J.L. Van den Brande

Mutation of the POU-Specific Domain of Pit-1 and Hypopituitarism Without Pituitary Hypoplasia

A point mutation in the POU-specific portion of the human gene that encodes the tissuespecific POU-domain transcription factor, Pit-1, results in hypopituitarism, with deficiencies of growth hormone, prolactin, and thyroid-stimulating hormone. In two unrelated Dutch families, a mutation in Pit-1 that altered an alanine in the first putative α helix of the POU-specific domain to proline was observed. This mutation generated a protein capable of binding to DNA response elments but unable to effectively activate its known target genes, growth hormone and prolactin. The phenotype of the affected individuals suggests that the mutant Pit-1 protein is competent to initiate other programs of gene activation required for normal proliferation of somatotrope, lactotrope, and thyrotrope cell types. Thus, a mutation in the POU-specific domain of Pit-1 has a selective effect on a subset of Pit-1 target genes.

The human insulin-like growth factor II gene contains two development-specific promoters

The insulin‐like growth factors (IGF) play an important role in fetal and postnatal development. Recently, the nucleotide sequences of the cDNAs encoding IGF‐I and IGF‐II and part of the human IGF genes were reported. In this communication we describe two distinct IGF‐II cDNAs isolated from a human adult liver and a human hepatoma cDNA library, respectively. Using these two cDNAs, we have established that the human IGF‐II gene contains at least 7 exons. Two different IGF‐II promoters have been identified, 19 kilobases (kb) apart, which are active in a development‐specific manner. The promoter, active in the adult stage, is located only 1.4 kb downstream from the insulin gene.

Nucleotide sequences of cDNAs encoding precursors of human insulin-like growth factor II (IGF-II) and an IGF-II variant

We have isolated 3 cDNA clones encoding human IGF‐II and a variant of IGF‐II. The amino acid sequence encoded by the IGF‐II cDNA is identical to the sequence previously described [(1978) FEBS Lett. 89, 283‐286]. In the amino acid sequence predicted by the IGF‐II variant cDNA, the Ser residue 29 in the B‐domain has been replaced by an Arg‐Leu‐Pro‐Gly sequence. The corresponding mRNAs probably arise by alternative splicing of a common RNA precursor. The IGF coding region of the cDNA inserts is flanked by sequences encoding a signal peptide and a carboxy‐terminal peptide indicating that both human IGF‐II and its variant are synthesized as precursors.

Biosynthetic Somatomedin C (SM-C/IGF-I) Increases the Length and Weight of Snell Dwarf Mice

ABSTRACT. An Escherichia coli derived somatomedin-C/IGF-I preparation (rec-IGF-I) with an amino acid sequence identical to the natural IGF-I derived from human plasma, increases body length and weight, as well as the growth of several organs of Snell dwarf mice, when administered for 4 wk. After 2 wk of treatment rec-IGF-I (22.2 μ/day) induced a significant increase over buffer treated controls, to a comparable degree as obtained with bacterially synthesized human growth hormone (bhGH; 8.4 μ/day). The weight/length ratio of rec-IGF-I and bhGH-treated dwarf mice after 4 wk of treatment were not significantly different. A significant increase over controls was obtained with both preparations. Organs with increased weights after bhGH treatment (brain; submandibular salivary glands; heart, liver, kidneys, thymus, and spleen) were also heavier after rec-IGF-I. Significance was only reached for the kidneys and the spleen and the musculus quadriceps femoris. Organs weights expressed as a percentage of body weight of bhGH and rec-IGF-I treated dwarfs were similar except for the relative weight of the heart of the bhGH group, which was significantly increased compared to the controls and the rec-IGF-I group. These data resolve the issue as to whether or not pure SM-C/IGF-I will induce growth in length and demonstrate the usefulness of recombinant IGF-I in the studies of growth regulation.

