CELL TRANSFECTION AS A TOOL TO STUDY GROWTH-HORMONE ACTION

The isolation of growth hormone receptor (GHR) cDNA clones has made po ssible the transfection of GHRs into cultured cells. Our aim in this m inireview is to show how the application of such approaches have benef ited GHR research. GH stimulation of cells expressing GHR cDNAs can ca use an alteration of cellular function that mimic those of the endogen ous GHR. GHR cDNA transfected cells also offer a system where the mech anism of GH action can be studied. Such a system has been used to demo nstrate that the GHR itself becomes tyrosine phosphorylated and that f urther phosphorylation of downstream proteins is important in GH actio n. The OH signals are transmitted to the nucleus and GH regulated gene s have now begun to be characterized. The ability to use cell transfec tion for mechanistic studies of GH action will be instrumental to defi ne domains within the receptor that are of functional importance and t o determine pathways whereby OH signals are conveyed within the cell.