Genomic imprinting of the insulin-like growth factor 2 gene in sheep

A number of genes in the human and mouse genomes are subject to genomic imprinting, with selective inactivation of one allele of a gene in a parent-of-origin specific manner. One of the first imprinted genes identified was the Insulin-like Growth Factor 2 gene (IGF2), which promotes growth of the fetus and is expressed from only the paternal allele in most tissues in both the mouse and human. The aim of this study was to establish the imprinting status of IGF2 in sheep (Ovis aries). Sheep provide an interesting model to study imprinting, owing to differences in their placental development and the fact that they have been subject to strong artificial selection for various production traits. We report the identification of a length polymorphism in the transcribed 3′-untranslated region of the ovine IGF2 gene. This polymorphism was used to map IGF2 to sheep Chromosome (Chr) 21 and demonstrate that IGF2 is indeed imprinted in sheep, being expressed from the paternal allele. We also report that the developmental switch from imprinted IGF2 expression in the fetal liver to biallelic IGF2 expression in the adult liver, which occurs in the human but not mouse, also occurs in sheep. Differences in male- and female-specific recombination values reported around the IGF2 locus in the human were also observed around the ovine IGF2 locus. The techniques developed in this study will enable the imprinting status of IGF2 to be assessed in a variety of tissues and stages of development in normal sheep. Received: 3 October 1998 / Accepted 29 January 1999     

Skin microbiota of first cousins affected by psoriasis and atopic dermatitis

Background

Psoriasis and atopic dermatitis (AD) are chronic inflammatory skin diseases, which negatively influence the quality of life. In the last years, several evidences highlighted the pivotal role of skin bacteria in worsening the symptomatology of AD and psoriasis. In the present study we evaluated the skin microbiota composition in accurately selected subjects affected by (AD) and psoriasis.

Methods

Three first cousins were chosen for the study according to strict selection of criteria. One subject was affected by moderate AD, one had psoriasis and the last one was included as healthy control. Two lesional skin samples and two non-lesional skin samples (for AD and psoriatic subjects) from an area of 2 cm² behind the left ear were withdrawn by mean of a curette. For the healthy control, two skin samples from an area of 2 cm² behind the left ear were withdrawn by mean of a curette. DNA was extracted and sequencing was completed on the Ion Torrent PGM platform. Culturing of Staphylococcus aureus from skin samples was also performed.

Results

The psoriatic subject showed a decrease in Firmicutes abundance and an increase in Proteobacteria abundance. Moreover, an increase in Streptococcaceae, Rhodobacteraceae, Campylobacteraceae and Moraxellaceae has been observed in psoriatic subject, if compared with AD individual and control. Finally, AD individual showed a larger abundance of S. aureus than psoriatic and healthy subjects. Moreover, the microbiota composition of non-lesional skin samples belonging to AD and psoriatic individuals was very similar to the bacterial composition of skin sample belonging to the healthy control.

Conclusion

Significant differences between the skin microbiota of psoriatic individual and healthy and AD subjects were observed.

     

A loss of insulin-like growth factor-2 imprinting is modulated by CCCTC-binding factor down-regulation at senescence in human epithelial cells

The imprinted insulin-like growth factor-2 (IGF2) gene is an auto/paracrine growth factor expressed only from the paternal allele in adult tissues. In tissues susceptible to aging-related cancers, including the prostate, a relaxation of IGF2 imprinting is found, suggesting a permissive role for epigenetic alterations in cancer development. To determine whether IGF2 imprinting is altered in cellular aging and senescence, human prostate epithelial and urothelial cells were passaged serially in culture to senescence. Allelic analyses using an IGF2 polymorphism demonstrated a complete conversion of the IGF2 imprint status from monoallelic to biallelic, in which the development of senescence was associated with a 10-fold increase in IGF2 expression. As a mechanism, a 2-fold decrease in the binding of the enhancer-blocking element CCCTC-binding factor (CTCF) within the intergenic IGF2-H19 region was found to underlie this switch to biallelic IGF2 expression in senescent cells. This decrease in CTCF binding was associated with reduced CTCF expression in senescent cells. No de novo increases in methylation at the IGF2 CTCF binding site were seen. The forced down-regulation of CTCF expression using small interfering RNA in imprinted prostate cell lines resulted in an increase in IGF2 expression and a relaxation of imprinting. Our data suggest a novel mechanism for IGF2 imprinting regulation, that is, the reduction of CTCF expression in the control of IGF2 imprinting. We also demonstrate that altered imprinting patterns contribute to changes in gene expression in aging cells.     

