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Biomedical subjects

T R Jackson

Publications and source records attributed to T R Jackson.

At least 19 recordsLinked to original sources
PubMed2005

Centaurin beta4 in cancer.

Centaurin beta4 proteins are products of the DDEF1 (development and differentiation-enhancing factor 1) locus on human chromosome 8q24.1-24.2. Recent reports have indicated that this region and its products are amplified during development of several human cancers. Centaurins are GAPs (GTPase-activating proteins) that, together with GEFs (guanine nucleotide-exchange factors), regulate cyclic activation of Arfs (ADP-ribosylation factors), members of the Ras GTPase superfamily. Centaurin beta4 proteins associate with a variety of cellular signalling components implicated in control of growth, survival and movement and may act to direct assembly and/or disassembly of molecular complexes in concert with Arf, lipid and protein phosphorylation signalling pathways.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Casein kinase I associates with members of the centaurin-alpha family of phosphatidylinositol 3,4,5-trisphosphate-binding proteins.

Mammalian casein kinases I (CKI) belong to a family of serine/threonine protein kinases involved in diverse cellular processes including cell cycle progression, membrane trafficking, circadian rhythms, and Wnt signaling. Here we show that CKIalpha co-purifies with centaurin-alpha(1) in brain and that they interact in vitro and form a complex in cells. In addition, we show that the association is direct and occurs through the kinase domain of CKI within a loop comprising residues 217-233. These residues are well conserved in all members of the CKI family, and we show that centaurin-alpha(1) associates in vitro with all mammalian CKI isoforms. To date, CKIalpha represents the first protein partner identified for centaurin-alpha(1). However, our data suggest that centaurin-alpha(1) is not a substrate for CKIalpha and has no effect on CKIalpha activity. Centaurin-alpha(1) has been identified as a phosphatidylinositol 3,4,5-trisphosphate-binding protein. Centaurin-alpha(1) contains a cysteine-rich domain that is shared by members of a newly identified family of ADP-ribosylation factor guanosine trisphosphatase-activating proteins. These proteins are involved in membrane trafficking and actin cytoskeleton rearrangement, thus supporting a role for CKIalpha in these biological events.

Actins↗
PubMed2001

Cerebellar liponeurocytoma. Case report and review of the literature.

Cerebellar liponeurocytoma is a rare tumor of the posterior fossa that has many morphological similarities to medulloblastoma and neurocytoma. Recently the World Health Organization working group for classification of central nervous system neoplasms adopted the term "cerebellar liponeurocytoma" to provide a unified nomenclature for a tumor variously labeled in the literature as lipomatous medulloblastoma, lipidized medulloblastoma, medullocytoma. neurolipocytoma, lipomatous glioneurocytoma, and lipidized mature neuroectodermal tumor of the cerebellum. The rarity of this tumor and paucity of pertinent information regarding its biological potential and natural history have resulted in the application of various treatment modalities. It is suggested in the available literature that these lesions have a much more favorable prognosis than typical medulloblastomas, and that adjuvant therapy for liponeurocytoma need not be as extensive as that administered for medulloblastomas.

Aged↗
PubMed2000

ACAPs are arf6 GTPase-activating proteins that function in the cell periphery.

The GTP-binding protein ADP-ribosylation factor 6 (Arf6) regulates endosomal membrane trafficking and the actin cytoskeleton in the cell periphery. GTPase-activating proteins (GAPs) are critical regulators of Arf function, controlling the return of Arf to the inactive GDP-bound state. Here, we report the identification and characterization of two Arf6 GAPs, ACAP1 and ACAP2. Together with two previously described Arf GAPs, ASAP1 and PAP, they can be grouped into a protein family defined by several common structural motifs including coiled coil, pleckstrin homology, Arf GAP, and three complete ankyrin-repeat domains. All contain phosphoinositide-dependent GAP activity. ACAP1 and ACAP2 are widely expressed and occur together in the various cultured cell lines we examined. Similar to ASAP1, ACAP1 and ACAP2 were recruited to and, when overexpressed, inhibited the formation of platelet-derived growth factor (PDGF)-induced dorsal membrane ruffles in NIH 3T3 fibroblasts. However, in contrast with ASAP1, ACAP1 and ACAP2 functioned as Arf6 GAPs. In vitro, ACAP1 and ACAP2 preferred Arf6 as a substrate, rather than Arf1 and Arf5, more so than did ASAP1. In HeLa cells, overexpression of either ACAP blocked the formation of Arf6-dependent protrusions. In addition, ACAP1 and ACAP2 were recruited to peripheral, tubular membranes, where activation of Arf6 occurs to allow membrane recycling back to the plasma membrane. ASAP1 did not inhibit Arf6-dependent protrusions and was not recruited by Arf6 to tubular membranes. The additional effects of ASAP1 on PDGF-induced ruffling in fibroblasts suggest that multiple Arf GAPs function coordinately in the cell periphery.

