RESUMO
The objective of this study was to understand how women living with the BRCA1 and BRCA2 genetic mutation adapt to this life transition and to identify the main adaptive tasks. A qualitative inquiry inspired by grounded theory revealed that participants cognitively appraised their test result in the same manner as women who have been diagnosed with breast cancer. Consequently, participants had to adapt to a condition that they perceived as a chronic illness. The following three main tasks were identified: Physical Task: Attempting to Limit the Impact of the Test Result, Psychological Task: Living with Uncertainty, and Social Task: Finding Effective Support. In conclusion, although these women live with the possibility of developing breast cancer, their experiences mirror those of individuals living with a chronic illness, and they must therefore adapt accordingly in a physical, psychological, and social manner.
Assuntos
Adaptação Psicológica , Neoplasias da Mama/psicologia , Predisposição Genética para Doença/psicologia , Testes Genéticos , Mulheres/psicologia , Neoplasias da Mama/genética , Neoplasias da Mama/prevenção & controle , Doença Crônica/psicologia , Feminino , Genes BRCA1 , Genes BRCA2 , Comportamentos Relacionados com a Saúde , Heterozigoto , Humanos , Modelos Psicológicos , Mutação/genética , Pesquisa Qualitativa , IncertezaRESUMO
Women carrying a BRCA1 or BRCA2 genetic mutation have an up to 80% lifetime risk of developing breast cancer. It is especially important to understand the experiences of these women, as their lives are permeated with the threat of cancer. This qualitative study examined the experiences of six young women of reproductive age (age < 45 years) who were identified as carriers. The analysis of the semi-structured interviews inspired by grounded theory methodology, showed that participants experienced the same type of uncertainty demonstrated by women who have already been diagnosed with breast cancer.
Assuntos
Adaptação Psicológica , Proteína BRCA1/genética , Proteína BRCA2/genética , Neoplasias da Mama/psicologia , Predisposição Genética para Doença/psicologia , Incerteza , Adulto , Neoplasias da Mama/genética , Saúde da Família , Medo , Feminino , Testes Genéticos , Heterozigoto , Humanos , Mutação , Pesquisa Qualitativa , AutoimagemRESUMO
BCL2 protein exerts an antiapoptotic effect on cells and decreases chemosensitivity. To determine whether BCL2 expression is prognostic of patient outcome in acute myelogenous leukemia (AML), we measured its level in 198 newly diagnosed, untreated AML patients by Western blotting using whole-cell lysates from low-density peripheral blood cells. BCL2 expression was not associated with the percentage of blasts (R2 = 0.10), French-American-British classification type, or cytogenetic abnormality. Smoothed martingale residual plots indicated that high BCL2 protein level was an adverse prognostic factor for patients with either favorable or intermediate prognosis cytogenetics [FIPC; inv(16), t(8:21), t(15:17), or diploid or insufficient metaphases] but was a favorable prognostic factor for patients with unfavorable prognosis cytogenetics (UC; -5, -7, +8, 11q23, Ph1, or miscellaneous changes). Patients with FIPC and high BCL2 (highest quartile) had a significantly shorter median survival (78 weeks versus not reached; P = 0.009) than did those with lower (lower three quartiles) levels of BCL2. Among those with UC, as BCL2 level decreased from the fourth quartile to the third or the combined first and second quartiles, the median survival decreased (from 94 to 45 or 17 weeks, respectively; P = 0.003). Lower expression of BCL2 in UC was associated with shorter remission duration (P = 0.05). In multivariate analyses performed using either overall or event-free survival as the end point, for either all patients or within either cytogenetic subgroup, BCL2 level was an independent prognostic factor. Similar analysis revealed that BCL2 level was an independent predictor of remission duration for UC patients as well. These data suggest that BCL2 is involved differently in different types (favorable versus unfavorable) of AML and that therapeutic strategies aimed at modulating BCL2 function may be more likely to work in patients with favorable cytogenetic abnormalities.
