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Biomedical subjects

B Jameson

Publications and source records attributed to B Jameson.

At least 19 recordsLinked to original sources
PubMed2001

Identification of overlapping but distinct cAMP and cGMP interaction sites with cyclic nucleotide phosphodiesterase 3A by site-directed mutagenesis and molecular modeling based on crystalline PDE4B.

Cyclic nucleotide phosphodiesterase 3A (PDE3A) hydrolyzes cAMP to AMP, but is competitively inhibited by cGMP due to a low k(cat) despite a tight K(m). Cyclic AMP elevation is known to inhibit all pathways of platelet activation, and thus regulation of PDE3 activity is significant. Although cGMP elevation will inhibit platelet function, the major action of cGMP in platelets is to elevate cAMP by inhibiting PDE3A. To investigate the molecular details of how cGMP, a similar but not identical molecule to cAMP, behaves as an inhibitor of PDE3A, we constructed a molecular model of the catalytic domain of PDE3A based on homology to the recently determined X-ray crystal structure of PDE4B. Based on the excellent fit of this model structure, we mutated nine amino acids in the putative catalytic cleft of PDE3A to alanine using site-directed mutagenesis. Six of the nine mutants (Y751A, H840A, D950A, F972A, Q975A, and F1004A) significantly decreased catalytic efficiency, and had k(cat)/K(m) less than 10% of the wild-type PDE3A using cAMP as substrate. Mutants N845A, F972A, and F1004A showed a 3- to 12-fold increase of K(m) for cAMP. Four mutants (Y751A, H840A, D950A, and F1004A) had a 9- to 200-fold increase of K(i) for cGMP in comparison to the wild-type PDE3A. Studies of these mutants and our previous study identified two groups of amino acids: E866 and F1004 contribute commonly to both cAMP and cGMP interactions while N845, E971, and F972 residues are unique for cAMP and the residues Y751, H836, H840, and D950 interact with cGMP. Therefore, our results provide biochemical evidence that cGMP interacts with the active site residues differently from cAMP.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

A novel candidate oncogene, MCT-1, is involved in cell cycle progression.

Using the arbitrarily primed-PCR (AP-PCR) assay to detect genetic abnormalities that occur in a panel of lymphoid cell lines, we identified an amplified stretch of genomic DNA that contained a putative open reading frame. Northern blot analysis with this genomic clone revealed widespread low level expression in normal human tissue. The full cDNA sequence was obtained with no significant homology to any known genes in the genome database. We termed this novel gene with multiple copies in a T-cell malignancy as MCT-1. MCT-1 was localized to the long arm of chromosome Xq22-24 by flourescence in situ hybridization analysis. Although there was no significant homology at the primary sequence level, there was a limited degree of amino acid homology with a domain of cyclin H that appears to specify protein-protein complexes. This relationship between MCT-1 and cyclin H implied a potential role for MCT-1 in cell cycle regulation. Overexpression of MCT-1 increased the proliferative rate of cells by decreasing the length of the G1 phase without a reciprocal increase in the S and G2-M phases. Recent work has established the role of cell cycle regulatory molecules in the development of certain human malignancies. Therefore, we investigated the transforming ability of MCT-1 overexpression using soft agar growth assays and demonstrated that only MCT-1-overexpressing cells were able to establish colonies. Taken together, MCT-1 is a novel candidate oncogene with homology to a protein-protein binding domain of cyclin H.

Amino Acid Sequence↗
PubMed1998

Association of Puralpha with RNAs homologous to 7 SL determines its binding ability to the myelin basic protein promoter DNA sequence.

