STAT transcription factors are induced by a number of growth factors and cytokines. Within minutes of induction, the STAT proteins are phosphorylated on tyrosine and serine residues and translocated to the nucleus, where they bind to their DNA targets. The leukemia inhibitory factor (LIF) mediates pleiotropic and sometimes opposite effects both in vivo and in cultured cells. It is known, for example, to prevent differentiation of embryonic stem (ES) cells in vitro. To get insights into LIF-regulated signaling in ES cells, we have analyzed protein-binding and transcriptional properties of STAT recognition sites in ES cells cultivated in the presence and in the absence of LIF. We have detected a specific LIF-regulated DNA-binding activity implicating the STAT3 protein. We show that STAT3 phosphorylation is essential for this LIF-dependent DNA-binding activity. The possibility that ERK2 or a closely related protein kinase, whose activity is modulated in a LIF-dependent manner, contributes to this phosphorylation is discussed. Finally, we show that the multimerized STAT3-binding DNA element confers LIF responsiveness to a minimal thymidine kinase promoter. This, together with our observation that overexpression of STAT3 dominant-negative mutants abrogates this LIF responsiveness, clearly indicates that STAT3 is involved in LIF-regulated transcriptional events in ES cells. Finally, stable expression of such a dominant negative mutant of STAT3 induces morphological differentiation of ES cells despite continuous LIF supply. Our results suggest that STAT3 is a critical target of the LIF signaling pathway, which maintains pluripotent cell proliferation.

The EIa‐inducible, EIIa transcription unit of adenovirus‐2 is transcribed early in infection from two start sites (+1 or EIIaE1 and ‐26 or EIIaE2), neither of which is preceded by canonical TATA box elements. Analysis of promoter deletion and linker scanning mutations for in vivo transcriptional activity after transfection into HeLa cells has indicated the existence of two overlapping promoters in the EIIaE gene. Two regions, each approximately 30 nucleotides upstream from start sites EIIaE1 and EIIaE2, function as TATA box substitutes. A sequence centered at position ‐42 (with respect to the major start site at position +1) is essential for transcription from both sites, while an element further upstream, localized between nucleotides ‐91 and ‐62, is also required for efficient EIIaE transcription, with the 3′ border being dispensable for EIIaE2 transcription. Analysis of the entire series of EIIaE mutants, co‐transfected with an EIa‐containing plasmid, revealed that no unique sequence elements in the EIIaE1 promoter region between ‐97 and +1 were responsible for the stimulation of EIIaE1 transcription by EIa. In contrast, the EIa‐mediated augmentation of EIIaE2 template activity was mainly dependent upon a sequence, the 5′‐TTAAATTT‐3′ putative TATA box substitute, located around position ‐59.

Src homology 2 (SH2) domains are found in a variety of signaling proteins and bind phosphotyrosinecontaining peptide sequences. To explore the binding properties of the SH2 domain of the Src protein kinase, we used immobilized phosphopeptides to bind purified glutathione S-transferase-Src SH2 fusion proteins. With this assay, as well as a free-peptide competition assay, we have estimated the affinities of the Src SH2 domain for various phosphopeptides relative to a Src SH2-phosphopeptide interaction whose Kd has been determined previously (YEEI-P; Kd = 4 nM). Two Src-derived phosphopeptides, one containing the regulatory C-terminal Tyr-527 and another containing the autophosphorylation site Tyr-416, bind the Src SH2 domain in a specific though low-affinity manner (with about 104-lower affinity than the YEEI-P peptide). A platelet-derived growth factor receptor (PDGF-R) phosphopeptide containing Tyr-857 does not bind appreciably to the Src SH2 domain, suggesting it is not the PDGF-R binding site for Src as previously reported. However, another PDGF-R-derived phosphopeptide containing Tyr-751 does bind the Src SH2 domain (with an affinity approximately 2 orders of magnitude lower than that of YEEI-P). All of the phosphopeptides which bind to the Src SH2 domain contain a glutamic acid at position -3 or -4 with respect to phosphotyrosine; changing this residue to alanine greatly diminishes binding. We have also tested Src SH2 mutants for their binding properties and have interpreted our results in light of the recent crystal structure solution for the Src SH2 domain. Mutations in various conserved and nonconserved residues (R155A, R155K, N198E, H201R, and H201L) cause slight reductions in binding, while two mutations cause severe reductions. The W148E mutant domain, which alters the invariant tryptophan that marks the N-terminal border of the SH2 domain, binds poorly to phosphopeptides. Inclusion ofthe SH3 domain in the fusion protein partially restores the binding by the W148E mutant. A change in the invariant arginine that coordinates twice with phosphotyrosine in the peptide (R175L) results in a nearly complete loss of binding. The R175L mutant does display high affinity for the PDGF-R peptide containing Tyr-751, via an interaction that is at least partly phosphotyrosine independent. We have used this interaction to show that the R175L mutation also disrupts the intramolecular interaction between the Src SH2 domain and the phosphorylated C terminus within the context of the entire Src protein; thus, the binding properties observed for mutant domains in an in vitro assay appear to mimic those that occur in vivo.Src homology 2 (SH2) domains are regions of approximately 100 amino acids that bind phosphotyrosine-containing peptide sequences (20,29,33). SH2 domains are implicated in the formation of signaling complexes, such as those that occur upon activation of the platelet-derived growth factor receptor (PDGF-R) and epidermal growth factor receptor. These receptors are autophosphorylated on several tyrosine residue...

