Association between the GH receptor/exon 3 genotype and the level of exon 3-positive GH-binding protein in human serum

Abstract

Objective: The human GH-binding protein (GHBP) is derived from the GH receptor (GHR) through proteolytic cleavage of its extracellular domain. Two isoforms of the GHBP exist, differing in the retention or exclusion of exon 3: E3(+)GHBP and E3(2 )GHBP. Our study aimed to answer the questions whether the level of E3(+)GHBP in the serum correlates with the GHR exon 3 expression and whether or not the E3 genotype matches the mRNA expression pattern. Methods: Since exon 3 retention/deletion can be detected at the protein level using epitope-specific antibodies, we were able to quantify the two isoforms by means of specific immunoassays in a total of 37 individuals. Additionally, these persons were also genotyped for exon 3 by genomic PCR and tested for GHR exon 3 mRNA expression by RT-PCR. Results: We found a significant correlation between GHR exon 3 genotype and the ratio of E3(+)GHBP and E3(2 )GHBP in the serum. Moreover, the genotype matched exactly the mRNA expression in fibroblasts and/or blood leukocytes in all samples investigated. The levels of E3(+)GHBP are more strongly correlated with body mass index, proinsulin and C-peptide than the levels of the E3(2 ) isoform. Conclusions: Our results show that the GHR exon 3 genotype is in accord with the type of GHBP isoforms found in the serum. Our data thus support the idea that the presence of exon 3-retaining and -excluding GHR/GHBP isoforms results from a genomic deletion rather than from alternative splicing.

Genetic variation at the growth hormone (GH1) and growth hormone receptor (GHR) loci as a risk factor for hypertension and stroke

“…There are no reported differences between these isoforms in their ligand specificity, ligand affinity or ability to shed GH binding protein, although the GHRd3 isoform has been shown to increase STAT5 activity in a luciferase reporter assay (Dos Santos et al 2004). In addition, serum concentration of exon 3-deleted GH binding protein (GHBP), which correlates with GHRd3 genotype (Seidel et al 2003), is higher in women than in men (Kratzsch et al 2001). GHBP isoforms are associated with metabolic risk factors such as visceral adiposity, raised triglycerides and hyperinsulinaemia (Kratzsch et al 2001;Seidel et al 2003) although this association is stronger for the exon 3-retained isoform than the exon 3-deleted variant.…”

“…In addition, serum concentration of exon 3-deleted GH binding protein (GHBP), which correlates with GHRd3 genotype (Seidel et al 2003), is higher in women than in men (Kratzsch et al 2001). GHBP isoforms are associated with metabolic risk factors such as visceral adiposity, raised triglycerides and hyperinsulinaemia (Kratzsch et al 2001;Seidel et al 2003) although this association is stronger for the exon 3-retained isoform than the exon 3-deleted variant. Thus, whilst the mechanisms by which GHR exon 3 genotype might influence metabolic risk are complex and probably multifactorial, the consistent gender-dependence of these effects merits further attention.…”

Genetic Polymorphisms Associated with Idiopathic Short Stature and First-Year Response to Growth Hormone Treatment

“…Briefly, candidate gene polymorphisms were analyzed using allele-specific restriction enzyme digestion of polymerase chain reaction (PCR) amplification products or commercially available TaqMan allelic discrimination assays with an ABI 7500 cycler. Presence or absence of GHR exon 3 was determined using multiplex PCR with size discrimination on polyacrylamide gels [17]. The PTHR tetranucleotide repeat size was analyzed using an ABI 3130 sequencer (methods adapted from Minagawa et al [18]).…”

Molecular genetics of human growth hormone, insulin-like growth factors and their pathways in common disease

“…A recent study has described an association between the presence of 0, 1 or 2 copies of GHRd3 and hypertension among stroke patients, particularly females (Horan et al 2006). Interestingly, other evidence shows that the serum concentration of GH binding protein (GHBP) correlates with GHRd3 (being higher in women than in men), and GHBP is associated with metabolic risk factors including visceral adiposity, raised triglycerides and hyperinsulinemia (Kratzsch et al 2001;Seidel et al 2003). On the other hand, a lower response to short and long-term human recombinant GH therapy has been reported in patients with growth hormone deWciency who are homozygous for GHRd3 (Jorge et al 2006).…”