SIRT1 regulates DNA damage signaling through the PP4 phosphatase complex

The Sirtuin family of NAD+-dependent enzymes plays an important role in maintaining genome stability upon stress. Several mammalian Sirtuins have been linked directly or indirectly to the regulation of DNA damage during replication through Homologous recombination (HR). The role of one of them, SIRT1, is intriguing as it seems to have a general regulatory role in the DNA damage response (DDR) that has not yet been addressed. SIRT1-deficient cells show impaired DDR reflected in a decrease in repair capacity, increased genome instability and decreased levels of γH2AX. Here we unveil a close functional antagonism between SIRT1 and the PP4 phosphatase multiprotein complex in the regulation of the DDR. Upon DNA damage, SIRT1 interacts specifically with the catalytical subunit PP4c and promotes its inhibition by deacetylating the WH1 domain of the regulatory subunits PP4R3α/β. This in turn regulates γH2AX and RPA2 phosphorylation, two key events in the signaling of DNA damage and repair by HR. We propose a mechanism whereby during stress, SIRT1 signaling ensures a global control of DNA damage signaling through PP4.

SIRT1 regulates the histone methyl-transferase SUV39H1 during heterochromatin formation

In contrast to stably repressive, constitutive heterochromatin and stably active, euchromatin, facultative heterochromatin has the capacity to alternate between repressive and activated states of transcription. As such, it is an instructive source to understand the molecular basis for changes in chromatin structure that correlate with transcriptional status. Sirtuin 1 (SIRT1) and suppressor of variegation 3-9 homologue 1 (SUV39H1) are amongst the enzymes responsible for chromatin modulations associated with facultative heterochromatin formation. SUV39H1 is the principal enzyme responsible for the accumulation of histone H3 containing a tri-methyl group at its lysine 9 position (H3K9me3) in regions of heterochromatin. SIRT1 is an NAD+-dependent deacetylase that targets histone H4 at lysine 16 (refs 3 and 4), and through an unknown mechanism facilitates increased levels of H3K9me3 (ref. 3). Here we show that the mammalian histone methyltransferase SUV39H1 is itself targeted by the histone deacetylase SIRT1 and that SUV39H1 activity is regulated by acetylation at lysine residue 266 in its catalytic SET domain. SIRT1 interacts directly with, recruits and deacetylates SUV39H1, and these activities independently contribute to elevated levels of SUV39H1 activity resulting in increased levels of the H3K9me3 modification. Loss of SIRT1 greatly affects SUV39H1-dependent H3K9me3 and impairs localization of heterochromatin protein 1. These findings demonstrate a functional link between the heterochromatin-related histone methyltransferase SUV39H1 and the histone deacetylase SIRT1.

Revealing domain structure through linker-scanning analysis of the murine leukemia virus (MuLV) RNase H and MuLV and human immunodeficiency virus type 1 integrase proteins

Linker-scanning libraries were generated within the 3' terminus of the Moloney murine leukemia virus (M-MuLV) pol gene encoding the connection-RNase H domains of reverse transcriptase (RT) as well as the structurally related M-MuLV and human immunodeficiency virus type 1 (HIV-1) integrase (IN) proteins. Mutations within the M-MuLV proviral vectors were Tn7 based and resulted in 15-bp insertions. Mutations within an HIV-1 IN bacterial expression vector were based on Tn5 and resulted in 57-bp insertions. The effects of the insertions were examined in vivo (M-MuLV) and in vitro (HIV-1). A total of 178 individual M-MuLV constructs were analyzed; 40 in-frame insertions within RT connection-RNase H, 108 in-frame insertions within IN, 13 insertions encoding stop codons within RNase H, and 17 insertions encoding stop codons within IN. For HIV-1 IN, 56 mutants were analyzed. In both M-MuLV and HIV-1 IN, regions are identified which functionally tolerate multiple-linker insertions. For MuLV, these correspond to the RT-IN proteolytic junction, the junction between the IN core and C terminus, and the C terminus of IN. For HIV-1 IN, in addition to the junction between the IN core and C terminus and the C terminus of IN, insertions between the N terminus and core domains maintained integration and disintegration activity. Of the 40 in-frame insertions within the M-MuLV RT connection-RNase H domains, only the three C-terminal insertions mapping to the RT-IN proteolytic junction were viable. These results correlate with deletion studies mapping the domain and subdomain boundaries of RT and IN. Importantly, these genetic footprints provide a means to identify nonessential regions within RT and IN for targeted gene therapy applications.

