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A Puisieux

Publications and source records attributed to A Puisieux.

At least 19 recordsLinked to original sources
PubMed2006

TRF2 inhibition promotes anchorage-independent growth of telomerase-positive human fibroblasts.

Although telomere instability is observed in human tumors and is associated with the development of cancers in mice, it has yet to be established that it can contribute to the malignant transformation of human cells. We show here that in checkpoint-compromised telomerase-positive human fibroblasts an episode of TRF2 inhibition promotes heritable changes that increase the ability to grow in soft agar, but not tumor growth in nude mice. This transforming activity is associated to a burst of telomere instability but is independent of an altered control of telomere length. Moreover, it cannot be recapitulated by an increase in chromosome breaks induced by an exposure to gamma-radiations. Since it can be revealed in the context of telomerase-proficient human cells, telomere dysfunction might contribute to cancer progression even at late stages of the oncogenesis process, after the telomerase reactivation step.

Alleles↗
PubMed2006

A twist for survival and cancer progression.

A major obstacle to the expansion of abnormal cells with significant proliferative potential is the induction of programmed cell death. Consequently, oncogene-driven hyperproliferation must be associated with apoptosis inhibition to allow malignant outgrowth. The oncogenic cooperation of N-Myc and Twist-1 in the development of neuroblastoma, the most common and deadly solid tumour of childhood, perfectly illustrates such a process. N-Myc promotes cell proliferation, whereas Twist-1 counteracts its pro-apoptotic properties by knocking-down the ARF/p53 pathway. On the basis of numerous recent studies reporting its overexpression in a variety of human cancers, we discuss in this review the role of Twist-1 as a potent inhibitor of the cell safety programs engaged in response to an abnormal mitogenic activity.

Apoptosis↗
PubMed2003

Drug resistance associated with loss of p53 involves extensive alterations in microtubule composition and dynamics.

In the present study, we compared the dynamics and composition of microtubules in cell lines derived from the human breast adenocarcinoma MCF-7 containing either the wild-type p53 (wt-p53; MN1) or a dominant-negative variant of p53 gene (mut-p53; MDD2). Mut-p53 cells were significantly resistant to the cytotoxicity of the microtubule-targeted drugs (vinca alkaloids and taxanes), as compared with wt-p53 cells. Studies by high-resolution time-lapse fluorescence microscopy in living cells indicated that the dynamics of microtubules of mut-p53 cells were altered in complex ways and were significantly increased as compared with microtubules in wt-p53 cells. The percentage of time microtubules spent in growing and shortening phases increased significantly, their catastrophe frequency increased, and their overall dynamicity increased by 33%. In contrast, their shortening rate and the mean length shortened decreased. Cells containing mut-p53 displayed increased polymerisation of tubulin, increased protein levels of the class IV beta-tubulin isotype, STOP and survivin, and reduced protein levels of class II beta-tubulin isotype, MAP4 and FHIT. We conclude that p53 protein may contribute to the regulation of microtubule composition and function, and that alterations in p53 function may generate complex microtubule-associated mechanisms of resistance to tubulin-binding agents.

Acid Anhydride Hydrolases↗
PubMed2001

Inactivation of wild-type p53 by a dominant negative mutant renders MCF-7 cells resistant to tubulin-binding agent cytotoxicity.

The present study was performed to gain insight into the role of p53 on the cytotoxicity of tubulin-binding agents (TBA) on cancer cells. Drug sensitivity, cell cycle distribution and drug-induced apoptosis were compared in 2 lines derived from the mammary adenocarcinoma MCF-7: the MN-1 cell line containing wild-type p53 (wt-p53) and the MDD2 line, containing a dominant negative variant of the p53 protein (mut-p53). The MDD2 cell line was significantly more resistant to the cytotoxic effects of vinblastine and paclitaxel than the MN1 cell line. MN1 cells, but not MDD2 cells, displayed wt-p53 protein accumulation as well as p21/WAF1 and cyclin G1 induction after exposure to TBA. Both cell lines arrested at G(2)/M after drug treatment. However exposure of MN1 cells to TBA resulted in a stronger variation in mitochondrial membrane potential, associated with cleavage of PARP, and more apoptosis, as measured by annexin V expression. After exposure to vinblastine, Raf 1 kinase activity was reduced in MDD2 cells but not in MN1 cells. Addition of flavopiridol to vinblastine- and paclitaxel-treated cells reversed the MDD2-resistant phenotype by inducing G(1)cell cycle arrest and inhibiting endoreduplication. We conclude that the p53 status of cancer cells influences their sensitivity to TBA cytotoxicity. This effect is likely to involve differences in the apoptotic cascade.

Antineoplastic Agents, Phytogenic↗
PubMed2001

p53 induction prevents accumulation of aberrant transcripts in cancer cells.

