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Biomedical subjects

A Bell

Publications and source records attributed to A Bell.

At least 37 records · Page 2Linked to original sources
PubMed2000

Pentamidine inhibits mitochondrial intron splicing and translation in Saccharomyces cerevisiae.

Pentamidine inhibits in vitro splicing of nuclear group I introns from rRNA genes of some pathogenic fungi and is known to inhibit mitochondrial function in yeast. Here we report that pentamidine inhibits the self-splicing of three group I and two group II introns of yeast mitochondria. Comparison of yeast strains with different configurations of mitochondrial introns (12, 5, 4, or 0 introns) revealed that strains with the most introns were the most sensitive to growth inhibition by pentamidine on glycerol medium. Analysis of blots of RNA from yeast strains grown in raffinose medium in the presence or absence of pentamidine revealed that the splicing of seven group I and two group II introns that have intron reading frames was inhibited by the drug to varying extents. Three introns without reading frames were unaffected by the drug in vivo, and two of these were inhibited in vitro, implying that the drug affects splicing by acting directly on RNA in vitro, but on another target in vivo. Because the most sensitive introns in vivo are the ones whose splicing depends on a maturase encoded by the intron reading frames, we tested pentamidine for effects on mitochondrial translation. We found that the drug inhibits mitochondrial but not cytoplasmic translation in cells at concentrations that inhibit mitochondrial intron splicing. Therefore, pentamidine is a potent and specific inhibitor of mitochondrial translation, and this effect explains most or all of its effects on respiratory growth and on in vivo splicing of mitochondrial introns.

Antifungal Agents↗
PubMed2000

Rapamycin inhibits human adipocyte differentiation in primary culture.

OBJECTIVE: The immunosuppressant drug rapamycin, has been reported to inhibit 3T3-L1 adipocyte differentiation by interfering with critical postconfluent mitoses that are required early on for successful differentiation of this cell line (clonal expansion phase). In contrast to the murine 3T3-L1 preadipocyte cell line, human preadipocytes in primary culture do not undergo clonal expansion during differentiation. We investigated whether rapamycin could inhibit human adipocyte differentiation. RESEARCH METHODS AND PROCEDURES: The effect of rapamycin on the induction of differentiation of human preadipocytes in primary culture into adipocytes was measured using Oil Red O staining and glycerol phosphate dehydrogenase activity. RESULTS: We have observed that rapamycin severely curtails human adipocyte differentiation of both omental and abdominal subcutaneous preadipocytes (to 14% and 19% of standard differentiation, respectively). The rapamycin-mediated inhibition of human adipocyte differentiation could be reversed in the presence of excess amounts of FK-506, which displaces rapamycin from its intracellular receptor, FKPB12. Measurement of cytosolic protein and [3H]thymidine incorporation into DNA confirmed the absence of proliferation during differentiation of human preadipocytes in primary culture. DISCUSSION: Our data indicate that rapamycin exerts important negative regulatory effects on adipogenesis in human preadipocytes, through a mechanism that does not depend on interruption of clonal expansion.

Adipocytes↗
PubMed2000

An analysis of the effect of chronic GvHD on relapse and survival following allogeneic PBSC transplantation.

BACKGROUND: PBSC are increasingly being used as the source of stem cells in allogeneic transplantation. An increased incidence of chronic GvHD has been suggested following unmanipulated allogeneic PBSC transplantation (PBSCT), however, how this affects overall survival is not yet clear. Our aim was to study the impact of chronic GvHD on survival and relapse following allogeneic PBSCT. METHODS: We have analyzed data from 73 patients undergoing HLA-matched allogeneic PBSCT. GvHD prophylaxis was with CYA and MTX in 97% of patients. We have studied the incidence of chronic GvHD and its affect on relapse and survival in these patients. All patients were at least 100 days post-transplant at the time of analysis. RESULTS: Seventy-three patients were evaluable for analysis of chronic GvHD. The overall incidence of chronic GvHD was 55% (limited in 18% and extensive in 37%). Overall median survival was 991 days, with a 4 year survival rate of 48%. Twelve patients relapsed. Patients with chronic GvHD had a significantly lower incidence of disease relapse (p = 0.005) with a relapse probability of 8% at 3 years, compared with 40% in patients with no chronic GvHD. In addition, the extent of chronic GvHD had a marked effect on survival, patients with limited chronic GvHD had a 4 year survival rate of 83%, compared with 45% in patients with extensive chronic GvHD and 38% in patients with no chronic GvHD. This difference was primarily due to the low incidence of relapse and low mortality seen in patients with limited chronic GvHD. DISCUSSION: The presence and extent of chronic GvHD is an important predictor of outcome following allogeneic PBSCT, in that patients who developed either limited or extensive chronic GvHD had a low risk of disease relapse.

