| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Reflotron performance in a community screening program: results of the Massachusetts Model Systems for Blood Cholesterol Screening Project Havas, S., R. Bishop, et al. (1991), Am J Prev Med 7(6): 397-405. Abstract: We evaluated the precision, accuracy, and durability of the Reflotron portable analyzer as part of the National Heart, Lung, and Blood Institute's Model Systems for Blood Cholesterol Screening Program. We conducted screenings in a wide variety of settings in four Massachusetts communities over a 16-month period. Fingerstick samples from 10,428 individuals were tested on the Reflotron at the screening sites. For comparison, we drew venous samples from 972 participants and analyzed them in a reference laboratory, which had met the requirements of the Centers for Disease Control's Lipid Standardization Program. All four Reflotrons tested met the 1988 guidelines for precision and accuracy established by the Laboratory Standardization Panel (LSP) of the National Cholesterol Education Program (NCEP). None of the analyzers consistently met the 1992 LSP standards for precision, although two met the 1992 standards for accuracy. More than 40% of Reflotron values differed from the reference laboratory values by more than 5%. As a consequence, more than 16% of individuals were misclassified in terms of the NCEP risk category into which their Reflotron readings fell. All four instruments malfunctioned at some point during the project, precluding their further usage. We recommend improvements in the precision, accuracy, and durability of this analyzer. |
| Regarding LDL cholesterol: the lower, the better (interview by Dr. Dirk Einecke) Nissen, S. (2004), MMW Fortschr Med 146(13): 65. |
| Regenerating sciatic nerve does not utilize circulating cholesterol Jurevics, H., T. W. Bouldin, et al. (1998), Neurochem Res 23(3): 401-6. Abstract: The rapid accumulation of myelin in the peripheral nervous system during the early postnatal period requires large amounts of cholesterol, a major myelin lipid. All of the cholesterol accumulating in the developing rat sciatic nerve is synthesized locally within the nerve, rather than being derived from the supply in lipoproteins in the systemic circulation (Jurevics and Morell, J. Lipid Res. 5:112-120; 1994). Since this lack of utilization of circulating cholesterol may relate to exclusion by the blood-nerve barrier, we examined the sources of cholesterol needed for regeneration following nerve injury, when the blood-nerve barrier is breached. One sciatic nerve was crushed or transected, and at various times later, the rate of cholesterol accumulation was compared with the rate of local in vivo synthesis of cholesterol within the nerve, utilizing intraperitoneally injected 3H2O as precursor. The accumulation of additional cholesterol in nerve during regeneration and remyelination could all be accounted for by that locally synthesized within the nerve. There was also an increase in cholesterol esters in injured nerve segments; in crushed nerves, these levels decreased during regeneration and remyelination, consistent with reutilization of cholesterol originally salvaged by phagocytic macrophages and Schwann cells. Thus, regeneration and remyelination following injury in sciatic nerve utilizes both salvaged cholesterol and cholesterol synthesized locally within the nerve, but not cholesterol from the circulation. |
| Regional cholesterol synthesis in the intestinal mucosa of the genetically hypercholesterolaemic RICO rat: kinetic study following whole-body gamma-irradiation Lutton, C., F. Milliat, et al. (1999), Int J Radiat Biol 75(2): 175-81. Abstract: PURPOSE: To investigate regional cholesterol synthesis and kinetics following whole-body gamma-irradiation in the genetically hypercholesterolaemic RICO rat. MATERIALS AND METHODS: Male RICO rats were fed a semi-purified diet for 1 month. At 10 weeks old they were exposed to gamma-irradiation (4 Gy, 1.5 Gy/min) together with controls. At intervals from 1-8 days after irradiation an intraperitoneal administration of 1-14C acetate was given in order to estimate cholesterogenesis in mucosal cells located at different sites in the small intestine. The protein and DNA contents of the different enterocytes isolated along the crypt/villus axis in four equal parts of the intestine were also determined. RESULTS: A marked decrease of the mean quantities of cholesterol, DNA or protein in mucosa was seen 1 and 2 days after irradiation, showing the loss of 30-40% of the intestinal epithelium. An overshoot of the cell amount was observed after 4 days with a return to basal values by 8 days after irradiation. The kinetic and topological evolution of cholesterol