Extracellular signal-regulated protein kinase activation is required for the anti-hypertrophic effect of atrial natriuretic factor in neonatal rat ventricular myocytes

Atrial natriuretic factor (ANF) inhibits proliferation in non-myocardial cells and is thought to be anti-hypertrophic in cardiomyocytes. We investigated the possibility that the anti-hypertrophic actions of ANF involved the mitogen-activated protein kinase signal transduction cascade. Cultured neonatal rat ventricular myocytes treated for 48 h with the alpha(1)-adrenergic agonist phenylephrine (PE) had an 80% increase in cross-sectional area (CSA). ANF alone had no effect but inhibited PE-induced increases in CSA by approximately 50%. The mitogen-activated protein kinase/ERK kinase (MEK) inhibitor PD098059 minimally inhibited PE-induced increases in CSA, but it completely abolished ANF-induced inhibition of PE-induced increases. ANF-induced extracellular signal-regulated protein kinase (ERK) nuclear translocation was also eliminated by PD098059. ANF treatment caused MEK phosphorylation and activation but failed to activate any of the Raf isoforms. ANF induced a rapid increase in ERK phosphorylation and in vitro kinase activity. PE also increased ERK activity, and the combined effect of ANF and PE appeared to be additive. ANF-induced ERK phosphorylation was eliminated by PD098059. ANF induced minimal phosphorylation of JNK or p38, indicating that its effect on ERK was specific. ANF-induced activation of ERK was mimicked by cGMP analogs, suggesting that ANF-induced ERK activation involves the guanylyl cyclase activity of the ANF receptor. These data suggest that there is an important linkage between cGMP signaling and the mitogen-activated protein kinase cascade and that selective ANF activation of ERK is required for the anti-hypertrophic action of ANF. Thus, ANF expression might function as the natural defense of the heart against maladaptive hypertrophy through its ability to activate ERK.

Assisted feeding is more reliable for infants with clefts--a randomized trial

OBJECTIVE

To compare the effectiveness of squeezable and rigid feeding bottles for infants with clefts.

DESIGN

Patients were randomly assigned at birth to feeding with a squeezable bottle (assisted feeding) or to feeding with a rigid bottle and were followed for 1 year. The data were analyzed on the basis of intention to treat.

SETTING

The trial was conducted within the existing arrangements for hospital and home care for children with clefts within the National Health Service in the north of England.

PATIENTS

The patients were 101 consecutively born children with cleft lip and/or palate who were otherwise healthy. All patients completed the trial. Two were excluded from the analysis when unrelated developmental problems became apparent.

MAIN OUTCOME MEASURES

Anthropometric measures-nude weight, crown-heel length (CHL), and occipito-frontal circumference (OFC)-were recorded.

RESULTS

There were statistically significant differences between the two groups in weight at 12 months (p = .038, with an adjusted mean difference of 0.43 kg) and in head circumference (p = .004 with an adjusted mean difference of 0.77 cm), indicating increased growth in the squeezable bottle group. The difference in CHL was not significant at conventional levels (p = .082). Whereas 25 of 52 (48%) rigid bottles required modification by the health visitor, this was needed for only 4 of 49 (8%) squeezable bottles. There was a highly significant difference when numbers of modifications for each method were compared (p < .0001). Despite modifications, six infants feeding with a rigid bottle (11%) were transferred to a squeezable bottle due to problems with feeding, but none were transferred from squeezable to rigid bottles. Thus, the squeezable bottle generally appeared to be a more satisfactory method, requiring less support or intervention after initial instruction.

CONCLUSIONS

Both feeding methods achieved similar anthropometric outcomes, with a beneficial effect on head circumference and weight in the assisted feeding group. We recommend that this last observation be treated with caution. The squeezable bottles were easier to use, and we recommend that they be routinely prescribed.

Fertility impairment in granulocyte-macrophage colony-stimulating factor-deficient mice

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been identified as a potentially important mediator of intercellular communication in the female reproductive tract, with principal target cells being the large populations of myeloid leukocytes in the cycling and pregnant uterus, the preimplantation embryo, and trophoblast cells of the developing placenta. To determine the physiological significance of this cytokine in reproduction, the fertility of genetically GM-CSF-deficient (GM-/-) mice was examined. Implantation rates were normal in GM-/- mice, and viable pups were produced. However, the mean litter sizes of GM-/- x GM-/- breeding pairs were 25% smaller at weaning than those of GM+/- x GM+/- pairs, due to fetal death late in gestation and early in postnatal life, with a disproportionate loss of male pups. On Day 17 of pregnancy, the mean number of resorbing and malformed fetuses was twice as high in pregnant GM-/- females (21%, vs. 11% in GM+/- females); the mean fetal weight and the mean fetal:placental ratio in surviving conceptuses were diminished by 7% and 6%, respectively; and the number of very small fetuses (< 500 mg) was 9-times as high (23% vs. 2.5%). Mortality during the first 3 wk of life was 4.5-times as high in pups born to GM-/- mothers (9%, vs. 2% in GM+/- females), and diminished size persisted in GM-/- pups, particularly males, into adulthood. The detrimental effect of maternal GM-CSF deficiency was less apparent when GM-/- females were mated with GM+/+ males; litter sizes at birth and at weaning were not significantly smaller than in GM+/- matings, and fetal weights and fetal:placental ratios were also comparable. When polymerase chain reaction was used to genotype embryonic tissue in heterozygote matings, GM-/- fetuses from GM-/- females were found to be smaller than their GM+/- littermates and smaller than GM-/- fetuses gestated in GM+/- females. The size and distribution of uterine granulocyte and macrophage populations were normal during the estrous cycle, during early pregnancy, and in midgestation. Analysis of placental structure revealed that the ratio of labyrinthine to spongiotrophoblast areas was reduced by approximately 28% in GM-/- placentae, and the proportion of vacuolated trophoblast "glycogen cells" in the spongiotrophoblast layer was diminished. Compromised placental function as a result of subtle developmental aberrations may therefore partially account for embryonic growth retardation in GM-CSF-deficient mice. Collectively, these studies show that fetal growth and viability are jeopardized in the absence of maternal GM-CSF. The detrimental effects are most clearly evident when the conceptus is also GM-CSF deficient, suggesting that GM-CSF of either maternal or fetal origin is required for optimal growth and survival of the fetus in mice.

Interaction in vitro of the product of the c-Crk-II proto-oncogene with the insulin-like growth factor I receptor

The Crk proto-oncogene product is an SH2 and SH3 domain-containing adaptor protein. We have previously demonstrated that Crk-II becomes rapidly tyrosine-phosphorylated in response to stimulation with insulin-like growth factor I (IGF-I) and might be involved in the IGF-I receptor signalling pathway. To determine whether this involvement includes the direct interaction of Crk-II with the cytoplasmic region of the receptor, studies were performed in vitro with glutathione S-transferase (GST) fusion proteins containing various domains of Crk-II. The kinase assay in vitro showed that activated IGF-I receptors efficiently phosphorylated the GST-Crk-II fusion protein. This phosphorylation was dependent on the presence of the SH2 domain and Tyr-221 located in the spacer region between the two SH3 domains. Mutation of Tyr-221 not only prevented phosphorylation of GST-Crk in vitro, but also significantly increased the ability of GST-Crk proteins to co-precipitate activated IGF-I receptors from total cell lysates. Additional binding experiments in vitro showed that Crk-II might interact with the phosphorylated IGF-I receptor through its SH2 domain. To elucidate which region of the IGF-I receptor interacts with Crk-II, a peptide association assay was used in vitro. Different domains of the IGF-I receptor were expressed as (His)6-tagged fusion peptides, phosphorylated with activated wheat germ agglutinin-purified IGF-I receptors and tested for association with GST-Crk-II fusion proteins. Using wild-type as well as mutated peptides, we showed that the SH2 domain of Crk-II preferentially binds the peptide encoding the juxtamembrane region of the IGF-I receptor. Phosphorylation of Tyr-950 and Tyr-943 of the receptor is important for this interaction. These findings allow us to propose a model of direct interaction of Crk-II and the IGF-I receptor in vivo. On activation of the IGF-I receptor, Crk-II binds to phosphorylated tyrosine residues, especially in the juxtamembrane region. As a result of this binding, the IGF-I receptor kinase phosphorylates Tyr-221 of Crk-II, resulting in a change in intramolecular folding and binding of the SH2 domain to the phosphorylated Tyr-221, which causes rapid disassociation of the Crk-II-IGF-I receptor complex.

Food restriction alters pregnancy-associated changes in IGF and IGFBP in the guinea pig

The effect of moderate food restriction on pregnancy-associated changes in weight gain, body composition, and circulating insulin-like growth factors (IGF) I and II and IGF-binding proteins (IGFBP)-1 through-4 and their relationship was determined in the guinea pig. Pregnancy did not stimulate weight gain but reduced fat deposition in ad libitum-fed animals and increased weight gain and fat deposition in food-restricted animals relative to their respective virginal group. Pregnancy increased the abundance of circulating IGF-I regardless of food intake and increased that of IGF-II in food-restricted animals only. Pregnancy also increased circulating IGFBP-1 and -2 in ad libitum-fed and food-restricted animals and IGFBP-4 in ad libitum-fed animals. Multiple regression analysis showed that maternal weight gain was negatively associated with circulating IGF-II and IGFBP-2. Fetal weight was positively associated with maternal circulating IGF-II and negatively associated with maternal circulating IGFBP-1 and -2. Significant interactions indicate, however, that the role of IGF-II and IGFBP-1 on fetal growth is dependent on the nutritional status of the mother.