Adolescent↗
PubMed2000

The activity of the Epstein-Barr virus BamHI W promoter in B cells is dependent on the binding of CREB/ATF factors.

The programme of Epstein-Barr virus (EBV) gene expression that leads to virus-induced growth transformation of resting B lymphocytes is initiated through activation of the BamHI W promoter, Wp. The factors regulating Wp, and the basis of its preferential activity in B cells, remain poorly understood. Previous work has identified a B cell-specific enhancer region which is critical for Wp function and which contains three binding sites for cellular factors. Here we focus on one of these sites and show, using bandshift assays, that it interacts with three members of the CREB/ATF family of cell transcription factors, CREB1, ATF1 and ATFa. A mutation which abrogates the binding of these factors reduces Wp reporter activity specifically in B cell lines, whereas a mutation which converts the site to a consensus CREB-binding sequence maintains wild-type promoter function. Furthermore Wp activity in B cell, but not in non-B cell, lines could be inhibited by cotransfection of expression plasmids expressing dominant negative forms of CREB1 and ATF1. Increasing the basal activity of CREB/ATF proteins in cells by treatment with protein kinase A or protein kinase C agonists led to small increases in Wp activity in B cell lines, but did not restore promoter activity in non-B cell lines up to B cell levels. We conclude that CREB/ATF factors are important activators of Wp in a B cell environment but require additional B cell-specific factors in order to mediate their effects.

Activating Transcription Factor 1↗
PubMed2000

The Epstein-Barr virus promoter initiating B-cell transformation is activated by RFX proteins and the B-cell-specific activator protein BSAP/Pax5.

Epstein-Barr virus (EBV)-induced B-cell growth transformation, a central feature of the virus' strategy for colonizing the human B-cell system, requires full virus latent gene expression and is initiated by transcription from the viral promoter Wp. Interestingly, when EBV accesses other cell types, this growth-transforming program is not activated. The present work focuses on a region of Wp which in reporter assays confers B-cell-specific activity. Bandshift studies indicate that this region contains three factor binding sites, termed sites B, C, and D, in addition to a previously characterized CREB site. Here we show that site C binds members of the ubiquitously expressed RFX family of proteins, notably RFX1, RFX3, and the associated factor MIBP1, whereas sites B and D both bind the B-cell-specific activator protein BSAP/Pax5. In reporter assays with mutant Wp constructs, the loss of factor binding to any one of these sites severely impaired promoter activity in B cells, while the wild-type promoter could be activated in non-B cells by ectopic BSAP expression. We suggest that Wp regulation by BSAP helps to ensure the B-cell specificity of EBV's growth-transforming function.

B-Lymphocytes↗
PubMed2000

Functional TSH receptor in human abdominal preadipocytes and orbital fibroblasts.

Controversy continues about whether, and to what levels of abundance, thyroid-stimulating hormone receptors (TSHR) are found in human tissues other than the thyroid gland. Restricted expression to the thyroid and orbit would suggest that TSHR represents the target autoantigen in thyroid-associated ophthalmopathy. A more generalized pattern of tissue expression would be inconsistent with TSHR acting as the autoantigen that is solely responsible for selectively targeting the immune system to the orbit. We have detected TSHR mRNA in human abdominal adipose tissue by Northern blot analysis. TSHR protein was also detected, by immunoblotting with two different antibodies, in preadipocytes isolated from human abdominal subcutaneous and omental adipose tissue and in derivative adipocytes differentiated in primary culture. Preadipocytes treated with thyroid-stimulating hormone (TSH) exhibited a sevenfold increase in the activity of p70 S6 kinase, a serine/threonine kinase recently recognized as a downstream target of TSHR in thyroid cells. Activation of p70 S6 kinase by TSH was also observed in orbital fibroblasts. Thus TSHR protein expression is found in fibroblasts from several anatomic locations, suggesting that factors other than site-limited TSHR expression must be involved in restricting the distribution of Graves' disease manifestations. Furthermore, the presence of functional TSHR in preadipocytes raises the possibility of a novel role for TSHR signaling in adipose tissue development.