Assuntos
Biomarcadores Tumorais/metabolismo , Leucemia Mieloide Aguda/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Western Blotting , Feminino , Humanos , Leucemia Mieloide Aguda/genética , Leucemia Mieloide Aguda/mortalidade , Masculino , Pessoa de Meia-Idade , Análise Multivariada , Prognóstico , Recidiva , Indução de Remissão , Análise de SobrevidaRESUMO
A prior retrospective study suggested that the level of retinoblastoma protein (RB) expression was prognostic for survival in acute myelogenous leukemia (AML). Individuals with no/low RB protein expression were considered to have loss of RB function, and those with maximally phosphorylated (maxphos) RB were also felt to have nonfunctional RB. To confirm this, we prospectively investigated whether the level of RB expression was prognostic in AML in a larger cohort of patients. RB level was measured by Western blot and immunohistochemical analysis on peripheral blood samples from 210 newly diagnosed AML patients. Patients were divided into three groups based on the level of RB protein expression (i.e., no or low, elevated, and maxphos) or into two groups on the basis of presumed RB function, altered function (AF-RB, low and maxphos RB), versus normal function (NF-RB, elevated RB). By combined results of Western blot and immunohistochemical analysis, 20%, 65%, and 15% of patients had low, elevated, and maxphos RB, respectively. Most patients with acute promyelocytic leukemia (APL) with a French-American-British classification of M3 were in the low RB group, likely reflecting a lower proliferative rate of promyelocytes. Analysis was performed with and without these APL patients. The median survival was significantly shorter for both patients with low RB expression (48 weeks, P = 0.05, including APL patients; 34 weeks, corrected P = 0.008, with APL patients excluded) and maxphos RB expression (51 weeks, P = 0.007) compared to those with elevated RB expression (122 weeks including and 98 weeks excluding APL patients). Differences were greatest among patients with nonfavorable prognosis cytogenetics (median survival, 34 weeks versus 85 weeks; corrected P = 0.001 for AF-RB versus NF-RB). Remission duration was also significantly shorter for non-APL patients with AF-RB versus NF-RB (median survival, 36 weeks versus not reached; corrected P = 0.02). In multivariate analyses, including cytogenetics, performance status, age, antecedent hematological disorder, and RB status, with and without APL patients included, no/low and maxphos-RB protein expression were independent predictors for poorer survival. This prospective study confirms that the level of expression of RB is a strong prognostic factor in AML, with an inferior survival experience being associated with no/low RB and maxphos RB expression. Therefore, therapeutic decisions based on the level of RB expression may be indicated, and protocols to incorporate this are currently under development.
Assuntos
Leucemia Mieloide Aguda/metabolismo , Proteína do Retinoblastoma/metabolismo , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Leucemia Mieloide Aguda/classificação , Leucemia Mieloide Aguda/diagnóstico , Masculino , Pessoa de Meia-Idade , Análise Multivariada , Fosforilação , Prognóstico , Estudos ProspectivosRESUMO
Metaphase preparations from 36 patients with acute lymphoblastic leukemia (ALL) have been retrospectively screened by fluorescence in situ hybridization (FISH) to determine the incidence of translocation (12;21) and the potential usefulness of FISH as an adjunct to conventional cytogenetic analysis. With the use of specific chromosome paints, 4 of 31 patients with B-lineage childhood ALL (13%) demonstrated rearrangements of chromosomes 12 and 21, and therefore, were considered to harbor the translocation, which had not previously been detected by conventional karyotyping. However, none of these positive cases revealed the standard reciprocal t(12;21)(p12;q22) as the sole abnormality involving chromosomes 12 and 21. The study confirms the feasibility and advantages of introducing FISH screening for t(12;21) in pediatric ALL cases and demonstrates the usefulness of FISH screening as a backup to concurrent cytogenetic analysis to resolve variant translocations and aberrant results. The presence of t(12;21) has also been correlated to clinical data to assess the prognostic significance of this translocation on its own or in association with other prognostic features.