Cell type and developmental stage expression of the myelin basic protein (MBP) gene in mouse brain is regulated at the transcriptional level. Earlier studies from our laboratory have led to the identification of a DNA binding protein from mouse brain, named Puralpha, which interacts with the MB1 regulatory motif of the MBP and stimulates its transcription in glial cells. In this report, we demonstrate that a cellular RNA, with significant homology to 7 SL RNA is associated with Puralpha. Results from band shift competition studies indicate that Puralpha-associated RNA (PU-RNA), inhibits the interaction of immunopurified Puralpha with the MB1 DNA sequence. Results from Northern blot studies indicated that PU-RNA is expressed during various stages of brain development. Of interest, this RNA was found in association with Puralpha that was produced in the mouse brain at the early stage of brain development. Results from Northwestern analysis using a PU-RNA probe identified the regions within Puralpha that are important for Puralpha/PU-RNA association. Production of Puralpha at the early stage of brain development and its association with PU-RNA at this stage, when Puralpha exhibits poor binding ability to the MB1 DNA sequence, suggests that PU-RNA may function as a co-factor that negatively regulates Puralpha interaction with the MBP promoter sequence.

Animals↗
PubMed1998

Structure and function of HIV-1 and SIV Tat proteins based on carboxy-terminal truncations, chimeric Tat constructs, and NMR modeling.

To further define the structure and function of the domains in HIV-1 and SIV Tat proteins, chimeric Tat cDNA expression constructs were generated with crossover points at the carboxy-terminal end of the cysteine rich domain. The chimera containing the amino-terminal region of SIV and carboxy-terminal region of HIV exhibited activity similar to HIV-1 Tat and SIV Tat on both the HIV-1 and SIV LTRs. In contrast, the reciprocal chimera functioned poorly. As determined by the activity of carboxy-terminal truncation mutants, the region immediately downstream of the basic domain is critical for efficient transactivation by HIV-1 Tat, but not SIV Tat protein. In this report, we present a model for Tat domains based on NMR data and the known functional properties of Tat protein. According to our modeling two sites for protein : protein interactions are present in HIV-1 and SIV Tat proteins. Site I, which is presumably involved in cyclin T binding, is similar in both HIV-1 and SIV Tat proteins as well as in Tat chimeras. Site II, however appears structurally different in HIV-1 and SIV Tat models, although in both cases is comprised of amino and carboxy-terminal residues. Differences in Site II may thus account for the differential activities of HIV-1 and SIV Tat carboxy-terminal truncations. Site II in the poorly active chimera differs significantly from that found in HIV-1 and SIV Tat proteins. The two site structural model presented here may have important implications for the role of Tat in HIV pathogenesis and may provide insights for the design of Tat vaccines and targeted therapeutics.

Amino Acid Sequence↗
PubMed1995

Listeriosis in bone marrow transplant recipients: incidence, clinical features, and treatment.

Cultures of blood and/or cerebrospinal fluid from four of 1,013 bone marrow transplant recipients treated at our center between January 1972 and April 1994 were positive for Listeria monocytogenes. The overall occurrence of listeriosis was 0.39 case per 100 transplantations. Allograft recipients had received prior treatment with parenteral methylprednisolone, thus supporting an association between listeriosis and corticosteroids. Treatment with parenteral ampicillin (200 mg/[kg.d]) and gentamicin is recommended for a minimum of 3 weeks before oral therapy. Two patients with penicillin allergies in this study failed to respond to chloramphenicol-based therapeutic regimens. Recurrent meningitis occurred in two patients, and the therapeutic use of intrathecal gentamicin/vancomycin did not confer a survival advantage (i.e., the patients did not survive).

Adolescent↗
PubMed1995

Three weeks of ganciclovir for cytomegaloviraemia after allogeneic bone marrow transplantation.

Cytomegaloviraemia diagnosed by early antigen detection or conventional viral culture from blood occurred 7-71 days (median 41 days) after transplant in 25 of 38 consecutive patients undergoing bone marrow transplantation (BMT) from HLA-identical siblings for haematological malignancies where patient and/or donor were CMV-seropositive. Prophylactic ganciclovir, high-dose intravenous acyclovir or immunoglobulin were not administered. Viraemia was treated with a short 3-week course of ganciclovir (10 mg/kg x 1 week, 5 mg/kg x 2 weeks). Clearance of viraemia occurred 3-47 days (median 6 days) after starting anti-viral therapy in 20 patients (18 with ganciclovir, 2 with foscarnet), and before therapy in 3 patients. The remaining 2 patients received inadequate anti-viral therapy for various reasons and died of CMV pneumonitis. There was no clinical evidence of CMV disease in the 13 patients who did not develop viraemia. One patient treated with ganciclovir before adequate haematological recovery died of graft failure. A second episode of viraemia occurred in four patients, and a third in one. We conclude that a short 3-week course of ganciclovir is adequate in most patients developing cytomegaloviraemia after allogeneic BMT. Treatment is not necessary in all patients but some inadequately treated patients develop CMV disease. Ganciclovir is tolerated well but may cause severe myelosuppression if used prior to adequate marrow recovery.