Loss of fidelity of the splicing process occurs during tumor progression and can have a deleterious effect on genes like tumor suppressor genes. It was reported recently that the presence of aberrant transcripts of the TSG101 gene in breast cancer cells was associated with the mutation of the p53 tumor suppressor gene. On the basis of this observation, we have analyzed TSG101 transcript patterns in p53-active and p53-inactive cells. Using several isogenic cellular models, we demonstrate that the induction of p53 in cancer cells leads to a significant decrease of aberrant transcripts levels. This indicates a novel implication of p53 in the regulation of the splicing process.

Alternative Splicing↗
PubMed2001

Absence of rearrangements in the BRCA2 gene in human cancers.

Mutations of BRCA2 in sporadic breast and ovarian carcinomas are exceedingly rare. This led to the suggestion that large genomic rearrangements could be involved. We performed Southern blots in genomic DNA from 130 primary breast cancers and 83 cancer cell lines (breast, ovarian, pancreatic and small cell lung carcinomas) and found no genomic rearrangements. These results suggest that a gene other than BRCA2 is the target of the frequent 13q12.3 allelic deletions in human cancers.

BRCA2 Protein↗
PubMed2000

Detection of exon deletions and duplications of the mismatch repair genes in hereditary nonpolyposis colorectal cancer families using multiplex polymerase chain reaction of short fluorescent fragments.

Large genomic deletions within the mismatch repair MLH1 and MSH2 genes have been identified in families with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome, and their detection represents a technical problem. To facilitate their detection, we developed a simple semiquantitative procedure based on the multiplex PCR of short fluorescent fragments. This method allowed us to confirm in HNPCC families three known deletions of MLH1 or MSH2 and to detect in 19 HNPCC families, in which analysis of mismatch repair genes using classical methods had revealed no alteration, a deletion of exon 5 and a duplication of MSH2 involving exons 9 and 10. The presence of such duplications, the frequency of which is probably underestimated, must be considered in HNPCC families in which conventional screening methods have failed to detect mutations.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Absence of p53-dependent induction of the metastatic suppressor KAI1 gene after DNA damage.

The p53 tumor suppressor protein functions to monitor the integrity of the genome. If a damage is detected, p53 binds tightly to specific sequence elements in the DNA and induces the transactivation of genes involved in various growth regulatory processes such as cell cycle progression, DNA repair and apoptosis. A p53-binding site was recently identified in the promoter region of the metastatic suppressor KAI1 gene, suggesting that this gene was a direct transcriptional target of p53. To test the relevance of this hypothesis, we studied the endogenous KAI1 expression in a series of human cell lines with varying p53 status in response to genotoxic treatment as well as in different cellular models exhibiting an inducible p53 activity. Overall, our data indicate that KAI1 expression is not significantly modulated by p53. This observation provides a direct evidence that the presence of a p53-binding site in regulatory domains is not a sufficient criteria to define a p53-transcriptional target gene.

Antigens, CD↗
PubMed2000

BTG gene expression in the p53-dependent and -independent cellular response to DNA damage.

Exposure of mammalian cells to genotoxic agents evokes a complex cellular response. An ordered series of molecular events is necessary to sense DNA damage, transduce the signal, and ultimately delay the cell cycle or trigger apoptosis. Recently, we have shown that BTG2/TIS21 gene expression was induced in response to DNA damage through a p53-dependent pathway. This gene belongs to a newly identified family of structurally related genes whose other known human members are BTG1, BTG3, and Tob. To define the respective involvement of these four related genes in the cellular response to DNA damage, we studied their expression in human cell lines after a variety of genotoxic treatments. Our results demonstrated that were BTG1, BTG2/TIS21, and Tob genes the DNA damage--inducible genes. However, BTG2/TIS21 appeared to be the only p53-transcriptional target gene. We speculate that BTG proteins may play a coordinate role in a general transduction pathway that is induced in response to DNA damage. It has been previously described that recombinant BTG1 and BTG2/TIS21 can physically interact with PRMT1, an arginine methyl transferase, suggesting that BTG1 and BTG2/TIS21 induction may lead to posttranslational modifications of cellular proteins. In support of this hypothesis, we showed that the endogenous induction of BTG1 and BTG2 after genotoxic treatment was correlated with a modulation of protein methylation.

Animals↗
PubMed1999

Neurofibromatosis and early onset of cancers in hMLH1-deficient children.

Hereditary nonpolyposis colon cancer is a common hereditary disorder caused by the germ-line mutations of DNA mismatch repair (MMR) genes, especially hMLH1 and hMSH2. We report here the first identification of human compounds with a homozygous inactivation of a MMR gene. In a typical hereditary nonpolyposis colon cancer family, MMR-deficient children conceived from matings between heterozygotes for a hMLH1 deleterious mutation exhibited clinical features of de novo neurofibromatosis type I and early onset of extracolonic cancers. This observation demonstrates that MMR deficiency is compatible with human development but may lead to mutations during embryogenesis. On the basis of clinical symptoms observed in MMR-deficient children, we speculate that the neurofibromatosis type 1 gene is a preferential target for such alterations.

Adaptor Proteins, Signal Transducing↗
PubMed1999

[Mechanisms of BTG2 activity, a transcriptional target of p53: evidences and hypothesis].

