Biomedical subjects

D Lallemand

Publications and source records attributed to D Lallemand.

At least 19 recordsLinked to original sources

PubMed2000

Cell cycle-dependent variations in c-Jun and JunB phosphorylation: a role in the control of cyclin D1 expression.

The transcription factor AP-1, composed of Jun and Fos proteins, is a major target of mitogen-activated signal transduction pathways. However, little is known about AP-1 function in normal cycling cells. Here we report that the quantity and the phosphorylation state of the c-Jun and JunB proteins vary at the M-G(1) transition. Phosphorylation of JunB by the p34(cdc2)-cyclin B kinase is associated with lower JunB protein levels in mitotic and early G(1) cells. In contrast, c-Jun levels remain constant while the protein undergoes N-terminal phosphorylation, increasing its transactivation potential. Since JunB represses and c-Jun activates the cyclin D1 promoter, these modifications of AP-1 activity during the M-G(1) transition could provide an impetus for G(1) progression by a temporal increase in cyclin D1 transcription. These findings constitute a novel example of a reciprocal connection between transcription factors and the cell cycle machinery.

Animals↗

PubMed2000

Down-regulation of AP1 activities after polarization of vas deferens epithelial cells correlates with androgen-induced gene expression.

Vas deferens epithelial cell subcultures were used to study the sequential regulation of jun/fos proto-oncogene expression and AP1 activities during cell proliferation, polarization and androgen-induced expression of a terminal differentiation marker, i. e. the mvdp gene. Proliferation of epithelial cells is associated with a high expression in the nucleus of most Jun and Fos oncoproteins. After cell seeding on an extracellular matrix which allows polarization and expression of the mvdp gene in response to androgens, AP1 protein accumulation is greatly altered and consists in a loss of JunB, Fra1, FosB and a decrease in c-Fos, c-Jun and Fra2, while JunD remained at the same level. This was correlated with a drop in AP1 binding activity as evaluated by gel shift assay using either AP1 consensus sequence or AP1 binding sites of the mvdp gene promoter region, and in AP1 transactivating activity, as estimated by stable transfection experiments using an AP1 responsive promoter (TRE-TK-luc). Androgens did not significantly influence AP1 activities. On the contrary, stimulation of AP1 proteins by the tumor-promoting phorbol ester caused a decrease in androgen-induced mvdp mRNA accumulation, and this effect was reversed by staurosporine, a potent inhibitor of PKC. Our data suggest that a down-regulation of AP1 activities induced by epithelial cell differentiation is a prerequisite to androgen-induced mvdp gene expression. The high AP1 activities observed during proliferative state or induced in TPA-treated polarized cells, exert a repressive effect on androgen action.

Aldehyde Reductase↗

PubMed1998

Stress-activated protein kinases are negatively regulated by cell density.

Stimulation by UV irradiation, TNFalpha, as well as PDGF or EGF activates the JNK/SAPK signalling pathway in mouse fibroblasts. This results in the phosphorylation of the N-terminal domain of c-Jun, increasing its transactivation potency. Using an antibody that specifically recognizes c-Jun phosphorylated at Ser63, we show that culture confluency drastically inhibited c-Jun N-terminal phosphorylation due to the inhibition of the JNK/SAPK pathway. Transfection experiments demonstrate that the inhibition occurs at the same level as, or upstream of, the small G-proteins cdc42 and Rac1. In contrast, the classical MAPK pathway was insensitive to confluency. The inhibition of JNK/SAPK activation depended on the integrity of the actin microfilament network. These results were confirmed and extended in monolayer wounding experiments. After PDGF, EGF or UV stimulation, c-Jun was predominantly phosphorylated in cells bordering the wound, which are the cells that move to occupy the wounded area. Thus, modulation of the stress-dependent signal cascade by confluency will restrict c-Jun N-terminal phosphorylation in response to mitogenic or chemotactic agents to cells that border a wounded area.

Actins↗

PubMed1998

Upregulation of Jun and Fos family members and permanent JNK activity lead to constitutive AP-1 activation in Theileria-transformed leukocytes.

