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P Silver

Publications and source records attributed to P Silver.

At least 19 recordsLinked to original sources
PubMed1992

A mutant nuclear protein with similarity to RNA binding proteins interferes with nuclear import in yeast.

We have isolated mutants of the yeast Saccharomyces cerevisiae that are defective in localization of nuclear proteins. Chimeric proteins containing the nuclear localization sequence from SV40 large T-antigen fused to the N-terminus of the mitochondrial F1 beta-ATPase are localized to the nucleus. Npl (nuclear protein localization) mutants were isolated by their ability to grow on glycerol as a consequence of no longer exclusively targeting SV40-F1 beta-ATPase to the nucleus. All mutants with defects in localization of nucleolar proteins and histones are temperature sensitive for growth at 36 degrees C. Seven alleles of NPL3 and single alleles of several additional genes were isolated. NPL3 mutants were studied in detail. NPL3 encodes a nuclear protein with an RNA recognition motif and similarities to a family of proteins involved in RNA metabolism. Our genetic analysis indicates that NPL3 is essential for normal cell growth; cells lacking NPL3 are temperature sensitive for growth but do not exhibit a defect in localization of nuclear proteins. Taken together, these results indicate that the mutant forms of Npl3 protein isolated by this procedure are interfering with nuclear protein uptake in a general manner.

Amino Acid Sequence↗
PubMed1991

A split zinc-finger protein is required for normal yeast growth.

We have identified a gene that, when present in multiple copies, partially inhibits nuclear protein localization in Saccharomyces cerevisiae. This gene encodes a protein that is a unique member of the Cys2His2 zinc-finger family of DNA-binding proteins. It is designated SFP1 for split finger protein because its two zinc-finger domains are separated from one another by 40 amino acids (aa) as opposed to the usual spacing of 7 or 8 aa for Cys2His2 proteins. Disruption of the SFP1 gene results in slow cell growth, with cells having multiple, nucleated buds.

Amino Acid Sequence↗
PubMed1991

External irradiation followed by an interstitial high activity iodine-125 implant "boost" in the initial treatment of malignant gliomas: NCOG study 6G-82-2.

Between January 1982 and January 1990, 107 patients with unifocal, circumscribed malignant gliomas participated in a non-randomized trial testing brachytherapy in their initial treatment. Focal external irradiation (6000 cGy) was combined with an implant of high-activity iodine-125 (5000-6000 cGy) and six courses of procarbazine, lomustine, and vincristine. Of the 101 evaluable patients, 63 received implants. Of these, 29 had non-glioblastoma anaplastic gliomas, and 34 had glioblastoma multiforme. The other 38 did not receive implants, in most cases because radiation therapy failed to reduce the size of the tumor. The median survival was 165 weeks for all evaluable patients with non-glioblastoma anaplastic gliomas, 157 weeks for those with implants, 67 weeks for all evaluable glioblastoma patients, and 88 weeks for those with implants. Of the glioblastoma patients with implants, nine were alive after 2 years, and three were alive after 3 years. In each of the groups, nearly half the patients underwent reoperation for clinical deterioration, increasing steroid dependency, and increasing mass effect at the implantation site after 46.1 weeks (median) for glioblastoma multiforme and 41.3 weeks for non-glioblastoma patients. Karnofsky Performance Scores showed only a small decline in performance after brachytherapy. Patients receiving implants for non-glioblastoma anaplastic gliomas had a mean Karnofsky Performance Score of 91% (range 90-100%) after 1 month and 78% (range 60-100%) 30 months after brachytherapy. Those treated for glioblastoma multiforme had a mean Karnofsky Performance Score of 86% (range 60-100%) at 1 month and 75% (range 60-100%) at 24 months. The quality of life of treated patients appears to be satisfactory. On the basis of comparisons with previous studies, we conclude that a brachytherapy "boost" after external irradiation may be valuable for some patients with glioblastoma multiforme but not for those with non-glioblastoma anaplastic gliomas.

Adult↗
PubMed1991

A yeast protein that binds nuclear localization signals: purification localization, and antibody inhibition of binding activity.

