Molecular cloning of insulin-like growth factor 3 (igf3) and its expression in the tissues of a female damselfish, Chrysiptera cyanea, in relation to seasonal and food-manipulated reproduction

Food availability is a permissive determinant that drives gonadal activity in fish. The present study aimed to clarify the interactions between reproductive and nutritive statuses in the sapphire devil (Chrysiptera cyanea), a tropical damselfish with a long-day preference for reproduction. Insulin-like growth factor 3 (IGF3), a novel IGF that likely plays a role in gonadal maturation, was closely monitored in the sapphire devil. The cDNA of sapphire devil igf3 had an open reading frame of 443 base pairs (146 amino acid residues). Phylogenetic analyses revealed that sapphire devil IGF3 was clustered within the teleost IGF3 family. The transcript levels of sapphire devil igf3 increased in the brain, liver, and ovary of the fish during the late vitellogenic phase, suggesting that it plays a role in reproduction. Immersion of the fish in seawater containing estradiol-17β suppressed transcript levels of sapphire devil igf3 in the liver, but not in the brain, suggesting that intensive protein synthesis in relation to vitellogenesis negatively impacts somatic metabolism in this tissue. When fish were reared with high or low food under conditions of photoperiod (LD = 14:10) and temperature (at 25-28 °C) during the non-reproductive season, ovarian development was induced in high-food fish. Furthermore, prior to ovarian development in the high-food fish, the transcript levels of sapphire devil igf3 increased in the brain, liver, and ovary. These results indicated crosstalk between the reproductive and growth networks and suggested that a metabolic shift, from growth mode to reproductive mode, occurs in peripheral tissues when nutritive status is improved under suitable conditions of photoperiod and water temperature.

Crystallization of ectonucleotide phosphodiesterase/pyrophosphatase-3 and orientation of the SMB domains in the full-length ectodomain

Ectonucleotide phosphodiesterase/pyrophosphatase-3 (NPP3, ENPP3) is an ATP-hydrolyzing glycoprotein that is located in the extracellular space. The full-length ectodomain of rat NPP3 was expressed in HEK293S GntI- cells, purified using two chromatographic steps and crystallized. Its structure at 2.77 Å resolution reveals that the active-site zinc ions are missing and a large part of the active site and the surrounding residues are flexible. The SMB-like domains have the same orientation in all four molecules in the asymmetric unit. The SMB2 domain is oriented as in NPP2, but the SMB1 domain does not interact with the PDE domain but extends further away from the PDE domain. Deletion of the SMB domains resulted in crystals that diffracted to 2.4 Å resolution and are suitable for substrate-binding studies.

A Novel igf3 Gene in Common Carp (Cyprinus carpio): Evidence for Its Role in Regulating Gonadal Development

Since the insulin-like growth factor 3 (igf3) gene was recently discovered in fish ovary, its function in the gonads has received much attention. In this study, we isolated two igf3 subtypes from common carp (Cyprinus carpio), which comprised full-length cDNA of 707 and 1153 nucleotides encoding 205 and 198 amino acids (aa), respectively. The Igf3 aa sequence had the highest gene homology of 72% with the corresponding sequence in zebrafish (Danio rerio). Phylogenetic tree construction revealed that the C. carpio igf3 gene was first clustered with D. rerio and then with other teleost species. Igf3 mRNA was widely expressed, with expression being highest in the gonads and blood. In the gonad development stage, igf3a mRNA expression was highest in the maturity and recession stage of the ovary, and decline phase of the testis, while igf3b was highest in the recession and fully mature periods of the ovaries and testes, respectively. Western blotting of testis protein samples showed two bands of approximately 21 kDa and 34 kDa corresponding to the calculated molecular mass of the two Igf3 subtypes; no signal was detected in the ovary. The Igf3 protein was localized in the ovary granulosa cells and testis spermatogonium and spermatids. 17β-Ethinylestradiol treatment increased both ovary and testis igf3 mRNA expression. These findings suggest that Igf3 may play an important role in C. carpio gonadal development.

Establishment and characterization of a gonad cell line from half-smooth tongue sole Cynoglossus semilaevis pseudomale

A new cell line was established from half-smooth tongue sole Cynoglossus semilaevis pseudomale gonad (CSPMG). Primary culture was initiated from gonad tissues pieces, and the CSPMG cells were cultured at 24 °C in Dulbecco's modified Eagle medium/F12 medium (1:1) (pH7.0), supplemented with 20 % fetal bovine serum, basic fibroblast growth factor, epidermal growth factor, insulin-like growth factor-I, 2-mercaptoethanol, penicillin and streptomycin. The cultured CSPMG cells, in fibroblast shape, proliferated to 100 % confluency 10 days later and had been subcultured to passage 109. Chromosome analyses indicated that the CSPMG cells exhibited chromosomal aneuploidy with a modal chromosome number of 42, which displayed the normal diploid karyotype of half-smooth tongue sole (2n = 42t, NF = 42). Reverse transcription polymerase chain reaction revealed CSPMG cells could express gonad somatic cell functional genes Sox9a, Wt1a and weakly germ cell marker gene Vasa, but not male specific gene Dmrt1. Transfection experiment demonstrated that CSPMG cells transfected with pEGFP-N3 plasmid and small RNA could express green and red fluorescence signals with high transfection efficiency. In conclusion, a continuous CSPMG cell line has been established successfully. The cell line might serve as a valuable tool for studies on the mechanism of sex determination, sex reversal and gonad development in flatfish.

[Research on expression of somatomedin b domain of proteoglycan 4 and recombinant protein aggregation]

Recombinant protein SMB(PRG4) containing two Somatomedin B domains and a small amount of glycosylation of repetitive sequences of proteoglycan 4 was cloned according to PGR4 gene polymorphism. Mature purification process was established and recombinant protein SMB(PRG4), with high-level expression was purified. By using size-exclusion chromatogaraphy and dynamic light scattering, we found that the recombinant protein self-aggregate to dimeric form. Structure prediction and non-reducing electrophoresis revealed that SMB(PRG4), was a non-covalently bonded dimer.

An insulin-like growth factor found in hepatopancreas implicates carbohydrate metabolism of the blue crab Callinectes sapidus

Hyperglycemia that is caused by the release of crustacean hyperglycemic hormone (CHH) from the sinus gland to hemolymph is one of the hallmark physiological phenomena, occurring in decapod crustaceans experiencing stressful conditions. However, the mechanism(s) by which such elevated glucose levels return to resting levels is still unknown. Interestingly, noted is a difference in the clearance rate of hemolymph glucose between adult females and adult males of the blue crab, Callinectes sapidus: the former with more rapid clearance than the latter. The presence of an endogenous-insulin-like molecule is suggested in C. sapidus because an injection of bovine insulin, significantly reduces the levels of hemolymph glucose that were previously elevated by emersion stress or the glucose injection. Using 5' and 3' RACE, the full-length cDNA of an insulin-like molecule is isolated from the hepatopancreas of an adult female C. sapidus and shows the same putative sequence of an insulin-like androgenic gland factor (IAG) but differs in 5' and 3' UTR sequences. A knock-down study using five injections of double-stranded RNA of CasIAG-hep (dsRNA-CasIAG-hep, 10μg/injection) over a 10-day period reduces CasIAG-hep expression by ∼50%. The levels of hemolymph glucose are also kept higher in dsRNA-CasIAG-hep injected group than those treated with dsRNA-green fluorescent protein (dsRNA-IAG-hep) or saline. Most importantly, the hepatopancreas of dsRNA-CasIAG-hep injected animals contains amounts of carbohydrate (glucose, trehalose, and glycogen) significantly lower than those of control groups, indicating that the function of CasIAG-hep in carbohydrate metabolism in crustaceans is similar to carbohydrate metabolism in vertebrates.

