Biomedical subjects

J T Parsons

Publications and source records attributed to J T Parsons.

At least 37 records · Page 2Linked to original sources

PubMed2001

A significant increase in both basal and maximal calcineurin activity in the rat pilocarpine model of status epilepticus.

This study focused on the effects of status epilepticus on the activity of calcineurin, a neuronally enriched, calcium-dependent phosphatase. Calcineurin is an important modulator of many neuronal processes, including learning and memory, induction of apoptosis, receptor function and neuronal excitability. Therefore, a status epilepticus-induced alteration of the activity of this important phosphatase would have significant physiological implications. Status epilepticus was induced by pilocarpine injection and allowed to continue for 60 min. Brain region homogenates were then assayed for calcineurin activity by dephosphorylation of p-nitrophenol phosphate. A significant status epilepticus-dependent increase in both basal and Mn(2+)-dependent calcineurin activity was observed in homogenates isolated from the cortex and hippocampus, but not the cerebellum. This increase was resistant to 150 nM okadaic acid, but sensitive to 50 microM okadaic acid. The increase in basal activity was also resistant to 100 microM sodium orthovanadate. Both maximal dephosphorylation rate and substrate affinity were increased following status epilepticus. However, the increase in calcineurin activity was not found to be due to an increase in calcineurin enzyme levels. Finally, increase in calcineurin activity was found to be NMDA-receptor activation dependent. The data demonstrate that status epilepticus resulted in a significant increase in both basal and maximal calcineurin activity.

Animals↗

PubMed2001

Chronic inhibition of cortex microsomal Mg(2+)/Ca(2+) ATPase-mediated Ca(2+) uptake in the rat pilocarpine model following epileptogenesis.

In the rat pilocarpine model, 1 h of status epilepticus caused significant inhibition of Mg(2+)/Ca(2+) ATPase-mediated Ca(2+) uptake in cortex endoplasmic reticulum (microsomes) isolated immediately after the status episode. The rat pilocarpine model is also an established model of acquired epilepsy. Several weeks after the initial status epilepticus episode, the rats develop spontaneous recurrent seizures, or epilepsy. To determine whether inhibition of Ca(2+) uptake persists after the establishment of epilepsy, Ca(2+) uptake was studied in cortical microsomes isolated from rats displaying spontaneous recurrent seizures for 1 year. The initial rate and total Ca(2+) uptake in microsomes from epileptic animals remained significantly inhibited 1 year after the expression of epilepsy compared to age-matched controls. The inhibition of Ca(2+) uptake was not due to individual seizures nor an artifact of increased Ca(2+) release from epileptic microsomes. In addition, the decreased Ca(2+) uptake was not due to either selective isolation of damaged epileptic microsomes from the homogenate or decreased Mg(2+)/Ca(2+) ATPase protein in the epileptic microsomes. The data demonstrate that inhibition of microsomal Mg(2+)/Ca(2+) ATPase-mediated Ca(2+) uptake in the pilocarpine model may underlie some of the long-term plasticity changes associated with epileptogenesis.

Animals↗

PubMed2001

Serine phosphorylation of focal adhesion kinase in interphase and mitosis: a possible role in modulating binding to p130(Cas).

Focal adhesion kinase (FAK) is an important regulator of integrin signaling in adherent cells and accordingly its activity is significantly modulated during mitosis when cells detach from the extracellular matrix. During mitosis, FAK becomes heavily phosphorylated on serine residues concomitant with its inactivation and dephosphorylation on tyrosine. Little is known about the regulation of FAK activity by serine phosphorylation. In this report, we characterize two novel sites of serine phosphorylation within the C-terminal domain of FAK. Phosphorylation-specific antibodies directed to these sites and against two previously characterized sites of serine phosphorylation were used to study the regulated phosphorylation of FAK in unsynchronized and mitotic cells. Among the four major phosphorylation sites, designated pS1-pS4, phosphorylation of pS1 (Ser722) is unchanged in unsynchronized and mitotic cells. In contrast, pS3 and pS4 (Ser843 and Ser910) exhibit increased phosphorylation during mitosis. In vitro peptide binding experiments provide evidence that phosphorylation of pS1 (Ser722) may play a role in modulating FAK binding to the SH3 domain of the adapter protein p130(Cas).

