ABSTRACT
Wnt proteins initiate signaling by binding to seven transmembrane spanning receptors of the frizzled (Fz) family together with the members of the low-density lipoprotein receptor-related protein (LRP) 5 and 6. A chimera of human Wnt3 and Fz1 receptor was developed that efficiently activated the TCF-luciferase reporter. Deletion of the cytoplasmic tail and point mutations in the PDZ binding region in the chimera resulted in the loss of Wnt signaling, suggesting a critical role for the Fz cytoplasmic region in Wnt signaling. The Fz CRD is also critical for Wnt signaling, as a deletion of 29 amino acids in the 2nd cysteine loop resulted in the total loss of TCF-luciferase activation. DKK-1 protein blocks upregulation of the TCF-luciferase reporter by the Wnt3-Fz1 chimera, suggesting involvement of LRP in Wnt3-Fz1 signaling. Expression of a Wnt3-Fz1 chimera in C3H10T1/2 cells resulted in the upregulation of alkaline phosphatase activity and inhibition of adipocyte formation, demonstrating that the Wnt3-Fz1 chimera is a potent activator of differentiation of C3H10T1/2 cells into osteoblasts and an inhibitor of their differentiation into the adipocyte lineage. In summary, the Wnt-Fz chimera approach has the potential to better our understanding of the mechanism of Wnt action and its role, particularly in stem cell differentiation. In addition, this methodology can be utilized to identify inhibitors of either Wnt, Fz or interactors of the canonical pathway, which may have potential therapeutic value in the treatment of cancers and other diseases.
Subject(s)
Frizzled Receptors/metabolism , Models, Biological , Recombinant Fusion Proteins/metabolism , Signal Transduction , Wnt Proteins/metabolism , Amino Acid Sequence , Animals , Cell Differentiation , Cell Line , Frizzled Receptors/chemistry , Humans , Mesenchymal Stem Cells/cytology , Mesenchymal Stem Cells/metabolism , Mice , Molecular Sequence Data , Mutant Proteins/chemistry , Mutant Proteins/metabolism , Protein Binding , Protein Structure, Tertiary , Recombinant Fusion Proteins/chemistry , Wnt Proteins/chemistry , Wnt3 ProteinABSTRACT
Secreted frizzled related protein-1 (sFRP-1) inhibitors have the potential to be used for the treatment of osteoporosis or other bone related disorders, since the level of sFRP-1 affects osteoblast apoptosis and proliferation. From high throughput screening, we have identified a class of iminooxothiazolidines as sFRP-1 inhibitors. Structure-activity relationships were established for various regions of the scaffold along with the biochemical characterization of this class to probe selectivity, binding and ex vivo activity.
Subject(s)
Osteogenesis/physiology , Proteins/isolation & purification , Calcification, Physiologic , Cell Differentiation/physiology , Cells, Cultured , Frizzled Receptors/antagonists & inhibitors , Frizzled Receptors/isolation & purification , Intracellular Signaling Peptides and Proteins , Molecular Structure , Proteins/antagonists & inhibitors , RANK LigandABSTRACT
Canonical Wnt signaling has been demonstrated to increase bone formation, and Wnt pathway components are being pursued as potential drug targets for osteoporosis and other metabolic bone diseases. Deletion of the Wnt antagonist secreted frizzled-related protein (sFRP)-1 in mice activates canonical signaling in bone and increases trabecular bone formation in aged animals. We have developed small molecules that bind to and inhibit sFRP-1 in vitro and demonstrate robust anabolic activity in an ex vivo organ culture assay. A library of over 440,000 drug-like compounds was screened for inhibitors of human sFRP-1 using a cell-based functional assay that measured activation of canonical Wnt signaling with an optimized T-cell factor (TCF)-luciferase reporter gene assay. One of the hits in this screen, a diarylsulfone sulfonamide, bound to sFRP-1 with a K(D) of 0.35 microM in a tryptophan fluorescence quenching assay. This compound also selectively inhibited sFRP-1 with an EC(50) of 3.9 microM in the cell-based functional assay. Optimization of this high throughput screening hit for binding and functional potency as well as metabolic stability and other pharmaceutical properties led to improved lead compounds. One of these leads (WAY-316606) bound to sFRP-1 with a K(D) of 0.08 microM and inhibited it with an EC(50) of 0.65 microM. Moreover, this compound increased total bone area in a murine calvarial organ culture assay at concentrations as low as 0.0001 microM. This work demonstrates the feasibility of developing small molecules that inhibit sFRP-1 and stimulate canonical Wnt signaling to increase bone formation.