radioactivity, which reflects in situ cholesterol synthesis, showed a typical gradient in controls and at 8 days after irradiation. Cholesterogenesis decreased from the first to the third quarter of the small intestine (duodenum to proximal ileum), and then increased in the fourth quarter (distal ileum). In all segments of the small intestine, cholesterogenesis decreased from crypt cells to villus tip. At days 1 and 2 the gradient of cholesterogenesis on the villus was abolished. A slow recovery was seen from day 4 with a strong overshoot of cholesterol synthesis in crypt cells in every part of the small intestine. CONCLUSIONS: The RICO rat is a useful model for studying the effect of irradiation on regional cholesterogenesis in intestinal mucosa. Cholesterol synthesis in crypt cells was lowered 1 and 2 days after irradiation, over-expressed after 4 days and subsequently returned to its normal level. |
| Regional interlaboratory standardization of determinations of cholesterol, high-density lipoprotein cholesterol, and triglycerides Tetrault, G. A., W. G. Miller, et al. (1990), Clin Chem 36(1): 145-9. Abstract: The Clinical Chemistry Forum of Central Virginia initiated a lipid standardization program to help ensure that its members meet the current National Cholesterol Education Program guidelines for cholesterol testing, and to standardize assays of high-density lipoprotein (HDL) cholesterol and triglycerides so as to provide accurate lipid profiles. We found that freshly collected, never-frozen human sera must be used to assess interlaboratory accuracy for cholesterol, HDL cholesterol, and triglycerides assays, and that at least 23 samples are required to detect a 3% bias with 90% power when the between-laboratory imprecision (CV) is 3%. After recalibration, all 12 laboratories had a mean HDL cholesterol bias less than or equal to 5%, nine of 10 laboratories had a mean HDL cholesterol bias less than or equal to 40 mg/L for samples with values less than or equal to 570 mg/L, and 10 of 12 laboratories had a mean triglycerides bias less than or equal to 10% for fresh human sera split between participants and the Centers for Disease Control. Pools of frozen human sera were shown to have matrix biases greater than 3% for cholesterol in seven of 11 laboratories, and greater than 40 mg/L for HDL cholesterol in six of nine laboratories. |
| Regional serum cholesterol differences in Belgium: do genetically determined cardiovascular risk factors contribute? Cobbaert, C. and P. Mulder (1998), Int J Epidemiol 27(4): 605-13. Abstract: BACKGROUND: Differences in serum lipid distribution and mortality from ischaemic heart disease have repeatedly been reported between Belgian northerners and southerners. We investigated whether serum lipoprotein(a) (Lp(a)) and apolipoprotein (apo) E polymorphism were involved. METHODS: Fasting serum lipids, apo A-I and B, and Lp(a) levels were examined in randomly selected, 20-39 year old Belgian males and females from the north (Flanders) and the south (Wallonia) of Belgium (N = 900). Apo E phenotype distribution was investigated in random subsamples from either region (N = 249). RESULTS: Mean serum cholesterol, low density lipoprotein cholesterol (LDL-c), apo B and triglyceride levels were higher in Walloons compared to Flemings within each gender, the difference being significant in 30-39 year old males. Average high density lipoprotein cholesterol and apo A-I levels were significantly lower in 30-39 year old male southerners, compared to their northern counterparts. Median Lp(a) was 67 mg/l in northerners and 75 mg/l in southerners (NS). The apo E phenotype distribution was similar in both regions (chi2 = 7.213; d.f. = 5; P = 0.2053), whereas the average effects of the apo E alleles differed between the regions. In southerners the epsilon4 effect upon adjusted apo B and LDL-c levels was approximately+12% and the epsilon2 effect was approximately-15%; in northerners the epsilon4 and epsilon2 effects were approximately+5% and approximately-25%, respectively. The apo E polymorphism did not affect serum Lp(a) levels. CONCLUSIONS: Regional cholesterol differences between Flemings and Walloons cannot be explained by differences in serum Lp(a) or apo E phenotype distribution. The less favourable epsilon2 and epsilon4 effects in southerners compared to northerners reflect modulation of the apo E gene by particular environments. |