Metals affect the structure and activity of human plasminogen activator inhibitor-1. I. Modulation of stability and protease inhibition

Human plasminogen activator inhibitor type 1 (PAI-1) is a serine protease inhibitor with a metastable active conformation. Under physiological conditions, half of the inhibitor transitions to a latent state within 1-2 h. The interaction between PAI-1 and the plasma protein vitronectin prolongs this active lifespan by ∼50%. Previously, our group demonstrated that PAI-1 binds to resins using immobilized metal affinity chromatography (Day, U.S. Pat. 7,015,021 B2, March 21, 2006). In this study, the effect of these metals on function and stability was investigated by measuring the rate of the transition from the active to latent conformation. All metals tested showed effects on stability, with the majority falling into one of two types depending on their effects. The first type of metal, which includes magnesium, calcium and manganese, invoked a slight stabilization of the active conformation of PAI-1. A second category of metals, including cobalt, nickel and copper, showed the opposite effects and a unique vitronectin-dependent modulation of PAI-1 stability. This second group of metals significantly destabilized PAI-1, although the addition of vitronectin in conjunction with these metals resulted in a marked stabilization and slower conversion to the latent conformation. In the presence of copper and vitronectin, the half-life of active PAI-1 was extended to 3 h, compared to a half-life of only ∼30 min with copper alone. Nickel had the largest effect, reducing the half-life to ∼5 min. Together, these data demonstrate a heretofore-unknown role for metals in modulating PAI-1 stability.

Cyr61/CCN1 displays high-affinity binding to the somatomedin B(1-44) domain of vitronectin

Background

Cyr61 is a member of the CCN (Cyr61, connective tissue growth, NOV) family of extracellular-associated (matricellular) proteins that present four distinct functional modules, namely insulin-like growth factor binding protein (IGFBP), von Willebrand factor type C (vWF), thrombospondin type 1 (TSP), and C-terminal growth factor cysteine knot (CT) domain. While heparin sulphate proteoglycans reportedly mediate the interaction of Cyr61 with the matrix and cell surface, the role of other extracellular associated proteins has not been revealed.

Methods and Findings

In this report, surface plasmon resonance (SPR) experiments and solid-phase binding assays demonstrate that recombinant Cyr61 interacts with immobilized monomeric or multimeric vitronectin (VTNC) with K_D in the nanomolar range. Notably, the binding site for Cyr61 was identified as the somatomedin B domain (SMTB ^1–44) of VTNC, which mediates its interaction with PAI-1, uPAR, and integrin αvβ3. Accordingly, PAI-1 outcompetes Cyr61 for binding to immobilized SMTB ^1–44, and Cyr61 attenuates uPAR-mediated U937 adhesion to VTNC. In contrast, isothermal titration calorimetry shows that Cyr61 does not display high-affinity binding for SMTB ^1-44 in solution. Nevertheless, competitive ELISA revealed that multimeric VTNC, heat-modified monomeric VTNC, or SMTB ^1–44 at high concentrations attenuate Cyr61 binding to immobilized VTNC, while monomeric VTNC was ineffective. Therefore, immobilization of VTNC exposes cryptic epitopes that recognize Cyr61 with high affinity, as reported for a number of antibodies, β-endorphin, and other molecules.

Conclusions

The finding that Cyr61 interacts with the SMTB ^1–44 domain suggests that VTNC represent a point of anchorage for CCN family members to the matrix. Results are discussed in the context of the role of CCN and VTNC in matrix biology and angiogenesis.

Overexpression of IGF2R and IGF1R mRNA in SCNT-produced goats survived to adulthood

The procedure of somatic cell nuclear transfer (SCNT) is likely to affect the expression level of growth-related genes especially imprinting genes. In this study, expressions of growth-related genes including three imprinting genes (H19, IGF2, and IGF2R) and four non-imprinting genes (IGF1, IGF1R, GHR, and GHSR) in adult nuclear transferred (NT) goats were investigated by real-time PCR. The expressions of these genes in adult clones were found largely normal, but IGF2R and IGF1R were more highly expressed in cloned goats than in non-NT goats (P < 0.01). Analysis on mono-allelic expression pattern of imprinting genes indicated that mono-allelic expression patterns of H19 and IGF2 in cloned goats were similar to that in non-NT goats. In addition, the sequence of goat IGF2 gene and the putative amino acid sequence were obtained. The 986 nucleotide cDNA of goat IGF2 gene contained an open-reading frame of 540 nucleotides coding for 179 amino acids. Both cDNA sequence and amino acid sequence of IGF2 in goat showed their higher homology with that in sheep than in cattle; the partial cDNA fragments of H19, IGF2R, GHSR, IGF1R, and GHR in goat were also cloned and sequenced, which shared higher sequence identities with those in sheep than in cattle.

Solution structure of recombinant somatomedin B domain from vitronectin produced in Pichia pastoris

The cysteine-rich somatomedin B domain (SMB) of the matrix protein vitronectin is involved in several important biological processes. First, it stabilizes the active conformation of the plasminogen activator inhibitor (PAI-1); second, it provides the recognition motif for cell adhesion via the cognate integrins (alpha(v)beta(3), alpha(v)beta(5), and alpha(IIb)beta(3)); and third, it binds the complex between urokinase-type plasminogen activator (uPA) and its glycolipid-anchored receptor (uPAR). Previous structural studies on SMB have used recombinant protein expressed in Escherichia coli or SMB released from plasma-derived vitronectin by CNBr cleavage. However, different disulfide patterns and three-dimensional structures for SMB were reported. In the present study, we have expressed recombinant human SMB by two different eukaryotic expression systems, Pichia pastoris and Drosophila melanogaster S2-cells, both yielding structurally and functionally homogeneous protein preparations. Importantly, the entire population of our purified, recombinant SMB has a solvent exposure, both as a free domain and in complex with PAI-1, which is indistinguishable from that of plasma-derived SMB as assessed by amide hydrogen ((1)H/(2)H) exchange. This solvent exposure was only reproduced by one of three synthetic SMB products with predefined disulfide connectivities corresponding to those published previously. Furthermore, this connectivity was also the only one to yield a folded and functional domain. The NMR structure was determined for free SMB produced by Pichia and is largely consistent with that solved by X-ray crystallography for SMB in complex with PAI-1.

Functional structure of the somatomedin B domain of vitronectin

The N-terminal somatomedin B domain (SMB) of vitronectin binds PAI-1 and the urokinase receptor with high affinity and regulates tumor cell adhesion and migration. We have shown previously in the crystal structure of the PAI-1/SMB complex that SMB, a peptide of 51 residues, is folded as a compact cysteine knot of four pairs of crossed disulfide bonds. However, the physiological significance of this structure was questioned by other groups, who disputed the disulfide bonding shown in the crystal structure (Cys5-Cys21, Cys9-Cys39, Cys19-Cys32, Cys25-Cys31), notably claiming that the first disulfide is Cys5-Cys9 rather than the Cys5-Cys21 bonding shown in the structure. To test if the claimed Cys5-Cys9 bond does exist in the SMB domain of plasma vitronectin, we purified mouse and rat plasma vitronectin that have a Met (hence cleavable by cyanogen bromide) at residue 14, and also prepared recombinant human SMB variants from insect cells with residues Asn14 or Leu24 mutated to Met. HPLC and mass spectrometry analysis showed that, after cyanogen bromide digestion, all the fragments of the SMB derived from mouse or rat vitronectin or the recombinant SMB mutants are still linked together by disulfides, and the N-terminal peptide (residue 1-14 or 1-24) can only be released when the disulfide bonds are broken. This clearly demonstrates that Cys5 and Cys9 of SMB do not form a disulfide bond in vivo, and together with other structural evidence confirms that the only functional structure of the SMB domain of plasma vitronectin is that seen in its crystallographic complex with PAI-1.

