Methylation of the protein phosphatase 2A catalytic subunit is essential for association of Balpha regulatory subunit but not SG2NA, striatin, or polyomavirus middle tumor antigen

Binding of different regulatory subunits and methylation of the catalytic (C) subunit carboxy-terminal leucine 309 are two important mechanisms by which protein phosphatase 2A (PP2A) can be regulated. In this study, both genetic and biochemical approaches were used to investigate regulation of regulatory subunit binding by C subunit methylation. Monoclonal antibodies selectively recognizing unmethylated C subunit were used to quantitate the methylation status of wild-type and mutant C subunits. Analysis of 13 C subunit mutants showed that both carboxy-terminal and active site residues are important for maintaining methylation in vivo. Severe impairment of methylation invariably led to a dramatic decrease in Balpha subunit binding but not of striatin, SG2NA, or polyomavirus middle tumor antigen (MT) binding. In fact, most unmethylated C subunit mutants showed enhanced binding to striatin and SG2NA. Certain carboxy-terminal mutations decreased Balpha subunit binding without greatly affecting methylation, indicating that Balpha subunit binding is not required for a high steady-state level of C subunit methylation. Demethylation of PP2A in cell lysates with recombinant PP2A methylesterase greatly decreased the amount of C subunit that could be coimmunoprecipitated via the Balpha subunit but not the amount that could be coimmunoprecipitated with Aalpha subunit or MT. When C subunit methylation levels were greatly reduced in vivo, Balpha subunits were found complexed exclusively to methylated C subunits, whereas striatin and SG2NA in the same cells bound both methylated and unmethylated C subunits. Thus, C subunit methylation is critical for assembly of PP2A heterotrimers containing Balpha subunit but not for formation of heterotrimers containing MT, striatin, or SG2NA. These findings suggest that methylation may be able to selectively regulate the association of certain regulatory subunits with the A/C heterodimer.

Probing the mechanism of transport and compartmentalisation of polyamines in mammalian cells

BACKGROUND

Many mammalian cells possess an active polyamine uptake system but little is known about the molecular mechanism of this transporter. The fate of polyamines taken up from the medium and the relationship to polyamine homeostasis remains to be fully established. The aim of this study was to develop a range of modified polyamines, particularly ligands incorporating a fluorophore, to explore the structural tolerances of the polyamine transport system and to probe the intracellular location of polyamines acquired from the medium.

RESULTS

We synthesised a wide range of polyamine analogues incorporating cytotoxic agents, fluorescent chromophores and bulky substituents. All of these analogues have been shown to be good competitive inhibitors of spermidine uptake in a range of mammalian cells. Direct evidence for uptake of the fluorescent polyamine analogues and their subcellular distribution was obtained from confocal laser scanning fluorescence microscopy, which showed that they accumulated in granular structures within the cytoplasm and not in the nucleus. We demonstrated that their uptake is through the polyamine transport system by showing that pretreatment with DFMO, a potent inhibitor of polyamine biosynthesis, led to enhanced uptake, and cells deficient in the polyamine transport system did not accumulate these polyamine analogues.

CONCLUSIONS

The polyamine transport system has a surprisingly broad structural tolerance. Fluorophore-containing polyamine analogues derived from the extracellular pool are located in granular structures within the cytoplasm and not to any great extent in the nuclei of mammalian cells. These observations might be consistent with a mechanism involving receptor-mediated endocytosis, and the granular 'structures' seen might reflect polyamine compartmentalisation within vesicles.

The case of the amnesic intelligence officer

This paper describes a patient whose amnesia for an offence (fraud) and two fugue episodes occurred against the background of an underlying organic amnesia. The fugue states conformed in their duration and precipitating factors to previous accounts in the literature. The organic, anterograde memory impairment was attributed to multiple small infarcts and a larger infarction in the left medial temporal lobe, which were evident on MRI and PET scans after the patient had developed transient neurological signs. At follow-up, the anterograde amnesia had persisted, and the patient also showed some difficulty in retrieving autobiographical memories of past incidents or events, although other aspects of his retrograde memory were intact (including his knowledge of facts about his past life and his general knowledge of public events). The difficulty in retrieving autobiological incidents may have resulted from the presence of a moderate degree of frontal lobe dysfunction or, just possibly, from ischaemia in the left anterior temporal lobe. The persistence of the organic memory impairment and the importance of both the clinical history and neuropsychological testing in assessment are discussed, as well as the need to examine for possible organic factors in patients who may initially appear to manifest purely 'psychogenic' memory loss.

On the existence of independent explicit and implicit learning systems: an examination of some evidence

Hayes and Broadbent (1988), among others, have proposed that there are two independent systems of learning in humans. In their theory, they postulate that the explicit learning system gives rise to knowledge that is verbally describable, whereas the implicit learning system deals with knowledge that is not amenable to verbal report. Hayes and Broadbent presented data that they claimed supports a distinction between these two systems of learning. Their experiments involved the performance of subjects on two superficially similar tasks, and their claim was that one of the tasks induced learning in the explicit system, and the other induced learning in the implicit system. However, in five experiments here, we failed to find any convincing support for their empirical or theoretical claims. Our results suggest that the two tasks do not differ by inducing different types of learning, but simply differ in their degree of difficulty.