Animals↗

PubMed2001

Selective expression of an endogenous inhibitor of FAK regulates proliferation and migration of vascular smooth muscle cells.

Extracellular matrix signaling via integrin receptors is important for smooth muscle cell (SMC) differentiation during vasculogenesis and for phenotypic modulation of SMCs during atherosclerosis. We previously reported that the noncatalytic carboxyl-terminal protein binding domain of focal adhesion kinase (FAK) is expressed as a separate protein termed FAK-related nonkinase (FRNK) and that ectopic expression of FRNK can attenuate FAK activity and integrin-dependent signaling (A. Richardson and J. T. Parsons, Nature 380:538-540, 1996). Herein we report that in contrast to FAK, which is expressed ubiquitously, FRNK is expressed selectively in SMCs, with particularly high levels observed in conduit blood vessels. FRNK expression was low during embryonic development, was significantly upregulated in the postnatal period, and returned to low but detectable levels in adult tissues. FRNK expression was also dramatically upregulated following balloon-induced carotid artery injury. In cultured rat aortic smooth muscle cells, overexpression of FRNK attenuated platelet-derived growth factor (PDGF)-BB-induced migration and also dramatically inhibited [(3)H]thymidine incorporation upon stimulation with PDGF-BB or 10% serum. These effects were concomitant with a reduction in SMC proliferation. Taken together, these data indicate that FRNK acts as an endogenous inhibitor of FAK signaling in SMCs. Furthermore, increased FRNK expression following vascular injury or during development may alter the SMC phenotype by negatively regulating proliferative and migratory signals.

Adenoviridae↗

PubMed2001

A double epidemic: crystal methamphetamine drug use in relation to HIV transmission among gay men.

Emerging research on methamphetamine use among gay men suggests that growth in the use of this drug could present serious problems for HIV/AIDS prevention within the gay community. This article summarizes current studies on the extent, role, and context of methamphetamine use among gay men and its relationship to high risk sexual behaviors related to HIV transmission. Methamphetamine is often used by gay men to initiate, enhance, and prolong sexual encounters. Use of the drug is, therefore, associated with particular environments where sexual contact among gay men is promoted, such as sex clubs and large "circuit" parties. Research with gay and bisexual men indicates that methamphetamine use is strongly associated with risky sexual behaviors that may transmit HIV. This relationship, coupled with emerging evidence that methamphetamine use is on the rise among gay men, suggests that the drug could exacerbate the HIV/AIDS epidemic among this community. The article offers recommendations for further research and suggestions for prevention programs regarding methamphetamine use by gay men.

Adult↗

PubMed2001

Awareness and use of untested barrier methods by HIV-seropositive gay and bisexual men.

Little is known about HIV-seropositive men's awareness and use of untested barrier methods during anal intercourse. A sample of 240 HIV-seropositive men (69.2% men of color) completed a self-administered survey that included items on nonoxynol-9 (N-9), female condoms, and the simultaneous use of two male condoms (double bagging). Most participants (79.6%) had heard of N-9 being used to prevent HIV transmission during anal intercourse. Of these, 20.0% rated N-9 as more effective than condoms, and 14.6% had used N-9 instead of condoms. Fewer men (35.4%) were aware of female condoms being used during anal intercourse. Overall, few respondents (5.4%) had used female condoms; 53.8% of whom rated the device as more pleasurable than male condoms. Most men (69.6%) had heard of double bagging, and 35.2% had engaged in this practice. Of these, 45.1% rated the practice as less pleasurable than using a single condom. Few associations were observed between participant characteristics and the awareness or use of these barrier methods. The widespread use of these untested methods emphasizes the urgent need to further educate HIV-seropositive men about the potential risks of N-9 use and to test the effectiveness of other strategies that may serve as alternatives to male condom use.

Bisexuality↗

PubMed2000

Identification of two focal adhesion targeting sequences in the adapter molecule p130(Cas).