Kidney growth in normal and diabetic mice is not affected by human insulin-like growth factor binding protein-1 administration

Insulin-like growth factor I (IGF-I) accumulates in the kidney following the onset of diabetes, initiating diabetic renal hypertrophy. Increased renal IGF-I protein content, which is not reflected in messenger RNA (mRNA) levels, suggests that renal IGF-I accumulation is due to sequestration of circulating IGF-I rather than to local synthesis. It has been suggested that IGF-I is trapped in the kidney by IGF binding protein 1 (IGFBP-1). We administered purified human IGFBP-1 (hIGFBP-1) to nondiabetic and diabetic mice as three daily sc injections for 14 days, starting 6 days after induction of streptozotocin diabetes when the animals were overtly diabetic. Markers of early diabetic renal changes (i.e., increased kidney weight, glomerular volume, and albuminuria) coincided with accumulation of renal cortical IGF-I despite decreased mRNA levels in 20-day diabetic mice. Human IGFBP-1 administration had no effect on increased kidney weight or albuminuria in early diabetes, although it abolished renal cortical IGF-I accumulation and glomerular hypertrophy in diabetic mice. Increased IGF-I levels in kidneys of normal mice receiving hIGFBP-1 were not reflected on kidney parameters. IGFBP-1 administration in diabetic mice had only minor effects on diabetic renal changes. Accordingly, these results did not support the hypothesis that IGFBP-1 plays a major role in early renal changes in diabetes.     

Identification of receptors for insulin-like growth factor II in two insulin-like growth factor II producing cell lines

Specific high affinity membrane receptor(s) for insulin-like growth factor II have been characterized in two cell lines which produce this hormone and have the ability to proliferate in serum-free media. These receptor(s) have no affinity for either insulin or biosynthetic insulin-like growth factor I. Affinity cross-linking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed an apparent Mr of 250K which does not change with disulfide bond reduction. Our findings are consistent with an autocrine function for insulin-like growth factor II and indicate that these continuous cell lines may provide unique systems for further investigations of this hormone and its receptor.     

The thermodynamic stability of insulin disulfides is not affected by the C-domain of insulin-like growth factor 1

Both Insulin and insulin-like growth factor 1 are members of insulin superfamily. They share homologous primary and tertiary structure as well as weakly overlapping biological activity. However, their folding behavior is different: insulin and its recombinant precursor (PIP) fold into one unique tertiary structure, while IGF-1 folds into two disulfides isomers with similar thermodynamic stability. To elucidate the molecular mechanism of their different folding behavior, we prepared a singlechain hybrid of insulin and IGF-1, [B10Glu]Ins/IGF-1(C), and studied its folding behavior compared with that of PIP and IGF-1. We also separated a major non-native disulfides isomer of the hybrid and studied its refolding. The data showed that the C-domain of IGF-1 did not affect the folding thermodynamics of insulin, that is, the primary structure of the hybrid encoded only one thermodynamically stable disulfides linkage. However, the folding kinetics of insulin was affected by the C-domain of IGF-1.     

The thermodynamic stability of insulin disulfides is not affected by the C-domain of insulin-like growth factor 1

Both Insulin and insulin-like growth factor 1 are members of insulin superfamily. They share homologous primary and tertiary structure as well as weakly overlapping biological activity. However, their folding behavior is different: insulin and its recombinant precursor (PIP) fold into one unique tertiary structure, while IGF-1 folds into two disulfides isomers with similar thermody-namic stability. To elucidate the molecular mechanism of their different folding behavior, we prepared a single-chain hybrid of insulin and IGF-1, [B10Glu]lns/IGF-1(C), and studied its folding behavior compared with that of PIP and IGF-1. We also separated a major non-native disulfides iso-mer of the hybrid and studied its refolding. The data showed that the C-domain of IGF-1 did not affect the folding thermodynamics of insulin, that is, the primary structure of the hybrid encoded only one thermodynamically stable disulfides linkage. However, the folding kinetics of insulin was affected by the C-domain of IGF-1.     