Driver fatalities and DUI offenders in New Jersey

Comparisons of driving and demographic characteristics were made on 407 driver fatalities (DFs) and 407 motorists convicted of driving under the influence (DUI). Significantly more DUI offenders (DOs) than DFs were men and had previous DUIs, accidents, license suspensions, and weekend "index" events. DFs with a blood or brain alcohol concentration (BAC) of 100 or above mg/dL matched most closely with DOs on negative driving events, "index" event days, and demographics. Conversely, DFs with negative BACs differed significantly with DOs on virtually all characteristics. High-BAC DFs and DOs may well be drawn from the same subpopulation of deviant drivers, whereas DFs with negative BACs seem similar to licensed drivers in general.

Passive smoking and middle ear effusions in children of British servicemen in West Germany--a point prevalence survey by clinics of outpatient attendance

Three hundred and twenty eight children of British servicemen serving in West Germany were studied in order to ascertain any relationship between parental smoking and the presence of middle ear effusion. The age range of the children was 18 months to 8 years. A questionnaire was completed by the parents of each child, and clinical examination and audiological tests demonstrated the presence or otherwise of middle ear effusions. One hundred and sixty four patients who had been referred with otological symptoms to the Ear, Nose and Throat Out Patient Department (ENT OPD) were surveyed, as were 164 other patients drawn from the Paediatric, Orthopaedic and Ophthalmic Out Patient Departments (OPDs) at BMH Rinteln. These 2 groups had similar age and sex distributions. The presence of middle ear effusions amongst children attending the ENT OPD was strongly associated with maternal cigarette smoking. This finding implies that mothers should not smoke at all in the same living accommodation as that used by their children. Paternal cigarette smoking showed no significant association with the presence of middle ear effusions.

ABO blood groups in hematologic malignancies

This article examines the genetic predisposition of individuals to lymphoma and leukemia with regard to the ABO blood groups. Blood samples from 558 patients suffering from various forms of lymphoma and leukemia were collected and typed for ABO blood groups. The ABO blood group phenotype frequencies of lymphoma patients were similar to those in control samples. Among leukemia patients, a significant increase in the frequency of the A2 phenotype was found in chronic lymphocytic leukemia. Possible mechanisms underlying the predisposition of individuals with the A2 blood group to chronic lymphocytic leukemia suggested by these preliminary results are discussed.

Management of traumatic rupture of the globe in aphakic patients

We report the successful treatment of three cases of traumatic ruptures of the globe complicated by massive choroidal hemorrhage, uveal prolapse and retinal detachment. All three of the eyes were aphakic prior to injury and all patients were age 64 or older. The presenting visual acuity in all patients was light perception. The blunt injury in each case caused a wound dehiscence at the site of previous cataract extraction. All injuries were associated with uveal prolapse. Secondary surgical intervention was performed when the hemorrhagic choroidal detachments had decreased as demonstrated by echography in the suprachoroidal space, occurring at an average of 14 days after injury. The management consisted of surgical drainage of the choroidal hemorrhage combined with vitrectomy and silicone oil injection. Successful reattachment of the retina was achieved in all cases. Postoperative epiretinal membranes formed in two cases but all were anatomically successful at six months. Final visual acuities varied from 20/70 to 1/200, visual acuity being a function of secondary contusive damage to the retina and choroid. We believe that in eyes sustaining severe blunt injuries resulting in rupture of the globe complicated by massive choroidal hemorrhage and retinal detachment, properly timed external drainage of the choroidal hemorrhage combined with pars plana vitrectomy and silicone oil injection is a useful approach.

Using optical correlation to measure leak rates in sealed packages

An optical correlation technique has been shown to accurately measure leak conduction rates from 10(-1) to 10(-6) atm cc/sec. Using hybrid microcircuit packages with glass capillary leakers, dimensional changes were detected as the packages were exposed to a small increase in external pressure. The rate at which the package returns to its original dimensions is measured and used, along with the internal free volume, to compute the leak rate. Because of its several advantages, the technique has the potential to become a useful nondestructive quality-control technique.

Multiparameter system for investigation of the effects of high-power ultrasound on metals

A multiparameter system has been developed which, for the first time, permits simultaneous measurement of sufficient quantities to test all of the proposed mechanisms for the influence of high-power ultrasound on metal specimens. Results of measurements using this system give new insight into the mechanical and thermal processes involved. Data are presented which show typical results obtained during tensile elongation of polycrystalline and single-crystal aluminum specimens.

Poly-HEMA sponge: a biocompatible calcification implant

Poly-hydroxyethyl methacrylate (Poly-HEMA) was investigated for biocompatibility and calcification potential. S.C. and I.M. implants and transplants to subperiosteal sites were examined. The material was judged to be tolerated by the host tissue since no inflammatory or degenerative changes were observed. This study established that calcification does occur. This calcification does not simulate bone formation; osteoblasts were not observed. The x-ray diffraction pattern resembles that of calcium hydroxyapatite.

Disseminated Nocardia brasiliensis infection

We report a 40-year-old man with advanced Hodgkin disease who received combination chemotherapy and developed disseminated Nocardia brasiliensis infection. We discuss opportunistic infections in the compromised host, with particular reference to nocardial disease and certain biologic characteristics of that organism.

Automatic platelet counting with the Couler particle counter

A method for accurately counting platelets is described using the Coulter counter model B fitted with a standard 100mu aperture tube. This enables the counter to be used for red and white cell as well as platelet counts using the same aperture tube. The method uses standard equipment except for a small inexpensive electronic speed controller.