Syndecan-1 and Syndecan-4 Capture Epidermal Growth Factor Receptor Family Members and the α3ß1 Integrin Via Binding Sites in Their Ectodomains: NOVEL SYNSTATINS PREVENT KINASE CAPTURE AND INHIBIT α6ß4-INTEGRIN-DEPENDENT EPITHELIAL CELL MOTILITY.

The α6ß4 integrin is known to associate with receptor tyrosine kinases when engaged in epithelial wound healing and in carcinoma invasion and survival. Prior work has shown that HER2 associates with α6ß4 integrin and syndecan-1 (Sdc1), in which Sdc1 engages the cytoplasmic domain of the ß4 integrin subunit allowing HER2-dependent motility and carcinoma cell survival. In contrast, EGFR associates with Sdc4 and the α6ß4 integrin, and EGFR-dependent motility depends on cytoplasmic engagement of ß4 integrin with Sdc4. However, how HER2 and EGFR assimilate into a complex with the syndecans and integrin, and why kinase capture is syndecan-specific has remained unknown. In the present study, we demonstrate that HER2 is captured via a site, comprised of amino acids 210-240, in the extracellular domain of human Sdc1, and EGFR is captured via an extracellular site comprised of amino acids 87-131 in human Sdc4. Binding assays using purified recombinant proteins demonstrate that the interaction between the EGFR family members and the syndecans is direct. The α3ß1 integrin, which is responsible for the motility of the cells, is captured at these sites as well. Peptides based on the interaction motifs in Sdc1 and Sdc4, called synstatins (SSTN210-240 and SSTN87-131) competitively displace the receptor tyrosine kinase and α3ß1 integrin from the syndecan with an IC50 of 100-300 nm. The syndecans remain anchored to the α6ß4 integrin via its cytoplasmic domain, but the activation of cell motility is disrupted. These novel SSTN peptides are potential therapeutics for carcinomas that depend on these HER2- and EGFR-coupled mechanisms for their invasion and survival.

Cytoplasmic domain interactions of syndecan-1 and syndecan-4 with α6ß4 integrin mediate human epidermal growth factor receptor (HER1 and HER2)-dependent motility and survival.

Epithelial cells are highly dependent during wound healing and tumorigenesis on the α6ß4 integrin and its association with receptor tyrosine kinases. Previous work showed that phosphorylation of the ß4 subunit upon matrix engagement depends on the matrix receptor syndecan (Sdc)-1 engaging the cytoplasmic domain of the ß4 integrin and coupling of the integrin to human epidermal growth factor receptor-2 (HER2). In this study, HER2-dependent migration activated by matrix engagement is compared with migration stimulated by EGF. We find that whereas HER2-dependent migration depends on Sdc1, EGF-dependent migration depends on a complex consisting of human epidermal growth factor receptor-1 (HER1, commonly known as EGFR), α6ß4, and Sdc4. The two syndecans recognize distinct sites at the extreme C terminus of the ß4 integrin cytoplasmic domain. The binding motif in Sdc1 is QEEXYX, composed in part by its syndecan-specific variable (V) region and in part by the second conserved (C2) region that it shares with other syndecans. A cell-penetrating peptide containing this sequence competes for HER2-dependent epithelial migration and carcinoma survival, although it is without effect on the EGFR-stimulated mechanism. ß4 mutants bearing mutations specific for Sdc1 and Sdc4 recognition act as dominant negative mutants to block cell spreading or cell migration that depends on HER2 or EGFR, respectively. The interaction of the α6ß4 integrin with the syndecans appears critical for it to be utilized as a signaling platform; migration depends on α3ß1 integrin binding to laminin 332 (LN332; also known as laminin 5), whereas antibodies that block α6ß4 binding are without effect. These findings indicate that specific syndecan family members are likely to have key roles in α6ß4 integrin activation by receptor tyrosine kinases.

dCREB2-mediated enhancement of memory formation.

CREB-responsive transcription has an important role in adaptive responses in all cells and tissue. In the nervous system, it has an essential and well established role in long-term memory formation throughout a diverse set of organisms. Activation of this transcription factor correlates with long-term memory formation and disruption of its activity interferes with this process. Most convincingly, augmenting CREB activity in a number of different systems enhances memory formation. In Drosophila, a sequence rearrangement in the original transgene used to enhance memory formation has been a source of confusion. This rearrangement prematurely terminates translation of the full-length protein, leaving the identity of the "enhancing molecule" unclear. In this report, we show that a naturally occurring, downstream, in-frame initiation codon is used to make a dCREB2 protein off of both transgenic and chromosomal substrates. This protein is a transcriptional activator and is responsible for memory enhancement. A number of parameters can affect enhancement, including the short-lived activity of the activator protein, and the time-of-day when induction and behavioral training occur. Our results reaffirm that overexpression of a dCREB2 activator can enhance memory formation and illustrate the complexity of this behavioral enhancement.

Septate-junction-dependent luminal deposition of chitin deacetylases restricts tube elongation in the Drosophila trachea.

The function of tubular epithelial organs like the kidney and lung is critically dependent on the length and diameter of their constituting branches. Genetic analysis of tube size control during Drosophila tracheal development has revealed that epithelial septate junction (SJ) components and the dynamic chitinous luminal matrix coordinate tube growth. However, the underlying molecular mechanisms controlling tube expansion so far remained elusive. Here, we present the analysis of two luminal chitin binding proteins with predicted polysaccharide deacetylase activities (ChLDs). ChLDs are required to assemble the cable-like extracellular matrix (ECM) and restrict tracheal tube elongation. Overexpression of native, but not of mutated, ChLD versions also interferes with the structural integrity of the intraluminal ECM and causes aberrant tube elongation. Whereas ChLD mutants have normal SJ structure and function, the luminal deposition of the ChLD requires intact cellular SJs. This identifies a new molecular function for SJs in the apical secretion of ChLD and positions ChLD downstream of the SJs in tube length control. The deposition of the chitin luminal matrix first promotes and coordinates radial tube expansion. We propose that the subsequent structural modification of chitin by chitin binding deacetylases selectively instructs the termination of tube elongation to the underlying epithelium.

