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Biomedical subjects

P B Johnston

Publications and source records attributed to P B Johnston.

At least 19 recordsLinked to original sources
PubMed2006

Early lymphocyte recovery after autologous stem cell transplantation predicts superior survival in mantle-cell lymphoma.

Autologous stem cell transplantation (ASCT) is an effective treatment strategy for mantle-cell lymphoma (MCL) demonstrating significantly prolonged progression-free survival (PFS) when compared to interferon-alpha maintenance therapy of patients in first remission. The study of absolute lymphocyte count at day 15 (ALC-15) after ASCT as a prognostic factor in non-Hodgkin lymphoma (NHL) included different lymphoma subtypes. The relationship of ALC-15 after ASCT in MCL has not been specifically addressed. We evaluated the impact of ALC-15 recovery on survival of MCL patients undergoing ASCT. We studied 42 consecutive MCL patients who underwent ASCT at the Mayo Clinic in Rochester from 1993 to 2005. ALC-15 threshold was set at 500 cells/microl. The median follow-up after ASCT was 25 months (range, 2-106 months). The median overall survival (OS) and PFS times were significantly better for the 24 patients who achieved an ALC-15 >or=500 cells/microl compared with 18 patients with ALC-15 <500 cells/microl (not reached vs 30 months, P<0.01 and not reached vs 16 months, P<0.0006, respectively). Multivariate analysis demonstrated ALC-15 to be an independent prognostic factor for OS and PFS. The ALC-15 >or=500 cells/microl is associated with a significantly improved clinical outcome following ASCT in MCL.

Female↗
PubMed2001

Mutations within the putative membrane-spanning domain of the simian immunodeficiency virus transmembrane glycoprotein define the minimal requirements for fusion, incorporation, and infectivity.

The membrane-spanning domain (MSD) of a number of retroviral transmembrane (TM) glycoproteins, including those from the human and simian immunodeficiency viruses (HIV and SIV), have been predicted to contain a charged arginine residue. The wild-type SIV TM glycoprotein is 354 amino acids long. The entire putative cytoplasmic domain of SIV (amino acids 193 to 354) is dispensable for virus replication in vitro, and such truncation-containing viruses are capable of reaching wild-type titers after a short delay. We show here that further truncation of eight additional amino acids to TM185 results in a protein that lacks fusogenicity but is, nevertheless, efficiently incorporated into budding virions. By analyzing a series of nonsense mutations between amino acids 193 and 185 in Env expression vectors and in the SIVmac239 proviral clone, a region of the SIV TM that contains the minimum requirement for glycoprotein-mediated cell-to-cell fusion and that for virus replication was identified. Virus entry and infectivity were evident in truncations to a minimum of 189 amino acids, whereas cell-cell fusion was observed for a protein of only 187 amino acids. Glycoprotein was efficiently incorporated into budding virions in truncations up to 185 amino acids, indicating that such proteins are membrane anchored and are transported to the cell surface. However, truncation of the TM to 180 amino acids resulted in a protein that displays a transport defect and may be retained in the endoplasmic reticulum. Based on our analyses of these mutants, an alternative model for the MSD of SIV is proposed. Our model suggests that membrane-imbedded charged residues can be neutralized by side-chain interactions with lipid polar head groups. As a consequence, the membrane-spanning region can be reduced by more than a helical turn. This new model accounts for the ability of truncations within the predicted MSD to remain membrane anchored and maintain biological activity.

Amino Acid Motifs↗
PubMed1995

Transport of a lysosomally targeted Rous sarcoma virus envelope glycoprotein involves transient expression on the cell surface.

The details of intracellular transport pathways for glycosylated proteins remain incompletely described. We previously described a mutant Rous sarcoma virus envelope glycoprotein (gp), mu 26, with an altered membrane-spanning domain that was targeted to lysosomes after traversing the trans-Golgi. This mutant protein was not detectable on the cell surface by immunofluorescence, but its pathway for degradation remained unclear. To investigate this we have employed a second env mutation, S19, that results in a protein which is defective for normal cleavage/activation by intracellular enzymes, but remains susceptible to cleavage by extracellular proteases. Cleavage/activation of the double mutant by trypsin, which could only occur if it was exposed on the cell surface, was observed, indicating that the plasma membrane is an intermediate destination in the transport of this mutant protein. To substantiate these results, cells expressing the mu 26 glycoprotein were incubated with an antibody specific for the native protein in the presence of chloroquine. The specific accumulation of this antibody/gp complex in vesicles, as detected by internal immunofluorescence, confirmed the trypsin cleavage results. We conclude that this rapidly degraded mutant protein is transported from the trans-Golgi to the cell surface, where it is only transiently exposed, and then rapidly endocytosed and lysosomally degraded. The relevance of these results to the targeting of lysosomal proteins is discussed.

Amino Acid Sequence↗
PubMed1995

Treatment and long-term follow up of a capillary angioma of the optic disc.

This case report describes the treatment of a capillary angioma involving the temporal aspect of the optic disc by photocoagulation therapy. It chronicles the effect of creating a retinal-choroidal adhesion at the temporal margin of the lesion in reducing exudation from the angioma spreading to involve the macula. The patient in question has been followed for sixteen years and vision in this eye has been maintained at 6/6 following the course of therapy described. Our experience suggests that direct laser treatment to capillary angiomas of the optic disc combined with photocoagulation barrier protection of the macula is beneficial and should be considered early when the lesion is relatively small.

Adult↗
PubMed1994

Is genetic predisposition an important risk factor in age-related macular degeneration?

Age-related macular degeneration (ARMD) is the most common cause of visual morbidity in the aged in the Western world. The aetiology of ARMD is unknown. Although clinicians have noted that ARMD demonstrates a familial tendency, the question regarding the role of hereditary factors in ARMD remains unanswered. The aims of this study were to assess the level of genetic input into ARMD and to assess the mode of inheritance of the disease. Fifty affected patients and 50 age- and sex-matched controls and their immediate families were invited to take part in the study. Thirty-six patients, controls and their families were studied. Eighty-one siblings of affected patients and 78 control siblings were available. Twenty of the 81 affected siblings were found to suffer from ARMD. In contrast only 1 of 78 control siblings had ARMD. This was statistically significant. The results confirm that hereditary factors are important in the aetiology of ARMD.

Disease Susceptibility↗
PubMed1993

Peripapillary subretinal neovascular membranes: the natural history.

We studied the natural course of peripapillary subretinal neovascular membranes in 20 eyes. The membranes were either idiopathic in nature or associated with underlying disease. We found that the visual prognosis was related to the behaviour of the membrane and to the patient's age. Patients under the age of 40 years had unilateral disease and a more favourable visual prognosis. Older patients had a uniformly poor visual prognosis and a high incidence of bilateral disease. Fifty-four per cent of patients over 45 years and 62% over 70 years of age had bilateral membranes. In those over the age of 70 years, 75% of untreated eyes lost vision to a level of 3/60 or less in both eyes. The probability of the second eye becoming involved in the older group of patients was 62%. The period of time elapsing between involvement of the first and second eye varied between simultaneous occurrence and a delay of 7 years.

Adult↗
PubMed1993

Ocular siderosis.

The authors report their experience in the management of 8 patients with ocular siderosis due to a retained intraocular foreign body (IOFB). All patients were male, aged between 19 and 39 years. Seven had a definite history of trauma; 3 had presented at the time of injury to a casualty department, and the diagnosis had been missed. The interval between injury and diagnosis ranged from 2 to 24 months. IOFB removal was performed in 7 patients: through a sclerotomy and magnet or foreign body forceps in 4 eyes and via a pars plana vitrectomy and intraocular foreign body forceps in 3 eyes. Cataract extraction was performed in 4 patients. Histological examination of specimens removed at the time of surgery showed iron deposition in the conjunctiva, anterior lens capsule and pars plana. Transmission electron microscope X-ray microanalysis showed that iron was contained in siderosomes, intracytoplasmic membrane-bound dense bodies. Final visual acuity was 6/12 or better in 6 patients and reduced to light perception in the remaining 2 due to proliferative vitreoretinopathy.

Adult↗
PubMed1993

Truncations of the simian immunodeficiency virus transmembrane protein confer expanded virus host range by removing a block to virus entry into cells.

We have investigated how truncation of the cytoplasmic domain of the transmembrane (TM) glycoprotein of simian immunodeficiency virus (SIV) modulates the host range of this virus. Termination codons were introduced into the env gene of SIVmac239 which resulted in the truncation of the transmembrane protein from a wild-type 354 amino acids (TM354) to 207 (TM207) and 193 (TM193) amino acids. Expression of the wild-type and mutant env genes from a simian virus 40-based vector resulted in normal biosynthesis and processing of the glycoproteins to gp130 and gp41 or the truncated TM proteins (gp28 and gp27). When expressed on the surface of COS-1 cells, all three glycoproteins mediated fusion of both CEMX174 and HUT78 cells. Virions containing the wild-type and mutant glycoproteins were capable of efficient replication in macaque peripheral blood lymphocytes and CEMX174 cells; in contrast, only virions that contained TM207 were capable of rapid infection of HUT78 cells. Both truncated glycoproteins were capable of efficiently mediating infection of both CEMX174 and HUT78 cells by an env-deficient human immunodeficiency virus. The wild-type SIV glycoprotein, however, was unable to mediate human immunodeficiency virus infection of HUT78 cells when assayed with this system. An analysis of the protein composition of SIV released from infected CEMX174 cells showed that the mutant virions contained significantly higher levels of glycoprotein compared with the wild type. These results demonstrate that truncation of the SIV cytoplasmic domain removes a block at the level of glycoprotein-mediated virus entry into HUT78 cells and points to a role for glycoprotein density in determining virus tropism.

Animals↗
PubMed1993

Expression and characterization of glycophospholipid-anchored human immunodeficiency virus type 1 envelope glycoproteins.

Four chimeric human immunodeficiency virus type 1 (HIV-1) env genes were constructed which encoded the extracellular domain of either the wild-type or a cleavage-defective HIV-1 envelope glycoprotein (gp160) fused at one of two different positions in env to a C-terminal glycosyl-phosphatidylinositol (GPI) attachment signal from the mouse Thy-1.1 glycoprotein. All four of the constructs encoded glycoproteins that were efficiently expressed when Rev was supplied in trans, and the two cleavable forms were processed normally to gp120 and a chimeric "gp41." The chimeric glycoproteins, in contrast to the wild-type glycoprotein, could be cleaved from the surface of transfected cells by treatment with phosphatidylinositol-specific phospholipase C, indicating that they were anchored in the plasma membrane by a GPI moiety. These GPI-anchored glycoproteins were transported intracellularly at a rate only slightly lower than that of the full-length HIV-1 glycoprotein and were present on the cell surface in equivalent amounts. Nevertheless, all four glycoproteins were defective in mediating both cell-cell and virus-cell fusion as determined by syncytium formation in COS-1-HeLa-T4 cell mixtures and trans complementation of an env-defective HIV-1 genome.

Amino Acid Sequence↗