Assuntos
Cromossomos Humanos Par 12 , Cromossomos Humanos Par 21 , Proteínas de Ligação a DNA , Hibridização in Situ Fluorescente , Leucemia-Linfoma Linfoblástico de Células Precursoras/genética , Proteínas Proto-Oncogênicas , Translocação Genética , Adolescente , Adulto , Idoso , Criança , Pré-Escolar , Subunidade alfa 2 de Fator de Ligação ao Core , Feminino , Humanos , Lactente , Masculino , Pessoa de Meia-Idade , Fatores de Transcrição/genéticaRESUMO
OBJECTIVES: To summarize new knowledge surrounding the physiological activity of tocotrienol, a natural analogue of tocopherol. RESULTS: The biological activity of vitamin E has generally been associated with its well-defined antioxidant property, specifically against lipid peroxidation in biological membranes. In the vitamin E group, alpha-tocopherol is considered to be the most active form. However, recent research has suggested tocotrienol to be a better antioxidant. Moreover, tocotrienol has been shown to possess novel hypocholesterolemic effects together with an ability to reduce the atherogenic apolipoprotein B and lipoprotein(a) plasma levels. In addition, tocotrienol has been suggested to have an anti-thrombotic and anti-tumor effect indicating that tocotrienol may serve as an effective agent in the prevention and/or treatment of cardiovascular disease and cancer. CONCLUSION: The physiological activities of tocotrienol suggest it to be superior than alpha-tocopherol in many situations. Hence, the role of tocotrienol in the prevention of cardiovascular disease and cancer may have significant clinical implications. Additional studies on its mechanism of action, as well as, long-term intervention studies, are needed to clarify its function. From the pharmacological point-of-view, the current formulation of vitamin E supplements, which is comprised mainly of alpha-tocopherol, may be questionable.
Assuntos
Vitamina E/análogos & derivados , Vitamina E/uso terapêutico , Animais , Doenças Cardiovasculares/tratamento farmacológico , Doenças Cardiovasculares/prevenção & controle , Humanos , Neoplasias/tratamento farmacológico , Neoplasias/prevenção & controleRESUMO
Herpetic geometric glossitis, a recently described form of lingual herpes simplex virus type 1 (HSV-1) infection, has been reported in 6 human immunodeficiency virus (HIV) patients and 1 cardiac transplant patient who was receiving immunosuppressant therapy. An HIV-seronegative immunocompromised pediatric patient with acute myelogenous leukemia who developed herpetic geometric glossitis is described. Herpetic geometric glossitis can present in both adult and pediatric immunocompromised patients. The symptoms, morphology, laboratory findings and treatment of this infection are summarized. The possible consequences of untreated herpetic glossitis include superinfection and undernourishment. Although previously described patients responded to 1000 mg per day (divided in 5 doses) or oral acyclovir, with complete resolution of fissures, this patient developed herpetic geometric glossitis while receiving acyclovir and required higher doses of oral antiviral therapy (acyclovir, 3000 mg/day divided in 5 doses) to treat his HSV-1 lingual infection. Empiric treatment of an immunocompromised patient who has newly acquired painful tongue fissures or furrows with systemic acyclovir should be considered.
