Other articles by Claudia Litterst on PubMed

• An LXXLL Motif in the Transactivation Domain of STAT6 Mediates Recruitment of NCoA-1/SRC-1 The Journal of Biological Chemistry. Sep, 2002  |   Pubmed ID: 12138096 Signal transducer and activator of transcription 6 (STAT6) regulates transcriptional activation in response to interleukin-4 (IL-4)-induced tyrosine phosphorylation by direct interaction with coactivators. The CREB-binding protein and the nuclear coactivator 1 (NCoA-1), a member of the p160/steroid receptor coactivator family, bind independently to specific regions of STAT6 and act as coactivators. In this study we show that an LXXLL motif in the STAT6 transactivation domain mediates the interaction with NCoA-1. Peptides representing this motif as well as antibodies generated against this motif inhibited STAT6/NCoA-1 interaction in glutathione S-transferase pulldown assays. Peptides derived from the STAT6 transactivation domain adjacent to the LXXLL motif as well as antibodies against these peptides showed no inhibitory effect. Mutagenesis of the LXXLL motif eliminated the STAT6/NCoA-1 interaction in vitro and in vivo, supporting the specific role of this motif in NCoA-1 binding. Importantly, mutagenesis of the STAT-LXXLL motif strongly diminished the IL-4-regulated activation of the endogenous STAT6 target gene eotaxin-3. Taken together, these results indicate that the STAT6-LXXLL-binding motif mediates the interaction with NCoA-1 in transcriptional activation and represents a new potential drug target for the inhibition of the STAT6 transactivation function in allergic diseases.
• NCoA-1/SRC-1 is an Essential Coactivator of STAT5 That Binds to the FDL Motif in the Alpha-helical Region of the STAT5 Transactivation Domain The Journal of Biological Chemistry. Nov, 2003  |   Pubmed ID: 12954634 Signal transducer and activator of transcription 5 (STAT5) is a transcription factor that activates prolactin (PRL)-dependent gene expression in the mammary gland. For the activation of its target genes, STAT5 recruits coactivators like p300 and the CREB-binding protein (CBP). In this study we analyzed the function of p300/CBP-associated members of the p160/SRC/NCoA-family in STAT5-mediated transactivation of beta-casein expression. We found that only one of them, NCoA-1, acts as a coactivator for both STAT5a and STAT5b. The two coactivators p300/CBP and NCoA-1 cooperatively enhance STAT5a-mediated transactivation. For NCoA-1-dependent coactivation of STAT5, both the activation domain 1 and the amino-terminal bHLH/PAS domain are required. The amino-terminal region mediates the interaction with STAT5a in cells. A motif of three amino acids in an alpha-helical region of the STAT5a-transactivation domain is essential for the binding of NCoA-1 and for the transcriptional activity of STAT5a. Moreover we observed that NCoA-1 is involved in the synergistic action of the glucocorticoid receptor and STAT5a on the beta-casein promoter. These findings support a model in which STAT5, in concert with the glucocorticoid receptor, recruits a multifunctional coactivator complex to initiate the PRL-dependent transcription.
• Structure of the NCoA-1/SRC-1 PAS-B Domain Bound to the LXXLL Motif of the STAT6 Transactivation Domain Journal of Molecular Biology. Feb, 2004  |   Pubmed ID: 14757047 Signal transducer and activator of transcription 6 (STAT6) regulates transcriptional activation in response to interleukin-4 (IL-4) by direct interaction with coactivators. The CREB-binding protein (p300/CBP) and the nuclear coactivator 1 (NCoA-1), a member of the p160/steroid receptor coactivator family, bind independently to specific regions of the STAT6 transactivation domain and act as coactivators. The interaction between STAT6 and NCoA-1 is mediated by an LXXLL motif in the transactivation domain of STAT6. To define the mechanism of coactivator recognition, we determined the crystal structure of the NCoA-1 PAS-B domain in complex with the STAT6 LXXLL motif. The amphipathic, alpha-helical STAT6 LXXLL motif binds mostly through specific hydrophobic interactions to NCoA-1. A single amino acid of the NCoA-1 PAS-B domain establishes hydrophilic interactions with the STAT6 peptide. STAT6 interacts only with the PAS-B domain of NCoA-1 but not with the homologous regions of NCoA-2 and NCoA-3. The residues involved in binding the STAT6 peptide are strongly conserved between the different NCoA family members. Therefore surface complementarity between the hydrophobic faces of the STAT6 fragment and of the NCoA-1 PAS-B domain almost exclusively defines the binding specificity between the two proteins.
