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P N Schofield

Publications and source records attributed to P N Schofield.

17 recordsLinked to original sources
PubMed1992

Concentration-dependent modulation of basic fibroblast growth factor action on multiplication and locomotion of human teratocarcinoma cells.

A human teratoma cell line (Tera 2) was grown in serum-free medium, and the population multiplication was stimulated by the addition of 1-10 ng basic fibroblast growth factor (bFGF)/ml. The bFGF-effect was abrogated by the addition of protamine sulphate. When high concentrations of bFGF were added, a preferential effect on cell locomotion was observed. 100 ng bFGF/ml stimulated cell movement but only exerted a marginal effect on cell multiplication. These observed exogenous requirements for multiplication and locomotion were complemented by the expression of bFGF receptors. Scatchard analysis of binding data suggests the existence of a high-affinity and a low-affinity class of receptors.

Cell Division↗
PubMed1992

Molecular analysis of patients with Wiedemann-Beckwith syndrome. I. Gene dosage on the short arm of chromosome 11.

Wiedemann-Beckwith syndrome (WBS) is characterised by a specific group of congenital malformations associated with an increased concurrent risk for development of a defined group of childhood neoplasms. The mode of inheritance is complex, but recently compiled family data suggest that it is an autosomal dominant trait of varying expression. It has previously been suggested that major rearrangements on the short arm of chromosome 11 may be involved in the aetiology of the disease, particularly in the region of the insulin like growth factor II (IGF-II) gene (11p15.5). This gene is thought to be parentally imprinted in the mouse and it has been suggested that in the human, duplication of the non-imprinted locus in WBS patient might lead to diploid expression of the gene and consequent general hyperplasia. This model predicts that there should be both frequent and parental origin specific duplication of the IGF-II gene in the patients. It was the aim of this study to examine the IGF-II locus and its surrounding chromosomal environment for such lesions in a large number of WBS patients. Using restriction fragment length polymorphism analysis for four linked markers on 11p and genomic clones internal to the IGF-II locus we could find no evidence of alteration or amplification of this area in any of the 11 patients investigated. In one patient who developed a Wilms tumour we could find no evidence for loss of any material on the short arm of chromosome 11 as reported previously.(ABSTRACT TRUNCATED AT 250 WORDS)

Beckwith-Wiedemann Syndrome↗
PubMed1992

Molecular analysis of patients with Wiedemann-Beckwith syndrome. II. Paternally derived disomies of chromosome 11.

In Wiedemann-Beckwith syndrome (WBS) a putative disease gene resides at the tip of the short arm of chromosome 11 in the region of the insulin growth like factor II (IGF-II) gene. Whilst changes in gene dosage in this area do not appear to be common in the syndrome, in familial cases the lesion appears to be dominant only when inherited through the female line. We undertook to examine the parental origin of the copies of chromosome 11 in a large group of WBS patients using a series of restriction fragment length polymorphisms (RFLPs) on 11p, and report here that in one sporadic case of WBS out of 14 both copies of chromosome 11 are derived from the father and are present in a normal dosage. This suggests that at least one mode of expression of the lesion is modified by genomic imprinting.

Beckwith-Wiedemann Syndrome↗
PubMed1992

The role of insulin-like growth factors and IGF-binding proteins in the physiological and pathological processes of the kidney.

Insulin-like growth factors (IGFs) and their binding proteins are implicated in the growth regulation of the kidney during embryogenesis and differentiation. Recent evidence also suggests that IGFs play a role in kidney physiology (glomerular filtration rate, renal plasma flow) and pathology (diabetic renal hypertrophy, nephritis, glomerulosclerosis, kidney tumours, chronic renal failure). This review focuses on the biology of IGFs at the molecular, protein and receptor levels and considers their importance in renal physiology and pathology. The current data demonstrate a central role for the IGFs in the mediation of a wide variety of effects on renal growth, function and malignancy.

Amino Acid Sequence↗
PubMed1991

Differentiation associated modulation of K-FGF expression in a human teratocarcinoma cell line and in primary germ cell tumours.

The human teratocarcinoma cell line Tera 2 can be induced to differentiate in vitro after exposure to retinoic acid. We show in this paper that whereas the K-FGF oncogene is expressed in undifferentiated cells, addition of retinoic acid rapidly (less than 60 min) downregulates the expression of this gene. However, when cells are cultured in RA for an extended period of time (greater than 15 days) K-FGF transcripts reappear. We also report that K-FGF is expressed in approximately one-third of primary human germ cell tumours but not in the corresponding normal testicular tissue.

Cell Differentiation↗
PubMed1991

Stimulatory effect of insulin like growth factor II on DNA synthesis in the human embryonic cornea.

