| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Enzymatic quantitation of cholesterol esters in lipid extracts Van Veldhoven, P. P., E. Meyhi, et al. (1998), Anal Biochem 258(1): 152-5. |
| Enzymatic reagents for quantifying total plasma cholesterol from dogs, rats, and hamsters Weingand, K. W., C. L. Hudson, et al. (1990), Clin Chem 36(11): 1995. |
| Enzymatic reducibility in relation to cytotoxicity for various cholesterol hydroperoxides Korytowski, W., P. G. Geiger, et al. (1996), Biochemistry 35(26): 8670-9. Abstract: Phospholipid hydroperoxide glutathione peroxidase (PHGPX) is a selenoenzyme that can catalyze the direct reduction of various membrane lipid hydroperoxides and by so doing could play a vital role in cytoprotection against peroxidative damage. The activity of purified testicular PHGPX on several photochemically-generated cholesterol hydroperoxide (ChOOH) species was investigated, using high-performance liquid chromatography with electrochemical detection for peroxide analysis and thinlayer chromatography with 14C-radiodetection for diol product analysis. The following ChOOH isomers were monitored: 5 alpha-OOH, 6 alpha-OOH, 6 beta-OOH (singlet oxygen adducts), and unresolved 7 alpha,7 beta-OOH (derived from 5 alpha-OOH rearrangement). Apparent first-order rate constants for GSH/PHGPX-induced peroxide loss (or diol accumulation) in Triton X-100 micelles, unilamellar liposomes, or erythrocyte ghost membranes increased in the following order: 5 alpha-OOH < 6 alpha-OOH approximately equal to 7 alpha,7 beta-OOH < 6beta-OOH. A similar trend was observed when the peroxides were incubated with Triton Iysates of Se-replete L1210 or K562 cells, implicating PHGPX in these reactions. Consistent with this, there was little or no ChOOH reduction if GSH was omitted or if lysates from Se-deprived cells were used. Liposomal 5 alpha-OOH was found to be much more cytotoxic than equimolar liposomal 6 beta-OOH, producing a 50% loss of L1210 clonogenicity at approximately 1/5 the concentration of the latter. Faster uptake of 5 alpha-OOH was ruled out as the basis for greater cytotoxicity, suggesting that relatively inefficient metabolism by the GSH/PHGPX system might be the reason. As supporting evidence, it was found that cells accumulate the diol reduction product of 5 alpha-OOH more slowly than that of 6 beta-OOH during incubation with the respective peroxides. Slow detoxification coupled with rapid formation makes 5 alpha-OOH potentially the most damaging ChOOH to arise in cells exposed to singlet oxygen. |
| Enzymatic reduction of phospholipid and cholesterol hydroperoxides in artificial bilayers and lipoproteins Thomas, J. P., P. G. Geiger, et al. (1990), Biochim Biophys Acta 1045(3): 252-60. Abstract: Lipid hydroperoxides (LOOHs) in various lipid assemblies are shown to be efficiently reduced and deactivated by phospholipid hydroperoxide glutathione peroxidase (PHGPX), the second selenoperoxidase to be identified and characterized. Coupled spectrophotometric analyses in the presence of NADPH, glutathione (GSH), glutathione reductase and Triton X-100 indicated that photochemically generated LOOHs in small unilamellar liposomes are substrates for PHGPX, but not for the classical glutathione peroxidase (GPX). PHGPX was found to be reactive with cholesterol hydroperoxides as well as phospholipid hydroperoxides. Kinetic iodometric analyses during GSH/PHGPX treatment of photoperoxidized liposomes indicated a rapid decay of total LOOH to a residual level of 35-40%; addition of Triton X-100 allowed the reaction to go to completion. The non-reactive LOOHs in intact liposomes were shown to be inaccessible groups on the inner membrane face. In the presence of iron and ascorbate, photoperoxidized liposomes underwent a burst of thiobarbituric acid-detectable lipid peroxidation which could be inhibited by prior GSH/PHGPX treatment, but not by GSH/GPX treatment. Additional experiments indicated that hydroperoxides of phosphatidylcholine, cholesterol and cholesteryl esters in low-density lipoprotein are also good substrates for PHGPX. An important role of PHGPX in cellular detoxification of a wide variety of LOOHs in membranes and internalized lipoproteins is suggested from these findings. |