Mapping of the Vitronectin-binding Site on the Urokinase Receptor

The urokinase-type plasminogen activator receptor (uPAR) has been implicated as a modulator of several biochemical processes that are active during tumor invasion and metastasis, e.g. extracellular proteolysis, cell adhesion, and cell motility. The structural basis for the high affinity interaction between the urokinase-type plasminogen activator (uPA) and uPAR, which focuses cell surface-associated plasminogen activation in vivo, is now thoroughly characterized by site-directed mutagenesis studies and x-ray crystallography. In contrast, the structural basis for the interaction between uPAR and the extracellular matrix protein vitronectin, which is involved in the regulation of cell adhesion and motility, remains to be clarified. In this study, we have identified the functional epitope on uPAR that is responsible for its interaction with the full-length, extended form of vitronectin by using a comprehensive alanine-scanning library of purified single-site uPAR mutants (244 positions tested). Interestingly, the five residues identified as "hot spots" for vitronectin binding form a contiguous epitope consisting of two exposed loops connecting the central fourstranded beta-sheet in uPAR domain I (Trp(32), Arg(58), and Ile(63)) as well as a proximal region of the flexible linker peptide connecting uPAR domains I and II (Arg(91) and Tyr(92)). This binding topology provides the molecular basis for the observation that uPAR can form a ternary complex with uPA and vitronectin. Furthermore, it raises the intriguing possibility that the canonical receptor and inhibitor for uPA (uPAR and PAI-1) may have reached a convergent solution for binding to the somatomedin B domain of vitronectin.

Crosstalk between IGF signaling and steroid hormone receptors in breast cancer

Breast cancer development and progression is regulated by crosstalk between steroid hormones (SHs) (e.g., estrogens, progestins and androgens) and growth factors such as insulin-like growth factors (IGFs), insulin, epidermal growth factors (EGFs), transforming growth factors, and vascular endothelial growth factor. The biological effects of SHs are mediated by the nuclear receptors acting as transcriptional activators. Steroid hormone receptors (SRs), in addition to being induced by their own ligands, are also regulated by cellular kinases activated by growth factors. Growth factors are known to influence the expression and activity of SRs as well as regulate the action of various SR transcriptional co-factors. In turn, the expression of growth factor receptors, their ligands, and signaling molecules is often controlled by SHs. This review will focus on crosstalk between the IGF-I system and several SRs implicated in breast cancer.

The uPA receptor and the somatomedin B region of vitronectin direct the localization of uPA to focal adhesions in microvessel endothelial cells

Vitronectin is a plasma protein which can deposit into the extracellular matrix where it supports integrin and uPA dependent cell migration. In earlier studies, we have shown that the plasma protein, vitronectin, stimulates focal adhesion remodeling by recruiting urokinase-type plasminogen activator (uPA) to focal adhesion sites [Wilcox-Adelman, S. A., Wilkins-Port, C. E., McKeown-Longo, P. J., 2000. Localization of urokinase-type plasminogen activator to focal adhesions requires ligation of vitronectin integrin receptors. Cell. Adhes. Commun.7, 477-490]. In the present study, we used a variety of vitronectin constructs to demonstrate that the localization of uPA to adhesion sites requires the binding of both vitronectin integrin receptors and the uPA receptor (uPAR) to vitronectin. A recombinant fragment of vitronectin containing the connecting sequence (VN(CS)) was able to support integrin-dependent adhesion, spreading and focal adhesion assembly by human microvessel endothelial cells. Cells adherent to this fragment were not able to localize uPA to focal adhesions. A second recombinant fragment containing both the amino-terminal SMB domain and the CS domain was able to restore the localization of uPA to adhesion sites. This fragment, which contains a uPAR binding site, also resulted in the localization of uPAR to adhesion sites. uPAR blocking antibodies as well as phospholipase C treatment of cells inhibited uPA localization to adhesion sites confirming a role for uPAR in this process. The SMB domain alone was unable to direct either uPAR or uPA to adhesion sites in the absence of the CS domain. Our results indicate that vitronectin-dependent localization of uPA to adhesion sites requires the sequential binding of vitronectin integrins and uPAR to vitronectin.

Defining the native disulfide topology in the somatomedin B domain of human vitronectin

The N-terminal 44 amino acid residues of the human plasma glycoprotein vitronectin, known as the somatomedin B (SMB) domain, mediates the interaction between vitronectin and plasminogen activator inhibitor 1 (PAI-1) in a variety of important biological processes. Despite the functional importance of the Cys-rich SMB domain, how its four disulfide bridges are arranged in the molecule remains highly controversial, as evidenced by three different disulfide connectivities reported by several laboratories. Using native chemical ligation and orthogonal protection of selected Cys residues, we chemically synthesized all three topological analogs of SMB with predefined disulfide connectivities corresponding to those previously published. In addition, we oxidatively folded a fully reduced SMB in aqueous solution, and prepared, by CNBr cleavage, the N-terminal segment of 51 amino acid residues of intact vitronectin purified from human blood. Proteolysis coupled with mass spectrometric analysis and functional characterization using a surface plasmon resonance based vitronectin-PAI-1-SMB competition assay allowed us to conclude that 1) only the Cys(5)-Cys(21), Cys(9)-Cys(39), Cys(19)-Cys(32), and Cys(25)-Cys(31) connectivity is present in native vitronectin; 2) only the native disulfide connectivity is functional; and 3) the native disulfide pairings can be readily formed during spontaneous (oxidative) folding of the SMB domain in vitro. Our results unequivocally define the native disulfide topology in the SMB domain of human vitronectin, providing biochemical as well as functional support to the structural findings on a recombinant SMB domain by Read and colleagues (Zhou, A., Huntington, J. A., Pannu, N. S., Carrell, R. W., and Read, R. J. (2003) Nat. Struct. Biol. 10, 541-544).

IGFL: A secreted family with conserved cysteine residues and similarities to the IGF superfamily

We have discovered a family of small secreted proteins in Homo sapiens and Mus musculus. The IGF-like (IGFL) genes encode proteins of approximately 100 amino acids that contain 11 conserved cysteine residues at fixed positions, including two CC motifs. In H. sapiens, the family is composed of four genes and two pseudogenes that are referred as IGFL1 to IGFL4 and IGFL1P1 and IGFL1P2, respectively. Human IGFL genes are clustered together on chromosome 19 within a 35-kb interval. M. musculus has a single IGFL family member that is located on chromosome 7. Further, evolutionary analysis shows a lack of direct orthology between any of the four human members and the mouse gene. This relationship between the mouse and the human family members suggests that the multiple members in the human complement have arisen from recent duplication events that appear limited to the primate lineage. Structural considerations and sequence comparisons would suggest that IGFL proteins are distantly related to the IGF superfamily of growth factors. IGFL mRNAs display specific expression patterns; they are expressed in fetal tissues, breast, and prostate, and in many cancers as well, and this pattern is consistent with that of the IGF family members.

The reduced, denatured somatomedin B domain of vitronectin refolds into a stable, biologically active molecule

The high-affinity binding site in human vitronectin (VN) for plasminogen activator inhibitor-1 (PAI-1) has been localized to the NH(2)-terminal cysteine-rich somatomedin B (SMB) domain (residues 1-44). A number of published structural and biochemical studies show conflicting results for the disulfide bonding pattern and the overall fold of the SMB domain, possibly because this domain may undergo disulfide shuffling and/or conformational changes during handling. Here we show that bacterially expressed recombinant SMB (rSMB) can be refolded to a single form that shows maximal activity in binding to PAI-1 and to a conformation-dependent monoclonal antibody (mAb 153). The oxidative refolding pathway of rSMB can be followed in the presence of glutathione redox buffers. This approach allowed the isolation and analysis of a number of intermediate folding species and of the final stably folded species at equilibrium. Competitive surface plasmon resonance analysis demonstrated that the stably refolded rSMB regained biological activity since it bound efficiently to PAI-1 and to mAb 153. In contrast, none of the folding intermediates bound to PAI-1 or to mAb 153. We also show by NMR analysis that the stably refolded rSMB is identical to the material used for the solution structure determination [Kamikubo et al. (2004) Biochemistry 43, 6519] and that it binds specifically to mAb 153 via an interface that includes the three aromatic side chains previously implicated in binding to PAI-1.