Aberrant CpG methylation of the imprinting control region KvDMR1 detected in assisted reproductive technology-produced calves and pathogenesis of large offspring syndrome

Although somatic cell nuclear transfer (NT) and in vitro fertilization (IVF) have the potential to produce genetically superior livestock, considerable numbers of abnormally large animals, including sheep and cattle affected by "large offspring syndrome" (LOS), have been produced by these assisted reproductive technologies (ART). Interestingly, these phenotypes are reminiscent of Beckwith-Wiedemann syndrome (BWS) in humans, which is an imprinting disorder characterized by pre- and/or postnatal overgrowth. The imprinting control region KvDMR1, which regulates the coordinated expression of growth control genes such as Cdkn1c, is known to be aberrantly hypomethylated in BWS. Therefore, we hypothesized that aberrant imprinting in this region could contribute to LOS. In this study, we analyzed the DNA methylation status of the Kcnq1ot1/Cdkn1c and Igf2/H19 domains on bovine chromosome 29 and examined the coordinated expression of imprinted genes surrounding them in seven calves derived by NT (which showed signs of developmental abnormality), two calves conceived by IVF (both developmentally abnormal), and three conventional calves that died of unrelated causes. Abnormal hypomethylation status at an imprinting control region of Kcnq1ot1/Cdkn1c domain was observed in two of seven NT-derived calves and one of two IVF-derived calves in almost all organs. Moreover, increased expression of Kcnq1ot1 and diminished expression of Cdkn1c were observed by RT-PCR analysis. This study is the first to describe the abnormal hypomethylation of the KvDMR1 domain and subsequent changes in the gene expression of Kcnq1ot1 and Cdkn1c in a subset of calves produced by ART. Our findings provide strong evidence for a role of altered imprinting control in the development of LOS in bovines.     

Binding between insulin-like growth factor 1 and insulin-like growth factor-binding protein 3 is not influenced by glucose or 2-deoxy-D-glucose

A recent report (Zhong, D., Xiong, L., Liu, T., Liu, X., Liu, X., Chen, J., Sun, S. Y., Khuri, F. R., Zong, Y., Zhou, Q., and Zhou, W. (2009) J. Biol. Chem. 284, 23225-23233) details that 2-deoxy-D-glucose (2-DG), a well known inhibitor of glycolysis and a candidate antineoplastic agent, also induces insulin-like growth factor 1 receptor (IGF-1R) signaling through the inhibition of insulin-like growth factor 1-insulin-like growth factor-binding protein 3 (IGF-1-IGFBP-3) complex formation. Zhong et al. hypothesized that disrupted IGF-1/IGFBP-3 binding by 2-DG led to increased free IGF-1 concentrations and, consequently, activation of IGF-1R downstream pathways. Because their report suggests unprecedented off-target effects of 2-DG, this has profound implications for the fields of metabolism and oncology. Using ELISA, surface plasmon resonance, and novel "intensity-fading" mass spectrometry, we now provide a detailed characterization of complex formation between IGF-1 and IGFBP-3. All three of these independent methods demonstrated that there was no effect of glucose or 2-DG on the interaction between IGF-1 and IGFBP-3. Furthermore, we show examples of 2-DG exposure associated with reduced rather than increased IGF-1R and AKT activation, providing further evidence against a 2-DG increase in IGF-1R activation by IGF-1-IGFBP-3 complex disruption.     

alpha 2-Macroglobulin: a new component in the insulin-like growth factor/insulin-like growth factor binding protein-1 axis

