Classification of the insulin-like growth factor binding proteins into three distinct categories according to their binding specificities

Competitive binding experiments with insulin-like growth factor (IGF)-1, IGF-2 and des-(1-3)-IGF-1 have confirmed the interpretation based on limited amino-terminal sequence analysis that at least three types of IGF binding protein occur. In addition to the acid stable subunit of the large serum binding protein which exhibits des-(1-3)-IGF-1 binding only slightly less than IGF-1, the small IGF binding proteins can be separated into two classes based on differences in des-(1-3)-IGF-1 and IGF-2 binding potencies.     

Specific binding of insulin-like growth factors 1 and 2 to the type 1 and type 2 receptors respectively.

1. Competitive binding and receptor cross-linking experiments have been used to examine the receptor-ligand interactions between three bovine insulin-like growth factors (IGF) and monolayer cultures of myoblasts and fibroblasts. 2. Labelled IGF-2 bound predominantly to the type 2 receptor with negligible label cross-linked to the type 1 receptor, notwithstanding the ability of IGF-2 to compete effectively for the binding of IGF-1 to the type 1 receptor. Approx. 100-fold higher concentrations of IGF-1 or the N-terminal truncated (des-Gly-Pro-Glu) IGF-1 (-3N:IGF-1) were required to produce competition equivalent to IGF-2. 3. All IGF peptides, but especially IGF-1, enhanced the binding of labelled IGF-2 to the type 2 receptor of lung fibroblasts. This unusual effect was probably a consequence of the displacement of labelled IGF-2 otherwise bound to a medium protein, a conclusion supported by the demonstration of a 38 kDa membrane protein cross-linked to labelled IGF-2. 4. Both IGF-1 and -3N:IGF-1 bound only to the type 1 IGF receptor in L6 myoblasts, rat vascular smooth-muscle cells and human lung fibroblasts. The peptides competed for labelled IGF-1 binding with potencies in the order -3N:IGF-1 greater than IGF-1 greater than IGF-2 much greater than insulin. Since the IGF peptides were equipotent in skin fibroblasts, it was proposed that the apparently higher affinity of -3N:IGF-1 for receptors in the other cell types was instead a consequence of a low affinity of this peptide for the competing 38 kDa binding protein.     

Natural and synthetic forms of insulin-like growth factor-1 (IGF-1) and the potent derivative, destripeptide IGF-1: biological activities and receptor binding

Insulin-like growth factor-1 (IGF-1), whether recombinant, chemically-synthesised or purified from bovine colostrum, was equipotent in radioreceptor assays with IGF-1 or insulin-like growth factor-2 (IGF-2) as radioligand as well as in its ability to stimulate protein synthesis in L6 myoblasts. The N-terminal truncated, destripeptide derivative of IGF-1 was approximately 7 times more potent than IGF-1 in the protein synthesis bioassay. This increased activity occurred equally with the peptide purified from bovine colostrum as with chemically-synthesised material. The higher potency of the truncated form was not associated with an increased ability to compete for IGF-1 binding to L6 myoblasts.     

The influence of blood cells and PDGF on porcine theca cell function in vitro

The role of red and white blood cells in the regulation of porcine theca cell function is poorly understood. Interactions between these cell types and a potential mediator of any interaction, PDGF, were investigated using a serum-free culture system. Theca cells were collected from 6-9mm antral follicles and plated at 50x10(3) viable cells/well. In the first experiment, macrophages were removed and theca cells+/-macrophages were cultured with a range of PDGF doses (0.1, 1, and 10ng/ml)+/-IGF-1. In the second experiment, red blood cells were removed with lysing buffer. In both experiments the effect of treatment on steroidogenesis and viable cell number was examined. Macrophage removal decreased oestradiol production but increased androstenedione output irrespective of the presence of IGF-1 (oestradiol+/-IGF-1, P<0.001; androstenedione P=0.02 without IGF-1, P<0.001 with IGF-1). PDGF increased oestradiol synthesis by whole and macrophage-free theca cell preparations but only in the presence of IGF-1 (P<0.001). In contrast, androstenedione production was unaffected by PDGF dose in the presence of IGF-1 (P=0.67). Without IGF-1, 10ng/ml PDGF tended to decrease androstenedione levels (P=0.06). Macrophage removal increased viable cell number at 144h (P<0.001+/-IGF-1) as did PDGF (P<0.001+/-IGF-1). In the absence of IGF-1, there was a PDGF x cell type interaction (P=0.02). Macrophage-free cultures with 10ng/ml PDGF had twice as many viable cells as whole preparations with no PDGF. In the second experiment, red blood cell removal did not affect steroidogenesis or the number of viable cells present at 144h when cells were cultured with IGF-1. The data show that theca cell/macrophages interactions do occur, and influence both steroidogenesis and viable cell number during culture. The macrophage product(s) enhanced oestradiol synthesis but reduced androstenedione production and the number of viable cells. As all these interactions were not mimicked by PDGF, PDGF cannot be the only factor mediating the theca/macrophage interaction. When cultured under optimised conditions the presence of red blood cells was not detrimental to theca cell steroidogenesis or the number of viable cells.     