3T3 Cells↗
PubMed2000

Phosphoinositide-dependent activation of the ADP-ribosylation factor GTPase-activating protein ASAP1. Evidence for the pleckstrin homology domain functioning as an allosteric site.

The ADP-ribosylation factor (Arf) family of GTP-binding proteins are regulators of membrane traffic and the actin cytoskeleton. Both negative and positive regulators of Arf, the centaurin beta family of Arf GTPase-activating proteins (GAPs) and Arf guanine nucleotide exchange factors, contain pleckstrin homology (PH) domains and are activated by phosphoinositides. To understand how the activities are coordinated, we have examined the role of phosphoinositide binding for Arf GAP function using ASAP1/centaurin beta4 as a model. In contrast to Arf exchange factors, phosphatidylinositol 4, 5-bisphosphate (PtdIns-4,5-P(2)) specifically activated Arf GAP. D3 phosphorylated phosphoinositides were less effective. Activation involved PtdIns-4,5-P(2) binding to the PH domain; however, in contrast to the Arf exchange factors and contrary to predictions based on the current paradigm for PH domains as independently functioning recruitment signals, we found the following: (i) the PH domain was dispensable for targeting to PDGF-induced ruffles; (ii) activation and recruitment could be uncoupled; (iii) the PH domain was necessary for activity even in the absence of phospholipids; and (iv) the Arf GAP domain influenced localization and lipid binding of the PH domain. Furthermore, PtdIns-4,5-P(2) binding to the PH domain caused a conformational change in the Arf GAP domain detected by limited proteolysis. Thus, these data demonstrate that PH domains can function as allosteric sites. In addition, differences from the published properties of the Arf exchange factors suggest a model in which feedforward and feedback loops involving lipid metabolites coordinate GTP binding and hydrolysis by Arf.

ADP-Ribosylation Factors↗
PubMed2000

Cytohesins and centaurins: mediators of PI 3-kinase-regulated Arf signaling.

Receptor-activated phosphoinositide (PI) 3-kinases produce PtdIns(3, 4,5)P(3) and its metabolite PtdIns(3,4)P(2) that function as second messengers in membrane recruitment and activation of target proteins. The cytohesin and centaurin protein families are potential targets for PtdIns(3,4,5)P(3) that also regulate and interact with Arf GTPases. Consequently, these families are poised to transduce PI 3-kinase activation into coordinated control of Arf-dependent pathways. Proposed downstream events in PI 3-kinase-regulated Arf cascades include modulation of vesicular trafficking and the actin cytoskeleton.

ADP-Ribosylation Factor 1↗
PubMed1999

Identification of centaurin-alpha1 as a potential in vivo phosphatidylinositol 3,4,5-trisphosphate-binding protein that is functionally homologous to the yeast ADP-ribosylation factor (ARF) GTPase-activating protein, Gcs1.

Centaurin-alpha is a 46 kDa in vitro binding protein for the lipid second messenger PtdIns(3,4,5)P3. In this report we have addressed whether centaurin-alpha1, a human homologue of centaurin-alpha, binds PtdIns(3,4,5)P3 in vivo and furthermore, identified a potential physiological function for centaurin-alpha1. Using confocal microscopy of live PC12 cells, transiently transfected with a chimera of green fluorescent protein (GFP) fused to the N-terminus of centaurin-alpha1 (GFP-centaurin-alpha1), we demonstrated the rapid plasma membrane recruitment of cytosolic GFP-centaurin-alpha1 following stimulation with either nerve growth factor or epidermal growth factor. This recruitment was dependent on the centaurin-alpha1 pleckstrin homology domains and was blocked by the PtdIns(4,5)P2 3-kinase (PI 3-kinase) inhibitors wortmannin (100 nM) and LY294002 (50 microM), and also by co-expression with a dominant negative p85. Functionally, we demonstrated that centaurin-alpha1 could complement a yeast strain deficient in the ADP-ribosylation factor (ARF) GTPase-activating protein Gcs1; a complementation that was blocked by mutagenesis of conserved cysteine residues within the ARF GTPase-activating protein analogous domain of centaurin-alpha1. Taken together, our data demonstrated that centaurin-alpha1 could potentially function as an ARF GTPase-activating protein that, on agonist stimulation, was recruited to the plasma membrane possibly through an ability to interact with PtdIns(3,4,5)P3.