Abdomen↗
PubMed2000

Hemodynamic homeostasis during acute hypoxia in septic and nonseptic piglets: differential role of prostaglandins and nitric oxide.

We studied the hemodynamic responses of 29 anesthetized and mechanically ventilated piglets to acute hypoxia [reduction of Pao2 from 130 to 38 mm Hg induced by inhalation of 7% fraction of inspired oxygen (Fio2) for 7.5 min] before and during group B beta-hemolytic streptococci (GBS) sepsis. During hypoxia, nonseptic piglets maintained stable systemic blood pressure [105+/-9 (SD) to 97+/-14 mm Hg] and cardiac output (CO) (667+/-72 to 685+/-113 mL/min). However, during GBS/hypoxia, systemic blood pressure fell from 94+/-17 to 49+/-25 mm Hg, CO fell from 397+/-146 to 223+/-142 mL/min (both p < 0.001 versus pre-GBS), and cardiac arrest often ensued. We tested three hypotheses that might underlie GBS-induced intolerance to systemic hypoxia: 1) GBS-induced reduction of systemic CO/systemic oxygen delivery (QO2) below a critical QO2 beyond which the superimposition of hypoxia becomes intolerable; this mechanism is unlikely as nonseptic piglets with comparable reductions in CO/QO2 (induced by inflation of a left atrial balloon) tolerated hypoxia well; 2) GBS-induced inhibition of nitric oxide (NO) synthesis that is vital to tolerance of hypoxia; this mechanism is unlikely as infusion of the NO substrate L-arginine did not restore tolerance to hypoxia during GBS infusion (as it did after inhibition of NO synthesis during infusion of N-nitro-L-arginine in nonseptic piglets); and 3) GBS-induced production of pathologic prostaglandins that impaired the piglet's capacity to tolerate hypoxia; this mechanism finds support in the observation that inhibition of prostaglandins with the cyclooxygenase inhibitor indomethacin completely restored the ability of septic piglets to tolerate hypoxia. Further evaluation of GBS-induced intolerance to systemic hypoxia may provide insight into the incompletely understood mechanisms by which sepsis induces circulatory collapse in experimental animals and in humans.

Animals↗
PubMed2000

Antimalarial activity of cyclolinopeptide A and its analogues.

Cyclolinopeptide A (CLA) is an immunosuppressive peptide of the sequence c-(-Leu-Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe-), isolated from linseed. Since another cyclic, hydrophobic, immunosuppressive peptide, cyclosporin A, has potent antimalarial activity, CLA and a series of its analogues were synthesized on solid phase and tested for inhibition of the human malarial parasite Plasmodium falciparum in culture. The results were compared with the influence of these agents on humoral and cellular immune responses. There was no clear correlation between the structure of the peptides, their immunosuppressive activity, and their antimalarial activity. However, the antimalarial activity of the peptides was apparently connected with the strong hydrophobic nature of CLA. Substitution of a less hydrophobic residue into the peptide chain led to a decrease in or even loss of detectable activity, although such peptides retained the immunosuppressive properties. A possible explanation is that the antimalarial effect of CLA and analogues may result from their influence on cell membranes rather than on some specific receptor such as cyclophilin. In agreement with this idea, binding of CLA to purified P. falciparum cyclophilin was not detected except at very high concentrations. Substitution of D-aromatic residues into the CLA molecule led to a decrease in immunosuppressive activity but had little effect on antimalarial activity, which for these peptides was of the same order as for CLA. We have therefore demonstrated that the cyclolinopeptides are a class of compound not previously shown to have antimalarial activity, and that in a series of analogues there was no correlation between antimalarial and immunosuppressive effects.

Animals↗
PubMed1999

The five amino acid-deleted isoform of hepatocyte growth factor promotes carcinogenesis in transgenic mice.

Hepatocyte growth factor (HGF) is a polypeptide with mitogenic, motogenic, and morphogenic effects on different cell types including hepatocytes. HGF is expressed as two biologically active isotypes resulting from alternative RNA splicing. The roles of each HGF isoform in development, liver regeneration and tumorigenesis have not yet been well characterized. We report the generation and analysis of transgenic mice overexpressing the five amino acid-deleted variant of HGF (dHGF) in the liver by virtue of an albumin expression vector. These ALB-dHGF transgenic mice develop normally, have an enhanced rate of liver regeneration after partial hepatectomy, and exhibit a threefold higher incidence of hepatocellular carcinoma (HCC) beyond 17 months of age. Moreover, overexpression of dHGF dramatically accelerates diethyl-nitrosamine induced HCC tumorigenesis. These tumors arise faster, are significantly larger, more numerous and more invasive than those appearing in non-transgenic littermates. Approximately 90% of female dHGF-transgenic mice had multiple macroscopic HCCs 40 weeks after injection of DEN; whereas the non-transgenic counterparts had only microscopic nodules. Liver tumors and cultured tumor cell lines from dHGF transgenics showed high levels of HGF and c-Met mRNA and protein. Together, these results reveal that in vivo dHGF plays an active role in liver regeneration and HCC tumorigenesis.