| Enzyme blockade: a nonradioactive method to determine the absolute rate of cholesterol synthesis in the brain Keller, R. K., M. Small, et al. (2004), J Lipid Res 45(10): 1952-7. Abstract: The standard in vivo method to determine rates of brain cholesterol synthesis involves systemic injection of (3)H(2)O and measurement of incorporated radioactivity in sterols. Herein, we describe an alternative method ("enzyme blockade") that obviates the use of radioactivity. The method relies on the ability of AY9944, a potent and relatively selective inhibitor of cholesterol synthesis, to cause the time-dependent accumulation of 7-dehydrocholesterol (DHC), a cholesterol precursor detected with sensitivity and specificity by reverse-phase HPLC-coupled spectrophotometry at 282 nm. To validate the method, adult AY9944-treated and control mice were injected with (3)Hacetate. After 24 h, most of the radioactivity in brain sterols from treated mice accumulated in DHC, without significantly perturbing overall sterol pathway activity, compared with controls (where cholesterol was the dominant radiolabeled sterol, with no label found in DHC). When adult mice were treated continuously with AY9944, the time-dependent accumulation of DHC in brain was linear (after approximately 8 h) for 3 days. The rate of brain cholesterol synthesis determined by this method (approximately 30 microg/g/day) closely agrees with that determined by the radioactive method. We also determined the cholesterol synthesis rate in different regions of adult mouse brain, with frontal cortex having the highest rate and cerebellum having the lowest rate. |
| Enzyme inhibition during the conversion of squalene to cholesterol Lewis, D., H. Galczenski, et al. (1995), Steroids 60(7): 475-83. Abstract: Two separate enzymatic assays were developed in order to test the selectivity of inhibitors in cholesterol biosynthesis. One assay detects inhibition of delta 5.7-sterol delta 7-reductase, the enzyme involved in the conversion of 7-dehydrocholesterol to cholesterol. Delta 5.7-Sterol delta 7-reductase was inhibited by both RPR 101821, a protonated cyclohexylamine, and BM 15.766, a piperazine derivative, with IC50 values of 1 microM. The second assay detects accumulation of any of five intermediates (squalene oxide, squalene dioxide, lanosterol, desmosterol, and 7-dehydrocholesterol) upon inhibition of enzymes catalyzing reactions in the conversion of squalene to cholesterol. In this assay, inhibition data were most accurate when control assays exhibited a conversion of squalene to cholesterol in the order of 50%. The time required to attain 50% conversion of squalene to cholesterol was 6 h. Given a high inhibitor to substrate concentration ratio and the possible values of Ki, kon, and koff for the reaction between enzymes and inhibitor to form enzyme-inhibitor complexes, it was predicted that in the presence of inhibitors, intermediate accumulation could still be observed after 6 h incubation. The experimental results were in agreement with this prediction. |
| Enzyme-catalyzed oxidation of cholesterol in mixed phospholipid monolayers reveals the stoichiometry at which free cholesterol clusters disappear Slotte, J. P. (1992), Biochemistry 31(24): 5472-7. Abstract: In this study, we have used cholesterol oxidase as a probe to study cholesterol/phospholipid interactions in mixed monolayers at the air/water interface. Mixed monolayers, containing a single phospholipid class and cholesterol at differing cholesterol/phospholipid molar ratios, were exposed to cholesterol oxidase at a lateral surface pressure of 20 mN/m (at 22 degrees C). At equimolar ratios of cholesterol to phospholipid, the average rate of cholesterol oxidation was fastest in unsaturated phosphatidylcholine mixed monolayers (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and egg yolk phosphatidylcholine), intermediate in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, and slowest in sphingomyelin monolayers (egg yolk or bovine brain sphingomyelin). The average oxidation rate in mixed monolayers was not exclusively a function of monolayer packing density, since egg yolk and bovine brain sphingomyelin mixed monolayers occupied similar mean molecular areas even though the measured average oxidation rate was different with these two phospholipids. This suggests that the phospholipid acyl chain composition influenced the oxidation rate. The importance of the phospholipid acyl chain length on influencing the average oxidation rate was further examined in defined phosphatidylcholine mixed monolayers. The average oxidation rate decreased linearly with increasing acyl chain lengths (from di-8:0 to di-18:0). When the average oxidation rate was examined as a function of the cholesterol to phospholipid (C/PL) molar ratio in the monolayer, the otherwise linear function displayed a clear break at a 1:1 stoichiometry with phosphatidylcholine mixed monolayers, and at a 2:1 C/PL stoichiometry with sphingomyelin mixed monolayers.