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Biomedical subjects

A J Flint

Publications and source records attributed to A J Flint.

At least 37 records · Page 2Linked to original sources
PubMed1997

Development of "substrate-trapping" mutants to identify physiological substrates of protein tyrosine phosphatases.

The identification of substrates of protein tyrosine phosphatases (PTPs) is an essential step toward a complete understanding of the physiological function of members of this enzyme family. PTPs are defined by a conserved catalytic domain harboring 27 invariant residues. From a mutagenesis study of these invariant residues that was guided by our knowledge of the crystal structure of PTP1B, we have discovered a mutation of the invariant catalytic acid (Asp-181 in PTP1B) that converts an extremely active enzyme into a "substrate trap." Expression of this D181A mutant of PTP1B in COS and 293 cells results in an enzyme that competes with endogenous PTP1B for substrates and promotes the accumulation of phosphotyrosine primarily on the epidermal growth factor (EGF) receptor as well as on proteins of 120, 80, and 70 kDa. The association between the D181A mutant of PTP1B and these substrates was sufficiently stable to allow isolation of the complex by immunoprecipitation. As predicted for an interaction between the substrate-binding site of PTP1B and its substrates, the complex is disrupted by vanadate and, for the EGF receptor, the interaction absolutely requires receptor autophosphorylation. Furthermore, from immunofluorescence studies, the D181A mutant of PTP1B appeared to retain the endogenous EGF receptor in an intracellular complex. These results suggest that the EGF receptor is a bona fide substrate for PTP1B in vivo and that one important function of PTP1B is to prevent the inappropriate, ligand-independent, activation of newly synthesized EGF receptor in the endoplasmic reticulum. This essential catalytic aspartate residue is present in all PTPs and has structurally equivalent counterparts in the dual-specificity phosphatases and the low molecular weight PTPs. Therefore we anticipate that this method may be widely applicable to facilitate the identification of substrates of other members of this enzyme family.

Animals↗
PubMed1997

Two-year outcome of elderly patients with anxious depression.

The purpose of this study was to determine whether there was a difference in the long-term outcome between elderly patients with anxious depression and those with non-anxious depression. Eighty-three patients with non-bipolar, non-psychotic major depression who had responded to treatment of the index episode were maintained on full-dose antidepressant medication and followed on a monthly basis over a period of 2 years. Anxiety status at index assessment was not related to outcome as defined by rates of relapse and recurrence or time to these events. However, the few patients who remained anxious at the point of remission of the index episode had a significantly shorter time to relapse/recurrence. These findings suggest that, once they achieve remission and are given adequate prophylactic treatment, most older patients with anxious depression have a similar long-term outcome to patients without anxiety.

Aged↗
PubMed1997

Effect of demographic and clinical variables on time to antidepressant response in geriatric depression.

The authors examined the effect of demographic and clinical variables on time to treatment response in geriatric depression. One hundred and one patients, aged 60-92 years, with nonpsychotic, nonbipolar major depression were treated in an open fashion with 6 weeks of nortriptyline followed, if necessary, by 2 weeks of lithium augmentation. Univariate Cox proportional hazards analyses showed that 3 of 19 variables predicted time to response: high baseline anxiety was associated with delayed response (median of 5 weeks vs. 4 weeks for patients with low anxiety scores), whereas hospitalization for the index episode of depression and attempted suicide predicted shorter time to response. In the final multivariate Cox regression model, baseline anxiety and inpatient status were most predictive of outcome; attempted suicide did not significantly improve the predictive power of the model. Our findings strengthen existing evidence that concomitant anxiety can adversely affect the outcome of geriatric depression.

Aged↗
PubMed1997

Poverty status and cigarette smoking prevalence and cessation in the United States, 1983-1993: the independent risk of being poor.