Alternative Splicing↗
PubMed1999

Multinational outbreak of Salmonella enterica serotype Newport infections due to contaminated alfalfa sprouts.

CONTEXT: In December 1995, reported Salmonella enterica serotype Newport (SN) infections increased sharply in Oregon and British Columbia but not elsewhere in North America. Similar unexplained increases had been noted in 6 other states in the fall of 1995. OBJECTIVE: To determine the source of the outbreak(s). DESIGN: Case-control studies, environmental investigations, bacterial subtyping, and surveillance information review. SETTINGS: Oregon and British Columbia communities (winter 1995-1996) and Georgia, Oklahoma, Pennsylvania, Vermont, Virginia, and West Virginia (fall 1995). PARTICIPANTS: Oregon and British Columbia residents with culture-confirmed SN infections and onset from December 1, 1995, through February 29, 1996, and healthy community controls. MAIN OUTCOME MEASURES: Odds ratio (OR) of illness associated with exposures; distribution patterns and culture of alfalfa seeds and sprouts; subtyping of SN isolates. RESULTS: We identified 133 cases in Oregon and British Columbia; 124 (93%) occurred in patients older than 18 years; 87 (65%) were female. Case patients were more likely than community control subjects to report having eaten alfalfa sprouts in the 5 days preceding illness (41% [17/41] vs 4% [3/75]; OR, 17.0; 95% confidence interval, 4.3-96.0). Case isolates shared a distinctive pulsed-field gel electrophoresis (PFGE) pattern. The SN was grown from seeds and alfalfa sprouts. The distribution of 1 seed lot to multiple growers corresponded to the distribution of cases. Distribution of a second seed lot from the same European wholesaler corresponded to the location of the fall outbreak, which was characterized by a similar demographic profile. The PFGE pattern of fall outbreak isolates and confiscated sprouts and seeds was indistinguishable from the Oregon and British Columbia outbreak and differed from background isolates. CONCLUSIONS: The SN-contaminated alfalfa seeds were distributed to multiple growers across North America in 1995 and resulted in a protracted international outbreak scattered over many months. Current sprouting methods are inadequate to protect consumers from such events. Alfalfa sprouts may be an elusive but important vehicle for salmonellosis and other enteric infections.

Case-Control Studies↗
PubMed1999

Comparative effects of cyclo-oxygenase and nitric oxide synthase inhibition on the development and reversal of spinal opioid tolerance.

1. This study examined the effects of the COX inhibitors, ketorolac and ibuprofen, and the NOS inhibitor L-NAME for their potential to both inhibit the development and reverse tolerance to the antinociceptive action of morphine. 2. Repeated administration of intrathecal morphine (15 micrograms), once daily, resulted in a progressive decline of antinociceptive effect and an increase in the ED50 value in the tailflick and paw pressure tests. Co-administration of ketorolac (30 and 45 micrograms) or S(+) ibuprofen (10 micrograms) with morphine (15 micrograms) prevented the decline of antinociceptive effect and increase in ED50 value. Similar treatment with L-NAME (100 micrograms) exerted weaker effects. Administration of S(+) but not R(-) ibuprofen (10 mg kg-1) had similar effects on systemic administration of morphine (15 mg kg-1). 3. Intrathecal or systemic administration of the COX or NOS inhibitors did not alter the baseline responses in either tests. Acute keterolac or S(+) ibuprofen also did not potentiate the acute actions of spinal or systemic morphine, but chronic intrathecal administration of these agents increased the potency of acute morphine. 4. In animals already tolerant to intrathecal morphine, subsequent administration of ketorolac (30 micrograms) with morphine (15 micrograms) partially restored the antinociceptive effect and ED50 value of acute morphine, reflecting the reversal of tolerance. Intrathecal L-NAME (100 micrograms) exerted a weaker effect. 5. These data suggest that spinal COX activity, and to a lesser extent NOS activity, contributes to the development and expression of opioid tolerance. Inhibition of COX may represent a useful approach for the prevention as well as reversal of opioid tolerance.