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Enzyme-catalyzed oxidation of cholesterol in pure monolayers at the air/water interface Slotte, J. P. (1992), Biochim Biophys Acta 1123(3): 326-33. Abstract: Mean molecular area vs. lateral surface pressure isotherms were determined for monolayers containing cholesterol, 4-cholesten-3-one (cholestenone), or binary mixtures of the two. At all lateral surface pressures examined, cholestenone had a larger mean molecular area requirement than cholesterol. Results with the binary mixtures of cholesterol and cholestenone suggested that the sterols did not mix ideally (non additive mean molecular area) with each other in the monolayer; the observed mean molecular area for mixtures was less than would be expected based on ideal mixing. The mixed sterol monolayers also displayed a reduction in the lateral collapse pressure which appeared to be a linear function of the mole fraction of cholestenone in the monolayer, suggesting that cholesterol and cholestenone were completely miscible in the mixed monolayer. The pure cholesterol monolayer was next used to examine the cholesterol oxidase-catalyzed (Brevibacterium sp.) oxidation of cholesterol to cholestenone at different lateral surface pressures at 22 degrees C. The difference in mean molecular area requirements of cholesterol and cholestenone was directly used to convert monolayer area changes (at constant lateral surface pressure) into average reaction rates. It was observed that the average catalytic activity of cholesterol oxidase increased linearly with increased lateral surface pressure in the range of 1 to 20 mN/m. In addition, the enzyme was capable to oxidize cholesterol in monolayers with a lateral surface pressure close to the collapse pressure of cholesterol monolayers (collapse pressure 45 mN/m; oxidation was observed at 40 mN/m). The adsorption of cholesterol oxidase to an inert sterol monolayer film at low surface pressures (around 9 mN/m) was marginal, although clearly detectable at very low (0.5-4 mN/m) lateral surface pressures, suggesting that the enzyme did not penetrate deeply into the monolayer in order to reach the 3 beta-hydroxy group of cholesterol. This interpretation is further supported by the finding that a maximally compressed cholesterol monolayer (40 mN/m) was readily susceptible to enzyme-catalyzed oxidation. It is concluded that cholesterol oxidase is capable of oxidizing cholesterol in laterally expanded monolayers as well as in tightly packed monolayers, where the lateral surface pressure is close to the collapse pressure. The kinetic results suggested that the rate-limiting step in the overall process was the substrate availability per surface area (or surface concentration) at the water/lipid interface. |
| Enzyme-resistant fractions of beans lowered serum cholesterol and increased sterol excretions and hepatic mRNA levels in rats Han, K. H., M. Fukushima, et al. (2003), Lipids 38(9): 919-24. Abstract: Feeding rats beans with resistant starch reduces their serum cholesterol concentration; however, the mechanism by which this occurs is not fully understood. We examined the effects of enzyme-resistant fractions of adzuki (Vigna angularis) and tebou (Phaseolus vulgaris, var.) beans on serum cholesterol and hepatic mRNA in rats. Rats were fed a cholesterol-free diet with 50 g of cellulose powder (CP)/kg, 50 g of an enzyme-resistant fraction of adzuki starch (AS)/kg, or 50 g of an enzyme-resistant fraction of tebou starch (TS)/kg diet for 4 wk. There were no significant differences in body weight, liver weight, and cecum contents among the groups, nor was there a significant difference in food intake among the groups. The levels of serum total cholesterol, VLDL + intermediate density lipoprotein + LDL-cholesterol, and HDL cholesterol in the AS and TS groups were significantly (P < 0.05) lower than in the CP group throughout the feeding period. Total hepatic cholesterol in the CP group was significantly (P < 0.05) lower than in the AS and TS groups, fecal cholesterol excretion in the TS group was significantly (P < 0.05) greater than in the CP and AS groups, and the fecal total bile acid concentrations in the AS and TS groups were significantly (P < 0.05) higher than in the CP group. Cecal acetate, propionate, and n-butyrate concentrations in the AS and TS groups were significantly (P < 0.05) higher than in the CP group. The level of hepatic scavenger receptor class B1 (SR-B1) mRNA in the TS group was significantly (P < 0.05) higher than in the CP group, and the levels of hepatic cholesterol 7alpha-hydroxylase mRNA in the AS and TS groups were significantly (P < 0.05) higher than in the CP group. These results suggest that AS and TS have a serum cholesterol-lowering function due to the enhanced levels of hepatic SR-B1 and cholesterol 7alpha-hydroxylase mRNA. |
