Tissue-specific regulation of the growth hormone receptor gene in streptozocin-induced diabetes in the rat

Abnormalities of GH secretion and clearance are well-documented in poorly controlled insulin-dependent diabetes mellitus (IDDM), but the contribution of the receptor (GHR) and the GH-binding protein (GHBP) to these abnormalities has not been defined. We studied the expression of the GHR/GHBP gene in the livers, hearts and kidneys in streptozocin-induced diabetes (STZ-D) in the rat. GHR and GHBP mRNA levels were measured by Northern blot and ribonuclease protection assays. Whereas levels of GHR and GHBP mRNA were significantly decreased in liver and heart of STZ-D rats when compared with the control group (P < 0.01), GHR mRNA was significantly increased in the kidneys of STZ-D rats (P = 0.03). Six days of insulin treatment did not significantly alter the levels of GHR/GHBP mRNA in the liver or heart of STZ-D rats, but significantly decreased GHBP mRNA (P = 0.04) in the kidney. Circulating IGF-I was reduced, as was IGF-I mRNA in the liver and heart of STZ-D rats; only circulating IGF-I was restored by insulin treatment. Neither STZ-D nor insulin treatment affected IGF-I or IGF-I receptor mRNA concentrations in the kidney. We conclude that (1) STZ-D modulates the expression of the GHR/GHBP gene and (2) that these changes in GHR/GHBP mRNA concentrations are tissue-specific; STZ-D decreases GHR/GHBP mRNA in liver and heart tissue but increases GHR mRNA concentrations in the kidney. Our results indicate a role for decreased numbers of hepatic GHRs in the pathogenesis of resistance to GH's actions in terms of IGF-I generation and promotion of linear growth in IDDM. We postulate that increased GHR expression in the kidney may be involved in the renal complications of IDDM.

Embryonic-maternal cell interactions at implantation in the fat-tailed dunnart, a dasyurid marsupial

BACKGROUND

In marsupials implantation occurs about two-thirds the way through the short gestation before which time the embryo is surrounded by the permeable shell membrane which prevents physical contact between the trophoblast and uterine epithelium. Although the trophoblast has been shown to be invasive to varying degrees in several species of marsupials, the ultrastructure of the embryonic-uterine cell interactions at the time of implantation has not been described in this group.

METHODS

Thick plastic sections and transmission electron microscopy were employed to investigate the cellular interactions at implantation in the fat-tailed dunnart (Sminthopsis crassicaudata), a dasyurid Australian marsupial.

RESULTS

Our results show that epithelial penetration begins when the embryo is at the late presomite/early somite stage. In the trilaminar region of the yolk sac (TYS), trophoblast cells adjacent to the embryo form desmosomes with uterine epithelial cells and also appear to fuse with them to form hybrid cells, the cytoplasm of which resembles that of trophoblast. Later in the TYS, as the placenta develops, trophoblast microvilli and larger cell processes invaginate, and interdigitate with, the highly folded maternal epithelium but do not invade it. At this time in the bilaminar, or avascular, yolk sac (BYS), multinucleate trophoblast giant cells (TGCs) from an annular region adjacent to the sinus terminalis intrude between, and possibly fuse with, the maternal epithelium. The invading TGCs spread laterally above the residual basal lamina before migrating into the stroma.

CONCLUSIONS

In this species of marsupial at least, the cell interactions at the time of implantation are similar to those seen in some eutherian species despite the fact that the fetal chorion is of yolk sac rather than allantoic origin.

Role of GH and IGF-I in the regulation of IGF-I, IGF-I receptor and IGF binding protein gene expression in the rat spleen

To characterize the expression of the IGF-I system in the spleen and its role in spleen growth, we have studied the effect of hypophysectomy and the action of either GH or IGF-I treatment on the expression of several components of the IGF system in the rat. Female Sprague-Dawley rats were hypophysectomized (Hx) on postnatal day 50, and five animals each received twice-daily sc injections of saline, bovine GH (bGH; 84 micrograms/animal/day), or recombinant human IGF-I (rhIGF-I; 125 micrograms/animal/day) for 11 days. Compared to sham-operated controls, Hx animals exhibited a reduction in both body (192.6 +/- 5.6 g (mean +/- S.E.M.) vs. 268.6 +/- 6.0 g; P < 0.001) and spleen weights (0.42 +/- 0.03 g vs. 0.84 +/- 0.06 g; P < 0.001). The reduction in body and spleen weights in Hx animals was partially prevented by both bGH and rhIGF-I. Body weights were 234.2 +/- 5.3 g (P < 0.001) after bGH and 213.8 +/- 6.3 g (P < 0.05) after rhIGF-I. Spleen weights were 0.56 +/- 0.048 after bGH P < 0.01 and 0.53 +/- 0.05 g after rhIGF-I (P < 0.05). Serum GH and IGF-I levels were markedly reduced in Hx animals and bGH partially maintained IGF-I levels. Hypophysectomy reduced spleen IGF-I mRNA levels (30.6 +/- 7.5% of control values; P < 0.05) and this reduction was prevented by bGH (96.6 +/- 24.2%; NS) but not by rhIGF-I (39.9 +/- 5.0% NS vs. Hx). There were no changes in GH receptor or IGF-I receptor mRNA levels in Hx or bGH or rhIGF-I-treated animals. When IGF-I binding protein (IGFBP) mRNA levels were studied under these conditions, we found that IGFBP-1 mRNA was not detected in spleen; IGFBP-2 mRNA levels were reduced in Hx rats (67.9 +/- 7.4% of control values, P < 0.05) and bGH treatment prevented this reduction (95.5 +/- 12.2%, NS). IGFBP-3 mRNA levels were not affected by hypophysectomy or by bGH treatment, but were reduced in rhIGF-treated rats (69.6 +/- 3.0%, P < 0.05). On the other hand, IGFBP-4 mRNA levels were increased in Hx rats (136.4 +/- 15.9% of control values, P < 0.05) and bGH treatment prevented this increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the genes for insulin-like growth factors and their receptors in bone during skeletal growth

Insulin-like growth factors (IGF) are important regulators of skeletal growth. To determine whether the capacity to produce and respond to these growth factors changes during skeletal development, we measured the protein and mRNA levels for IGF-I, IGF-II, and their receptors (IGF-IR and IGF-IIR, respectively) in the tibia and femur of rats before and up to 28 mo after birth. The mRNA levels remained high during fetal development but fell after birth, reaching a nadir by 3-6 wk. This fall was most pronounced for IGF-II and IGF-IIR mRNA and least pronounced for IGF-I mRNA. However, after 6 wk, both IGF-I and IGF-IR mRNA levels recovered toward the levels observed at birth. In the prenatal bones, the signals for the mRNAs of IGF-II and IGF-IIR were stronger than the signals for the mRNAs of IGF-I and IGF-IR, although the content of IGF-I was three- to fivefold greater than that of IGF-II. IGF-II levels fell postnatally, whereas the IGF-I content rose after birth such that the ratio IGF-I/IGF-II continued to increase with age. We conclude that, during development, rat bone changes its capacity to produce and respond to IGFs with a progressive trend toward the dominance of IGF-I.

Growth hormone (GH) stimulates insulin-like growth factor-I (IGF-I) and IGF-binding protein (IGFBP)-2 gene expression in spleens of juvenile rats

Growth and development of the spleen involves the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. To evaluate the molecular mechanism of these effects we studied the effect of hypophysectomy (Hx) and GH replacement therapy on the expression of IGF-I, the IGF-I receptor and IGF-binding protein-2 (IGFBP-2) in juvenile rats. Hx resulted in a 30% reduction in body weight. GH replacement therapy for seven days partially prevented these effects. IGF-I mRNA levels were reduced 30% by Hx, IGFBP-2 mRNA levels fell 50% whereas IGF-I receptor mRNA levels were unaffected. GH therapy prevented the reduction in IGF-I and IGFBP-2 mRNA levels. These results suggest that the GH effect on splenic growth and development is via local (paracrine) IGF-I expression, in addition to any effect by circulating (endocrine) IGF-I.