Adolescent↗
PubMed1994

Fatal pneumococcal infections following allogeneic bone marrow transplant.

Six cases of fatal pneumococcal sepsis are described, occurring in the post-allograft setting, between 3 and 39 months after transplantation. Five of the six patients were suffering from chronic graft-versus-host disease and were receiving immunosuppressive therapy. Most were receiving prophylactic antibiotic therapy. This represents approximately 2% of the allograft population treated during the study period who survived for > 3 months after transplant. Pneumococcal sepsis is thus still a significant cause of death after allogeneic BMT and approaches to minimise its occurrence are discussed.

Acute Disease↗
PubMed1994

Unusual infections following allogeneic bone marrow transplantation for chronic lymphocytic leukemia.

Unusually severe infections phenomena were observed in three patients with chronic lymphocytic leukemia (CLL) who had undergone allogeneic bone marrow transplantation (BMT) from matched sibling donors. The first developed three episodes of cytomegaloviremia requiring anti-viral therapy; the third episode accompanied by cytomegalovirus hepatitis which required prolonged therapy with foscarnet. Another had Listeria monocytogenes meningitis which was difficult to eradicate and required prolonged maintenance antimicrobial therapy with oral trimethoprim-sulfamethoxazole and intrathecal gentamicin until death due to chronic graft-versus-host disease. The third patient had cytomegaloviremia lasting 47 days, which did not clear within 4 weeks of full-dose ganciclovir. Although the number of patients is small, in our experience the problems encountered were unusually severe compared with patients allografted for other disease. We conclude that CLL patients undergoing allogeneic BMT may be at a higher risk of infectious complications than patients allografted for other diseases, and require careful monitoring.

Adult↗
PubMed1993

The tight junction protein ZO-1 is homologous to the Drosophila discs-large tumor suppressor protein of septate junctions.

Tight junctions form an intercellular barrier between epithelial cells, serve to separate tissue compartments, and maintain cellular polarity. Paracellular sealing properties vary among cell types and are regulated by undefined mechanisms. Sequence of the full-length cDNA for human ZO-1, the first identified tight junction component, predicts a protein of 1736 aa. The N-terminal 793 aa are homologous to the product of the lethal(1)discs-large-1 (dlg) tumor suppressor gene of Drosophila, located in septate junctions, and to a 95-kDa protein located in the postsynaptic densities of rat brain, PSD-95. All three proteins contain both a src homology region 3 (SH3 domain), previously identified in membrane proteins involved in signal transduction, and a region homologous to guanylate kinase. ZO-1 contains an additional 943-aa C-terminal domain that is proline-rich (14.1%) and contains an alternatively spliced domain, whose expression was previously shown to correlate with variable properties of tight junctions. dlg mutations result in loss of apical-basolateral epithelial cell polarity and in neoplastic growth. These results suggest a protein family specialized for signal transduction on the cytoplasmic surface of intercellular junctions. These results also provide biochemical evidence for similarity between invertebrate septate and vertebrate tight junctions. The C-terminal domain of ZO-1, and its alternatively spliced region, appears to confer variable properties unique to tight junctions.

Alternative Splicing↗
PubMed1993

Alloactivated cytotoxic T cells recognize the carboxy-terminal domain of human immunodeficiency virus-1 gp120 envelope glycoprotein.