Differential expression of renal growth hormone receptor and its binding protein in experimental diabetes mellitus

Growth hormone (GH) may have a role in the development of diabetic nephropathy. The effect of experimental diabetes on renal expression of the growth hormone receptor gene products, including the receptor itself (GHR) and its binding protein (GHBP) was examined. Adult female rats received i.v. streptozotocin and were killed at 7, 30, 90 and 180 days after the induction of diabetes. Diabetic animals had a pronounced increase in kidney weight and progressive albuminuria. In renal cortex, no change was seen in GHR mRNA levels throughout the observation period of 6 months, while a significant increase in cortical GHBP mRNA levels was observed after 1 month of diabetes and sustained for the rest of the study period. Immunohistochemical analysis of kidney sections revealed a stronger staining for GHBP at the cortical and inner medullary areas in the diabetic animals. These data indicate that although the GHR and GHBP mRNAs originate from the same gene, their renal levels are differentially regulated during the development of experimental diabetic kidney disease, suggesting a functional role for GHBP.

Identification of a family of low-affinity insulin-like growth factor binding proteins (IGFBPs): characterization of connective tissue growth factor as a member of the IGFBP superfamily

The insulin-like growth factor (IGF) binding proteins (IGFBPs) modulate the actions of the insulin-like growth factors in endocrine, paracrine, and autocrine settings. Additionally, some IGFBPs appear to exhibit biological effects that are IGF independent. The six high-affinity IGFBPs that have been characterized to date exhibit 40-60% amino acid sequence identity overall, with the most conserved sequences in their NH2 and COOH termini. We have recently demonstrated that the product of the mac25/IGFBP-7 gene, which shows significant conservation in the NH2 terminus, including an "IGFBP motif' (GCGCCXXC), exhibits low-affinity IGF binding. The closely related mammalian genes connective tissue growth factor (CTGF) gene, nov, and cyr61 encode secreted proteins that also contain the conserved sequences and IGFBP motifs in their NH2 termini. To ascertain if these genes, along with mac25/IGFBP-7, encode a family of low-affinity IGFBPs, we assessed the IGF binding characteristics of recombinant human CTGF (rhCTGF). The ability of baculovirus-synthesized rhCTGF to bind IGFs was demonstrated by Western ligand blotting, affinity cross-linking, and competitive affinity binding assays using 125I-labeled IGF-I or IGF-II and unlabeled IGFs. CTGF, like mac25/IGFBP-7, specifically binds IGFs, although with relatively low affinity. On the basis of these data, we propose that CTGF represents another member of the IGFBP family (IGFBP-8) and that the CTGF gene, mac25/IGFBP-7, nov, and cyr61 are members of a family of low-affinity IGFBP genes. These genes, along with those encoding the high-affinity IGFBPs 1-6, together constitute an IGFBP superfamily whose products function in IGF-dependent or IGF-independent modes to regulate normal and neoplastic cell growth.

Altered expression of the WT1 wilms tumor suppressor gene in human breast cancer

The product of the WT1 Wilms tumor suppressor gene controls the expression of genes encoding components of the insulin-like growth factor and transforming growth factor beta signaling systems. The role of these growth factors in breast tumor growth led us to investigate possible WT1 gene expression in normal and cancerous breast tissue. WT1 was detected by immunohistochemistry in the normal mammary duct and lobule, and the patterns of expression were consistent with developmental regulation. In a survey of 21 infiltrating tumors, 40% lacked immunodetectable WT1 altogether and an additional 28% were primarily WT1-negative. Cytoplasmic, but not nuclear, localization of WT1 was noted in some tumor cells and WT1 was detected, sometimes at high levels, in more-advanced estrogen-receptor-negative tumors. In this highly malignant subset, the tumor suppressor protein p53, which can physically interact with WT1, was also sometimes detected. WT1 mRNA was detected in normal and tumor tissue by reverse transcription-coupled PCR. Alternative splicing of the WT1 mRNA may regulate gene targeting of the WT1 protein through changes either in its regulatory or zinc-finger domains. The relative proportions of WT1 mRNA splice variants were altered in a random sample of breast tumors, providing evidence that different tumors may share a common WT1-related defect resulting in altered regulation of target genes.

Autonomic control of the pulmonary surfactant system and lung compliance in the lizard

An increase in body temperature in the bearded dragon, Pogona vitticeps, is accompanied by an increase in the amount of pulmonary surfactant, a mixture of proteins and lipids, with the latter consisting predominantly of phospholipid and cholesterol. This increase may result from a temperature-induced change in autonomic input to the lungs, as perfusing the isolated lungs of P. vitticeps with either acetylcholine or adrenaline increases surfactant phospholipid release. However, whether acetylcholine acts via intrapulmonary sympathetic ganglia or directly on alveolar Type II cells is unknown. Moreover, the relative importance of circulating catecholamines and pulmonary sympathetic nerves on the control of the surfactant system is also obscure. Here, we describe the mechanism of the modulation of the surfactant system and the effect of this modulation on lung compliance. The role of acetylcholine was determined by perfusing isolated lungs with acetylcholine, acetylcholine and the ganglionic antagonist hexamethonium, or acetylcholine, hexamethonium, and the muscarinic antagonist atropine. Perfusing with acetylcholine significantly increased phospholipid release but did not affect cholesterol release. While histological examination of the lung revealed the presence of a large autonomic ganglion at the apex, blocking sympathetic ganglia with hexamethonium did not prevent the acetylcholine-mediated increase in phospholipid. However, the increase was inhibited by blocking muscarinic receptors with atropine, which indicates that acetylcholine acts on muscarinic receptors to stimulate phospholipid release. By increasing pulmonary smooth muscle tone, acetylcholine decreased opening pressure and increased static inflation pressures. Plasma levels of noradrenaline and adrenaline increased with increasing temperature and were accompanied by a greater surfactant content in the lungs. While surfactant content was also higher in animals that exercised, plasma levels of adrenaline, noradrenaline, and dopamine were not elevated following exercise. Hence, surfactant release in the lizard lung may increase in response to an increase in plasma catecholamine levels. Acetylcholine, and hence the parasympathetic nervous system, may act to stimulate surfactant release but does not act via pulmonary sympathetic ganglia. We conclude that promoting surfactant secretion via an increase in circulating catecholamines may be inappropriate for a cold lizard with a requirement to conserve energy. As body temperature decreases, release of surfactant via nonadrenergic mechanisms, including cholinergic stimulation, may become increasingly important.

Decreased expression of Wilms' tumor gene WT-1 and elevated expression of insulin growth factor-II (IGF-II) and type 1 IGF receptor genes in prostatic stromal cells from patients with benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a common proliferative disorder of unknown etiology. We have previously documented that the insulin-like growth factor (IGF) axis is critical for prostate cell growth and is abnormal in BPH. The type 1 IGF receptor (IGF-1R) is constitutively expressed by most body tissues and plays a significant role in regulating cell proliferation, consistent with the role of its ligands (IGF-I and IGF-II) as important mitogenic factors. The Wilms' tumor gene product (WT-1) is a tumor suppressor that has been shown to be altered in rare kidney tumors and is known to regulate IGF-II and IGF-1R. We investigated the possibility that the expression of prostatic WT-1, IGF-1R, and IGF-II genes is altered in patients with BPH. We utilized primary cultures of prostatic stromal cells grown from normal (n = 9) and hyperplastic (n = 9) surgical specimens and analyzed WT-1, IGF-1R, and IGF-II messenger RNA levels. In all of the BPH cell strains, WT-1 expression (measured by RT-PCR and RNase protection assays) was strikingly lower than that found in normal strains (0-20% of normal, mean 14% of normal, P < 0.01). The expression of both the IGF-1R (300% of normal, P < 0.05) and IGF-II (1000% of normal, P < 0.01) messenger RNAs was higher in BPH strains as compared with normal strains. No changes were seen in stromal cell strains derived from prostatic adenocarcinoma. Thus, in cultured human prostatic stromal cell strains from patients with BPH, decreased WT-1 gene expression is associated with increases in the expression of the IGF-1R and IGF-II genes that are known transcriptional targets of WT-1. These findings indicate that reduced expression of the WT-1 tumor suppressor gene and elevated IGF-1R and IGF-II gene expression may be involved in the pathophysiology of prostatic hyperplasia, implying a new role for the Wilms' tumor gene in nonmalignant states.