Theileria parasitises bovine leukocytes and transforms them into proliferating, metastatic tumours, where the infection resembles a leukaemia-like disease. We have studied the signal transduction pathways leading to activation of the transcription factor AP-1 in different transformed leukocytes. Parasite infection leads to an up-regulation of all members of the Jun/Fos family of proteins and surprisingly, this occurs in the absence of any detectable ERK, or p38 MAP kinase activity. In the parasitised B-sarcoma TBL3, AP-1 induction occurs in the absence of any JNK activity. In contrast, in infected macrophage and B-cell lines, AP-1 transcriptional activity is strictly associated with the parasite-induced constitutive activation of JNK and subsequent c-Jun N-terminal phosphorylation. Thus, constant AP-1 transcriptional activity involves both an upregulation in the levels of Jun and Fos proteins and constitutive JNK activation.

Animals↗

PubMed1998

Phosphorylation of c-Jun is necessary for apoptosis induced by survival signal withdrawal in cerebellar granule neurons.

Cerebellar granule neurons die by apoptosis when deprived of survival signals. This death can be blocked by inhibitors of transcription or protein synthesis, suggesting that new gene expression is required. Here we show that c-jun mRNA and protein levels increase rapidly after survival signal withdrawal and that transfection of the neurons with an expression vector for a c-Jun dominant negative mutant protects them against apoptosis. Phosphorylation of serines 63 and 73 in the c-Jun transactivation domain is known to increase c-Jun activity. By using an antibody specific for c-Jun phosphorylated on serine 63, we show that this site is phosphorylated soon after survival signal withdrawal. To determine whether c-Jun phosphorylation is necessary for apoptosis, we have expressed c-Jun phosphorylation site mutants in granule neurons. c-Junasp, a constitutively active c-Jun mutant in which the known and potential serine and threonine phosphoacceptor sites in the transactivation domain have been mutated to aspartic acid, induces apoptosis under all conditions tested. In contrast, c-Junala, which cannot be phosphorylated because the same sites have been mutated to alanine, blocks apoptosis caused by survival signal withdrawal. Finally, we show that cerebellar granule neurons contain high levels of Jun kinase activity and low levels of p38 kinase activity, neither of which increases after survival signal withdrawal. Mitogen-activated protein kinase activity decreases under the same conditions. These results suggest that c-Jun levels and c-Jun phosphorylation may be regulated by novel mechanisms in cerebellar granule neurons.

Animals↗

PubMed1997

Cross-species characterization of the promoter region of the cystic fibrosis transmembrane conductance regulator gene reveals multiple levels of regulation.

The cystic fibrosis transmembrane conductance regulator (CFTR) gene is highly conserved within vertebrate species. Its pattern of expression in vivo seems to be tightly regulated both developmentally and in a tissue-specific manner, but shows differences with species. To identify transcriptional regulatory elements in the CFTR promoter region, we have used a combined approach based both on the analysis of the chromatin structure in vivo in rat tissues and on evolutionary clues (i.e. phylogenetic footprinting). In CFTR-expressing tissues, 15 DNase I-hypersensitive sites were identified within a 36 kb region encompassing exon 1. Eleven of them are clustered in a 3.5 kb region that exhibits eleven phylogenetic footprints observed when comparing sequences from eight mammalian species representing four orders (Primates, Artiodactylia, Lagomorpha and Rodentia). Comparison of the two sets of data allows the identification of two types of regulatory elements. Some are conserved between species, such as a non-consensus cAMP response element (CRE) and a PMA-responsive element (TRE) located respectively at positions -0.1 and -1.3 kb relative to ATG. Some are species-specific elements such as a 300 bp purine.pyrimidine (Pu.Py) stretch that is present only in rodents. Analysis of protein/DNA interactions in vitro with rat tissue protein extracts on the conserved elements revealed that the TRE site binds a specific heterodimeric complex composed of Fra-2, Jun D and a protein immunologically related to Jun/CRE-binding protein in the duodenum, whereas the CRE-like site binds ATF-1 ubiquitously. Functional analysis in Caco-2 cells showed that the CRE-like site supports a high basal transcriptional activity but is not able by itself to induce a response to cAMP, whereas the TRE site acts as a weak transactivator stimulated by PMA. Lastly, we found that the rodent-specific Pu.Py stretch confers nuclease S1 hypersensitivity under conditions of acidic pH and supercoiling. This indicates a non-B DNA conformation and thus reinforces the biological significance of non-random Pu.Py strand asymmetry in the regulation of transcription. Thus the tight transcriptional regulation of CFTR expression involves the combination of multiple regulatory elements that act in the chromatin environment in vivo. Some of them are conserved throughout evolution, such as the CRE-like element, which is clearly involved in the basal level of transcription; others are species-specific.