| Epidemiologic evidence for high-density lipoprotein cholesterol as a risk factor for coronary artery disease Franceschini, G. (2001), Am J Cardiol 88(12A): 9N-13N. Abstract: Plasma high-density lipoprotein cholesterol (HDL-C) is inversely related to coronary artery disease incidence in both women and men, with a proportionately increasing effect of HDL-C throughout the average (or slightly above average)-to-low concentration range. A substantial body of evidence from major epidemiologic studies has established that this coronary artery disease risk associated with HDL-C is entirely independent of plasma low-density lipoprotein cholesterol, other lipid parameters (triglycerides, total cholesterol), and other nonlipid risk factors. The coronary artery disease relative risk for patients with low levels of HDL-C in conjunction with low total cholesterol is also markedly higher than in patients with a profile of high levels of these 2 lipid parameters. Similarly, the risk associated with a low HDL-C level is of particular significance in patients with established coronary artery disease or with type 2 diabetes, and it is a more pertinent factor to consider when managing dyslipidemia. |
| Epidemiological aspects of high density lipoprotein cholesterol de Backer, G., D. de Bacquer, et al. (1998), Atherosclerosis 137 Suppl: S1-6. Abstract: Most of the results from epidemiologic studies support the general idea that high density lipoproteins (HDL) cholesterol is inversely related to coronary heart disease (CHD) incidence. Results from the literature and from a large cohort study in Belgium (the BIRNH study) are used to describe the distribution and the major determinants of HDL cholesterol. HDL cholesterol is influenced by a variety of biologic, environmental and behavioral characteristics. Results of a 10-year mortality follow-up of the BIRNH study are presented and compared to those observed in other large cohort studies. The inverse relationship between HDL cholesterol and CHD is confirmed, although the strength of the association varies between studies and is weakened after adjustment for other coronary risk factors. The results from the BIRNH study also suggest that the relation between HDL cholesterol and CVD mortality is curvilinear. At present, only indirect evidence is available to support the idea that raising HDL cholesterol is useful in primary and secondary prevention of CHD. |
| Epidemiological correlation between chromium content in gallstones and cholesterol in blood Shigeta, A., S. Ratanamaneechat, et al. (2002), J Med Assoc Thai 85(2): 183-94. Abstract: The authors measured the chromium in gallstones and bile from patients in three areas (Kawasaki (a city adjacent to Tokyo) in Japan, Chiang Mai and Bangkok in Thailand) by means of neutron activation analysis. The chromium in three types of gallstones (cholesterol, pigment, and rare stones) and bile from patients living in Bangkok were evidently larger than those from patients living in Kawasaki and Chiang Mai. The high chromium intake by Bangkok patients continued from the start of gallstone formation until the time the stones were removed. The total-cholesterol, triglyceride, and hemoglobin A(1C) levels in the blood from Bangkok residents with high chromium intake over a long period were clearly lower than those of Japanese and Chiang Mai residents. The authors showed that the high dietary intake of chromium over a long period may play a role in the lowering of total-cholesterol, triglyceride, and hemoglobin A(1C) in blood. |