Short stretches of amino acids, termed nuclear localization sequences (NLS), can mediate assembly of proteins into the nucleus. Proteins from the yeast, Saccharomyces cerevisiae, have been identified that specifically recognize nuclear localization peptides (Silver, P., I. Sadler, and M. A. Osborne. 1989. J. Cell Biol. 109:983-989). We now further define the role of one of these NLS-binding proteins in nuclear protein localization. The NLS-binding protein of 70-kD molecular mass can be purified from salt extracts of nuclei. Antibodies raised against the NLS-binding protein localized the protein mainly to the nucleus with minor amounts in the cytoplasm. These antibodies also inhibited the association of NLS-protein conjugates with nuclei. Incubation of nuclei with proteases coupled to agarose removed NLS-binding protein activity. Extracts enriched for NLS-binding proteins can be added back to salt or protease-treated nuclei to restore NLS-binding activity. These results suggest that the first step of nuclear protein import can be reconstituted in vitro.

Amino Acid Sequence↗
PubMed1991

Gemistocytic astrocytomas: a reappraisal.

Although gemistocytic astrocytomas are considered slow-growing astrocytomas, they often behave aggressively. To clarify the biological and clinical behavior of these rare tumors, the authors retrospectively identified 59 patients with gemistocytic astrocytoma whose tumors were diagnosed and treated between June, 1976, and July, 1989. Three patients who were lost to follow-up review were excluded, as were two whose original slides could not be obtained and three whose tumors were diagnosed at recurrence or at autopsy. The pathological material of the remaining 51 patients was reviewed using two sets of histological criteria. Thirteen patients (Group A) had "pure" gemistocytic astrocytoma, defined as a glial tumor with more than 60% gemistocytes/high-power field and a background of fibrillary astrocytes. Fifteen patients (Group B) had "mixed" gemistocytic astrocytoma, defined as a glial tumor with 20% to 60% gemistocytes/high-power field and a background of anaplastic astrocytes. Twenty-three tumors did not meet these criteria and were excluded from analysis. The median age of the patients was 48.5 years in Group A and 38.3 years in Group B (p less than 0.05). In both groups, the median Karnofsky Performance Scale score was greater than 90%. All patients underwent surgical procedures (four total and 19 partial resections, and five biopsies) and postoperative radiation therapy. The majority also had interstitial brachytherapy, chemotherapy, or both. Ten patients had one reoperation for tumor recurrence and one had two reoperations; other treatments for recurrence included brachytherapy, chemotherapy, and repeat irradiation. All four patients who originally underwent gross total resection are still alive; all five who had a biopsy have died. There was no significant difference in median survival times between groups: 136.5 weeks in Group A (range 10 to 310+ weeks) and 135.6 weeks in Group B (range 31 to 460+ weeks). Analysis of all 28 patients showed a better prognosis for patients less than 50 years of age (185 vs. 36 weeks survival time; p less than 0.001), patients with preoperative symptoms lasting for more than 6 months (228.1 vs. 110.2 weeks survival time; p less than 0.05), and patients with seizures as the first symptom (185.7 vs. 80 weeks survival time; p less than 0.01). Survival time did not correlate with the presence of perivascular lymphocytic infiltration. The authors conclude that the presence of at least 20% gemistocytes in a glial neoplasm is a poor prognostic sign, irrespective of the pathological background. It is proposed that gemistocytic astrocytomas be classified with anaplastic astrocytomas and treated accordingly.

Adult↗
PubMed1991

Management of chiasmal and hypothalamic gliomas of infancy and childhood with chemotherapy.