| Regionalization and redistribution of membrane phospholipids and cholesterol in mouse spermatozoa during in vitro capacitation Lin, Y. and F. W. Kan (1996), Biol Reprod 55(5): 1133-46. Abstract: Fracture-label, surface-replica, and routine freeze-fracture techniques were used in combination with phospholipase A2-colloidal gold (PLA2-CG) and filipin as probes to study changes in the distribution of phospholipids and cholesterol, respectively, in morphologically defined plasma membrane domains of mouse spermatozoa during in vitro capacitation. In noncapacitated spermatozoa, quantitative analysis revealed that the fractured plasma membrane overlying the equatorial segment carried the highest PLA2-CG labeling density. The next highest labeling densities were found in the anterior acrosome region and the post-acrosomal region. On the external surface of the plasma membrane revealed by surface replicas, a uniform distribution of PLA2-CG was confined mainly to the acrosomal region of the head. The plasma membrane of the sperm tail had a relatively low labeling density for PLA2-CG. In freeze-fracture replicas of filipin-treated spermatozoa, the labeling density of filipin/sterol complexes (FSCs) was high in the plasma membrane over the acrosomal region where the FSCs were uniformly distributed. The postacrosomal region was weakly labeled. After in vitro capacitation, the densities of PLA2-CG and FSCs were significantly reduced in the fractured plasma membrane of the sperm head and the middle piece of the tail. However, surface replicas revealed an increased PLA2-CG labeling on the external surface of the plasma membrane covering the postacrosomal region, the middle piece, and the principal piece. Another major change detected in capacitated spermatozoa was the presence of small aggregates and patches of elevated, membrane-associated particles on the surface-replicated plasma membrane in the upper portion of the postacrosomal domain. Here the PLA2-CG labeling density was found to be higher than in noncapacitated spermatozoa. These results provide new information with respect to the reorganization and redistribution of phospholipids in specific regions of the plasma membrane during capacitation and provide further support for the concept that removal or loss of antifusigenic sterol from the sperm plasma membrane constitutes an important step of the capacitation process. |
| Regression dilution bias in blood total and high-density lipoprotein cholesterol and blood pressure in the Glostrup and Framingham prospective studies Lewington, S., T. Thomsen, et al. (2003), J Cardiovasc Risk 10(2): 143-8. Abstract: BACKGROUND: In epidemiological studies, within-person variability in measured values of a risk factor may underestimate the association between prolonged or 'usual' levels of a risk factor with risk of disease - 'regression dilution'. The importance of regression dilution for high-density lipoprotein (HDL)-cholesterol and the extent to which this may differ from that for total cholesterol is not known. The aim of this study was to assess the magnitude of regression dilution bias for HDL-cholesterol, total cholesterol and blood pressure after varying intervals of follow-up in two prospective cohort studies. METHODS: Regression dilution ratios were estimated for each risk factor using the correlations between baseline and re-survey values in the Glostrup Population Studies and the NHLBI Framingham Heart Study after various time intervals. The regression dilution ratios in each cohort after a fixed interval between measurements were compared. RESULTS: The regression dilution ratios after 10 years were 0.51 and 0.56 for systolic blood pressure in Glostrup and Framingham, respectively; 0.52 and 0.54 for diastolic blood pressure; and 0.68 and 0.63 for total cholesterol. In both studies, the regression dilution ratios for these risk factors became more extreme with increasing intervals between measurements. The regression dilution ratio for HDL-cholesterol after 10 years in Glostrup was 0.72, which suggests that the importance of regression dilution for HDL-cholesterol was similar to that for total cholesterol. CONCLUSION: Failure to correct for increasing regression dilution with longer follow-up may account for some of the discrepant results obtained for the importance of these risk factors in epidemiological studies at varying intervals of follow-up. |