OBJECTIVE: To analyse the independent relations between poverty status and cigarette smoking prevalence and cessation in the United States, 1983-1993. DESIGN: An analysis of eight cross-sectional national surveys. SETTING: The United States, 1983-1993. PARTICIPANTS: 236,311 civilian, non-institutionalised adult residents of the United States, aged 18 years and older. MAIN OUTCOME MEASURES: Probability of current cigarette smoking and proportion of former smokers among ever-smokers (quit ratio) in surveyed subjects below the poverty threshold, compared with those at or above the poverty threshold. RESULTS: The odds ratio for current smoking among persons below the poverty threshold ranged from a low of 1.10 in 1985 to a high of 1.45 in 1990, and remained between 1.26 and 1.30 during 1991-1993. The odds ratio for smoking cessation (quit ratio) among persons below the poverty threshold ranged from 0.81 in 1985 to 0.64 in 1991, and remained between 0.73 and 0.66 during 1991-1993. These measures of the relations between poverty status and smoking were derived using multiple logistic regression models, which adjusted for the effects of sex, age, education, race, employment status, marital status, and geographic region. CONCLUSIONS: Persons below the poverty threshold continue to be more likely than those at or above the threshold both to be current smokers and not to have quit. Poverty may be an indicator of underparticipation in the changing social norms regarding smoking behaviour in recent years. Individuals below the poverty threshold may need focused efforts to help achieve the Healthy People 2000 objectives for reducing adult smoking prevalence. Further understanding of the relation between poverty and smoking is essential to develop effective programmes for this vulnerable population subgroup.

Adult↗
PubMed1997

The effect of treatment on the two-year course of late-life depression.

BACKGROUND: The purpose of this study was to examine the effect of treatment on the long-term course of geriatric depression. METHOD: Eighty-four elderly patients who had responded to treatment of the index episode of major depression were maintained on full-dose antidepressant medication and followed on a monthly basis for two years. Relapse and recurrence were treated in a systematic manner. RESULTS: The cumulative probability of surviving for two years without relapse or recurrence was 74%. Of the 14 patients who suffered recurrence following recovery from the index episode, all responded to a change of treatment, and 71% remained well for the remainder of the study. The risk of recurrence was significantly increased by a delayed response to treatment of the index episode. CONCLUSIONS: Continuation and maintenance treatment with full-dose antidepressant medication, frequent follow-up, and vigorous treatment of relapses and recurrences, were associated with a good outcome in this group of elderly patients.

Age of Onset↗
PubMed1997

Epidemiology and comorbidity of anxiety disorders in later life: implications for treatment.

Anxiety disorders have a peak age of onset in early adulthood and their prevalence and incidence decline in later life. Most cases of anxiety disorder in late life are chronic, having persisted from younger years. Generalized anxiety and agoraphobia account for most cases of late-onset anxiety. Late-onset generalized anxiety is usually associated with a depressive illness. On the other hand, most individuals with late-onset agoraphobia do not have comorbid depression or a history of panic attacks, and the illness often starts after a traumatic event. Case reports and uncontrolled trials indicate that older persons with anxiety disorders can respond to the same treatments that have been found to be efficacious in younger patients, although it is unknown whether the two groups have similar rates of response. The current clinical reality is that most cases of anxiety disorder in late life are undetected and, when treatment is given, benzodiazepines are overused and antidepressants and behavioral treatments are underused. The high rate of comorbidity between late-onset generalized anxiety and depression in old age suggests that antidepressant medication, rather than benzodiazepines, should be the treatment of choice for this condition.

Aged↗
PubMed1997

Anxious depression in elderly patients. Response to antidepressant treatment.

The authors asked whether elderly patients with anxious depression were less responsive to antidepressant treatment than nonanxious depressed patients. A group of 101 depressed patients were treated with 6 weeks of nortriptyline and then, if necessary, 2 weeks of adjunctive lithium. Patients who did not respond to or were intolerant of this first line of treatment were then given 6 weeks of phenelzine (+/- lithium augmentation). Finally, patients failing this second line of treatment were given either a course of electroconvulsive therapy or 6 weeks of fluoxetine (+/- lithium augmentation). Based on their score on the Hospital Anxiety and Depression Scale at index assessment, subjects were divided into anxious and nonanxious groups. Anxious depressed patients were significantly less responsive to nortriptyline on both intent-to-treat and efficacy analyses. They were also more likely to discontinue treatment and, as a result, were significantly less responsive on the intent-to-treat analysis for overall treatment. These results suggest that concurrent symptoms of anxiety have prognostic importance in geriatric depression.