Insulin and insulin-like growth factor-I receptors similarly stimulate deoxyribonucleic acid synthesis despite differences in cellular protein tyrosine phosphorylation

Signal transduction pathways stimulated by insulin or insulin-like growth factor-I (IGF-I) were compared in transfected NIH3T3 fibroblast cell lines expressing the human insulin receptor, IGF-I receptor, or a chimeric IGF-I receptor with its carboxy-terminal tail replaced with that of the insulin receptor (approximately 1 x 10(6) receptors/cell). Although receptor autophosphorylation was very similar in the three cell lines overexpressing receptors (EC50 = 1-3 nM), there were differences detected in the protein tyrosine phosphorylation stimulated by insulin and IGF-I in these cells. Although no substrates specific for the insulin receptor were detected, phosphorylation of a 170-kilodalton (kDa; IRS-1) and a 70-kDa protein was 10 times more sensitive to insulin than to IGF-I (EC50 = 1.5-2.5 vs. 14-23 nM). The chimeric receptor stimulated significantly lower levels of phosphorylation of several proteins relative to the wild-type IGF-I receptor. Activation of phosphatidylinositol 3'-kinase paralleled phosphorylation of the 170- and 70-kDa proteins. Despite these differences in protein tyrosine phosphorylation, stimulation of mitogen-activated protein (MAP) kinase and DNA synthesis were very similar in the three cell lines overexpressing receptors. Little difference was detected in Shc phosphorylation or MAP kinase activation through the three receptors, although activation of MAP kinase was more efficiently coupled to the platelet-derived growth factor receptor than to any of the overexpressed receptors. All three receptors stimulated DNA synthesis to levels comparable to 10% serum, with similar sensitivities (EC50 = 1.5-3.5 nM).

Expression of the genes encoding the insulin-like growth factors (IGF-I and II), the IGF and insulin receptors, and IGF-binding proteins-1-6 and the localization of their gene products in normal and polycystic ovary syndrome ovaries

To discern the potential role of the insulin-like growth factors (IGFs) in polycystic ovary syndrome (PCOS), we examined the expression of the genes encoding the IGFs, IGF receptors (IGFr), insulin receptor (Ir), and IGF-binding proteins (IGFBPs-1-6) as well as the localization of the gene products in specific cellular compartments of normal and PCOS human ovaries. Messenger ribonucleic acid (mRNA) was localized by in situ hybridization with specific 35S-labeled human antisense RNA probes, and protein was detected by immunohistochemistry using specific antisera. Thecal cells, but not granulosa cells (GC), of small antral follicles (3-6 mm) from PCOS ovaries expressed both IGF-I and IGF-II transcripts. Abundant IGF-Ir mRNA was found only in GC, IGF-IIr mRNA was found in both granulosa and thecal cells, and Ir mRNA was detected in all cell types, including granulosa, thecal, and stromal cells. Localization of the gene products revealed no IGF-I immunoreactivity; however, immunostaining for each of the other gene products was colocalized with its corresponding mRNA. The cellular distribution of mRNA and protein in PCOS follicles was indistinguishable from that observed in small antral follicles from normal ovaries. In dominant follicles, however, IGF-I mRNA was no longer detectable, but abundant IGF-II mRNA was expressed exclusively in GC. Although IGF-Ir mRNA was expressed in GC, IGF-IIr mRNA was found in both granulosa and thecal cells. In follicles taken from PCOS ovaries, no IGFBP-1 mRNA was detected, IGFBP-2 mRNA was abundant in both granulosa and thecal cells, moderate IGFBP-3 mRNA was found only in thecal cells, IGFBP-4 and -5 mRNAs were present in all cellular compartments, and IGFBP-6 mRNA was not detected. Localization of the gene products by immunostaining revealed that each protein colocalized with its corresponding mRNA. The cellular distribution of IGFBP mRNA and protein in PCOS follicles was also indistinguishable from that in small antral follicles of normal ovaries, but remarkable differences were found in dominant follicles, where abundant IGFBP-1 mRNA was seen exclusively in GC, IGFBP-2 mRNA in thecal cells, and IGFBP-3 mRNA in both granulosa and thecal cells. Moderate expression of the IGFBP-4 and IGFBP-5 genes was seen in all cell types, including stromal cells, but no IGFBP-6 mRNA was detected. Again, each of the gene products colocalized with its corresponding mRNA. We conclude the following.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of the carboxyl-terminal domains of the insulin and insulin-like growth factor I receptors in receptor function

The insulin and insulin-like growth factor I receptors (IR and IGF-IR, respectively) are heterotetrameric tyrosine kinases consisting of two extracellular ligand-binding alpha subunits and two transmembrane catalytic beta subunits. A number of lines of evidence have suggested that the IR and IGF-IR differ with respect to their ability to elicit mitogenic versus metabolic events upon activation by cognate ligands. To ascertain the contribution of the poorly conserved carboxyl-terminal domains to the differential functioning of the IR and IGF-IR, we have constructed receptor chimeras in which the carboxyl-terminal domain of one receptor was fused to the remainder of the heterologous receptor. The responses of a number of parameters after ligand stimulation were examined in stably transfected NIH-3T3 cells expressing the chimeric receptors or the analogous wild-type receptor sequence. Replacement of the IR carboxyl terminus with that of the IGF-IR severely affected insulin-stimulated responses, whereas substitution of the carboxyl terminus of the IGF-IR with that of the IR had a minimal effect. These data suggest that the carboxyl-terminal domains of the IR and IGF-IR are not interchangeable and that the mitogenic activity of the IR can be influenced by sequences present in the carboxyl-terminal domain. The analogous functions of the IGF-IR, on the other hand, do not appear to be greatly affected by the presence of the IR carboxyl-terminal domain.

Isolation of a second nonallelic insulin-like growth factor I gene from the salmon genome

We have characterized a second nonallelic insulin-like growth factor-I (IGF-I) gene in the chum salmon (Oncorhynchus keta) genome. This gene, IGF-I.2, differs from the previously described chum salmon IGF-I gene, IGF-I.1, in the E peptide-coding portion of exon 3; specifically, the IGF-I.2 gene lacks one codon present in the IGF-I gene and contains two potential splice donor sites at the 3' end of exon 3 rather than the single, more distal site present in the IGF-I.1 gene. The expression of these two IGF-I genes could give rise to as many as six IGF-I mRNA species, each of which would encode a unique E-peptide moiety of the IGF-I prohormone. Thus, the presence of multiple, distinct IGF genes adds an additional level of complexity to IGF-I gene expression and IGF-I biosynthesis in salmon.

Use of the Index of Orthodontic Treatment Need (IOTN) in assessing the need for orthodontic treatment pre- and post-appliance therapy

The Index of Orthodontic Treatment Need (IOTN) was used to assess the need for orthodontic treatment before and after treatment, on a systematic sample of 1225 cases. On the whole, full upper and lower fixed appliances brought about a greater improvement in Aesthetics and Dental Health Components compared to other appliance techniques, and were less likely to make the occlusion worse. It was found that certain occlusal traits were more likely to be successfully treated than others. A common problem resulting from treatment was the development of a cross-bite.

Effect of training and growth hormone suppression on insulin-like growth factor I mRNA in young rats

The growth hormone (GH)-insulin-like growth factor I (IGF-I) axis plays a role in the adaptation to exercise training, but IGF-I gene expression in response to exercise training and GH suppression has not been studied. Twenty female rates underwent a 4-wk treadmill training program begun in the prepubertal period (day 14 of life). In 10 of the training rats, GH production was suppressed by anti-GH-releasing hormone antibodies (GH suppressed). IGF-I mRNA and protein levels were measured in liver and hindlimb skeletal muscle. GH suppression reduced IGF-I mRNA expression in the liver to a much greater extent than in the muscle. In the GH control rats, training induced significant increases in hepatic exon 1-derived IGF-I mRNA (mean increase 30%; P < 0.05) and muscle exon 2-derived mRNA (mean increase 35%; P < 0.05). In the GH-suppressed rats, only muscle exon 1-derived transcripts were significantly increased by training (55%; P < 0.05) and this was associated with a significant increase in muscle IGF-I protein levels (P < 0.05). We speculate that the anabolic response to training may involve both GH-dependent increases in IGF-I mRNA in the liver and GH-independent increases in the muscle.