Activating Transcription Factor 1↗

PubMed1997

Transformation by ras modifies AP1 composition and activity.

The Ras proteins play a central role in regulating cell growth and their mutation can lead to abnormal proliferation. To analyse the potential link betwen AP1 activity, encoded by members of the jun and fos gene families, and Ras-mediated cellular transformation, we have studied several NIH3T3 clones which overexpress the Ha-Ras or Ki-Ras oncogenes. These transformed fibroblasts accumulated higher levels of cJun, JunB, Fra1 and Fra2 proteins relative to their normal counterparts. They also displayed increased AP1 DNA binding activity which was predominantly composed of cJun and Fra1 containing dimers. Following serum stimulation of Ras clones, the elevated levels of cJun and Fral remained steady, while the induction of JunB and Fra2 was partially attenuated. Moreover, deregulated Ras signaling resulted in a complete loss of the serum inducibility of cFos and FosB. Ectopic co-expression of cJun and Fra1 in NIH3T3 fibroblasts led to a transformed phenotype, attenuation of cFos serum inducibility, increased AP1 activity and Cyclin D1 accumulation, all characteristics of oncogenic Ras expressing cells. These results demonstrate that cJun and Fra1 are crucial mediators of the Ras-transformation process.

3T3 Cells↗

PubMed1997

Variations in Jun and Fos protein expression and AP-1 activity in cycling, resting and stimulated fibroblasts.

We have analysed the different Jun and Fos proteins as NIH3T3 fibroblasts pass from exponential growth to quiescence and during the first 24 h after their re-entry into the cell cycle following serum stimulation. We show that these proteins can be divided into 3 subgroups based on their pattern of expression. The first contains c-Jun, Jun-D and Fra-2 which are expressed at high level in cycling cells and are only mildly induced by serum. The second contains Jun-B, c-Fos, Fos-B and deltaFos-B whose levels are low in cycling cells but increase strongly and rapidly after stimulation by serum. The third group contains only Fra-1, which is absent from cycling cells and behaves as a delayed early response protein after serum stimulation. AP-1 binding activity is low both in cycling and quiescent fibroblasts but increases after stimulation by serum with kinetics matching the induction of the various Jun and Fos proteins. Antibody supershift analyses demonstrate that the composition of AP-1 binding activity reflects the relative abundance of each Jun and Fos protein. Furthermore, the state of post-translational modification varies continuously for all of the AP-1 proteins as growth conditions change. These data indicate that AP-1 activity during the G0-G1 transition is finely regulated and complex, involving changes both in protein expression and in posttranslational modification.

3T3 Cells↗

PubMed1997

Lovastatin-induced inhibition of renal epithelial tubular cell proliferation involves a p21ras activated, AP-1-dependent pathway.