Expression of insulin-like growth factor system genes in liver and brain tissue during embryonic and post-hatch development of the turkey

A molecular cloning strategy employing primer-directed reverse transcription polymerase chain reaction (RT-PCR) was devised to sequence 1300 bp of a turkey liver-derived cDNA corresponding to the complete coding region and the 5'- and 3'-untranslated regions of the insulin-like growth factor (IGF)-II mRNA transcript (GenBank accession no. ). The turkey IGF-II gene codes for a 187 amino acid precursor protein that includes a signal peptide, the mature IGF-II hormone, and a C-terminal extension peptide comprised of 24, 67 and 96 amino acids, respectively. Turkey IGF-II showed greater than 95% sequence identity at both the nucleotide and amino acid level with chicken IGF-II. Expression of IGF-I, IGF-II, IGF type-I receptor (IGF-IR), and IGF binding protein (IGFBP)-2 and -5 genes was quantified relative to an internal 18S rRNA standard by RT-PCR in liver and whole brain tissue on days 14, 16, 18, 20, 22, 24 and 26 of embryonic development, as well as at hatch (H, day 28) and at 3 weeks post-hatching (PH). Expression of liver IGF-I was low throughout embryonic development, but increased more than 8-fold by 3 weeks PH. In contrast, IGF-I was expressed in brain tissue at much higher levels than liver throughout development and this level of expression in brain increased gradually, reaching its highest point at 3 weeks PH. IGF-II was expressed at comparable levels in brain and liver tissue during embryonic development, except for transient increases in liver just prior to hatching (days 24 and 26) and at 3 weeks PH. Expression of IGF-IR declined in brain throughout development reaching its lowest level at 3 weeks PH. In liver, IGF-IR expression was lower than that of brain throughout development. An inverse relationship was observed for the expression of IGF-I and IGF-IR genes in brain, but not in liver, through 3 weeks PH. Expression of the IGFBP-2 gene increased in liver around the time of hatch (days 26-28) and declined by 3 weeks PH, whereas the level of expression of IGFBP-5, which was higher than IGFBP-2, remained fairly constant in both brain and liver throughout the developmental period studied. Our data indicates differential expression of selected genes that comprise the IGF system in the turkey during embryonic and PH growth and development.

Differential expression of IGF components and insulin receptor isoforms in human seminoma versus normal testicular tissue

Insulin-like growth factors (IGF) have mitogenic and antiapoptotic functions, and may be involved in tumor growth. The purpose of the study was to investigate the role of IGF components in seminoma compared to normal testis. Normal testicular tissues from autopsy cases and seminoma from surgery cases were obtained for microarray and real-time reverse transcription polymerase chain reaction (RT-PCR) analysis of IGF-1, IGF-2, IGF receptor type 1 (IGF-R1), IGF-R2, insulin receptor isoforms A (IR-A) and B (IR-B), and IGF-binding proteins (IGFBP) 1-6. IGF-2 was localized by immunohistochemistry. IGFBP-5 protein expression was evaluated by Western blot analysis. mRNA expression in microarray and real-time RT-PCR showed similar tendencies: IGF-1, IGF-R1, IGF-R2, IR-A, and IGFBP-2 were not different in both groups. IGF-2, IR-B, IGFBP-1, IGFBP-4, and IGFBP-6 mRNA were downregulated in seminoma. IGFBP-3 tended to be upregulated in pT1 seminoma, but downregulated in pT2 stages. IGFBP-5 and IGF-2 protein expression correlated with mRNA expression. In conclusion, downregulation of mainly inhibiting IGFBPs may allow a stimulated tumor growth. The downregulated IGF-2 does not seem to be involved in the growth regulation of seminoma. Constantly expressed genes (e.g., IGF-1, IGF-R1, IR-A, and IGFBP-2) may reflect an involvement in spermatogenesis, but may also play a major role in tumor growth as their expression is not downregulated despite the lack of spermatogenesis in tumor tissue.

Signaling mechanism for the insulin-like effects of growth hormone--another example of a classical hormonal negative feedback loop

Growth hormone (GH) exerts many effects in addition to its ability to stimulate growth. The metabolic effects are either chronic diabetogenic or acute insulin-like. The latter effects are only seen in cells that have been deprived of the hormone for a few hours. After exposure to GH the ability of the cells to respond with insulin-like effects disappears within a couple of hours, a negative feedback loop, which is a part of the chronic effects of the hormone. The insulin-like effects are mediated by the cytosolic tyrosine kinase Janus kinase 2 (JAK2) upon GH-GH receptor interaction, resulting in tyrosine phosphorylation of downstream targets including the GH receptor itself and insulin receptor substrate-1 (IRS-1) and IRS-2. Analogous to the post-receptor events for insulin this results in recruitment of phosphatidylinositol-3 kinase (PI3-kinase) to the IRS-proteins. Downstream PI3-kinase protein kinase B/Akt participates in the activation of glucose transporters (GLUT4) and increased glucose uptake as well as activation of phosphodiesterase 3B and hydrolysis of cAMP leading to a net dephosphorylation of the hormone sensitive lipase and inhibition of lipolysis. Simultaneously, JAK2 phosphorylates STAT-family transcription factors that move into the nucleus and activate the transcription of, among others, genes coding for negatively regulatory proteins called Suppressors of cytokine signalling (SOCS). The turnover of SOCS is rapid and in their presence JAK2 will still activate STAT-proteins (and the diabetogenic effects), but no longer phosphorylate the IRS-proteins (and induce insulin-like effects), closing the loop of yet another classical hormonal negative feedback loop.

Graph-representation of oxidative folding pathways

Background

The process of oxidative folding combines the formation of native disulfide bond with conformational folding resulting in the native three-dimensional fold. Oxidative folding pathways can be described in terms of disulfide intermediate species (DIS) which can also be isolated and characterized. Each DIS corresponds to a family of folding states (conformations) that the given DIS can adopt in three dimensions.

Results

The oxidative folding space can be represented as a network of DIS states interconnected by disulfide interchange reactions that can either create/abolish or rearrange disulfide bridges. We propose a simple 3D representation wherein the states having the same number of disulfide bridges are placed on separate planes. In this representation, the shuffling transitions are within the planes, and the redox edges connect adjacent planes. In a number of experimentally studied cases (bovine pancreatic trypsin inhibitor, insulin-like growth factor and epidermal growth factor), the observed intermediates appear as part of contiguous oxidative folding pathways.

Conclusions

Such networks can be used to visualize folding pathways in terms of the experimentally observed intermediates. A simple visualization template written for the Tulip package can be obtained from V.A.

A Model for the Three-Dimensional Structure of Human Plasma Vitronectin from Small-Angle Scattering Measurements

Small-angle X-ray scattering (SAXS) measurements were used to characterize vitronectin, a circulatory protein found in human plasma that functions in regulating cell adhesion and migration, as well as proteolytic cascades that affect blood coagulation, fibrinolysis, and pericellular proteolysis. SAXS measurements were taken over a 3-fold range of protein concentrations, yielding data that characterize a monodisperse system of particles with an average radius of gyration of 30.3 +/- 0.6 A and a maximum linear dimension of 110 A. Shape restoration was applied to the data to produce two models of the solution structure of the ligand-free protein. A low-resolution model of the protein was generated that indicates the protein to be roughly peanut-shaped. A better understanding of the domain structure of vitronectin resulted from low-resolution models developed from available high-resolution structures of the domains. These domains include the N-terminal domain that was determined experimentally by NMR [Mayasundari, A., Whittemore, N. A., Serpersu, E. H., and Peterson, C. B. (2004) J. Biol. Chem. 279, 29359-29366] and the docked structure of the central and C-terminal domains that were determined by computational threading [Xu, D., Baburaj, K., Peterson, C. B., and Xu, Y. (2001) Proteins: Struct., Funct., Genet. 44, 312-320]. This model provides an indication of the disposition of the central domain and C-terminal heparin-binding domains of vitronectin with respect to the N-terminal somatomedin B (SMB) domain. This model constructed from the available domain structures, which agrees with the low-resolution model produced from the SAXS data, shows the SMB domain well separated from the central and heparin-binding domains by a disordered linker (residues 54-130). Also, binding sites within the SMB domain are predicted to be well exposed to the surrounding solvent for ease of access to its various ligands.

