[Show abstract][Hide abstract] ABSTRACT: Maintenance of stem/progenitor cell-progeny relationships is required for tissue homeostasis during normal turnover and repair.
Wnt signaling is implicated in both maintenance and differentiation of adult stem/progenitor cells, yet how this pathway serves
these dichotomous roles remains enigmatic. We previously proposed a model suggesting that specific interaction of β-catenin
with either of the homologous Kat3 co-activators, p300 or CBP, differentially regulates maintenance vs. differentiation of
embryonic stem cells. Limited knowledge of endogenous mechanisms driving differential β-catenin-co-activator interactions
and their role in adult somatic stem/progenitor cell maintenance vs. differentiation led us to explore this process in defined
models of adult progenitor cell differentiation. We focused primarily on alveolar epithelial type II (AT2) cells, progenitors
of distal lung epithelium, and identified a novel axis whereby Wnt5a/protein kinase C (PKC) signaling regulates specific β-catenin-co-activator
interactions to promote adult progenitor cell differentiation. p300/β-catenin but not CBP/β-catenin interaction increases
as AT2 cells differentiate to a type I (AT1) cell-like phenotype. Additionally, p300 transcriptionally activates AT1 cell-specific
gene aquaporin-5. IQ-1, a specific inhibitor of p300/β-catenin interaction, prevents differentiation of not only primary AT2
cells, but also tracheal epithelial cells, and C2C12 myoblasts. p300 phosphorylation at S89 enhances p300/β-catenin interaction,
concurrent with alveolar epithelial cell differentiation. Wnt5a, a traditionally non-canonical Wnt ligand regulates S89 phosphorylation
and p300/β-catenin interactions in a PKC-dependent manner, likely involving PKCζ. These studies identify a novel intersection
of canonical and non-canonical Wnt signaling in adult progenitor cell differentiation that has important implications for
targeting β-catenin to modulate adult progenitor cell behavior in disease.
Preview · Article · Feb 2016 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: CREB-binding protein (CBP) and p300 are highly homologous transcriptional coactivators with unique, non-redundant roles that bind a wide array of proteins, including catenins-β and γ. ICG-001 is a small-molecule inhibitor that specifically inhibits the CBP/catenin interaction. Importantly, ICG-001 does not inhibit the p300/catenin interaction. We demonstrate that specifically inhibiting the interaction between CBP and catenin with ICG-001 results in the differentiation of quiescent drug-resistant chronic myelogenous leukemia-initiating cells (CML LICs), thereby sensitizing them to BCR-ABL tyrosine kinase inhibitors, for example, Imatinib. Using ICG-001 in a NOD/SCID/IL2Rγ(-/-) mouse model of engrafted human chronic myelogenous leukemia, we now demonstrate the complete elimination of engrafted leukemia after only one course of combined chemotherapy. Combination-treated animals live as long as their non-engrafted littermates. Results from these studies demonstrate that specifically antagonizing the CBP/catenin interaction with ICG-001 can eliminate drug-resistant CML LICs without deleterious effects to the normal endogenous hematopoietic stem cell population.Oncogene advance online publication, 14 December 2015; doi:10.1038/onc.2015.438.
[Show abstract][Hide abstract] ABSTRACT: The Wnt signaling pathway is critically involved in both the development and homeostasis of tissues via regulation of their endogenous stem cells. Aberrant Wnt signaling has been described as a key player in the initiation of and/or maintenance and development of many cancers, via affecting the behavior of Cancer Stem Cells (CSCs). CSCs are considered by most to be responsible for establishment of the tumor and also for disease relapse, as they possess inherent drug-resistance properties. The development of new therapeutic compounds targeting the Wnt signaling pathway promises new hope to eliminate CSCs and achieve cancer eradication. However, a major challenge resides in developing a strategy efficient enough to target the dysregulated Wnt pathway in CSCs, while being safe enough to not damage the normal somatic stem cell population required for tissue homeostasis and repair. Here we review recent therapeutic approaches to target the Wnt pathway and their clinical applications.
No preview · Article · Dec 2015 · Critical reviews in oncology/hematology
[Show abstract][Hide abstract] ABSTRACT: The Wnt signaling cascade is critically important in stem cell biology, both in homeostatic maintenance and repair and regeneration of tissues and organs, through their respective somatic stem cells (SSCs). However, aberrant Wnt signaling is associated with a wide array of tumor types and Wnt signaling is important in the so-termed cancer stem cell/tumor-initiating cell (CSC/TIC) population. The ability to safely therapeutically target the Wnt signaling pathway offers enormous promise. However, just like the Sword of Damocles, significant risks and concerns regarding targeting such a critical pathway in normal stem cell maintenance and tissue homeostasis remain ever present. With this in mind, we review our current understanding of the role of Wnt signaling in SSCs and CSC/TICs and the potential to pharmacologically manipulate these endogenous stem cell populations (both normal and tumor).