The adapter molecule CAS is localized primarily within focal adhesions in fibroblasts. Because many of the cellular functions attributed to CAS are likely to be dependent on its presence in focal adhesions, this study was undertaken to identify regions of the protein that are involved in its localization. The SH3 domain of CAS, when expressed in isolation from the rest of the protein, was able to target to focal adhesions, whereas a variant containing a point mutation that rendered the SH3 domain unable to associate with FAK remained cytoplasmic. However, in the context of full-length CAS, this mutation did not prevent CAS localization to focal adhesions. Two other variants of CAS that contained deletions of either the SH3 domain alone, or the SH3 domain together with an adjoining proline-rich region, also retained the capacity to localize to focal adhesions. A second focal adhesion targeting region was mapped to the extreme carboxy terminus of CAS. The identification of this second focal adhesion targeting domain in CAS ascribes a previously unknown function to the highly conserved C terminus of CAS. The regulated targeting of CAS to focal adhesions by two independent domains may reflect the important role of CAS within this subcellular compartment.

Animals↗

PubMed2000

Structure of the BH domain from graf and its implications for Rho GTPase recognition.

Cellular signaling by small G-proteins is down-regulated by GTPase-activating proteins (GAPs), which increase the rate of GTP hydrolysis. The GTPase regulator associated with focal adhesion kinase (Graf) exhibits GAP activity toward the RhoA and Cdc42 GTPases, but is only weakly active toward the closely related Rac1. We determined the crystal structure of a 231-residue fragment of Graf (GrafGAP), a domain containing the GAP activity, at 2.4-A resolution. The structure clarifies the boundaries of the functional domain and yields insight to the mechanism of substrate recognition. Modeling its interaction with substrate suggested that a favorable interaction with Glu-95 of Cdc42 (Glu-97 of RhoA) would be absent with the corresponding Ala-95 of Rac1. Indeed, GrafGAP activity is diminished approximately 40-fold toward a Cdc42 E95A mutant, whereas a approximately 10-fold increase is observed for a Rac1 A95E mutant. The GrafGAP epitope that apparently interacts with Glu-95(Glu-97) contains Asn-225, which was recently found mutated in some myeloid leukemia patients. We conclude that position 95 of the GTPase is an important determinant for GrafGAP specificity in cellular function and tumor suppression.

Amino Acid Sequence↗

PubMed2000

Focal adhesion kinase: a regulator of focal adhesion dynamics and cell movement.

Engagement of integrin receptors with extracellular ligands gives rise to the formation of complex multiprotein structures that link the ECM to the cytoplasmic actin cytoskeleton. These adhesive complexes are dynamic, often heterogeneous structures, varying in size and organization. In motile cells, sites of adhesion within filopodia and lamellipodia are relatively small and transient and are referred to as 'focal complexes,' whereas adhesions underlying the body of the cell and localized to the ends of actin stress fibers are referred to as 'focal adhesions'. Signal transduction through focal complexes and focal adhesions has been implicated in the regulation of a number of key cellular processes, including growth factor induced mitogenic signals, cell survival and cell locomotion. The formation and remodeling of focal contacts is a dynamic process under the regulation of protein tyrosine kinases and small GTPases of the Rho family. In this review, we consider the role of the focal complex associated protein tyrosine kinase, Focal Adhesion Kinase (FAK), in the regulation of cell movement with the emphasis on how FAK regulates the flow of signals from the ECM to the actin cytoskeleton.

Actins↗

PubMed2000

Cortactin localization to sites of actin assembly in lamellipodia requires interactions with F-actin and the Arp2/3 complex.

