Biomedical subjects

D Trouche

Publications and source records attributed to D Trouche.

27 records · Page 2Linked to original sources

PubMed1996

E2F1 and E1A(12S) have a homologous activation domain regulated by RB and CBP.

The E2F1 transcription factor has a well-characterized activation domain at its C terminus and the E1A protein has a recently defined activation domain at its N terminus. Here we show that these activation domains are highly related in sequence. The sequence homology reflects, at least partly, the conservation of common binding sites for the RB and CBP/p300 proteins, which are preserved in the same relative order along E2F1 and E1A. Furthermore, the interaction of RB and CBP with these two activation domains results in the same functional consequences: RB represses both activation domains, whereas CBP stimulates them. We conclude that the activation domains of E1A(12s) and E2F1 belong to a novel functional class, characterized by specific protein binding sites. The implication of this conservation with respect to E1A-induced stimulation of E2F activity is discussed.

Adenovirus E1A Proteins↗

PubMed1995

Stimulation of E2F1/DP1 transcriptional activity by MDM2 oncoprotein.

The MDM2 proto-oncogene is found amplified in a variety of tumours. The oncogenic capacity of the MDM2 protein is attributed to its ability to bind the p53 tumour-suppressor protein and mask its transcriptional activation potential. Here we show that MDM2 makes a functional contact with two cooperating transcription factors, E2F1 and DP1 (refs 4,5), which are involved in S-phase progression. MDM2 contacts the activation domain of E2F1 using residues conserved in the activation domain of p53. However, in contrast to its repression of p53 activity, MDM2 stimulates the activation capacity of E2F1/DP1. These results indicate that MDM2 not only releases a proliferative block by silencing the tumour suppressor p53, it also positively augments proliferation by stimulating the S-phase inducing transcription factors E2F1/DP1.

3T3 Cells↗

PubMed1995

Myogenin binds to and represses c-fos promoter.

Myogenin (a member of the myogenic basic helix-loop-helix transcription factor family) seems to be the main effector of proliferation repression, a crucial step which precedes muscle cell terminal differentiation during muscle development. Proliferation repression most likely occurs through inhibition of proliferation-associated genes such as the proto-oncogene, c-fos. Here, we demonstrate that myogenin binds to an E-box located in the main element of the c-fos promoter, the serum response element (SRE). Results from co-transfection experiments indicate that myogenin acts as a repressor for the SRE. Our data suggest that myogenin could play a role in c-fos inhibition at the onset of muscle cell terminal differentiation.

3T3 Cells↗

PubMed1995

Regulation of transcription by E2F1/DP1.

The E2F1 transcription factor, in co-operation with DP1, controls the expression of several S-phase specific genes. This activity is most likely responsible for the oncogenic and S-phase inducing properties of E2F1, suggesting that this transcription factor plays a key role in regulating the cell cycle. The transcriptional activation functions of E2F1 are resident in a small C-terminal domain which can independently activate transcription. Here we review the protein-protein interactions which impinge upon and regulate this activation domain and put forward some models on their mechanism of action.

Animals↗

PubMed1993

The serum unresponsive Rous sarcoma virus promoter sustains a high serum response factor-dependent transcription in vitro.

CArG boxes are cis-regulatory elements which are represented both in serum responsive and unresponsive promoters. Here we show that the RSV Long Terminal Repeat contains two CArG boxes, which were efficiently recognised by purified Serum Response Factor, although they remained unresponsive to serum in transient transfection assays. However, RSV CArG boxes were as efficient as c-fos Serum Response Element in mediating a Serum Response Factor-dependent transcription in vitro. Thus, the fact that a CArG box is able to bind Serum Response Factor in an active form is insufficient for serum responsiveness in vivo.

3T3 Cells↗

PubMed1993

Repression of c-fos promoter by MyoD on muscle cell differentiation.