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No preview · Article · Aug 2015 · Seminars in Reproductive Medicine
[Show abstract][Hide abstract] ABSTRACT: Despite their high degree of identity and even higher homology, the two Kat3 transcriptional coactivators, CBP and p300, have distinct functions, particularly within the Wnt/β-catenin signaling cascade. ICG-001, by directly binding to CBP but not p300, inhibits CBP/β-catenin transcription and has served as an invaluable chemical genomic tool to dissect the Wnt signaling cascade and the divergent roles of these two coactivators. However, to date no direct antagonist of the p300/β-catenin interaction has been reported. We now report the identification and validation of the first highly specific, direct p300/β-catenin antagonists, YH249/250 and their ability to maintain pluripotency in ESC.
No preview · Article · May 2015 · Current Molecular Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Wnt/β-catenin signaling has been suggested to regulate proximal-distal determination of embryonic lung epithelium based upon genetically modified mouse models. The previously identified and characterized small molecule inhibitor IQ1 can pharmacologically decrease the interaction between β-catenin and its transcriptional coactivator p300, thereby enhancing the β-catenin/CBP interaction. Inhibition of the β-catenin/p300 interaction by IQ1 blocks the differentiation of embryonic stem cells and epicardial progenitor cells; however, whether differential coactivator usage by β-catenin plays a role in proximal-distal determination of lung epithelium is unknown.
We examined the effects of inhibiting the β-catenin/p300 interaction with IQ1 on lung branching morphogenesis in mouse embryos in utero and mouse embryonic lung organ culture ex vivo. The phenotype of IQ1 treated lungs was analyzed by epithelial staining, histology, quantitative PCR and in situ hybridization.
Inhibition of the β-catenin/p300 interaction by IQ1 disrupted the distal branching of mouse lung epithelium both in utero and ex vivo. IQ1 proximalized lung epithelium with decreased expression of the genes Bmp4 and Fgf10, hallmarks of distal lung determination, and increased expression of the proximal genes Sox2 and Scgb1a1 (CC10) as shown by quantitative PCR and in situ hybridization. The disruption of branching was reversible ex vivo as branching was reinitiated after removal of IQ1 from the media.
The results demonstrate that the β-catenin/p300 interaction plays a critical role in proximal-distal determination of the epithelium in mouse lung branching morphogenesis and β-catenin/p300 inhibition pharmacologically proximalizes lung epithelium.
[Show abstract][Hide abstract] ABSTRACT: Cancer stem cells (CSCs), also known as tumor initiating cells are now considered to be the root cause of most if not all cancers, evading treatment and giving rise to disease relapse. They have become a central focus in new drug development. Prospective identification, understanding the key pathways that maintain CSCs, and being able to target CSCs, particularly if the normal stem cell population could be spared, could offer an incredible therapeutic advantage. The Wnt signaling cascade is critically important in stem cell biology, both in homeostatic maintenance of tissues and organs through their respective somatic stem cells and in the CSC/tumor initiating cell population. Aberrant Wnt signaling is associated with a wide array of tumor types. Therefore, the ability to safely target the Wnt signaling pathway offers enormous promise to target CSCs. However, just like the sword of Damocles, significant risks and concerns regarding targeting such a critical pathway in normal stem cell maintenance and tissue homeostasis remain ever present. With this in mind, we review recent efforts in modulating the Wnt signaling cascade and critically analyze therapeutic approaches at various stages of development.
[Show abstract][Hide abstract] ABSTRACT: WNT-β-catenin signalling is involved in a multitude of developmental processes and the maintenance of adult tissue homeostasis by regulating cell proliferation, differentiation, migration, genetic stability and apoptosis, as well as by maintaining adult stem cells in a pluripotent state. Not surprisingly, aberrant regulation of this pathway is therefore associated with a variety of diseases, including cancer, fibrosis and neurodegeneration. Despite this knowledge, therapeutic agents specifically targeting the WNT pathway have only recently entered clinical trials and none has yet been approved. This Review examines the problems and potential solutions to this vexing situation and attempts to bring them into perspective.