Cortactin is an actin-binding protein that is enriched within the lamellipodia of motile cells and in neuronal growth cones. Here, we report that cortactin is localized with the actin-related protein (Arp) 2/3 complex at sites of actin polymerization within the lamellipodia. Two distinct sequence motifs of cortactin contribute to its interaction with the cortical actin network: the fourth of six tandem repeats and the amino-terminal acidic region (NTA). Cortactin variants lacking either the fourth tandem repeat or the NTA failed to localize at the cell periphery. Tandem repeat four was necessary for cortactin to stably bind F-actin in vitro. The NTA region interacts directly with the Arp2/3 complex based on affinity chromatography, immunoprecipitation assays, and binding assays using purified components. Cortactin variants containing the NTA region were inefficient at promoting Arp2/3 actin nucleation activity. These data provide strong evidence that cortactin is specifically localized to sites of dynamic cortical actin assembly via simultaneous interaction with F-actin and the Arp2/3 complex. Cortactin interacts via its Src homology 3 (SH3) domain with ZO-1 and the SHANK family of postsynaptic density 95/dlg/ZO-1 homology (PDZ) domain-containing proteins, suggesting that cortactin contributes to the spatial organization of sites of actin polymerization coupled to selected cell surface transmembrane receptor complexes.

Actin-Related Protein 2↗

PubMed2000

A role for focal adhesion kinase in phenylephrine-induced hypertrophy of rat ventricular cardiomyocytes.

A variety of agonists including phenylephrine (PE) induce hypertrophy in neonatal ventricular cardiomyocytes. Here we report that signals provided by extracellular matrix proteins (ECM) augment the PE-induced hypertrophic response of cardiomyocytes and provide evidence that ECM-dependent signaling is mediated in part by the protein tyrosine kinase, focal adhesion kinase (FAK). Addition of PE to cultured neonatal cardiomyocytes stimulated sarcomeric organization, increased cell size, and induced atrial natriuretic factor in cardiomyocytes plated on the ECM protein laminin or fibronectin. In contrast, cardiomyocytes plated on the non-adhesive substrate gelatin exhibited a reduced capacity to undergo these PE-stimulated hypertrophic changes. In cardiomyocytes cultured on ECM, PE stimulated a rapid increase in tyrosine phosphorylation of focal adhesion proteins including FAK, paxillin, and p130 Crk-associated substrate and subsequent formation of peripheral focal complexes. Inhibition of the PE-induced hypertrophic response by genistein and herbimycin-A indicated a requirement for protein tyrosine kinases in PE signaling. To determine whether activation of FAK is required for PE-induced hypertrophy, a dominant-interfering mutant form of FAK, termed FRNK (FAK-related non-kinase), was ectopically expressed in cardiomyocytes using a replication-defective adenovirus expression system. FRNK expression attenuated PE-stimulated hypertrophy as assessed by cell size, sarcomeric organization, and induction of atrial natriuretic factor. These data indicate that the signal transduction pathways leading to cardiomyocyte hypertrophy are strongly influenced by and/or dependent upon an integrin-mediated signaling process requiring FAK.

Animals↗

PubMed2000

Skin cancer of the head and neck with clinical perineural invasion.

PURPOSE: To review treatment and outcomes in 62 patients with clinical and/or gross evidence of perineural invasion from skin cancer of the head and neck. METHODS AND MATERIALS: Sixty-two patients received radiotherapy at the University of Florida as part or all of their treatment between January 1965 and April 1995. All patients had clinical signs and symptoms of perineural involvement and/or documentation of tumor extending to grossly involve nerve(s). Twenty-one patients underwent therapy for previously untreated lesions, including 12 who received radiotherapy alone and nine who had surgery with postoperative radiotherapy. Forty-one patients underwent therapy for recurrent lesions, including 18 treated with radiotherapy alone and 23 who received preoperative or postoperative radiotherapy. RESULTS: Factors on multivariate analysis that predicted local control included patient age, previously untreated vs. recurrent lesions, presence of clinical symptoms, and extent of radiotherapy fields. Recurrence patterns were predominantly local; 26 of 31 patients (84%) who developed local recurrence after treatment had recurrent cancer limited to the primary site. CONCLUSIONS: Many patients with skin cancer and symptomatic perineural invasion have disease that is incompletely resectable. Approximately half these patients will be cured with aggressive irradiation alone or combined with surgery. Age, prior treatment, and clinical symptoms influence the likelihood of cure.