Antiserum to the egg coats of the fat-tailed dunnart (Marsupialia, Dasyuridae) cross-reacts with egg coats of other marsupial and eutherian species

We are examining the extracellular coats of the brush-tailed possum as a possible target for an immunocontraceptive vaccine for biocontrol of this pest species in New Zealand. In this study we have compared the composition of the extracellular coats of the fat-tailed and stripe-faced dunnarts, brush-tailed possum, domestic rabbit, and laboratory mouse using histochemistry, immunocytochemistry, and immunofluorescence. The histochemistry of the luminal epithelium of the oviduct and mucoid coats of the marsupials and rabbit indicated that they contain acidic glycoproteins. Immunofluorescence showed that polyclonal antiserum raised against the extracellular coats of the oocyte and early embryo of the fat-tailed dunnart, cross-reacted with the extracellular coats of the oocytes of all five species. These results suggest that there are common epitopes on the extracellular coats of oocytes and early embryos of distinctly related therian species. Further work to characterise these proteins is required to determine whether there is close homology between the oviductal glycoproteins of these species.

Differential regulation of insulin-like growth factor-I (IGF-I) receptor gene expression by IGF-I and basic fibroblastic growth factor

Insulin-like growth factor-I receptor (IGF-IR) gene expression is regulated by various stimuli, including hormones, growth factors, and nutritional status. We have investigated the molecular mechanism by which two growth factors, insulin-like growth factor-I (IGF-I) and basic fibroblast growth factor (bFGF) regulate IGF-IR gene expression. bFGF increases the endogenous IGF-IR mRNA levels and IGF-IR promoter activity. This effect is mediated by a region of the IGF-IR promoter located between nucleotides -476 and -188 in the 5'-flanking region. In contrast, IGF-I decreases the IGF-IR mRNA levels. IGF-I down-regulates IGF-IR transcriptional activity as deduced from experiments in which the levels of pre-mRNA and mRNA were measured. IGF-I reduced pre-mRNA and mRNA levels in parallel, while the mRNA stability was found to be unchanged by IGF-I treatment. While these results strongly suggest an effect of IGF-I on IGF-IR transcriptional activity, no specific IGF-I response element was demonstrated in the 5'-untranslated region or 5'-flanking region studied. Thus, bFGF and IGF-I have differential effects on IGF-IR gene transcription, with the IGF-I response region as yet unidentified.

A reference cross DNA panel for zebrafish (Danio rerio) anchored with simple sequence length polymorphisms

The ultimate informativeness of the zebrafish mutations described in this issue will rest in part on the ability to clone these genes. However, the genetic infrastructure required for the positional cloning in zebrafish is still in its infancy. Here we report a reference cross panel of DNA, consisting of 520 F2 progeny (1040 meioses) that has been anchored to a zebrafish genetic linkage map by 102 simple sequence length polymorphisms. This reference cross DNA provides: (1) a panel of DNA from the cross that was used to construct the genetic linkage map, upon which polymorphic gene(s) and genetic markers can be mapped; (2) a fine order mapping tool, with a maximum resolution of 0.1 cM; and (3) a foundation for the development of a physical map (an ordered array of clones each containing a known portion of the genome). This reference cross DNA will serve as a resource enabling investigators to relate genes or genetic markers directly to a single genetic linkage map and avoid the problem of integrating different maps with different genetic markers, as must be currently done when using randomly amplified polymorphic DNA markers, or as has occurred with human genetic linkage maps.

Control of insulin-like growth factor (IGF) action by regulation of IGF-I receptor expression

The insulin-like growth factors (IGFs) control many aspects of growth, development and differentiation, and aberrant IGF action is implicated in a number of pathological states. Most of the actions of both IGF-I and IGF-II are mediated by their activation of the IGF-I receptor, a transmembrane tyrosine kinase that is structurally and functionally related to the insulin receptor. Control of the IGF-I receptor number at the cell surface is an important level at which IGF action can be regulated. Cell-surface receptor number, in turn, is principally determined by the level of expression of the IGF-I receptor gene. An important transcriptional regulatory factor that appears to be responsible for controlling IGF-I receptor gene expression is the product of the WT1 Wilms tumor suppressor gene. This latter protein functions by binding to specific sequences in the IGF-I receptor promoter and repressing transcription. During normal renal development, increased expression of the WT1 gene leads to repression of IGF-I receptor gene expression, allowing differentiation of the metanephrogenic blastema into renal epithelium. Persistent receptor expression due to mutational loss of WT1 function may contribute to the etiology of Wilms tumor. Decreased WT1 expression and subsequent up-regulation of the IGF-I receptor has also been implicated in non-malignant proliferative disorders such as benign prostatic hyperplasia.

Lack of association of trinucleotide repeat polymorphisms in very-low-density lipoprotein receptor gene with Alzheimer's disease

Inheritance of the apolipoprotein E epsilon 4 allele is a risk factor for Alzheimer's disease (AD). A recent report studying Japanese patients suggested that a polymorphism of a trinucleotide repeat in the 5' untranslated region of an apolipoprotein E receptor, the very-low-density lipoprotein receptor, is genetically associated with AD, with overrepresentation of the allele containing five copies of the repeat. We determined the allele frequencies of the very-low-density lipoprotein receptor in 3 white populations totaling 469 individuals. In contrast to the previous report, we found no differences in allele frequencies between case patients and control subjects. The discrepancy could be due to differences in Japanese and white populations. Nonetheless, these data weaken the likelihood that this polymorphism in the very-low-density lipoprotein receptor gene is strongly associated with AD.

Regulation of insulin-like growth factor I receptor gene expression by the Wilms' tumor suppressor WT1

THe insulin-like growth factor I receptor (IGF-I-R) has been implicated in the etiology and/or progression of Wilms' tumor, or nephroblastoma, a pediatric neoplasm of the kidney that is often associated with deletion or mutation of the WT1 tumor suppressor gene. The levels of IGF-I-R mRNA in the tumors were sixfold higher than in normal adjacent kidney tissue and were inversely correlated to the levels of WT1 mRNA, suggesting that the expression of the IGF-I-R gene is under inhibitory control by WT1. Cotransfection of an IGF-I-R promoter-luciferase reporter construct together with a WT1 expression vector resulted in a dose-dependent suppression of promoter activity. Multiple WT1 binding sites were mapped in the 5'-flanking and 5'-untranslated regions of the IGF-I-R gene using gel retardation and DNaseI footprinting assays. Thus, suppression of the IGF-I-R promoter by WT1 involves multiple interactions of its zinc finger domain with sites located both upstream and downstream of the transcription initiation site. Finally, we showed that expression of the endogenous IGF-I-R gene is decreased in G401 cells stably transfected with a WT1 expression vector. Reduction in expression of the IGF-I-R gene is associated with a decrease in a number of IGF-I-mediated biological effects. Thus, deletion or mutation of the WT1 gene in Wilms' tumor and other malignancies can result in overexpression of the receptor, with enhanced autocrine/paracrine activation by locally produced or circulating IGFs.

Effect of hypoxia on lung, heart, and liver insulin-like growth factor-I gene and receptor expression in the newborn rat

OBJECTIVES

We examined the effect of 7 days of hypoxia in the newborn rat on: a) body, heart, and lung growth; b) circulating insulin-like growth factor-I (IGF-I); c) lung, heart, and liver IGF-I gene expression; and d) lung IGF-I type 1 receptor gene expression and IGF-I receptor binding. We hypothesize that hypoxic exposure would modify body and organ growth and alter IGF-I gene and receptor expression in an organ specific manner.

DESIGN

Randomized, controlled prospective study.

SETTING

University research laboratory.

SUBJECTS

Eleven newborn rat litters (n = 10 per litter) comprised the hypoxia-exposed group and 11 litters comprised the control group (room air).

INTERVENTIONS

Hypoxia-group rats were placed in a chamber with an FIO2 of 0.12 on postnatal day 1. Control group rats breathed room air. Exposure to hypoxia continued for 7 days.

MEASUREMENTS AND MAIN RESULTS

Hepatic, lung, and cardiac IGF-I mRNA levels and lung IGF-I type 1 receptor mRNA were analyzed, using the ribonuclease protection assay. Crude membrane extracts were used for competitive binding studies with IGF-I and insulin. Somatic growth in the hypoxic group was reduced by 22% (final weight: hypoxic, 14.8 +/- 1.2 g; control, 17.1 +/- 1.5 g; p < .001). The relative weight (organ weight/body weight [mg/g]) of the heart was increased by 39% (p < .001) in the hypoxic pups compared with the normoxic animals, while the relative weight of the lung was unchanged. With hypoxia, IFG-I mRNA concentrations were significantly increased both in the heart and lung (30% and 33%, respectively, p < .02); but, in contrast, IGF-I mRNA concentrations were not significantly different in the liver. The IGF-I receptor mRNA in the lung was increased by 200% (p < .02) in hypoxia compared with controls. There was no effect of hypoxia on specific or nonspecific binding of IGF-I or insulin in the lung tissue. However, specific binding was 33% greater in the IGF-I compared with the insulin experiments.

CONCLUSIONS

a) Hypoxia increased IGF-I mRNA in the heart, and increased both IGF-I mRNA and IGF-I type 1 receptor mRNA in the lung. b) The effects of hypoxia on IFG-I are tissue-specific.

Nutritional regulation of insulin-like growth factor-I receptor mRNA levels in growing chickens

Insulin-like growth factor-I (IGF-I) exerts its effect through the IGF-I receptor. To investigate the effects of nutritional status on chicken IGF-I receptor gene expression, a solution hybridization/RNase protection assay for IGF-I receptor mRNA was developed. A cDNA clone corresponding to the carboxyl-terminal region of the IGF-I receptor was obtained by reverse transcription-PCR (RT-PCR). Sequence analysis of the clone showed that this region of the chicken IGF-I receptor is highly divergent from the human IGF-I receptor. IGF-I receptor mRNA was detected in all tissues examined from newly hatched chickens. The rank order of the IGF-I receptor mRNA levels was liver < thigh muscle < stomach < heart < lung < kidney < brain. In 1-week-old chickens, 5 days of starvation caused a 2.5- to 3-fold increase in the mRNA in muscle and kidney. Starvation of 4-week-old chickens for 5 days caused a 1.7 to 2.2-fold increase in IGF-I receptor mRNA levels in kidney, liver, and muscle. In contrast, IGF-I receptor mRNA levels in brain failed to change. The mRNA levels were reduced to the control level by refeeding of the starved chickens for 24h. These data suggest a tissue- and development-specific response of chicken IGF-I receptor gene expression to nutritional status.

Involution of the lactating mammary gland is inhibited by the IGF system in a transgenic mouse model

Development of the mammary gland during puberty, pregnancy, and lactation is controlled by steroid and peptide hormones and growth factors. To determine the role of the insulin-like growth factors (IGFs) in this process we developed a transgenic model using the whey acidic protein (WAP) gene to direct expression of rat IGF-I and human IGF binding protein-3 (IGFBP-3) to mammary tissue during late pregnancy and throughout lactation. High levels of expression of transgenic IGF-I and IGFBP-3 were seen in lobular-alveolar cells by in situ hybridization. There was no obvious effect on mammary development during pregnancy and lactation; indeed, mothers were capable of nursing their pups normally and the only structural difference seen in the mammary glands at peak lactation was an overall smaller size of the alveoli. We also evaluated the role of IGF-I and IGFBP-3 in the remodeling of mammary tissue during involution. Compared with control animals, the process of involution was modified in both transgenic lines. The degree of apoptotic cells was lower in the WAP-IGF-I and WAP-BP-3 expressing mice. In addition, there was a more quiescent pattern of involution with residual lobular secretary ability and a muted host inflammatory reaction with fewer lumenal microcalcifications. These results demonstrate that IGF-I and IGFBP-3 may modulate the involutionary process of the lactating mammary gland.

The marsupial shell membrane: an ultrastructural and immunogold localization study

In the dasyurid marsupial, Sminthopsis crassicaudata, as the oocytes/embryos travel down the female reproductive tract two extracellular coats, the mucoid and shell membrane, come to surround them. Embryos recovered from the oviduct have a mucoid coat but no shell membrane which is only found surrounding uterine embryos. Initially, the shell membrane has a compact granular consistency but it later thins and becomes fibrous in texture with fibres oriented mainly in the plane of the membrane. Immunogold labelling with polyclonal antibodies raised against the extracellular coats was employed to determine the location and ultrastructural appearance of the secretory granules which contain mucoid and shell membrane precursors. Secretory granules in the luminal epithelium of the ampulla of the oviduct are of irregular electron density, while those in the isthmus are electron-dense and homogeneous. Both types give rise to the mucoid coat. Secretory granules in the epithelia of the utero-tubal junction and some endometrial glands are electron-lucent and contain some flocculent material which, after exocytosis, gives rise to the shell membrane.

Interaction between the insulin receptor and its downstream effectors. Use of individually expressed receptor domains for structure/function analysis

A structural analysis has been carried out to determine which part of the intracellular domain of the insulin receptor (IR) beta subunit is involved in direct interaction with the receptor substrates IRS-1 and Shc. Toward this end, the juxtamembrane (JM) domain (amino acids 943-984) and the carboxyl-terminal (CT) region (amino acids 1245-1 331) of IR were expressed in bacteria as (His)6-fusion peptides, and their interaction with IRS-1 and Shc was studied. We could demonstrate that the CT region of IR was sufficient to bind Shc, although significant, but much lower binding of Shc to the JM region could be detected as well. Furthermore, in vitro Tyr phosphorylation of the CT region potentiated its interactions with Shc 2-fold. In contrast, the JM region, but not the CT domain of the IR, was sufficient to mediate interactions between the IR and IRS-1. These interactions did not involve the pleckstrin homology (PH) region of IRS-1, since an IRS-1 mutant, in which four "blocks" of the PH domain (Pro5-Pro65) were deleted, interacted with the JM region of IR with the same efficiency as native IRS-1. These results suggest that the IR interacts with its downstream effectors through distinct receptor regions, and that autophosphorylation of Tyr residues located at the CT domain of the IR can modulate these interactions.

Stimulation of endometrial cancer cell growth by tamoxifen is associated with increased insulin-like growth factor (IGF)-I induced tyrosine phosphorylation and reduction in IGF binding proteins

A significant increase in endometrial cancer incidence in tamoxifen-treated breast cancer patients has been reported in many recent studies. The major growth stimulators of endometrial tumors are estrogens, but paradoxically, tamoxifen, a known antiestrogen, also stimulates their growth. The mode of action of estrogen can be partially explained by the modulation of insulin-like growth factor (IGF) autocrine or paracrine action. The purpose of the present study was to examine the involvement of the IGF system in the tamoxifen-stimulated growth of Ishikawa endometrial cancer cells by quantitating the IGF-I receptors and their phosphorylation, as well as membrane associated and secreted IGF-binding proteins (IGFBPs). Tamoxifen did not affect the number or affinity of IGF-I receptors. On the other hand, tamoxifen, similar to estradiol, increased IGF-I-stimulated tyrosine phosphorylation of cellular substrates. In contrast, in MCF-7 mammary cancer cells, tamoxifen reduced IGF-induced tyrosine phosphorylation in the presence of estradiol. The pure antiestrogen LY156758 did not affect Ishikawa basal cell growth but inhibited estradiol- and tamoxifen-induced growth. Growth inhibition by LY156758 of tamoxifen and estradiol-stimulated cells was accompanied by a corresponding inhibition of IGF-stimulated tyrosine phosphorylation. Tamoxifen caused a 3-fold decrease in membrane-associated IGFBPs. Moreover, a reduction in soluble IGFBPs was also observed, making the IGF peptides more available to the receptors. A parallel decrease in IGFBP-3 mRNA was also detected. These experiments suggest that tamoxifen, like estradiol, directly sensitizes endometrial cancer cells to the effects of IGFs that act through the type I receptor. Furthermore, the decrease in IGFBPs and the increase in tyrosine phosphorylation in the presence of tamoxifen provides a molecular mechanism that accounts for the uterotropic effects that are seen with tamoxifen therapy.

Growth hormone (GH) status regulates GH receptor and GH binding protein mRNA in a tissue- and transcript-specific manner but has no effect on insulin-like growth factor-I receptor mRNA in the rat

The effect of growth hormone-deficiency (GHD) and treatment with recombinant bovine GH (bGH) or human IGF-I (hIGF-I) for 10 days on the expression of GH receptor (GHR), GH binding protein (GHBP) and of insulin-like growth factor-I receptor (IGF-IR) mRNA was examined using dw/dw and normal Lewis rats. Hepatic GHR and GHBP mRNA expression was significantly lower in dw/dw rats in comparison to Lewis rats (P < 0.01) while specific 125I-bGH binding to hepatic microsomal membranes was significantly higher (P < 0.01), suggesting a reduction in hepatic GHR turnover with GHD. Treatment with bGH reduced hepatic specific 125I-bGH binding in dw/dw rats, but had no effect in Lewis rats. Treatment with hIGF-I increased hepatic specific 125I-bGH binding in Lewis rats. Hepatic GHR and GHBP mRNA expression was not changed by bGH or hIGF-I treatment, suggesting that differences in hepatic specific 125I-bGH binding may be due to posttranscriptional mechanisms. GHBP mRNA expression was higher in kidney, heart, and muscle of dw/dw rats in comparison to Lewis rats (P < 0.01), while GHR mRNA abundance was not changed. Treatment of dw/dw rats with hIGF-I or bGH resulted in a coordinate reduction of GHR and GHBP mRNAs in kidney (P < 0.01). IGF-IR mRNA was not detected in liver and despite reduced plasma IGF-I levels and IGF-I mRNA expression IGF-IR mRNA abundance was not changed in nonhepatic tissues by GHD. Our data suggest that changes in plasma IGF-I levels and local IGF-I mRNA do not influence IGF-IR mRNA expression, while GHR and GHBP mRNA expression in different rat tissues are regulated independently. The increased nonhepatic GHBP mRNA expression with GHD suggests that nonhepatic GHBP may have an important physiological function distinct from that of GHBP in liver or in plasma.