Synthesis and characterization of biotinylated forms of insulin-like growth factor-1: topographical evaluation of the IGF-1/IGFBP-2 AND IGFBP-3 interface

Activation of the insulin-like growth factor-1 (IGF)-1 receptor signaling pathways by IGF-1 and IGF-2 results in mitogenic and anabolic effects. The bioavailability of the IGFs is regulated by six soluble binding proteins, the insulin-like growth factor binding proteins (IGFBPs), which bind with approximately 0.1 nM affinity to the IGFs and often serve as endogenous antagonists of IGF action. To identify key domains of IGF-1 involved in the interaction with IGFBP-2 and IGFBP-3, we employed IGF-1 selectively biotinylated on residues Gly 1, Lys 27, Lys 65, and Lys 68. All monobiotinylated species of IGF-1 exhibited high affinity ( approximately 0.1-0.2 nM) for IGFBP-2 and IGFBP-3 in solid-phase-binding assays. However, different labeling intensities were observed in ligand blot analysis of IGFBP-2 and IGFBP-3. The N(epsilon)(Lys65/68)(biotin)-IGF-1 (N(epsilon)(Lys65/68b)-IGF-1) probe exhibited the highest signal intensity, while N(alpha)(Gly1b)-IGF-1 and N(epsilon)(Lys27b)-IGF-1 demonstrated significantly lower signals. When taken together, these results suggest that, once bound to IGFBP-2 or IGFBP-3, the biotin moieties of N(alpha)(Gly1b)-IGF-1 and N(epsilon)(Lys27b)-IGF-1 are inaccessible to NeutrAvidin-peroxidase, the secondary binding component. Ligand blots using IGF-1 derivatized with a long chain form of the N-hydroxysuccinimide biotin (NHS-biotin) to yield N(alpha)(Gly1)(LC-biotin)-IGF-1 and N(epsilon)(Lys27)(LC-biotin)-IGF-1 demonstrated increased signal intensity compared with their NHS-biotin counterparts. In BIAcore analysis, IGFBP-2 and IGFBP-3 bound only to the N(epsilon)(Lys65/68b)-IGF-1-coated flowcell of a biosensor chip, confirming the inaccessibility of Gly 1 and Lys 27 when IGF-1 is bound to IGFBP-2 and IGFBP-3. These data confirm the involvement of the IGFBP-binding domain on IGF-1 in binding to IGFBP-2 and IGFBP-3 and support involvement of the IGF-1R-binding domain in IGFBP binding.     

Binding properties and biological potencies of insulin-like growth factors in L6 myoblasts.