Direct effect of insulin and insulin-like growth factor-I on the secretory activity of rat pancreatic beta cells

SummaryPurified pancreatic Beta cells were labelled with 3H-tyrosine before studying their secretory activity in perifusion. At 1.4 mmol/l glucose, the cells released similar fractions (0.01% per min) of their contents in preformed and in newly formed insulin. At 20 mmol/l glucose plus 10−8 mol/l glucagon, these fractional release rates increased by 16 and 40-fold respectively. The preferential release of newly synthesized as compared to stored insulin is attributable to a heterogeneity in individual cell responses. The secretory responsiveness to glucose plus glucagon was completely suppressed by 10−7 mol/l clonidine. Insulin induced a 20% reduction at 10−6 mol/l, but remained without effect at 10−7 mol/l. Insulin-like growth factor-I provoked a 30% decrease at 5.10−9 mol/l. It is concluded that the type-I insulin-like growth factor receptors on pancreatic Beta cells mediate a suppressive action on the insulin release process. Their high affinity for insulin-like growth factor-I allows physiologic levels of this peptide to participate in the regulation of insulin release. Their low affinity for insulin provides the basis for a minor feedback action by this hormone at concentrations exceeding the normal circulating levels.

Cerebral gigantism (Sotos syndrome). Compiled data of 22 cases

An in depth study on growth, bone age, cranial CT scans and plasma somatomedin activity (SM-act) was made of 22 children with Sotos syndrome. In addition to the known characteristics of the syndrome, thin and brittle nails were found in three adolescent patients. The mean body stature, expressed as standard deviation score, increased from 2.2–2.8 in the 1st year of life, followed by a fall to 2.0 in the 2nd year. Thereafter the SDS increased slowly to values of 3.0 at 10 years of age. At least two subjects have reached an exceptionally tall final stature. After the age of 2 years, Δ SDS/year remained very stable (−0.1–0.2), concurring with growth velocities in the upper normal range. Bone age was advanced in all patients. Cranial CT scans showed ventricular widening, mid-line cava and Sylvian anomalies in nine, six, and three patients respectively. SM-act dropped from high or normal values in the 1st year, to below normal from 1–5 years, and returned thereafter to the lower half of normal or below the normal range.

Total Deficiency of Growth Hormone and Prolactin, and Partial Deficiency of Thyroid Stimulating Hormone in Two Dutch Families: a New Variant of Hereditary Pituitary Deficiency

Four out of 10 children in two unrelated families presented with a total pituitary growth hormone (GH) and prolactin deficiency and a partial thyrotropin (TSH) deficiency. The GH gene was intact in family I. The pituitaries, visualized by magnetic resonance imaging, were normal. All children responded well to GH and L-thyroxine therapy. Baseline plasma somatostatin and its peak response to arginine infusion were elevated in family I and they had a milder TSH deficiency than family II. Plasma insulin showed a poor response to arginine infusion. This hereditary combination of pituitary deficiencies suggests a deficiency of a common positive transcription factor.

Growth hormone treatment in Turner syndrome accelerates growth and skeletal maturation

Sixteen girls with Turner syndrome (TS) were treated for 4 years with biosynthetic growth hormone (GH). The dosage was 4IU/m2 body surface s.c. per day over the first 3 years. In the 4th year the dosage was increased to 61 U/m2 per day in the 6 girls with a poor height increment and in 1 girl oxandrolone was added. Ethinyl oestradiol was added after the age of 13. Mean (SD) growth velocities were 3.4 (0.9), 7.2 (1.7), 5.3 (1.3), 4.3 (2.0) and 3.6 (1.5) cm/year before and in the 1st, 2nd, 3rd and 4th year of treatment. Skeletal maturation advanced faster than usual in Turner patients especially in the youger children. Although the mean height prediction increased by 5.6 cm and 11 of the 16 girls have now exceeded their predicted height, the height of the 4 girls who stopped GH treatment exceeded the predicted adult height by only 0 to 3.4 cm.

Sex hormone profiles of premenarcheal athletes.

SummaryFemale gymnasts have a delayed onset and probably retarded progression of puberty. The aim of this study was to test the hypothesis that the delay in onset of puberty in gymnasts as compared to girl swimmers is modulated by a lower estrone level due to a smaller amount of body fat. The sex-hormone and gonadotropin levels of 46 gymnasts and 37 girl swimmers of the same biological maturation (breast development: M=1 or M=2) were studied. In each subject the following hormones were measured in plasma: estrone, 17-Β-estradiol, DHEAS, testosterone, androstenedione, LH, and FSH. In prepubertal children (M=1) the levels of estrone, testosterone, and androstenedione were lower in the gymnastic group as compared to the swimming group. In the early pubertal (M=2) gymnastic and swimming groups these hormone levels were no longer different. The other hormone levels were not significantly different in either the prepubertal groups or the early pubertal ones. Within the total prepubertal group there is a clear relationship between the estrone levels and the levels of testosterone and androstenedione, but not between estrone and 17-Β-estradiol, nor between the calculated fat mass and any of the hormone levels. It appears that the androstenedione and testosterone levels are responsible for the difference in estrone level, rather than the amount of body fat.