Drosophila Reptin and other TIP60 complex components promote generation of silent chromatin.

Histone acetyltransferase (HAT) complexes have been linked to activation of transcription. Reptin is a subunit of different chromatin-remodeling complexes, including the TIP60 HAT complex. In Drosophila, Reptin also copurifies with the Polycomb group (PcG) complex PRC1, which maintains genes in a transcriptionally silent state. We demonstrate genetic interactions between reptin mutant flies and PcG mutants, resulting in misexpression of the homeotic gene Scr. Genetic interactions are not restricted to PRC1 components, but are also observed with another PcG gene. In reptin homozygous mutant cells, a Polycomb response-element-linked reporter gene is derepressed, whereas endogenous homeotic gene expression is not. Furthermore, reptin mutants suppress position-effect variegation (PEV), a phenomenon resulting from spreading of heterochromatin. These features are shared with three other components of TIP60 complexes, namely Enhancer of Polycomb, Domino, and dMRG15. We conclude that Drosophila Reptin participates in epigenetic processes leading to a repressive chromatin state as part of the fly TIP60 HAT complex rather than through the PRC1 complex. This shows that the TIP60 complex can promote the generation of silent chromatin.

Antineoplastic effects of histone deacetylase inhibitors in neuroendocrine cancer cells are mediated through transcriptional regulation of Notch1 by activator protein 1.

Notch signaling is minimally active in neuroendocrine (NE) cancer cells. While histone deacetylase inhibitors (HDACi) suppress NE cancer growth by inducing Notch, the molecular mechanism underlying this interplay has not yet been defined. NE cancer cell lines BON, H727, and MZ-CRC-1 were treated with known HDACi Thailadepsin-A (TDP-A) and valproic acid (VPA), and Notch1 mRNA expression was measured with RT-PCR. Truncated genomic fragments of the Notch1 promotor region fused with luciferase reporter were used to identify the potential transcription factor (TF) binding site. The key regulatory TF was identified with the electrophoretic mobility shift assay (EMSA). The effect of HDACi on Notch1 level was determined before and after silencing the TF. TDP-A and VPA induced Notch1 mRNA in a dose-dependent manner. A functional DNA motif at -80 to -52 from the Notch1 start codon responsible for the HDACi-dependent Notch1 induction was identified. Mutation of this core sequence failed to induce luciferase activity despite HDACi treatment. EMSA showed the greatest gel shift with AP-1 in nuclear extracts. Knockdown of AP-1 significantly attenuated the effect of HDACi on Notch1 induction. Interestingly, AP-1 transfection did not alter Notch1 level, suggesting that AP-1 is necessary but insufficient for HDACi activation of Notch1. Therefore, AP-1 is the TF that binds to a specific transcription-binding site within the Notch1 promotor region to trigger Notch1 transcription. Elucidating the HDACi activation mechanism may lead to the development of novel therapeutic options against NE cancers and facilitate the identification of clinical responders and prevent adverse effects.

Influences on gene expression in vivo by a Shine-Dalgarno sequence.

The Shine-Dalgarno (SD+: 5'-AAGGAGG-3') sequence anchors the mRNA by base pairing to the 16S rRNA in the small ribosomal subunit during translation initiation. We have here compared how an SD+ sequence influences gene expression, if located upstream or downstream of an initiation codon. The positive effect of an upstream SD+ is confirmed. A downstream SD+ gives decreased gene expression. This effect is also valid for appropriately modified natural Escherichia coli genes. If an SD+ is placed between two potential initiation codons, initiation takes place predominantly at the second start site. The first start site is activated if the distance between this site and the downstream SD+ is enlarged and/or if the second start site is weakened. Upstream initiation is eliminated if a stable stem-loop structure is placed between this SD+ and the upstream start site. The results suggest that the two start sites compete for ribosomes that bind to an SD+ located between them. A minor positive contribution to upstream initiation resulting from 3' to 5' ribosomal diffusion along the mRNA is suggested. Analysis of the E. coli K12 genome suggests that the SD+ or SD-like sequences are systematically avoided in the early coding region suggesting an evolutionary significance.

Cis control of gene expression in E.coli by ribosome queuing at an inefficient translational stop signal.

An UGA stop codon context which is inefficient because of the 3'-flanking context and the last two amino acids in the gene protein product has a negative effect on gene expression, as shown using a model protein A' gene. This is particularly true at low mRNA levels, corresponding to a high intracellular ribosome/mRNA ratio. The negative effect is smaller if this ratio is decreased, or if the distance between the initiation and termination signals is increased. The results suggest that an inefficient termination codon can cause ribosomal pausing and queuing along the upstream mRNA region, thus blocking translation initiation of short genes. This cis control effect is dependent on the stop codon context, including the C-terminal amino acids in the gene product, the translation initiation signal strength, the ribosome/mRNA ratio and the size of the mRNA coding region. A large proportion of poorly expressed natural Escherichia coli genes are small, and the weak termination codon UGA is under-represented in small, highly expressed E.coli genes as compared with the efficient stop codon UAA.