Insulin-like growth factor binding protein-5 modulates muscle differentiation through an insulin-like growth factor-dependent mechanism.

The insulin-like growth factor binding proteins (IGFBPs) are a family of six secreted proteins which bind to and modulate the actions of insulin-like growth factors-I and -II (IGF-I and -II). IGFBP-5 is more conserved than other IGFBPs characterized to date, and is expressed in adult rodent muscle and in the developing myotome. We have shown previously that C2 myoblasts secrete IGFBP-5 as their sole IGFBP. Here we use these cells to study the function of IGFBP-5 during myogenesis, a process stimulated by IGFs. We stably transfected C2 cells with IGFBP-5 cDNAs under control of a constitutively active promoter. Compared with vector-transfected control cells, C2 myoblasts expressing the IGFBP-5 transgene in the sense orientation exhibit increased IGFBP-5 levels in the extracellular matrix during proliferation, and subsequently fail to differentiate normally, as assessed by both morphological and biochemical criteria. Compared to controls, IGFBP-5 sense myoblasts show enhanced survival in low serum medium, remaining viable for at least four weeks in culture. By contrast, myoblasts expressing the IGFBP-5 antisense transcript differentiate prematurely and more extensively than control cells. The inhibition of myogenic differentiation by high level expression of IGFBP-5 could be overcome by exogenous IGFs, with des (1-3) IGF-I, an analogue with decreased affinity for IGFBP-5 but normal affinity for the IGF-I receptor, showing the highest potency. These results are consistent with a model in which IGFBP-5 blocks IGF-stimulated myogenesis, and indicate that sequestration of IGFs in the extracellular matrix could be a possible mechanism of action. Our observations also suggest that IGFBP-5 normally inhibits muscle differentiation, and imply a role for IGFBP-5 in regulating IGF action during myogenic development in vivo

Art, Sex, and Jewishness: Peggy Guggenheim as a Modern Object

Today, Peggy Guggenheim (born 1898, died 1979) is remembered for her incredible collection of modern art. Beyond her collection, however, she was an interesting character. She ignited issues of art, sex, and Jewishness in her time, and her legacy remains controversial. This thesis seeks to explain why. To do so, it will rely primarily on Guggenheim’s memoir, which she revisited throughout her life and published in 1946, 1960, and 1979. The first chapter will consider how Guggenheim came to promote art and champion the avant-garde. Because Guggenheim is principally remembered as a collector, any thorough investigation of her life and legacy must discuss her art world activities. After establishing this background, the second chapter will explore how Guggenheim’s gender proved both an advantage and a vulnerability throughout her lifetime. It will look at her narration of sex, abuse, friendships, and affairs within the memoir, and how this narration rankled biographers and reviewers alike. Finally, the third chapter will investigate Guggenheim’s complex Jewish identity, and how this identity was further complicated by World War II and subsequent reactions to it.Histor

How to Remain a Stranger / Encountering, in a Basement

How to Remain a Stranger / Encountering, in a Basement consists of two parallel essays. On the lefthand side of the page, How to Remain a Stranger explores the ways that the legend of the Wandering Jew, the Tradescantia genus of plants, peddlers, and exile relate to my practice of collecting, sorting, and combining found objects. On the righthand side, Encountering, in a Basement describes my thesis exhibition at the Institute for Contemporary Art at Virginia Commonwealth University. Focusing on the idea of the encounter, I detail the materials, considerations, and processes behind four of the ten sculptures in the show. Together, the two texts meander, mimicking the movement of objects and the paths I take as I encounter them in the world

Pro-protein convertases control the maturation and processing of the iron-regulatory protein, RGMc/hemojuvelin