Protein synthesis in rat L6 myoblasts is stimulated and protein breakdown inhibited in a co-ordinate manner by insulin-like growth factors (IGF) or insulin. For both processes, bovine IGF-1 was somewhat more potent than human IGF-1, which was effective at a tenth the concentration of insulin, rat IGF-2 or human IGF-2. A similar order of potency is noted when DNA synthesis or protein accumulation is monitored over a 24 h period, but between 20- and 50-fold higher concentrations of each growth factor are required than those needed to produce effects in the 4 h protein-synthesis or -breakdown measurements. Binding experiments with labelled human or bovine IGF-1 as ligand demonstrated competition at concentrations of IGF-2, especially human IGF-2, lower than that of either IGF-1 preparation. This pattern was much more pronounced when the radioligand was either human IGF-2 or rat IGF-2. Insulin competed 10-15% for the binding of labelled IGF-1, but not at all with labelled IGF-2. Ligand-receptor cross-linking experiments showed that labelled bovine IGF-1 bound approximately equally to the type 1 IGF receptor (Mr 130000 after reduction) and to the type 2 IGF receptor (Mr 270000 after reduction), and that unlabelled IGF-1 competed equally with radioligand binding to both receptors. On the other hand, rat IGF-2 competed more effectively for binding to the type-2 receptor, and insulin competed only for binding to the type-1 receptor. Further cross-linking experiments with rat IGF-2 as radioligand demonstrated binding only to the type-2 receptor and to proteins with Mr values after reduction of 230000 and 200000. This binding was prevented by high rat IGF-2 concentrations, less effectively by bovine IGF-1 and not at all by insulin. The apparently conflicting biological potencies and receptor binding of the different growth factors can be explained if all the biological actions are mediated via the type-1 IGF receptor, rather than through the abundant type-2 receptor.     

Synthesis and characterization of insulin-like growth factor (IGF)-1 photoprobes selective for the IGF-binding proteins (IGFBPS). photoaffinity labeling of the IGF-binding domain on IGFBP-2

Elevated insulin-like growth factor (IGF)-1 levels are prognostic for the development of prostate and breast cancers and exacerbate the complications of diabetes. In each case, perturbation of the balance between IGF-1/2, the IGF-1 receptor, and the IGF-binding proteins (IGFBPs) leads to elevated IGF-1 sensitivity. Blockade of IGF action in these diseases would be clinically significant. Unfortunately, effective IGF antagonists are currently unavailable. The IGFBPs exhibit high affinity and specificity for the IGFs and serve as natural IGF antagonists, limiting their mitogenic/anti-apoptotic effects. As an initial step in designing IGFBP-based agents that antagonize IGF action, we have begun to analyze the structure of the IGF-binding site on IGFBP-2. To this end, two IGF-1 photoprobes, N(alphaGly1)-(4-azidobenzoyl)-IGF-1 (abG(1)IGF-1) and N(alphaGly1)-([2-6-(biotinamido)-2(p-azidobenzamido)hexanoamido]ethyl-1,3'-dithiopropionoyl)-IGF-1 (bedG(1)IGF-1), selective for the IGFBPs were synthesized by derivatization of the alpha-amino group of Gly(1), known to be part of the IGFBP-binding domain. Mass spectrometric analysis of the reduced, alkylated, and trypsin-digested abG(1)IGF-1.recombinant human IGFBP-2 (rhIGFBP-2) complex indicated photoincorporation near the carboxyl terminus of rhIGFBP-2, between residues 266 and 287. Mass spectrometric analysis of avidin-purified tryptic peptides of the bedG(1)IGF-1.rhIGFBP-2 complex revealed photoincorporation within residues 212-227. Taken together, these data indicate that the IGFBP-binding domain on IGF-1 contacts the distal third of IGFBP-2, providing evidence that the IGF-1-binding domain is located within the C terminus of IGFBP-2.     

Novel fed-batch strategy for the production of insulin-like growth factor 1 (IGF-1)

The production of Long-R -IGF-1 (an IGF-1 fusion analog) by constant-rate, fed-batch fermentation of Escherichia coli yielded 2.6 g fusion protein/L, corresponding to an actual IGF-1 concentration of 2.2 g/L. A novel strategy employing three distinct feeding stages was developed which raised product concentration to 4.3 g/L (3.6 g/L of IGF-1) while minimising glucose and acetate accumulation. This improved productivity was not accompanied by an increase in inclusion body size.     

Insulin-like growth factor binding protein secretion by muscle cells: effect of cellular differentiation and proliferation