Composition and histone substrates of polycomb repressive group complexes change during cellular differentiation

Changes in the substrate specificities of factors that irreversibly modify the histone components of chromatin are expected to have a profound effect on gene expression through epigenetics. Ezh2 is a histone-lysine methyltransferase with activity dependent on its association with other components of the Polycomb Repressive Complexes 2 and 3 (PRC2/3). Ezh2 levels are increasingly elevated during prostate cancer progression. Other PRC2/3 components also are elevated in cancer cells. Overexpression of Ezh2 in tissue culture promotes formation of a previously undescribed PRC complex, PRC4, that contains the NAD+-dependent histone deacetylase SirT1 and isoform 2 of the PRC component Eed. Eed2 is expressed in cancer and undifferentiated embryonic stem (ES) cells but is undetectable in normal and differentiated ES cells. The distinct PRCs exhibit differential histone substrate specificities. These findings suggest that formation of a transformation-specific PRC complex may have a major role in resetting patterns of gene expression by regulating chromatin structure.

Human SirT1 interacts with histone H1 and promotes formation of facultative heterochromatin

We characterized human SirT1, one of the human homologs of the budding yeast Sir2p, an NAD+-dependent histone deacetylase involved in establishing repressive chromatin and increased life span. SirT1 deacetylates histone polypeptides with a preference for histone H4 lysine 16 (H4-K16Ac) and H3 lysine 9 (H3-K9Ac) in vitro. RNAi-mediated decreased expression of SirT1 in human cells causes hyperacetylation of H4-K16 and H3-K9 in vivo. SirT1 interacts with and deacetylates histone H1 at lysine 26. Using an inducible system directing expression of SirT1 fused to the Gal4-DNA binding domain and a Gal4-reporter integrated in euchromatin, Gal4-SirT1 expression resulted in the deacetylation of H4-K16 and H3-K9, recruitment of H1 within the promoter vicinity, drastically reduced reporter expression, and loss of H3-K79 methylation, a mark restricting silenced chromatin. We propose a model for SirT1-mediated heterochromatin formation that includes deacetylation of histone tails, recruitment and deacetylation of histone H1, and spreading of hypomethylated H3-K79 with resultant silencing.

Perinatal asphyxia: timing and mechanisms of injury in neonatal encephalopathy

This article summarizes the recent medical literature regarding perinatal asphyxia with respect to timing and mechanisms of injury for neonates who were clinically diagnosed with an encephalopathy in the newborn period. Multiple mechanisms of injury are reviewed, including genetic vulnerability, acquired inflammatory responses, and clotting defects that can lead to ischemic-induced brain damage. Before effective treatments for fetal and neonatal brain disorders can be developed, accurate and timely diagnoses of fetal or neonatal brain injury must be achieved. Specific subsets of children can then benefit from neuroprotective strategies that can target the specific developmental aspects of brain adaptation or plasticity relative to the specific etiology and timing of injury after asphyxia.

A psychiatrist-rated battery of measures for assessing the clinical status of psychiatric inpatients

Despite the increasing demand for outcome assessment measures, no published reports have provided a standardized way to assess psychiatric inpatients that includes diagnosis and observer ratings of psychopathology. This paper reviews general principles for selecting outcome assessment measures, proposes a battery of instruments based on already available measures to assess clinical status in psychiatric inpatients, reviews methods of implementing the battery in an academic inpatient psychiatric setting, and presents preliminary data on its interrater reliability, construct validity, and range of response to acute hospitalization. Preliminary results suggest that the battery may be useful for resident and medical student education and for enhancing quality assurance and continuous quality improvement.