<p>Abstract</p> <p>Background</p> <p>Repulsive guidance molecule c (RGMc or hemojuvelin), a glycosylphosphatidylinositol-linked glycoprotein expressed in liver and striated muscle, plays a central role in systemic iron balance. Inactivating mutations in the RGMc gene cause juvenile hemochromatosis (JH), a rapidly progressing iron storage disorder with severe systemic manifestations. RGMc undergoes complex biosynthetic steps leading to membrane-bound and soluble forms of the protein, including both 50 and 40 kDa single-chain species.</p> <p>Results</p> <p>We now show that pro-protein convertases (PC) are responsible for conversion of 50 kDa RGMc to a 40 kDa protein with a truncated COOH-terminus. Unlike related molecules RGMa and RGMb, RGMc encodes a conserved PC recognition and cleavage site, and JH-associated RGMc frame-shift mutants undergo COOH-terminal cleavage only if this site is present. A cell-impermeable peptide PC inhibitor blocks the appearance of 40 kDa RGMc in extra-cellular fluid, as does an engineered mutation in the conserved PC recognition sequence, while the PC furin cleaves 50 kDa RGMc <it>in vitro </it>into a 40 kDa molecule with an intact NH₂-terminus. Iron loading reduces release of RGMc from the cell membrane, and diminishes accumulation of the 40 kDa species in cell culture medium.</p> <p>Conclusion</p> <p>Our results define a role for PCs in the maturation of RGMc that may have implications for the physiological actions of this critical iron-regulatory protein.</p

Gene expression of the insulin-like growth factors and their receptors in cultured human retinal pigment epithelial cells

Insulin-like growth factors I and II (IGF I and II) are polypeptides with both growth-promoting and insulin-like metabolic effects16,27. Immunoreactive IGF I is present in the retina14 and both IGF I and II are present in vitreal fluid12. The type I and type II IGF receptors are also localized within the neural retina3,15,20,33. The presence of IGFs and IGF receptors within the eye suggests a possible growth-promoting effect of IGFs on ocular tissues. IGF may enter the eye from the blood or, alternatively, arise from an ocular cell type which synthesizes and secretes IGF. IGF I and II mRNA synthesis in scleral cells13 and IGF I synthesis in rat retina14 suggests endogenous IGF production in the eye. We hypothesized that IGFs and IGF receptors are synthesized by one ocular cell type, the retinal pigment-epithelium (RPE). As a first step in studying IGF production by the RPE, we analyzed expression of the IGF and IGF receptor genes by cultured human RPE cells. Using Northern analysis, RNase protection and reverse-transcriptase polymerase chain reaction (RT-PCR), we found that cultured RPE cells synthesize mRNA for IGF I and the type II IGF receptors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30318/1/0000720.pd

A highly conserved insulin-like growth factor-binding protein (IGFBP-5) is expressed during myoblast differentiation

Insulin-like growth factor-binding proteins (IGFBPs) are a family of secreted proteins that bind insulin-like growth factors I and II (IGFs I and II) and are capable of modulating IGF actions on target cells. We have shown previously that C2 myoblasts secrete a single approximately 29-kDa IGFBP during their terminal differentiation (Tollefsen, S. E., Lajara, R., McCusker, R. H., Clemmons, D. R., and Rotwein, P. (1989) J. Biol. Chem. 264, 13810-13817). In this study, we have purified the protein from C2 cell-conditioned media by conventional and IGF-affinity chromatography, cloned its cDNA by PCR-based and traditional library screening, and identified it as mouse IGFBP-5. The resultant 5561 nucleotide cDNA encodes a 252-amino acid mature protein (predicted M(r) approximately 28,400) that is 97% identical to rat and human IGFBP-5. In differentiating C2 myoblasts and in F3 azamyoblasts the > 6-kilobase IGFBP-5 mRNA accumulates concomitantly with induction of myogen mRNA, an early marker of muscle differentiation. Ligand blot analysis shows that IGFBP-5 protein is secreted within 12 h of the onset of differentiation in these cells and that it is the only IGFBP produced in several fusing skeletal muscle cell lines. In vivo, IGFBP-5 transcripts are expressed in a variety of mouse tissues including striated muscle, but, unlike other IGFBPs, it is barely detectable in liver. IGFBP-5 is more conserved than other IGFBPs in mammals; its conserved structure and sequence also extends to non-mammalian vertebrates. Hybridization of a mouse BP5 coding region probe to RNA from several chicken and Xenopus tissues demonstrated similarly sized transcripts in these species. A partial Xenopus cDNA is identical in 38/45 deduced amino acids to the mammalian proteins. Identification of an IGF-binding protein that is produced during myoblast differentiation provides a model system in which to study the potential modulatory role of IGFBPs in development

Insulin-like growth factors (IGF) in muscle development. Expression of IGF-I, the IGF-I receptor, and an IGF binding protein during myoblast differentiation.

