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Joëlle Thillet

Publications and source records attributed to Joëlle Thillet.

15 recordsLinked to original sources
PubMed2007

MGMT prognostic impact on glioblastoma is dependent on therapeutic modalities.

MGMT promoter methylation, which has been correlated with the response to alkylating agents, was investigated in a retrospective series of 219 glioblastomas (GBMs) treated with various modalities. MGMT methylation had no impact on survival for the whole group, but showed a significant advantage (17.1 months vs. 13.1) for patients treated with RT+ adjuvant chemotherapy (relative risk of death (RR) = 0.53; P = 0.041), particularly when patients received CT during the course of RT (MS = 19.9 months vs. 12.5 months; RR = 0.227, P = 0.001). This suggests that the prognostic impact of MGMT methylation is dependent on therapeutic modalities and schedules. MGMT methylation was not correlated with the main molecular alterations, such as 10q loss and p53 expression.

Adult↗
PubMed2007

The 61 A/G EGF polymorphism is functional but is neither a prognostic marker nor a risk factor for glioblastoma.

The A/G61 polymorphism located in the 5'UTR of the EGF gene has been found to be both a risk factor and a prognostic factor in glioblastoma (GBM), but the functional consequences have not been investigated. Here we show, in vitro, that this polymorphism is functional, in that the G allele promoter is 40% more active than the A variant (P < 0.001). However, analysis of a large series of 209 GBM patients and 214 control subjects did not confirm that A/G61 polymorphism is a significant risk factor for GBM, despite a trend for higher GG frequency in these patients. Furthermore, A/G61 polymorphism was not a prognostic factor for survival in GBM patients, although it does appear to affect progression-free survival.

5' Untranslated Regions↗
PubMed2006

MGMT methylation: a marker of response to temozolomide in low-grade gliomas.

The methylation status of the O6-methylguanine-methyltransferase promoter (MGMTP) was evaluated in 68 low-grade gliomas treated by neoadjuvant temozolomide. Methylated MGMTP was detected in 63 of 68 (92.6 %) patients and was a favorable predictor of progression-free survival as compared with unmethylated MGMTP tumors (p < 0.0001). Assessment of MGMTP status could help identifying low-grade gliomas patients more likely to respond to chemotherapy or to benefit from MGMT depletion strategies.

Adult↗
PubMed2006

Genetic alterations associated with acquired temozolomide resistance in SNB-19, a human glioma cell line.

Gliomas are highly lethal neoplasms that cannot be cured by currently available therapies. Temozolomide is a recently introduced alkylating agent that has yielded a significant benefit in the treatment of high-grade gliomas. However, either de novo or acquired chemoresistance occurs frequently and has been attributed to increased levels of O6-methylguanine-DNA methyltransferase or to the loss of mismatch repair capacity. However, very few gliomas overexpress O6-methylguanine-DNA methyltransferase or are mismatch repair-deficient, suggesting that other mechanisms may be involved in the resistance to temozolomide. The purpose of the present study was to generate temozolomide-resistant variants from a human glioma cell line (SNB-19) and to use large-scale genomic and transcriptional analyses to study the molecular basis of acquired temozolomide resistance. Two independently obtained temozolomide-resistant variants exhibited no cross-resistance to other alkylating agents [1,3-bis(2-chloroethyl)-1-nitrosourea and carboplatin] and shared genetic alterations, such as loss of a 2p region and loss of amplification of chromosome 4 and 16q regions. The karyotypic alterations were compatible with clonal selection of preexistent resistant cells in the parental SNB-19 cell line. Microarray analysis showed that 78 out of 17,000 genes were differentially expressed between parental cells and both temozolomide-resistant variants. None are implicated in known resistance mechanisms, such as DNA repair, whereas interestingly, several genes involved in differentiation were down-regulated. The data suggest that the acquisition of resistance to temozolomide in this model resulted from the selection of less differentiated preexistent resistant cells in the parental tumor.

Antineoplastic Agents, Alkylating↗
PubMed2005

Chromosome 1p loss: a favorable prognostic factor in low-grade gliomas.