| Epidemiological reference ranges for low-density lipoprotein cholesterol and apolipoprotein B for identification of increased risk of ischaemic heart disease Vermaak, W. J., J. P. Kotze, et al. (1991), S Afr Med J 79(7): 367-71. Abstract: Although there is widespread acceptance that total cholesterol (TC) value reference ranges should be based on epidemiological rather than statistical considerations, the epidemiological action limits for low-density lipoprotein cholesterol (LDL-C) are still incomplete and only statistical reference ranges for apolipoprotein B (Apo-B) levels are available. The combined use of epidemiological reference ranges for TC and incomplete or statistical reference ranges for LDL-C and Apo-B is illogical, since these parameters may fall into discordant risk categories that will hamper and complicate the management of hypercholesterolaemia. Based on a study of lipograms obtained from +/- 3,000 inhabitants of two industrialised Transvaal towns, the age-related epidemiological reference ranges for LDL-C and Apo-B were established. A comparison with published observational studies of other populations, in which comparable lipid, lipoprotein and apolipoprotein methodologies were used, reflected the severity of these lipid-related abnormalities in white South Africans, especially after the age of 30 years. In addition, the serum TC values found in this survey were not significantly different from those obtained 10 years ago. |
| Epidemiological remarks on low serum cholesterol level and cancer risk of all sites Tamakoshi, A., Y. Ohno, et al. (1994), Nippon Koshu Eisei Zasshi 41(5): 393-403. Abstract: Epidemiological studies which examine an association between low serum cholesterol level and cancer risk of all sites were reviewed and a summary of major findings are as follows: (1) In most reports, low serum cholesterol level, which associated with cancer of all sites, cancer deaths/incidence occurred within a few years after cholesterol measurement were performed. This short-term association is believed to be a preclinical cancer effect, i.e., preclinical cancer itself reduces serum cholesterol level. (2) A long-term inverse association between serum cholesterol and cancer risk of all sites was observed in some studies. This association cannot be explained by either a preclinical cancer effect or by chance. The epidemiological implications of this association was discussed in depth. (3) A long-term inverse association between serum cholesterol level and cancer mortality/incidence was observed mainly in men, but not in women. In a few studies which reported an inverse association in women, follow-up periods were rather short. (4) A few epidemiological studies conducted in Japan also detected a long-term inverse relationship between serum cholesterol level and cancer risk of all sites in men, but not in women. Since low serum cholesterol level may possibly be a risk factor for cancer of all sites, further investigation involving experimental studies on animals and longitudinal population-based study appear to be necessary for confirmation of this factor. |
| Epidemiology of low cholesterol levels in older adults. The Cardiovascular Health Study Manolio, T. A., W. H. Ettinger, et al. (1993), Circulation 87(3): 728-37. Abstract: BACKGROUND. Low cholesterol levels have been associated with increased mortality from stroke, cancer, and other noncardiovascular diseases, but the reasons for this association remain unclear. One explanation is that persons with low cholesterol levels have early or occult disease that eventually leads to their deaths. METHODS AND RESULTS. This possibility was explored in 2,091 men and 2,714 women 65-100 years old in the Cardiovascular Health Study, a multicenter observational study of risk factors for heart disease and stroke in older adults. Cholesterol levels < or = 160 mg/dL were present in 11.6% of men and 3.7% of women and increased in prevalence with age. After adjustment for age, total cholesterol levels in this range were associated with a twofold increased prevalence of treated diabetes in men and women and with a twofold increased prevalence of cancer diagnosed in the preceding 5 years in women only. Low cholesterol was also associated with lower levels of hemoglobin, albumin, and factor VII, suggesting a link with hepatic synthetic function. On multivariate analysis, factors most strongly associated with low cholesterol levels in men and women were decreased factor VII levels, decreased albumin, and diabetes. CONCLUSIONS. Cross-sectional associations with low cholesterol levels differ by sex and suggest poorer health by some measures. The observed relations with treated diabetes and impaired hepatic synthetic function should be examined for risk of mortality in longitudinal data from this and other observational studies. |