Analgesics, Opioid↗
PubMed1999

Genetic analysis of multiplex rheumatoid arthritis families.

To examine the genetic contribution of HLA and non-HLA genes in the etiopathogenesis of rheumatoid arthritis (RA), 60 Caucasian multiplex families were identified and DNA analyzed for over 52 markers including DRB1, DQA1 and DQB1 alleles. Many of the markers were chosen because of close proximity to candidate genes suggested by previous studies or models of pathogenesis. Sibling pair analysis (SIBPAL), relative pair analysis (RELPAL) and linkage studies using two different models of inheritance suggested linkage for the MHC and two additional chromosomal regions: chromosome 2 (D2S443 near CD8 and IGk; 2p13-2p11.1), and chromosome 15 (CYP19-estrogen synthase; 15q15). No support was found for two chromosomal regions, 1p36 and 3q13, recently suggested by other studies. We used transmission disequilibrium testing (TDT), conditional logistic regression, and segregation analysis to study the contributions that the shared epitope and TNF-c have in contributing to risk for RA. These studies provide additional evidence that the association of HLA alleles in RA patients from multiplex families is similar to that observed in sporadic disease, suggest candidate regions for further analysis and find additional support for an association of TNF-c alleles with RA susceptibility.

Adult↗
PubMed1999

Linkage analysis for ATM in familial B cell chronic lymphocytic leukaemia.

B cell chronic lymphocytic leukaemia (CLL) shows evidence of familial aggregation, but the inherited basis is poorly understood. Mutations in the ATM gene have been demonstrated in CLL. This, coupled with a possibly increased risk of leukaemia in relatives of patients with Ataxia Telangiectasia, led us to question whether the ATM gene is involved in familial cases of CLL. To examine this proposition we typed five markers on chromosome 11q in 24 CLL families. No evidence for linkage between CLL and ATM in the 24 families studied and the best estimates of the proportion of sibling pairs that share no, one or both haplotypes at ATM were not different from their null expectations. This would imply that ATM is unlikely to make a significant contribution to the three-fold increase in risk of CLL seen in relatives of patients.

Adult↗
PubMed1999

The effect of saliva on fluoride release by a glass-ionomer filling material.

The initial aim of this study was to investigate the effect of saliva and the formation of pellicle on the fluoride release in vitro of the glass-ionomer filling material, Chemfil Superior. For the first study glass-ionomer discs of 6 mm in diameter and 1.5 mm thick were made. Ten discs were immersed in whole stimulated saliva each day for 10 min and 10 control discs were immersed in deionized water. For the remaining 23 h and 50 min of each day, over the 20-day experimental period, both test and control discs were placed in deionized water. A considerable amount of fluoride was released on the first day (14.5 ppm F control and 13.3 ppm F test). The concentration of fluoride released on the second day fell sharply to 5.3 ppm F for controls and 4.9 ppm F for tests. This release had almost reached a plateau by day 10 and at day 20 the pellets continued to release low levels of fluoride. The concentration of fluoride released was only slightly higher for controls than for test discs when both were immersed in deionized water until day 20. However, during the 10-min period between 1.5 and 2 times as much fluoride was released into the deionized water as into saliva until day 20 when the ratio fell to 1.2:1. The second experiment assessed fluoride release when specimens were incubated for 1 h using an identical protocol. Again, less fluoride was released from the saliva-coated specimens compared with the controls (17%), which was not substantially different to the comparable 10-min samples (13%). This study indicates that saliva retards the release of fluoride from glass-ionomer and that this retarding effect is still present when discs are subsequently immersed in water compared with those that were placed in water alone. This suggests that salivary deposits have formed within minutes of immersion in saliva. This retarding effect was observed throughout the study period with the exception of the 20-day samples which had been incubated in saliva for 10 min.

Dental Deposits↗
PubMed1999

Pharmacokinetics of oral zidovudine entrapped in biodegradable nanospheres in rabbits.

The pharmacokinetic profile of oral zidovudine entrapped in a 50:50 polyactide-coglycolide matrix (nanospheres) was compared to those of standard oral and parenteral zidovudine formulations in rabbits. The bioavailability of zidovudine nanospheres at 50 mg/kg of body weight was 76%, and this dose achieved prolonged exposure to zidovudine compared to standard formulations without an increase in the drug's peak concentration.

