Short Stature Caused by a Biologically Inactive Mutant Growth Hormone (GH-C53S)

Abstract

Human GH has two disulfide bridges linking Cys-53 to Cys-165 and Cys-182 to Cys-189. Although absence of the first disulfide bridge has been shown to affect the bioactivity of GH in transgenic mice, little is known of the importance of this bridge in mediating the GH/GH-receptor (GHR) interaction in humans. However, we have identified a missense mutation (G705C) in the GH1 gene of a Serbian patient. This mutation was found in the homozygous state and leads to the absence of the disulfide bridge Cys-53 to Cys-165. To study the impact of this mutation in vitro, GHR binding and Janus kinase (Jak)2/signal transducer and activator of transcription (Stat)5 activation experiments were performed, in which it was observed that at physiological concentrations (3-50 ng/ml) both GHR binding and Jak2/Stat5 signaling pathway activation were significantly reduced in the mutant GH-C53S, compared with wild-type (wt)-GH. Higher concentrations (400 ng/ml) were required for this mutant to elicit responses similar to wt-GH. These results demonstrate that the absence of the disulfide bridge Cys-53 to Cys-165 affects the binding affinity of GH for the GHR and subsequently the potency of GH to activate the Jak2/Stat5 signaling pathway. In conclusion, we have demonstrated that GH-C53S is a bioinactive GH at the physiological range and that the disulfide bridge Cys-53 to Cys-163 is required for mediating the biological effects of GH.

Short stature in two siblings heterozygous for a novel bioinactive GH mutant (GH-P59S) suggesting that the mutant also affects secretion of the wild-type GH

“…To confirm that the mutation P59S does not affect the affinity of the antibody used in DSL-ELISA, two different GH assays were performed on two samples of CHO supernatant and the results were compared (21).…”

“…Further, six GH variants found in the heterozygous state were suggested to be bioinactive by Millar et al (20), but no clear correlation between laboratory/clinical phenotype and patient genotype was demonstrated. Moreover, in one of the more convincing cases of bioinactive GH reported to date, a homozygous missense mutation C53S in the GH1 gene led to disruption of the disulfide bridge between Cys-53 and Cys-165 in a short Serbian boy (21). Functional studies demonstrated that both GHR binding and Jak2/Stat5 signaling activity were significantly reduced in the GH-C53S compared with wt-GH.…”

A mosaic de novo duplication of 17q21–25 is associated with GH insensitivity, disturbed in vitro CD28-mediated signaling, and decreased STAT5B, PI3K, and NF-κB activation

“…The differential diagnosis of proportional short stature associated with low serum insulin-like growth factor 1 (IGF1) and a normal or high GH peak in a provocation test includes a GH1 mutation leading to a bioinactive GH molecule (1,2) and four well-established causes of GH insensitivity: i) mutations in the GH receptor gene (GHR), affecting the extracellular, transmembrane, or intracellular domains leading to the GH insensitivity syndrome (3,4); ii) mutations of STAT5B, the major component of the GH signaling pathway (3,4,5); iii) IGFALS defects (6); and iv) IGF1 defects (7,8,9,10). In addition, it has been shown that activation of the mitogen-activated protein kinase (MAPK) pathway, as in Noonan syndrome, is associated with partial GH insensitivity (11).…”

Investigação de baixa estatura: aspectos clínicos, laboratoriais e moleculares da insensibilidade ao hormônio de crescimento

“…Menos freqüentemente, ocorrem mutações no gene do GH (GH1) com geração de molécula de GH biologicamente inativa (14), ou na STAT5b que provoca defeito pós-receptor de GH (13) (Tabela 5). Defeitos isolados da síntese ou ação do IGF-1 apresentam algumas características laboratoriais semelhantes à IGH, porém apresentam quadro clínico distinto (15-18) (Tabela 5).…”