Gastric carcinoma is the third leading cause of cancer-related death worldwide. This cancer, most of the time metastatic, is essentially treated by surgery associated with conventional chemotherapy, and has a poor prognosis. The existence of cancer stem cells (CSC) expressing CD44 and a high aldehyde dehydrogenase (ALDH) activity has recently been demonstrated in gastric carcinoma and has opened new perspectives to develop targeted therapy. In this study, we evaluated the effects of all-trans-retinoic acid (ATRA) on CSCs in human gastric carcinoma. ATRA effects were evaluated on the proliferation and tumorigenic properties of gastric carcinoma cells from patient-derived tumors and cell lines in conventional 2D cultures, in 3D culture systems (tumorsphere assay) and in mouse xenograft models. ATRA inhibited both tumorspheres initiation and growth in vitro, which was associated with a cell-cycle arrest through the upregulation of cyclin-dependent kinase (CDK) inhibitors and the downregulation of cell-cycle progression activators. More importantly, ATRA downregulated the expression of the CSC markers CD44 and ALDH as well as stemness genes such as Klf4 and Sox2 and induced differentiation of tumorspheres. Finally, 2 weeks of daily ATRA treatment were sufficient to inhibit gastric tumor progression in vivo, which was associated with a decrease in CD44, ALDH1, Ki67 and PCNA expression in the remaining tumor cells. Administration of ATRA appears to be a potent strategy to efficiently inhibit tumor growth and more importantly to target gastric CSCs in both intestinal and diffuse types of gastric carcinoma.

The Lasp-1 gene, which has been localized to the q12-q2 1 region of human chromosome 17, is amplified and overexpressed in human breast cancers. In addition to the previously reported LIM and SH3 domains of Lasp-1, we report here the identification of an actin-binding domain in the core of the protein. This domain is functional as we demonstrate that Lasp-1 binds actin in vivo and in vitro. In addition, confocal analysis of the Lasp-1 subcellular distribution shows that the protein is colocal

Gastric carcinomas (GC) are heterogeneous tumors, composed of a subpopulation of cluster of differentiation‐44 (CD44)+ tumorigenic and chemoresistant cancer stem cells (CSC). YAP1 and TAZ oncoproteins (Y/T) interact with TEA domain family member 1 (TEAD) transcription factors to promote cell survival and proliferation in multiple tissues. Their activity and role in GC remain unclear. This work aimed to analyze Y/T‐TEAD activity and molecular signature in gastric CSC, and to assess the effect of verteporfin, a Food and Drug Administration‐approved drug preventing Y/T‐TEAD interaction, on gastric CSC tumorigenic properties. Y/T‐TEAD molecular signature was investigated using bioinformatical (KmPlot database), transcriptomic and immunostaining analyses in patient‐derived GC and cell lines. Verteporfin effects on Y/T‐TEAD transcriptional activity, CSC proliferation and tumorigenic properties were evaluated using in vitro tumorsphere assays and mouse models of patient‐derived GC xenografts. High expressions of YAP1, TAZ, TEAD1, TEAD4 and their target genes were associated with low overall survival in nonmetastatic human GC patients (n = 444). This Y/T‐TEAD molecular signature was enriched in CD44+ patient‐derived GC cells and in cells resistant to conventional chemotherapy. Verteporfin treatment inhibited Y/T‐TEAD transcriptional activity, cell proliferation and CD44 expression, and decreased the pool of tumorsphere‐forming CD44+/aldehyde dehydrogenase (ALDH)high gastric CSC. Finally, verteporfin treatment inhibited GC tumor growth in vivo; the residual tumor cells exhibited reduced expressions of CD44 and ALDH1, and more importantly, they were unable to initiate new tumorspheres in vitro. All these data demonstrate that Y/T‐TEAD activity controls gastric CSC tumorigenic properties. The repositioning of verteporfin targeting YAP1/TAZ‐TEAD activity could be a promising CSC‐based strategy for the treatment of GC.

PIAS proteins, cytokine-dependent STAT-associated repressors, exhibit intrinsic E3-type SUMO ligase activities and form a family of transcriptional modulators. Three conserved domains have been identi¢ed so far in this protein family, the SAP box, the MIZ-Zn ¢nger/RING module and the acidic C-terminal domain, which are essential for protein interactions, DNA binding or SUMO ligase activity. We have identi¢ed a novel conserved domain of 180 residues in PIAS proteins and shown that its 'PINIT' motif as well as other conserved motifs (in the SAP box and in the RING domain) are independently involved in nuclear retention of PIAS3L, the long form of PIAS3, that we have characterized in mouse embryonic stem cells.

LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine.