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D G Jackson

Publications and source records attributed to D G Jackson.

At least 55 records · Page 3Linked to original sources
PubMed1994

Expression of alternatively spliced forms of the CD44 extracellular-matrix receptor on human lung carcinomas.

Expression of isoforms of the CD44 hyaluronan receptor/lymph-node endothelial receptor by human tumour cells is thought to play a role in tumour growth and metastasis. These isoforms which vary in the length of the extracellular domain are generated by differential RNA splicing that involves the 10 alternative exons (v1 to v10) encoding the membrane proximal region of the molecule. Several tumours have been shown to over-express CD44 containing the v6 exon, and this, together with other evidence, has led to the suggestion that v6 may play a causative role in tumour metastasis. In this report we have compared the expression of CD44 isoforms between different lung tumour lines, including SCLC, squamous-cell carcinoma, adenocarcinoma and mesothelioma, using both RT-PCR and fluorescent antibody staining with a panel of CD44 exon-specific monoclonal antibodies (MAbs). Our results show large differences in vCD44 expression between individual tumour lines. Little or no vCD44 containing the metastasis-associated v6 exon was detected in most tumours, including the highly metastatic SCLC lines. Indeed, the SCLC lines and some squamous-cell carcinomas contained only very low levels of either vCD44 or CD44H, indicating that CD44 expression may not always correlate with tumour development or dissemination. One of the squamous-cell carcinomas studied (HOTZ) was found to express a complex mixture of CD44 splice variants similar to the immortalized normal bronchial epithelial line BEAS-2B. Cloning and sequencing of vCD44 from the HOTZ cell line yielded several splice variants that have also been identified on leukaemic cells, normal keratinocytes and activated peripheral-blood lymphocytes.

Alternative Splicing↗
PubMed1994

CD44 isoform expression mediated by alternative splicing: tissue-specific regulation in mice.

CD44 is a widely distributed cell surface glycoprotein which shows heterogeneity in molecular expression as a result of post-translational modification as well as alternative splicing of CD44 mRNA. Functional studies have indicated that CD44 plays a role as an adhesion molecule and that different CD44-expressing cells differ in their capacities for CD44-dependent ligand binding. These observations have raised the possibility that structural modifications of CD44, including those resulting from alternatively spliced mRNA isoforms, are involved in the functional heterogeneity of CD44. To assess the expression of CD44 isoforms in the mouse, we examined CD44 cDNA by reverse transcription polymerase chain reaction (RT-PCR). Southern blotting of PCR products with a CD44 cDNA probe or with internal oligonucleotides revealed the expression in mouse tumor cell lines and normal tissues of multiple CD44 mRNA products which are larger than that observed in the absence of variable exon expression. Interestingly, different mouse tissues, including lymphoid cells, showed unique patterns of alternative CD44 mRNA in Southern blotting analysis. The use of exon-specific primers allowed detection of multiple alternatively spliced mRNA species involving expression of at least seven variable exons. Cloning and sequencing of these PCR products revealed sequence identity with recently identified genomic CD44 sequences and confirmed that the PCR products correspond to mature mRNA expressing alternatively spliced CD44 exons. Taken together, these findings demonstrate that the mouse expresses multiple variably spliced CD44 isoforms and that expression is regulated in a tissue- and cell-type specific manner.

Alternative Splicing↗
PubMed1993

Human lymphocyte antigen CD38 catalyzes the production of cyclic ADP-ribose.

The human lymphocyte antigen CD38 has been shown to share sequence homology with ADP-ribosyl cyclase, the enzyme that catalyzes the conversion of NAD+ to cyclic ADP-ribose (cADPR), a potent Ca(2+)-mobilizing agent. In this study COS1 cells from African Green Monkey kidney were transiently transfected with CD38 cDNA, inducing expression of authentic CD38 on the cell surface. We demonstrate that CD38 expressed in this manner can convert NAD+ to cADPR in the extracellular medium as assessed by Ca2+ release from sea-urchin egg microsomes.