Subject(s)
Osteogenesis/drug effects , Proteins/antagonists & inhibitors , Sulfonamides/pharmacology , Wnt Proteins/antagonists & inhibitors , Animals , Apoptosis/drug effects , Cell Line, Tumor , Humans , Intracellular Signaling Peptides and Proteins , Mice , Organ Culture Techniques , Osteoblasts/cytology , Osteoblasts/drug effects , Osteocytes/cytology , Osteocytes/drug effects , Proteins/genetics , Proteins/metabolism , Skull/cytology , Skull/drug effects , Spectrometry, Fluorescence , Sulfonamides/chemistryABSTRACT
Inhibitor of secreted frizzled related protein-1 (sFRP-1) would be a novel potential osteogenic agent, since loss of sFRP-1 affects osteoblast proliferation, differentiation, and activity, resulting in improved bone mineral density, quality, and strength. We have identified small molecule diarylsulfone sulfonamide derivatives as sFRP-1 inhibitors. Structure-activity relationship generated for various regions of the scaffold was utilized to improve the biochemical profile, resulting in the identification of potent selective analogues, such as 16 with desirable pharmaceutical profile.
Subject(s)
Osteoblasts/metabolism , Proteins/antagonists & inhibitors , Sulfonamides/chemistry , Sulfones/chemistry , Animals , Biochemistry/methods , Bone Density , Cells, Cultured , Drug Design , Humans , Intracellular Signaling Peptides and Proteins , Mice , Models, Chemical , Signal Transduction , Structure-Activity RelationshipABSTRACT
Individual therapy goals of psychotherapy patients either focus on symptom relief (disorder specific) or on improvements also in other functional areas (generic). The present study with 62 outpatients in a cognitive behavioral group psychotherapy (CBGT) investigated whether patients attain their disorder specific goals better than their generic therapy goals. Results indicated that patients reached disorder specific goals to a higher degree than the generic goals, although the group treatment specifically targeted the disorder specific goals. Implications of the results for the assessment and therapy of phobic patients are discussed.
Subject(s)
Goals , Phobic Disorders/psychology , Phobic Disorders/therapy , Psychotherapy, Group , Adult , Agoraphobia/psychology , Agoraphobia/therapy , Cognitive Behavioral Therapy , Diagnostic and Statistical Manual of Mental Disorders , Female , Humans , Male , Middle Aged , Neuropsychological Tests , Panic Disorder/psychology , Panic Disorder/therapy , Psychiatric Status Rating Scales , Treatment OutcomeABSTRACT
Secreted frizzled-related proteins (sFRPs) are glycoproteins that are recognized as Wnt antagonists. To identify the functional domains that are involved in Wnt antagonist function, several sFRP-1 mutants and sFRP-1/sFRP-2 chimeras were generated. These mutants were characterized in an optimized T-cell factor (TCF)-luciferase based assay in U2OS human osteosarcoma cells. Deletions of the sFRP-1 cysteine rich domain (CRD) lead to the complete loss of Wnt antagonist function. A region between amino acids 73-86 within the second loop of the CRD of sFRP-1 was necessary for the optimal Wnt inhibitory function. Within this region, a conserved tyrosine residue played a critical role, and its change to neutral or polar amino acids lead to decreased Wnt inhibitory activity. The sFRP-1/sFRP-2 chimeras with the netrin domain of sFRP-1 replaced by corresponding sFRP-2 sequences showed 40-70% loss of Wnt antagonist function. The sFRP-1/sFRP-2 chimera with the replacement of C-terminal 19 amino acids of sFRP-1 with 11 amino acids of sFRP-2 resulted in 70% loss of activity indicating that carboxyl-terminal region of sFRP-1 is important for its Wnt inhibitory activity. The structure-function analysis studies of sFRP-1 clearly demonstrate the interaction of several functional domains for its optimal Wnt antagonist function.
Subject(s)
Intercellular Signaling Peptides and Proteins/chemistry , Membrane Proteins/chemistry , Structure-Activity Relationship , Wnt Proteins/antagonists & inhibitors , Amino Acid Sequence , Amino Acid Substitution , Cell Line, Tumor , Conserved Sequence , Gene Deletion , Genes, Reporter , Humans , Intercellular Signaling Peptides and Proteins/genetics , Luciferases/metabolism , Membrane Proteins/genetics , Molecular Sequence Data , Mutant Chimeric Proteins/metabolism , Osteosarcoma/pathology , Plasmids , Protein Binding , Protein Structure, Secondary , Protein Structure, Tertiary , Sequence Homology, Amino Acid , Transfection , Tryptophan/chemistry , Tyrosine/chemistryABSTRACT
Mechanisms controlling human bone formation remain to be fully elucidated. We have used differential display-polymerase chain reaction analysis to characterize osteogenic pathways in conditionally immortalized human osteoblasts (HOBs) representing distinct stages of differentiation. We identified 82 differentially expressed messages and found that the Wnt antagonist secreted frizzled-related protein (sFRP)-1 was the most highly regulated of these. Transient transfection of HOBs with sFRP-1 suppressed canonical Wnt signaling by 70% confirming its antagonistic function in these cells. Basal sFRP-1 mRNA levels increased 24-fold during HOB differentiation from pre-osteoblasts to pre-osteocytes, and then declined in mature osteocytes. This expression pattern correlated with levels of cellular viability such that the pre-osteocytes, which had the highest levels of sFRP-1 mRNA, also had the highest rate of cell death. Basal sFRP-1 mRNA levels also increased 29-fold when primary human mesenchymal stem cells were differentiated to osteoblasts supporting the developmental regulation of the gene. Expression of sFRP-1 mRNA was induced 38-fold following prostaglandin E2 (PGE2) treatment of pre-osteoblasts and mature osteoblasts that had low basal message levels. In contrast, sFRP-1 expression was down-regulated by as much as 80% following transforming growth factor (TGF)-beta1 treatment of pre-osteocytes that had high basal mRNA levels. Consistent with this, treatment of pre-osteoblasts and mature osteoblasts with PGE(2) increased apoptosis threefold, while treatment of pre-osteocytes with TGF-beta1 decreased cell death by 50%. Likewise, over-expression of sFRP-1 in HOBs accelerated the rate of cell death threefold. These results establish sFRP-1 as an important negative regulator of human osteoblast and osteocyte survival.