Proliferation of tubular epithelial cells underlies the development of cystic lesions and the subsequent impairment of renal function after renal mass reduction. The effect of HMG CoA reductase inhibitors (HRI) on cell proliferation was investigated in rat renal proximal tubular epithelial cells in primary culture. Treatment of renal tubular epithelial cells with three different HRI reduced fetal calf serum (FCS)-induced [3H]-thymidine incorporation (IC50 values were 0.7 microM, 1.7 microM, and 1.6 microM for simvastatin, lovastatin, and compactin, respectively), and lovastatin blocked BrdUrd incorporation, as assessed by immunocytochemical studies. The proliferative effect of epidermal growth factor (EGF) was similarly abolished by lovastatin. The effect of lovastatin (1 microM) was prevented by 100 microM mevalonate, 5 microM farnesyl-pyrophosphate and 5 microM geranylgeranyl-pyrophosphate (in percent of control value, 31% vs. 102%, 60%, and 82%, respectively) while cholesterol and other products of the mevalonate pathway were inactive. Immunoblot analysis showed that lovastatin decreased membrane-bound p21ras and inhibited FCS-induced c-fos and c-jun protein expression. Furthermore, electrophoretic mobility shift assay demonstrated the functional impairement of AP-1 DNA binding activity in lovastatin-treated cells. In conclusion, these results demonstrate that HRI are antiproliferative in epithelial tubule cells and that this effect is exerted, at least in part, via inhibition of the p21ras-activated and AP-1 dependent mitogenic cascade.

Animals↗

PubMed1996

A double-blind CT study comparing the safety and efficacy of iopentol and ioxaglate in paediatric patients.

Iopentol (Imagopaque); 300 mg I/ml was compared with ioxaglate (Hexabrix; 320 mg I/ml in 89 patients (45 and 44 patients, mean age 8.5 and 7.9 years in the contrast groups, respectively), in paediatric intravenous CT contrast enhancement. The dose injected was 2 ml/kg b.w. with an upper limit of 100 ml. There was a total of 18 patients who reported adverse events other than sensations of heat or cold, 6 (13%) in the iopentol group and 12 (27%) in the ioxaglate group. Two patients (4%) in the iopentol group reported possible contrast-related events as described above, whereas the number was 8 (18%) in the ioxaglate group. There was no statistically significant difference between the two groups regarding adverse events, blood pressure, nor heart rate changes after injection. The overall quality of CT enhancement was excellent or sufficient in 96 and 93% of the cases in the iopentol and ioxaglate groups, respectively. Iopentol was shown to be a safe and effective contrast medium in examinations of children.

Adolescent↗

PubMed1996

The anomalous origin of bronchus from the esophagus: report of three cases.

Two cases of esophageal lung and one case of esophageal bronchus are described. The diagnosis was established by esophagogram and fibroscopy. In the newborn period in two cases reimplantation of the main bronchus in the trachea was performed with favorable evolution. In the third case diagnosis was made in the patient at 1 month of age and a right upper lobectomy was performed.

Abnormalities, Multiple↗

PubMed1996

Magnetic resonance imaging for diagnosis of Shwachman's syndrome.

Shwachman's syndrome is a rare disease characterized by the association of chronic diarrhea due to exocrine pancreatic insufficiency, metaphyseal dysostosis, and neutropenia. The diagnosis requires demonstration of lipomatosis, or fatty replacement of the pancreas, which is the typical pathological feature of the disease. Magnetic resonance imaging (MRI) was performed in 13 patients with exocrine pancreatic insufficiency, 7 with Shwachman's syndrome, 2 with Pearson's syndrome, 1 with normal sweat test later diagnosed as cystic fibrosis, and 3 without identified syndrome, and in 7 control children. Ultrasonography in the patients did not differentiate between atrophy and lipomatosis and could not be performed in 3. MRI visualized the pancreas in all. The same image was noted in all patients with Shwachman's syndrome with a normal-sized or enlarged pancreas, a hyperintense signal on T1- and T2-weighted image, and a null signal on short time inversion recovery (STIR)-weighted image, characteristic of fat. In all other patients, the findings were very different: The pancreas was a small structure surrounded with fat. In 1 patient without identified syndrome, the pancreas appeared to be partially replaced with fat. MRI is an excellent imaging technique to correlate the nature of a tissue and its radiological representation, especially fat, which gives a very typical signal. In our brief series of patients with Shwachman's syndrome, MRI had 100% positive predictive value in demonstrating lipomatosis. In atypical cases of pancreatic insufficiency in which some of the clinical features of Shwachman's syndrome are absent. MRI is an invaluable aid in the diagnostic procedure.