| Epidemiology of low total plasma cholesterol concentration among young adults: the CARDIA study. Coronary Artery Risk Development in Young Adults Iribarren, C., D. R. Jacobs, Jr., et al. (1997), Prev Med 26(4): 495-507. Abstract: BACKGROUND: Data on stability of plasma total cholesterol levels and its determinants among young adults are lacking. Knowledge of factors associated with low levels of plasma total cholesterol during young adulthood may help clarify the nature of associations between hypocholesterolemia and health or illness. METHODS: Tracking of plasma total cholesterol was investigated using data from the baseline (1985-1986), Year 5 (1990-1991), and Year 7 (1992-1993) examinations of the Coronary Artery Risk Development in Young Adults Study. Lifestyle (including dietary), physiological, medical, and psychological correlates of plasma total cholesterol were examined cross-sectionally at baseline using ANCOVA and multivariate logistic regression. The attributes of participants with persistently low plasma total cholesterol level after 7 years (i.e., remaining below the 10th percentile of sex- and race-specific distributions) were also examined. RESULTS: The cohort in this analysis comprised 720 black men, 922 white men, 899 black women, and 944 white women who were between the ages of 18 and 30 years at baseline. Between 44 and 52% of those with plasma total cholesterol levels below the 10th percentile remained below the same percentile 7 years later. Among black men, a difference of 1 SD in age 3.7 years; odds ratio (OR) = 0.69; 95% CI = 0.52-0.91 and a difference of 1 SD in systolic blood pressure (10.5 mm Hg; OR = 0.73; 95% CI = 0.54-0.97) were independently associated with lower odds, respectively, of being in the lowest 10th percentile of the plasma total cholesterol distribution. Also among black men, current smoking and more calories from carbohydrates were associated with nonsignificantly higher odds of low total cholesterol level. Among white men, a 1 SD older age (3.4 years; OR = 0.78; 95% CI = 0.61-1.00) and a 1 SD higher physical fitness (118 sec; OR = 1.41; 95% CI = 1.09-1.82) predicted lower and higher odds, respectively, of low plasma total cholesterol. Among black women, a 1 SD difference in albumin (0.3 g/dL; OR = 0.80; 95% CI = 0.63-1.03) was related to lower odds of low plasma total cholesterol. Among white women, the factors independently associated with low plasma total cholesterol were body mass index (OR for a difference in 4.0 kg/m2 = 0.73; 95% CI = 0.54-1.00) and gamma-glutamyl transferase (OR for an increase in 9.6 IU/L = 0.41; 95% CI = 0.18-0.93). The independent predictive factors of stably low total cholesterol levels were age and uric acid among black men (both inversely related) and age, Framingham Type A Behavior (inversely), and calories from carbohydrates (positively related) among white men. CONCLUSION: Young adults with low plasma total cholesterol level have characteristics generally associated with good cardiovascular health. However, adverse attributes such as current cigarette smoking (notably among black men) may confound future associations between low total cholesterol and disease. |
| Epidermal growth factor and c-Jun act via a common DNA regulatory element to stimulate transcription of the ovine P-450 cholesterol side chain cleavage (CYP11A1) promoter Pestell, R. G., C. Albanese, et al. (1995), J Biol Chem 270(31): 18301-8. Abstract: The P-450 side chain cleavage (CYP11A1) gene encodes the enzyme that catalyzes the initial step in steroid biosynthesis, resulting in the conversion of cholesterol to pregnenolone. Expression of the CYP11A1 gene is increased by hormones, such as adrenocorticotropin and luteinizing hormone, as well as by a number of growth factors, suggesting that its promoter may contain regulatory elements that respond to multiple signal transduction pathways. Using transient expression assays of the ovine CYP11A1 promoter in JEG-3 placental cells, distinct regulatory elements were found to mediate transcriptional stimulation by cAMP and epidermal growth factor (EGF). The cAMP response was mediated through a GC-rich sequence localized between -117 and -92. In contrast, EGF induced CYP11A1 transcription through an adjacent but distinct sequence (-92 to -77 base pairs) that was shown previously to bind nuclear proteins in DNase I footprinting reactions. This EGF-responsive element (EGF-RE) resembles an activator protein-1 (AP-1) site and was also required for transactivation by co-transfected c-Jun. A point mutation within the EGF-RE impaired stimulation by both EGF and c-Jun, suggesting that these pathways converge on a common regulatory element. Transfer of single or multiple copies of the EGF-RE upstream of an heterologous promotor conferrd EGF and c-Jun responses, providing