Tumorigenic and mitogenic capacities are reduced in transfected fibroblasts expressing mutant insulin-like growth factor (IGF)-I receptors. The role of tyrosine residues 1250, 1251, and 1316 in the carboxy-terminus of the IGF-I receptor

Regulation of ligand-mediated signal transduction through transmembrane tyrosine kinase growth factor receptors involves phosphorylation of tyrosine residues in the intracellular domain of the receptor. The insulin-like growth factor-I (IGF-I) receptor contains three tyrosine residues in the carboxy-terminal domain at positions 1250, 1251, and 1316. Of these, only the tyrosine at position 1316 is conserved in the homologous position of the insulin receptor. Mutational analysis was used to study the role of these tyrosines in specific outcomes of IGF-I-mediated signal transduction. Mutations in the human IGF-I receptor were either replacement of tyrosines 1250 and 1251 with phenylalanine and histidine (yyFH), respectively, or replacement of the conserved distal tyrosine (position 1316) with phenylalanine (yCF). The yyFH mutation results in an IGF-I receptor with the amino acids found in the homologous position of the human insulin receptor. Cells overexpressing mutated IGF-I receptors were compared with cells expressing only endogenous IGF-I receptors or overexpressing wild-type IGF-I receptors. The ability of yyFH mutant IGF-I receptors to autophosphorylate the beta-subunit or phosphorylate insulin receptor substrate-1 was not significantly different from wild-type type IGF-I receptors. However, one or both of the proximal tyrosine residues (positions 1250 and 1251) in the carboxy-terminus of the IGF-I receptor are essential for IGF-I-stimulation of mitogenic and tumorigenic pathways. IGF-I-induced mitogenesis, measured as thymidine incorporation and cellular proliferation, was abrogated in cells overexpressing mutant IGF-I receptors with replacement of the proximal double tyrosines (positions 1250 and 1251). Fibroblasts expressing this mutant IGF-I receptor formed fewer tumors than the negative control cells, whereas cells expressing wild-type IGF-I receptors formed large tumors in all recipient mice injected. Conversely, cells expressing mutant IGF-I receptors with only the conserved distal tyrosine (position 1316) replaced had slightly reduced IGF-I-stimulated beta-subunit autophosphorylation, thymidine incorporation, and cellular proliferation when compared with cells expressing wild-type receptors. Phosphorylation of insulin receptor substrate-1 by the yCF mutant receptors was not impaired. Despite the ability of these mutant receptors to stimulate mitogenic growth, fibroblasts expressing this mutant receptor were also incapable of forming tumors in recipient nude mice. The distal tyrosine (position 1316) of the IGF-I receptor is crucial for tumor formation but is not essential for IGF-I stimulated mitogenesis. Thus, the tyrosine moieties in the carboxy-terminus of the IGF-I receptor participate in the signal transduction pathways that affect the mitogenic and tumorigenic potentials of cells expressing mutant IGF-I receptors.

Variation in ultrastructure of mucoid coat and shell membrane secretion of a dasyurid marsupial

In the dasyurid marsupial Sminthopsis crassicaudata, the shell membrane of cleaving embryos has a compact granular structure but becomes fibrous around blastocysts. Polyclonal antibodies were raised against the extracellular coats, mucoid and shell membrane, of oocytes and early embryos. Immunogold cytochemistry resulted in labelling of secretory granules in the epithelia of both the ampulla and isthmus of the oviduct, although the secretory granules of these two regions differed in their ultrastructural appearance. Those in the ampulla were heterogeneous with areas of varying electron density, whereas those in the isthmus were electron dense and homogeneous. Shell membrane precursors were found in secretory granules in the epithelia of the uterotubal junction and endometrial glands and were electron lucent.

Changes in structure of the trophectoderm of a marsupial in Mid-pregnancy up to the time of implantation

Pre- and peri-implantation embryos of the dasyurid marsupial Sminthopsis crassicaudata were examined for morphological differentiation of the trophectoderm. The cells of unilaminar blastocysts were all squamous and stained intensely with toluidine blue. In bilaminar blastocysts and embryos at the early embryonic-disc stage, the trophectoderm was similar in appearance to, but stained more lightly than, the underlying endoderm. Trophoblast differentiation did not appear to occur until the mesoderm had begun to migrate between the trophoblast and endoderm beyond the embryonic disc. At this stage, trophoblasts had three distinct morphologies: (1) vacuolated, tall and columnar cells in the trilaminar region; (2) large cuboidal cells in the adjacent bilaminar region; and (3) squamous cells in the abembryonic pole of the bilaminar region. These variations in cell structure correlate with differences in subsequent functional activity in these three regions of the yolk sac placenta.

Single tyrosine substitution in the insulin-like growth factor I receptor inhibits ligand-induced receptor autophosphorylation and internalization, but not mitogenesis

The tyrosine kinase domains of the insulin and insulin-like growth factor I (IGF-I) receptors play an essential role in signal transduction. After ligand binding, these receptors undergo autophosphorylation, with a cluster of three tyrosines (residues 1131, 1135, and 1136 in the IGF-I receptor) being the first to be phosphorylated. Mutation of the ATP-binding site or substitution of this triple tyrosine cluster in the catalytic domain blocks essentially all of the functions of these receptors. Using stably transfected NIH-3T3 cell lines, we studied the effect of a mutation of tyrosine 1131 of the triple tyrosine cluster of the IGF-I receptor to phenylalanine. This mutation significantly reduced IGF-I-induced beta-subunit autophosphorylation, whereas phosphorylation of the endogenous substrate IRS-1 was unaffected. Despite the reduction in autophosphorylation and receptor internalization, IGF-I-induced thymidine incorporation and cellular proliferation were unaffected. Thus, the extent of receptor autophosphorylation and internalization does not appear to be a limiting factor for IGF-I-stimulated mitogenesis.

Growth inhibition of MCF-7 breast cancer cells by stable expression of an insulin-like growth factor I receptor antisense ribonucleic acid

Insulin-like growth factors (IGFs) play an important role in cellular proliferation, and IGF action appears to be involved in tumorigenesis. To determine the role of the IGF-I receptor in breast cancer cell growth, we stably transfected MCF-7 breast cancer cells with a construct encoding an antisense RNA complementary to the region surrounding the translation initiation site of the IGF-I receptor messenger RNA (mRNA). Control cells were transfected with vector alone. Clones expressing the antisense RNA exhibited a 30% reduction in endogenous IGF-I receptor mRNA levels and a significant reduction in receptor protein levels, as measured by both ligand binding assays and Western blot analysis. Antisense-expressing clones expressed approximately 30,000 receptors/cell compared with approximately 48,000-58,000 receptors/cell in control (neo) cells (P < 0.05). Although endogenous RNA:RNA hybrids were demonstrable in antisense-expressing cells, our results suggest that the major effect of the antisense may be the reduction in mRNA levels and not via an inhibition of translation. The reduction in receptor expression reduced both IGF-I- and serum-stimulated cellular proliferation. The maximum cell number reached at 96 h in the presence of IGF-I (100 ng/ml) was significantly reduced in antisense-expressing clones (22,000-30,000) compared with that in control (neo) cells (39,000-42,000). Furthermore, IGF-I-induced c-fos gene expression was reduced by 30% in the clones expressing the antisense RNA. These results strongly support a role for the IGF-I receptor in the proliferation of human breast cancer cells and suggest that strategies using this type of technology may prove useful in cancer therapy.

Alternative leader sequences in insulin-like growth factor I mRNAs modulate translational efficiency and encode multiple signal peptides

Rat insulin-like growth factor I (IGF-I) mRNAs contain multiple 5'-untranslated regions due to the use of leader exons transcribed from several transcription initiation sites and to alternative splicing within leader exon 1. Synthetic RNAs with 5'-ends corresponding to the use of exon 1 transcription initiation sites were translated in vitro into prepro-IGF-I peptides initiated at a Met-48 codon in exon 1 or a Met-22 codon in exon 3, and RNAs with a 5'-end corresponding to the major exon 2 transcription start site were translated into a prepro-IGF-I peptide initiated at a Met-32 codon in exon 2. All forms of prepro-IGF-I were processed by canine pancreatic microsomes, suggesting that all these prepeptides function as signal peptides. The translational efficiency of IGF-I RNAs was inversely proportional to the length of the 5'-untranslated region. Mutation of the first of three upstream AUG codons in exon 1, which potentially initiates a 14-amino acid open reading frame, did not affect prepro-IGF-I translation. The other two AUG codons are immediately followed by stop codons. The absence of both upstream AUG codons in a completely spliced exon 1-derived RNA enhanced the in vitro and in vivo translatability of this RNA as compared with the full-length RNA. Mutation of the downstream initiation codon in particular increased translational efficiency in vitro and in intact cells, suggesting that an inefficient reinitiation event at the Met-48 codon contributes to the poorer translation of IGF-I mRNAs in which these upstream AUGUGA motifs occur. We conclude that IGF-I mRNAs potentially encode multiple forms of preproIGF and that specific differences in their 5'-untranslated regions provide a molecular basis for translational control of IGF-I biosynthesis.