Assuntos
Glossite/complicações , Herpes Labial/complicações , Leucemia Mieloide Aguda/complicações , Aciclovir/uso terapêutico , Adolescente , Antivirais/uso terapêutico , Glossite/tratamento farmacológico , Glossite/virologia , Soronegatividade para HIV , Herpes Labial/tratamento farmacológico , Herpesvirus Humano 1 , Humanos , Hospedeiro Imunocomprometido , Leucemia Mieloide Aguda/virologia , MasculinoRESUMO
We have established the human hepatoma cell line, HepG2, in a defined, serum-free medium. These cells were maintained and studied over a 100-generation period (i.e. 10 serial transfers). Cells maintained in serum-free medium exhibited growth parameters (i.e. saturation density, efficiency of plating, and population doubling time) similar to those obtained with HepG2 cells maintained in serum-supplemented medium. Serum-free cells were also similar to their serum-supplemented counterparts with respect to the expression of cathepsin B activity and the induction of aryl hydrocarbon hydroxylase by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Significantly, HepG2 cells maintained in serum-free conditions also retained the ability to synthesize and secrete proteins, including the liver plasma protein, apo-lipoprotein B. These results indicate that the serum-free medium used in this study supports the long-term growth and maintenance of human hepatoma, HepG2, cells in culture. Inasmuch as these cells retain phenotypes, including differentiated markers previously reported for their serum-supplemented counterparts, they may provide a more reliable, standardized culture system to study the expression, secretion, and regulation of proteins during biological and pathologic processes.
Assuntos
Apolipoproteínas B/biossíntese , Hidrocarboneto de Aril Hidroxilases/biossíntese , Carcinoma Hepatocelular/metabolismo , Catepsina B/biossíntese , Meios de Cultura Livres de Soro , Células Tumorais Cultivadas/metabolismo , Carcinoma Hepatocelular/enzimologia , Divisão Celular , Proteínas da Matriz Extracelular/análise , Humanos , Proteínas/análise , Células Tumorais Cultivadas/enzimologiaRESUMO
This cross-sectional study explored the relation between mammographic densities (a predictor of breast cancer risk), ethnicity, and dietary factors among women in Hawaii. Thirty-nine postmenopausal women with Japanese, Chinese, Caucasian, and Native Hawaiian ancestry who had received a screening mammogram completed a medical, reproductive, and dietary history. Using a computerized method, we determined the total and the dense area of the breast and calculated the ratio between the two. Blood lipids were measured using standard methods. For statistical analysis, we applied analysis of variance and multiple linear regression. Whereas the mean dense area of the breast was one third smaller in Asian than in Caucasian and Native Hawaiian women, the percent of the breast occupied by dense tissue in the Asian women was slightly higher than in the Caucasian/Hawaiian group, possibly a result of the Asian women's smaller breast size. The exploratory analysis indicated inverse relations of body mass index, high-density lipoprotein cholesterol (HDLC), age at menarche, and soy intake with mammographic densities, as well as direct relations of estrogen use and family history with mammographic densities. The results of this study suggest that variations in these factors may be responsible for ethnic differences in mammographic densities and in breast cancer risk.
Assuntos
Asiático , Neoplasias da Mama/etnologia , Mamografia , População Branca , Índice de Massa Corporal , Neoplasias da Mama/sangue , Neoplasias da Mama/diagnóstico por imagem , Neoplasias da Mama/fisiopatologia , HDL-Colesterol/análise , Estudos Transversais , Feminino , Havaí , Humanos , Pessoa de Meia-IdadeRESUMO
OBJECTIVE: Evaluate the new Active human leptin ELISA available through Diagnostic Systems Laboratories Inc for use in clinical research laboratories. DESIGN: Fasting plasma samples for this study were obtained randomly from human subjects. Precision, linearity, recovery, and interference studies were performed, in addition to method comparison with the conventional leptin RIA method and comparison between laboratories. SETTING: University of Hawaii at Manoa, Division of Medical Technology and the Native Hawaiian Health Research-RCMI laboratory. PARTICIPANTS: Native Hawaiians were selected for this study since this population has consistently demonstrated a higher incidence rate of obesity and Type 2 diabetes and thus, potentially have high leptin levels. RESULTS: At leptin concentrations of 2.3, 16.6, and 45.6 ng/ mL, within-run imprecision (n = 5) ranged from 3.1%, 1.6%, and 4.2%, and the between-run imprecision (n = 10) ranged from 6.8%, 4.1%, and 2.7%. The comparison-of-method gave a linear regression equation of y = 0.92x + 1.6 mg/dL (r = 0.96, n = 74, S(y/x) 2.0) when compared to the Linco human leptin RIA method. The dilution curve showed acceptable linearity within the reportable range of the assay, and the recovery was 88.5% to 112%. No interference was detected with hemoglobin up to 1 g/dL, and with triglyceride, up to 1.8 g/dL. However, bilirubin, 10 mg/dL, did show significant interference. CONCLUSION: Overall, we feel that the new Active Human Leptin assay offers a safe and rapid alternative method appropriate for clinical research laboratories and epidemiological studies.
