulation of the rGH receptor in stably transfected Buffalo rat liver cells results in specific induction of LPL gene expression. This provides a novel model to study the mechanism of GH action, particularly in relation to gene regulation.