By using an organ culture technique, corneal endothelial cells in human embryonic eyes could be stimulated to initiate DNA synthesis by exposure to insulin like growth factor II (IGF-II). The thymidine-labelling index doubled after IGF-II supplementation. However, this stimulatory effect was neither augmented nor abrogated by the simultaneous addition of Mannose-6-Phosphate. Nor did Mannose-6-phosphate stimulate DNA synthesis in the absence of IGF II. In contrast, the IGF II effect was partly counteracted by addition of an antibody that blocks binding to the IGF type I receptor. Taken together, this data suggests that IGF II stimulates DNA-synthesis in corneal endothelium by binding to the IGF type I rather than the IGF type II/ mannose-6-phosphate receptor.

Cornea↗
PubMed1991

Tumour suppression associated with expression of human insulin-like growth factor II.

Recent circumstantial evidence has implicated Insulin-like growth factor II in the genesis of several tumour types, notably developmental tumours (Scott et al., 1985; Schofield & Tate, 1987; Wilkins et al., 1989). This type of tumour, thought to originate during the defective differentiation of organ precursors (Miereau et al., 1987), often expresses greatly elevated levels of mRNA for IGF-II, a known mitogen for these cells and abundantly expressed in their presumed normal counterparts (Scott et al., 1985; Schofield & Tate, 1987; Gray et al., 1987). It has been proposed that continued, inappropriate expression of this gene drives tumour growth by an autocrine mechanism. In order to examine the potential role of IGF-II in the growth of tumour cells an IGF-II cDNA was introduced into a retroviral expression vector, and used to infect a cloned fibroblast cell line. Expression of IGF-II conferred a degree of serum independence of growth in cell culture, however, when cells were injected into nude mice as subcutaneous grafts, clones expressing IGF-II from the retrovirus were found to have a greatly increased (five fold) latency of sarcoma formation. After a prolonged lag all cell lines eventually gave rise to tumours in which the introduced IGF-II genes had either been lost or inactivated, suggesting that in this system IGF-II acts as a tumour suppressor gene.

Animals↗
PubMed1991

Developmental tumours.

Recent advances in the genetics and cell biology of developmental tumours have lead to new insights into the causes of neoplasia and the tumour cell phenotype. While much investigation has centered around the mechanism whereby tumour cells are able to proliferate, and the relation of these mechanisms to normal cellular growth and differentiation during development, the molecular characterization of genes associated with chromosome lesions predisposing to tumours has shed light on a new class of tumour suppressing gene, whose continued expression is selected against during tumour formation. This review concentrates on two systems in which these phenomena are currently being addressed, teratocarcinoma and Wilms' tumour, embryonal nephroblastoma.

Animals↗
PubMed1990

Stimulatory effects of basic fibroblast growth factor on DNA synthesis in the human embryonic cornea.

First trimester human embryonic eye globes were micro-dissected so that a passage was opened between the outer environment and the anterior chamber, which rendered free access of tissue culture medium to the endothelial cell monolayer. The dissected eye globes were maintained in organ culture for 24h in the continuous presence of tritiated thymidine. Sections were cut through the whole eye globes and were subject to autoradiographic analysis in order to estimate the mitogenic response of human corneal endothelial cells to externally supplied growth factors and hormones. It was found that the corneal endothelial cells could be stimulated to initiate DNA synthesis by exposure to basic fibroblast growth factor (bFGF). The thymidine labelling index nearly doubled after bFGF addition. Northern blot analysis revealed the presence of bFGF transcripts in the embryonic eye. In contrast we were unable to trace any bFGF transcripts in other first trimester human embryonic organs. In an attempt to determine the topographical distribution of bFGF mRNA within the eye, we found that transcript levels were higher in the posterior regions of the eye globe. Immunostaining with the appropriate antibody showed conclusively that bFGF protein was present in both the anterior and posterior human eye. These results suggest that local production of bFGF may stimulate cell proliferation in vivo.

Blotting, Northern↗
PubMed1989

Analysis of gene dosage on chromosome 11 in children suffering from Beckwith-Wiedemann syndrome.

The Beckwith-Wiedemann syndrome (BWS) is composed of multiple congenital malformations coupled with a high concurrent risk for the development of specific rare childhood tumours. The syndrome is characterised by a complex mode of inheritance, but recent evidence indicates that it is an autosomal dominant trait with variable penetrance. It has been previously suggested that major rearrangements of the short arm of chromosome 11 are involved in the aetiology of the disease. We undertook to search for rearrangements in 11p in four patients with BWS and their parents and siblings. By using cloned DNA fragments homologous to four genes located on 11p, namely catalase, parathyroid hormone, insulin-like growth factor II and the proto-oncogene c-Ha-Ras, we subjected DNA from the patients to a restriction fragment length polymorphism (RFLP) analysis after digestion with restriction enzymes. We found no evidence for any large scale deletions or amplifications in this chromosomal region. We therefore conclude that altered gene dosage is not, as has been suggested, a requirement for the development of BWS. This raises the question of whether some other molecular mechanism is responsible for the malformations observed.