Assuntos
Ensaio de Imunoadsorção Enzimática/métodos , Leptina/sangue , Ensaio de Imunoadsorção Enzimática/normas , Jejum , Humanos , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
BACKGROUND: Risk factors for drowning are largely undocumented among military populations. HYPOTHESIS: Accident report narratives will provide important information about the role of alcohol use and other behaviors in drownings among active duty male U.S. Army soldiers. METHODS: Using a case series design, we describe drowning deaths reported to the U.S. Army Safety Center (1980-1997), documenting associated demographic factors, alcohol use, and other risk-taking behaviors. RESULTS: Drowning victims (n = 352) were disproportionately young, black, and single, with less time-in-service, and no college experience. Most drownings occurred off-duty (89%). Alcohol use was involved in at least 31% of the cases overall. Alcohol use was also associated with a 10-fold increase in reckless behavior (OR 9.6, 95% Cl 4.5-20.7) and was most common among drownings in Europe (OR = 4.3, 95% Cl 1.5-13.4). Most drownings occurred where no lifeguard was present (68%), but almost two-thirds occurred in the presence of others, with CPR initiated in less than one-third of these cases. Drownings involving minority victims were less likely to involve alcohol, but more likely to occur in unauthorized swimming areas. While most drownings did not involve violations of safety rules, over one-third of the cases involved some form of reckless behavior, particularly for those under age 21. CONCLUSIONS: Intervention programs should be tailored to meet the needs of the demographic subgroups at highest risk since behavioral risk factors vary by race and age. CPR training and skills maintenance can improve survival rates. Narrative data are important for developing hypotheses and understanding risk factors for injuries.
Assuntos
Consumo de Bebidas Alcoólicas , Afogamento/epidemiologia , Militares , Adolescente , Adulto , Humanos , Masculino , Fatores de Risco , Assunção de Riscos , Estados Unidos/epidemiologiaRESUMO
Cerebral palsy is a leading cause of disability in children and reducing its effects on arm function will improve quality of life. Our goal is to train children with CP after wrist tendon transfer surgery using a robotic therapy system consisting of two robot arms and wrist robots. The therapeutic goal is to determine if the robot training combined with surgery intervention improved functional outcomes significantly more than surgery alone. To accomplish this long-term goal we have developed a Bilateral ADL Exercise Robot, BiADLER aimed at training children with CP in reach to grasp coordination on ADLs. Specifically, the robot will provide active training using an assist-as-needed. This paper presents the design concepts.
Assuntos
Atividades Cotidianas , Paralisia Cerebral/reabilitação , Reabilitação/instrumentação , Robótica/instrumentação , Punho/cirurgia , Adolescente , Paralisia Cerebral/cirurgia , Criança , Desenho de Equipamento , Humanos , Reabilitação/métodosAssuntos
Apolipoproteínas B/genética , Insulina/farmacologia , Biossíntese de Proteínas/efeitos dos fármacos , Apolipoproteínas B/biossíntese , Carcinoma Hepatocelular/metabolismo , Sistema Livre de Células , Humanos , Neoplasias Hepáticas/metabolismo , RNA Mensageiro/análise , Células Tumorais CultivadasRESUMO
Insulin modulation of apolipoprotein B gene expression was studied at the translational level by the use of a cell-free translation system from a hepatoma cell-line, HepG2. Extracts of HepG2 cells lysed with lysolecithin were found to have high in vitro protein synthesizing activity utilizing endogenous mRNA. The level of peptide chain initiation was high, as suggested by a significant inhibition of translation by edeine. The translation products of endogenous mRNA in HepG2 cell-free lysate were probed with anti-apolipoprotein B antibodies to investigate its synthesis. A 550 kilodalton (kDa) polypeptide was selected by a polyclonal antibody, as well as a monoclonal antibody, against the C-terminal end of apolipoprotein B molecule. This in vitro synthesized polypeptide was also found to compare well in size with the in vivo product. The HepG2 lysate was also shown to efficiently synthesize in vitro a number of other proteins including albumin, apolipoprotein E, apolipoprotein A1, and actin. The in vitro synthesis of polypeptides as large as 500 kDa was unexpected and has not previously been demonstrated in a cell-free system. The HepG2 translation system was used to investigate the effect of insulin on the in vitro translation of apolipoprotein B. Lysates prepared from HepG2 cells treated with insulin were found to have lower translational activity (by an average of 52.3%) for apolipoprotein B compared with lysates from control untreated cells. In vitro synthesis of actin and apolipoprotein E were unaffected under these conditions. The insulin-stimulated decline in in vitro apolipoprotein B synthesis was not due to a change in apolipoprotein B mRNA levels as determined by slot- and Northern-blot analyses, suggesting that the inhibitory effect of insulin may be exerted partly at the level of apolipoprotein B mRNA translation.
Assuntos
Apolipoproteínas B/genética , Insulina/farmacologia , Biossíntese de Proteínas/efeitos dos fármacos , Actinas/biossíntese , Apolipoproteína A-I/biossíntese , Apolipoproteínas B/biossíntese , Apolipoproteínas E/biossíntese , Northern Blotting , Carcinoma Hepatocelular , Sistema Livre de Células , Expressão Gênica/efeitos dos fármacos , Humanos , Neoplasias Hepáticas , Lisofosfatidilcolinas , RNA Mensageiro/metabolismo , Albumina Sérica/biossíntese , Células Tumorais CultivadasRESUMO
1. Hormonal regulation of apolipoprotein E (apoE) gene expression by insulin and thyroid hormone was studied in a human hepatoma cell line, HepG2. 2. Changes at the mRNA level, mRNA translation, in vivo synthesis and secretion were monitored. 3. Both insulin and triiodothyronine were found to have no significant effect on apoE mRNA levels. 4. Insulin treatment caused an inhibition of: (a) the in vitro translation of endogenous apoE mRNA in a HepG2 cell-free system (25%), and (b) the incorporation of radioactivity into newly-synthesized apoE in an in vivo pulse-chase labeling experiment (32%). 5. Interestingly, apoE secretion rate was found to be significantly reduced with insulin (84%) suggesting that a major portion of newly-synthesized apoE may be shunted into a degradative pathway. 6. Using a similar experimental approach, triiodothyronine showed no significant effect on the rate of apoE synthesis or translation (6-15% decrease), however a slight reduction (20%) in secretion rate was shown. 7. Overall, apoE gene expression does not appear to be influenced by triiodothyronine significantly but is modulated by insulin at the translational and post-translational level.