Aged↗
PubMed1996

The effect of sequential antidepressant treatment on geriatric depression.

This study evaluated the outcome of elderly depressed patients who were refractory to, or intolerant of, an initial trial of nortriptyline and who then underwent systematic treatment with other antidepressant therapies. 101 patients entered the study and 61% responded to nortriptyline, 64% of patients who did not improve with nortriptyline eventually responded to other antidepressant treatments. Response to second-line treatment (phenelzine) was significantly slower than response to the tricyclic antidepressant. Treatment nonresponders were more likely to have a longer episode length at index assessment and higher baseline anxiety scores compared with responders. This study demonstrates the importance of persisting with systematic antidepressant therapy in elderly patients who do not respond to the first trial of treatment.

Aged↗
PubMed1996

Identification of p130(cas) as a substrate for the cytosolic protein tyrosine phosphatase PTP-PEST.

PTP-PEST is a ubiquitously expressed, cytosolic, mammalian protein tyrosine phosphatase (PTP) which exhibits high specific activity in vitro. We have investigated the substrate specificity of PTP-PEST by a novel substrate-trapping approach in combination with in vitro dephosphorylation experiments. We initially identified a prominent 130-kDa tyrosine-phosphorylated protein in pervanadate-treated HeLa cell lysates which was preferentially dephosphorylated by PTP-PEST in vitro. In order to identify this potential substrate, mutant (substrate-trapping) forms of PTP-PEST were generated which lack catalytic activity but retain the ability to bind substrates. These mutant proteins associated in stable complexes exclusively with the same 130-kDa protein, which was identified as p130(cas) by immunoblotting. This exclusive association was observed in lysates from several cell lines and in transfected COS cells, but was not observed with other members of the PTP family, strongly suggesting that p130(cas) represents a major physiologically relevant substrate for PTP-PEST. Our studies suggest potential roles for PTP-PEST in regulation of p130(cas) function. These functions include mitogen- and cell adhesion-induced signalling events and probable roles in transformation by various oncogenes. These results provide the first demonstration of a PTP having an inherently restricted substrate specificity in vitro and in vivo. The methods used to identify p130(cas) as a specific substrate for PTP-PEST are potentially applicable to any PTP and should therefore prove useful in determining the physiological substrates of other members of the PTP family.

Animals↗
PubMed1996

Circadian rhythms and psychiatric disorders in the elderly.

This article reviews changes in circadian rhythms that have been reported to occur in the elderly psychiatric population. Data relating to circadian changes in normal aging are included where relevant. Information was obtained from: (1) a computerized MEDLINE search from 1975 to May 1996; (2) a review of bibliographies of papers obtained through the computerized search; and (3) texts on chronobiology. We could not locate any information relating to circadian rhythms and mania, anxiety, or paranoid disorders in old age. Disruption to the sleep/wake cycle, temperature, melatonin, and motor activity rhythms have been reported in dementia and depression, and disruption to some neuroendocrine and cardiovascular rhythms are reported in dementia. Disruption to circadian rhythmicity has implications for the management of dementia patients: for example, the sleep/wake and behavioral disturbances, and for the long-term management of mood disorders. A number of circadian markers have not been studied and several patient groups have received no research attention to date.

Aged↗
PubMed1995

Determination of in vivo phosphorylation sites in protein kinase C.

The primary structure of rat protein kinase C beta II was probed by high pressure liquid chromatography directly coupled to an electrospray ionization mass spectrometer and by high energy collision-induced dissociation analysis to identify in vivo phosphorylation sites. The N-terminal methionine was found to be cleaved post-translationally and replaced with an acetyl group. Four phosphopeptides were identified. Two peptides, Thr500-Lys520 and Glu490-Lys520, are phosphorylated at Thr500 greater than 90%. Peptide His636-Arg649 is phosphorylated about 75% at Thr641. It is the only site that was previously identified during the in vitro autophosphorylation studies (Flint, A.J., Paladini, R.D., and Koshland, D.E., Jr. (1990) Science 249, 408-411). The fourth peptide Asn650-Lys672 is phosphorylated at Thr660. A discussion of the potential implication of these results follows.