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) treatment of the GH-deficient dwarf rat: differential effects on IGF-I transcription start site expression in hepatic and extrahepatic tissues and lack of effect on type I IGF receptor mRNA expression

The rat IGF-I gene consists of six exons, with exons 3 and 4 forming a 'core' mature IGF-I coding region to which alternate 5' and 3' regions are spliced. Transcription occurs from four dispersed start sites (ss) approximately 382 (ss 1), approximately 343 (ss 2), approximately 245 (ss 3) and approximately 30-40 (ss 4) basepairs (bp) from the 3' end of exon 1, and from a region 50-70 bp from the 3' end of exon 2. The expression of ss mRNAs displays tissue-specific and ontogenic regulation. Alternate splicing of exon 5 produces E-peptide coding domain variants (Ea and Eb mRNAs), with the Eb form found predominantly in the liver. The regulation of IGF-I mRNA expression by GH and IGF-I in the GH-deficient dwarf (dw/dw) rat was investigated using antisense RNA probes in a solution hybridization RNase protection assay to detect leader exon and E domain variant mRNAs. GH treatment of dw/dw and normal Lewis rats increased the expression of all liver leader exon ss and E domain variants coordinately (1.6-1.9-fold increase, p < 0.01), although the increase observed in Eb transcripts was significantly higher in the dw/dw compared to the normal rat (p < 0.05). In kidney, GH treatment significantly increased exon 1 ss 3 and ss 4 transcripts by approximately 40% (p < 0.05). The expression of the other start sites was not affected by GH, suggesting that transcription factors may regulate start site usage independently. GH treatment was associated with a significant increase in IGF-I mRNA expression in skeletal muscle (p < 0.05) but not cardiac muscle or spleen. IGF-I treatment was associated with minor (approximately 20%) but significant (p < 0.05) reductions in IGF-I mRNA expression in the liver and kidney of dw/dw rats, suggesting that IGF-I can suppress IGF-I mRNA expression. IGF-I treatment did not affect IGF-I mRNA expression in cardiac and skeletal muscle of dw/dw rats. IGF-I receptor mRNA was detected in extrahepatic tissues only, and was not affected by either GH or IGF-I treatment. In summary, start site-specific regulation by GH was observed in kidney. GH increased IGF-I mRNA expression in muscle, kidney and liver, but had no effect in heart or spleen in the dw/dw rat. Our data suggest that systemic IGF-I can feedback on hepatic and renal IGF-I mRNA expression in the GH-deficient state.

Transcriptional repression of the insulin-like growth factor I receptor (IGF-I-R) gene by the tumor suppressor WT1 involves binding to sequences both upstream and downstream of the IGF-I-R gene transcription start site

The insulin-like growth factor-I receptor (IGF-I-R) has been implicated in the etiology and/or progression of Wilms' tumor, a pediatric malignancy of the kidney that is often associated with deletion or mutation of the WT1 tumor suppressor gene. The expression of the IGF-I-R gene is increased in Wilms' tumor as compared with normal kidney tissue. Furthermore, the levels of IGF-I-R mRNA in individual tumors have been shown to be inversely correlated to the levels of WT1 mRNA, suggesting that the expression of the IGF-I-R gene is under the negative control of WT1. The activity of an IGF-I-R promoter/luciferase construct in Chinese hamster ovary cells was reduced by cotransfection of a WT1 expression vector. An analysis of various reporter constructs containing different portions of the IGF-I-R 5'-flanking and 5'-untranslated regions suggested that the effect of WT1 depends on the number of WT1 binding sites present, with sites located both upstream and downstream of the IGF-I-R transcription start site involved in mediating this effect. Using the purified zinc finger domain of WT1 in gel retardation and DNase I footprinting assays, we mapped five sites in the 5'-flanking and six sites in the 5'-untranslated regions that were involved in WT1 binding. In addition, the initiator element of the IGF-I-R gene contains a sequence that binds WT1. Thus, the repression of IGF-I-R promoter activity by the WT1 tumor suppressor gene product involves multiple interactions of its zinc finger domain with WT1 binding sites located both 5' and 3' of the transcription initiation site.

Differential accumulation of insulin-like growth factor-I in kidneys of pre- and postpubertal streptozotocin-diabetic rats

Nephropathy, one of the major complications of diabetes mellitus, is characterized by an early increase in kidney size. In experimental models of diabetes, this event is preceded by a rapid and transient rise in kidney IGF-I levels, at least in adult animals. Since diabetes-associated renal changes are uncommon in young patients, we investigated the early changes in the components of the IGF system following induction of diabetes in prepubertal and postpubertal rats. The rationale for this study was the evaluation of potential differences which could lead to kidney complications only at adult stages. Unlike the situation in the postpubertal kidney, in which there was a transient accumulation of extractable IGF-I 24-48 h after streptozotocin (STZ) administration, there was a decrease of approximately 12-fold in the level of IGF-I in the prepubertal kidney over the same period of time. Paradoxically, kidney IGF-I mRNA levels were reduced by approximately 50% in the postpubertal rat 24 h after STZ treatment, whereas in the prepubertal kidney IGF-I mRNA levels were unaltered. Furthermore, the levels of IGF-I receptor mRNA and 125I-labelled IGF-I binding to kidney membranes of postpubertal diabetic rats were similar to the levels in control kidneys. On the other hand, both the levels of IGF-I receptor mRNA and 125I-labelled IGF-I binding were increased (approximately 2.5-fold (after 24 h) and approximately 3-fold (after 48 h) respectively) in prepubertal animals. In addition, increased expression of IGF-binding protein (IGFBP)-1 mRNA was seen early in diabetes in both pre- and postpubertal rats. The results of this study suggest that the transient accumulation of IGF-I in the kidney of the postpubertal diabetic rat may not be due to an increase in the local synthesis of IGF-I, but rather to an increase in IGF-I uptake from the circulation due to non-membrane-associated IGFBP-1. The lack of accumulation of IGF-I in the prepubertal kidney probably reflects the approximately 10-fold lower levels of circulating IGF-I in young as compared with adult diabetic rats.

Platelet-derived growth factor increases the activity of the promoter of the insulin-like growth factor-1 (IGF-1) receptor gene

Stimulation by platelet-derived growth factor (PDGF) is known to increase the number of IGF-I binding sites in cells in culture. We show here that PDGF also increases the levels of IGF-1 receptor mRNA. Using cell lines stably transfected with an expression plasmid in which the reporter luciferase gene is under the control of the rat IGF-1 receptor gene promoter, we find that PDGF increases the activity of this promoter. A short IGF-1 receptor gene promoter, comprising about 100 base pairs of the sequence immediately upstream of the initiation of transcription site, is sufficient for a response to the stimulatory action of PDGF. These results suggest that an increase in RNA levels and in promoter activity may play an important role in the increase in IGF-1 receptor levels that occurs after stimulation by PDGF.

Elevated protein tyrosine phosphatase activity and increased membrane viscosity are associated with impaired activation of the insulin receptor kinase in old rats

Insulin resistance is very common in the elderly, and may be associated with glucose intolerance or frank diabetes. In previous studies we demonstrated that insulin resistance in old Wistar rats is associated with decreased autophosphorylation and activation of the hepatic insulin receptor kinase (IRK) in vivo. We now show that this defect can be reproduced in vitro, where the extent of insulin-induced activation of IRK in liver membranes of old rats was decreased by approximately 50% compared with young controls. The defect could be largely abolished after solubilization of the membranes with Triton X-100. We also show that: (a) the viscosity of membranes from the old rats was significantly (P < 0.001, n = 4) higher (by 15%) compared with young controls; (b) incubation of plasma membranes from old animals with lecithin liposomes, which lowered their cholesterol levels, partially abolished the defect in IRK activation; and (c) Triton extracts of liver membranes prepared from old rats did not interfere with the activation of IRK derived from young controls. Additionally, non-membrane components did contribute to the development of this defect. We observed a significant (approximately 30%) (P < 0.001, n = 18) elevation of cytosolic protein tyrosine phosphatase (PTP) activity directed against the beta subunit of the insulin receptor in livers of old rats. No such elevation of PTP activity could be demonstrated with synthetic substrates. Our findings are consistent with a model in which increased membrane viscosity as well as enhancement of a cytosolic PTP activity both markedly inhibit the activation in vivo of the hepatic IRK in old animals.