Localization of growth hormone receptor/binding protein messenger ribonucleic acid (mRNA) during rat fetal development: relationship to insulin-like growth factor-I mRNA

Although GH plays a key role in postnatal growth, prenatal growth is thought to be GH independent. However, recent data has shown GH receptor/binding protein (GHR/BP) to be present in rat fetal tissues as early as fetal stage E12. The aim of the present study was to investigate tissue-specific production of the GHR/BP messenger RNA (mRNA) and its relationship to locally transcribed insulin-like growth factor-I (IGF-I) mRNA in the fetus. We have used in situ hybridization to localize GHR/BP and IGF-I mRNAs in 16.5-, 18.5-, and 20.5-day-old rat fetuses. Furthermore, because the two parameters of the IGF-I gene differentially respond to GH stimulation, we have also investigated the presence and localization of promoter-specific IGF-I mRNAs. We found the distribution of IGF-I and GHR/BP mRNAs to be widespread but distinct during the fetal stages examined. High levels of IGF-I mRNA were found in connective tissues or their precursors, including the dermis, perichondrium, and gut. In contrast, GHR/BP mRNA exhibited three distinct patterns of distribution. First, GHR/BP mRNA was found at epithelial sites adjacent to sites of IGF-I transcription. Second, GHR/BP and IGF-I mRNAs were found to colocalize in some connective tissues, but GHR/BP mRNA levels in these sites were often lower than at other sites (i.e. epithelial) of GHR/BP gene transcription. Third, GHR/BP mRNA was also found in regions remote from IGF-I mRNA, including the nerve ganglia and inner olfactory bulb. Using promoter-specific IGF-I RNA probes, we detected only promoter 1 transcripts in all fetal tissues examined. The only exception occurred in specialized epithelial cells of the cochlea where we detected high levels of both promoter 1- and 2-derived IGF-I transcripts. We have thus demonstrated a distinct distribution of GHR/BP and IGF-I mRNAs in the developing rat fetus with coordinate expression at some sites. These findings suggest a role of GH or a GH-like peptide, acting both directly and indirectly via IGF-I, in fetal growth and development.

The accumulation of IGF-I in kidneys of streptozotocin-diabetic adult rats is not associated with elevated plasma GH or IGF-I levels

Nephropathy is a major complication of diabetes mellitus and is associated with expansion of the mesangium and an increase in kidney size in both humans and rats. Interestingly, early kidney enlargement occurs only in postpubertal animals, and is preceded by a significant increase in the levels of extractable renal IGF-I. This study examined the possibility that this difference is GH dependent, and that very early changes in plasma GH and/or IGF-I in the adult animal are associated with an early accumulation of renal IGF-I. Silastic jugular catheters were placed in adult (13-14 week) male Sprague-Dawley (S-D) rats for blood collection and drug injection. Serial blood samples were taken every 30 min in groups of saline control and streptozotocin (STZ) (50 μg/kg, IV) rats from 1-6 h, 9-15 h, and 24-30 h post-injection, and plasma GH profiles were determined by RIA. Renal IGF-I content was assessed following acid extraction. Following STZ, there was an immediate, step-wise reduction in peak GH levels (saline controls, 54±7 ng/mlvs 30±5 (1-6 h); 23±10 (9-15 h); and 13±3 ng/ml (24-30 h post-STZ);P<0.05 for all STZ groupsvs control). The same significant step-wise reduction was observed in the integrated area under the curve for GH. A separate group of rats were treated with a GH-releasing factor antagonist (GRF-AN) for 5 days prior to STZ, to suppress pulsatile GH release, and reduce plasma IGF-I. Chronic GRF-AN administration reduced plasma IGF-I levels significantly to 63% of control values (P<0.01). However, despite the reduction in plasma IGF-I, renal IGF-I remained significantly elevated 24 h post-STZ compared with controls and not significantly different from animals treated with STZ alone (467±49 ng IGF-I/g KW in control salinevs 778±100 in saline/STZ and 705±87 ng IGF-I/g KW in chronic GRF-AN/STZ rats (P<0.05)). In conclusion, following STZ administration in the adult rat, there is an immediate reduction in GH levels, indicating the renal IGF-I accumulation occurs without initial increases in plasma GH levels. Furthermore, when plasma IGF-I levels in the adult are significantly reduced renal IGF-I content remains elevated. These data suggest that early diabetic renal growth is not associated with elevated circulating GH levels, and that high basal plasma IGF-I levels are not necessary for IGF-I accumulation.

Regulation of insulin-like growth factor I receptor gene expression by Sp1: physical and functional interactions of Sp1 at GC boxes and at a CT element

The insulin-like growth factor I (IGF-I) receptor mediates signal transduction by the IGFs and plays a critical role in growth and development. The proximal promoter region of the rat IGF-I receptor gene contains multiple Sp1 consensus-binding sites (GC boxes). Various promoter fragments fused to a luciferase reporter gene were transiently cotransfected together with an Sp1 expression vector into Drosophila Schneider cells, which lack endogenous Sp1. A proximal promoter fragment containing 476 nucleotides of 5'-flanking region and 640 nucleotides of 5'-untranslated region was strongly activated by Sp1 (an average of 116-fold), and progressive 5'-deletions of the promoter that sequentially removed GC boxes reduced Sp1 activation to 15-fold over basal promoter activity. DNase I footprinting studies with purified Sp1 protein revealed four GC boxes in the 5'-flanking region of the promoter and one homopurine/homopyrimidine motif (CT element) in the 5'-untranslated region that bound Sp1. Mutation of the CT element reduced Sp1 activation by 70%. Taken together, these results demonstrate that Sp1 can regulate expression of the IGF-I receptor promoter by acting both on GC boxes in the 5'-flanking region of the promoter and on a CT element in the 5'-untranslated region.

Inhibition of cellular proliferation by the Wilms' tumor suppressor WT1 is associated with suppression of insulin-like growth factor I receptor gene expression

We have investigated the regulation of the insulin-like growth factor I receptor (IGF-I-R) gene promoter by the Wilms' tumor suppressor WT1 in intact cells. The levels of endogenous IGF-I-R mRNA and the activity of IGF-I-R gene promoter fragments in luciferase reporter constructs were found to be significantly higher in G401 cells (a Wilms' tumor-derived cell line lacking detectable WT1 mRNA) than in 293 cells (a human embryonic kidney cell line which expresses significant levels of WT1 mRNA). To study whether WT1 could suppress the expression of the endogenous IGF-I-R gene, WT1-negative G401 cells were stably transfected with a WT1 expression vector. Expression of WT1 mRNA in G401 cells resulted in a significant decrease in the rate of cellular proliferation, which was associated with a reduction in the levels of IGF-I-R mRNA, promoter activity, and ligand binding and with a reduction in IGF-I-stimulated cellular proliferation, thymidine incorporation, and anchorage-independent growth. These data suggest that a major aspect of the action of the WT1 tumor suppressor is the repression of IGF-I-R gene expression.

Modulation of insulin-like growth factor I (IGF-I) receptors and membrane-associated IGF-binding proteins in endometrial cancer cells by estradiol

Insulin-like growth factor I (IGF-I) receptors and membrane-associated IGF-binding proteins (IGFBPs) were examined in Ishikawa endometrial cancer cells. Our findings suggest that about 95% of [125I]IGF-I is bound to membrane-associated IGFBPs rather than to IGF-I receptors. Specifically, [125I]IGF-I binding to cell membranes could be completely displaced by cold IGF-I or IGF-II, but not by insulin, suggesting that binding was primarily due to IGFBPs. This was confirmed by using [125I]des-(1-3)IGF-I as the ligand. Des-(1-3) IGF-I binds with high affinity to IGF-I receptors, but with markedly lower affinity to IGFBPs. [125I]Des-(1-3)IGF-I bound to Ishikawa cells was displaced by IGF-I, IGF-II, and insulin. These results suggest that measuring IGF-I receptor levels using labeled IGF-I may be misleading. Accordingly, we evaluated the differential binding of [125I]IGF-I and [125I]des-(1-3)IGF-I to study the involvement of the IGF system in the stimulation of Ishikawa cell growth by estradiol. IGF-I stimulates Ishikawa cell proliferation, but at low concentrations, and this stimulation is largely dependent on the presence of estradiol. Estradiol caused a 2.5-fold increase in IGF-I receptor levels. Moreover, estradiol reduced soluble IGFBP levels, presumably increasing the availability of IGFs for their receptors. This elevation in IGF-I receptor levels and the decrease in IGFBP levels were accompanied by a 3.5-fold increase in IGF-I receptor messenger RNA and a 2.5-fold decrease in IGFBP messenger RNAs. These experiments suggest that estradiol sensitizes endometrial cancer cells to the effects of IGFs by simultaneously elevating receptor levels and decreasing (potentially inhibitory) IGFBP levels.

Calibration of dentists in the use of occlusal indices

Dentists' opinions as to both need for and outcome of orthodontic treatment show wide variation. Within the profession there is an opportunity to reduce subjective bias and standardise criteria by the use of occlusal indices. The results of this study demonstrate that a group of dentists can easily be trained to record the Aesthetic and Dental Health Components of the Index of Orthodontic Treatment Need and the PAR index to a satisfactory level.

The relationship between the index of orthodontic treatment need and consensus opinion of a panel of 74 dentists

This study looked at the aesthetic and dental health components of the index of orthodontic treatment need in relation to peer assessment of dental health and aesthetic need (panel of 74 dentists). The dental health component had a Spearmans correlation coefficient of +0.64 and the aesthetic component +0.86 when compared with the mean subjective opinion of 74 dentists. It has been proposed to have three categories for both the dental health and aesthetic components in accordance with consensus opinion. The panel of 74 examiners were more likely to regard aesthetics as a greater need for treatment than dental health.