further evidence that this element is sufficient for both responses. Transfection studies employing mutant c-Jun proteins confirmed a requirement for its DNA binding, leucine zipper and amino-terminal domains, each of which are required for activation of a classical AP-1 reporter. Gel shift studies demonstrated that protein binding to the CYP11A1 EGF-RE was competed specifically by a canonical AP-1 site, and the addition of an anti-JUN antibody confirmed the presence of AP-1 proteins. Consistent with the possibility that EGF may act in part via c-Jun, EGF stimulated the activity of a chimeric GAL4 c-Jun protein, indicating that JUN can serve as a potential target of EGF in JEG-3 cells. EGF also induced mitogen-activated protein kinase activity, and a dominant negative mutant of mitogen-activated protein kinase partially blocked EGF stimulation of GAL4 c-Jun activity. We conclude that EGF stimulates the CYP11A1 promoter through an AP-1 like element and that c-Jun is one of the targets of EGF action. |
| Epidermal growth factor receptor transactivation in angiotensin II-induced signaling: role of cholesterol-rich microdomains Shah, B. H. (2002), Trends Endocrinol Metab 13(1): 1-2. |
| Epidermal growth factor-mediated caveolin recruitment to early endosomes and MAPK activation. Role of cholesterol and actin cytoskeleton Pol, A., A. Lu, et al. (2000), J Biol Chem 275(39): 30566-72. Abstract: The endocytic compartment of eukaryotic cells is a complex intracellular structure involved in sorting, processing, and degradation of a great variety of internalized molecules. Recently, the uptake through caveolae has emerged as an alternative internalization pathway, which seems to be directly related with some signal transduction pathways. However, the mechanisms, molecules, and structures regulating the transport of caveolin from the cell surface into the endocytic compartment are largely unknown. In this study, normal quiescent fibroblasts (normal rat kidney (NRK)) were used to demonstrate that epidermal growth factor causes partial redistribution of caveolin from the cell surface into a cellubrevin early endocytic compartment. Treatment of NRK cells with cytochalasin D or latrunculin A inhibits this pathway and the concomitant activation of Mek and mitotic-activated protein (MAP) kinase; however, if cells were pre-treated with filipin, cytochalasin D does not inhibit the phosphorylation of MAP kinase induced by epidermal growth factor. From these results we conclude that in NRK cells the intact actin cytoskeleton is necessary for the EGF-mediated transport of caveolin from the cell surface into the early endocytic compartment and the activation of MAP kinase pathway. |
| Epidermal HMG CoA reductase activity in essential fatty acid deficiency: barrier requirements rather than eicosanoid generation regulate cholesterol synthesis Proksch, E., K. R. Feingold, et al. (1992), J Invest Dermatol 99(2): 216-20. Abstract: We showed previously that the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, the rate-limiting enzyme of cholesterol biosynthesis, increases after both barrier disruption with organic solvents and in essential fatty acid deficiency (EFAD). Here, we treated EFAD hairless mice with linoleic acid, columbinic acid (C18: 3, n-6, trans; not metabolizable to known regulatory eicosanoids), prostaglandin E2 (PGE2), or latex occlusion, and determined transepidermal water loss (TEWL), epidermal protein content, and epidermal HMG CoA reductase activity. Increased TEWL rates in EFAD were accompanied by increased HMG CoA reductase activity (+130%, n = 6, p less than 0.01) and protein content (+69%; n = 6, p less than 0.025). Artificial restoration of the barrier by occlusion reduced the increase in enzyme activity and protein content toward normal, but barrier function, measured immediately after removal of the latex wrap, deteriorated further (TEWL: two-fold greater than EFAD unoccluded; p less than 0.01). Topical applications of either linoleate or columbinate (but not PGE2), normalized barrier function, HMG CoA reductase activity, and protein content. These results show that a) barrier function modulates HMG CoA reductase activity; b) reduction of cholesterol synthesis with occlusion results in a further deterioration in barrier function, suggesting that increased synthesis is a protective homeostatic response; and c) the barrier abnormality reflects a requirement for specific fatty acids for the barrier rather than resulting from epidermal hyperplasia or decreased prostaglandin generation. |