Dentists variation in the determination of orthodontic treatment need

The criteria that dentists use to judge the need for orthodontic treatment are not clear. This study investigates variation in dentists' perception of orthodontic treatment need. Seventy-four dentists were asked to assess 320 dental casts in relation to aesthetic and dental health need. The results of this investigation revealed that the panel was divided as what constituted a need for orthodontic treatment on dental health grounds. It is suggested that one method of achieving a more uniform evaluation of orthodontic treatment need is the use of an occlusal index. Until an occlusal index is accepted and used by the profession, the distortion of need and demand for orthodontic treatment by dentists' unequal perceptions will continue.

How does the mitogenic insulin-like growth factor I receptor differ from the metabolic insulin receptor?

Under normal physiological conditions, insulin regulates intermediary metabolism by interacting with insulin receptors in liver, fat and muscle cells. The insulin-like growth factors (IGF-I and IGF-II), on the other hand, are primarily involved in the regulation of growth and development of the whole organism and interact with IGF receptors expressed by most, if not all, tissues of the body. As the insulin and IGF-I receptors are both structurally and functionally similar, one of the fundamental questions in this area of research has been the basis for the distinct pathways of hormone action elicited by insulin and the IGFs. Several features are involved in the divergence of the signalling pathways of insulin and the IGFs. The insulin receptor binds insulin with high affinity, and this specificity is determined by domains lying to the N-terminal and C-terminal sides of the cysteine-rich region in the alpha-subunit. The high-affinity IGF binding by the IGF-I receptor is determined by its cysteine-rich domain. Secondly, the IGF-binding proteins (IGFBPs), of which six have been characterized, bind the IGFs with an affinity higher than that of the IGF receptors. They bind all the circulating IGFs, protect them from degradation and deliver them to the IGF receptors in the target tissues, where they modulate IGF action. As they have no affinity for insulin, insulin is free to interact with its own receptor. Finally, structural differences in the beta-subunits of the insulin and IGF-I receptors may result in divergence of the signal pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor I produces renal hyperfiltration by a kinin-mediated mechanism

Insulin-like growth factor-I (IGF-I) infusion into rats and humans reduces renal vascular resistance and raises glomerular filtration rate (GFR) and renal plasma flow (RPF). To investigate whether kinins mediate the renal vasodilatory effects of IGF-I, we infused rats with IGF-I alone or in the presence of a B2 kinin receptor antagonist. Left kidney GFR, RPF, and kinin excretion were measured during infusion of vehicle and subsequently during 60-min infusion of IGF-I or IGF-I plus kinin antagonist. IGF-I was given as a bolus (150 micrograms/kg body wt), followed by infusion at a rate of 8.3 micrograms.kg-1 x min-1 for 60 min. The kinin antagonist was infused at a dose of 1 microgram.kg-1 x min-1 for 60 min before the start of IGF-I infusion. GFR and RPF increased significantly after IGF-I infusion was begun, from baseline levels of 1.70 +/- 0.12 and 6.21 +/- 0.34 to 2.12 +/- 0.11 and 7.91 +/- 0.29 ml/min, respectively, at 20 min (P < 0.001). This effect was maintained throughout 60 min of infusion. The increase in GFR and RPF was associated with a marked rise in urinary kinin excretion, from a baseline of 8.51 +/- 6.7 to 24.7 +/- 6.7 pg/min at 20 min and 40.3 +/- 10.4 pg/min at 40 min (P < 0.001). Pretreatment with the kinin receptor antagonist blocked the rise in GFR and RPF in response to IGF-I. These data suggest that the renal vasodilatory effect of IGF-I is mediated by kinins.

Placentation in the dasyurid marsupial, Sminthopsis crassicaudata, the fat-tailed dunnart, and notes on placentation of the didelphid, Monodelphis domestica

A light microscope study of the choriovitelline (yolk sac) placenta of the dasyurid marsupial, Sminthopsis crassicaudata, and some comparative observations on that of the didelphid, Monodelphis domestica, were performed. In the former species, the placenta was composed of an invasive bilaminar, avascular, yolk sac and a non-invasive trilaminar, vascular yolk sac. The bilaminar yolk sac placenta had trophoblast giant cells that eroded the maternal epithelium, but there was no evidence of invasion of maternal capillaries; thus, an endotheliochorial placenta was present. In the trilaminar yolk sac placenta, the convoluted chorion followed the contours of the highly folded endometrial epithelium but did not erode it and, therefore, an epitheliochorial placenta was formed. In late pregnancy, the choriovitelline placenta of Monodelphis domestica also had two regions, but the fetal trophoblast did not invade the uterine epithelium in either region. Rather, there were discontinuous areas of adhesion between trophoblast giant cells and uterine epithelium in the trilaminar yolk sac placenta and some extensive areas of adhesion in the attenuated bilaminar yolk sac placenta. The yolk sac placenta in M. domestica, unlike that of S. crassicaudata, therefore appears to be epitheliochorial in the vascular and non-vascular regions.

Insulin-like growth factor-binding protein enhancement of insulin-like growth factor-I (IGF-I)-mediated DNA synthesis and IGF-I binding in a human breast carcinoma cell line

The insulin-like growth factors (IGFs) are potent mitogens for malignant cell proliferation. The majority of secreted IGFs are bound to specific IGF-binding proteins (IGFBPs) that are secreted by a large number of cells. These proteins may either inhibit or enhance IGF actions. Breast carcinoma cells secrete a variety of IGFBPs. We have previously demonstrated that retinoic acid (RA) inhibition of IGF-I-stimulated MCF-7 cell proliferation is associated with increased IGFBP-3 levels in the conditioned media. We therefore investigated the effect of recombinant IGFBP-3 as well as IGFBP-2, -4 and -5 on IGF-I stimulation of DNA synthesis and IGF-I binding in the MCF-7 human breast carcinoma cell line. IGFBP-2 and -3 enhanced IGF-I stimulation of DNA synthesis in MCF-7 cells while IGFBP-4 and -5 had no effect. Transfection of MCF-7 cells with an IGFBP-3 expression vector resulted in the enhanced secretion of IGFBP-3 with an accompanying increase in IGF-I binding as well as increased cell proliferation upon treatment of the cells with IGF-I. IGF-I preincubation of MCF-7 cells transfected with control pSVneo plasmids results in cells refractory to further IGF-I stimulation of thymidine incorporation while IGF-I continues to stimulate [3H]-thymidine incorporation in IGFBP-3-transfected MCF-7 cells, suggesting that IGFBP-3 protects the cells from IGF-I-mediated down regulation of its receptor. Therefore, IGFBP-3 secreted by MCF-7 cells can enhance IGF-I stimulation of DNA synthesis, increase IGF-I binding to these cells, and prevent IGF-I-induced desensitization of its own receptor, suggesting that IGFBP-3 plays a significant role in IGF-I-mediated breast carcinoma proliferation.

Essential role of tyrosine residues 1131, 1135, and 1136 of the insulin-like growth factor-I (IGF-I) receptor in IGF-I action

The insulin and insulin-like growth factor-I (IGF-I) receptors are related heterotetramers consisting of two extracellular ligand-binding alpha-subunits and two transmembrane beta-subunits whose cytoplasmic domains exhibit tyrosine kinase activity. Previous studies have shown that ATP binding by the cytoplasmic tyrosine kinase domains of these receptors is necessary to initiate the signal transduction pathway triggered by ligands or by ligand-mimetic antibodies, suggesting that receptor autophosphorylation is a necessary proximal step in this pathway. In the case of the insulin receptor, it has additionally been demonstrated that a cluster of three tyrosines in the kinase domain itself are the first to be phosphorylated, and that autophosphorylation of these particular residues is necessary for receptor activity. Using stably transfected NIH-3T3 cell lines, we now show that mutation of the analogous residues in the IGF-I receptor abolishes all short, intermediate, and long-term responses to IGF-I. These data suggest that the initial mechanisms of activation of the insulin and IGF-I receptors are very similar. Additionally, we have identified two parameters, induction of c-fos gene expression and ornithine decarboxylase enzyme activity, which are extremely sensitive to IGF-I stimulation and which will be particularly useful in evaluating the biological activity of other mutated versions of the IGF-I receptor.

The regulation of IGF-I receptor gene expression by positive and negative zinc-finger transcription factors

The IGF-I-R gene promoter is a TATA-less, CAAT-less, GC-rich promoter which contains potential binding sites for the Sp1 and WT1 zinc-finger transcription factors. We have shown that Sp1 positively activates the IGF-I-R promoter. Since both the Sp1 and IGF-I-R genes are widely expressed, it is possible that Sp1 is one of the main regulators of IGF-I-R gene expression. This is supported by the correlation between the distribution and developmental regulation of Sp1 and IGF-I-R gene expression, in that both genes appear to be co-regulated during normal development. In a model of human neoplasm, WT, we have demonstrated increased expression of the IGF-I-R gene, which may result from loss of repression of the IGF-I-R promoter by another Zn(2+)-finger protein, the WT1 tumor suppressor gene product. Future studies will define whether other disease states in which the IGF-I-R gene is highly expressed are also associated with loss of negative regulation of the IGF-I-R promoter by WT1 or other tumor suppressor gene products.

Consultant opinion on orthodontic treatment plans used by dental practitioners: a pilot study

Prior to 1987, dental practitioners in England and Wales intending to carry out all but the simplest orthodontic treatment within the National Health Service, were required to submit pretreatment study models, details of the orthodontic assessment and the proposed treatment plan to the Dental Estimates Board prior to starting treatment. Models taken at the end of treatment were required by the Board to enable payment to be made. In this pilot study, the acceptability of orthodontic treatment plans used by practitioners working in the General Dental Services was assessed by eight hospital consultants, using information about 40 cases submitted to the Dental Estimates Board in 1987/88. All consultants considered a high proportion of plans to be unacceptable, but agreement between the consultants was variable and some agreed with one another on very few plans. A single scorer used the weighted PAR (Peer Assessment Rating) index to assess the degree of departure from normal occlusion of both pre- and post-treatment models. Using accepted standards, only nine cases were greatly improved (PAR reduction > 70%) and the mean percentage reduction in PAR score was low. Consultant opinion on the appropriateness of treatment planning was not related to the outcome of orthodontic treatment.

The role of insulin-like growth factors in diabetic kidney disease

Early renal manifestations of type I diabetes include kidney enlargement, increased glomerular filtration rate, and renal plasma flow. These hemodynamic changes may be caused by a number of factors, including growth hormone and/or insulin-like growth factor-I (IGF-I). Streptozotocin-induced insulinopenic diabetes in rats represents a model of human type I diabetes and is associated with the early hemodynamic changes in the kidney seen in poorly controlled type I diabetic patients. These changes are preceded by an accumulation of IGF-I peptide in the kidney. Insulin-like growth factor-I is not locally produced, but rather accumulates from circulating IGF-I, trapped by increased levels of IGF-binding proteins, particularly IGF-binding protein-1. The hemodynamic effects, reproduced by infusions of recombinant human IGF-I in normal rats, may be blocked by co-infusion of a kinin-receptor antagonist, suggesting that at least one of the mechanisms involved is the kallikrein-kinin system. These studies strongly support the notion that the IGF system may play a role in early hemodynamic manifestations of the diabetic kidney. Whether these effects lead to long-term diabetic renal disease remains to be studied.

The provision of orthodontic care in the general dental services of England and Wales: extraction patterns, treatment duration, appliance types and standards

A systematic sample of 1010 cases was collected by the Dental Practice Board. The commonest type of treatment involved extraction of the first premolars followed by removable appliances. Treatment duration was on average 1.9 years, one-arch fixed appliances were started in an older age group and two-arch fixed appliance treatment took longer to complete than other appliance types. The best standard of treatment was achieved using upper and lower fixed appliances.

Hepatic tyrosine-phosphorylated proteins identified and localized following in vivo inhibition of protein tyrosine phosphatases: effects of H2O2 and vanadate administration into rat livers

Injection of a combination of H2O2 and vanadate (H/V) into the portal vein of rat livers resulted in inhibition of protein tyrosine phosphatase activity and led to a dramatic enhanced in vivo protein tyrosine phosphorylation. Some of the phosphorylated proteins were identified as the beta-subunit of the insulin receptor, the insulin receptor substrate 1 (pp185), PLC-gamma (pp145), and a 100 kDa PLC-gamma-associated protein. Immunofluorescense and immune electron microscopy of frozen liver sections with anti-P-Tyr antibodies revealed that most of the tyrosine-phosphorylated proteins are localized in close proximity to the plasma membrane in intercellular adherence junctions and tight junction regions. This close in vivo association between membranal protein tyrosine kinases, their target proteins, and cytoskeletal elements could enable formation of 'signaling complexes' which may play a role in transmembrane signal transduction. By affinity chromatography over immobilized anti-P-Tyr antibodies, a large number of these tyrosine-phosphorylated proteins were partially purified.

Regulation of insulin-like growth factor (IGF) binding protein-5 in the T47D human breast carcinoma cell line by IGF-I and retinoic acid

The T47D human breast carcinoma cell line has been shown to synthesize insulin-like growth factor-I (IGF-I) binding proteins (IGFBPs) and IGF-I receptors, and to exhibit a mitogenic response to exogenous IGF-I. We have used T47D cells to investigate the regulation of IGFBPs by IGF-I and retinoic acid (RA), agents that affect cell proliferation and have been shown to regulate IGFBP levels in other cell types. Exposure of T47D cells to IGF-I resulted in the appearance of IGFBP-2, -4, and -5 in conditioned medium but had no effect on the levels of IGFBPs in Triton X-100-extracted cells. This effect was most pronounced for IGFBP-5 and was also elicited by an IGF-I analog that retains affinity for IGFBPs but not by insulin or IGF analogs that have decreased affinity for IGFBPs. Additionally, this effect was not associated with a change in IGFBP-5 messenger RNA (mRNA) levels; however, the appearance of IGFBP-5 in the conditioned medium was inhibited by an anti-IGF-I receptor antibody (alpha IR-3). RA decreased IGFBP-5 mRNA levels and cell-associated IGFBP-5 in both the presence and absence of IGF-I and inhibited the IGF-I-stimulated secretion of IGFBP-5 into T47D cell conditioned medium. These results suggest that IGF-I increases IGFBP-5 levels in the T47D cell line both through direct interaction with IGFBP-5 as well as through a receptor-mediated process that does not require direct interaction with IGFBPs. The latter results are consistent with an effect of IGF-I on a factor that may modulate an IGFBP protease activity. The inhibitory effect of RA, on the other hand, appears to be due primarily to regulation of IGFBP-5 mRNA levels. Thus, IGFBP-5 accumulation appears to be positively regulated by IGF-I, potentially at the level of susceptibility to proteolysis, and negatively regulated at the level of gene expression by RA.

Expression of insulin-like growth factor-I (IGF-I) and IGF-II and the IGF-I, IGF-II, and insulin receptor genes and localization of the gene products in the human ovary

We examined the expression of the genes encoding the insulin-like growth factors (IGFs) and their receptors (r) and the localization of their gene products in specific cellular compartments of the human ovary. mRNA was localized by in situ hybridization with specific human 35S-labeled antisense RNA probes, and protein was detected by immunocytochemistry with specific antisera. We studied 34 follicles (10 ovaries), which included both dominant and small antral follicles. In dominant follicles, no IGF-I mRNA was seen in either thecal or granulosa cells (GC), but IGF-Ir mRNA was expressed in GC. In contrast, abundant IGF-II mRNA was found exclusively in GC, whereas the IGF-IIr gene was expressed in both thecal cells and GC. Insulin receptor mRNA was widely distributed and expressed in all cell types, including stromal cells. Small antral follicles contained both IGF-I and IGF-II mRNA, which was restricted to thecal cells. Although IGF-Ir message was detected only in GC, IGF-IIr mRNA was expressed in both granulosa and thecal cells. As in dominant follicles, insulin receptor mRNA was found in thecal, granulosa, and stromal cells. No IGF-I immunoreactivity was seen in either dominant or small antral follicles; however, immunostaining for the other gene products demonstrated that each of these proteins colocalized with its corresponding mRNA. Thus, the relative distribution of ligand and receptor transcripts and protein in cellular compartments of the human ovary observed in this study supports the presence of an intraovarian IGF system and suggests that both autocrine and paracrine mechanisms of IGF action occur between GC and thecal cells. We conclude that 1) IGF-II, rather than IGF-I, is the principal IGF in human ovarian follicles, being synthesized in thecal cells in small antral follicles and in GC in dominant follicles; 2) in small antral follicles, IGF-II acts in an autocrine fashion in thecal cells and in a paracrine fashion in GC; 3) in dominant follicles, granulosa-derived IGF-II acts in an autocrine manner in GC; and 4) the presence of transcripts and proteins corresponding to the IGF and insulin receptors in cellular compartments of human ovaries may also provide target sites for the action of circulating ligands with a potential extraovarian role in the regulation of folliculogenesis.