Neonatal phenobarbital and phenytoin binding profiles

Phenobarbital and phenytoin binding profiles were determined in 27 neonates. Binding of both drugs decreased compared with that in older subjects. In vitro binding of both agents correlated significantly with total protein and albumin concentrations. In vivo binding at 0.5 hours correlated significantly with birthweight and gestational age. Phenobarbital, but not phenytoin, binding decreased when three other therapeutic agents were concomitantly administered. Bilirubin concentrations, free fatty-acid concentrations, and pH values encountered in this population did not significantly influence binding. An in vitro binding profile accurately predicted in vivo free fractions (percent drug unbound) and plasma concentrations of both drugs.

Enhancement of differentiation and cytotoxicity of leukemia cells by combinations of fluorinated pyrimidines and differentiation inducers: development of DNA double-strand breaks

We have previously shown that pretreatment of mouse erythroleukemia (MEL) cells with the fluorinated pyrimidines 5-fluorouracil (FUra) or 5-fluorodeoxyuridine (FUdR) followed by the differentiation inducer hexamethylene bisacetamide (HMBA) greatly enhanced the magnitude of their differentiation and caused extensive cell death. We have now extended these studies to address the mechanism that may be responsible for this enhancement and have also examined a human leukemic cell line (HL-60) for its sensitivity to this combination cytotoxic-differentiation therapy. We found that in HL-60 cells, pretreatment with FUdR, but not FUra, followed by 1.2% dimethylsulfoxide (DMSO) led to an 8 to 10-fold enhancement of cell death as compared to FUdR alone. When all-trans-retinoic acid (ATRA) was used instead of DMSO, the enhancement of differentiation and cytotoxicity was 5-fold. The percent of cells induced to differentiate was dependent on the concentration of both FUdR and ATRA. In HL-60 cells resistant to ATRA-induced differentiation, the combination of FUdR and ATRA did not result in enhanced cytotoxicity. Leucovorin (LV), a compound known to enhance the inhibitory effect of FUra or FUdR on DNA synthesis, increased the effectiveness of the cytotoxic-differentiation therapy, whereas thymidine inhibited its effectiveness. This suggests that inhibition of DNA metabolism may be an integral part of the differentiation-enhancing cytotoxic mechanism. To further explore inhibition of DNA synthesis, DNA was extracted under alkaline or neutral conditions from 3H-thymidine-labelled cells that were treated with FUra/LV and HMBA individually or in combination. The emergence of single and double-strand DNA breaks was monitored by agarose gel electrophoresis. In parallel to the enhancement of cytotoxicity, the combination treatment (FUra/LV followed by HMBA) also produced a 2.5-3-fold increase in the DNA breaks when compared to the same effect obtained by the agents applied individually. Thus, we propose that DNA degradation may be the mechanism responsible for the enhanced loss of cell viability. In summary, we report here an approach which is targeted to increasing the death rate of leukemic cells through the combined use of low doses of cytotoxic drugs and differentiation inducers.

Prenatal marijuana use and neonatal outcome

In a longitudinal study of marijuana and other substance use during pregnancy, women were interviewed at each trimester of pregnancy. Growth parameters, morphological abnormalities and gestational age were assessed for the 519 liveborn singletons. There were few significant effects of marijuana use during pregnancy on birth weight, head or chest circumference, gestational age, or growth retardation after adjustment for covariates using a regression model for analysis. There was a small but significant negative effect of marijuana use during the first two months of pregnancy on birth length and a positive effect of marijuana use during the third trimester on birth weight.

The effects of prenatal alcohol use on the growth of children at three years of age

In this prospective study of substance use during pregnancy, women were interviewed in their 4th and 7th prenatal months, and women and children were assessed at 24 hr, 8, 18, and 36 months postpartum. Data are presented on the outcome of 519 children at age 3. At 3 years, children who were exposed prenatally to alcohol were smaller in weight, length, and head circumference. They also had an increased number of minor physical anomalies. These effects were found even after controlling for nutritional and environmental factors. The persistence of growth effects at age 3 suggests that children exposed to alcohol prenatally may have a diminished capacity for growth.

