GH Responsiveness Is not Correlated to IGF1 P2 Promoter Methylation in Children With Turner Syndrome, GHD and SGA Short Stature.

Background: The methylation of IGF1 promoter P2 was reported to negatively correlate with serum IGF-1 concentration and rhGH treatment response in children with idiopathic short stature. These findings have not yet been confirmed. Objective: This study aimed to determine IGF1 promoter P2 methylation in short children treated with rhGH and correlate clinical parameters with the methylation status. In addition, long-term stability of methylation during rhGH treatment was studied. Design: This was a single tertiary center study analyzing clinical GH response and IGF-1 serum concentration changes in patients with GHD (n=40), SGA short stature (n=36), and Turner syndrome (n=16) treated with rhGH. Data were correlated to the methylation of two cytosine residues (-137, +97) of the P2 promoter of IGF1 in blood cells measured by pyrosequencing in 443 patient samples. Results: Basal and stimulated IGF-1 concentrations, first year increment in height velocity and studentized residuals of a prediction model did not correlate to the methylation of -137 und +97 in IGF1 P2 promoter. The methylation of these two sites was relatively stable during treatment. Conclusions: This study did not confirm IGF1 P2 promotor being a major epigenetic locus for GH responsiveness in patients treated with a normal dose of rhGH. Additional studies are warranted.

Corrigendum: GH responsiveness is not correlated to IGF1 P2 promoter methylation in children with Turner syndrome, GHD and SGA short stature.

[This corrects the article DOI: 10.3389/fendo.2022.897897.].

Very High Dehydroepiandrosterone Sulfate (DHEAS) in Serum of an Overweight Female Adolescent Without a Tumor.

Introduction: An increase of serum dehydroepiandrosterone (DHEA) sulfate (DHEAS) is observed in premature adrenarche and congenital adrenal hyperplasia. Very high DHEAS levels are typical for adrenal tumors. Approximately 74% of DHEAS is hydrolyzed to DHEA by the steroid sulfatase (STS). The reverse reaction is DHEA sulfation. Besides these two enzyme reactions, the DHEAS transported through the cell membrane is important for its distribution and excretion. Case Presentation: We present a female adolescent with overweight and a very high DHEAS. The presence of a DHEAS-producing tumor was rejected using ultrasonography, Magnetic Resonance Tomography (MRT), and dexamethasone suppression. STS deficiency was suspected. Sequence analysis revealed a heterozygous nonsense mutation which predicts a truncation of the carboxyl region of the STS that is implicated in substrate binding. No partial gene deletion outside exon 5 was detected by multiplex ligation-dependent probe amplification. The bioassay revealed normal enzyme activity in the patient's leukocytes. A defect of transporter proteins was suggested. Both efflux [multidrug-resistance protein (MRP)2 and breast cancer-resistance protein (BCRP)] and uptake [organic anion-transporting polypeptide (OATP) and organic anion transporter (OAT) carriers] transporters were studied. Sequence analysis of exons revealed a heterozygous Q141K variant for BCRP. Conclusions: A novel heterozygous nonsense mutation in the STS gene and a known heterozygous missense variant in the BCRP gene were found. The heterozygous nonsense mutation in the STS gene is not supposed to be responsible for STS deficiency. The BCRP variant is associated with reduced efflux transport activity only in its homozygous state. The combination of the two heterozygous mutations could possibly explain the observed high levels of DHEAS and other sulfated steroids.

Structural analysis of human growth hormone with respect to the dominant expression of growth hormone (GH) mutations in isolated GH deficiency type II.