In vitro elucidation of substrate specificity and bioassay of proprotein convertase 4 using intramolecularly quenched fluorogenic peptides

The fourth member of Ca2+-dependent mammalian secretory subtilase, PC4 (proprotein convertase 4), is primarily expressed in testicular germ cell and ovarian macrophage. Its role in sperm fertilization and in early embryonic development has been demonstrated earlier through several studies, including those with PC4 null mice. A number of physiological substrates found in reproductive tissues have been postulated or identified for PC4 by various biochemical studies. These include growth factors IGF-1 (insulin-like growth factor-1) and IGF-2, hormonal polypeptide proPACAP (where PACAP stands for pituitary adenylate cyclase-activating polypeptide) and a number of surface proteins of ADAM (ADisintegrin And Metalloproteinase-like) family such as ADAM-1 (fertilin a), ADAM-2 (fertilin b), ADAM-3 (procyritestin) and ADAM-5. To provide further evidence in support of this notion and also to study the substrate specificity and bioassay of PC4, a series of intramolecularly quenched fluorogenic peptides containing the cleavage sites and several mutants were prepared. A comparative kinetic analysis and measurement of Vmax (app)/Km (app) ratio of these fluorogenic substrates against PC4 and PC7 revealed that the mutant variants of h (human) proPACAP and m (mouse) ADAM-5 derived peptides Q-PACAP141-151-mutant [Abz-141RVKNKGRRI150P151SY(NO2)-A-CONH2] (150A151Y replaced by PS) and Q-ADAM-5380-388-mutant [Abz-380E381PKPARRP388RY(NO2)A-CONH2] (381R replaced by P) are most efficiently and selectively cleaved by PC4. Using these two and Q-IGF-263-71 peptides, we showed that the sperm extract of normal adult mice is much higher when compared with that of PC4-null mice. This suggests that these fluorogenic peptides are useful for specific bioassay of PC4 activity. In addition, kinetic studies with various peptidyl-MCA indicate that the hexapeptide Ac-KTKQLR-MCA (where MCA stands for 4-methyl coumaryl-7-amide) is most efficiently and selectively cleaved by PC4 at RMCA, making it another effective agent for bioassay of PC4 activity. The study concludes that the most probable sequence motif for recognition by PC4 is KXKXXR or KXXR, where X is any amino acid other than cysteine and that it prefers proline at P3, P5 and/or P2' positions. It was also revealed that PC4 is a good candidate processing enzyme for growth factors IGF-1 and -2, neuropeptide proPACAP and several ADAM proteins such as ADAM-1, -2, -3 and -5.

Assignment of the four disulfides in the N-terminal somatomedin B domain of native vitronectin isolated from human plasma

The primary sequence of the N-terminal somatomedin B (SMB) domain of native vitronectin contains 44 amino acids, including a framework of four disulfide bonds formed by 8 closely spaced cysteines in sequence patterns similar to those found in the cystine knot family of proteins. The SMB domain of vitronectin was isolated by digesting the protein with endoproteinase Glu-C and purifying the N-terminal 1-55 peptide by reverse-phase high performance liquid chromatography. Through a combination of techniques, including stepwise reduction and alkylation at acidic pH, peptide mapping with matrix-assisted laser desorption ionization mass spectrometry and NMR, the disulfide bonds contained in the SMB domain have been determined to be Cys(5):Cys(9), Cys(19):Cys(31), Cys(21):Cys(32), and Cys(25):Cys(39). This pattern of disulfides differs from two other connectivities that have been reported previously for recombinant forms of the SMB domain expressed in Escherichia coli. This arrangement of disulfide bonds in the SMB domain from native vitronectin forms a rigid core around the Cys(19): Cys(31) and Cys(21):Cys(32) disulfides. A small positively charged loop is created at the N terminus by the Cys(5): Cys(9) cystine. The most prominent feature of this disulfide-bonding pattern is a loop between Cys(25) and Cys(39) similar to cystine-stabilized alpha-helical structures commonly observed in cystine knots. This alpha-helix has been confirmed in the solution structure determined for this domain using NMR (Mayasundari, A., Whittemore, N. A., Serpersu, E. H., and Peterson, C. B. (2004) J. Biol. Chem. 279, 29359-29366). It confers function on the SMB domain, comprising the site for binding to plasminogen activator inhibitor type-1 and the urokinase receptor.

Biology of insulin-like growth factors in development

Insulin-like growth factors (IGFs) provide essential signals for the control of embryonic and postnatal development in vertebrate species. In mammals, IGFs act through and are regulated by a system of receptors, binding proteins, and related proteases. In each of the many tissues dependent on this family of growth factors, this system generates a complex interaction specific to the tissue concerned. Studies carried out over the last decade, mostly with transgenic and gene knockout mouse models, have demonstrated considerable variety in the cell type-specific and developmental stage-specific functions of IGF signals. Brain, muscle, bone, cartilage, pancreas, ovary, skin, and fat tissue have been identified as major in vivo targets for IGFs. Concentrating on several of these organ systems, we review here phenotypic analyses of mice with genetically modified IGF systems. Much progress has also been made in understanding the specific intracellular signaling cascades initiated by the binding of circulating IGFs to their cognate receptor. We also summarize the most relevant aspects of this research. Considerable efforts are currently focused on deciphering the functional specificities of intracellular pathways, particularly the molecular mechanisms by which cells distinguish growth-stimulating insulin-like signals from metabolic insulin signals. Finally, there is a growing body of evidence implicating IGF signaling in lifespan control, and it has recently been shown that this function has been conserved throughout evolution. Very rapid progress in this domain seems to indicate that longevity may be subject to IGF-dependent neuroendocrine regulation and that certain periods of the life cycle may be particularly important in the determination of individual lifespan.

Contact-based sequence alignment

This paper introduces the novel method of contact-based protein sequence alignment, where structural information in the form of contact mutation probabilities is incorporated into an alignment routine using contact-mutation matrices (CAO: Contact Accepted mutatiOn). The contact-based alignment routine optimizes the score of matched contacts, which involves four (two per contact) instead of two residues per match in pairwise alignments. The first contact refers to a real side-chain contact in a template sequence with known structure, and the second contact is the equivalent putative contact of a homologous query sequence with unknown structure. An algorithm has been devised to perform a pairwise sequence alignment based on contact information. The contact scores were combined with PAM-type (Point Accepted Mutation) substitution scores after parameterization of gap penalties and score weights by means of a genetic algorithm. We show that owing to the structural information contained in the CAO matrices, significantly improved alignments of distantly related sequences can be obtained. This has allowed us to annotate eight putative Drosophila IGF sequences. Contact-based sequence alignment should therefore prove useful in comparative modelling and fold recognition.

Characterization of insulin-like growth factor-free interaction between insulin-like growth factor binding protein 3 and acid labile subunit expressed from Xenopus oocytes

The acid-labile subunit (ALS) is known to interact with the IGF binding protein (IGFBP) in the presence of insulin-like growth factors (IGFs). Studies, however, indicate that ALS forms a doublet with IGFBP3, independent of IGFs. To characterize the structural domain required for the IGF-free ALS-IGFBP3 interaction, seven recombinant human IGFBP3 mutants were generated: three deletion mutants and four site-specific mutants that had altering N-terminal regions of IGFBP3. ALS and IGFBP3 mRNAs were co-injected into Xenopus oocytes, and their products were cross-linked and immunoprecipitated using antisera against ALS or IGFBP3. Among the deletion mutants, the mutant of D40 (deleted in 11-40th amino acids) exerted no effect in the interaction with ALS, while D60 (Delta11-60) demonstrated a moderate reduction. D88 (Delta11-88), however, showed a significant decrease. In the case of site-specific mutants, the mutation that alterated the IGF binding site (codons 56 or 80) exerted a significant reduction in the interaction, whereas codons 72 or 87 showed no significant change in the interaction with ALS. The stability of the ALS-IGFBP3 interaction was analyzed according to a time-dependent mode. Consistent with the binding study, mutants on the IGF binding sites (56 or 80) consistently show a weakness in the ALS-IGFBP3 interaction when compared to the mutants that covered the non-IGF binding sites (72 or 87). This study suggests that the N-terminal of IGFBP3, especially the IGF binding site, plays an important role in interacting with ALS as well as in stabilizing the dual complex, independent of IGFs.