• Coactivators in Gene Regulation by STAT5 Vitamins and Hormones. 2005  |   Pubmed ID: 15727811 Signal transducer and activator of transcription 5 (STAT5) is a member of the STAT family of transcription factors that relay the effect of diverse cytokines, hormones, and growth factors by regulating the transcription of distinct target genes. This function is emphasized by its crucial role in the development of the mammary gland and the hematopoietic system. Cytokine receptor-associated Janus kinases (JAKs) induce dimerization, nuclear translocation, and DNA binding through tyrosine phosphorylation of STAT5. STAT5 regulates the expression of cytokine target genes by binding to gamma interferon-activated sequence (GAS) motifs. Transcriptional activation requires the contact of STAT5 to coactivators and components of the transcription machinery. Another important point in transcriptional activation is the cooperation with other transcription factors that bind in close vicinity to the target gene promoters and enhancers. Their concerted action can result in an enhanced binding to the promoters or in cooperative recruitment of coactivators. In addition, cross-talk with other signaling pathways as well as secondary modifications of STAT5 have been described to affect transactivation function.
• Cadherins Mediate Both the Association Between PS1 and Beta-catenin and the Effects of PS1 on Beta-catenin Stability The Journal of Biological Chemistry. Oct, 2005  |   Pubmed ID: 16126725 Presenilin1 (PS1), a protein involved in cellular development, forms functional complexes with beta-catenin, a regulator of Wnt signaling and cell-cell adhesion. In addition, both proteins have been shown to play important roles in disease including cancer and Alzheimer disease. Although PS1 and beta-catenin are found in the same complexes, it is not clear whether they bind directly to each other or a third complex component, like cadherin, may mediate their interactions. Here we show that PS1 and beta-catenin form no detectable complexes in cells that express no cadherin. In contrast, these complexes are readily found in E-cadherin containing cells. Furthermore, binding of both PS1 and beta-catenin to E-cadherin is necessary for the formation of PS1/beta-catenin complexes. Importantly, our data show that binding of PS1 to cadherin mediates the effects of PS1 on the phosphorylation, ubiquitination, and destabilization of beta-catenin. Thus, cadherins mediate both the association of PS1 and beta-catenin and the effects of PS1 on the cellular levels of beta-catenin.
• Metalloproteinase/Presenilin1 Processing of EphrinB Regulates EphB-induced Src Phosphorylation and Signaling The EMBO Journal. Mar, 2006  |   Pubmed ID: 16511561 Bidirectional signaling triggered by interacting ephrinB receptors (EphB) and ephrinB ligands is crucial for development and function of the vascular and nervous systems. A signaling cascade triggered by this interaction involves activation of Src kinase and phosphorylation of ephrinB. The mechanism, however, by which EphB activates Src in the ephrinB-expressing cells is unknown. Here we show that EphB stimulates a metalloproteinase cleavage of ephrinB2, producing a carboxy-terminal fragment that is further processed by PS1/gamma-secretase to produce intracellular peptide ephrinB2/CTF2. This peptide binds Src and inhibits its association with inhibitory kinase Csk, allowing autophosphorylation of Src at residue tyr418. EphrinB2/CTF2-activated Src phosphorylates ephrinB2 and inhibits its processing by gamma-secretase. These data show that the PS1/gamma-secretase system controls Src activation and ephrinB phosphorylation by regulating production of Src activator ephrinB2/CTF2. Accordingly, gamma-secretase inhibitors prevented the EphB-induced sprouting of endothelial cells and the recruitment of Grb4 to ephrinB. PS1 FAD and gamma-secretase dominant-negative mutants inhibited the EphB-induced cleavage of ephrinB2 and Src autophosphorylation, raising the possibility that FAD mutants interfere with the functions of Src and ephrinB2 in the CNS.
• FAD Mutants Unable to Increase Neurotoxic Abeta 42 Suggest That Mutation Effects on Neurodegeneration May Be Independent of Effects on Abeta Journal of Neurochemistry. May, 2007  |   Pubmed ID: 17254019 Strong support for a primary causative role of the Abeta peptides in the development of Alzheimer's disease (AD) neurodegeneration derives from reports that presenilin familial AD (FAD) mutants alter amyloid precursor protein processing, thus increasing production of neurotoxic Abeta 1-42 (Abeta 42). This effect of FAD mutants is also reflected in an increased ratio of peptides Abeta 42 over Abeta 1-40 (Abeta 40). In the present study, we show that several presenilin 1 FAD mutants failed to increase production of Abeta 42 or the Abeta 42/40 ratio. Our data suggest that the mechanism by which FAD mutations promote neurodegeneration and AD may be independent of their effects on Abeta production.