Several cell types have been shown to secrete insulin-like growth factor binding proteins (IGF-BP) in vitro. Since IGF-BP influences cell responsiveness to IGF, three muscle cell types were investigated to determine if they produced IGF-BP and to identify factors that regulate IGF-BP secretion. Porcine smooth muscle cells (pSMC), rat L6 skeletal muscle cells, and mouse BC3H-1 myocytes were used. IGF-BP activity in serum-free conditioned media was quantitated with a polyethylene glycol precipitation method. All three cell types secreted IGF-BP activity into the medium. Insulin was a potent stimulant of IGF-BP secretion for each cell type. Specifically, 1 microgram/ml insulin increased the IGF-BP concentration in conditioned media from 10.5 +/- 1.3 to 15.0 +/- 1.5 ng/ml in confluent L6 myotubes, from 42.5 +/- 11.1 to 90.5 +/- 9.8 ng/ml in confluent BC3H-1 cells, and from 2.1 +/- 0.1 to 3.8 +/- 0.1 ng/ml in confluent pSMC. L6 myotubes required more insulin (8 micrograms/ml) to achieve a half-maximal stimulation of IGF-BP secretion than confluent pSMC, differentiation deficient L6.DD cells or BC3H-1 cells, where half-maximal stimulation occurred between 125 and 300 ng/ml. L6 myoblasts were 40-fold more sensitive to insulin stimulation of IGF-BP secretion than L6 myotubes. IGF-I, although it interferes with the assay and thereby lowers the amount of detectable IGF-BP, stimulated the secretion of IGF-BP from all three cell types. Dexamethasone, (10(-7) M) decreased IGF-BP secretion into the media by approximately 50% for all three cell types. Affinity cross-linking and ligand blotting of 125I-IGF-I to conditioned media from each cell type showed (IGF-BP)-(IGF-I) complexes with molecular weights ranging 32-40 kDa (24-32 kDa for IGF-BP and 7.5 kDa for IGF-I). Insulin stimulated cell proliferation for both L6 myoblasts and BC3H-1 myocytes. This cell proliferative response was associated with an increase in IGF-BP secretion/cell in response to insulin. In contrast dexamethasone decreased L6 myoblast proliferation and decreased IGF-BP secretion/cell. We conclude that IGF-BP is secreted by each muscle cell type and that the state of cellular differentiation or quiescence influences its basal and insulin-stimulated secretion. Insulin and IGF-I are stimulators of IGF-BP secretion, whereas dexamethasone inhibits IGF-BP secretion. Because these hormones control muscle cell growth and differentiation, the IGF-BP may play an important regulatory role in these processes.     

The biological potency of covalent insulin-receptor complexes. Dependence on site of cross-linkage

A radioactive photosensitive insulin analogue, 125I-N epsilon B29-(4-azido-2-nitrophenyl-acetyl)insulin, was covalently bound to the receptors of isolated rat adipocytes by irradiation with UV light. This caused a stimulation of lipogenesis. The relative potency of the covalent complexes to that of normal reversible complexes was calculated by comparing the amounts of radioactivity required to be covalently or reversibly bound by adipocytes to cause the same levels of stimulation. For several different occupancies , this relative potency was constant at 50 +/- 3%. Previous studies had shown that the relative potency of covalently bound 125I-N alpha B2-(4-azido-2- nitrophenylacetyl )des- PheB1 -insulin was only 25 +/- 4% under identical conditions. This demonstrates that the sites of crosslinking have a marked effect on the potency of the covalent hormone-receptor complex. It appears that attachment through the C-terminus of the B-chain leads to a better stabilization of the biologically active form than linking through the more flexible N-terminus.     

Results of a two-year treatment with slow release lanreotide in acromegaly.

In this open sequential study we evaluated the long-term effectiveness and tolerability of the i.m. administration of slow release lanreotide 30 mg (SRL) in 18 acromegalics (7 M/11 F, age 50.9+/-12.7 yr). Baseline mean GH and IGF-1 levels were 15.8+/-6.6 ng/ml and 702+/-74 ng/ml, respectively. Four hours, 1, 7, and 14 days after SRL, mean GH levels were 8.9+/-5.9 (p < 0.005), 11.4+/-6.9 (p < 0.05), 9.1+/-4.5 (p < 0.05), and 9.1+/-4.1 ng/ml (p < 0.05), respectively; and the IGF-1 values at 1, 7, and 14 days were 624+/-77 (p < 0.05), 555+/-83 (p < 0.001), and 467+/-58 ng/ml (p < 0.0001), respectively. Four hours after SRL administration GH was < 2.5 ng/ml in 11 patients and decreased 85% of the basal value, without normalizing, in another case. In the following 2 weeks, 7 and 2 patients maintained GH < 2.5 ng/ ml or < 50% of baseline; 3 and 2 of them attained IGF-1 values in the normal range or < 50% of basal levels. A patient developed acute pancreatitis after the injection of the drug and therefore stopped the treatment. Another patient did not continue SRL, and she was turned on octreotide, s.c. administered (OCT), because only the latter treatment ameliorated significantly the headache. In 16/18 patients the treatment was continued until the 24th month. SRL was administered every 14 days until the 24th month in 3 cases, whereas in 13 patients the dose schedule was increased every 10 days since the 7th month because they did not normalize serum GH and IGF-1 levels. In these 16 patients baseline GH and IGF-1 levels were 10.0+/-2.5 ng/ml and 671+/-75 ng/ml, respectively. At the 1st, 3rd, and 6th month of treatment mean GH levels fell to 5.4+/-1.4 (p < 0.05), 5.3+/-1.8 (p < 0.05), and 5.0+/-1.6 (p < 0.05) ng/ml, respectively; and IGF-1 declined to 511+/-87 (p < 0.005), 565+/-85 (p < 0.05), and 525+/-94 (p < 0.01) ng/ml, respectively. Throughout the first semester GH was < 2.5 ng/ml in 5 patients and decreased > 50% in another three. IGF-1 levels normalized in 3/5. Throughout the following 18 months of treatment, mean GH (3.4+/-1.0 ng/ml) and IGF-1 (413+/-75 ng/ml) values decreased significantly in comparison with both the baseline concentrations (GH p < 0.01, IGF-1 p < 0.001) and the levels measured during the 1st semester of treatment (GH p < 0.05, IGF-1 p < 0.001). GH remained < 2.5 ng/ml in 11 patients, and in 8/11 cases IGF-1 fell in the normal range. Serum GH and IGF-1 levels decreased by more than 50% of baseline levels in 2 other cases. At MRI, pituitary adenoma was no longer evident in one patient previously treated with OCT and significantly decreased in another patient previously treated with surgery plus radiotherapy, as well as in a patient previously untreated. During treatment the percentage of patients complaining of headache and fatigue decreased significantly (chi2, p < 0.05 and p < 0.0005, respectively). Overall, the headache (p < 0.005), arthralgia (p < 0.05), and paresthesia (p < 0.01) ameliorated significantly. Ultrasound scan showed gallbladder sludge or sand-like stones in 5/11 patients. This study, which is one of the longest surveys on a relatively large series of acromegalics treated with SRL, confirms the long-term effectiveness of this drug for the treatment of patients with active acromegaly. SRL decreases significantly GH and IGF-1 in most cases and induces the shrinkage of the pituitary tumor in some patients previously either untreated or both treated for acromegaly. SRL improves significantly clinical symptoms and it is well tolerated.     

Modulation of insulin-like growth factor actions in L6A1 myoblasts by insulin-like growth factor binding protein (IGFBP)-4 and IGFBP-5: A dual role for IGFBP-5

We have previously shown that the insulin-like growth factors (IGFs) stimulate both proliferation and differentiation of skeletal muscle cells in culture, and that these actions in L6A1 muscle cells may be modulated by three secreted IGF binding proteins (IGFBPs), IGFBP-4, -5, and -6. Since we found that the temporal expression pattern of IGFBP-4 and IGFBP-5 differed dramatically during the transition from proliferating myoblasts to differentiated myotubes, we undertook the current study to examine the effects of purified IGFBP-4 and IGFBP-5 on IGF- stimulated actions in L6A1 muscle cells. As has been shown for other cell types, we found that IGFBP-4 had only inhibitory actions, inhibiting IGF-I and IGF-II- stimulated proliferation and differentiation. In contrast, IGFBP-5 exhibited both inhibitory and stimulatory actions. When added in the presence of 30 ng/ml IGF-I, IGFBP-5 (250 ng/ml) inhibited all markers of the early proliferative response: the tyrosine phosphorylation of the cytoplasmic signaling molecules IRS-1 and Shc, the activation of the MAP kinases, ERK1 and 2, the elevation of c-fos mRNA, the early inhibition of the elevation in myogenin mRNA, and the increase in cell number. In contrast, IGFBP-5 stimulated all aspects of the myogenic response to IGF-I: the later rise in myogenin mRNA, the elevation of creatine kinase activity, and the fusion of myoblasts into myotubes. This dual response to IGFBP-5 was greatest when it was added at a molar ratio of IGFBP-5 to IGF-I of 2:1. In contrast, when IGFBP-5 was added in the presence of IGF-II, it inhibited both proliferation and differentiation. Neither IGFBP had any effect when added in the presence of R3 IGF-I, an analog with substantially reduced affinity for IGFBPs. Our results suggest that the role of IGFBP-4 is mainly to sequester excess IGFs, and thus inhibit all actions. IGFBP-5, however, is capable of eliciting a dual response, possibly due to its unique ability to associate with the cell membrane. J. Cell. Physiol. 177:47–57, 1998. © 1998 Wiley-Liss, Inc.     