Fisher's information in maximum-likelihood macromolecular crystallographic refinement

Fisher's information is a statistical quantity related to maximum-likelihood theory. It is a matrix defined as the expected value of the squared gradient of minus the log-likelihood function. This matrix is positive semidefinite for any parameter value. Fisher's information is used in the quasi-Newton scoring method of minimization to calculate the shift vectors of model parameters. If the matrix is non-singular, the scoring-minimization step is always downhill. In this article, it is shown how the scoring method can be applied to macromolecular crystallographic refinement. It is also shown how the computational costs involved in calculation of the Fisher's matrix can be efficiently reduced. Speed is achieved by assuming a continuous distribution of reciprocal-lattice points. Matrix elements calculated with this method agree very well with those calculated analytically. The scoring algorithm has been implemented in the program REFMAC5 of the CCP4 suite. The Fisher's matrix is used in its sparse approximation. Tests indicate that the algorithm performs satisfactorily.

Expression of the cytokine leukemia inhibitory factor and pro-apoptotic insulin-like growth factor binding protein-3 in Alzheimer's disease

Amyloid-beta (Abeta) deposition in cerebral blood vessel walls is one of the key features of Alzheimer's disease (AD). Abeta(1-40) carrying the "Dutch" mutation (DAbeta(1-40)) induces rapid degeneration of cultured human brain pericytes (HBP). To study the mechanisms of this Abeta-induced toxicity, a comparative cDNA expression array was performed to detect differential gene expression of Abeta-treated versus untreated HBP. Messenger RNA expression of leukemia inhibitory factor (LIF) and insulin-like growth factor binding protein 3 (IGFBP-3) was increased in DAbeta(1-40)-treated HBP, whereas early growth response factor-1 (Egr-1) expression was decreased. Corresponding protein expression was investigated in AD and control brains. In all AD cases examined, LIF expression was observed in senile plaques and cerebral amyloid angiopathy, whereas IGFBP-3 expression in these lesions was only observed in a subset of cases. LIF and IGFBP-3 were also expressed in neurofibrillary tangles, as well as in neurons in AD and control brains. Egr-1 was predominantly expressed in astrocytes. Given its known involvement in both neuronal and immune responses to injury, the cytokine LIF may be a mediator of the inflammatory reaction seen in AD. IGFBP-3 is known to inhibit cell proliferation and induce apoptosis and may therefore contribute to neuronal degeneration in AD.

Identification of the disulfide bonds in the recombinant somatomedin B domain of human vitronectin

The NH(2)-terminal somatomedin B (SMB) domain (residues 1-44) of human vitronectin contains eight Cys residues organized into four disulfide bonds and is required for the binding of type 1 plasminogen activator inhibitor (PAI-1). In the present study, we map the four disulfide bonds in recombinant SMB (rSMB) and evaluate their functional importance. Active rSMB was purified from transformed Escherichia coli by immunoaffinity chromatography using a monoclonal antibody that recognizes a conformational epitope in SMB (monoclonal antibody 153). Plasmon surface resonance (BIAcore) and competitive enzyme-linked immunosorbent assays demonstrate that the purified rSMB domain and intact urea-activated vitronectin have similar PAI-1 binding activities. The individual disulfide linkages present in active rSMB were investigated by CNBr cleavage, partial reduction and S-alkylation, mass spectrometry, and protein sequencing. Two pairs of disulfide bonds at the NH(2)-terminal portion of active rSMB were identified as Cys(5)-Cys(9) and Cys(19)-Cys(21). Selective reduction/S-alkylation of these two disulfide linkages caused the complete loss of PAI-1 binding activity. The other two pairs of disulfide bonds in the COOH-terminal portion of rSMB were identified as Cys(25)-Cys(31) and Cys(32)-Cys(39) by protease-generated peptide mapping of partially reduced and S-alkylated rSMB. These results suggest a linear uncrossed pattern for the disulfide bond topology of rSMB that is distinct from the crossed pattern present in most small disulfide bond-rich proteins.

Model for the three-dimensional structure of vitronectin: predictions for the multi-domain protein from threading and docking

The structure of vitronectin, an adhesive protein that circulates in high concentrations in human plasma, was predicted through a combination of computational methods and experimental approaches. Fold recognition and sequence-structure alignment were performed using the threading program PROSPECT for each of three structural domains, i.e., the N-terminal somatomedin B domain (residues 1-53), the central region that folds into a four-bladed beta-propeller domain (residues 131-342), and the C-terminal heparin-binding domain (residues 347-459). The atomic structure of each domain was generated using MODELLER, based on the alignment obtained from threading. Docking experiments between the central and C-terminal domains were conducted using the program GRAMM, with limits on the degrees of freedom from a known inter-domain disulfide bridge. The docked structure has a large inter-domain contact surface and defines a putative heparin-binding groove at the inter-domain interface. We also docked heparin together with the combined structure of the central and C-terminal domains, using GRAMM. The predictions from the threading and docking experiments are consistent with experimental data on purified plasma vitronectin pertaining to protease sensitivity, ligand-binding sites, and buried cysteines.

A maize insulin-like growth factor signals to a transduction pathway that regulates protein synthesis in maize

Insulin and insulin-like growth factors (IGFs) are well-characterized regulators in higher eukaryotic cells that control biological processes such as cell growth and survival, and selective translation of mRNAs. This research presents the purification of a 20 kDa protein, isolated from maize tissue, with IGF activity. The protein was purified from 48 h-germinated maize embryonic axes by G-50 Sephadex fractionation followed by affinity chromatography through a bovine insulin antibody-Sepharose column. This protein proved to significantly speed up maize germination and seedling growth. At the molecular level, Zea mays IGF (ZmIGF) enhanced phosphorylation of S6 ribosomal protein (rp) on the 40 S ribosomal subunit, in a similar way as observed when bovine insulin is applied to maize axes during germination. Rapamycin, a specific inhibitor of the insulin-stimulated signal transduction pathway, prevented S6 rp phosphorylation in maize axes. Moreover, ZmIGF stimulated [(35)S]methionine incorporation into rps, above the level of overall cytoplasmic proteins. Either incubation with anti-insulin antibody, heat treatment (60 degrees C) or trypsin digestion abolished this ZmIGF effect. It is proposed that ZmIGF is an endogenous maize growth factor that regulates the synthesis of specific proteins through a pathway similar to that of insulin or IGFs in animal tissues.

Ligand blot analysis of insulin-like growth factor-binding proteins using biotinylated insulin-like growth factor-I

A nonradioactive method for the detection of insulin-like growth factor-binding proteins (IGFBPs) was developed utilizing human recombinant insulin-like growth factor-I (IGF-I) biotinylated with N-hydroxysuccinimido-biotin. Human plasma samples were separated by 15% SDS polyacrylamide gel electrophoresis, and proteins were transferred to nitrocellulose by Western blotting. The nitrocellulose sheets were incubated overnight with IGF-I-biotin at 4 degrees C. The next day streptavidin-peroxidase was added for 1 h, and IGFBPs were visualized by an enhanced chemiluminescence system. Five characteristic bands with molecular weights of 41 and 39 (IGFBP-3), 34 (IGFBP-2), 30 (IGFBP-1) and 24 kD (IGFBP-4) were detected. Binding was specific for IGFs, since unlabeled IGF-I inhibited IGF-I-biotin binding. IGFBP ligand blots with biotinylated IGF-I and (125)I-IGF-I yielded comparable results. The suitability of the new assay for clinical purposes was demonstrated by several clinical examples. In summary, a rapid, reliable, nonradioactive assay for qualitative analysis of IGFBPs has been developed.

