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Biomedical subjects

C E Stewart

Publications and source records attributed to C E Stewart.

14 recordsLinked to original sources
PubMed1996

Insulin-like growth factor-II is an autocrine survival factor for differentiating myoblasts.

Recent studies indicate that insulin-like growth factor-II (IGF-II) acts as an autocrine differentiation factor for skeletal myoblasts in culture. IGF-II mRNA and protein are induced as early events in muscle differentiation, and the rate and extent of IGF-II secretion correlate with both biochemical and morphological differentiation. Here we show that IGF-II also functions as an essential survival factor during the transition from proliferating to differentiating myoblasts. Stably transfected C2 muscle cell lines were established in which a mouse IGF-II cDNA was expressed in the antisense orientation relative to the constitutively active Moloney sarcoma virus promoter. IGF-II antisense cells proliferated normally in growth medium containing 20% serum but underwent rapid death when placed in low serum differentiation medium. Death was accompanied by characteristic markers of apoptosis with more than 90% of cells showing DNA fragmentation within 12-16 h. Myoblast death was prevented by IGF-I, des [1-3] IGF-I, IGF-II, and insulin with a dose potency consistent with activation of the IGF-I receptor; death also could be blocked by the protein synthesis inhibitor, cycloheximide. Exogenous IGFs additionally stimulated passage through a single cell cycle and subsequently induced terminal differentiation. Cell survival and cell cycle progression also were enhanced by fibroblast growth factor-2 and platelet-derived growth factor-bb, but these peptides did not promote differentiation. Our results define a novel system for studying apoptotic cell death and its prevention by growth factors, underscore the importance of IGF action in minimizing inappropriate cell death, and indicate that shared signal transduction pathways may mediate myoblast survival in vitro.

Animals↗
PubMed1996

Overexpression of insulin-like growth factor-II induces accelerated myoblast differentiation.

Previous studies have shown that exogenous insulin-like growth factors (IGFs) can stimulate the terminal differentiation of skeletal myoblasts in culture and have established a correlation between the rate and the extent of IGF-II secretion by muscle cell lines and the rate of biochemical and morphological differentiation. To investigate the hypothesis that autocrine secretion of IGF-II plays a critical role in stimulating spontaneous myogenic differentiation in vitro, we have established C2 muscle cell lines that stably express a mouse IGF-II cDNA under control of the strong, constitutively active Moloney sarcoma virus promoter, enabling us to study directly the effects of IGF-II overproduction. Similar to observations with other muscle cell lines, IGF-II overexpressing myoblasts proliferated normally in growth medium containing 20% fetal serum, but they underwent enhanced differentiation compared with controls when incubated in low-serum differentiation medium. Accelerated differentiation of IGF-II overexpressing C2 cells was preceded by the rapid induction of myogenin mRNA and protein expression (within 1 h, compared with 24-48 h in controls) and was accompanied by an enhanced proportion of the retinoblastoma protein in an underphosphrylated and potentially active form, by a marked increase in activity of the muscle-specific enzyme, creatine phosphokinase, by extensive myotube formation by 48 h, and by elevated secretion of IGF binding protein-5 when compared with controls. These results confirm a role for IGF-II as an autocrine/paracrine differentiation factor for skeletal myoblasts, and they define a model cell system that will be useful in determining the biochemical mechanisms of IGF action in cellular differentiation.

Animals↗
PubMed1996

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.

Animals↗
PubMed1996

Growth, differentiation, and survival: multiple physiological functions for insulin-like growth factors.

The insulin-like growth factors (IGFs), IGF-I and IGF-II, comprise a conserved pair of secreted proteins with diverse effects on growth, development, and metabolism. Insulin-like growth factor action is initiated upon binding to cell-surface receptors and is modulated through interactions with secreted IGF binding proteins (IGFBPs). The last decade has seen an explosion of new information about the physiological roles of the IGFs. In this review, we critically examine this information from biochemical, cell biological, and molecular genetic perspectives. We discuss the structures and functions of the two IGF receptors, outline the actions of the six IGFBPs, and summarize and interpret recent studies highlighting essential roles for components of the IGF system in the growth and development of the embryo and fetus, in tissue differentiation, in cell survival and proliferation, and in cancer. These results are discussed in the context of new opportunities for understanding the mechanisms of IGF action in multiple biological processes.