Subject(s)
Apoptosis/physiology , Osteoblasts/metabolism , Osteocytes/metabolism , Proteins/metabolism , Proteins/pharmacology , Wnt Proteins/antagonists & inhibitors , Animals , Annexin A5/metabolism , Annexin A5/pharmacology , Apoptosis/drug effects , Cell Differentiation/drug effects , Cells, Cultured , Dinoprostone/metabolism , Dinoprostone/pharmacology , Gene Expression Regulation/drug effects , Humans , In Situ Hybridization , Intracellular Signaling Peptides and Proteins , Mice , Osteoblasts/drug effects , Osteocytes/drug effects , RNA, Messenger/metabolism , Rats , Recombinant Fusion Proteins/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction/physiology , Transforming Growth Factor beta/metabolism , Transforming Growth Factor beta/pharmacology , Transforming Growth Factor beta1 , Wnt Proteins/metabolismABSTRACT
The GeneSwitch system is a mifepristone-inducible expression system that provides exceptionally low uninduced and high-induced protein expression in mammalian cells. We have developed an adenovirus recombinant containing GeneSwitch protein driven by the GAL4-tk promoter, as well as recombinants containing sFRP-1 and luciferase reporter under the control of the GAL4-E1b promoter. Luciferase activity in A549 cells infected with the GeneSwitch and Luciferase viruses is very low in ethanol-treated cells, while the level of luciferase activity increases 200-fold in cells treated with mifepristone. Conditional expression of functional sFRP-1 is demonstrated in A549, human osteoblast, and CHO cell lines by either the co-infection of cells with sFRP-1 and GeneSwitch viruses or the infection of GeneSwitch expressing cell lines with sFRP-1 virus and subsequent treatment with mifepristone. The expression of sFRP-1 is seen as early as 4 h post-mifepristone treatment, reaching the highest levels at 20 h. The sFRP-1 protein is present in conditioned media, and the protein is functional based upon its ability to inhibit the Wnt-mediated activation of TCF-Luciferase reporter activity. The regulated expression of sFRP-1 utilizing adenovirus vectors provides an opportunity to address the contribution of sFRP-1 in the regulation of stem cell differentiation, maturation, and their function by modulating the Wnt signaling.
Subject(s)
Genetic Techniques , Intercellular Signaling Peptides and Proteins/biosynthesis , Intercellular Signaling Peptides and Proteins/genetics , Membrane Proteins/biosynthesis , Membrane Proteins/genetics , Mifepristone/pharmacology , Adenoviridae/genetics , Animals , CHO Cells , Cell Line , Cricetinae , Culture Media, Conditioned/pharmacology , DNA-Binding Proteins/metabolism , Electrophoresis, Polyacrylamide Gel , Ethanol/pharmacology , Gene Expression Regulation , Hormone Antagonists/pharmacology , Humans , Intercellular Signaling Peptides and Proteins/metabolism , Luciferases/metabolism , Lymphoid Enhancer-Binding Factor 1 , Models, Genetic , Osteoblasts/metabolism , Plasmids/metabolism , RNA/metabolism , Recombinant Proteins/chemistry , Time Factors , Transcription Factors/metabolism , Wnt ProteinsABSTRACT
The two known estrogen receptors, ER alpha and ER beta, are hormone inducible transcription factors that have distinct roles in regulating cell proliferation and differentiation. The natural ligand, 17 beta-estradiol (E2), binds with high affinity to both ER alpha and ER beta. However, a close analogue, 16 alpha-iodo-17 beta-estradiol (16 alpha IE2) showed about 10-fold selectivity for ER alpha over ER beta. From X-ray studies, it has been shown that the ligand-binding domains (LBD) of the two receptors are strikingly similar, and that only two changes fall within the binding cavity (ER alpha Leu384 to ER beta Met336, and ER alpha Met421 to ER beta Ile373). To understand the molecular basis for the ER alpha selectivity of 16 alpha IE2, mutants and chimeras of ER alpha and ER beta were generated, and ligand-binding and transactivation functions were studied. The ER alpha Leu384 Met mutant behaved like ER alpha WT in the presence of 16 alpha IE2; whereas the profile of the ER alpha Met421 Ile mutant was similar to that of ER beta WT. The ER beta mutant Ile373 Met behaved like ER alpha with 16 alpha IE2. The results clearly demonstrate the role of ER alpha Met421 in the ER alpha selectivity of 16 alpha IE2.