Insulin-like growth factors (IGFs) are crucial for many aspects of development, growth, and metabolism yet control of their activity by IGF-binding proteins (IGFBPs) remains controversial. The effect of IGFBP-1 depends on its phosphorylation status; phosphorylated IGFBP-1 inhibits IGF actions whereas the nonphosphorylated isoform is stimulatory. In order to understand this phenomenon, we purified phosphorylated IGFBP-1 from normal human plasma by immunoaffinity chromatography. Unexpectedly, the resulting preparation enhanced IGF-stimulated 3T3-L1 fibroblast proliferation, due to the presence of a co-purified protein of approximately 700 kDa. Matrix-assisted laser desorption ionization-mass spectrometry and Western immunoblotting analysis identified this co-purified protein as alpha(2)-macroglobulin (alpha(2)M). Anti-alpha(2)M antibodies co-immunoprecipitated IGFBP-1 from human plasma and from (125)I-IGFBP-1.alpha(2)M complexes formed in vitro. The (125)I-IGFBP-1/alpha(2)M association could be inhibited with excess unlabeled IGFBP-1. Surface plasmon resonance analysis indicated that alpha(2)M preferentially associates with the phosphorylated isoform of IGFBP-1 and that when complexed to alpha(2)M, IGFBP-1 can still bind IGF-I. These findings have functional significance since alpha(2)M protects IGFBP-1 from proteolysis and abrogates the inhibitory effect of phosphorylated IGFBP-1 on IGF-I stimulated 3T3-L1 cell proliferation. We conclude that alpha(2)M is a binding protein of IGFBP-1 which modifies IGF-I/IGFBP-1 actions resulting in enhanced IGF effects. In line with its role in regulating the clearance and activity of other growth factors, we predict that alpha(2)M has a novel and important role in controlling the transport and biological activity of IGFs.     

Interruption of intrachromosomal looping by CCCTC binding factor decoy proteins abrogates genomic imprinting of human insulin-like growth factor II

Monoallelic expression of IGF2 is regulated by CCCTC binding factor (CTCF) binding to the imprinting control region (ICR) on the maternal allele, with subsequent formation of an intrachromosomal loop to the promoter region. The N-terminal domain of CTCF interacts with SUZ12, part of the polycomb repressive complex-2 (PRC2), to silence the maternal allele. We synthesized decoy CTCF proteins, fusing the CTCF deoxyribonucleic acid-binding zinc finger domain to CpG methyltransferase Sss1 or to enhanced green fluorescent protein. In normal human fibroblasts and breast cancer MCF7 cell lines, the CTCF decoy proteins bound to the unmethylated ICR and to the IGF2 promoter region but did not interact with SUZ12. EZH2, another part of PRC2, was unable to methylate histone H3-K27 in the IGF2 promoter region, resulting in reactivation of the imprinted allele. The intrachromosomal loop between the maternal ICR and the IGF2 promoters was not observed when IGF2 imprinting was lost. CTCF epigenetically governs allelic gene expression of IGF2 by orchestrating chromatin loop structures involving PRC2.     

Constitutive expression of insulin-like growth factor 1 and insulin-like growth factor 1 receptor abrogates all requirements for exogenous growth factors.

BALB/c3T3 cells are exquisitely growth regulated and require both platelet-derived growth factor and insulin-like growth factor-1 (IGF-1) for optimal proliferation. BALB/c3T3 cells that constitutively express IGF-1 and elevated levels of IGF-1 receptor (IGF-1R) are capable of growth in serum-free medium without the addition of any exogenous growth factors. BALB/c3T3 cells overexpressing only the IGF-1R plasmid required IGF-1 or insulin for serum-free growth. Antisense oligodeoxynucleotides complementary to IGF-1R mRNA inhibited IGF-1-mediated cell growth. Under these conditions, neither the epidermal growth factor receptor nor phospholipase C gamma 1 was autophosphorylated. These findings indicate that constitutive expression of IGF-1 and IGF-1R allows 3T3 cells to grow in serum-free medium without addition of those exogenous growth factors that are required by the parent cell line.     

Demonstration of two subtypes of insulin-like growth factor receptors by affinity cross-linking

The structure of receptors for insulin-like growth factors in rat liver plasma membranes and the BRL 3A2 rat liver cell line has been examined by chemical cross-linking with disuccinimidyl suberate and sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing and nonreducing conditions. Two receptor subtypes have been identified: (i) 125I multiplication-stimulating activity cross-linked to liver membranes or intact cells appeared in a complex of Mr = 260,000 (reduced) and 220,000 (nonreduced) and (ii) 125I-insulin-like growth factor I cross-linked to BRL 3A2 cells appeared predominantly in two bands of Mr greater than 300,000 without disulfide reduction and in a Mr = 130,000 complex following reduction. The two subtypes of insulin-like growth factor receptors identified by structural analysis correspond to previously observed differences in their specificity for insulin and insulin-like growth factors.     