Terminal differentiation and cell proliferation are in many cases, as in muscle cells, mutually exclusive processes. While differentiating myoblasts are withdrawn from the cell cycle, myogenesis is inhibited by some mitogens and overexpression of some oncogenes, including proto-oncogene c-fos (which expresses a growth-associated protein constituting the regulatory factor AP-1 in conjunction with c-Jun). MyoD, a muscle-specific transcription factor of the basic helix-loop-helix family, acts at both levels because it triggers a muscle differentiation programme in non-muscle cells, and induces a complete block of cell proliferation. Antagonistic interaction between MyoD and c-Jun has been demonstrated. We here show that c-fos expression greatly decreases upon muscle cell differentiation, concomitant with MyoD-induced activity. We have identified a MyoD-binding site overlapping with the serum-responsive element in the c-fos promoter. We demonstrate that MyoD can act as a negative regulator for c-fos transcription by blocking serum responsiveness through this binding site. These data suggest that the MyoD negative effect on cell growth could be partly mediated by transcriptional inactivation of growth-responsive genes.

3T3 Cells↗

PubMed1991

Universality of c-fos transcriptional regulation: the Dyad Symmetry Element mediates activation by PMA in T lymphocytes.

We here have delineated the regulatory sequences responsible for c-fos transcriptional activation in human primary T lymphoblasts and in a human tumor T cell line (Jurkat), using transient transfection assays. Our results indicate that, as it has been demonstrated for fibroblastic or epithelial cells, the Dyad Symmetry Element is necessary and sufficient to confer responsiveness to an heterologous promoter in both cell types. Protein binding to this element was constitutive, as assessed by gel shift assays. These results suggest that c-fos transcriptional regulation occurs through a widely conserved mechanism in highly differentiated tissues.

Base Sequence↗

PubMed1991

c-fos transcriptional activation by IL-2 in mouse CTL-L2 cells is mediated through two distinct signal transduction pathways converging on the same enhancer element.

The c-fos protooncogene is suspected to play a major role during the activation of cells from different lineages. In particular, c-fos transcription is induced upon entry into a proliferation cycle in a wide variety of cell types. In this study, we have transfected an IL-2-dependent murine T cell line with chloramphenicol acetyl transferase (CAT) reporter constructs, harboring various regions of the human c-fos promoter. We show that IL-2 induces activation of fos CAT reporter constructs in these cells. Furthermore, the induction by IL-2 is mediated through a dyad symmetry element, the serum response element, which is also responsible for fos CAT reporter constructs activation by PMA, a pharmacologic activator of the protein kinase C (PKC). To assess any involvement of PKC in signal transduction for fos CAT reporter activation by IL-2, CTL-L2 cells were PKC-depleted by treatment with high doses of PMA. Such a treatment abolished the transcriptional response of fos CAT reporter constructs to PMA. In contrast, IL-2 was still able to activate fos CAT transcription, albeit with a lower efficiency. These results suggest that PMA-sensitive PKC might be part of intracellular transduction pathways leading to c-fos transcriptional activation by IL-2, and that at least one alternate pathway participates in the complete response. However, these distinct signal transduction pathways have the same DNA target on c-fos promoter, the serum response element.

Animals↗

PubMed1991

The dyad symmetry element is the molecular target for c-fos induction and inhibition during K 562 differentiation along mutually exclusive lineages.

The c-fos proto-oncogene seems to play an important role during differentiation and activation of cells from the hematopoietic lineage. Therefore, it is of interest to investigate the mechanism underlying its transcriptional activation in these cells. To delineate the sequences and factors involved in c-fos transcriptional activation during the course of myeloid cell differentiation, we have used the K 562 chronic leukemic cell line as a model. K 562 cells were transfected with chloramphenicol transacetylase (CAT) reporter constructs, including various regions of the human c-fos promoter, and induced to differentiate by two distinct agents: 12-O-tetradecanoyl phorbol-13-acetate (TPA), which activates a differentiation program along the megakaryoblastic pathway; and hemin, which induces erythroid differentiation. We show here that TPA treatment of K 562 cells induces fos CAT reporter constructs activation, whereas treatment with hemin does not. Furthermore, predifferentiation of the cells with hemin blocks a subsequent induction by TPA, in correlation with the inhibition by hemin of megakaryoblastic differentiation markers appearance. Both the induction by TPA and the inhibition by hemin are mediated by a dyad symmetry element (DSE) located in the upstream regulatory region, between -318 and -296. These results suggest that the protein complex binding to the DSE regulatory element is the target for c-fos activation by TPA and inhibition by hemin in K 562 cells. However, no modulation of protein affinity for the DSE sequence was detected by gel shift assay during the course of induction or inhibition, suggesting that the structural change responsible for the transcriptional modulation is too unstable or too subtle to be detected by this method.

Base Sequence↗