The insulin-like growth factors (IGFs) I and II exert pleiotropic effects on diverse cell types through interaction with specific high affinity cell surface receptors and with locally produced binding proteins. In skeletal muscle and in myoblast cell lines, the functions of IGF-I and -II are complex. Both growth factors appear capable of stimulating cellular proliferation and differentiation, as well as exerting insulin-like effects on intermediary metabolism. We have demonstrated recently that the expression of IGF-II and its receptor is induced during the terminal differentiation of the myoblast cell line, C2, and have suggested that IGF-II may be an autocrine growth factor in these cells (Tollefsen, S.E., Sadow, J.L., and Rotwein, P. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 1543-1547). We now have examined this cell line for expression of other components involved in IGF signaling. The synthesis of IGF-I is low during myoblast proliferation; IGF-I mRNA can be detected only through use of a sensitive solution hybridization assay. Typical IGF-I receptors can be measured in myoblasts, whereas IGF binding proteins cannot be detected in proliferating cells or in conditioned culture medium. During myogenic differentiation, IGF-I mRNA levels increase transiently by 6-10-fold within 48-72 h. The expression of IGF-I mRNA is accompanied by a 2.5-fold accumulation of IGF-I in the culture medium. IGF-I receptors also increase transiently, doubling by 48 h after the onset of differentiation. By contrast, secretion of a Mr 29,000 IGF binding protein is induced 30-fold to 100 ng/ml within 16 h and continues to increase throughout differentiation. These studies demonstrate that several components critical to IGF action are produced in a fusing skeletal muscle cell line in a differentiation-dependent manner and suggest that both IGF-I and IGF-II may be autocrine factors for muscle

Regulation of insulin-like growth factor-II expression and its role in autocrine growth of human neuroblastoma cells

Insulin-like growth factor-II (IGF-II) is highly expressed in fetal tissues and may act as an autocrine growth factor during early embryogenesis. The SH-SY5Y human neuroblastoma cell line also expresses IGF-II and its receptors and responds to exogenous IGF-II with increased DNA synthesis, cell division, and neuritic outgrowth. For this study, we tested the hypothesis that IGF-II mediates autocrine growth of SH-SY5Y cells in serum-free media. SH-SY5Y cells plated at high densities proliferated in serum-free media, whereas sparsely plated cells did not. IGF-II mRNA levels increased within 24 hours of serum deprivation and were associated with increased immunoreactive IGF-II protein. Exogenous addition of IGF-II increased 3 H-TdR incorporation and cell number in a dose- and time-dependent fashion. By nuclear labelling experiments using 5-Bromo-2′ deoxyuridine (BrdU), we detected a twofold higher percentage of S phase nuclei after a 24-hour incubation in IGF-II. Treatment of SH-SY5Y cells with anti-IGF-II antibodies in serum-free media inhibited cell proliferation, and this inhibition was partially overcome by the addition of increasing concentrations of IGF-II. Collectively, our results indicate that IGF-II mediates an autocrine growth mechanism in SH-SY5Y cells that is associated with increased IGF-II expression. © 1993 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49884/1/1041550210_ftp.pd

Absence of the common Insulin-like growth factor-1 19-repeat allele is associated with early age at breast cancer diagnosis in multiparous women

Multiparity decreases the risk of breast cancer in white women, whereas it is a risk factor in black women <50 years. Early-onset breast cancer (<50 years) has been associated with high insulin-like growth factor-1 (IGF-1) levels. Absence of the common IGF1 19 cytosine-adenine (CA)-repeat allele (IGF1-19/-19) inverts the effect of several non-genetic factors on breast cancer risk but the interaction between IGF1-19/-19 and multiparity on breast cancer risk is unknown. As IGF1-19/-19, multiparity and early-onset breast cancer are more common in black than in white women, we aimed to study whether multiparity combined with IGF1-19/-19 increases the risk of early-onset breast cancer. Four hundred and three breast cancer patients diagnosed in Lund, Sweden, at age 25–99 years were genotyped for the IGF1 CA-repeat length using fragment analysis. Overall, 12.9% carried the IGF1-19/-19 genotype. There was a highly significant interaction between multiparity and IGF1-19/-19 on age at breast cancer diagnosis (P=0.007). Among IGF1-19/-19 patients, multiparity was associated with a 9.2 year earlier age at diagnosis compared with uniparity or nulliparity (P=0.006). Multiparity combined with IGF1-19/-19 was associated with an early age at breast cancer diagnosis. If confirmed, IGF1-19/-19 may help identify a subgroup of women for earlier breast cancer screening