Human GH protein consists of four alpha-helices and contains two disulfide bridges. Isolated GH deficiency type II (IGHD II) is mainly caused by heterozygous splice site mutations of GH-1 leading to the disruption of one disulfide bridge (Cys53-Cys165) and to the loss of amino acids (aa) 32-71, which comprise the complete loop between alpha-helices 1 and 2. The mutant GH protein exerts a dominant negative effect on wild-type (wt) GH secretion by unclear mechanisms. For study of the structure-function relationship of GH mutants concerning the dominant negative effect, expression vectors harboring mutated GH cDNAs were transiently cotransfected with a vector encoding wtGH (pwtGH) into GH4C1 cells. Plasmids encoding beta-galactosidase, luciferase, or IGF-binding protein-2 were cotransfected with pwtGH and either of the GH mutants. Compared with the control transfection with pwtGH, GH secretion was mildly decreased by coexpressing wtGH and different GH point mutants with isolated disruption of the disulfide bridge Cys53-Cys165. Similar results were observed with GH mutants deleted in aa 32-46 or 32-52. Deletion of more aa (32-53, 32-63, 32-69, 32-71) ascendingly decreased GH secretion and content in parallel with the increasing length of the deleted stretch. An inhibitory dose-dependent effect of del32-69GH and del32-71GH on the activity/amount of coexpressed beta-galactosidase, luciferase, and IGF-binding protein-2 was found, whereas mRNA levels were unaffected. Hence, the extent of deletion played the major role in expression of the dominant negative effect. The inhibitory effect of GH mutants on heterologously expressed, non-GH proteins suggests that the dominant negative effect is not limited to GH or to proteins of the regulated secretory pathway, but may depend on expression levels.

Effect of zinc binding residues in growth hormone (GH) and altered intracellular zinc content on regulated GH secretion.

Endocrine cells store hormones in concentrated forms (aggregates) in dense-core secretory granules that are released upon appropriate stimulation. Zn(2+) binding to GH through amino acid residues His18, His21, and Glu174 are essential for GH dimerization and might mediate its aggregation and storage in secretory granules. To investigate whether GH-1 gene mutations at these positions interfere with this process, GH secretion and intracellular production were analyzed in GC cells (rat pituitary cell line) transiently expressing wt-GH and/or GH Zn mutant (GH-H18A-H21A-E174A) in forskolin-stimulated vs nonstimulated conditions. Reduced secretion of the mutant variant (alone or coexpressed with wt-GH) compared with wt-GH after forskolin stimulation was observed, whereas an increased intracellular accumulation of GH Zn mutant vs wt-GH correlates with its altered extracellular secretion. Depleting Zn(2+) from culture medium using N,N,N',N'-tetrakis(2-pyridylemethyl)ethylenediamine, a high-affinity Zn(2+) chelator, led to a significant reduction of the stimulated wt-GH secretion. Furthermore, externally added Zn(2+) to culture medium increased intracellular free Zn(2+) levels and recovered wt-GH secretion, suggesting its direct dependence on free Zn(2+) levels after forskolin stimulation. Confocal microscopy analysis of the intracellular secretory pathway of wt-GH and GH Zn mutant indicated that both variants pass through the regulated secretory pathway in a similar manner. Taken together, our data support the hypothesis that loss of affinity of GH to Zn(2+) as well as altering intracellular free Zn(2+) content may interfere with normal GH dimerization (aggregation) and storage of the mutant variant (alone or with wt-GH), which could possibly explain impaired GH secretion.

In vitro analysis of hGH secretion in the presence of mutations of amino acids involved in zinc binding.

Zinc (Zn(2+)) binding by human GH through amino acid residues His18, His21, and Glu174 has been described as a prerequisite for GH dimerization and storage in secretory granules. Our aim was to investigate in vitro whether disturbed Zn(2+) binding of mutant GH inhibits wild-type GH (wtGH) secretion and contributes to the pathogenetic mechanisms involved in dominantly transmitted isolated GH deficiency type II. Seven expression vectors harboring mutated human GH cDNAs were constructed in which nucleotide triplets encoding histidine or glutamine at positions 18, 21, and 174 were mutated to triplets encoding alanine: H18A, H21A, G174A, H18A-G174A, H21A-G174A, H18A-H21A, and H18A-H21A-G174A. These vectors were transiently cotransfected with a vector encoding wtGH or were singly transfected into rat pituitary GH(4)C(1) cells. Plasmids encoding beta -galactosidase were cotransfected. 48h after transfection, GH in media and cell extracts was measured using a GH-specific RIA, and results were normalized for transfection efficiency by means of beta -galactosidase activity. In comparison with the control transfection (wtGH/wtGH set at 100%), GH secretion remained unaffected when coexpressing wtGH and any of the GH mutants in which Zn(2+) binding was partially or completely prevented. When these mutants were singly expressed, the amount of GH in both media and cell extracts was decreased by about 50% when compared with cells expressing only wtGH. Our in vitro data do not support the hypothesis of disturbed Zn(2+) binding as a major pathogenetic mechanism in dominantly transmitted GH deficiency.