A central domain binding site in insulin-like growth factor binding protein-5 for the acid-labile subunit

Like insulin-like growth factor binding protein-3 (IGFBP-3), IGFBP-5 forms a ternary complex with insulin-like growth factor (IGF)-I or IGF-II, and the acid-labile subunit (ALS). The study of IGFBP-5/IGFBP-6 chimeric proteins with amino-terminal and middle domain swaps, has revealed the existence of a site in the middle domain of IGFBP-5, that binds to ALS in the absence of the IGFBP-5 carboxy-terminal domain. An IGFBP-6 chimeric protein containing the central domain of IGFBP-5 complexed efficiently with ALS, and a carboxy-terminally truncated IGFBP-5 mutant, IGFBP-5'(1-169), also bound to ALS in the presence of IGFs, although with much less potency than full length rhIGFBP-5. In contrast to the latter, IGFBP-5(1-169) preferentially formed ternary complexes with IGF-II rather than IGF-I. These results indicate that a site which binds ALS exists in IGFBP-5 mutants which lack the IGFBP-5 carboxy-terminal domain.

Analysis of the extent of unfolding of denatured insulin-like growth factor

Insulin-like growth factor (IGF-1) contains three disulfide bonds. In the presence of denaturant and thiol catalyst, IGF-1 shuffles its native disulfide bonds and denatures to form a mixture of scrambled isomers. The composition of scrambled IGF varies under different denaturing conditions. Among the 14 possible scrambled IGF isomers, the yield of the beads-form isomer is shown to be directly proportional to the strength of the denaturing condition. This paper demonstrates a new approach to quantify the extent of unfolding of the denatured protein.

Nutritional and developmental regulation of insulin-like growth factors in fish

The insulin-like growth factors (IGF) are evolutionarily ancient growth factors present in all vertebrates. The central importance of IGF for normal development and growth has been illustrated by the severe growth-retarded phenotype exhibited by IGF-I, IGF-II or IGF-I receptor "knockout" mice. Although we know much about the gross effects of IGF on the overall size of the fetus and the clinical manifestations that result from fetal and neonatal deficiency of IGF (i.e., severe growth retardation leads to dwarfism), very little is known about the in vivo actions of IGF during embryogenesis at the cellular and molecular levels. Most research on the developmental role of IGF has relied on rodent models, and attempts to elucidate the molecular and cellular basis of IGF actions have been hampered by the inaccessibility of the mammalian fetus enclosed in the uterus. During the past decade, there has been growing support for the concept that the IGF have been highly conserved in all vertebrates. Both IGF-I and IGF-II are present in fish, and their structures are highly conserved. Human and fish IGF-I are equally potent in mammalian and fish bioassay systems. Insulin-like growth factor mRNA is found in all life stages of fish, ranging from unfertilized egg to adult. The temporal and spatial expression patterns of fish IGF-I seem to be similar to those in mammals. Nutritional status and growth hormone both have a profound effect on IGF-I expression in fish, as they do in mammals. These features suggest that the IGF system is highly conserved between teleost fish and mammals. Because fish embryos develop externally, they provide excellent animal models for understanding the regulatory roles of IGF, IGF receptor and IGF-binding proteins in vertebrate embryonic development. Current research on the developmental and nutritional roles of IGF in fish will undoubtedly contribute to knowledge of the basic physiology of vertebrates in general.

Effect of the somatostatin analog, octreotide, and of other hormones on the release of the acid-labile subunit of the 150 kDa complex by rat hepatocyte in primary culture

OBJECTIVE

In normal subjects, the major form of circulating IGF is the GH-dependent 150 kDa complex. The liver appears to be the main source of the three components of the 150 kDa complex and, in particular, hepatocytes synthesize the insulin-like growth factor (IGF) peptide and the acid-labile subunit (ALS), whereas Kupffer and sinusoidal endothelial cells produce IGF-binding protein-3 (IGFBG-3). We have studied the effects of the somatostatin analog octreotide, IGF-II des(1-3)IGF-I, transforming growth factor (TGF)-beta 1 and tri-iodothyronine (T3) on ALS secretion into the medium conditioned by rat hepatocytes in primary culture.

METHODS

The regulation of ALS release was evaluated in the conditioned medium of adult rat hepatocytes exposed to increasing concentrations of test substances or to vehicle alone (control), after gel filtration in basic conditions, by immunoblot using an antiserum generated against the N-terminal 34 amino acids of human ALS.

RESULTS

The results demonstrate that: 1) octreotide in vitro produces a dose-dependent inhibition of both basal and GH-stimulated ALS secretion into the hepatocyte conditioned medium; 2) the release of ALS by adult rat hepatocytes is not affected by the presence during the incubation of des(1-3)IGF-I or IGF-II; 3) an inhibitory effect, although only with very high doses, can be observed after treatment with TGF-beta 1; and 4) a small but significant increase of ALS released into the medium can be seen when hepatocytes are treated with T3.

CONCLUSIONS

Evaluation of the effect of substances known to affect the production of IGF peptides, the IGFBPs, or both, on adult rat hepatocytes in primary culture revealed no powerful stimulator, but instead a potent inhibitor of ALS release/synthesis. Our data suggest that the effect of somatostatin on the 150 kDa complex is mediated not only by the reduction in GH concentration, but also by a direct inhibition of ALS release or synthesis.

The glycosaminoglycan binding site governs ligand binding to the somatomedin B domain of vitronectin

The ligand binding functions of vitronectin (Vn) are regulated by its conformational state/degree of multimerization. In the native plasma form of Vn, the C-terminal glycosaminoglycan (GAG) binding domain is believed to be cryptic. Here, evidence is provided that the addition of fucoidan or dextran sulfate to unfractionated plasma results in the formation of covalently and non-covalently stabilized Vn multimers. These multimers express conformationally sensitive antibody epitopes and ligand binding sites located in the N terminus of the Vn molecule. While heparin forms complexes with monomeric plasma Vn and induces conformational changes, a reduction in ionic strength is required for induction of multimerization. In addition, heparin serves as a template for the assembly of type 1 plasminogen activator inhibitor-induced disulfide-linked Vn multimers. These results support a new model for the structure of native Vn. The C-terminal GAG binding domain is predicted to be exposed in the native conformation, whereas the N terminus is cryptic. Ligand binding to the GAG binding site unfolds the N terminus, thereby exposing cryptic ligand binding sites.

Evolution of insulin-like growth factor (IGF) function: production and characterization of recombinant hagfish IGF

While there is considerable structural evidence that insulin-like growth factors (IGFs) share a long evolutionary history, little is known about the conservation of IGF function. In order to address this, we have made recombinant hagfish IGF, hence allowing characterization of an IGF from a representative of the primitive vertebrate class, Agnatha. The production of recombinant hagfish IGF has been complicated by a number of factors including the requirement of a longer leader peptide for fusion protein expression, reduced solubility of the protein, as well as problems in the refolding procedure. However, we were able to produce a small quantity of hagfish IGF with an N-terminal glycine addition which is biologically active. Furthermore, N-terminal amino acid sequencing and mass spectrometry confirm that we have produced hagfish IGF. In vitro assessment of recombinant hagfish IGF in cultured cells indicates that hagfish IGF indeed shares functional properties with mammalian IGFs. Thus, hagfish IGF stimulates protein synthesis in rat myoblasts, but 20- and 5-fold more peptide, respectively, is required to achieve the same half-maximal responses as with human IGF-I (hIGF-I) or IGF-II (hIGF-II). Hagfish IGF also competes for binding to the type-1 IGF receptor present both on rat myoblasts and on salmon embryo fibroblasts, though with somewhat lower affinity than either hIGF-I or hIGF-II. However, studies investigating binding to the IGF-II-specific type-2 receptor suggest that hagfish IGF may in fact be more closely related to IGF-I than to IGF-II. These results indicate that motifs important for functions associated with mammalian IGFs appear to have evolved prior to the Agnathans diverging from the main line of vertebrate evolution 550 million years ago. Accordingly, we now have functional as well as structural evidence that the IGFs have a long evolutionary history.

