Solution structure of porcine delta sleep-inducing peptide immunoreactive peptide A homolog of the shortsighted gene product

Novel Nuclear Factor-KappaB Targeting Peptide Suppresses β-Amyloid Induced Inflammatory and Apoptotic Responses in Neuronal Cells

In the central nervous system (CNS), activation of the transcription factor nuclear factor-kappa B (NF-κβ) is associated with both neuronal survival and increased vulnerability to apoptosis. The mechanisms underlying these dichotomous effects are attributed to the composition of NF-κΒ dimers. In Alzheimer’s disease (AD), β-amyloid (Aβ) and other aggregates upregulate activation of p65:p50 dimers in CNS cells and enhance transactivation of pathological mediators that cause neuroinflammation and neurodegeneration. Hence selective targeting of activated p65 is an attractive therapeutic strategy for AD. Here we report the design, structural and functional characterization of peptide analogs of a p65 interacting protein, the glucocorticoid induced leucine zipper (GILZ). By virtue of binding the transactivation domain of p65 exposed after release from the inhibitory IκΒ proteins in activated cells, the GILZ analogs can act as highly selective inhibitors of activated p65 with minimal potential for off-target effects.

Novel p65 binding glucocorticoid-induced leucine zipper peptide suppresses experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a neurological disease characterized by inflammatory demyelination in the brain and spinal cord. The immune-mediated inflammation involves well orchestrated intermolecular interactions that exhibit rapid binding kinetics. The binding interfaces of transient interactions frequently include proline residues that favor an extended conformation for molecular recognition. Linear interface peptides are excellent lead inhibitors of specific protein-protein interactions because only small segments of the interface contribute to the binding. Glucocorticoid-induced leucine zipper (GILZ), a recently identified molecule exhibits potent anti-inflammatory properties. Mechanistically, a proline-rich segment in the carboxyl terminus of GILZ physically binds the p65 subunit of nuclear factor-κB and inhibits the transactivation of inflammatory cytokines. Integrating knowledge derived from the mechanism of action of GILZ with in silico structure prediction identified an immunomodulatory peptide, the GILZ-P. Treatment with GILZ-P exhibited therapeutic efficacy in experimental autoimmune encephalomyelitis, a model for human MS.

Bunched, the Drosophila homolog of the mammalian tumor suppressor TSC-22, promotes cellular growth

BACKGROUND

Transforming Growth Factor-beta1 stimulated clone-22 (TSC-22) is assumed to act as a negative growth regulator and tumor suppressor. TSC-22 belongs to a family of putative transcription factors encoded by four distinct loci in mammals. Possible redundancy among the members of the TSC-22/Dip/Bun protein family complicates a genetic analysis. In Drosophila, all proteins homologous to the TSC-22/Dip/Bun family members are derived from a single locus called bunched (bun).

RESULTS

We have identified bun in an unbiased genetic screen for growth regulators in Drosophila. Rather unexpectedly, bun mutations result in a growth deficit. Under standard conditions, only the long protein isoform BunA - but not the short isoforms BunB and BunC - is essential and affects growth. Whereas reducing bunA function diminishes cell number and cell size, overexpression of the short isoforms BunB and BunC antagonizes bunA function.

CONCLUSION

Our findings establish a growth-promoting function of Drosophila BunA. Since the published studies on mammalian systems have largely neglected the long TSC-22 protein version, we hypothesize that the long TSC-22 protein is a functional homolog of BunA in growth regulation, and that it is antagonized by the short TSC-22 protein.

Profile of Transforming Growth Factor-β Responses During the Murine Hair Cycle

Transforming growth factor-beta (TGF-beta) appears to promote the regression phase of the mammalian hair cycle, in vivo in mice and in organ culture of human hair follicles. To assess the relationship between TGF-beta activity and apoptosis of epithelial cells during the murine hair cycle, we identified active TGF-beta responses using phospho-Smad2/3-specific antibodies (PS2). Strong, nuclear PS2 staining was observed in the outer root sheath throughout the anagen growth phase. Some bulb matrix cells were positive for PS2 during late anagen. Extensive, but weak, staining was observed in this region at the anagen-catagen transition. We also examined expression of TGF-beta-stimulated clone-22 (TSC-22), which is associated with TGF-beta-induced apoptosis of some cell lines. Recombinant rat TSC-22 was used to generate a rabbit anti-TSC-22 antibody useful for immunohistochemistry. TSC-22 RNA accumulation and immunoreactivity were observed in follicles throughout the murine hair cycle, including the dermal papilla and lower epithelial strand of late-catagen hair follicles. Neither the expression pattern nor the presence of nuclear TSC-22 correlated with the sites of apoptosis, suggesting that TSC-22 is not an effector of apoptosis in mouse catagen hair follicles. These studies support a complex role for TGF-beta in regulating the regression phase of the cycle, with potential for indirect promotion of apoptosis during the anagen-catagen transition.

