Growth Hormone (GH) Increases Lipoprotein Lipase mRNA in Cells Transfected with the Rat GH Receptor cDNA

The growth hormone (GH) receptor is phosphorylated on tyrosine residues after ligand binding (Foster et al. 1988). However the mechanism of intracellular signalling is unclear, since the receptor shows no apparent homology to classical tyrosine kinase receptors (Leung et al. 1987). One obstacle to in vitro studies is that few cultured cells express high levels of the GH receptor. The approach taken here was to transfect cultured cells with expression plasmids containing the rat GH receptor cDNA and the gene coding for neomycin resistance. Drug resistant cell colonies expressing high levels of GH receptors, both at the mRNA and protein level, were selected. Several different cell lines were stably transfected in this manner : Chinese hamster ovary cells showed GH-induced protein synthesis as well as GH-induced phosphorylation of MAP kinases (Emtner et al. 1990; Moller et al. 1992). The transfected Buffalo rat liver (BRL) cells in this study showed a GH-induced increase in lipoprotein lipase (LPL) mRNA indicating that the expressed receptor is functional.