Dissociation of mitogenesis and transforming activity by C-terminal truncation of the insulin-like growth factor-I receptor

We have investigated the mitogenic and transforming ability of an IGF-I receptor with a 108-amino-acid C-terminal truncation in R- cells, which are 3T3-like cells derived from mouse embryos in which the IGF-I receptor genes have been disrupted by targeted homologous recombination. R- cells stably transfected with expression plasmids encoding either a wild-type or a truncated human IGF-I receptor were capable of growing in serum-free medium supplemented solely with IGF-I. This response was observed over a wide range of receptor levels. R- cells overexpressing the wild-type IGF-I receptor also formed colonies in soft agar, and colony formation was augmented by coexpression of the SV40 large T antigen. However, all the examined clones of R- cells expressing the truncated IGF-I receptor exhibited a dramatically impaired ability to grow in soft agar, even in the presence of the T antigen. The inability to form colonies in soft agar was not due to a quantitative impairment of signal transduction, because: (1) SV40-transformed cells with a physiological level of the wild-type IGF-I receptor did not respond to IGF-I with cell proliferation, but grew in soft agar; (2) R- cells stably transfected with both a truncated receptor and T antigen, on the contrary, responded with mitogenesis to IGF-I but could not form colonies in soft agar; (3) some clones with the truncated receptor expressed levels of receptor roughly 100-fold the level of wild-type cells; and (4) several parameters of IGF-I receptor signal transduction were not impaired in cells stably transfected with a truncated receptor. Furthermore, overexpression of an activated ras in cells with the truncated IGF-IR did not restore their ability to proliferate under anchorage-independent conditions. We conclude that the 108 amino acids of the IGF-I receptor are not essential for a mitogenic response to IGF-I, but are required for transformation (as assessed by the ability to grow in soft agar), indicating that these two functions can be dissociated at an intramolecular level. Moreover, although ras (activated) certainly plays a role in transformation, the transforming activity of the IGF-IR also requires signaling elements that are ras-dependent.

Expression of insulin-like growth factor binding proteins in the rat kidney: effects of long-term diabetes

Recent studies have shown that the renal synthesis of insulin-like growth factor binding proteins (IGFBPs) is altered in insulin-deficient diabetes mellitus, suggesting that these changes may be implicated in the alterations in renal function and morphology that accompany diabetes. To investigate the time course and the precise cellular distribution of changes in IGFBP expression, we used quantitative in situ hybridization to analyze renal IGF-I and IGFBP-1 to -5 messenger RNA (mRNA) localization and levels from 2 days to 6 months after the onset of streptozotocin-induced diabetes. There was an immediate sharp decline in IGF-I mRNA levels in the outer medulla that persisted for up to 3 months and a much smaller reduction in IGF-I mRNA levels in the medullary thick ascending limbs (MTALs). In nondiabetic animals, IGFBP-1 mRNA is most abundant in the MTALs. Immediately after the induction of diabetes, however, there was a greater than 2-fold increase in cortical IGFBP-1 mRNA and a 75% decrease in IGFBP-1 mRNA in MTALs. These changes persisted for up to 6 months in the diabetic animals. In contrast, IGFBP-5 mRNA levels were increased in the outer medulla and decreased in the cortex of diabetic kidneys. No significant changes in renal IG-FBP-2 mRNA levels or distribution were noted, and changes in IG-FBP-3 and -4 mRNA levels were subtle. In summary, streptozotocin-induced diabetes is associated with very prominent and complex alterations in renal IGF system gene expression, including robust increases in cortical IGFBP-1 and profound decreases in cortical IG-FBP-5 mRNA and medullary IGF-I mRNA levels. The divergent changes in IGFBP-1 and -5 mRNA levels in cortex vs. outer medulla indicate that regulation of IGFBP mRNA levels is quite complex.

Endogenous plasma growth hormone and the occurrence of pregnancies in patients undergoing in-vitro fertilization and embryo transfer with ovarian stimulation

This study was undertaken to investigate a possible relationship between endogenous secretion of growth hormone (GH) during ovarian stimulation and treatment outcome in patients undergoing in-vitro fertilization (IVF) and embryo transfer. Plasma samples obtained from 19 women who had successfully completed all stages of IVF/embryo transfer were analysed retrospectively. Based on the increase in GH during treatment, 11 GH responders and eight GH non-responders were identified. Mean daily GH concentrations for the GH responders and GH non-responders were 3.5 +/- 1.8 and 1.8 +/- 0.8, 5.4 +/- 2.3 and 0.5 +/- 0.2, and 9.0 +/- 1.9 and 0.7 +/- 0.1 ng/ml (P < 0.05) for days 10, 11 and 12 respectively. Plasma insulin-like growth factor-I slightly increased with treatment in both groups. No significant difference between these groups was found in relation to treatment duration, number of human menopausal gonadotrophin ampoules used, oestradiol peak values, and number of oocytes retrieved or fertilization rate. Seven of the 11 GH responder women conceived in comparison with one pregnancy among eight GH non-responder patients (P < 0.05). In view of the absence of differences in the clinical and laboratory parameters, we suggest that the occurrence of pregnancies among GH responder patients might be related to a positive local effect of GH or its mediators on uterine receptivity at the time of nidation.

Growth hormone (GH) modulates insulin-like growth factor I (IGF-I) and type I IGF receptor mRNA levels in the ovary of prepubertal GH-deficient rats

In order to explore the potential role of growth hormone (GH) in modulating insulin-like growth factor I (IGF-I) gene expression in the prepubertal rat ovary, female rats were rendered GH deficient by neonatal administration of monosodium glutamate (MSG). One group of rats received vehicle and served as the control. At 21 days of age, MSG-treated rats received either GH or vehicle for 2 weeks. On days 21, 24, 28 and 31 animals were weighed and subsets were sacrificed for liver RNA extraction. The remaining animals were sacrificed at day 35 when livers and ovaries were collected, and serum was obtained for GH determinations. The IGF-I mRNA levels were estimated by Northern blots and corroborated further by slot-blot analysis. The MSG-treated rats had lower body weights (p < 0.01) and GH levels (p < 0.05) than controls. Growth hormone replacement significantly accelerated the weight gain of MSG-treated rats. At day 24 and thereafter, three RNA IGF-I species (7.5, 1.8 and 0.8-1.2 kB) were seen in the liver. In the ovary, at age 35 days, two major IGF-I mRNA species (7.5 and 0.8-1.2 kb) were seen. The MSG treatment consistently reduced the levels of both IGF-I mRNA species in the ovary. Growth hormone administration partially restored their expression, both in the liver and in the ovary. In addition, ovarian type IIGF receptor mRNA levels were increased in the MSG-treated rats when compared to controls. This trend was reversed by GH replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat growth hormone receptor/growth hormone-binding protein mRNAs with divergent 5'-untranslated regions are expressed in a tissue-specific manner

In the rat, the growth hormone receptor (GH-R) gene generates two transcripts, one encoding the transmembrane GH-R, and a shorter one encoding the GH-binding protein (GH-BP). These transcripts exhibit a high degree of heterogeneity in their 5'-untranslated regions (5'-UTRs). Some of the exons encoding these 5'-UTR variants may be flanked by distinct promoter regions whose activity would result in the tissue-specific expression of the GH-R gene. To assess this possibility, we used single-sided polymerase chain reaction (PCR) amplification to characterize 5'-UTR variants in rat GH-R cDNAs, and by using 5'-UTR-specific probes, we determined their pattern of expression in several tissues. Besides two previously described variants (V1 and V2), three new 5'-UTR variants were identified, extending 56 nucleotides (V3), 135 nucleotides (V4), and 209 nucleotides (V5) upstream of the ATG translation initiation codon. The expression of GH-R and GH-BP transcripts was clearly tissue specific. In the liver, GH-BP mRNA was the predominant transcript, whereas in other tissues, there was equivalent expression of both transcripts or predominant expression of GH-R mRNA. With respect to the tissue distribution of the 5'-UTR variants in particular, variants V1 and V5 exhibited a pattern of expression closely resembling that seen with an exon 2 probe, with the overall expression of variant V1 being much higher than that of variant V5. The V2 species was exclusively expressed in liver. Variant V3 was expressed at low levels in liver, muscle, heart, and kidney; in muscle and heart, it was preferentially associated with GH-BP transcripts. Variant V4, although present in liver, was more abundant in extrahepatic tissues and predominantly found in GH-R mRNA transcripts. Southern blot analyses were consistent with exon 2 and the exons encoding the V1 and V2 sequences being in proximity, with the other 5'-UTR sequences being encoded by exons located further upstream of exon 2. These findings support the concept that different 5'-UTR variants are the result of the different promoters acting in a tissue-specific manner. The association of specific 5'-UTR variants with either GH-R or GH-BP transcripts raises the possibility that the alternative splicing process that generates GH-BP mRNA in the rat might be controlled by the 5'-flanking region regulating the expression of specific leader exons.