Search for loss of heterozygosity on chromosomes 1p, 9p, 10q, and 19q, epidermal growth factor receptor (EGFR) gene amplification, and p53 expression was performed in a series of 131 low-grade gliomas. The profile of molecular changes, clinical findings, and histology were subsequently correlated with the course of the disease, mainly progression-free survival. When these parameters were considered as candidate variables in a multivariate analysis, only loss of heterozygosity on chromosome 1p was associated with increased progression-free survival (hazard ratio, 0.521), indicating a major favorable prognostic role of this genetic alteration in low-grade gliomas.

Adolescent↗
PubMed2004

Transcription factor sterol regulatory element binding protein 2 regulates scavenger receptor Cla-1 gene expression.

OBJECTIVE: The human scavenger receptor class B type I (Cla-1) plays a key role in cellular cholesterol movement in facilitating transport of cholesterol between cells and lipoproteins. Indirect evidence has suggested that Cla-1 gene expression is under the feedback control of cellular cholesterol content. To define the molecular mechanisms underlying such putative regulation, we evaluated whether Cla-1 is a target gene of the sterol regulatory element binding protein (SREBP) transcription factor family. METHODS AND RESULTS: Transient transfections demonstrated that SREBP factors induce Cla-1 promoter activity and that SREBP-2 is a more potent inducer than the SREBP-1a isoform. The 5'-deletion analysis of 3 kb of the 5'-flanking sequence of the Cla-1 gene, combined with site-directed mutagenesis and electrophoretic mobility shift assay, allowed identification of a unique sterol responsive element. SREBP-mediated Cla-1 regulation was confirmed in stably transfected human embryonic kidney 293 cells expressing the active form of SREBP-2 at incremental levels. In these cell lines, Cla-1 mRNA and protein levels were increased in direct proportion to the level of SREBP-2 expression. CONCLUSIONS: These findings provide evidence that SREBP-2, a key regulator of cellular cholesterol uptake through modulation of the expression of the low-density lipoprotein receptor gene, may influence cellular cholesterol homeostasis via regulation of Cla-1 gene expression.

Binding Sites↗
PubMed2004

Common promoter C516T polymorphism in the ApoB gene is an independent predictor of carotid atherosclerotic disease in subjects presenting a broad range of plasma cholesterol levels.

OBJECTIVE: A common polymorphism in the promoter of the apolipoprotein B (apoB) gene, a C to T change at position -516, increases the transcription rate of apoB, resulting in elevated circulating levels of low-density lipoprotein (LDL) cholesterol. METHODS AND RESULTS: We tested the hypothesis that carriers of the -516T allele, who may display consistent elevation in plasma cholesterol over their lifetime, may present more extensive atherosclerotic disease than noncarriers. Genotyping of the apoB 516 C/T promoter polymorphism was performed in 326 subjects at low cardiovascular risk. Homozygotes for allele T displayed higher plasma levels of apoB and LDL than did heterozygotes. Furthermore, both homozygotes and heterozygotes for allele T exhibited higher plasma levels of apoB and LDL than did homozygotes for allele C (P<0.0001). In addition, homozygotes for allele T displayed higher carotid intima-media thickness (IMT) than subjects who were heterozygous. Moreover, both groups had higher carotid IMT than subjects of genotype -516C/C (P<0.001). Only age, high-density lipoprotein, and the presence of allele T were identified as independent predictors of the presence of carotid plaque. No association existed between the polymorphism and plasma concentrations of triglycerides, high-density lipoprotein, or apoAI. CONCLUSIONS: Our data indicate that a C to T change at position -516 of the apoB gene is independently associated with the presence of carotid atherosclerotic disease. Identification of the -516C/T polymorphism may therefore contribute to the estimation of overall cardiovascular risk.

Apolipoproteins↗
PubMed2004

Molecular changes in gliomas.

PURPOSE OF REVIEW: Despite optimal clinical treatment, the prognosis for gliomas remains poor, and little progress has been observed during the last few years. Meanwhile, understanding of glioma oncogenesis has improved greatly. This review focuses on recent advances in molecular biology of glial tumors, with particular emphasis on lineage markers, genetic mechanisms underlying tumor progression, new diagnostic and prognostic markers, and potential therapeutic targets. RECENT FINDINGS: The question of the cell of origin, illustrated by the evidence of tumor-derived multipotent progenitors, by the animal models of gliomas, and by lineage markers such as Olig1/2 markers, remains unsolved. Genotype/phenotype correlation studies have identified early and late genetic alterations related either to astrocytic or oligodendroglial phenotype. They complement the existing World Health Organization morphologic classification and provide additional prognostic markers such as 1p/19q deletion in oligodendrogliomas. Most of these genetic alterations result in the disruption of three main cellular systems: RB1, P53, and tyrosine kinase receptor pathways. New gene alterations have also been identified in glioma, promoting mitotic signal transduction, cell cycle regulation, apoptosis, angiogenesis, or invasion. Gene and protein profiling has been correlated with outcome. SUMMARY: Management of gliomas, especially oligodendrogliomas with 1p19q deletion, benefits from advances in molecular genetics. A better understanding of the molecular pathogenesis and cellular lineage of gliomas will improve tumor classification and define more reliable prognostic markers. There is a hope that it will also lead to novel targets for therapy.