Nectinepsin: a new extracellular matrix protein of the pexin family. Characterization of a novel cDNA encoding a protein with an RGD cell binding motif

We report the isolation and characterization of a novel cDNA from quail neuroretina encoding a putative protein named nectinepsin. The nectinepsin cDNA identifies a major 2.2-kilobase mRNA that is detected from ED 5 in neuroretina and is increasingly abundant during embryonic development. A nectinepsin mRNA is also found in quail liver, brain, and intestine and in mouse retina. The deduced nectinepsin amino acid sequence contains the RGD cell binding motif of integrin ligands. Furthermore, nectinepsin shares substantial homologies with vitronectin and structural protein similarities with most of the matricial metalloproteases. However, the presence of a specific sequence and the lack of heparin and collagen binding domains of the vitronectin indicate that nectinepsin is a new extracellular matrix protein. Furthermore, genomic Southern blot studies suggest that nectinepsin and vitronectin are encoded by different genes. Western blot analysis with an anti-human vitronectin antiserum revealed, in addition to the 65- and 70-kDa vitronectin bands, an immunoreactive protein of about 54 kDa in all tissues containing nectinepsin mRNA. It seems likely that the form of vitronectin found in chick egg yolk plasma by Nagano et al. ((1992) J. Biol. Chem. 267, 24863-24870) is the protein that corresponds to the nectinepsin cDNA. This new protein could be an important molecule involved in the early steps of the development.

Statistical approach for evolutionary relationship of alpha-conotoxins and members of insulin-superfamily

Similar conserved structures appear in apparently unrelated protein families. Thus, the superfamily of insulin shows an evolutionary relationship with the alpha-conotoxins of marine fish-hunting snails as indicated by methods of protein comparison. In order to reach statistical significance, the A-chains of different insulins, insulin-like growth factors, relaxins, insulin related peptides from invertebrates were drawn for comparison. These data were correlated with sequences from randomly chosen proteins. The alpha-conotoxins show identity scores up to 37.5% and similarity up to 56.2% toward the members of the insulin-superfamily. These scores conform to values achieved by comparing the relaxin and the insulin/IGF-sequences. The data show clearly that the identity and similarity values obtained in the comparison with the insulins are significantly higher than the scores of randomly chosen protein primary structures. According to our calculated data, this hormone system regulating metabolism and growth in vertebrates and the mentioned toxin-receptor system share the same evolutionary ancestor. However, this statistical approach has to be substantiated on gene level.

Characterization of insulin-like growth factors and their binding proteins in peritoneal dialysate

Serum insulin-like growth factors (IGFs), which circulate bound to specific IGF binding proteins (IGFBPs), must exit the intravascular space before acting on target tissues. Little is known about the nature of IGF/IGFBPs in extravascular fluids of patients with chronic renal failure (CRF). Peritoneal dialysate (PD) was studied since, after a short incubation, PD contains proteins which have entered an extravascular space; thus, IGF/IGFBP forms in PD are more likely than serum forms to interact with target tissues. IGF-I and IGF-II, and IGFBPs 1-4, were readily identified by specific immunoassays and/or 125iodine-IGF ligand blotting of simultaneously obtained PD and serum samples from seven CRF children; IGFBP-3 was a major IGFBP in PD as in serum. Where quantitated, IGF and IGFBP levels in PD were approximately 10% of serum concentrations. After separation of PD and serum by size-exclusion chromatography, serum had more IGFBP-3 in 150-kilodalton (kDa) than 35-kDa fractions, while PD had far less IGFBP-3 in 150-kDa than 35-kDa fractions. Immunoblot studies revealed a major 29-kDa IGFBP-3 fragment, in addition to intact 41- and 38-kDa IGFBP-3 forms, in PD and CRF serum; the 29-kDa form predominated in the 35-kDa PD fractions. These data suggest that the 29-kDa fragment is the IGFBP-3 form most likely to modulate IGF effects on target tissues of CRF individuals.

Molecular cloning and expression of the relaxin-like factor from the mouse testis

A complementary DNA encoding the mouse homolog of the testicular relaxin-like factor was cloned from a subtractive complementary DNA library, comprising clones preferentially expressed in the testes of mutant w/wv mice. The predicted amino acid structure conforms with that for other members of the insulin, insulin-like growth factor, and relaxin hormone family, with A, B, and C (connecting) domains. Northern and in situ transcript hybridization showed that the gene is exclusively expressed at a high level in the Leydig cells of both mutant and wild type testes and is up-regulated at puberty. The level of the specific messenger RNA is such as to imply that this novel member of the insulin family represents a major secretory product of Leydig cells, with a potential to be a part of a novel systemic feedback loop to other organs, including the brain.

The 'LXCXE' hydropathic superfamily of ligands for retinoblastoma protein: a proposal

The present study reports structural similarities between viral oncoproteins, growth factors belonging to the insulin family, members of the steroid/thyroid receptor superfamily, a D-type cyclin, the Elf-1 transcription factor and Bcl oncoproteins in regions that have been shown or proposed to mediate complex formation of these proteins with the tumor suppressor retinoblastoma protein (RB). This relationship predicts a common intracellular pathway for mitogenic signals and molecules promoting cell survival. Conversely, the structural evidence described here suggests that RB may play a central role both at the boundary between negative and positive cell growth regulation as well as in developmental decisions between cell death and cell survival.

Conservation of IGFBP structure during evolution: cloning of chicken insulin-like growth factor binding protein-5

The insulin-like growth factor binding proteins (IGFBPs) have conserved characteristics of their genomic organization, including similar locations of exon borders relative to nucleotides encoding conserved cysteine residues. Furthermore, the human IGFBP genes, as well as the human homeobox (HOX) genes, are localized to chromosomes 2, 7, 12, and 17. Although little is known about the evolution of the IGFBP genes, the association of human IGFBP and homeobox (HOX) genes at four chromosomal loci may indicate that their ancestral genes were linked prior to the first duplication of chromosomal DNA containing the ancestral HOX cluster. The hypothesis that IGFBPs are ancient proteins is supported by the reported detection of IGFBP activity in serum from the Agnathan species, Geotria australis, a primitive vertebrate. Further studies of IGFBPs in different species are needed to understand the evolution of this protein/gene family. Chicken provides a good intermediate model, since birds diverged from mammals approximately 300 million years ago. A complementary DNA (cDNA) clone encoding chicken insulin-like growth factor binding protein-5 (cIGFBP-5) was isolated. The deduced amino acid sequence is 83% identical to human IGFBP-5 and encodes a mature polypeptide of 251 amino acids. The conservation of IGFBP-5 primary structure across vertebrate species suggests maintenance of important functions during evolution.

High-potency hybrid compounds related to insulin and amphioxus insulin-like peptide

We describe the synthesis and biological evaluation of five two-chain, insulin-like compounds structurally related both to insulin and to a putative insulin like peptide (ILP) whose sequence was deduced from a cDNA cloned from Branchiostoma californiensis (amphioxus), a primitive vertebrate [Chan, S. J., Cao, Q.-P., & Steiner, D. F. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 9319-9323]. The present compounds feature an A-chain corresponding to the A-domain of the putative amphioxus ILP A-domain, except that amino acid substitutions have been made at positions A2, A3, A5, and/or A8, linked via disulfide bonds to the B-chain of bovine insulin. Amphioxus ILP [2 Ile] A/insulin B, amphioxus ILP [2 Ile, 8 His] A/insulin B, amphioxus ILP [2 Ile, 5 Gln, 8 His] A/insulin B, and amphioxus ILP [2 Ile, 3 Ile, 5 Gln, 8 His] A/insulin B all display insulin-like metabolic activity and growth-promoting activity (mitogenesis) equal to or greater than that of natural insulin. Amphioxus ILP [8 His] A/insulin B shows activity in these assays greater than that of its parent compound, but not as high as compounds featuring Ile rather than Leu at position A2. In contrast, the parent compound of the present analogues, i.e., amphioxus ILP A/insulin B, displays potencies ranging from 4.0 to 9.8% relative to insulin in insulin receptor binding and lipogenesis assays, respectively. This parent compound displayed activity in growth factor assays too low for exact quantitation [Chu, Y.-C., Hu, S. Q., Zong, L., Burke, G. T., Gammeltoft, S., Chan, S. J., Steiner, D. F., & Katsoyannis, P. G. (1994) Biochemistry (in press)].(ABSTRACT TRUNCATED AT 250 WORDS)