ADP-Ribosylation Factors↗
PubMed1999

GCS1, an Arf guanosine triphosphatase-activating protein in Saccharomyces cerevisiae, is required for normal actin cytoskeletal organization in vivo and stimulates actin polymerization in vitro.

Recent cloning of a rat brain phosphatidylinositol 3,4, 5-trisphosphate binding protein, centaurin alpha, identified a novel gene family based on homology to an amino-terminal zinc-binding domain. In Saccharomyces cerevisiae, the protein with the highest homology to centaurin alpha is Gcs1p, the product of the GCS1 gene. GCS1 was originally identified as a gene conditionally required for the reentry of cells into the cell cycle after stationary phase growth. Gcs1p was previously characterized as a guanosine triphosphatase-activating protein for the small guanosine triphosphatase Arf1, and gcs1 mutants displayed vesicle-trafficking defects. Here, we have shown that similar to centaurin alpha, recombinant Gcs1p bound phosphoinositide-based affinity resins with high affinity and specificity. A novel GCS1 disruption strain (gcs1Delta) exhibited morphological defects, as well as mislocalization of cortical actin patches. gcs1Delta was hypersensitive to the actin monomer-sequestering drug, latrunculin-B. Synthetic lethality was observed between null alleles of GCS1 and SLA2, the gene encoding a protein involved in stabilization of the actin cytoskeleton. In addition, synthetic growth defects were observed between null alleles of GCS1 and SAC6, the gene encoding the yeast fimbrin homologue. Recombinant Gcs1p bound to actin filaments, stimulated actin polymerization, and inhibited actin depolymerization in vitro. These data provide in vivo and in vitro evidence that Gcs1p interacts directly with the actin cytoskeleton in S. cerevisiae.

ADP-Ribosylation Factor 1↗
PubMed1999

Optimizing accuracy in magnetic resonance imaging-guided stereotaxis: a technique with validation based on the anterior commissure-posterior commissure line.

OBJECT: Some of the earliest successful frame-based stereotactic interventions directed toward the thalamus and basal ganglia depended on identifying the anterior commissure (AC) and posterior commissure (PC) in a sagittal ventriculogram and defining the intercommissural line that connects them in the midsagittal plane. The AC-PC line became the essential landmark for the localization of neuroanatomical targets in the basal ganglia and diencephalon and for relating them to stereotactic atlases. Stereotactic/functional neurosurgery has come to rely increasingly on magnetic resonance (MR) imaging guidance, and methods for accurately determining the AC-PC line on MR imaging are being developed. The goal of the present article is to present the authors' technique. METHODS: The technique described uses MR sequences that minimize geometric distortion and registration error, thereby maximizing accuracy in AC-PC line determinations from axially displayed MR data. The technique is based on the authors' experience with the Leksell G-frame but can be generalized to other MR imaging-based stereotactic systems. This methodology has been used in a series of 62 stereotactic procedures in 47 adults (55 pallidotomies and seven thalamotomies) with preliminary results that compare favorably with results reported when using microelectrode recordings. The measurements of the AC-PC line reported here also compare favorably with those based on ventriculography and computerized tomography scanning. CONCLUSIONS: The methodology reported here is critical in maintaining the accuracy and utility of MR imaging as its role in modern stereotaxy expands. Accurate parameters such as these aid in ensuring the safety, efficacy, and reproducibility of MR-guided stereotactic procedures.

Adult↗
PubMed1996

Outcome of a second episode of methadone maintenance.

This paper reports the treatment progress of methadone maintenance clients who were discharged or withdrew from treatment and then were readmitted for a second episode of treatment. Thirty-nine clients in a contingency contract condition remained in treatment long enough (6 months) during both the initial and a second treatment episode, to be exposed to discharge sanctions that were part of the contingency contract. Of these clients 34 failed treatment during the initial treatment episode. Nine (26%) of these initial treatment failures improved their performance in the second episode compared to the first, and only one (20%) of five initial treatment successes who left treatment during their first treatment episode for non-contract reasons showed a poorer performance (failing the second after succeeding in the first episode). Of 17 clients in a condition that applied no contingencies for positive urines, three of 14 (21%) who failed during the initial treatment episode improved their performance, and two of three (67%) who succeeded during the initial treatment episode failed in the second episode. For a subset of clients the efficacy of contingency contracting may not be realized until it is reapplied during a subsequent admission.