Normal dosage of the insulin and insulin-like growth factor II genes in patients with the Beckwith-Wiedemann syndrome.

Several patients in whom the Beckwith-Wiedemann syndrome (BWS) is associated with duplication of chromosomal region 11p15 have recently been observed. The genes encoding insulin and insulin-like growth factor II (IGF-II), proteins that affect cellular growth and pancreatic function, have been mapped to 11p15, and their increased expression might, thus, account for the physical features of BWS. To determine whether BWS is frequently associated with small duplications of 11p15, we performed dosage analyses of the insulin and IGF-II genes in somatic DNAs of seven patients with BWS. In each case, we observed apparent diploid representation of these genes. These data suggest that BWS is not frequently associated with small duplications of 11p15 material that embed the insulin and IGF-II genes.     

Mutants of human insulin-like growth factor II with altered affinities for the type 1 and type 2 insulin-like growth factor receptor.

With the aim to produce insulin-like growth factors (IGF) with enhanced specificity for the type 1 or type 2 IGF receptors, three mutants of IGF II have been prepared and expressed in NIH-3T3 cells. IGF II mutated at Tyr27 to Leu and Glu showed a 25- and 54-fold decrease in affinity for the type 1 IGF receptor and a 3.4- and 9.2-fold decrease in affinity for the type 2 IGF receptor. IGF II mutated at Phe48 to Glu showed a 18-fold decrease in affinity for the type 2 IGF receptor and a 2.8-fold decrease in affinity for the type 1 IGF receptor. These affinities were measured in radioreceptor assays using type 1 or 2 IGF receptor overexpressing cells. Data obtained on receptor cross-linking and thymidine incorporation assays confirmed the results of the radioreceptor assays. It is concluded that mutations of Tyr27 preferentially decrease binding to the type 1 IGF receptor and of Phe48 to the type 2 IGF receptor, either by the loss of a residue involved in receptor binding or by preferentially destabilizing the region involved in receptor binding.     

The insulin-like growth factor type 1 and insulin-like growth factor type 2/mannose-6-phosphate receptors independently regulate ERK1/2 activity in HEK293 cells

Insulin-like growth factor types 1 and 2 (IGF-1; IGF-2) and insulin-like peptides are all members of the insulin superfamily of peptide hormones but bind to several distinct classes of membrane receptor. Like the insulin receptor, the IGF-1 receptor is a heterotetrameric receptor tyrosine kinase, whereas the IGF-2/ mannose 6-phosphate receptor is a single transmembrane domain protein that is thought to function primarily as clearance receptors. We recently reported that IGF-1 and IGF-2 stimulate the ERK1/2 cascade by triggering sphingosine kinase-dependent "transactivation" of G protein-coupled sphingosine-1-phosphate receptors. To determine which IGF receptors mediate this effect, we tested seven insulin family peptides, IGF-1, IGF-2, insulin, and insulin-like peptides 3, 4, 6, and 7, for the ability to activate ERK1/2 in HEK293 cells. Only IGF-1 and IGF-2 potently activated ERK1/2. Although IGF-2 was predictably less potent than IGF-1 in activating the IGF-1 receptor, they were equipotent stimulators of ERK1/2. Knockdown of IGF-1 receptor expression by RNA interference reduced the IGF-1 response to a greater extent than the IGF-2 response, suggesting that IGF-2 did not signal exclusively via the IGF-1 receptor. In contrast, IGF-2 receptor knockdown markedly reduced IGF-2-stimulated ERK1/2 phosphorylation, with no effect on the IGF-1 response. As observed previously, both the IGF-1 and the IGF-2 responses were sensitive to pertussis toxin and the sphingosine kinase inhibitor, dimethylsphingosine. These data indicate that endogenous IGF-1 and IGF-2 receptors can independently initiate ERK1/2 signaling and point to a potential physiologic role for IGF-2 receptors in the cellular response to IGF-2.