Antineoplastic Agents↗
PubMed2003

Regulation of the expression of the apolipoprotein(a) gene: evidence for a regulatory role of the 5' distal apolipoprotein(a) transcription control region enhancer in yeast artificial chromosome transgenic mice.

OBJECTIVE: The apolipoprotein(a) [apo(a)] gene locus is the major determinant of the circulating concentration of the atherothrombogenic lipoprotein Lp(a). In vitro analysis of the intergenic region between the apo(a) and plasminogen genes revealed the presence of a putative apo(a) transcription control region (ACR) approximately 20 kb upstream of the apo(a) gene that significantly increases the minimal promoter activity of the human apo(a) gene. METHODS AND RESULTS: To examine the function of the ACR in its natural genomic context, we used the Cre-loxP recombination system to generate 2 nearly identical apo(a)-yeast artificial chromosome transgenic mouse lines that possess a single integration site for the human apo(a) transgene in the mouse genome but differ by the presence or absence of the ACR enhancer. Analysis of the 2 groups of animals revealed that the deletion of the ACR was associated with 30% reduction in plasma and mRNA apo(a) levels. Apo(a)-yeast artificial chromosome transgenic mice with and without the ACR sequence were similar in all other aspects of apo(a) regulation, including liver-specific apo(a) expression and alteration in expression levels in response to sexual maturation and a high-fat diet. CONCLUSIONS: This study provides the first experimental in vivo evidence for a functional role of the ACR enhancer in determining levels of apo(a) expression.

5' Untranslated Regions↗
PubMed2003

Regulation of human CETP gene expression: role of SP1 and SP3 transcription factors at promoter sites -690, -629, and -37.

Cholesteryl ester transfer protein (CETP) is a key factor in plasma reverse cholesterol transport and is implicated in the pathophysiology of atherogenic dyslipidemia. Variations observed in plasma CETP mass and activity in both normolipidemic and dyslipidemic individuals may reflect differences in CETP gene expression. We evaluated the respective roles of the Sp1 and Sp3 transcription factors on the promoter activity of the human CETP gene at a new Sp1/Sp3 site identified at position -690, and at two previously described Sp1/Sp3 sites at positions -37 and -629. In transient transfection in HepG2 cells, site-directed mutagenesis using luciferase reporter constructs containing a promoter fragment from +32 to -745 indicated that the new -690 site acts as a repressive element in reducing CETP promoter activity (-22%; P < 0.05); equally, this site exerts an additive effect with the -629 site, inducing marked repression (-42%; P < 0.005). In contrast, in NCTC cells that display a 16-fold lower level of Sp3, the repressive effect at the -690 site was enhanced 2-fold (-45%; P < 0.05), whereas the -629 site exerted no effect. Cotransfection of Sp1 and/or Sp3 in SL2 insect cells lacking endogenous Sp factors demonstrated that Sp1 and Sp3 act as activators at the -690 and -37 sites, whereas Sp3 acts as a repressor at the -629 site. Taken together, our data demonstrate that Sp1 and Sp3 regulate human CETP promoter activity through three Sp1/Sp3 binding sites in a distinct manner, and that the Sp1/Sp3 ratio is a key factor in determining the relative contribution of these sites to total promoter activity.

Animals↗
PubMed2003

VLDL-induced triglyceride accumulation in human macrophages is mediated by modulation of LPL lipolytic activity in the absence of change in LPL mass.

