EFFECT OF DIFFERENT SERUM CONCENTRATIONS OF GROWTH HORMONE-BINDING PROTEIN (GHBP) ON THE REGULATION OF GH RECEPTOR GHBP GENE-TRANSCRIPTION IN A HUMAN HEPATOMA-CELL LINE/

Although high-affinity growth hormone (GH)-binding protein (GHBP) seem s to mirror tissue GH receptor (GH-R) status and affects GH kinetics, the physiological importance and ultimate biological role of GHBP rema in largely unknown and obscure. Therefore, the aims of this study were , first, to test the hypothesis that different serum concentrations of GHBP may regulate GHR/GHBP gene transcription and, second, to define a new nonradioactive polymerase chain reaction (PCR) method to quantif y GH-R/GHBP mRNA levels which was to compare with the RNase protection assay. Sera from patients with Laron-type dwarfism (n = 10) and adult obese patients (n = 7) containing distinct GH and GHBP concentrations were added to human hepatoma cells (HuH 7) cultured in a hormonally-a dapted medium. GH-R/GHBP gene expression was studied 3 h after the add ition of the sera. The results of the regulated GH-R/GHBP mRNA levels imply a direct impact of GHBP on GHR/GHBP gene transcription under the se circumstances. In conclusion, we set up a nonradioactive quantitati ve PCR method which enables the measurement and quantification of GH-R /GHBP mRNA. The results were identical with the data obtained using RN ase protection assay. In addition, these results provide evidence that GHBP may have some effect on the regulation of the GH-R/GHBP transcri ption and that it is more than simply a shed or secreted product with extracellular destinations and functions. Our personal view, therefore , is that; GHBP is rather an active player than an erratic extracellul ar domain of a receptor.