| Regression of atherosclerosis in cholesterol-fed rabbits: effects of fish oil and verapamil Zhu, B. Q., R. E. Sievers, et al. (1990), J Am Coll Cardiol 15(1): 231-7. Abstract: Previous studies have shown that either fish oil or verapamil can attenuate the development of atherosclerosis in the lipid-fed rabbit. The present study was designed to evaluate the individual and combined effects of these two interventions on regression. Seventy New Zealand rabbits in seven groups (10 each) were fed a 0.3% cholesterol diet for 10 weeks. Control group C10 was then killed. Control group C20 was fed a 0.3% cholesterol diet and the other five groups were fed a normal diet for an additional 10 weeks. Group F in three treated groups received 2 ml/day of fish oil (Proto-Chol, eicosapentaenoic acid, 180 mg/ml and docosahexaenoic acid, 120 mg/ml) by gavage. Group V received verapamil, 2 g/1,000 ml drinking water, and group FV received both fish oil and verapamil for an additional 10 weeks. Group CF (control for fish oil) received 2 ml/day of water by gavage and group CV (control for verapamil) received water without gavage for an additional 10 weeks. The percent of aortic and pulmonary atherosclerosis was measured by planimetry of sudanophilic lesions. The percent of aortic lesions in the four control groups (C20, C10, CF and CV) was 57 +/- 22, 40 +/- 15, 40 +/- 14 and 33 +/- 25%, respectively. The fish oil or verapamil groups (F, V, FV) showed a significant reduction in aortic lesions: 15 +/- 17%, p less than 0.05; 16 +/- 12%, p less than 0.05; and 26 +/- 24%, p = NS, respectively.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Regression of atherosclerosis in humans by lowering serum cholesterol Yamamoto, A. (1991), Atherosclerosis 89(1): 1-10. |
| Regression of atherosclerotic lesions by high density lipoprotein plasma fraction in the cholesterol-fed rabbit Badimon, J. J., L. Badimon, et al. (1990), J Clin Invest 85(4): 1234-41. Abstract: The effects of homologous plasma HDL and VHDL fractions on established atherosclerotic lesions were studied in cholesterol-fed rabbits. Atherosclerosis was induced by feeding the animals a 0.5% cholesterol-rich diet for 60 d (group 1). Another group of animals were maintained on the same diet for 90 d (group 2). A third group was also fed the same diet for 90 d but received 50 mg HDL-VHDL protein per wk (isolated from normolipemic rabbit plasma) during the last 30 d (group 3). Aortic atherosclerotic involvement at the completion of the study was 34 +/- 4% in group 1, 38.8 +/- 5% in group 2, and 17.8 +/- 4% in group 3 (P less than 0.005). Aortic lipid deposition was also significantly reduced in group 3 compared with group 1 (studied at only 60 d) and group 2. This is the first in vivo, prospective evidence of the antiatherogenic effect of HDL-VHDL against preexisting atherosclerosis. Our results showed that HDL plasma fractions were able to induce regression of established aortic fatty streaks and lipid deposits. Our results suggest that it may be possible not only to inhibit progression but even to reduce established atherosclerotic lesions by HDL administration. |
| Regression of carotid plaques during low density lipoprotein cholesterol elimination Hennerici, M., W. Kleophas, et al. (1991), Stroke 22(8): 989-92. Abstract: We performed serial prospective ultrasound examinations of four flat and 17 soft carotid plaques during an average of 17 months in seven patients with heterozygous hypercholesterolemia during heparin-induced extracorporeal low density lipoprotein elimination on precipitation from plasma. By means of a specially designed quantitative three-dimensional ultrasound analysis, significant plaque volume reduction could be evaluated in all subjects, along with a marked reduction of total and low density lipoprotein cholesterol and fibrinogen serum levels. |
| Regression of cholesterol induced venous plaques after cholesterol withdrawal in rabbits Buyssens, N., M. M. Kockx, et al. (1999), Exp Toxicol Pathol 51(1): 53-7. Abstract: Rabbits receiving a dietary cholesterol supplement of 0.5% develop atheromatous plaques in the systemic arteries, the pulmonary artery, the pulmonary veins and the venous cavities of the plexus pampiniformis in the funiculus spermaticus. Six months after the withdrawal of the cholesterol supplement the arterial lesions are still present, and show a fibrous transformation. This study is the first report of the total regression of the lesions in the particular venous localizations of the lungs and the plexus pampiniformis. The level of intraluminal pressure is discussed as the possible mechanism responsible for the diverging vascular reactivity. |
| Regression of severe atherosclerotic plaque in patients with mild elevation of LDL cholesterol Schaefer, S., H. Hussein, et al. (1997), J Investig Med 45(9): 536-41. Abstract: BACKGROUND: Intensive risk factor reduction in patients with dyslipidemias and coronary atherosclerosis has been shown to result in alterations in coronary artery morphology and reduced clinical events. However, the impact of such interventions in populations with relatively normal levels of low-density lipoproteins (LDL) is unclear. METHODS: To test the hypothesis that intensive risk factor reduction results in angiographic regression in patients with only mildly elevated levels of LDL, 14 patients with angiographically proven coronary atherosclerosis were entered