Adolescent↗
PubMed1989

Molecular and functional characterization of amylin, a peptide associated with type 2 diabetes mellitus.

The 37-amino acid peptide called amylin is a major component of the islet amyloid deposited in the pancreases of persons with type 2 diabetes mellitus. We report the isolation of a partial cDNA clone and a phage lambda genomic clone of the coding region of the amylin gene. The DNA sequence encodes a protein sequence identical to that of amylin isolated from the amyloid found in the diabetic pancreas and shows that amylin is likely to be synthesized as a precursor peptide, now named proamylin. We have demonstrated that the amylin gene is present on chromosome 12 and that it is probably transcribed in the islets of Langerhans. The sequences of the genes for amylin and the calcitonin gene-related peptides (CGRPs) show strong similarity, especially over their 5' coding regions, where both peptides have a conserved intramolecular disulfide bridge, and also over their 3' coding regions, where the presence of a glycine codon strongly suggests that the carboxyl-terminal residue of amylin, like that of CGRP, is amidated. To examine the functional relevance of these posttranslational modifications, the biological activity of amylin synthesized with or without the disulfide bridge and/or amidation was measured. It was found that both features are necessary for full biological activity, thereby confirming the functional importance of those regions of the molecule whose sequences are conserved at both protein and genetic levels.

Amino Acid Sequence↗
PubMed1989

Temporal changes in the expression of the insulin-like growth factor II gene associated with tissue maturation in the human fetus.

The insulin-like growth factors are broadly distributed in the human conceptus and are thought to play a role in the growth and differentiation of tissues during development. Using in situ hybridization we have shown that a wide variety of specific cell types within tissues express the gene for insulin-like growth factor II at times of development from 18 days to 14 weeks of gestation. Examination of blastocysts produced by in vitro fertilization showed no expression, thus bracketing the time of first accumulation of IGF-II mRNA to between 5 and 18 days postfertilization. The pattern of IGF-II expression shows specific age-related differences in different tissues. In the kidney, for example, expression is found in the cells of the metanephric blastema which is dramatically reduced as the blastema differentiates. The reverse is also seen, and we have noted an increase in expression of IGF-II in the cytotrophoblast layer of the placenta with gestational age. The sites of expression do not correlate with areas of either high mitotic activity or specific types of differentiation, but the observed pattern of expression in the kidney, adrenal glands and liver suggests an explanation for the abnormally high IGF-II mRNA expression in developmental tumours such as Wilms' tumour.

Adrenal Cortex↗
PubMed1987

Glucose regulates preproinsulin messenger RNA levels in a clonal cell line of simian virus 40-transformed B cells.

In HIT-T15 cells grown in the absence of glucose, Northern blot analysis of total RNA revealed a major 0.5 kb preproinsulin (ppI) mRNA transcript which co-migrated with the mature transcript from a human insulinoma. In 4 h tissue cultures, glucose (2-20 mM) stimulated HIT cell ppI mRNA levels in a markedly dose-dependent manner. Glucose-stimulated ppI mRNA was (i) inhibited by actinomycin D, suggesting that regulation may be in part transcriptional, and (ii) potentiated by agents known to activate B cell protein kinases. HIT cells represent a unique model for investigating long term regulation of insulin gene expression and biosynthesis.

Animals↗
PubMedDate not supplied

Expression of the 3-hydroxy-3-methylglutaryl coenzyme A-reductase and LDL-receptor genes in human embryonic tumours and in normal foetal tissues.

The expression of the HMG-CoA-reductase and LDL-receptor genes was examined in primary human embryonic tumours and in normal human first trimester foetal tissues. All embryonic and extra-embryonic tissues examined contained RNA that hybridized with the HMG-CoA-reductase and LDL-receptor cDNA-probes. However, the transcript levels varied considerably between organs. By using Northern blotting, we confirmed that normal foetal tissues contained HMG-CoA-reductase and LDL-receptor transcripts of normal size (4.2 kB and 5.3 kB, respectively). All human developmental tumours examined were characterized by high levels of HMG-Co-A-reductase RNA. However, when the quality of this RNA was examined in greater detail it was found that the 4.2 kB band only accounted for a minor portion of the RNA. Instead we found a range of other transcripts (3.1, 1.1., 0.95, 0.78 and 0.55 kB) that hybridized with the probe. There was a qualitative difference in that only the non-seminomas contained high levels of the three smaller transcripts (0.95, 0.78 and 0.55 kB). In contrast, only one tumor--an embryonal carcinoma--contained increased levels of LDL-receptor transcript. This was found to be of the expected size (5.3 kB).

Cell Division↗