ADP-ribosyl Cyclase↗
PubMed1993

TAP1 alleles in insulin-dependent diabetes mellitus: a newly defined centromeric boundary of disease susceptibility.

It has been previously demonstrated that individuals with certain DR alleles have an increased relative risk of developing insulin-dependent diabetes mellitus (IDDM). The disease association is even stronger with certain DQ alleles but there is little association with DP providing a boundary of disease association to the 430 kb between DQ and DP. The recently described TAP (transporter associated with antigen processing) genes have been mapped approximately midway between DP and DQ. Therefore, it was of interest to determine if any TAP alleles were associated with IDDM. In addition to the alleles of TAP1 that have been described, others were identified during this study. Diabetics and normal controls were screened for TAP1 using single-stranded conformational polymorphism and relative risk was determined. In the same population group we have studied extensively in the past, we found a higher association of a TAP1 allele with IDDM than with any single HLA-DP allele but the risk was lower than with HLA-DQB1*0302. These data provide new limits for IDDM susceptibility to the 190-kb interval between TAP1 and HLA-DQB1.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

The identification of a new alternative exon with highly restricted tissue expression in transcripts encoding the mouse Pgp-1 (CD44) homing receptor. Comparison of all 10 variable exons between mouse, human, and rat.

The human CD44 cell surface glycoprotein family which has been implicated in lymphocyte homing, tumor metastasis, and extracellular matrix attachment consists of a large number of related isoforms that derive from the differential splicing of a single CD44 gene transcript. Recent mapping of the CD44 locus in man indicated the presence of at least nine alternative exons within the region of the gene encoding the variable membrane proximal extracellular domain. Here we report the identification of a 10th alternative exon (termed V1) in the mouse, human, and rat CD44 genes. We demonstrate tissue-specific patterns of expression for transcripts containing exons V1-V10 in the mouse and a highly restricted usage of exon V1 in transcripts from mouse gastric tissue. Close sequence homology between exons V1-V10 from mouse rat and human points to a specific functional role rather than a purely structural role for the membrane proximal extracellular domain of the CD44 molecule.

Alternative Splicing↗
PubMed1993

The identification, purification, and characterization of two invariant surface glycoproteins located beneath the surface coat barrier of bloodstream forms of Trypanosoma brucei.

Two new polypeptides, termed ISG70 and ISG64, have been found in Trypanosoma brucei, using enzyme-catalyzed radioiodination techniques. Both are externally disposed integral membrane glycoproteins, containing N-linked carbohydrate chains. No structural homology was detected between ISG70, ISG64, or the variant surface glycoprotein (VSG) when assessed by 1) comparative peptide mapping, 2) immunoprecipitation analysis, and 3) lectin affinity chromatography. ISG70 occurred in 5.1 x 10(4) copies/cell and has been purified 880-fold from detergent extracts of plasma membranes by a procedure that includes gel filtration, lectin affinity chromatography, and preparative SDS-polyacrylamide gel electrophoresis. ISG70 was present only in bloodstream forms and was specifically detected in six different cloned variants from the Molteno Institute trypanosomal antigen type (MITat) serodeme of T. brucei and from the single cloned variant of the International Laboratory for Research on Animal Diseases trypanosomal antigen type (ILTat) serodeme that was examined. Rabbits with chronic infections of T. brucei displayed circulating antibodies against ISG70. Both the immunogenicity of ISG70 and its invariant nature suggest that it may be useful in the development of an effective serodiagnostic test. Furthermore, its stage-specific location combined with its invariant nature implies that its function is strictly related to a physiological role required for the parasite's residence in its mammalian host.

Animals↗
PubMed1993

Cloning of a novel surface antigen from the insect stages of Trypanosoma brucei by expression in COS cells.