into the University of California Davis Coronary Artery Disease Regression Program and intensively treated with pharmacologic and nonpharmacologic interventions for 2 years. Quantitative angiography was performed prior to and after 2 years of therapy to determine changes in coronary artery diameter. RESULTS: As a result of this program, dietary fat intake was reduced by 58% and LDL fell from 120 +/- 7 mg/dL to 104 +/- 6 mg/dL (p = 0.05). The average diameter of the measured arterial locations (including all 53 stenoses and 292 nondiscrete regions) on study entry was 2.74 +/- 0.05 mm. After 24 months, there was a net increase in arterial diameter (regression) of +0.05 +/- 0.04 mm to 2.81 +/- 0.05 mm (p = 0.01). While there was no significant change in the average diameter of discrete stenoses, all 8 lesions > or = 50% initial diameter narrowing regressed, with a mean diameter change of + 0.2 mm. Conversely, only 1 of 8 mild lesions < or = 20% regressed, while 4 progressed. Intermediate lesions (20% to 50%, n = 37) had balanced progression and regression. CONCLUSIONS: When examined as a continuous variable, there was a significant linear correlation between initial lesion severity (% stenosis) and the extent of regression (mm). Therefore, risk factor reduction (dietary therapy, exercise, psycho-social counseling, and lipid lowering therapy) in patients with only mild dyslipidemia results in angiographic regression of more severe lesions (> 50% initial stenosis), but does not prevent progression of mild lesions (< 20%). These findings demonstrate that intensive risk factor reduction in patients with only mild elevation of lipids beneficially influences the morphology of the most severe lesions. |
| Regular non-vigorous physical activity and cholesterol levels in the elderly Knight, S., M. A. Bermingham, et al. (1999), Gerontology 45(4): 213-9. Abstract: BACKGROUND: High-density lipoprotein cholesterol (HDL-C) is a powerful independent risk factor for coronary heart disease (CHD) among the elderly. Regular vigorous physical activity has been found to raise the concentration of HDL-C and thus reduce the risk of CHD. There is little data on the effect of non-vigorous activity on HDL-C in the elderly. OBJECTIVE: The aim of this study was to compare CHD risk factors, especially HDL-C, in a group of elderly persons who engage in regular non-vigorous physical activity with a group of frail elderly examined in a previous study. METHODS: Each subject (51 women and 19 men) had anthropometric measures taken and completed a questionnaire on lifestyle and medical history. Total cholesterol (TC), HDL-C and lipoprotein (a) were analysed. Results were compared with those of a frail group examined previously using similar methodology. RESULTS: HDL-C, adjusted for age, body mass index (BMI) and waist-to-hip ratio (WHR), was greater among women (p < 0.01) and men (p < 0.05) who were engaged in a regular physical activity at least once a week. TC was higher among active women (p < 0.001), but there was also a trend towards a lower TC/HDL ratio. Therefore, although TC is higher in active women, this could be due to a higher proportion of the cholesterol fraction consisting of HDL-C. WHR was negatively associated with HDL-C in frail men (p < 0. 05), active men (p < 0.01) and active women (p < 0.05). BMI was negatively associated with HDL-C in frail women (p < 0.05). CONCLUSIONS: This sample of elderly people who participate in regular weekly non-vigorous physical activity have a higher HDL-C than frail individuals who do little or no exercise. Since HDL-C is consistently reported to be inversely associated with CHD in the elderly, an elevation in HDL-C concentration may provide some protection to elderly persons who participate in regular nonvigorous physical activity compared to frail elderly individuals who are largely sedentary. Caution should be exercised in the interpretation of a TC only reading in active elderly women without an accompanying measure of HDL. |
| Regular use of margarine-containing stanol/sterol esters reduces total and low-density lipoprotein (LDL) cholesterol and allows reduction of statin therapy after cardiac transplantation: preliminary observations Vorlat, A., V. M. Conraads, et al. (2003), J Heart Lung Transplant 22(9): 1059-62. Abstract: Seventeen stable cardiac transplant recipients, of whom 16 were on statin therapy, used margarine with stanol/sterol esters. Total cholesterol in the treatment group was lowered from 211 mg/dl (range 168 to 244) to 177 mg/dl (136 to 241) (17% reduction, p = 0.003) and low-density lipoprotein (LDL) cholesterol was reduced from 125 mg/dl (73 to 161) to 98 mg/dl (57 to 146) (22% reduction, p = 0.0006). LDL cholesterol reached the pre-defined cut-off level of 115 mg/dl in 12 of 17 patients and statin dosages were reduced. In 8 of 12 patients, LDL cholesterol remained at <115 mg/dl 6 weeks after statin reduction. |