Adult↗

PubMed2000

Perceptions of the benefits and costs associated with condom use and unprotected sex among late adolescent college students.

To assess the differential effects of the perceived benefits and costs associated with both condom use and unprotected sex on sexual risk behaviors, data were collected from 704 ethnically diverse male and female sexually experienced late adolescent college students (aged 17-25). Perceived benefits and costs for condom use and perceived benefits and costs for unprotected sex were measured separately through an anonymous self-report survey. In addition, participants completed measures of self-efficacy for practicing safer sex and temptation for unsafe sex in various situations, and three measures of sexual risk-taking (stage of change for condom use, consistency of condom use during the past month, and whether or not a condom was used for the last act of intercourse). Univariate analyses indicated that benefits and costs of condom use, benefits of unprotected sex, self-efficacy and situational temptation were all related to sexual risk-taking. Gender differences were identified, with females reporting more benefits of condom use and costs of unprotected sex, fewer benefits of unprotected sex and costs of condom use, greater self-efficacy for practicing safer sex, and less situational temptation for unsafe sex. Multivariate analyses indicated that sexual risk behaviors were most related to situational temptation, self-efficacy for safer sex, and perceived benefits of unprotected sex. The results suggest that, among late adolescents, perceived benefits of the unhealthy behavior (unprotected sex) were better determinants of sexual risk-taking than were perceived benefits (or costs) associated with the healthy behavior (condom use). Perceived costs associated with unprotected sex were unrelated to sexual behaviors. These findings support previous work identifying adolescents as more driven by their perceptions of the positive benefits associated with risky behaviors, rather than knowledge of the costs or dangers involved in risk-taking.

Acquired Immunodeficiency Syndrome↗

PubMed2000

Maintenance of safer sexual behaviours: evaluation of a theory-based intervention for HIV seropositive men with haemophilia and their female partners.

A theory-based HIV risk-reduction intervention was developed for HIV-positive men with haemophilia and their HIV-negative female romantic partners. The intervention was based on Prochaska and DiClemente's Transtheoretical Model which describes behaviour change as an incremental, stage-based process. The intervention targeted both communication about safer sex and safer sex behaviours (consistent condom use or abstinence from vaginal intercourse). A total of 255 males and 158 females from six funded haemophilia treatment centres or patient organizations (and 27 associated subsites) participated in the study. Baseline and follow-up (15 months after baseline) measures were administered to assess safer sexual behaviours, communication about safer sex and condom self-efficacy. A quasi-experimental, repeated measures design was utilized to compare two naturally occurring groups; those who received the full intervention package and those who received incomplete or no intervention components. Significant intervention effects for safer sex behaviours, communication about safer sex and condom self-efficacy were identified for the male participants, with those receiving the full intervention package demonstrating better outcomes at follow-up. Women who received the full intervention package were more likely to report the use of a condom by their male partner during the last act of vaginal intercourse.

Adult↗

PubMed2000

Pilocarpine-induced status epilepticus causes N-methyl-D-aspartate receptor-dependent inhibition of microsomal Mg(2+)/Ca(2+) ATPase-mediated Ca(2+) uptake.

Status epilepticus is associated with sustained and elevated levels of cytosolic Ca(2+). To elucidate the mechanisms associated with changes of cytosolic Ca(2+) after status epilepticus, this study was initiated to evaluate the effect of pilocarpine-induced status epilepticus on Mg(2+)/Ca(2+) ATPase-mediated Ca(2+) uptake in microsomes isolated from rat cortex, because the Ca(2+) uptake mechanism plays a major role in regulating intracellular Ca(2+) levels. The data demonstrated that the initial rate and overall Ca(2+) uptake in microsomes from pilocarpine treated animals were significantly inhibited compared with those in microsomes from saline-treated control animals. It was also shown that the inhibition of Ca(2+) uptake caused by status epilepticus was not an artifact of increased Ca(2+) release from microsomes, selective isolation of damaged microsomes from the homogenate, or decreased Mg(2+)/Ca(2+) ATPase protein in the microsomes. Pretreatment with the NMDA antagonist dizocilpine maleate blocked status epilepticus-induced inhibition of the initial rate and overall Ca(2+) uptake. The data suggest that inhibition of microsomal Mg(2+)/Ca(2+) ATPase Ca(2+) uptake is involved in NMDA-dependent deregulation of cytosolic Ca(2+) homeostasis associated with status epilepticus.