Animals↗
PubMed1999

Antifungal activity of LY303366, a novel echinocandin B, in experimental disseminated candidiasis in rabbits.

The safety and antifungal activity of LY303366 (LY), a new broad-spectrum semisynthetic echinocandin, were studied against disseminated candidiasis in persistently neutropenic rabbits. In vitro time-kill assays demonstrated that LY has concentration-dependent fungicidal activity. The pharmacokinetics of LY in the plasma of nonneutropenic rabbits suggested a linear relationship between dose and area under the curve (AUC). The times spent above the MIC during the experimental dosing interval of 24 h were 4 h for LY at 0.1 mg/kg of body weight/day (LY0.1), 8 h for LY at 0.25 mg/kg/day (LY0.25), 12 h for LY at 0.5 mg/kg/day (LY0.5), and 20 h for LY at 1 mg/kg/day (LY1). Antifungal therapy was administered to infected rabbits for 10 days starting 24 h after the intravenous (i.v.) inoculation of 10(3) Candida albicans blastoconidia. Study groups consisted of untreated controls (UCs) and animals treated with amphotericin B (AmB; 1 mg/kg/day i.v.), fluconazole (FLU; 10 mg/kg/day i.v.), and LY0.1, LY0.25, LY0.5, or LY1 i.v. Rabbits treated with LY0.5, LY1, AmB, and FLU had similarly significant clearance of C. albicans from the liver, spleen, kidney, lung, vena cava, and brain in comparison to that for UCs. There was a dose-dependent clearance of C. albicans from tissues in response to LY. Among rabbits treated with LY0.1 there was a significant reduction of C. albicans only in the spleen. In animals treated with LY0.25 there was a significant reduction in all tissues but the brain. By comparison, LY0.5 and LY1 cleared all tissues, including the brain, of C. albicans. These in vivo findings were consistent with the results of in vitro time-kill assays. A dose-dependent effect of altered cell wall morphology was observed among UCs and animals treated with LY0.1, and LY0.25, with a progressive transition from hyphal structure to disrupted yeast forms. Serum creatinine levels were higher and serum potassium levels were lower in AmB-treated rabbits than in UCs and LY- and FLU-treated rabbits. LY0.5 and LY1 were well tolerated, displayed predictable pharmacokinetics in plasma, and had activities comparable to those of AmB and FLU in the treatment of disseminated candidiasis in persistently neutropenic rabbits.

Amphotericin B↗
PubMed1999

Critical role of p42/44(MAPK) activation in anisomycin and hepatocyte growth factor-induced LDL receptor expression: activation of Raf-1/Mek-1/p42/44(MAPK) cascade alone is sufficient to induce LDL receptor expression.

The protein synthesis inhibitor anisomycin activates stress-related mitogen-activated protein kinases (MAPKs), namely, c-jun NH(2)-terminal kinase (p46/54(JNK)) and p38(MAPK) in mammalian cells. In this paper, we show that although exposure to anisomycin resulted in rapid and strong activation of p46/54(JNK) and p38(MAPK), with a delayed low level dual-phosphorylation of mitogen/extracellular protein kinase (p42/44(MAPK)), low density lipoprotein (LDL) receptor induction depends solely on the mild activation of p42/44(MAPK) signaling cascade in HepG2 cells. Unlike hepatocyte growth factor (HGF) which caused LDL receptor induction via rapid, strong, and Ras-dependent p42/44(MAPK) activation, anisomycin-induced p42/44(MAPK) activity and increased LDL receptor expression in a Ras-independent manner. Finally, we examined the role of the p42/44(MAPK) signaling cascade in LDL receptor induction by activating this kinase independently of anisomycin or HGF. By using estrogen-dependent human Raf-1 protein kinase in transient transfection assays, we show that the exclusive activation of the Raf-1/MEK-1/p42/44(MAPK) signaling cascade with antiestrogen ICI 182, 780 caused induction of LDL receptor expression to the same level as observed with either HGF or anisomycin. Consistent with the role of p42/44(MAPK), induction was strongly inhibited by pretreatment with the MEK-1/2 inhibitor PD98059. Our observation that anisomycin can use p42/44(MAPK) signaling cascade is a departure from established thinking, and the results presented shows that activation of the p42/44(MAPK) alone is sufficient to fully induce LDL receptor transcription.

Anisomycin↗