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 vec tor 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 lipas e (LPL) mRNA were increased in a time- and dose-dependent fashion, whi le glyceraldehyde-3-phosphate-dehydrogenase mRNA levels were unaffecte d. No GH binding or LPL mRNA could be detected in untransfected cells. Treatment of transfected cells with actinomycin D inhibited the GH-st imulated increase in LPL mRNA, indicating that GH acts at a transcript ional level. When protein synthesis was inhibited using cycloheximide, basal levels of LPL mRNA were increased, and there was no GH stimulat ion. This suggests that LPL gene expression is constantly repressed by a labile protein. Chloramphenicol acetyltransferase constructs contai ning the human LPL promoter could be regulated by GH. In conclusion, s timulation of the rGH receptor in stably transfected Buffalo rat liver cells results in specific induction of LPL gene expression. This prov ides a novel model to study the mechanism of GH action, particularly i n relation to gene regulation.