Adolescent↗

PubMed1995

Mitogen-activated protein kinase pathway and AP-1 are activated during cAMP-induced melanogenesis in B-16 melanoma cells.

In mammalian melanocytes, melanin synthesis is controlled by tyrosinase, the critical enzyme in the melanogenic pathway. We and others showed that the stimulation of melanogenesis by cAMP is due to an increased tyrosinase expression at protein and mRNA levels. However, the molecular events connecting the rise of intracellular cAMP and the increase in tyrosinase activity remain to be elucidated. In this study, using B16 melanoma cells, we showed that cAMP-elevating agents stimulated mitogen-activated protein (MAP) kinase, p44mapk. This effect was mediated by the activation of MAP kinase kinase. cAMP-elevating agents induced a translocation of p44mapk to the nucleus and an activation of the transcription factor AP-1. cAMP-induced AP-1 contained FOS-related antigen-2 in association with JunD, while after phorbol ester stimulation AP-1 complexes consist mainly of JunD/c-Fos heterodimers. In an attempt to connect these molecular events to the control of tyrosinase expression that appears to be the pivotal point of melanogenesis regulation, we hypothesized that following its activation by cAMP, p44mapk activates AP-1. Then AP-1 could stimulate tyrosinase expression through the interaction with specific DNA sequences present in the mouse tyrosinase promoter.

1-Methyl-3-isobutylxanthine↗

PubMed1995

Cyclic AMP stimulates a JunD/Fra-2 AP-1 complex and inhibits the proliferation of interleukin-6-dependent cell lines.

Interleukin-6 (IL-6) is a proinflammatory cytokine which also acts as a growth factor for some murine hybridomas (7TD1) or human myelomas (U266). We demonstrate that elevation of cAMP cellular content inhibits IL-6-stimulated cell growth, by blocking cells mainly in G1 phase. This inhibition is associated with increased expression of the Fos family protein Fra-2. Treatment of cells with 8Br-cAMP results in increased DNA-binding activity of two distinct AP-1 complexes; JunD/Fra-2 and JunB/Fra-2, and also in elevated AP-1 transactivation. When 8Br-cAMP is withdrawn from the medium, cells enter S phase and Fra-2 protein levels and AP-1 DNA-binding activity decrease to their basal value indicating that a temporally correlation exists between the 8Br-cAMP-mediated induction of JunD/Fra-2 AP-1 complex and the 7TD1 and U266 cell growth inhibition.

1-Methyl-3-isobutylxanthine↗

PubMed1995

Specific c-myc and max regulation in epithelial cells.

We have investigated c-myc, max and c-fos mRNA and protein expression in proliferating, quiescent and stimulated immortalized, SV40 T antigen (LT) transformed and tumor-derived epithelial cells as well in human primary keratinocytes and have compared them to their expression in fibroblasts. In proliferating immortalized and tumor-derived epithelial cells, the levels of c-myc, max and c-fos expression were comparable and much higher than in transformed fibroblasts. c-myc and c-fos mRNA and protein levels remained high even during quiescence, when cells stopped dividing. In contrast, whereas max mRNA was constitutively expressed, max protein levels decreased in both fibroblasts and epithelial cells at high cell density. Changing the medium to serum-free medium of confluent epithelial cells induced a complete proliferative response which started with a transient increase in c-fos and c-myc mRNA, followed by the expression of max. Addition of serum to the medium did not induce additional effects. In fibroblasts, similar treatment induced the arrest of c-myc expression and growth, but max expression was also induced in these cells by serum. Our results therefore show that max expression is growth regulated in both immortalized and transformed epithelial as well as fibroblast cells. In contrast, in epithelial cells, c-myc displayed two contrasting behaviors.