Involvement of polyamines in epidermal growth factor (EGF), transforming growth factor (TGF)-α and -β1 action on culture of L6 and fetal bovine myoblasts

• 1.1. α-Difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase significantly abolished stimulation of protein synthesis evoked by EGF, TGF-α or -β 1 in L6 and fetal bovine myoblasts.
• 2.2. The participation of polyamines in early events evoked by growth factors was shown by a significant stimulation of ornithine decarboxylase and Sdenosylmethionine decarboxylase activity as well as increased concentration of spermidine and spermine in L6 cells exposed to TGF-α and EGF.
• 3.3. TGF-β 1 at a high concentration (1 ng/ml) increased protein synthesis in L6 myoblasts but inhibited it in fetal bovine myoblasts. Metabolic effects of TGF-β 1 in L6 cells was associated with an enhancement of decarboxylase activities, however there were no significant changes in cellular polyamine concentrations. Presented data suggest that polyamines are involved in the signal transduction pathway of EGF, TGF-α, and -β 1 in L6 and fetal bovine myoblasts.

     

Application of peptide-mediated ring current shifts to the study of neurophysin-peptide interactions: a partial model of the neurophysin-peptide complex

Perdeuteriated peptides were synthesized that are capable of binding to the hormone binding site of neurophysin but that differ in the position of aromatic residues. The binding of these peptides to bovine neurophysin I and its des-1-8 derivative was studied by proton nuclear magnetic resonance spectroscopy in order to identify protein residues near the binding site through the observation of differential ring current effects on assignable protein resonances. Phenylalanine in position 3 of bound peptides was shown to induce significant ring current shifts in several resonances assignable to the 1-8 sequence, including those of Leu-3 and/or Leu-5, but was without effect on Tyr-49 ring protons. The magnitude of these shifts was dependent on the identity of peptide residue 1. By contrast, the sole demonstrable direct effect of an aromatic residue in position 1 was a downfield shift in Tyr-49 ring protons. Study of peptide binding to des-1-8-neurophysin demonstrated similar conformations of native and des-1-8 complexes except for the environment of Tyr-49, confirmed the peptide-induced ring current shift assignments in native neurophysin, and indicated an effect of binding on Thr-9. These observations are integrated with other results to provide a partial model of neurophysin-peptide complexes that places the ring of Tyr-49 at a distance 5-10 A from residue 1 of bound peptide and that places both the 1-8 sequence and the protein backbone region containing Tyr-49 proximal to each other and to peptide residue 3.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison of hormone levels in follicle-lutein-cysts and in normal bovine ovarian follicles

Insulin-like growth factors 1 and 2 (IGF-1 and 2), oxytocin, progesterone, estradiol and ubiquitin were measured in bovine follicle-lutein-cysts and in follicular fluid after the classification of ovarian follicles by size (Class I = <4 mm; Class II = 5-8 mm; Class III = 9-12 mm; Class IV = preovulatory; Class V = cystic). It was found that IGF-1 concentrations increased during growth from 280 ng/ml in small follicles to 489 ng/ml in preovulatory follicles; IGF-2 appeared to remain constant in follicular fluid and in cysts (275 ng/ml). Oxytocin values were low in Class I, II and III follicles (30 pg/ml) but increased in preovulatory and cystic follicles (75 pg/ml). Estradiol increased significantly only in preovulatory follicles. Ubiquitin, a protein reflecting cellular replicative activity, could be found in bovine follicular fluid in high concentrations: 1.6 mug/ml in Class I,II and III follicles with the highest amounts in preovulatory follicles (2.3 mug/ml). In contrast with normal follicles, cysts were found to have a minimal concentration of ubiquitin (0.3 mug/ml). Progesterone levels were 5 times higher in cysts (325 ng/ml) and IGF-1 concentrations were markedly higher in cystic follicles (881 ng/ml) than in the other follicles. Simultaneously, maximum gene expression for IGF-1 was found in granulosa/lutein cells of cystic follicles (Class V), suggesting de novo synthesis of IGF-1. Between the different follicle classes progesterone, oxytocin and IGF-1 concentrations correlated positively (r=0.82). Hormonal levels in follicle-lutein-cysts indicated an arrested stage of insufficient luteinization as a possible result from the premature release of LH or from the release of amounts of LH inadequate to cause ovulation.     