Mutation of a conserved amino acid residue (tryptophan 1173) in the tyrosine kinase domain of the IGF-I receptor abolishes autophosphorylation but does not eliminate biologic function

The amino acid sequence of the tyrosine kinase domain of the insulin-like growth factor-I (IGF-I) receptor is 84% identical to the sequence of the analogous region of the insulin receptor. A naturally occurring mutation of the tryptophan residue at position 1200 of the insulin receptor to serine results in impaired beta subunit autophosphorylation of wheat germ agglutinin-purified receptors, severely impaired thymidine incorporation and moderately reduced glycogen synthesis; however, glucose uptake was unaffected. To study the importance of this residue in IGF-I receptor function, we mutated the analogous tryptophan residue at position 1173 of the IGF-I receptor to serine and overexpressed the mutant receptor in NIH-3T3 cells. In cell lines overexpressing this mutant IGF-I receptor, beta subunit autophosphorylation was severely reduced. Additionally, the overexpressed mutant receptors exhibited a dominant-negative effect on IGF-I-stimulated autophosphorylation of endogenous mouse IGF-I receptors. Phosphorylation of insulin receptor substrate (IRS)-1 in intact cells by the mutant IGF-I receptors was similar to the level of IRS-1 phosphorylation seen in the parental NIH-3T3 cells, but there was no obvious dominant-negative effect on IRS-1 phosphorylation. Wheat germ agglutinin-purified mutant receptors were as active in phosphorylating poly-(Glu,Tyr) 4:1 as wild-type IGF-I receptors, suggesting that, in intact cells, additional factors are necessary in order for the IGF-I receptor to phosphorylate IRS-1. Thymidine incorporation was severely reduced in one clone overexpressing the mutant IGF-I receptor and abolished in a second clone. Glucose uptake in both clones was reduced to about half of that seen in a cell line over-expressing wild-type IGF-I receptors. Thus, we propose that the tryptophan residue at position 1173 of the IGF-I receptor is important in the regulation of autophosphorylation in vivo. This study again confirms that high levels of autophosphorylation are not required for mediation of all of the biologic activities of the IGF-I receptor.

Continuous nitric oxide inhalation reduces pulmonary arterial structural changes, right ventricular hypertrophy, and growth retardation in the hypoxic newborn rat

Breathing low oxygen levels for several weeks produces progressive pulmonary artery hypertension and smooth muscle hypertrophy and hyperplasia in many species. Because nitric oxide (NO) is an important regulator of pulmonary vascular tone, we examined whether the continuous inhalation of low levels of NO gas would attenuate pulmonary arterial structural changes in hypoxic rat pups. Nine-day-old rat pups and their mothers continuously breathed at FIO2 0.21 or 0.10 with or without adding 20 ppm (by volume) NO for 2 weeks. Lung tissue was obtained for vascular morphometric analysis, and the hearts were dissected to measure right ventricular weight and levels of mRNA encoding rat atrial natriuretic factor (rANF). In addition, femur and skull length were radiographically determined. Breathing at FIO2 0.10 for 14 days increased pulmonary arterial wall thickness and the proportion of muscular arteries in the lung periphery. Right ventricular weight and right ventricular rANF gene expression increased, whereas body weight and skeletal growth were reduced (all P < .05). Continuous inhalation of 20 ppm NO at FIO2 0.10 for 2 weeks decreased hypoxic pulmonary vascular structural changes and somatic growth retardation and prevented the increase of right ventricular weight and right ventricular rANF mRNA levels. These observations suggest that chronically breathing NO attenuates pulmonary vascular smooth muscle hypertrophy and/or hyperplasia and extension into distal arterial walls, right ventricular hypertrophy, and growth retardation of newborns breathing at a low oxygen level.

Insulin-like growth factors and cancer

The insulin-like growth factor (IGF) family of peptides, binding proteins, and receptors are important for normal human growth and development and are involved in the specialized functions of most physiologic systems. Most members of the IGF system are expressed by different cancer cells and may play an important role in the propagation of these malignancies. New therapies aimed at modulating various components of the IGF system could affect the progression and metastasis of cancer.

Components of the IGF system mediate the opposing effects of tamoxifen on endometrial and breast cancer cell growth

The involvement of the IGF system in the growth regulation of hormone-dependent (e.g. endometrial and breast) cancer cells was studied. We chose two opposing effects of tamoxifen: the paradoxical stimulation of Ishikawa endometrial cancer cells growth and its inhibitory effect on MCF-7 mammary cancer cells. The results clearly confirm our working hypothesis that the IGF system is involved in growth regulation of these cancer cells irrespective of the direction of the drug effect. The following parameters of the IGFs system were studied: IGF-I receptors, IGF-I stimulated protein tyrosine phosphorylation, and membrane-associated and secreted IGF-binding proteins (IGFBPs). In Ishikawa cells, tamoxifen, similar to estradiol, increased IGF-I stimulated tyrosine phosphorylation of cellular substrates in accordance with its effect on cell growth. This effect of tamoxifen was inverted in MCF-7 cells. Tamoxifen did not affect the number or affinity of IGF-I receptors in both Ishikawa and MCF-7 cells, however, it caused a three-fold decrease in membrane-associated IGFBPs in the endometrial cells but an increase in these proteins in breast cancer cells. Similar but much less pronounced changes in soluble IGFBPs were observed. Our results indicate that the opposing growth effects of tamoxifen an endometrial and mammary cancer cells are associated with modulation of the IGF system components, mainly with reciprocal changes in membrane-associated IGFBPs.

Regulation of insulin-like growth factor I transcription by prostaglandin E2 in osteoblast cells

Insulin-like growth factor I (IGF-I) is a widely expressed abundant autocrine and paracrine factor that regulates the proliferation and differentiation of a variety of cell types. Prostaglandin E2 (PGE2) is a potent stimulator of IGF-I synthesis in bone. We examined the regulation of IGF-I synthesis by PGE2 in osteoblast-enriched (Ob) cells from fetal rat calvaria. PGE2 treatment of Ob cells at 1 microM for 2 h resulted in a 5-fold increase in heterogeneous nuclear RNA levels, as measured by a reverse transcriptase-polymerase chain reaction assay, suggesting an increase in IGF-I gene transcription. RNase protection analysis was used to map the transcriptional start sites in the IGF-I gene that are used in Ob cells. Consistent with other extrahepatic tissues, initiation of transcription occurs primarily at three sites within the 5'-regions of exon 1 of the IGF-I gene. PGE2 treatment did not alter start site usage. The regions upstream of these transcriptional start sites were analyzed by transiently transfecting Ob cells with putative rat IGF-I promoter sequences ligated to a luciferase reporter gene. Constructs containing 1.4 kilobases of the 5'-regions regions of exons 1 and 2 had significant promoter activity. PGE2 treatment of transfected Ob cells increased luciferase activity 5-fold when a 1.4-kilobase exon 1 promoter fragment was tested. This increase in luciferase activity was time and dose dependent. Smaller regions of the exon 1 promoter sequence gave higher basal activity and were less responsive to PGE2. We conclude that regions involved in IGF-I regulation by PGE2 are contained within the IGF-I promoter.

Origin of the oocyte shell membrane of a dasyurid marsupial: an immunohistochemical study

Polyclonal antibodies were raised against the extracellular coats (mucoid and shell membrane) of unfertilized oocytes and early embryos of a dasyurid marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata). Indirect immunofluorescence was used to test the specificity of the antibodies to the shell membrane. Streptavidin/biotin immunoperoxidase cytochemistry revealed that precursors of the tertiary egg membranes are secreted by the luminal epithelium of the ampulla, isthmus (including the crypts), utero-tubal junction, and adjacent endometrial glands. Histochemistry distinguished between the sites of mucoid and shell membrane precursor secretion. The mucoid coat stained positively with Alcian blue at pH 1.0 and 2.5, with Alcian blue at pH 0.2 after performic acid oxidation, and with PAS which was amylase resistant. Some of the luminal epithelial cells of the ampulla and isthmus, as well as its crypts, also stained positively by these histochemical methods but the luminal epithelium of the utero-tubal junction and endometrial glands were negative for all methods. The shell membrane did not stain with any of the above methods nor with dihydroxy-dinapthyl-disulphide (DDD) or ferric ferricyanide but it was eosinophilic and stained positively with the red cytoplasmic stain of Masson's trichrome. Therefore, it is concluded that shell membrane precursors are secreted by the luminal epithelium of the utero-tubal junction, adjacent glands, and by scattered glands in the anterior region of the uterus but not by any cell population of the oviduct.

Characterization of a salmon insulin-like growth factor I promoter

We have identified four transcription initiation sites in the salmon insulin-like growth factor I (IGF-I) gene. Use of the most upstream transcription start site generates a minor mRNA species with a 5' untranslated region (UTR) of approximately 450-550 nucleotides, whereas transcription starting at the downstream initiation sites results in more abundant IGF-I mRNAs with 5'-UTRs approximately 250, 245, and 165 nucleotides in length. No consensus TATA box-like elements are present immediately upstream of the most upstream start site identified, nor is this region particularly GC-rich. Transient expression assays, however, demonstrated orientation-dependent promoter activity in a 386-nucleotide-long fragment containing the major downstream transcription start sites. Additionally, reverse transcriptase polymerase chain reaction (RT-PCR) analyses demonstrated tissue and developmental stage-specific use of the various transcription start sites identified.