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.

Abstract

Although high-affinity growth hormone (GH)-binding protein (GHBP) seems to mirror tissue GH receptor (GH-R) status and effects GH kinetics, the physiological importance and ultimate biological role of GHBP remain largely unknown and obscure. Therefore, the aims of this study were, first, to test the hypothesis that different serum concentrations of GHBP may regulate GH-R/GHBP gene transcription and, second, to define a new nonradioactive polymerase chain reaction (PCR) method to quantify 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-adapted medium. GH-R/GHBP gene expression was studied 3 h after the addition of the sera. The results of the regulated GH-R/GHBP mRNA levels imply a direct impact of GHBP on GH-R/GHBP gene transcription under these circumstances. In conclusion, we set up a nonradioactive quantitative PCR method which enables the measurement and quantification of GH-R/GHBP mRNA. The results were identical with the data obtained using RNase protection assay. In addition, these results provide evidence that GHBP may have some effect on the regulation of the GH-R/GHBP transcription 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 extracellular domain of a receptor.