Adult↗
PubMed1996

Identification and cloning of centaurin-alpha. A novel phosphatidylinositol 3,4,5-trisphosphate-binding protein from rat brain.

Using an affinity resin and photoaffinity label based on phospholipid analogs of inositol 1,3,4,5-tetrakisphosphate (InsP4), we have isolated, characterized, and cloned a 46-kDa protein from rat brain, which we have named centaurin-alpha. Binding specificity was determined using displacement of 1-O-[3H](3-[4-benzoyldihydrocinnamidyl]propyl)-InsP4 photoaffinity labeling. Centaurin-alpha displayed highest affinity for phosphatidylinositol 3,4,5-trisphosphate (PtdInsP3) (IC50 = 120 nM), whereas InsP4, PtdInsP2, and InsP3 bound with 5-, 12-, and >50-fold lower affinity, respectively. Screening a rat brain cDNA library with a polymerase chain reaction product, generated using partial amino acid sequence from tryptic peptides, yielded a full-length clone. The 2,450-base pair cDNA contained an open reading frame (ORF) encoding a novel protein of 419 amino acids. Northern analysis revealed a 2.5-kilobase transcript that is highly expressed in brain. The deduced sequence contains a novel putative zinc finger motif, 10 ankyrin-like repeats, and shows homology to recently identified yeast and mammalian Arf GTPase-activating proteins. Given the specificity of binding and enrichment in brain, centaurin-alpha is a candidate PtdInsP3 receptor that may link the activation of phosphoinositide 3-kinase to downstream responses in the brain.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Pre-treatment characteristics, program philosophy and level of ancillary services as predictors of methadone maintenance treatment outcome.

Predictors of methadone maintenance treatment outcome have not been extensively studied as they relate to variations in program philosophy, nor have such predictors received much examination among recently treated, older cohorts of opioid addicts for whom drug use patterns have changed. Predictors of outcome were examined at 18 months post-treatment entry for 353 admissions to methadone maintenance who received random assignment to one of three counseling conditions: (1) medication only, (2) standard counseling and (3) enhanced services; and one of two contingency conditions: (1) no contingencies, and (2) contingency contracting in a six-cell 3 x 2 design. Subjects in contingency contracting conditions were placed on contingency contracts for positive urine toxicology results and ultimately discharged for unremitting drug use. All subjects completed the Addiction Severity Index (ASI) and provided weekly urine specimens. Predictors of urinalysis results and treatment retention were determined using bivariate and multivariate techniques. Interactions between subject characteristics by experimental condition assignment were also examined as predictors. Higher rates of total positive urine specimens were predicted by younger age, greater pre-treatment frequency of smoking cocaine, lower ASI psychiatric composite scores, and higher ASI legal composite scores. Higher rates of opiate positive specimens were predicted by younger age, lower pre-treatment frequency of alcohol intoxication, higher ASI legal and lower ASI employment and psychiatric composite scores, and assignment to medication only/no contingencies condition. Higher rates of cocaine positives were predicted by younger age, black race, lower ASI psychiatric composite score, greater pre-treatment frequency of intravenous and smoked cocaine use, less pre-treatment frequency of marijuana use, and lower methadone dose level. Assignment to enhanced/contingency contracting predicted lower rates of cocaine positives. Treatment retention was predicted by older age, non-black race, lower ASI legal composite score, higher methadone dose level and assignment to non-contingent conditions. While subject variables over which treatment providers have little control were, thus, related to outcome, type of treatment provided and methadone dose also influenced outcome.

Adolescent↗
PubMed1996

Initiation and maintenance of NGF-stimulated neurite outgrowth requires activation of a phosphoinositide 3-kinase.