Trypanosoma brucei cDNA libraries constructed in the vector pCDM8 were screened selectively for insect (procyclic) stage surface antigen cDNAs by transient expression in mammalian COS-7 fibroblasts and "panning" with a rabbit polyclonal antiserum. This strategy yielded two surface antigen cDNAs termed PSSA-1 and PSSA-2. The PSSA-1 cDNA encoded an isotype of procyclin, the major phosphatidylinositol-linked stage-specific glycoprotein antigen of the tsetse fly infective forms of T. brucei. The PSSA-2 cDNA encoded a new and previously unidentified stage-specific surface antigen with the features of a typical transmembrane glycoprotein but with an unusual cytoplasmic tail composed of a proline-rich tandem repeat. Fluorescent antibody staining of PSSA-1 transfected COS cells with a panel of procyclin-specific monoclonal antibodies confirmed that the protein was located on the outer surface of the plasma membrane. Furthermore, the antigen on COS cells was insensitive to treatment with phosphatidylinositol-specific phospholipase C suggesting that the inositol of the glycosylinositol phospholipid-lipid anchor contained the same fatty acyl modification reported recently for the procyclin molecule in cultured procyclic trypanosomes. In contrast the PSSA-2 antigen on COS cells was stained very weakly by whole parasite antisera. Northern blot hybridization revealed that the PSSA-2 antigen was encoded by a single 1.7-kilobase transcript which was present in parasites from the insect procyclic stage of the life cycle but not from the animal bloodstream stage. Southern blot hybridization analysis of DNA from procyclic stage trypanosomes indicated that the gene for PSSA-2 may be present in more than one copy in procyclic trypanosomes.

Amino Acid Sequence↗
PubMed1993

CD44 and cancer.

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Humans↗
PubMed1993

Expression of the CMRF-35 antigen, a new member of the immunoglobulin gene superfamily, is differentially regulated on leucocytes.

A new monoclonal antibody, CMRF-35, has been generated that recognized a 224 amino acid cell surface protein which is a novel member of the immunoglobulin gene superfamily. The antibody, raised against large granular lymphocytes (LGL), stains LGL, monocytes, macrophages and granulocytes but not platelets or erythrocytes. In addition, a subset of peripheral blood T lymphocytes (26.6 +/- 13.4% CD5+ cells) and B lymphocytes (13.7 +/- 6.8% CD20+ cells) stained with CMRF-35 but tonsil T and B cells were essentially negative. Expression of the CMRF-35 antigen (Ag) on different leucocyte populations was markedly influenced by stimulation of the cells with mitogens and cytokines. Activation of peripheral blood T cells with phytohaemagglutinin (PHA), or phorbol myristate acetate (PMA) and calcium ionophore (CaI) led to a decrease in the proportion of CMRF-35+ T lymphocytes. In contrast, PHA activation of tonsil T lymphocytes resulted in an increase in CMRF-35 Ag expression (47.1 +/- 1.5% CD5 cells at 6 days). An increase in CMRF-35 Ag was also seen on phorbol ester and CaI-activated tonsil B cells. No change in CMRF-35 expression on natural killer (NK) cells occurred following activation with interleukin-2 (IL-2) but the CMRF-35 Ag was down-regulated following Fc receptor stimulation. A moderate increase in CMRF-35 expression occurred during monocyte-macrophage differentiation and the expression of the Ag on monocytes was differentially regulated by interferon-gamma (IFN-gamma). This regulation of the CMRF-35 Ag on the leucocyte surface suggests that the molecule has an important function common to diverse leucocyte types.

Antibodies, Monoclonal↗
PubMed1992

Genomic structure of DNA encoding the lymphocyte homing receptor CD44 reveals at least 12 alternatively spliced exons.