Insulin-Like Peptides of the Cerebropleural Ganglion of the Mollusc Anodonta cygnea: Isolation, Purification, and Radioligand Analysis

Cerebropleural ganglia from 4000 individuals of the mollusc Anodonta cygnea were submitted to procedures developed for isolation of vertebrate pancreatic insulins: homogenization and extraction, stage-like isoelectrical sedimentation, and ion-exchange chromatography. As a result of purification of the obtained preparation, using high-effective liquid chromatography, there were identified 7 protein peaks differing by time of retention on the reverse-phase sorbent in acetonitryl gradient and designated as insulin-related peptides (IRP), IRP1-IRP7. The material was characterized by the peptide ability to inhibit specific binding of ¹²⁵I-insulin and of insulin-related factor-1 (¹²⁵I-IGF-1) by plasma membranes of the rat liver and brain. The IC₅₀ value of peptide concentration (nM) able to replace 50% of the labeled hormone bound with the receptor amounted in the insulin radioreceptor system for IRP1 to 330, for IRP3 to 130, for IRP4 to 17, for IRP5 to130, for IRP6 to 420 nM. Peptide IRP7 at a maximal concentration (10⁴ ng/ml) replaced less than 50% of labeled hormone, whereas in IRP2 no inhibitory ability was detected under these experimental conditions. The IC₅₀ value in the case of ¹²⁵I-IGF-1 amounted for IRP1, IRP4, and IRP5 to17, for IRP2 to 50, for IRP3 to 83, for IRP6 to 133 nM. IRP7 at a concentration of 10⁴ ng/ml replaced less than 50% of labeled hormone. The same high relative affinity of the peptide IRP4 (12% of activity of standard insulin and IGF-1) to both receptor types is revealed. The results of analysis in two types of hormonal test systems indicate the ability of the insulin-related peptides of the anodonta cerebropleural ganglion to interact with the vertebrate receptor of insulin and IGF-1. This gives grounds to suggest the presence of the metabolic and growth-stimulating properties in these peptides. For the first time, the IGF-1 activity is revealed in insulin-like molecules in invertebrates. Taking into account the chromatographically revealed differences of physicochemical characteristics of individual IRP as well as predominance of their IGF-1-binding properties, there is suggested another organization of the IRP receptor-binding domains in IPR of this mollusc species, as compared with mammalian insulins.     

Effectiveness of slow-release lanreotide in previously operated and untreated patients with GH-secreting pituitary macroadenoma.