Assuntos
Apolipoproteínas E/genética , Regulação da Expressão Gênica/efeitos dos fármacos , Insulina/farmacologia , Fígado/efeitos dos fármacos , RNA Mensageiro/metabolismo , Tri-Iodotironina/farmacologia , Apolipoproteínas E/metabolismo , Divisão Celular/efeitos dos fármacos , Eletroforese em Gel de Poliacrilamida , Humanos , Fígado/metabolismo , Biossíntese de Proteínas , RNA Mensageiro/genética , Células Tumorais CultivadasRESUMO
We have investigated the modulation of apolipoprotein B gene expression in HepG2 cells by thyroid hormone. ApoB secretion rate in serum-free media was found to be significantly increased in the presence of the hormone in long-term cultures (48 h, 37%). This stimulatory effect was dose-dependent. The mechanisms underlying the stimulatory effect of triiodothyronine on apoB production were investigated. Triiodothyronine increased apoB mRNA levels by about 25-36% as determined by slot- and Northern-blot analysis of total RNA. ApoB synthesis rate was also found to be increased both in in vivo pulse-chase experiments (61%) and in in vitro translation studies (54.5%). Despite the 54.5-61% increase in apoB synthesis with triiodothyronine, only a 30% increase in apoB secretion was noted suggesting that part of the increase in the intracellular apoB pool may be lost by degradation. Overall, apoB gene expression appears to be modulated by thyroid hormone at both transcriptional and posttranscriptional levels.
Assuntos
Apolipoproteínas B/genética , Tri-Iodotironina/farmacologia , Northern Blotting , Carcinoma Hepatocelular , Linhagem Celular , Sondas de DNA , Expressão Gênica/efeitos dos fármacos , Humanos , Cinética , Neoplasias Hepáticas , Biossíntese de Proteínas/efeitos dos fármacos , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Neoplásico/genética , RNA Neoplásico/isolamento & purificação , Transcrição Gênica/efeitos dos fármacosRESUMO
An mRNA-dependent cell-free system has been developed from HepG2 cells by hydrolysis of endogenous mRNA with micrococcal nuclease. When supplied with RNA extracted from HepG2 cells, the system synthesized liver specific proteins such as albumin and apolipoprotein B100. Significant amounts of microsomes were also detected in the lysate by measuring NADH-cytochrome c reductase activity and ultracentrifugation. Protease protection assays showed the capability of the HepG2 lysate to translocate newly-synthesized proteins such as apolipoprotein Al, albumin, and apoB into the microsomes as they were protected from digestion with exogenously added protease K, but not protected in the presence of protease K and Triton X-100. The system also proved to be very active toward translation of exogenous mRNAs as evidenced by efficient translation of brome mosaic virus RNA. The HepG2 translation-translocation system appears to provide a unique homologous system for studies on the biogenesis of liver specific proteins, particulary apoB100.
Assuntos
Apolipoproteínas B/metabolismo , Biossíntese de Proteínas , Apolipoproteínas B/genética , Transporte Biológico , Linhagem Celular , Sistema Livre de Células , Humanos , RNA Mensageiro/genéticaRESUMO
gamma-Tocotrienol (gamma-T3), a naturally occurring analog of tocopherol (vitamin E), has been shown to have a hypocholesterolemic effect in animals and humans. Unlike tocopherol, it has also been shown to reduce plasma apoB levels in hypercholesterolemic subjects. The aim of this study was to define the mechanism of action of gamma-T3 on hepatic modulation of apoB production using cultured HepG2 cells as the model system. HepG2 cells preincubated with gamma-T3 were initially shown to inhibit the rate of incorporation of [14C]acetate into cholesterol in a concentration- and time-dependent manner, with a maximum 86+/-3% inhibition at 50 micromol/L observed within 6 hours. gamma-T3, on the other hand, had no significant effect on the uptake of [14C]glycerol into pools of cellular triacylglycerol and phospholipid relative to untreated control. The rate of apoB synthesis and secretion was then studied by an [35S]methionine pulse-labeling experiment and quantified by immunoprecipitating apoB on chasing up to 3 hours. An average reduction of 24+/-3% in labeled apoB in the media was apparent with gamma-T3 despite a 60+/-2% increase in apoB synthesis. Fractionation of secreted apoB revealed a relatively denser lipoprotein particle, suggesting a less stable particle. Using a digitonin-permeabilized HepG2 cell system, the effects of gamma-T3 on apoB translocation and degradation in the endoplasmic reticulum were further investigated. The generation of a specific N-terminal 70-kDa proteolytic fragment proved to be a sensitive measure of the rate of apoB translocation and degradation. The abundance of this fragment increased significantly in gamma-T3-treated cells relative to untreated control cells (50+/-21%) after 2 hours of chase. In addition, the presence of gamma-T3 resulted in an average decrease of 64+/-8% in intact apoB. Taken together, the data suggest that gamma-T3 stimulates apoB degradation possibly as the result of decreased apoB translocation into the endoplasmic reticulum lumen. It is speculated that the lack of cholesterol availability reduces the number of secreted apoB-containing lipoprotein particles by limiting translocation of apoB into the endoplasmic reticulum lumen.