The human BTG2 gene is one of the four members of a newly identified antiproliferative genes family. BTG2 was first described as an immediate early gene whose expression is induced in response to mitogenic as well as differentiative and antiproliferative factors. More recently, we have shown that BTG2 expression is also induced in response to genotoxic stress through a p53-dependent mechanism. Experimental overexpression of the BTG2 gene in NIH3T3 and PC12 cells leads to a partial inhibition of cell proliferation. BTG2 protein physically interacts with the protein CAF1, an element of a general transcription complex, and with a protein-arginine N-methyl transferase, PRMT1. We speculate on the role of BTG2 as a modulator of the intracellular signal transduction cascade.

3T3 Cells↗
PubMed1999

[HNPCC syndrome, microsatellite instability and NF1 gene alteration].

Hereditary predisposition to non polyposis colorectal cancer is caused by a heterozygous germline mutation in a DNA mismatch repair gene (essentially hMLH1 or hMSH2). Cancer progression in predisposed individuals results from the occurrence of a somatic alteration of the normal copy of the gene. Recently, we identified children with a constitutional deficiency of mismatch repair activity, due to a homozygous germline mutation of the hMLH1 gene. These children exhibited clinical features of de novo neurofibromatosis type 1 and early onset of hematopoietic cancers. This observation demonstrates that mismatch repair deficiency is compatible with human development. However, the subsequent genetic instability leads to a high cancer susceptibility. In this context, the NF1 gene appears to be a preferential mutational target. Implications of this observation are discussed.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Prognostic value of P53 gene mutations in a large series of node-negative breast cancer patients.

The most important subgroup of breast cancer patients for which reliable prognostic factors are needed are women without axillary lymph node involvement. Although overall, these patients have a good prognosis, it is known that 20-30% will experience a recurrence of the disease. To determine the prognostic significance of P53 tumor suppressor gene mutation, specimens from 113 primary breast cancers were evaluated for the presence of P53 alterations, as detected by cDNA sequencing of the entire coding sequence of the gene. The median follow-up for patients was 105 months. P53 gene mutation was an independent prognostic marker of early relapse and death. Our results suggest that P53 gene mutations could be an important factor to identify node-negative patients who have a poor prognosis in the absence of adjuvant therapy. Prospective studies should be designed to determine which therapy should be performed in this subgroup of patients.

Adult↗
PubMed1998

Low frequency of TSG101/CC2 gene alterations in invasive human breast cancers.

Large intragenic deletions of the TSG101/CC2 gene were recently reported in seven of 15 primary metastatic breast cancers. Although the number of samples was small, this observation suggested that TSG101/CC2 alterations were a major event in breast carcinogenesis. To study the frequency of these deletions in invasive breast cancers we analysed 189 primary invasive breast tumours and 59 breast cancer metastases. We detected intragenic rearrangements in only three samples (two primary tumours and one metastasis). Northern blot analysis of 43 tumours without rearrangements failed to detect any abnormalities. Furthermore, we studied TSG101/CC2 in 11 human breast adenocarcinoma cell lines by Southern blot, RT-PCR and sequencing of the entire coding region of the gene, and detected no abnormalities. These results show that genetic alteration of TSG101/CC2 is a rare event in breast cancer.

Adenocarcinoma↗
PubMed1998

Cell cycle gene regulation in reversibly differentiated new human hepatoma cell lines.

Several novel differentiated cell lines have been derived from a human hepatocarcinoma named HBG. Analysis of their functional properties evidenced a gradual differentiation process as they became confluent and a remarkable stability of the whole quiescent population for at least 6 weeks. However, when replated at low density after several weeks of quiescence, the differentiated cells were able to rapidly reverse to active proliferation, accompanied by transient dedifferentiation. Demonstration that the differentiated hepatic cells were growth-arrested in G1 phase was provided by the increased number of cells with 2C DNA content and decreased expression of S-phase markers. Characteristic features of oncogenes and cell cycle genes were defined during the differentiation process: (a) a biphasic expression of c-myc, with the latter wave covering the quiescence period; (b) opposite kinetics of c-Ki-ras and of N-ras expression with a pattern of changes paralleling that of c-myc; and (c) a decrease of cyclin D1 protein expression and of the cyclin D1-associated kinase activity. The mechanisms by which quiescent differentiated cells might reinitiate active proliferation were analyzed by studying several genes involved in cell growth and death regulation. We found: (a) a point mutation and loss of the specific activity of the tumor suppressor gene p53 without alteration of the apoptotic response to transforming growth factor beta1; (b) a gradual decrease of retinoblastoma protein, which was constantly present, mainly in a hyperphosphorylated form; and (c) an increase of cyclin-dependent kinase inhibitor p27 expression in confluent differentiating cells, as expected, whereas, surprisingly, a disappearance of the p21 protein was observed in parallel. These data may reflect specific mechanisms of cell cycle regulation in liver parenchymal cells through which these cells can proceed to control their reversible differentiation program.

Animals↗