Peroxisome proliferator-activated receptor gamma and transforming growth factor-beta pathways inhibit intestinal epithelial cell growth by regulating levels of TSC-22

Peroxisome proliferator-activated receptor gamma (PPARgamma) and transforming growth factor-beta (TGF-beta) are key regulators of epithelial cell biology. However, the molecular mechanisms by which either pathway induces growth inhibition and differentiation are incompletely understood. We have identified transforming growth factor-simulated clone-22 (TSC-22) as a target gene of both pathways in intestinal epithelial cells. TSC-22 is member of a family of leucine zipper containing transcription factors with repressor activity. Although little is known regarding its function in mammals, the Drosophila homolog of TSC-22, bunched, plays an essential role in fly development. The ability of PPARgamma to induce TSC-22 was not dependent on an intact TGF-beta1 signaling pathway and was specific for the gamma isoform. Localization studies revealed that TSC-22 mRNA is enriched in the postmitotic epithelial compartment of the normal human colon. Cells transfected with wild-type TSC-22 exhibited reduced growth rates and increased levels of p21 compared with vector-transfected cells. Furthermore, transfection with a dominant negative TSC-22 in which both repressor domains were deleted was able to reverse the p21 induction and growth inhibition caused by activation of either the PPARgamma or TGF-beta pathways. These results place TSC-22 as an important downstream component of PPARgamma and TGF-beta signaling during intestinal epithelial cell differentiation.

Glucocorticoid-induced leucine zipper inhibits the Raf-extracellular signal-regulated kinase pathway by binding to Raf-1

Glucocorticoid-induced leucine zipper (GILZ) is a leucine zipper protein, whose expression is augmented by dexamethasone (DEX) treatment and downregulated by T-cell receptor (TCR) triggering. Stable expression of GILZ in T cells mimics some of the effects of glucocorticoid hormones (GCH) in GCH-mediated immunosuppressive and anti-inflammatory activity. In fact, GILZ overexpression inhibits TCR-activated NF-kappaB nuclear translocation, interleukin-2 production, FasL upregulation, and the consequent activation-induced apoptosis. We have investigated the molecular mechanism underlying GILZ-mediated regulation of T-cell activation by analyzing the effects of GILZ on the activity of mitogen-activated protein kinase (MAPK) family members, including Raf, MAPK/extracellular signal-regulated kinase (ERK) 1/2 (MEK-1/2), ERK-1/2, and c-Jun NH(2)-terminal protein kinase (JNK). Our results indicate that GILZ inhibited Raf-1 phosphorylation, which resulted in the suppression of both MEK/ERK-1/2 phosphorylation and AP-1-dependent transcription. We demonstrate that GILZ interacts in vitro and in vivo with endogenous Raf-1 and that Raf-1 coimmunoprecipitated with GILZ in murine thymocytes treated with DEX. Mapping of the binding domains and experiments with GILZ mutants showed that GILZ binds the region of Raf interacting with Ras through the NH(2)-terminal region. These data suggest that GILZ contributes, through protein-to-protein interaction with Raf-1 and the consequent inhibition of Raf-MEK-ERK activation, to regulating the MAPK pathway and to providing a further mechanism underlying GCH immunosuppression.

Opposing effects on TSC-22 expression by BMP and receptor tyrosine kinase signals in the developing feather tract

TSC-22 (transforming growth factor-beta-stimulated clone 22) belongs to a family of leucine zipper transcription factors that includes sequences from invertebrates and vertebrates. The single Drosophila family member, encoded by the bunched gene, serves to integrate opposing bone morphogenic protein (BMP) and epidermal growth factor (EGF) signals during oogenesis. Similarly, mammalian TSC-22 expression is regulated by several families of secreted signaling molecules in cultured cells. Here, we show that chick TSC-22 is dynamically expressed in the condensing feather bud, as well as in many tissues of the chick embryo. BMP-2/4, previously shown to inhibit bud development, repress TSC-22 expression during feather bud formation in vivo. Noggin, a BMP antagonist, promotes TSC-22 expression. EGF, TGF-alpha, and fibroblast growth factor all promote both feather bud development and TSC-22 expression; each can promote ectopic feather buds that are regularly spaced between existing feather buds. Thus, TSC-22 is a candidate to integrate small imbalances in receptor tyrosine kinase and BMP signaling during feather tract development to generate stable and reproducible morphogenetic responses.