Regulation of endometrial cancer cell growth by insulin-like growth factors and the luteinizing hormone-releasing hormone antagonist SB-75

The involvement of IGFs in growth regulation of the Ishikawa endometrial tumor cell line and the possible interference of LH-RH analogues with a potential autocrine or paracrine loop involving IGFs was evaluated. The mitogenic effects of IGF-I, IGF-II, and insulin were compared. IGF-I was found to be 3-fold more potent than IGF-II and 30-fold more potent than insulin, suggesting that the effects of these growth factors are mediated by the IGF-I receptor. Ishikawa endometrial cancer cells secrete IGF-II, but not IGF-I, and insulin (1 microM) stimulates IGF-II release. The LH-RH antagonist [Ac-D-Nal(2)1, D-Phe(4Cl)2, D-Pal(3)3, D-Cit6, D-Ala10]-GnRH (SB-75, CETRORELIX) inhibited basal and IGF-induced growth. Moreover, this antagonist almost completely inhibited IGF-II release from Ishikawa cells, while having no significant effect on the number or affinity of IGF-I binding sites. Inhibition of IGF-II release occurred at a lower SB-75 concentration than that needed for a reduction in cell number. The ED50 of SB-75 for IGF-II release was 0.3 microM as compared to 1.5 microns concentration which is required for reduction in cell number, suggesting that inhibition of growth factor release precedes cell growth inhibition. We conclude that the LH-RH antagonist SB-75 can inhibit the growth of endometrial cancer cells by interfering with the autocrine action of IGF-II and also by directly inhibiting the growth-stimulatory effects of IGFs, probably through effects on a post-receptor mechanism.

Structure of the chum salmon insulin-like growth factor I gene

Insulin-like growth factor I (IGF-I) plays a major role in development and metabolism. Currently, the cDNA-derived primary structure of IGF-I is known for some mammals and for chicken, frog, and salmon. Additionally, the organization of the human, rat, and chicken IGF-I genes has been established. The investigation of IGF-I gene structure in fish would extend the evolutionary picture for this hormone and facilitate our understanding of the features of the IGF-I gene that are common to all vertebrate species. The cloned chum salmon IGF-I gene appears to be much more compact than the mammalian and avian genes, being less than 20 kb in length. As in other species, however, the mature IGF-I peptide appears to consist of 70 amino acids and is encoded by exons 2 and 3. Intriguingly, exon 1-encoded 5'-untranslated region sequences are highly conserved, while the coding sequences at the 3' end of the same exon are less conserved. The amino terminus of the signal peptide is four amino acids shorter than in the mammalian and avian peptides. The end of the B domain, the C, A, and D domains, and the first part of the E peptide are encoded by exon 3, but the exon 3-encoded E peptide sequence is 27 amino acids longer than in other species. These extra 27 amino acids, encoded by both coho and chum salmon cDNAs, may be deleted by alternative splicing, as suggested from the sequence of a coho salmon IGF-I cDNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteinizing hormone-releasing hormone antagonists interfere with autocrine and paracrine growth stimulation of MCF-7 mammary cancer cells by insulin-like growth factors

Several studies have supported the idea that LH-releasing hormone (LHRH) antagonists have a direct effect on mammary tumor cells. In this study, we have evaluated the potential role of the insulin-like growth factors (IGFs) on the growth of MCF-7 mammary tumor cells and the effect of LHRH analogs on IGF action. The mitogenic effects of IGF-I, IGF-II, and insulin were compared. IGF-I was found to be 3 times more potent than IGF-II and 30 times more potent than insulin, suggesting that the effects of these growth factors are mediated by the IGF-I receptor. IGFs released by MCF-7 cells were measured by specific RIA after acid extraction and chromatography, so as to avoid the interference of IGF-binding proteins. MCF-7 cells secreted IGF-II, but not IGF-I. Estradiol (10(-9) mol/L) stimulated IGF-II release; this release preceded the effect of estradiol on cell growth. The LHRH antagonist [Ac-D-Nal(2)1,D-Phe(4Cl)2,D-Pal(3)3,D-Cit6,D-Ala10] LHR H (SB-75, CETRORELIX) inhibited basal, estrogen-induced, and IGF-induced growth. Moreover, this antagonist almost completely inhibited IGF-II release from MCF-7 cells. This effect preceded the inhibition of tumor cell growth. We conclude that a LHRH antagonist can inhibit the growth of breast tumors by interfering with the autocrine action of IGF-II and by directly inhibiting the growth stimulatory effect of IGFs.

Insulin-like growth factors

The purpose of this review has been to emphasize, in general terms, the major aspects of the structure, expression, and regulation of the IGF-I and IGF-II genes. The complex organization of these genes provides ample opportunities for control of gene expression at multiple levels. It is important to realize that regulation at one level can influence regulation at a different level. While such regulatory interactions are characteristic of both the IGF-I and IGF-II genes, they are particularly evident in the case of IGF-I gene expression. For example, the choice of transcription start site influences the length and the sequence of the 5'-UTR, which can influence mRNA translatability and prepeptide sequence, which may influence the amounts of protein produced and, potentially, the intracellular processing and secretion of the final gene product, the mature hormone. Another example is provided by the alternative splicing of E-peptide-encoding exons, which determines the primary structure of the prohormone, which could influence its processing, stability, or function. Thus, this complex gene organization may reflect the need to carefully control, through a multilevel process, the synthesis, processing, and secretion of these important regulatory peptides.

Failure of senescent human fibroblasts to express the insulin-like growth factor-1 gene

Senescent human diploid fibroblasts express several growth-regulated genes but fail to express others. In this paper we show, by a very sensitive technique (reverse transcriptase-polymerase chain reaction), that senescent cells fail to express insulin-like growth factor-1 (IGF-1) mRNA, which is expressed in moderate amounts by young cells. Human fibroblasts immortalized by transfection with a temperature-sensitive SV40 T antigen gene regain the ability to express IGF-1 mRNA, but only at the permissive temperature of 34 degrees C. Under these conditions, the immortalized human fibroblasts grow even in 1% serum. At the restrictive temperature of 39 degrees C, the temperature-sensitive T antigen is nonfunctional, IGF-1 RNA is not detectable, and the cells fail to grow even in 10% serum. The failure to express IGF-1 mRNA in postsenescent cells can be ascribed, at least in part, to a transcriptional mechanism. Despite the correlation among immortalization by SV40 T antigen, expression of IGF-1, and growth, it seems unlikely that the failure to express IGF-1 is the sole cause of cellular senescence; other requirements must be postulated.