Animals↗

PubMed2000

Altered fractionation in definitive irradiation of squamous cell carcinoma of the head and neck.

The likelihood of local control after radiation therapy may be improved by increasing total dose or decreasing overall time. The probability of late complications increases with dose per fraction. Altered fractionation techniques usually employ two or more fractions per day using a dose per fraction that is similar or less than that employed in conventional fractionation. Altered fractionation may be broadly classified as hyperfractionation or accelerated fractionation. Data suggest that altered fractionation schedules may improve local control (and to a lesser extent, survival) compared with conventional irradiation.

Carcinoma, Squamous Cell↗

PubMed2000

Laryngeal or hypopharyngeal squamous cell carcinoma: can follow-up CT after definitive radiation therapy be used to detect local failure earlier than clinical examination alone?

PURPOSE: To determine if follow-up computed tomography (CT) after definitive radiation therapy for laryngeal or hypopharyngeal (laryngopharyngeal) carcinoma allows the detection of local failure earlier than clinical examination alone. MATERIALS AND METHODS: Pre- and post-radiation therapy follow-up CT scans in 66 patients were reviewed retrospectively. All patients underwent definitive hyperfractionated radiation therapy and were followed up clinically for at least 2 years after its completion. Post-radiation therapy CT scans (N = 153) were evaluated for posttreatment changes with a three-point score: A score of 1 represented expected posttreatment changes; 2, focal mass with a maximal diameter of less than 1 cm and/or asymmetric obliteration of laryngeal tissue planes; or 3, focal mass with a maximal diameter equal to or greater than 1 cm or estimated tumor volume reduction of less than 50%. All patients underwent the first posttreatment CT study 1-6 months after therapy. New or progressive laryngeal cartilage changes were noted. The clinical impression of the larynx at the time of each follow-up CT scan was also recorded. RESULTS: In 12 of 29 (41%) patients with treatment failure at the primary site, follow-up CT scans were definite for local failure (score, 3) a mean of 5.5 months (median, 3.5 months; range, 1-17 months) before clinical examination results. CONCLUSION: In many patients, follow-up CT shows local failure earlier than does clinical examination alone.

Adult↗

PubMed2000

Sexual behavior change among human immunodeficiency virus-infected adolescents with hemophilia. Adolescent Hemophilia Behavioral Intervention Evaluation Project Study Group.

PURPOSE: To determine the factors associated with the adoption or maintenance of consistent safer sexual behaviors among human immunodeficiency virus-positive adolescents and young adults with hemophilia. METHODS: One hundred eleven adolescents at 10 hemophilia care sites participated in an intervention program designed to increase safer sexual behaviors (abstinence, condom use, or nonpenetrative behavior). The theory-based intervention spanned 1 year. Adolescents attended individual sessions, small group activities, and an intensive group retreat. RESULTS: Patients who maintained or improved safer sexual behaviors were compared with those who relapsed or did not improve. Logistic regression analyses found that improvement and maintenance of safer sexual behavior were significantly associated with perceived peer support for outercourse (odds ratio [OR]: 5.47; confidence interval [CI]: 1.4-20.8), perceived peer support for abstinence (OR: 5.08; CI: 1.2-20.1), and decreased general emotional distress (OR: 4.65; CI: 1.04-20.6). Perceived health status and previous sexual behavior were unrelated to change in safer sexual behavior. CONCLUSIONS: These longitudinal data indicate that improvement and maintenance of safer sexual behavior among adolescents during an intervention is strongly associated with perceptions of peer support for safer sex and lesser degrees of emotional distress. Programs for human immunodeficiency virus-infected adolescents may require developmentally appropriate social and psychological approaches to impact peer norms and emotional well-being.

Adolescent↗