No preview · Article · Jul 2014 · Nature Reviews Drug Discovery
[Show abstract][Hide abstract] ABSTRACT: Throughout our life, long lived somatic stem cells (SSCs) regenerate adult tissues both during homeostatic processes and repair after injury. The role of aberrant regulation of SSC has also recently gained prominence in the field of cancer research. Following malignant transformation, so termed cancer stem cells (CSCs), endowed with the same properties as SSCs (i.e. the ability to both self-renew as well as generate differentiated progenitors) play a major part in tumor initiation, therapy resistance and ultimately relapse. The same signaling pathways involved in regulating SSC maintenance are also involved in the regulation of CSCs. CSCs have been demonstrated to exist in a wide array of tumor types including leukemias, brain, breast, prostate, colon etc.. Consequently, one of the key goals in cancer research over the past decade has been to develop therapeutic strategies to safely eliminate the CSC population without damaging the endogenous SSC population. A major hurdle to this goal lies in the identification of the key mechanisms that distinguish CSCs from the normal endogenous tissue stem cells. This review will discuss the discovery and of the specific CBP/catenin antagonist ICG-001 and the ongoing clinical development of the second generation CBP/catenin antagonist PRI-724. Importantly, specific CBP/catenin antagonists appear to have the ability to safely eliminate CSCs by taking advantage of an intrinsic differential preference in the way SSCs and CSCs divide.This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Wnt signaling plays an important role in development and disease. In this review we focus on the role of the canonical Wnt signaling pathway in somatic stem cell biology and its critical role in tissue homeostasis. We present current knowledge how Wnt/β-catenin signaling affects tissue stem cell behavior in various organ systems, including the gut, mammary gland, the hematopoietic and nervous system. We discuss evidence that canonical Wnt signaling can both maintain potency and an undifferentiated state as well as cause differentiation in somatic stem cells, depending on the cellular and environmental context. Based on studies by our lab and others, we will attempt to explain the dichotomous behavior of this signaling pathway in determining cell fate decisions and put special emphasis on the interaction of β-catenin with two highly homologous co-activator proteins, CBP and p300, to shed light on the their differential role in the outcome of Wnt/β-catenin signaling. Furthermore, we review current knowledge regarding the aberrant regulation of Wnt/β-catenin signaling in cancer biology, particularly its pivotal role in the context of cancer stem cells. Finally, we discuss data demonstrating that small molecule modulators of the β-catenin/co-activator interaction can be used to shift the balance between undifferentiated proliferation and differentiation, which potentially presents a promising therapeutic approach to stem cell based disease mechanisms.
Full-text · Article · May 2014 · Stem cell reviews
[Show abstract][Hide abstract] ABSTRACT: The Wnt signaling pathway controls several cell processes, such as motility and proliferation during embryonic development. Wnt signaling is also involved in the maintenance of potency and the induction of differentiation in stem cells. Aberrant Wnt signaling is implicated in several cancer types. Particularly in colorectal cancer (CRC), the Wnt-β-catenin signaling cascade is at the center of the carcinogenesis, and mutations in this pathway can be found in almost all CRC patients. We discuss the potential of targeting Wnt-β-catenin signaling with a brief overview of the pathway and the most promising pathway inhibitors.
[Show abstract][Hide abstract] ABSTRACT: Hypoxia has been reported to regulate both stem cell maintenance and differentiation. Wnt signaling is also a key regulator in stem cells. The recent discovery of functional cross-regulation between the Wnt pathway and HIF-1α/HIF-2α signaling further highlights the complexity of the role of hypoxia in the regulation of stem cells. In this report we reveal that human CML cell lines treated under hypoxic conditions increase the percentage of leukemia stem/initiating-like cells, as judged by surface marker expression, colony forming ability and quiescence. We demonstrate that differential usage of the Kat3 coactivators, CREBBP/Creb Binding Protein (CBP) and EP300 (p300) by catenin, with increased CBP/catenin signaling at the expense of p300/catenin signaling, is mechanistically correlated with the increase in the leukemia stem/initiating-like population. A specific small molecule inhibitor of CBP/catenin dependent transcription, ICG-001, can reverse these effects further demonstrating the critical involvement of CBP/catenin signaling in enhancing and maintaining the leukemia stem/initiating-like cell population under hypoxic conditions.
No preview · Article · Feb 2014 · Current Molecular Pharmacology
[Show abstract][Hide abstract] ABSTRACT: The adult mammalian heart has limited capability for self-repair after myocardial infarction. Therefore, therapeutic strategies that improve post-infarct cardiac function are critically needed. The small molecule ICG-001 modulates Wnt signaling and increased the expression of genes beneficial for cardiac regeneration in epicardial cells. Lineage tracing experiments, demonstrated the importance of β-catenin/p300 mediated transcription for epicardial progenitor contribution to the myocardium. Female rats given ICG-001 for 10 days post-occlusion significantly improved ejection fraction by 8.4%, compared to controls (P<0.05). Taken together, Wnt modulation via β-catenin/CBP inhibition offers a promising therapeutic strategy towards restoration of myocardial tissues and an enhancement of cardiac functions following infarction.