Effect of prenatal alcohol exposure on growth and morphology of offspring at 8 months of age

In this prospective study of alcohol and other substance use during pregnancy, a cohort of women was interviewed at each trimester of pregnancy and when the offspring were 8 months of age. Data are presented concerning the outcome for 461 infants. A significant relationship was found between alcohol use during pregnancy and the growth and morphology of the offspring at the 8-month follow-up observation. Alcohol use during the second and third trimesters of pregnancy and continuous use of alcohol throughout pregnancy were significantly related to lower weight, length, and head circumference in the exposed infants at the follow-up observation. A significant increase in the risk of minor physical anomalies and fetal alcohol effects was also predicted by prenatal alcohol exposure.

Patients' satisfaction with care received in teaching settings

Voluntary psychiatric patients (N=118) on a teaching ward were asked to identify their medical personnel and rate their satisfaction with the care they received. The patients were proficient in distinguishing between psychiatrists, psychiatric residents, and medical students and were highly satisfied with the care they received. Patients over 35 were better at identifying residents than younger patients and also rated the quality of care pro-vided by psychiatrists more highly. Patients with adjustment reaction with depressed mood rated the quality of care provided by psychiatrists lower than did patients with major depression, bipolar affective disorder, or psychosis. Female patients rated their psychiatrists more highly than did male patients.

Carbamazepine adjunct for nonresponsive psychosis with prior hallucinogenic abuse

Some patients diagnosed as schizophrenic report persistent polymodal hallucinosis following a period of extensive hallucinogenic drug abuse unrelieved by the usual antipsychotic drugs. In this open study, carbamazepine (Tegretol, an anticonvulsant) was administered to three patients with polymodal hallucinosis which had failed to diminish on antipsychotic drugs alone. All three patients showed a marked to complete reduction in symptomatology.

Prenatal exposure to alcohol: effect on infant growth and morphologic characteristics

In this prospective study of alcohol and other substance use during pregnancy, a cohort of 650 women was interviewed at each trimester of pregnancy. Data are presented concerning the status of 595 live singleton births. A relationship was demonstrated between prenatal maternal alcohol use and growth and morphologic abnormalities in the offspring. Low birth weight, decreased head circumference and length, and an increased rate of fetal alcohol effects were all found to be significantly correlated with exposure to alcohol during the first 2 months of the first trimester.

Koro in a native born citizen of the U.S

A case of Koro in a native born citizen of the U.S. is presented. The similarity to earlier culture-bound cases is discussed, as well as the psychological and constitutional substrate present in this case.

Trazodone and priapism

Trazodone, an antidepressant with antianxiety effects, has been available in the United States since March 1982. Since then 11 cases of priapism, five requiring surgical procedures, have been reported. The authors present one of the latter cases.

Metabolic interconversion of dolichol and dolichyl phosphate during development of the sea urchin embryo

The in vivo and in vitro synthesis and turnover of dolichol and dolichyl phosphate have been studied over the course of early development in sea urchin embryos. Synthesis of dolichol and dolichyl phosphate was studied in vivo and in vitro using [3H]acetate and [14C] isopentenylpyrophosphate, respectively, as precursors. Both the in vivo and in vitro results indicate that the principal labeled end product of de novo synthesis is the free alcohol, and that this alcohol is subsequently phosphorylated to produce dolichyl phosphate. The presence of 30 microM compactin inhibits the de novo synthesis of dolichol from [3H]acetate by greater than 90%, but has no effect on the incorporation of 32Pi into dolichyl phosphate for more than 6 h, thus suggesting that during this time interval the major source of dolichyl phosphate is preformed dolichol. The rate of turnover of the [3H]acetate-labeled polyisoprenoid backbone of dolichyl phosphate is very slow (t1/2 = 40-70 h). In contrast, the rate of loss of the [32P]phosphate headgroup is more rapid (t1/2 = 5.7-7.7 h) and increases over the course of development. Finally, dolichyl phosphate phosphatase activity has been measured in vitro. The activity of this enzyme, which can be distinguished from phosphatidic acid phosphatase, was found to increase as a function of development, in qualitative agreement with the increased turnover of 32P from dolichyl phosphate observed in vivo. These results suggest that the phosphate moiety of dolichyl phosphate is in a dynamic state, and that dolichol kinase and dolichyl phosphate phosphatase play key roles in regulating the cellular level of dolichyl phosphate.