Mixed dyslipidemia of phenotype IIB is characterized by elevated levels of very low density lipoprotein (VLDL)-1 and VLDL-2 subfractions and of low density lipoprotein (LDL), which are associated with premature formation of atherosclerotic plaques, characterized by the presence of lipid-rich macrophage foam cells. Lipoprotein lipase (LPL) is a key factor in mediating macrophage lipid accumulation and foam-cell formation from native VLDL particles. The action of macrophage-derived LPL in the induction of intracellular lipid accumulation from triglyceride-rich lipoprotein (TRL) subfractions (VLDL-1, VLDL-2) is, however, indeterminate, as is the potential role of VLDL-1 and VLDL-2 in modulating macrophage LPL expression. We evaluated the role of LPL in the interaction of type IIB VLDL-1 and VLDL-2 with human macrophages. Both VLDL-1 and VLDL-2 subfractions induced significant accumulation of triglyceride (9.8-fold, P<0.0001, and 4.8-fold, P<0.0001, respectively) and of free cholesterol content (1.4-fold, P<0.001, and 1.2-fold, P=0.02, respectively). Specific inhibition (90%) of the lipolytic activity of endogenous LPL by tetrahydrolipstatin (THL) in the presence of VLDL-1 or VLDL-2 resulted in marked reduction in cellular loading of both triglycerides (-89%, P=0.008, and -89%, P=0.015, respectively) and free cholesterol (-76%, P=0.02, and -55%, P=0.06 respectively). Furthermore, VLDL-1 and VLDL-2 induced marked increase in macrophage-derived LPL enzyme activity (+81%, P=0.002, and +45%, P=0.02), but did not modulate macrophage-derived LPL mRNA and protein expression; consequently, LPL specific activity was significantly increased from 1.6 mU/microg at baseline to 4.1 mU/microg (P=0.01) and 3.1 mU/microg (P=0.05), in the presence of VLDL-1 and VLDL-2, respectively. We conclude that type IIB VLDL-1 and VLDL-2 induce triglyceride accumulation in human monocyte-macrophages primarily via the lipolytic action of LPL, which may involve stabilization and activation of the macrophage-secreted enzyme, rather than via modulation of enzyme production.

Cells, Cultured↗
PubMed2002

A novel cholesteryl ester transfer protein promoter polymorphism (-971G/A) associated with plasma high-density lipoprotein cholesterol levels. Interaction with the TaqIB and -629C/A polymorphisms.

The plasma cholesteryl ester transfer protein (CETP) plays a key role in reverse cholesterol transport (RCT) by mediating the transfer of cholesteryl ester (CE) from high-density lipoprotein (HDL) to atherogenic ApoB-containing lipoproteins, including VLDL, IDL and LDL. We describe a new polymorphism located at position -971 in the human CETP gene promoter, which corresponds to a G/A substitution at a potential AvaI restriction site. The relationship between the -971G/A polymorphism, plasma lipid parameters and plasma CETP concentration was evaluated in the Etude Cas-Témoins de l'Infarctus du Myocarde (control-myocardial infarction cases) cohort, and revealed that the -971G/A polymorphism (A allele frequency: 0.491) was significantly associated with both plasma high-density lipoprotein cholesterol (HDL-C) levels and CETP concentration (P=0.006 and 0.009, respectively). Subjects with genotype -971GG displayed both low HDL-C levels and high plasma CETP concentration, while genotype -971AA subjects displayed the inverse relationship. Evaluation of potential interactions between the -971G/A and the -629C/A or TaqIB polymorphisms demonstrated that the -971G/A polymorphism interacts significantly with the functional -629C/A site and the TaqIB polymorphism with respect to plasma HDL-C levels (P=0.0014 and 0.012, respectively), but does not affect plasma CETP concentration. These results clearly suggest that the interaction between the 971G/A polymorphism and either the -629C/A or the TaqIB polymorphism on plasma CETP concentration is different than that implicated in HDL-C levels. Transient transfection of HepG2 cells revealed that the -971G/A polymorphism did not modulate transcriptional activity of the human CETP gene promoter. The -971G/A promoter polymorphism therefore constitutes a non-functional marker. Furthermore, the observed effects of the -971G/A polymorphism on both plasma CETP concentration and HDL-C levels are due to functional variants in linkage disequilibrium with it. Our findings strongly suggest the existence of as yet unidentified functional polymorphisms in the CETP gene promoter that could explain the association between specific polymorphisms of the CETP gene and both plasma HDL-C and CETP concentrations.