Growth hormone (GH) stimulates insulin-like growth factor-I (IGF-I) and IGF-I-binding protein-3, but not GH receptor gene expression in livers of juvenile rats

In the adult rat, expression of the liver GH receptor, insulin-like growth factor-I (IGF-I), and IGF-I-binding protein-3 (IGFBP-3) genes has been shown to be under GH control. Additionally, hypophysectomy and GH treatment have a differential effect on the relative abundance of liver IGF-I mRNA variants in adult rats. To further elucidate the time of appearance and the extent of GH control of liver GH receptor, IGF-I, and IGFBP-3 gene expression, we studied the effect of hypophysectomy and GH and IGF-I treatment in juvenile rats. Male Wistar rats were hypophysectomized (Hx) on postnatal day 26 and received twice daily sc injections of saline, recombinant human GH (2.5 U/kg.day), or recombinant human IGF-I (500 micrograms/kg.day) for 7 days. Sham-operated rats received the same treatment. Hx animals also received T4 (20 micrograms/kg.day). In Hx animals, there was a significant reduction in body weight (69.8 +/- 6.6 vs. 100.4 +/- 5.4 g; P < 0.001). GH, but not IGF-I, treatment increased body weight (79.6 +/- 9.6 g after GH vs. 69.8 +/- 6.6 g before GH; P < 0.05). GH treatment partially maintained liver, kidney, and lung weights in Hx animals and increased them in intact animals, whereas IGF-I treatment did so only in the lungs of intact and Hx animals. Serum GH and IGF-I levels were markedly reduced in Hx animals compared with those in intact controls, and GH treatment maintained, albeit partially, circulating IGF-I levels compared with those in saline-treated Hx animals. IGF-I mRNA levels were markedly reduced in Hx liver (25.0 +/- 5.4%; P < 0.001 compared with intact controls). GH treatment for 7 days increased IGF-I mRNA levels by 4.8-fold over the levels in 9-day Hx animals and increased IGF-I mRNA levels by 2.2-fold in control rats. Hypophysectomy decreased exon 2-containing transcripts by 7.0-fold and exon 1-containing transcripts by 4.1-fold. GH treatment, however, affected both exon 1- and exon 2-containing transcripts similarly. Hepatic IGFBP-3 mRNA levels were reduced in Hx (53.2 +/- 1.8%; P < 0.01 compared with intact controls) and IGF-treated Hx animals, but were not decreased in Hx GH-treated animals (100.6 +/- 9.5). No changes in GH receptor or GH-binding protein mRNA levels were caused by Hx, GH, or IGF-I treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Phylogeny of the insulin-like growth factors (IGFs) and receptors: a molecular approach

The IGFs (IGF-I and IGF-II) are essential for normal mammalian growth and development. Their actions are mediated primarily by their interactions with the type I IGF receptor (IGF-I receptor), a transmembrane tyrosine kinase. The ligands and the IGF-I receptor are structurally related to insulin and to the insulin receptor, respectively. Analysis of evolutionary conservation has often provided insights into essential regions of molecules such as hormones and their receptors. The genes for insulin and IGFs have been partially characterized in a number of vertebrate species extending evolutionarily from humans as far back as fish. The sequences of the exons encoding the mature insulin and IGF peptides are highly conserved among vertebrate species, and IGF-I-like molecules are found in species whose origins extend back as much as 550 million years. The insulin receptor is also highly conserved in vertebrate species, and an insulin-receptor-like molecule has been characterized in Drosophila. In contrast, IGF-I receptors have only been characterized in mammalian species and partially studied in Xenopus, in which the tyrosine kinase domain is highly conserved. Studies are presently being undertaken to analyze in more detail the regulation of the genes encoding this important family of growth factors and the structure/function relationships in the gene products themselves.

Insulin-like growth factors and their receptors in normal physiology and pathological states

The insulin-like growth factor system, which includes the IGFs, IGF-binding proteins and IGF receptors, plays an essential role in normal growth and development, as well as the cellular differentiation of a number of other important systems, including the reproductive and immune systems. IGF action has also been implicated in several pathological conditions, including tissue repair, malnutrition, diabetes and malignancy.

Paradoxical biological effects of overexpressed insulin-like growth factor-1 receptors in Chinese hamster ovary cells

One major approach to the study of growth factor receptor action has been to overexpress wild-type or mutant receptors in cultured cells and to evaluate biological responses to exogenous ligand. Studies of this type with insulin and insulin-like growth factor-I (IGF-I) receptors often use Chinese hamster ovary (CHO) cells. We have compared the effect of receptor overexpression in CHO cells and in NIH-3T3 fibroblasts in order to assess the suitability of CHO cells for studies of this nature and the contribution of cell type-specific factors to those responses generally assayed. Overexpression of IGF-I receptors in NIH-3T3 cells resulted in increased sensitivity and maximal responsiveness of thymidine incorporation, 2-deoxyglucose uptake, and phosphatidylinositol-3 (PI3) kinase activation to IGF-I stimulation. In CHO cells, on the other hand, overexpression of either IGF-I or insulin receptors increased the sensitivity of thymidine incorporation to ligand, but maximal responsiveness was unchanged or decreased. Overexpression of the insulin receptor increased sensitivity of glucose uptake and the maximal response of PI3 kinase activation to insulin. Overexpression of the IGF-I receptor did not affect sensitivity or maximal responsiveness of glucose uptake or PI3 kinase activation to IGF-I. These data suggest that IGF-I and insulin signal pathways may differ in CHO cells, and that there may even be divergent IGF-I signaling pathways for short vs. long-term effects. Whether this is a result of differences in the number of endogenous receptors, hybrid receptor formation, or defects in post-receptor signaling, the use of CHO cells to assess receptor function must be approached with caution.

Retinoic acid and estrogen modulation of insulin-like growth factor binding protein-4 gene expression and the estrogen receptor status of human breast carcinoma cells

Retinoic acid (RA) and estrogen modulation of insulin like-growth factor binding protein-4 (IGFBP-4) gene expression was investigated in a number of human breast carcinoma (HBC) cell lines. Our results indicate that RA and/or estrogen modulation of IGFBP-4 mRNA levels appear to correlate with the ER-status of HBC cell lines. RA and estrogen enhanced IGFBP-4 mRNA levels in ER-positive MCF-7, RRO-I and ZR-75 cell lines and the effect of both of these agents in combination was additive. Although both individually also enhanced IGFBP-4 mRNA levels in ER-positive T47D cells, their effect in combination was antagonistic in this cell line. Transfection of human ER into ER-negative MDA-MB-231 cells conferred RA and estrogen the ability to enhance IGFBP-4 mRNA but both agents failed to concomitantly modulate IGFBP-4 levels in the CM suggesting a dual regulation by these agents at transcription/post-transcription and translation/secretion levels.

Increased expression of the insulin-like growth factor I receptor gene, IGF1R, in Wilms tumor is correlated with modulation of IGF1R promoter activity by the WT1 Wilms tumor gene product

Wilms tumor is a pediatric neoplasm that arises from the metanephric blastema. The expression of the gene encoding insulin-like growth factor II (IGF-II) is often elevated in these tumors. Since many of the actions of IGF-II are mediated through activation of the IGF-I receptor (IGF-IR), we have measured the levels of IGF-IR mRNA in normal kidney and in Wilms tumor samples using solution hybridization/RNase protection assays. IGF-IR mRNA levels in the tumors were 5.8-fold higher than in adjacent normal kidney tissue. Among the tumors themselves, the levels of IGF-IR mRNA in those containing heterologous stromal elements were 2-fold higher (P < 0.01) than in tumors without these elements. IGF-IR gene (designated IGF1R) expression in the tumors was inversely correlated with the expression of the Wilms tumor suppressor gene WT1, whose inactivation appears to be a key step in the etiology of Wilms tumor. Cotransfection of Chinese hamster ovary cells with rat and human IGF-IR gene promoter constructs driving luciferase reporter genes and with WT1 expression vectors showed that the active WT1 gene product represses IGF-IR promoter activity in a dose-dependent manner. These results suggest that underexpression, deletion, or mutation of WT1 may result in increased expression of the IGF-IR, whose activation by IGF-II may be an important aspect of the biology of Wilms tumor.