Comparison of course evaluations by random and volunteer student samples

Ratings of the effectiveness of courses are usually based on students' voluntary responses to evaluation questionnaires. It is a rare course for which all students complete evaluation forms. This self-selection may result in an overrepresentation of students who are highly pleased or greatly disgruntled, thus biasing the evaluation. Responses of an unbiased random sample of students were compared with the responses of a self-selected sample for the evaluations of two medical school courses. There was no evidence of bias introduced by self-selection for either mean ratings or the variance of responses on a question-by-question basis for eight questions included in the evaluations of both classes. When responses were investigated across items, the patterns of differences between the random and voluntary samples appeared to be unique to each class.

The management of chronic schizophrenia

With the movement of psychiatric patients from chronic mental hospitals to local communities over the past 20 years, family physicians have provided care for increasing numbers of chronic schizophrenia patients. The residual symptoms which these patients demonstrate require special communication skills on the part of the physician if a collaborative patient-physician relationship is to be established. The management of the disease should be founded on an understanding of its psychopathology. In this paper, the authors describe this psychopathology and suggest therapeutic interactions and interventions specific to the disease process.

Kinetic ratio as a parameter for product stability calculations

A new parameter, the kinetic ratio, is suggested for estimating product potency during storage under ambient warehouse temperatures. Actual warehouse temperature data were integrated using Arrhenius kinetics, and the resulting potency errors, due both to the integration method and to temperature averaging, were evaluated. Kinetic ratios and virtual temperatures then were compared to show seasonal and Arrhenius constant effects. Equations interrelating the kinetic ratio and virtual temperature are given. Finally, sample calculations using typical vitamin A data were analyzed to demonstrate the calculational and interpretation characteristics of the kinetic ratio compared to the virtual temperature.

Thrombocytopenia in the absence of leukopenia associated with the use of neuroleptics

Thrombocytopenia, a fairly uncommon side effect of phenothiazine treatment, usually appears in the presence of a concommitant leukopenia. The authors report 1 patient in whom the illness appeared in the presence of a long known Beta thalassemia but without evidence of alteration in myeloid or lymphoid series. Platelet changes were seen in the presence of a butyrophenone and an aliphatic phenothiazine. A piperazine derivative was used without difficulty.

Reviewing results of psychological tests in a patient group

Believing that much helpful information from psychological test results was not being transmitted to patients, psychologists on a teaching ward at a Veterans Administration hospital began holding group sessions to explain the results of psychological tests to patients. Attendance was voluntary, but 96 per cent of the patients who were tested in a one-year period attended, an average of four or five each session. The psychologist described routine tests and how the results were used and then presented individual test results, giving practical illustrations of the findings and emphasizing patients' strengths and coping styles. Scores from questionnaires administered to patients after they completed the tests and at the end of the group session showed that their attitudes toward tests became more positive after the group session, and that they felt that hearing their own and others' test results had been helpful.

Psychiatrist-wife-mother: some aspects of role integration

Throughout her professional life the woman who chooses to combine the roles of psychiatrist, wife, and mother may find them not only compatible but complementary. If she can adopt a philosophy of life that permits her to function in these roles, and if those around her support her activities, she can perform with relative ease and proficiency. Her lifestyle must of necessity differ from that of her male colleagues, but differing lifestyles among members of a profession vitalize the field. A broad perspective is desirable, especially in a profession that deals with the emotional and mental lives of people. Married women and mothers afford such a broadened perspective to the field of psychiatry.