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J Copeman

Publications and source records attributed to J Copeman.

10 recordsLinked to original sources
PubMed2000

Posttranscriptional regulation of human leukocyte antigen G during human extravillous cytotrophoblast differentiation.

Human maternal tolerance to a semiallogenic fetus may be maintained, in part, by the unusual expression pattern of antigen-presenting molecules in placental trophoblast cells. Extravillous cytotrophoblast (EVC) cells, which invade the maternal decidua, express high levels of human leukocyte antigen G (HLA-G), a nonclassical, major histocompatibility complex (MHC) class I molecule. HLA-G transcripts have been detected in tumors and other tissues, yet protein accumulation is rare. We show that, within EVC cells themselves, the mRNA is more broadly expressed than the protein. Specifically, accumulation of HLA-G protein was markedly delayed during EVC cell differentiation. To elucidate this mechanism, we performed a comprehensive analysis comparing the expression of HLA-G and proteins essential for MHC class I expression at the cell surface. The transporter for antigen processing proteins TAP1 and TAP2, as well as tapasin and beta(2)-microglobulin, appeared to be coordinately expressed throughout EVC cell columns. Strikingly, they all accumulated well in advance of the HLA-G protein but concurrently with its mRNA. A similar delay in the accumulation of the HLA-G protein was observed in vitro, using cultures of chorionic villi. We conclude that posttranscriptional regulation of HLA-G is fundamental to EVC cell development and is achieved independently of the peptide loading system. This represents a novel mechanism of MHC class I regulation.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Promoting nutrition in older people in nursing and residential homes.

Malnutrition and dehydration are serious and common problems among older people in nursing and residential care homes. The situation is exacerbated because staff may not be trained to recognize the signs and symptoms of malnutrition and dehydration and hence opportunities for early intervention are missed. A nutrition assessment should form part of the admission process to identify whether an individual has, or is at risk of developing, malnutrition and dehydration. This article suggests key questions that should be asked to assist this process. The individual and organizational risk factors that affect nutrition and health status are discussed, and practical suggestions given to help address any problems recognized. The causes and consequences of dehydration are explained and practices that place an individual at risk of dehydration considered. Suggestions are given to help identify when a person is not drinking sufficiently so that early rapid intervention can be initiated. Helping an older person to eat and drink independently is a practical activity that is often undervalued. Its importance needs to be recognized in all nursing and residential care settings.

Aged↗
PubMed1998

Assembly of MHC class I molecules with biosynthesized endoplasmic reticulum-targeted peptides is inefficient in insect cells and can be enhanced by protease inhibitors.

To study the requirements for assembly of MHC class I molecules with antigenic peptides in the endoplasmic reticulum (ER), we studied Ag processing in insect cells. Insects lack a class I recognition system, and their cells therefore provide a "blank slate" for identifying the proteins that have evolved to facilitate assembly of class I molecules in vertebrate cells. H-2Kb heavy chain, mouse beta 2-microglobulin, and an ER-targeted version of a peptide corresponding to Ova(257-264) were expressed in insect cells using recombinant vaccinia viruses. Cell surface expression of Kb-OVA(257-264) complexes was quantitated using a recently described complex-specific mAb (25-D1.16). Relative to TAP-deficient human cells, insect cells expressed comparable levels of native, peptide-receptive cell surface Kb molecules, but generated cell surface Kb-OVA(257-264) complexes at least 20-fold less efficiently from ER-targeted peptides. The inefficient assembly of Kb-OVA(257-264) complexes in the ER of insect cells cannot be attributed solely to a requirement for human tapasin, since first, human cells lacking tapasin expressed endogenously synthesized Kb-OVA(257-264) complexes at levels comparable to tapasin-expressing cells, and second, vaccinia virus-mediated expression of human tapasin in insect cells did not detectably enhance the expression of Kb-OVA(257-264) complexes. The assembly of Kb-OVA(257-264) complexes could be greatly enhanced in insect but not human cells by a nonproteasomal protease inhibitor. These findings indicate that insect cells lack one or more factors required for the efficient assembly of class I-peptide complexes in vertebrate cells and are consistent with the idea that the missing component acts to protect antigenic peptides or their immediate precursors from degradation.

Aedes↗
PubMed1998

Genomic analysis of the Tapasin gene, located close to the TAP loci in the MHC.

The Tapasin molecule is a member of the immunoglobulin (Ig) superfamily required for the association of TAP transporters and MHC class I heterodimers in the endoplasmic reticulum. In this study, the Tapasin gene was precisely mapped in relation to the MHC. The gene was centromeric of the HLA-DP locus between the HSET and HKE1.5 genes and within 500 kbp of the TAP1 and TAP2 genes. A homologous mouse EST was mapped to a syntenic position on chromosome 17, centromeric of the H-2 K locus. Similarly, the rat Tapasin gene was shown to be in an equivalent location with respect to the RT1.A locus. The localization of Tapasin, TAP, LMP and class I genes within such a short distance of each other on the chromosome implies some regulatory or functional significance. We determined the Tapasin gene sequence for comparison of its structure to that of other Ig superfamily members, such as MHC class I genes. The IgC domain was encoded by a separate exon. However, the positions of the other introns were not characteristic of other Ig superfamily genes, indicating that Tapasin has a distinct phylogeny.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Elucidation of the genetic basis of the antigen presentation defects in the mutant cell line .220 reveals polymorphism and alternative splicing of the tapasin gene.

Antigenic peptides are presented to cytotoxic T lymphocytes by heterodimers of MHC class I molecules and beta2-microglobulin. Peptides are generated in the cytosol and translocated into the endoplasmic reticulum (ER) through the transporter associated with antigen processing (TAP). Optimal binding of peptides to class I molecules is facilitated by the physical association between class I heterodimers and TAP. This association is mediated largely by the glycoprotein tapasin. Analysis of tapasin function has relied on a mutant cell line, .220, which is defective in tapasin expression and antigen presentation. We have investigated the genetic basis of these defects. In .220 cells, Tapasin transcripts lack exon two. This is caused by a single nucleotide substitution, disrupting the 5' splice site of the second intron. A tapasin protein is produced in .220 cells, but has a truncated signal peptide and lacks the N-terminal 49 amino acids encoded by full-length transcripts. Nonetheless, this truncated form is translocated into the ER and interacts with TAP. As a result of alternative splicing, transcripts lacking exon two are also present in wild-type cells, although no truncated protein was detected. Additionally we describe a polymorphism in the Tapasin gene, with two alleles encoding arginine or threonine at peptide position 240.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

A critical role for tapasin in the assembly and function of multimeric MHC class I-TAP complexes.

Newly assembled major histocompatibility complex (MHC) class I molecules, together with the endoplasmic reticulum chaperone calreticulin, interact with the transporter associated with antigen processing (TAP) through a molecule called tapasin. The molecular cloning of tapasin revealed it to be a transmembrane glycoprotein encoded by an MHC-linked gene. It is a member of the immunoglobulin superfamily with a probable cytoplasmic endoplasmic reticulum retention signal. Up to four MHC class I-tapasin complexes were found to bind to each TAP molecule. Expression of tapasin in a negative mutant human cell line (220) restored class I-TAP association and normal class I cell surface expression. Tapasin expression also corrected the defective recognition of virus-infected 220 cells by class I-restricted cytotoxic T cells, establishing a critical functional role for tapasin in MHC class I-restricted antigen processing.

ATP Binding Cassette Transporter, Subfamily B, Mem↗