Adult↗
PubMed2002

Atorvastatin lowers lipoprotein(a) but not apolipoprotein(a) fragment levels in hypercholesterolemic subjects at high cardiovascular risk.

The effect of statins on Lp(a) levels is controversial; furthermore, the potential action of statins on apo(a) fragmentation is indeterminate. We therefore determined the circulating levels of Lp(a) and of apo(a) fragments in hypercholesterolemic patients before and after treatment (6 weeks) with Atorvastatin 10 mg/day (A10) or Simvastatin 20 mg/day (S20). In a double blind study, hypercholesterolemic patients (n=391) at high cardiovascular risk (LDL-C>=4.13 mmol/l; TG<2.24 mmol/l; 34% with documented CHD; 45% hypertensive; and 29% current smokers) were assigned to treatment with A10 (n=199) or S20 (n=192). Plasma Lp(a) and apo(a) fragment levels (n=206) were measured prior to and after treatment. At baseline, A10 and S20 groups did not differ in plasma levels of lipids, Lp(a) (A10: 0.45+/-0.48 mg/ml, S20: 0.46+/-0.5), and apo(a) fragments (A10: 3.88+/-5.22 microg/ml; S20: 3.25+/-3), and equally in apo(a) isoform size (A10: 26+/-5 kr, S20: 25.5+/-5.3). After treatment, both statins significantly reduced Lp(a) levels (A10: 0.42+/-0.47 mg/ml, 6% variation, P<0.001; S20: 0.45+/-0.53 mg/ml, 0.02% variation, P=0.046). A10 and S20 did not significantly differ in their efficacy to lower Lp(a) levels. In a multivariate logistic regression analysis, the reduction of Lp(a) levels was independently associated with Lp(a) baseline concentration, but not to other variables, including LDL-C reduction. Plasma levels of apo(a) fragments were not modified by either statin. In conclusion, both A10 and S20 significantly lowered Lp(a), although this effect was of greater magnitude in atorvastatin-treated patients.

Adult↗
PubMed2000

Lipoprotein(a) in the nephrotic syndrome: molecular analysis of lipoprotein(a) and apolipoprotein(a) fragments in plasma and urine.

Plasma levels of lipoprotein(a) (Lp(a)), an atherogenic particle, are elevated in kidney disease, which suggests a role of this organ in the metabolism of Lp(a). Additional evidence for a role of the kidney in the clearance of Lp(a) is provided by the fact that circulating N-terminal fragments of apolipoprotein(a) (apo(a)) are processed and eliminated by the renal route. To further understand the mechanism underlying such renal excretion, the levels of apo(a) fragments in plasma and urine relative to plasma Lp(a) levels were determined in patients with nephrotic syndrome (n = 15). In plasma, the absolute (24.7 +/- 20.4 versus 2.16 +/- 2.99 microg/ml, P < 0.0001) as well as the relative amounts of apo(a) fragments (4.6 +/-3.4% versus 2.1 +/- 3.3% of total Lp(a), P < 0.0001) were significantly elevated in nephrotic patients compared with a control, normolipidemic population. In addition, urinary apo(a) excretion in patients with nephrotic syndrome was markedly elevated compared with that in control subjects (578 +/- 622 versus 27.7 +/- 44 ng/ml per mg creatinine, P < 0.001). However, the fractional catabolic rates of apo(a) fragments were similar in both groups (0.68 +/- 0.67% and 0.62 +/- 0.47% in nephrotic and control subjects, respectively), suggesting that increased plasma concentrations of apo(a) fragments in nephrotic subjects are more dependent on the rate of synthesis rather than on the catabolic rate. Molecular analysis of apo(a) immunoreactive material in urine revealed that the patterns of apo(a) fragments in nephrotic patients were distinct from those of control subjects. Full-length apo(a), large N-terminal apo(a) fragments similar in size to those present in plasma, as well as C-terminal fragments of apo(a) were detected in urine from nephrotic patients but not in urine from controls. All of these apo(a) forms were in addition to smaller N-terminal apo(a) fragments present in normal urine. This study also demonstrated the presence of Lp(a) in urine from nephrotic patients by ultracentrifugal fractionation. These data suggest that in nephrotic syndrome, Lp(a) and large fragments of apo(a) are passively filtered by the kidney through the glomerulus, whereas smaller apo(a) fragments are secreted into the urine.

Adult↗