| Regulated apical secretion of zymogens in rat pancreas. Involvement of the glycosylphosphatidylinositol-anchored glycoprotein GP-2, the lectin ZG16p, and cholesterol-glycosphingolipid-enriched microdomains Schmidt, K., M. Schrader, et al. (2001), J Biol Chem 276(17): 14315-23. Abstract: We examined the role of glycosphingolipid- and cholesterol-enriched microdomains, or rafts, in the sorting of digestive enzymes into zymogen granules destined for apical secretion and in granule formation. Isolated membranes of zymogen granules from pancreatic acinar cells showed an enrichment in cholesterol and sphingomyelin and formed detergent-insoluble glycolipid-enriched complexes. These complexes floated to the lighter fractions of sucrose density gradients and contained the glycosylphosphatidylinositol (GPI)-anchored glycoprotein GP-2, the lectin ZG16p, and sulfated matrix proteoglycans. Morphological and pulse-chase studies with isolated pancreatic lobules revealed that after inhibition of GPI-anchor biosynthesis by mannosamine or the fungal metabolite YW 3548, granule formation was impaired leading to an accumulation of newly synthesized proteins in the Golgi apparatus and the rough endoplasmic reticulum. Furthermore, the membrane attachment of matrix proteoglycans was diminished. After cholesterol depletion or inhibition of glycosphingolipid synthesis by fumonisin B1, the formation of zymogen granules as well as the formation of detergent-insoluble complexes was reduced. In addition, cholesterol depletion led to constitutive secretion of newly synthesized proteins, e.g. amylase, indicating that zymogens were missorted. Together, these data provide first evidence that in polarized acinar cells of the exocrine pancreas GPI-anchored proteins, e.g. GP-2, and cholesterol-sphingolipid-enriched microdomains are required for granule formation as well as for regulated secretion of zymogens and may function as sorting platforms for secretory proteins destined for apical delivery. |
| Regulated step in cholesterol feedback localized to budding of SCAP from ER membranes Nohturfft, A., D. Yabe, et al. (2000), Cell 102(3): 315-23. Abstract: SREBPs exit the ER in a complex with SCAP. Together, they move to the Golgi where SREBP is cleaved, releasing a fragment that activates genes encoding lipid biosynthetic enzymes. Sterols block ER exit, preventing cleavage, decreasing transcription, and achieving feedback control of lipid synthesis. Here, we report an in vitro system to measure incorporation of SCAP into ER vesicles. When membranes were isolated from sterol-depleted cells, SCAP entered vesicles in a reaction requiring nucleoside triphosphates and cytosol. SCAP budding was diminished in membranes from sterol-treated cells. Kinetics of induction of budding in vitro matched kinetics of ER exit in living cells expressing GFP-SCAP. These data localize the sterol-regulated step to budding of SCAP from ER and provide a system for biochemical dissection. |
| Regulating cholesterol by A, B, C Alfred, J. (2001), Nat Rev Genet 2(1): 4-5. |
| Regulating c-Ras function. cholesterol depletion affects caveolin association, GTP loading, and signaling Kranenburg, O., I. Verlaan, et al. (2001), Curr Biol 11(23): 1880-4. Abstract: Cholesterol-rich and caveolin-containing microdomains of the plasma membrane, termed "caveolae," have been implicated in signal transduction. However, the role of caveolae in regulating the Ras-MAP kinase cascade is incompletely understood. The mammalian Ras isoforms (H, N, and K) use different membrane anchors to attach to the plasma membrane and thereby may localize to functionally distinct microdomains, which might explain isoform-specific signaling. Here, we show that, in Cos epithelial cells, endogenous K-Ras colocalizes largely with caveolin, whereas N-Ras localizes to both caveolar and noncaveolar subdomains; H-Ras localization was below detection limits. We find that epidermal growth factor (EGF) activates N-Ras but fails to activate K-Ras in these cells. Extraction of cholesterol with methyl-beta-cyclodextrin disrupts complex formation between caveolin and K- and N-Ras and, strikingly, enables EGF to activate both K-Ras and N-Ras. While cholesterol depletion enhances GTP-loading on total c-Ras, activation of the downstream MEK-MAP kinase cascade by EGF and lysophosphatidic acid but not that by phorbol ester is inhibited. Thus, plasma membrane cholesterol is essential for negative regulation of c-Ras isoforms (complexed to caveolin), as well as for mitogenic signaling downstream of receptor-activated c-Ras. |