The CD44 molecule is known to display extensive size heterogeneity, which has been attributed both to alternative splicing and to differential glycosylation within the extracellular domain. Although the presence of several alternative exons has been partly inferred from cDNA sequencing, the precise intron-exon organization of the CD44 gene has not been described to date to our knowledge. In the present study we describe the structure of the human CD44 gene, which contains at least 19 exons spanning some 50 kilobases of DNA. We have identified 10 alternatively spliced exons within the extracellular domain, including 1 exon that has not been previously reported. In addition to the inclusion or exclusion of whole exons, more diversity is generated through the utilization of internal splice donor and acceptor sites within 2 of the individual exons. The variation previously reported for the cytoplasmic domain is shown to result from the alternative splicing of 2 exons. The genomic structure of CD44 reveals a remarkable degree of complexity, and we confirm the role of alternative splicing as the basis of the structural and functional diversity seen in the CD44 molecule.

Alternative Splicing↗
PubMed1992

Multiple variants of the human lymphocyte homing receptor CD44 generated by insertions at a single site in the extracellular domain.

The human CD44 cell-surface glycoprotein participates in a wide variety of cell-cell interactions including lymphocyte homing and tumor metastasis. The CD44 antigen is known to display extensive size heterogeneity when compared between different tissue sources although the structural basis for this variation is not yet clear. Recently, two further isotypes in addition to the basic hemopoietic form of the CD44 antigen have been cloned and sequenced and these have been found to contain all or part of a 200-400-base pair insert within the extracellular domain, suggesting that the characteristic heterogeneity in the molecule may be generated by a mechanism of alternative splicing. We have obtained further evidence for alternative splicing, and we report here the cloning and sequencing of six different CD44 sequence variants from a variety of cell lines using a combination of expression cloning and the polymerase chain reaction. Comparison of these variants indicates that each is probably assembled by the insertion of five different exon units in tandem into a discrete site within the membrane proximal region of the extracellular domain. One of the variants contains an exon that shares extensive amino acid sequence homology with a recently described rat CD44 variant that mediates tumor metastasis. Another variant contains a new exon that encodes a tandem repeat of the consensus sequence SG for covalent modification with chondroitin sulfate and is expressed predominantly on mammary tumors. We suggest that a mechanism of alternative exon splicing generates much of the observed structural heterogeneity of CD44 and that the particular set of CD44 variants expressed in a single cell may represent a precise postal code directing the final destination of migrating cells and metastatic tumors.

Amino Acid Sequence↗
PubMed1992

Molecular cloning of a novel member of the immunoglobulin gene superfamily homologous to the polymeric immunoglobulin receptor.

The CMRF35 monoclonal antibody recognizes a cell membrane antigen present on the surface of monocytes, neutrophils, a proportion of peripheral blood T and B lymphocytes and lymphocytic cell lines. Initial studies with CMRF35 suggested an unusual pattern of serological reactivity which did not correspond to any of the known leukocyte differentiation antigen clusters. We describe here the cloning and sequencing of a cDNA encoding the CMRF35 antigen by means of expression in COS cells and immunoselection with the CMRF35 monoclonal antibody. The cDNA encodes a novel integral membrane glycoprotein of 224 amino acids that represents a new member of the immunoglobulin (Ig) gene superfamily. The molecule comprises (a) a single extracellular Ig variable domain remarkably similar to the Fc receptor for polymeric IgA and IgM, (b) a membrane-proximal domain containing a high proportion of proline, serine and threonine residues that was predicted to be heavily O-glycosylated, (c) an unusual transmembrane anchor that contained a glutamic acid and a proline residue and (d) a short cytoplasmic tail. Transcripts encoding the CMRF35 protein were detected in early monocytic cell lines, in peripheral blood T cells and in some B lymphoblastoid cell lines, confirming the results of immunocytological staining. However, the level of CMRF35 expression on peripheral blood T cells was shown to decrease in response to mitogenic stimulation. The likelihood that the CMRF35 antigen shares a common evolutionary ancestor with the poly Ig Fc receptor is discussed.

Amino Acid Sequence↗
PubMed1992

Neuromyoblastoma in the rat.