• Ligand Binding and Calcium Influx Induce Distinct Ectodomain/gamma-secretase-processing Pathways of EphB2 Receptor The Journal of Biological Chemistry. Jun, 2007  |   Pubmed ID: 17428795 Binding of EphB receptors to ephrinB ligands on the surface of adjacent cells initiates signaling cascades that regulate angiogenesis, axonal guidance, and neuronal plasticity. These functions require processing of EphB receptors and removal of EphB-ephrinB complexes from the cell surface, but the mechanisms involved are poorly understood. Here we show that the ectodomain of EphB2 receptor is released to extracellular space following cleavage after EphB2 residue 543. The remaining membrane-associated fragment is cleaved by the presenilin-dependent gamma-secretase activity after EphB2 residue 569 releasing an intracellular peptide that contains the cytoplasmic domain of EphB2. This cleavage is inhibited by presenilin 1 familial Alzheimer disease mutations. Processing of EphB2 receptor depends on specific treatments: ephrinB ligand-induced processing requires endocytosis, and the ectodomain cleavage is sensitive to peptide inhibitor N-benzyloxycarbonyl-Val-Leu-leucinal but insensitive to metalloproteinase inhibitor GM6001. The ligand-induced processing takes place in endosomes and involves the rapid degradation of the extracellular EphB2. EphrinB ligand stimulates ubiquitination of EphB2 receptor. Calcium influx- and N-methyl-d-aspartic acid-induced processing of EphB2 is inhibited by GM6001 and ADAM10 inhibitors but not by N-benzyloxycarbonyl-Val-Leu-leucinal. This processing requires no endocytosis and promotes rapid shedding of extracellular EphB2, indicating that it takes place at the plasma membrane. Our data identify novel cleavages and modifications of EphB2 receptor and indicate that specific conditions determine the proteolytic systems and subcellular sites involved in the processing of this receptor.
• Peptide EphB2/CTF2 Generated by the Gamma-secretase Processing of EphB2 Receptor Promotes Tyrosine Phosphorylation and Cell Surface Localization of N-methyl-D-aspartate Receptors The Journal of Biological Chemistry. Oct, 2009  |   Pubmed ID: 19661068 Presenilin 1, a protein involved in the development of familial Alzheimer disease, is an important functional component of the gamma-secretase complex that processes many cell surface receptors including the EphB2 tyrosine kinase receptors (Litterst, C., Georgakopoulos, A., Shioi, J., Ghersi, E., Wisniewski, T., Wang, R., Ludwig, A., and Robakis, N. K. (2007) J. Biol. Chem. 282, 16155-16163). Recent evidence reveals that cytosolic peptides produced by the combined metalloproteinase/gamma-secretase processing of cell surface proteins function in signal transduction and protein phosphorylation. Here we show that peptide EphB2/CTF2 released to the cytosol by the gamma-secretase processing of EphB2 receptor, has tyrosine kinase activity, and directly phosphorylates the N-methyl-d-aspartate receptor (NMDAR) subunits in both cell lines and primary neuronal cultures. This phosphorylation occurs in the absence of Src kinases and is resistant to Src inhibitors revealing a novel pathway of NMDAR tyrosine phosphorylation independent of Src activity. EphB2/CTF2, but not a kinase-deficient mutant of EphB2/CTF2, promotes the cell surface expression of NMDAR. Because NMDAR plays central roles in synaptic plasticity and function, our results provide a potential link between the gamma-secretase function of presenilin 1 and learning and memory.
• Interaction of STAT6 with Its Co-activator SRC-1/NCoA-1 is Regulated by Dephosphorylation of the Latter Via PP2A Nucleic Acids Research. Apr, 2011  |   Pubmed ID: 21148148 Regulation of gene expression represents a central issue in signal-regulated cellular responses. STAT6 is a critical mediator of IL-4 stimulated gene activation. To mediate this function, STAT6 recruits co-activator complexes. We have previously shown that STAT6 binds the PAS-B domain of the co-activator NCoA-1 via an LXXLL motif in its transactivation domain. Our recent finding that the PAS-B domain of NCoA-1 is also essential for co-activator complex formation points to an additional level of regulation of the co-activator assembly. In this study, we discovered that dephosphorylation of NCoA-1 is essential for the interaction with STAT6 and for IL-4-dependent transcriptional activation. PP2A dephosphorylates NCoA-1 and facilitates the activation of STAT6 target genes. Interestingly, simultaneous inhibition of phosphatase and cyclin-dependent kinases rescues the NCoA-1/STAT6 interaction. Moreover, arrest of cells at G1/S results in enhanced NCoA-1 phosphorylation. In summary, our results indicate that the interaction of NCoA-1 and STAT6 is dynamically regulated by the phosphatase PP2A and by cyclin-dependent kinases. This provides a mechanism for integrating transcriptional regulation by STAT6 with cell cycle progression.