Between March, 1983, and February, 1989, 19 infants or children with chiasmal/hypothalamic gliomas were treated with chemotherapy after either surgical or radiological diagnosis. The patients ranged in age from 15 weeks to 15.6 years (median 3.2 years) at the start of therapy. Twelve patients were treated immediately after diagnosis because of progressive symptoms, and seven received chemotherapy after either radiographic progression or clinical deterioration, including progressive visual loss or intracranial hypertension. Based on biopsy results, seven of these tumors were classified as juvenile pilocytic astrocytomas, two as astrocytomas, two as highly anaplastic astrocytomas, and one as a subependymal giant-cell astrocytoma. There was associated neurofibromatosis in four patients. The two initial patients were treated with either actinomycin D and vincristine or 5-fluorouracil, hydroxyurea, and 6-thioguanine. The remaining patients received nitrosourea-based therapy; 15 evaluable patients were treated with a five-drug regimen that included 6-thioguanine, procarbazine, dibromodulcitol, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), and vincristine and one received 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and 5-fluorouracil. Fifteen of the 18 evaluable patients initially managed with chemotherapy either responded to therapy or their condition stabilized. Median time to tumor progression has not been reached at a median follow-up period of 79 weeks (range 6.6 to 303 weeks), and no tumor-related death has occurred with a median follow-up period of 79 weeks (range 18 to 322 weeks) from the initiation of therapy. The four patients who failed therapy or whose disease progressed after chemotherapy were treated satisfactorily with radiation therapy. Initial improvement or stabilization of visual function was obtained in 16 patients. Endocrine function remained stable in all patients during treatment, although three patients required pharmacological treatment for endocrinopathy that was present at diagnosis. These preliminary results suggest that nitrosourea-based cytotoxic regimens are useful for the initial treatment of children with chiasmal/hypothalamic gliomas, and allow potentially harmful radiation therapy to be deferred until progression of disease.

Adolescent↗
PubMed1990

Poorly differentiated gliomas of the cerebellum. A study of 18 patients.

Eighteen patients with poorly differentiated gliomas of the cerebellum were treated by the University of California San Francisco Neuro-Oncology Service between January 1977 and January 1987. Within this group pathologic diagnosis included five glioblastoma multiforme (28%), nine anaplastic astrocytomas (50%), and four mixed malignant gliomas (22%). The group included 13 male and five female patients with a median age at diagnosis of 23 years (range, 4-46 years). All patients underwent surgical resection, 16 of 18 received radiation therapy (12 limited-field irradiation and four whole-brain with or without a posterior fossa boost), and 16 of 18 received chemotherapy. Overall median survival was 31.5 months (range, 5-366 months). Ten patients (55%) died of recurrent disease with a median survival of 32 months (range, 5-128 months), two of whom manifested metastatic disease within the central nervous system (one parietal lobe and one cervical cord). Of the two extracerebellar metastatic recurrences, one patient failed at the junction of whole-brain irradiation and the cervical cord and one patient failed after inadequate posterior fossa irradiation. Eight patients (45%) are alive with a median follow-up of 27.5 months (range, 14-366 months). In this series recurrences of primary cerebellar anaplastic gliomas were locoregional failures. As a consequence, the authors suggest high-dose limited-field irradiation directed at the primary tumor as in their current strategy utilized for supratentorial gliomas.

Adolescent↗
PubMed1990

Fluphenazine dose, clinical response, and extrapyramidal symptoms during acute treatment.

Fifty-three patients with acute exacerbations of Research Diagnostic Criteria schizophrenic, schizoaffective (mainly schizophrenic), and other nonaffective psychoses completed 24 or 28 days of treatment with randomized, fixed, double-blind doses of 10, 20, or 30 mg of oral fluphenazine hydrochloride daily. In the sample as a whole, improvement was not predicted by dose but was negatively related to duration of illness and of lifetime hospitalization, and to the presence of akathisia during the study (which was unrelated to chronicity). But among patients showing 40% or greater improvement in positive symptoms, percent improvement was predicted by dose and dose per kilogram of body weight; this was not the case for negative symptoms. Severity of acute extrapyramidal symptoms (excluding acute dystonia, dyskinesia, and akathisia) was significantly correlated with dosage per kilogram. Doses greater than 0.2 mg/kg per day were associated with greater clinical improvement but also with a high incidence of extrapyramidal symptoms; doses over 0.3 mg/kg per day were associated with more severe extrapyramidal symptoms. These preliminary results suggest that there is a linear relationship between fluphenazine dosage and acute outcome, and that this relationship is observed in patients whose conditions improve to a criterion level. It is suggested that the nonresponder group may include many patients in whom dose is not relevant because they are unable (for a variety of reasons) to respond to the study treatment conditions; excluding them from analysis may allow a significant dose-response relationship to be observed. Akathisia deserves further study as a possible predictor of nonresponse.

Acute Disease↗
PubMed1990

Superiority of post-radiotherapy adjuvant chemotherapy with CCNU, procarbazine, and vincristine (PCV) over BCNU for anaplastic gliomas: NCOG 6G61 final report.

Data from Northern California Oncology Group protocol 6G61, which was closed in February 1983, were reanalyzed in December 1988. The protocol called for a randomized trial that compared the effects of following 60 Gy radiation/oral hydroxyurea treatment with either carmustine (BCNU) or the combination of procarbazine, lomustine (CCNU), and vincristine (PCV) for two histologic strata: glioblastoma multiforme and other anaplastic gliomas. PCV produced longer survival and time to tumor progression than BCNU for both histologic groups, although the difference was statistically significant only for the anaplastic gliomas. With PCV treatment, time to progression and survival doubled for anaplastic glioma patients in the 50th and 25th percentiles.

Adult↗
PubMed1989

Reevaluation of procarbazine for the treatment of recurrent malignant central nervous system tumors.

Ninety-nine patients with primary recurrent malignant tumors of the central nervous system were treated with procarbazine as a single agent. Procarbazine was not given as a specified protocol, but for patients who were ineligible or refused other protocols. All patients had been treated previously with radiotherapy and 96 patients had also received previous chemotherapy. Twenty-five patients were treated at the first progression of their tumor, 47 were treated at the second progression, and 27 were treated at the third progression of their tumor. For the aggregate, the response plus stabilization rate was 27% for glioblastoma multiforme with median time to tumor progression of 30 weeks, and 28% for other anaplastic gliomas with a median time to tumor progression of 49 weeks. With respect to the percent of patients who responded or stabilized to treatment, these results are inferior to those reported previously for patients treated with procarbazine at recurrence. With respect to duration of response and stabilization, the data are comparable.

Adolescent↗
PubMed1989

Yeast proteins that recognize nuclear localization sequences.

A variety of peptides can mediate the localization of proteins to the nucleus. We have identified yeast proteins of 70 and 59 kD that bind to nuclear localization peptides of SV-40 T antigen, Xenopus nucleoplasmin, and the yeast proteins Ga14 and histone H2B. These proteins are assayed by the binding of peptide-albumin conjugates to proteins immobilized on nitrocellulose filters. These binding proteins fractionate with nuclei and are extractable with salt but not detergent. Radiolabeled peptide-albumin conjugates also bind to isolated nuclei; the binding is saturable and can be extracted with salt. Different nuclear localization peptides compete with each other, implying that a single class of proteins is responsible for their recognition. The 70- and 59-kD proteins have the properties expected for a receptor that would act to direct proteins to the nucleus.

Amino Acid Sequence↗
PubMed1989

A yeast gene important for protein assembly into the endoplasmic reticulum and the nucleus has homology to DnaJ, an Escherichia coli heat shock protein.

When nuclear localization sequences (termed NLS) are placed at the N terminus of cytochrome c1, a mitochondrial inner membrane protein, the resulting hybrid proteins do not assemble into mitochondria when synthesized in the yeast Saccharomyces cerevisiae. Cells lacking mitochondrial cytochrome c1, but expressing the hybrid NLS-cytochrome c1 proteins, are unable to grow on glycerol since the hybrid proteins are associated primarily with the nucleus. A similar hybrid protein with a mutant NLS is transported to and assembled into the mitochondria. To identify proteins that might be involved in recognition of nuclear localization signals, we isolated conditional-lethal mutants (npl, for nuclear protein localization) that missorted NLS-cytochrome c1 to the mitochondria, allowing growth on glycerol. The gene corresponding to one complementation group (NPL1) encodes a protein with homology to DnaJ, an Escherichia coli heat shock protein. npl1-1 is allelic to sec63, a gene that affects transit of nascent secretory proteins across the endoplasmic reticulum. Rothblatt, J. A., R. J. Deshaies, S. L. Sanders, G. Daum, and R. Schekman. 1989. J. Cell Biol. 109:2641-2652. The npl1 mutants reported here also weakly affect translocation of preprocarboxypeptidaseY across the ER membrane. A normally nuclear hybrid protein containing a NLS fused to invertase and a nucleolar protein are not localized to the nucleus in npl1/sec63 cells at the nonpermissive temperature. Thus, NPL1/SEC63 may act at a very early common step in localization of proteins to the nucleus and the ER. Alternatively, by affecting ER and nuclear envelope assembly, npl1 may indirectly alter assembly of proteins into the nucleus.