Application of nerve growth factor (NGF) to PC12 cells stimulates a programme of physiological changes leading to the development of a sympathetic neuron like phenotype, one aspect of which is the development of a neuronal morphology characterised by the outgrowth of neuritic processes. We have investigated the role of phosphoinositide 3-kinase in NGF-stimulated morphological differentiation through two approaches: firstly, preincubation with wortmannin, a reputedly specific inhibitor of phosphoinositide kinases, completely inhibited initial morphological responses to NGF, the formation of actin filament rich microspikes and subsequent neurite outgrowth. This correlated with wortmannin inhibition of NGF-stimulated phosphatidylinositol(3,4,5)trisphosphate (PtdInsP3) and phosphatidylinositol(3,4)bisphosphate (PtdIns(3,4)P2) production and with inhibition of NGF-stimulated phosphoinositide 3-kinase activity in anti-phosphotyrosine immunoprecipitates. Secondly, the overexpression of a mutant p85 regulatory subunit of the phosphoinositide 3-kinase, which cannot interact with the catalytic p110 subunit, also substantially inhibited the initiation of NGF-stimulated neurite outgrowth. In addition, we found that wortmannin caused a rapid collapse of more mature neurites formed following several days exposure of PC12 cells to NGF. These results indicate that NGF-stimulated neurite outgrowth requires the activity of a tyrosine kinase regulated PI3-kinase and suggest that the primary product of this enzyme, PtdInsP3, is a necessary second messenger for the cytoskeletal and membrane reorganization events which occur during neuronal differentiation.

Androstadienes↗
PubMed1996

Retention in methadone maintenance is associated with reductions in different HIV risk behaviors for women and men.

Using AIDS Initial Assessment questionnaire (AIA) data from 353 injection drug users (IDUs) newly admitted to methadone maintenance (MM), three dimensions of injection risk behavior ("sharing with sexual partner," "sharing with others," and "new needle use") were identified. Among IDUs who continued to inject drugs at 1 year, men retained in treatment obtained lower scores on the "sharing with others" scale than men not retained, even when controlling for initial scale scores and injection frequency. Associations between retention in MM and changes in sexual risk were examined using two AIA measures of sexual risk behavior ("number of IDU sexual partners" and "relative frequency of protected vaginal intercourse"). Controlling for injection frequency, prior sexual risk, and age, there was no difference in sexual risk for men retained in treatment versus those not retained. Among women, those who stayed in MM for 1 year reported significantly fewer IDU partners.

Analgesics, Opioid↗
PubMed1995

Identification of a specific Ins(1,3,4,5)P4-binding protein as a member of the GAP1 family.

Inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) is produced rapidly from inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) in stimulated cells. Despite extensive experimentation, no clearly defined cellular function has yet been described for this inositol phosphate. Binding sites specific for Ins(1,3,4,5)P4 have been identified in several tissues, and we have purified one such protein to homogeneity. Its high affinity for Ins(1,3,4,5)P4, and its exquisite specificity for this isomeric configuration, suggest it may be an Ins(1,3,4,5)P4 receptor. Here we report the cloning and characterization of this protein as a GTPase-activating protein, specifically a member of the GAP1 family. In vitro it shows GAP activity against both Rap and Ras, but only the Ras GAP activity is inhibited by phospholipids and is specifically stimulated by Ins(1,3,4,5)P4.

Amino Acid Sequence↗
PubMed1994

1-Phosphatidylinositol 3-kinase activity is required for insulin-stimulated glucose transport but not for RAS activation in CHO cells.

Insulin stimulation drives the formation of a complex between tyrosine-phosphorylated insulin receptor substrate 1 (IRS-1) and 1-phosphatidylinositol 3-kinase (PI 3-kinase; ATP:1-phosphatidyl-1D-myo-inositol 3-phosphotransferase, EC 2.7.1.137), a heterodimer consisting of regulatory 85-kDa (p85) and catalytic 110-kDa (p110) subunits. This interaction takes place via the phosphorylated YMXM motifs of IRS-1 and the Src homology region 2 (SH2) domains of p85. In this study, the stable overexpression in a Chinese hamster ovary (CHO) cell line of a mutant p85 alpha (delta p85) protein, which lacks a binding site for p110, disrupted the complex formation between IRS-1 and the catalytic subunit of PI 3-kinase in intact cells during insulin stimulation. Activation of insulin receptor kinase and the tyrosine phosphorylation of IRS-1 remained unaffected. In this cell line, both insulin-stimulated accumulation of phosphatidylinositol 3,4,5-trisphosphate and the insulin-stimulated glucose uptake due to the translocation of GLUT1 glucose transporters were markedly impaired, whereas neither phorbol 12-myristate 13-acetate-stimulated glucose uptake nor the insulin-stimulated activation of RAS was impaired. These results suggest that PI 3-kinase is required for glucose transport in insulin signaling in CHO cells.

Animals↗