Amino Acid Sequence↗
PubMed1995

Structural basis for phosphotyrosine peptide recognition by protein tyrosine phosphatase 1B.

The crystal structures of a cysteine-215-->serine mutant of protein tyrosine phosphatase 1B complexed with high-affinity peptide substrates corresponding to an autophosphorylation site of the epidermal growth factor receptor were determined. Peptide binding to the protein phosphatase was accompanied by a conformational change of a surface loop that created a phosphotyrosine recognition pocket and induced a catalytically competent form of the enzyme. The phosphotyrosine side chain is buried within the period and anchors the peptide substrate to its binding site. Hydrogen bonds between peptide main-chain atoms and the protein contribute to binding affinity, and specific interactions of acidic residues of the peptide with basic residues on the surface of the enzyme confer sequence specificity.

Binding Sites↗
PubMed1995

Effects of respite care on patients with dementia and their caregivers.

The purpose of the literature review discussed in this article was to determine the effect of formal respite care on patients with dementia and their caregivers. Three computerized databases were searched for relevant English language articles published from 1975 to 1994, and the bibliographies of retrieved articles were systematically reviewed for additional references. Five studies met the following inclusion criteria: original research; controlled trial of a defined respite intervention; sample including a dementia population; and at least one outcome measure relating to at least one of eight specified caregiver and patient variables. Four studies met validity criteria and were included for the review. There was little evidence that formal respite care has a significant effect on caregivers' burden, psychiatric status, or physical health; or on patients' cognition, function, physical health, or rate of institutionalization. However, given the small number of controlled studies found and their methodological and conceptual limitations, these data should be interpreted with caution.

Caregivers↗
PubMed1995

Urinary incontinence associated with dementia.

Urinary incontinence is common in patients with dementia and is more prevalent in demented than in nondemented older individuals. It occurs with equal or greater frequency in males than in females, and this contrasts with the female preponderance in community-based, general older populations. Since the etiology of incontinence in dementia is multifactorial, a comprehensive assessment of factors within and outside the lower urinary tract is essential. A careful clinical evaluation is sufficient to guide treatment in most cases. Further research is needed to determine the role of simple cystometry and more complex urodynamic investigation in these patients. Research on the management of urinary incontinence in demented patients has focused almost exclusively on toileting programs and drug treatments for detrusor hyperactivity. To date, anticholinergic and antispasmodic medications have not been shown to be effective in treating incontinence in demented persons. However, the few studies undertaken have been in the most severely mentally and physically deteriorated patients, and it is possible that these medications have greater efficacy in less impaired individuals. Prompted voiding regimens have been shown to reduce incontinence by an average of 32% and appear to be a useful approach in managing incontinence in some of these patients. However, unless staff management systems are employed, staff compliance with these programs diminishes with time and the labor costs involved may limit their applicability in nursing homes. Patients who are the most severely cognitively impaired, least mobile, and have the greatest frequency of incontinence derive the least benefit from toileting programs, and palliative measures may be more appropriate in these cases.

Aged↗
PubMed1994

Purification and crystallization of the catalytic domain of human protein tyrosine phosphatase 1B expressed in Escherichia coli.

The amino-terminal 321 residues encoding the catalytic domain of human protein tyrosine phosphatase 1B (molecular mass 37 kDa) has been expressed in Escherichia coli, purified to homogeneity and crystallized. The crystals diffract to 2.4 A resolution when exposed to synchrotron radiation and belong to space group P3(1)21 (or its enantiomorph P3(2)21) with a = 88.4 A, b = 88.4 A, c = 104.0 A, alpha = beta = 90.0 degrees, gamma = 120.0 degrees. There is one molecule of protein tyrosine phosphatase 1B per asymmetric unit and the crystal form is suitable for the determination of the atomic structure of the enzyme.

Amino Acid Sequence↗