The aim of this study was to verify whether treatment with slow-release lanreotide (SRL) before surgery is useful in the management of patients with GH-secreting pituitary macroadenoma. Twenty untreated acromegalics were enrolled randomly in two groups. Ten patients (group 1: 2 males and 8 females aged 44.5 +/- 4.3 years) underwent surgery via transsphenoidal access. Only one of them was cured by surgery, whereas the other nine were treated with SRL. In the other ten patients (group 2: 3 males and 7 females aged 43.2 +/- 12.3 years), transsphenoidal surgery followed SRL treatment. Surgery induced the normalization of GH and IGF-1 levels in four group 2 patients - three of them had shown an evident shrinkage of the tumor after SRL treatment. After surgery, group 1 showed a significant decrease of mean IGF-1 (580 +/- 63 vs. 789 +/- 64 ng/ml, p < 0.02), but not of GH values (26.1 +/- 9.8 vs. 44.8 +/- 19.3 ng/ml, NS); the cured patient was excluded from the following evaluations. Group 2 showed an evident, but not significant, decrease of both GH and IGF-1 values compared to values measured at the end of medical treatment (GH: 22.4 +/- 9.7 vs. 7.7 +/- 4.7 ng/ml, NS. IGF-1: 570 +/- 69 vs. 402 +/- 58 ng/ml, NS). Gonadal, thyroid and adrenal impairment was evident in six, four and no patients in group 1 and in three, two and one patients in group 2, respectively. SRL 30 mg was administered every 14 days for three months and then every 10 days until the 6th month. Before SRL treatment, mean GH and IGF-1 levels did not differ significantly in group 1 vs. group 2 (GH: 29.3 +/- 10.5 vs. 43.4 +/- 22.0 ng/ml; IGF-1: 633 +/- 38 vs. 778 +/- 83 ng/ml). In group 1, a significant decrease of serum GH, but not of IGF-1 levels, was achieved at the end of 1st trimester of SRL (GH: 17.6 +/- 5.4 ng/ml, p < 0.05. IGF-1: 540 +/- 48 ng/ml, NS), whereas a significant decrease in both GH and IGF-1 values was evident during the 2nd trimester (GH: 6.1 +/- 3.0 ng/ml, p < 0.05. IGF-1: 433 +/- 74 ng/ml, p < 0.02). Serum GH levels, measured during the 2nd trimester of SRL therapy, were also significantly lower than levels measured at the end of the 1st trimester (p < 0.05). Group 2 serum GH and IGF-1 levels were not significantly decreased at the end of the 1st trimester (GH: 27.2 +/- 12.1 ng/ml, NS. IGF-1: 698 +/- 74 ng/ml, NS), whereas only serum IGF-1 (570 +/- 69 ng/ml, p < 0.05) was significantly reduced during the 2nd trimester of SRL (GH: 22.4 +/- 9.7 ng/ml, NS). Serum GH and IGF-I fell in the normal range in 4 patients in group 1 and one in group 2 at the end of the second trimester of SRL therapy. Independently of the trial applied, the mean clinical score level ameliorated significantly in both groups (group 1: p < 0.0005; group 2: p < 0.0001). In both groups, the proportion of patients complaining of headache and tissue swelling and the score level of headache, tissue swelling and excessive sweating decreased significantly. In group 1 the score level of fatigue and arthralgia also decreased significantly. In conclusion, this study proves that in patients with GH-secreting pituitary macroadenoma: (i) surgery followed by SRL induces a better clinical and biochemical status than SRL alone; (ii) SRL treatment before surgery ameliorates the clinical and biochemical outcome and reduces the prevalence of hypopituitarism due to surgery.     

Insulin-like growth factor 1 signaling regulates cytosolic sialidase Neu2 expression during myoblast differentiation and hypertrophy

Cytosolic sialidase (neuraminidase 2; Neu2) is an enzyme whose expression increases during myoblast differentiation. Here we show that insulin-like growth factor 1 (IGF1)-induced hypertrophy of myoblasts notably increases Neu2 synthesis by activation of the phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (P13K/AKT/mTOR) pathway, whereas the proliferative effect mediated by activation of the extracellular regulated kinase 1/2 (ERK1/2) pathway negatively contributed to Neu2 activity. Accordingly, the differentiation L6MLC/IGF-1 cell line, in which the forced postmitotic expression of insulin-like growth factor 1 stimulates a dramatic hypertrophy, was accompanied by a stronger Neu2 increase. Indeed, the hypertrophy induced by transfection of a constitutively activated form of AKT was able to induce high Neu2 activity in C2C12 cells, whereas the transfection of a kinase-inactive form of AKT prevented myotube formation, triggering Neu2 downregulation. Neu2 expression was strictly correlated with IGF-1 signaling also in C2 myoblasts overexpressing the insulin-like growth factor 1 binding protein 5 and therefore not responding to endogenously produced insulin-like growth factor 1. Although Neu2-transfected myoblasts exhibited stronger differentiation, we demonstrated that Neu2 overexpression does not override the block of differentiation mediated by PI3 kinase and mTOR inhibitors. Finally, Neu2 overexpression did not modify the ganglioside pattern of C2C12 cells, suggesting that glycoproteins might be the target of Neu2 activity. Taken together, our data demonstrate that IGF-1-induced differentiation and hypertrophy are driven, at least in part, by Neu2 upregulation and further support the significant role of cytosolic sialidase in myoblasts.