Infection with the human immunodeficiency virus (HIV) virus leads to clinical disease in humans but not in chimpanzees. Progression to disease is associated with activation of the immune system followed by loss of T helper cell function and a slow decline in CD4-positive lymphocytes. The presence of autoreactive and cytotoxic cells in humans but not chimpanzees suggests that mechanisms other than, or in addition to, direct virus-induced cell killing, are required for disease to develop. The observed changes are similar to those seen in chronic allogeneic disease. Here we show that a peptide from the carboxy terminus of gp120, predicted to have a structure similar to the major alpha-helices of major histocompatibility complex (MHC) class I and class II, acts as a cytolytic target when presented on syngeneic cells for alloactivated cytotoxic T effector cells. These data add further evidence to the hypothesis that HIV can act as an allostimulant due to its dual properties of CD4 binding and MHC mimicry. The ability to signal nonspecifically through the T cell receptor could explain the initially paradoxical responses of proliferation, anergy and apoptosis.

Amino Acid Sequence↗
PubMed1993

The surrogate light chain in B-cell development.

The proteins encoded by the VpreB and lambda 5 genes associate with each other to form a light (L) chain-like structure, the surrogate L chain. It can form Ig-like complexes with three partners-the classical heavy (H) chain, the DHJHC mu-protein, or the newly discovered p55 chain; these are expressed on the surface of pre-B cells at different stages of development. Here, Fritz Melchers and colleagues review the structures of the VpreB and lambda 5 genes in mouse and their relatives in humans, describe their pattern of expression, and speculate on their possible evolution and functions.

Amino Acid Sequence↗
PubMed1993

Phenoxyethanol is effective topical therapy of gram-negative cellulitis in neutropenic patients.

In neutropenic patients cellulitis caused by Gram-negative organisms may prove difficult to control and cause considerable tissue damage. Phenoxyethanol has activity against a range of bacteria, including Pseudomonas aeruginosa, and is absorbed by intact skin. Three severely neutropenic patients are described in whom cellulitis failed to respond to appropriate intravenous antibiotics. However the topical application of phenoxyethanol solution gave prompt local control. This cheap and nontoxic agent may give dramatic improvement in this difficult clinical situation.

Administration, Topical↗
PubMed1993

Serum titres of Pneumocystis carinii antibody in health care workers caring for patients with AIDS.

BACKGROUND: Pneumocystis carinii pneumonia was thought to occur from reactivation of latent infection, but recent studies with the polymerase chain reaction have failed to detect P carinii in normal subjects. If pneumocystis pneumonia is therefore caused by new infection the source and mode of transmission of P carinii remains unknown. METHODS: Natural exposure to P carinii was detected by measuring antibodies by indirect immunofluorescence in 24 health care workers working continuously with patients with AIDS and 24 control health care workers exclusively treating elderly patients. RESULTS: P carinii antibody titres were significantly higher in the health care workers exposed to AIDS than in the control group (median titre 1:32 v 1:16 respectively). Three control subjects had no antibodies compared with none of the subjects exposed to AIDS, and 10 of the 12 highest titres came from the exposed group. CONCLUSIONS: Raised P carinii antibody titres in health care workers caring for patients with AIDS suggest that patients infected with HIV may be a potentially infectious source of P carinii for susceptible subjects.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Localization and differential expression of two isoforms of the tight junction protein ZO-1.

ZO-1 is a peripheral membrane protein of approximately 225 kDa located on the cytoplasmic side of all tight junctions. ZO-1 cDNA sequencing disclosed the presence of a 240-bp sequence in only some of the ZO-1 cDNAs studied. This 240-bp region encoded an inframe insertion of 80 amino acids, named motif-alpha. Expression of the predicted transcripts in normal rat and human tissues and in human epithelial cell lines (Caco-2, T84, Hep G2) was shown by reverse transcription of RNA and then DNA amplification. Immunoblot analysis showed both protein isoforms were present; however, in different cell lines, their amounts differed markedly relative to each other. Immunolocalization at light and ultrastructural levels, using antibodies generated against motif-alpha or shared sequences flanking it, indicated both forms localized indistinguishably to tight junctions. These observations demonstrate the existence and variable expression of ZO-1 isoforms and raise the question whether these isoforms contribute to tight junction diversity in different epithelia.

Amino Acid Sequence↗