Expression screening for Lhx3 downstream genes identifies Thg-1pit as a novel mouse gene involved in pituitary development

Thg-1pit, a novel mouse gene, was detected in a screen for genes that are differentially expressed in the developing pituitary of wild-type and Lhx3 null mutant embryos. The predicted translation product of the Thg-1pit gene contains a C-terminal TSC-box adjacent to a leucine zipper motif. These features are characteristic for the TSC-22/DIP/bun family of proteins. The onset of prominent Thg-1pit expression coincides with Lhx3 activation at early stages of pituitary development. Expression is further enhanced as cells begin to differentiate within the developing pituitary gland. No expression is observed in the pituitary rudiment of mutants that lack Lhx3 function. A possible role is thus suggested for Lhx3 activities in the regulation of Thg-1pit function during early steps of pituitary organogenesis.

pH-dependent changes in the in vitro ligand-binding properties and structure of human clusterin

Clusterin is a glycoprotein which is locally overexpressed at sites of tissue damage or stress, leading to the proposal that it may be a cytoprotective protein. It has been shown that clusterin has chaperone-like activity, being able to protect proteins against precipitation under stress conditions. It has also been shown that local acidosis is common at sites of tissue damage or stress. We asked whether acidic pH induces structural changes in clusterin and enhances its ability to bind to other proteins. We found by affinity chromatography and ELISA that the binding of clusterin to glutathione-S-transferase, IgG, apolipoprotein A-I, and complement protein C9 was enhanced at mildly acidic compared to physiological pH. Analytical ultracentrifugation and gel filtration studies revealed that clusterin exists in different polymerization states with monomer occurring preferentially at pH 5.5 and multimeric species at pH 7.5. Although circular dichroism showed little difference in the alpha-helical and beta-sheet contents of clusterin at pH 5 compared to pH 7.5, evidence for pH-dependent structural changes in clusterin was obtained from fluorescence experiments. pH titrations showed reversible changes in the fluorescence of tryptophan residues in clusterin. There was a reversible 2-fold increase in the fluorescence of the extrinsic probe 4, 4'-bis(1-anilinonaphthalene-8-sulfonate) bound to clusterin at pH 5. 5 compared to pH 7.5. There was also a 3.5-fold increase in fluorescence resonance energy transfer from tryptophan residues in clusterin to 4,4'-bis(1-anilinonaphthalene-8-sulfonate) at pH 5.5 compared to pH 7.5. These data suggest that pH-induced changes in the structure of clusterin are responsible for its enhanced ability to bind protein ligands at mildly acidic pH.

Drosophila bunched integrates opposing DPP and EGF signals to set the operculum boundary

The Drosophila BMP homolog DPP can function as a morphogen, inducing multiple cell fates across a developmental field. However, it is unknown how graded levels of extracellular DPP are interpreted to organize a sharp boundary between different fates. Here we show that opposing DPP and EGF signals set the boundary for an ovarian follicle cell fate. First, DPP regulates gene expression in the follicle cells that will create the operculum of the eggshell. DPP induces expression of the enhancer trap reporter A359 and represses expression of bunched, which encodes a protein similar to the mammalian transcription factor TSC-22. Second, DPP signaling indirectly regulates A359 expression in these cells by downregulating expression of bunched. Reduced bunched function restores A359 expression in cells that lack the Smad protein MAD; ectopic expression of BUNCHED suppresses A359 expression in this region. Importantly, reduction of bunched function leads to an expansion of the operculum and loss of the collar at its boundary. Third, EGF signaling upregulates expression of bunched. We previously demonstrated that the bunched expression pattern requires the EGF receptor ligand GURKEN. Here we show that activated EGF receptor is sufficient to induce ectopic bunched expression. Thus, the balance of DPP and EGF signals sets the boundary of bunched expression. We propose that the juxtaposition of cells with high and low BUNCHED activity organizes a sharp boundary for the operculum fate.

Transforming growth factor-beta-stimulated clone-22 is a member of a family of leucine zipper proteins that can homo- and heterodimerize and has transcriptional repressor activity

TGF-beta-stimulated clone-22 (TSC-22) encodes a leucine zipper-containing protein that is highly conserved during evolution. Two homologues are known that share a similar leucine zipper domain and another conserved domain (designated the TSC box). Only limited data are available on the function of TSC-22 and its homologues. TSC-22 is transcriptionally up-regulated by many different stimuli, including anti-cancer drugs and growth inhibitors, and recent data suggest that TSC-22 may play a suppressive role in tumorigenesis. In this paper we show that TSC-22 forms homodimers via its conserved leucine zipper domain. Using a yeast two-hybrid screen, we identified a TSC-22 homologue (THG-1) as heterodimeric partner. Furthermore, we report the presence of two more mammalian family members with highly conserved leucine zippers and TSC boxes. Interestingly, both TSC-22 and THG-1 have transcriptional repressor activity when fused to a heterologous DNA-binding domain. The repressor activity of TSC-22 appears sensitive for promoter architecture, but not for the histone deacetylase inhibitor trichostatin A. Mutational analysis showed that this repressor activity resides in the non-conserved regions of the protein and is enhanced by the conserved dimerization domain. Our results suggest that TSC-22 belongs to a family of leucine zipper-containing transcription factors that can homodimerize and heterodimerize with other family members and that at least two TSC-22 family members may be repressors of transcription.