A Personal View on the Early History of the Insulin-Like Growth Factors

Salmon and Daughaday, when trying to set up an in vitro assay for Growth Hormone (GH), failed to obtain a direct effect on sulphate uptake in cartilage of hypophysectomized (hypox) rats. They recognisSalmon and Daughaday, when trying to set up an in vitro assay for Growth Hormone (GH), failed to obtain a direct effect on sulphate uptake in cartilage of hypophysectomized (hypox) rats. They recognised that this was not the consequence of poor methodology or materials, but an encrypted message from the examined system. They decided to turn around and to try and decipher it. Treatment with GH appeared to render hypox rat serum active in stimulating sulphation in hypox rat cartilage. They proposed that GH induced an intermediary substance, responsible for this biological effect: sulphation factor (SF), later renamed to Somatomedin(s) (SM). This hypothesis met with great criticism and very few took on to study this hypothetical substance. Besides disbelief, slow progress was also due to initial lack of a practical assay and to the failure to find a tissue with enriched concentration from which to extract the activity. From experimental evidence, the concept gradually evolved that SF/SM was insulin-like and might be identical to NSILA (non-suppressible insulin-like activity). This again generated controversy. This characteristic was too far away from the known effects of GH to be readily acceptable as a physiological phenomenon. The subsequent recognition of the distinct characteristics of the receptors for SM/NSILA and insulin, the discovery of the SM/NSILA binding proteins and, much later, a beginning understanding of their interactions, modifications and breakdown, have gradually resolved this apparent contradiction. When the sequence of two NSILA molecules became known, they were named IGF-I and -II. Structural similarity with proinsulin and identity of IGF-I with SM-C and -A were established and it was found that Multiplication Stimulating Activity (MSA), a growth factor isolated from fetal calf serum and subsequently from conditioned media of a rat liver cell line, was the rat equivalent of IGF-II. Structure-function relations could be studied, a quest which is not yet brought to an end. Meanwhile, the endocrine profile of SF/SM had gradually emerged by measuring plasma levels with bioassays. The main determinants were found to be age, body size, GH and the nutritional state. Later, radioimmunoassays were developed, enabling consolidation and detailing of these early observations, and allowing explorations at the tissue level. As another aspect of the endocrine paradigm, in vivo effects of IGFs were studied. The initial demonstration of an effect of crude preparations on longitudinal growth in experimental animals raised heavy scepticism, since the effect might have been an artefact caused by contaminants. It took confirmation with highly purified preparations and biosynthetic IGF-I to ease this concern. Still, not until recent years it was demonstrated, by knocking out the genes, that a true physiological and not a pharmacological effect had been induced previously.When it was found that most tissues produce SMs and are sensitive to their actions, the concept emerged that IGFs may have para- and autocrine functions. Early experiments with combinations of growth factors in cell cultures had begun to define their specific roles in the cell cycle as competence or progression factors. SM-C fell in the latter category. Still, the awareness grew that, for obtaining physiologically meaningful results on the role of IGFs in complex, dynamic and tissue-specific environments, involving interactions of many hormones and growth factors, the intactness of tissue was a prerequisite. One result of this approach was the discovery of a direct interaction of GH with cartilage, leading, in concert with IGFs, to a clonal expansion of the cartilage cells of the growth plate. The isolation and sequencing of the IGF-I and -II genes, and later, of six IFG-BPs initiated the gradual elucidation of structure and function at the DNA and RNA level and the study of natural and synthetic IGF-variants. The generation of transgenic animals became feasible and detailed studies at the tissue level were now possible. In situ hybridisation as well as immunohistochemistry have generated intriguing descriptions of the sequence and location of expression of IGFs, IGFBPs and other growth factors in pre- and postnatal life. These and many subsequent in vivo and in vitro studies in experimental animals and man have yielded much insight in the specific roles of the IGFs and their BPs. Hitherto, the IGFs have been quite relevant for understanding growth. Though they have an important role in diagnosing growth disorders, they have found but a modest use in treatment. This is perhaps not surprising, enclosed as they are in an intricate, time-, development- and tissue-specific network of other factors.