Assuntos
Apolipoproteínas B/biossíntese , Cromanos/farmacologia , Fígado/metabolismo , Vitamina E/análogos & derivados , Animais , Apolipoproteínas B/metabolismo , Transporte Biológico/fisiologia , Linhagem Celular , HDL-Colesterol/biossíntese , HDL-Colesterol/metabolismo , LDL-Colesterol/biossíntese , LDL-Colesterol/metabolismo , Relação Dose-Resposta a Droga , Retículo Endoplasmático/metabolismo , Humanos , Inibidores de Hidroximetilglutaril-CoA Redutases/metabolismo , Fígado/citologia , Fígado/efeitos dos fármacos , Metionina/metabolismo , Radioisótopos de Enxofre , Vitamina E/farmacologiaRESUMO
gamma-Tocotrienol (gamma-T3), a HMG CoA reductase inhibitor, was previously shown to stimulate the intracellular degradation of apolipoprotein B (apoB) in HepG2 cells. The aim of this study was to explore the effects of gamma-T3 on the proteasome dependent co-translational degradation and the proteasome independent post-translational degradation of apoB. Previous studies have shown that apoB translocation across the endoplasmic reticulum (ER) membrane governs the co-translational degradative pathway of apoB. Therefore, we first examined the effects of gamma-T3 on this pathway using a specific translocation assay derived from HepG2 cells. Our results indicated that gamma-T3 reduced the efficiency of apoB translocation across the ER membrane, suggesting that co-translational degradation may be partially involved. Evidence of an ER associated post-translational degradation was also provided upon pre-treating digitonin-permeabilized HepG2 cells with a proteasome inhibitor, lactacystin. When chased for 2h, ER degradation of apoB was observed and was further enhanced in the presence of gamma-T3 versus untreated control, in spite of proteasome inhibition. Combined with the ability of ALLN, a proteasome and cysteine protease inhibitor, to block the post-translational degradation of apoB, the data suggest that gamma-T3 diverted more apoB to a cytosolic proteasomal dependent and possibly an ER-associated proteasomal independent degradation pathways.
Assuntos
Apolipoproteínas B/metabolismo , Cromanos/farmacologia , Cisteína Endopeptidases/metabolismo , Retículo Endoplasmático/metabolismo , Inibidores de Hidroximetilglutaril-CoA Redutases/farmacologia , Fígado/metabolismo , Complexos Multienzimáticos/metabolismo , Vitamina E/análogos & derivados , Acetilcisteína/análogos & derivados , Acetilcisteína/farmacologia , Transporte Biológico , Permeabilidade da Membrana Celular , Inibidores de Cisteína Proteinase/farmacologia , Humanos , Leupeptinas/farmacologia , Complexo de Endopeptidases do Proteassoma , Processamento de Proteína Pós-Traducional , Células Tumorais Cultivadas , Vitamina E/farmacologiaRESUMO
In situ hybridisation using a biotinylated 1.8 kb human cDNA clone in both normal and structurally abnormal chromosomes supports regional localisation of the gene for human C1-inhibitor to chromosome 11q11-q13.1.