Insulin-like growth factor I gene expression by primary cultures of ovarian cells: insulin and dexamethasone dependence

A growing body of information now supports the existence of a complete intraovarian insulin-like growth Factor I (IGF-I) system replete with ligands, receptors, and binding protein(s). However, studies concerned with the regulation of ovarian IGF-I gene expression remain scarce. It was thus the objective of this communication to evaluate the expression of the IGF-I gene in the immature rat ovary under in vitro conditions. Whole ovarian dispersates or isolated granulosa cells were cultured for up to 96 h under serum-free conditions in the absence or presence of the indicated experimental agents. Extracted total RNA was subjected to a sensitive solution hybridization/RNase protection assay using 32P-labeled rat IGF-I and/or type I IGF receptor antisense RNA probes. Cultured in the absence or presence of FSH (100 ng/ml), whole ovarian dispersates (or isolated granulosa cells) displayed time-dependent (FSH-independent) decrements in the relative abundance of IGF-I transcripts apparent as early as 3 h after the onset of culture. No evidence of recovery was apparent by 96 h of culture. The apparent lack of an FSH effect did not reflect diminished biopotency as attested to by the ability of the hormone to promote time-dependent increments in the accumulation of progesterone. Importantly, the apparent decrease in ovarian IGF-I gene expression proved to be IGF-I specific in that type I IGF receptor transcripts displayed a substantial and sustained (for up to 96 h) FSH-independent increase beginning at the 24-h time point. At no point were IGF-II transcripts detected. The apparent decrease in the expression of IGF-I did not reflect the lack of extracellular matrix support in that neither laminin, collagen, nor whole serum supported sustained ovarian IGF-I gene expression. Treatment of whole ovarian dispersates with pharmacological concentrations of either insulin (1 micrograms/ml) or dexamethasone (10(-7) M) did not reverse the decline in IGF-I gene expression. Importantly, however, the combined application of both insulin and dexamethasone resulted in virtually complete preservation of IGF-I gene expression, the relative abundance of the corresponding transcripts proving uniform throughout. Taken together, these in vitro observations reveal irreversible (FSH-independent) decrements in ovarian IGF-I (but not type I IGF receptor) gene expression, the preservation of which required the concurrent provision of both insulin and dexamethasone.

Regulation of insulin-like growth factor-binding-protein-1, 2, 3, 4, 5, and 6: synthesis, secretion, and gene expression in estrogen receptor-negative human breast carcinoma cells

Insulin-like growth-factors I and II (IGF-I, II) are potent mitogens for breast carcinoma proliferation. In extracellular fluids, most of the IGF-I and II is associated with specific IGF-binding proteins (IGFBPs). The role of these IGFBPs in IGF action is still not clear, but it has been demonstrated that these proteins may either enhance or inhibit IGF-mediated cellular effects. Synthesis and secretion of IGFBPs have been demonstrated in breast carcinoma cells. In this study, we examined retinoic acid (RA) and IGF-I modulation of IGFBP mRNA and IGFBP levels in two ER-negative human breast carcinoma cell lines. Treatment of MDA-MB-231 and MDA-MB-468 cells with RA increased the levels in conditioned media of a M(r) 42-46-kDa IGFBP, which was immunoprecipitated by an IGFBP-3 antibody. IGF-I also increased the accumulated levels of IGFBP-3 in the conditioned media of both cell lines. Both cell lines expressed high basal levels of IGFBP-3 mRNA; the addition of RA increased IGFBP-3 mRNA levels by 1.5-fold, whereas the addition of IGF-I had no effect on IGFBP-3 mRNA levels in either cell line. The difference in the magnitude of the RA enhancement of IGFBP-3 mRNA levels (1.5-fold) and RA stimulation of IGFBP-3 levels in conditioned media (3.5-4-fold) suggests that some of the effect of RA is at a posttranscriptional level. IGF-I increased the levels of IGFBP-2 and IGFBP-5 in conditioned media by greater than tenfold but had no effect on IGFBP-2 and IGFBP-5 mRNA levels, again suggesting the involvement of posttranscriptional controls. Pretreatment of MDA-MB-468 and MDA-MB-231 cells with IGF-I receptor antibody (alpha IR3) blocked the IGF-I effect on IGFBP-3 levels in the media in both cell lines and IGFBP-2 and IGFBP-5 secreted levels in MDA-MB-468 cell conditioned media. The addition of RA also blocked IGF-I stimulation of IGFBP-2 and IGFBP-5 levels. Cycloheximide treatment completely blocked the RA and/or IGF-I-mediated modulation of these binding proteins, suggesting that these agents enhance IGFBP-3, IGFBP-2, and IGFBP-5 synthesis and consequent secretion. MDA-MB-468 cells expressed IGFBP-5 mRNA, whereas both MDA-MB-231 and MDA-MB-468 expressed IGFBP-6 mRNA. RA enhanced IGFBP-6 gene expression by threefold in MDA-MB-231 cells, whereas IGF-1 had no effect on IGFBP-6 gene expression in either cell line.(ABSTRACT TRUNCATED AT 400 WORDS)

Nutritional regulation of insulin-sensitive glucose transporter gene expression in rat cardiac muscle

The effects of fasting and refeeding on the levels of mRNA encoding the insulin-sensitive glucose transporter (GLUT4) in rat cardiac and skeletal muscle were investigated using solution hybridization/RNase protection assays with a rat GLUT4 antisense RNA probe. In addition, the effects of these nutritional states on GLUT1 mRNA levels in several non-insulin-sensitive tissues were examined using a GLUT1 antisense RNA probe. Fasting for 48 hr significantly decreased GLUT4 mRNA levels in heart, with levels significantly increased over control levels by 24 hr after refeeding. In contrast, GLUT4 mRNA levels in skeletal muscle increased with fasting and returned to control levels with refeeding. No significant changes in GLUT1 mRNA were seen after fasting and refeeding in several non-insulin-sensitive tissues studied. These results suggest that altered GLUT4 gene expression is observed in different nutritional (insulin) states in insulin-sensitive tissues, and suggests a potential role for insulin in mediating these changes in gene expression.

Orthodontics in the general dental service of England and Wales: a critical assessment of standards

Out of a sample of 1210 orthodontic patients treated within the General Dental Services in England and Wales, a high proportion showed no improvement. Upper and lower fixed appliances had the greatest influence on the outcome of treatment in terms of aesthetics, dental health need and standards. When treatment was analysed according to the appliance used, there were no statistically significant differences in the standard of treatment undertaken by specialist orthodontists and general dental practitioners. Methods for improving British orthodontic standards are considered.

Up-regulation of insulin-like growth factor-I (IGF-I) receptor gene expression in patients with reduced serum IGF-I levels

We have analysed the expression of the IGF-I receptor gene in lymphocytes of patients with low levels of circulating IGF-I (four patients with isolated GH deficiency (IGHD) and one Laron-type dwarf (LTD)) in comparison with a control group exhibiting normal serum IGF-I levels and endocrine profiles. 125I-Labelled IGF-I binding assays were performed on erythrocytes to determine the number of IGF-I binding sites per cell and their dissociation constants. Erythrocytes from patients with IGHD or LTD contained significantly (P = 0.002) more receptors per cell (10.9 +/- 3.1 binding sites/cell), with a reduced affinity (Kd = 0.49 +/- 0.05 nM), than erythrocytes from controls (2.0 +/- 0.4 sites/cell; Kd = 0.14 nM). The levels of IGF-I receptor mRNA in circulating lymphocytes were determined by an RNA template-specific reverse transcription/polymerase chain reaction method. There was a statistically significant increase in IGF-I receptor mRNA levels in lymphocytes from patients with LTD or IGHD when compared with controls (3108.1 +/- 775.9 vs 576.0 +/- 465.7 arbitrary units, P = 0.006). The increased level of IGF-I binding due to increased IGF-I receptor gene expression may represent a compensatory up-regulation process activated in response to the low levels of IGF-I in the circulation of patients with LTD or IGHD.

Two insulin genes are present in the salmon genome

According to the accepted hypothesis, polyploid evolution is necessary to achieve meaningful gene duplication. Some fish, namely those belonging to the suborder Salmonidae, appear to be autotetraploid species that probably originated from a diploid ancestor relatively recently and that appear to be progressing toward diploidization to various degrees. The Pacific chum salmon (Oncorhynchus keta) has almost completed this process of diploidization. Thus, with regard to practically any gene product, theory predicts a freshly diploidized, autotetraploid species to possess twice the number of gene loci as diploid animals. Here we show that the chum salmon genome contains two nonallelic insulin genes that are both expressed in chum salmon Brockman bodies. Nucleotide sequence analysis reveals structural diversification of this pair of duplicated genes.