Animals↗

PubMed1995

Two distinct signalling pathways are involved in the control of the biphasic junB transcription induced by interleukin-6 in the B cell hybridoma 7TD1.

We have measured the level of junB mRNA in the B hybridoma cell line 7TD1, under interleukin-6 (IL-6) stimulation. IL-6 increases junB mRNA in a biphasic fashion. The first early-induced peak was transient and likely corresponds to the well documented typical junB mRNA, stimulated in response to numerous growth factors, including IL-6. At variance, the second peak which has never been reported previously, lasted several hours. As a consequence of its effect on junB mRNA, IL-6 stimulated, in a biphasic fashion, the nuclear accumulation of the JunB protein. In this study, we demonstrated that IL-6 regulation occurred exclusively at the transcriptional level and that the bimodal increase of junB mRNA and JunB protein can be accounted for by a biphasic stimulation of junB transcription. Furthermore, our data point to two major differences between the mechanism of control of the early and the late IL-6-induced junB transcription waves. First, cycloheximide strongly potentiated the transcription of the second wave, whereas it failed to affect the early-induced burst. Second, tyrphostin, a tyrosine kinase inhibitor, impaired the expression of the first but not the second junB mRNA peak. Conversely, genistein, another tyrosine kinase inhibitor, totally abolished the expression of the second peak of junB mRNA whereas it did not affect the expression of the first peak. Altogether these data indicate that, in 7TD1 cells, IL-6 controls junB transcription in a biphasic fashion by means of two separate transduction pathways.

B-Lymphocytes↗

PubMed1995

A c-Jun dominant negative mutant protects sympathetic neurons against programmed cell death.

Sympathetic neurons depend on nerve growth factor (NGF) for survival and die by apoptosis in its absence. We have investigated the pattern of expression of the Jun and Fos family of transcription factors in dying sympathetic neurons using antibodies specific for each family member. When sympathetic neurons are deprived of NGF, the level of c-Jun protein significantly increases, whereas the levels of the other members of the Jun and Fos family remain relatively constant. c-Jun also becomes more phosphorylated, probably on its amino terminal transactivation domain. When microinjected into sympathetic neurons, an expression vector for a c-Jun dominant negative mutant protects them against NGF withdrawal-induced death, indicating that AP-1 activity is essential for neuronal cell death. Furthermore, overexpression of the full-length c-Jun protein is, in itself, sufficient to induce apoptosis in sympathetic neurons.

Animals↗

PubMed1995

[Preoperative X-ray computed tomographic evaluation of major aplasia of the ear in children].

PURPOSE: To describe computed tomography (CT) findings in congenital aural atresia (CAA) and to illustrate the impact of these findings in the preoperative evaluation. MATERIALS AND METHODS: Sixty-seven congenital aural atresia (bilateral: 10) in 57 children were studied using high resolution CT. Sections 1.5 mm thick were removed from the coronal and the axial plans without sedation (mean age: 9, 6 years). RESULTS AND DISCUSSION: A narrow bony external auditory canal (EAC) was present in 24% of the cases. In one of these cases, the EAC contained a cholesteatoma and was consequently a clear indication of surgery. An hyperpneumatized mastoïd (22%), a posterior position of the temporo mandibular joint (16%), and a bulging medial temporal fossa (12%) made the operation much more difficult. The tympanic cavity was small in 68% of the cases, normal in 28% and absent in 4% of the cases without any detectable ossicular chain. Ossicular chain anomalies were present in 91% of the cases. This consisted most frequently of a fusion of the malleus and the incus (76%) with or without fusion to the tympanic wall (33%). Lateral and anterior displacement of the descending portion of the facial nerve was present in 62%. Oval and round windows were normal in 86% of the cases. A soft tissue opacity (33%) in the tympanic cavity made it difficult to evaluate the stapes, the incudo stapedial articulation, and the facial nerve. Simultaneous abnormalities of inner ear were exceptional (1 case). CONCLUSION: High resolution CT is the best method in CAA evaluation and for guiding the planning of the surgical correction.

Child↗