We report three tumours arising in the brain stem or adjacent cranial nerves of the Alderly Park rat. Light microscopy with special stains, immunocytochemistry and electron microscopy supported the conclusion that both neuronal and myoid differentiation occurred in all neoplasms. This was shown by the presence in neural cells of axon-like cell processes and in myoblastic cells of striated myofibrils. Although medulloblastomas occur in man and rats the tumours reported here were not related to the cerebellum. We have termed this tumour neuromyoblastoma.

Animals↗
PubMed1991

Immunodetectable levels of the inhibitory guanine nucleotide-binding regulatory proteins in failing human heart: discordance with measurements of adenylate cyclase activity and levels of pertussis toxin substrate.

Human hearts with idiopathic dilated cardiomyopathy have diminished adenylate cyclase activity and increased amounts of the alpha-subunit of the inhibitory guanine nucleotide-binding regulatory protein (alpha Gi) as measured by pertussis toxin catalyzed ADP-ribosylation. We utilized specific antisera against synthetic peptides corresponding to amino sequences deduced from cDNA's encoding the three alpha Gi subspecies to compare the immunologic and bioactivity levels of Gi in failing and non-failing human hearts. The various antisera detected three peptides with Mr 42,000, 38,000, and 37,000. Only the Mr 42,000 peptide co-migrated with the pertussis toxin substrate. Although functional activity of alpha Gi was increased in the particulate fractions of the failing heart as measured by inhibition of guanine nucleotide-stimulated adenylate cyclase activity and the quantity of pertussis toxin substrate was also increased, there were not associated changes in the levels of immunodetectable Gi. Therefore, the increased functional activity of Gi in the failing human heart as assessed by adenylate cyclase measurements cannot be explained by a relative increase in the among of Gi protein.

Adenylate Cyclase Toxin↗
PubMed1991

Effects of chronic ethanol exposure on cardiac receptor-adenylyl cyclase coupling: studies in cultured embryonic chick myocytes and ethanol fed rats.

Ethanol effects in the brain appear to be mediated at least in part by an alteration in receptor-effector coupling via guanine nucleotide-binding regulatory proteins (G proteins). To test the hypothesis that a similar pathway participates in the cardiotoxic effects of ethanol, we assessed the effects of chronic ethanol on two commonly used experimental models: embryonic chick myocytes in culture and ventricular myocardium from chronically fed rats. Ethanol had no effect on either the function or quantity of G proteins as assessed by effector-stimulated adenylyl cyclase activity and the levels of ADP-ribosylation substrates. In contrast, effector-stimulated adenylyl cyclase activity was significantly altered in the liver of ethanol-fed rats. These results suggest that receptor-effector coupling via G proteins in our two cardiac models is insensitive to ethanol and that ethanol effects may be species or organ specific.

ADP-Ribosylation Factors↗
PubMed1990

Isolation of a cDNA encoding the human CD38 (T10) molecule, a cell surface glycoprotein with an unusual discontinuous pattern of expression during lymphocyte differentiation.

A cDNA clone encoding the human lymphocyte differentiation Ag CD38 was isolated from a mixture of four different lymphocyte CDNA libraries expressed transiently in COS cells and screened by panning with mAb. Transfected COS cells expressed a surface protein of Mr 46,000 that was similar to the native CD38 molecule expressed on the B cell line Daudi and the T cell leukemia HPB-ALL and which was recognized by each of the CD38 specific mAb HIT-2, T16, T168, HB7, 5D2, ICO-18, and ICO-20. The CD38 cDNA sequence predicts an unusual 30-kDa polypeptide with a short N-terminal cytoplasmic tail, and a carboxyl-terminal extracellular domain carrying the four potential N-linked glycosylation sites. The absence of significant homology with other known surface Ag including members of the Ig superfamily ruled out the possibility that CD38 was the human homologue of the murine Qa2 molecule as has been suggested previously. PvuII digests of human genomic DNA revealed a polymorphism linked to the CD38 gene.

ADP-ribosyl Cyclase↗