Animals↗
PubMed1994

Loss of the imprinted IGF2/cation-independent mannose 6-phosphate receptor results in fetal overgrowth and perinatal lethality.

Murine embryos that inherit a nonfunctional insulin-like growth factor-II/cation-independent mannose 6-phosphate receptor (Igf2r) gene from their fathers are viable and develop normally into adults. However, the majority of mice inheriting the same mutated allele from their mothers die around birth, as a consequence of major cardiac abnormalities. These mice do not express IGF2R in their tissues, are 25-30% larger than their normal siblings, have elevated levels of circulating IGF2 and IGF-binding proteins, and exhibit a slight kink in their tails. These results show that Igf2r is paternally imprinted and reveal that the receptor is crucial for regulating normal fetal growth, circulating levels of IGF2, and heart development.

Alleles↗
PubMed1993

Potentiation of insulin-like growth factor-I (IGF-I) activity by an antibody: supportive evidence for enhancement of IGF-I bioavailability in vivo by IGF binding proteins.

The effects of ovine polyclonal antibodies raised against human recombinant IGF-I were investigated in GH-deficient rodents in vivo both in the presence and absence of exogenous IGF-I. Dwarf mice (negligible endogenous serum IGF-I) treated with anti-IGF-I serum which had been pre-incubated with IGF-I exhibited a significantly greater rate of daily weight gain than did mice treated with the same dose of IGF-I alone (P < 0.001) or even a 2.5-fold higher dose (P < 0.001). Similar increases in whole body weight gain were observed in dwarf rats, with a concomitant increase in dissected muscle weight. Serum IGF-I concentrations were greater in all animals treated with the complex of anti-IGF-I antibodies and IGF-I than in those administered only IGF-I. Size exclusion chromatography of dwarf rat serum indicated the presence of high mol wt material (> 160 kDa) capable of binding 125I-IGF-I in the anti-IGF-I treated rats. We suggest that this particular polyclonal antibody is behaving in a similar manner to an enhancing IGF binding protein, maintaining a reservoir of bioactive IGF-I. Since the antibody has a slightly lower affinity (2 x 10(8) liters/M) than that of the type 1 receptor, these data provide tentative indirect evidence to support the hypothesis that the recently discovered mechanisms which apparently decrease the affinities of several IGFBPs may indeed result in increased IGF-I bioavailability.

Animals↗
PubMed1985

Chemical skin burns.

Copious lavage with water is the cornerstone of treatment for most types of chemical burns. Particularly dangerous are burns from hydrofluoric acid, which may act as both an alkali and an acid in its effects on the tissues. There are specific antidotes for certain types of chemical burns. For phenol burns, polyethylene glycol solutions are better solvents than water.

Acids↗
PubMed1984

Temporal bone trauma: high-resolution computed tomographic evaluation.

High-resolution computed tomography (CT) was used to examine 12 patients with temporal bone trauma. The CT findings were correlated with the clinical signs and symptoms (hearing loss, facial nerve dysfunction) and with the operative findings in the 5 patients who underwent surgery. CT was able to demonstrate ossicular chain disruption or fractures causing the clinical findings in the majority of cases. The CT findings affected patient care by alerting the otologist to the abnormalities likely to be encountered during surgery.

Adult↗
PubMed1977

A manual system for storage and inventory control of laboratory supplies.

The demand for laboratory supplies has increased in relation to the increase in the quantity and complexity of the laboratory workload. This has created many problems for the laboratory administration and a major one has been the lack of a good system for storage and inventory control of supplies. This paper presents a manual system for such control and suggests the use of two different control procedures.

Laboratories↗
PubMedDate not supplied

Computed tomography of local complications of temporal bone cholesteatomas.

The preoperative temporal bone CT scans of 13 patients with surgically proven acquired cholesteatoma were retrospectively reviewed for bony erosions and for extension beyond the temporal bone. A correlation with the clinical and surgical findings was also carried out. The CT findings are discussed and illustrated as well as some pitfalls in the evaluation of bony erosions. The appearance of "autoantrectomy" caused by a dry, self-cleaning, well ventilated cholesteatoma is also discussed and illustrated.

Adolescent↗