Amino Acid Sequence↗
PubMed1989

Context affects nuclear protein localization in Saccharomyces cerevisiae.

Proteins destined for the nucleus contain nuclear localization sequences, short stretches of amino acids responsible for targeting them to the nucleus. We show that the first 29 amino acids of GAL4, a yeast DNA-binding protein, function efficiently as a nuclear localization sequence when fused to normally cytoplasmic invertase, but not when fused to Escherichia coli beta-galactosidase. Moreover, the nuclear localization sequence from simian virus 40 T antigen functions better when fused to invertase than when fused to beta-galactosidase. A single amino acid change in the T-antigen nuclear localization sequence inhibits the nuclear localization of simian virus 40-invertase and simian virus 40-beta-galactosidase in Saccharomyces cerevisiae. From these results, we conclude that the relative ability of a nuclear localization sequence to act depends on the protein to which it is linked.

Amino Acid Sequence↗
PubMed1989

Treatment of recurrent gliomas with 1,3-bis(2-chloroethyl)-1-nitrosourea and alpha-difluoromethylornithine.

Thirty-eight patients with primary recurrent anaplastic gliomas and glioblastomas, were treated with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and the polyamine inhibitor alpha-difluoromethylornithine (DFMO). There were 5 brain stem, 1 cerebellar, and 32 supratentorial glioma tumors. All had been treated with surgery (except in the case of 4 brain stem tumors for which biopsies were not obtained) and radiotherapy. Eight patients had received prior chemotherapy. Of the 21 patients with evaluable supratentorial anaplastic gliomas, 2 (9.5%) had a partial response and 10 (47.6%) had stable disease. The median time to tumor progression for the anaplastic gliomas has not been attained yet. However, median survival for these 12 patients was 119 weeks measured from the initiation of chemotherapy. Median survival for the entire anaplastic glioma group of 21 was 56 weeks. Minimal activity was seen against glioblastoma multiforme. The median time to tumor progression was 8 weeks with median survival of 21 weeks. Of the 5 patients with brain stem tumors, 3 are alive with stable disease at 77, 93, and 220 weeks. The combination was well tolerated with dose-limiting toxicity being myelosuppression and hearing loss. Further trials are warranted to compare the combination of BCNU and DFMO against BCNU alone in a prospective randomized trial.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1989

Nuclear protein transport.

The nucleus, like all organelles, is composed of a unique set of proteins. This article discusses the possible mechanisms for localization of only certain proteins to the nucleus, transport of proteins across the nuclear envelope, and retention of proteins in the nuclear interior. In addition, nuclear protein transport is compared with transport of proteins into the endoplasmic reticulum and the mitochondria.

Amino Acid Sequence↗
PubMed1979

Histidyl and tyrosyl residue ionization studies of subtilisin Novo.

The low field portion of the 360 MHz 1H nuclear magnetic resonance spectrum of phenylmethanesulfonyl-subtilisin Novo (EC 3.4.21.14) has been studied as a function of pH. Analysis of the pH-induced chemical shift changes occurring between 6 to 7 ppm revealed five classes of ionizable residues with pK values (uncorrected) of 10.3, 10.7, 10.7, 10.8, and 11.0. With a single exception the titration curves can be fit by assuming a simple proton ionization equilibrium. Four classes of low intensity broad resonances, assigned to the histidyl residues, are observed between 8 and 9 ppm. Uncorrected pK values of 5.4, 5.7, 6.0, and 6.4 were determined for the residues comprising each of these classes. The spectral data are consistent with protonation of one or more histidyl residues upon acid induced denaturation of the protein. These results are compared with those of analogues studies performed by the use of other techniques.

Chemical Phenomena↗