[Show abstract][Hide abstract] ABSTRACT: Wnt/β-catenin signaling has a central role in the development and progression of most colon cancers (CCs). Germline variants in Wnt/β-catenin pathway genes may result in altered gene function and/or activity, thereby causing inter-individual differences in relation to tumor recurrence capacity and chemoresistance. We investigated germline polymorphisms in a comprehensive panel of Wnt/β-catenin pathway genes to predict time to tumor recurrence (TTR) in patients with stage III and high-risk stage II CC. A total of 234 patients treated with 5-fluorouracil-based chemotherapy were included in this study. Whole-blood samples were analyzed for putative functional germline polymorphisms in SFRP3, SFRP4, DKK2, DKK3, Axin2, APC, TCF7L2, WNT5B, CXXC4, NOTCH2 and GLI1 genes by PCR-based restriction fragment-length polymorphism or direct DNA sequencing. Polymorphisms with statistical significance were validated in an independent study cohort. The minor allele of WNT5B rs2010851 T>G was significantly associated with a shorter TTR (10.7 vs 4.9 years; hazard ratio: 2.48; 95% CI, 0.96-6.38; P=0.04) in high-risk stage II CC patients. This result remained significant in multivariate Cox's regression analysis. This study shows that the WNT5B germline variant rs2010851 was significantly identified as a stage-dependent prognostic marker for CC patients after 5-fluorouracil-based adjuvant therapy.The Pharmacogenomics Journal advance online publication, 2 July 2013; doi:10.1038/tpj.2013.20.
No preview · Article · Jul 2013 · The Pharmacogenomics Journal
[Show abstract][Hide abstract] ABSTRACT: Drug resistance in acute lymphoblastic leukemia (ALL) remains a major problem warranting new treatment strategies. Wnt/catenin signaling is critical for the self-renewal of normal hematopoietic progenitor cells. Deregulated Wnt signaling is evident in chronic and acute myeloid leukemia; however, little is known about ALL. Differential interaction of catenin with either the Kat3 coactivator CREBBP (CREB-binding protein (CBP)) or the highly homologous EP300 (p300) is critical to determine divergent cellular responses and provides a rationale for the regulation of both proliferation and differentiation by the Wnt signaling pathway. Usage of the coactivator CBP by catenin leads to transcriptional activation of cassettes of genes that are involved in maintenance of progenitor cell self-renewal. However, the use of the coactivator p300 leads to activation of genes involved in the initiation of differentiation. ICG-001 is a novel small-molecule modulator of Wnt/catenin signaling, which specifically binds to the N-terminus of CBP and not p300, within amino acids 1-110, thereby disrupting the interaction between CBP and catenin. Here, we report that selective disruption of the CBP/β- and γ-catenin interactions using ICG-001 leads to differentiation of pre-B ALL cells and loss of self-renewal capacity. Survivin, an inhibitor-of-apoptosis protein, was also downregulated in primary ALL after treatment with ICG-001. Using chromatin immunoprecipitation assay, we demonstrate occupancy of the survivin promoter by CBP that is decreased by ICG-001 in primary ALL. CBP mutations have been recently identified in a significant percentage of ALL patients, however, almost all of the identified mutations reported occur C-terminal to the binding site for ICG-001. Importantly, ICG-001, regardless of CBP mutational status and chromosomal aberration, leads to eradication of drug-resistant primary leukemia in combination with conventional therapy in vitro and significantly prolongs the survival of NOD/SCID mice engrafted with primary ALL. Therefore, specifically inhibiting CBP/catenin transcription represents a novel approach to overcome relapse in ALL.Oncogene advance online publication, 3 June 2013; doi:10.1038/onc.2013.169.
[Show abstract][Hide abstract] ABSTRACT: An optimal culture system for human pluripotent stem cells should be fully defined and free of animal components. To date, most xeno-free culture systems require human feeder cells and/or highly complicated culture media that contain activators of the fibroblast growth factor (FGF) and transforming growth factor-β (TGFβ) signaling pathways, and none provide for replacement of FGF/TGFβ ligands with chemical compounds. The Wnt/β-catenin signaling pathway plays an important role in mouse embryonic stem cells in leukemia inhibitory factor-independent culture; however, the role of Wnt/β-catenin signaling in human pluripotent stem cell is still poorly understood and controversial because of the dual role of Wnts in proliferation and differentiation. Building on our previous investigations of small molecules modulating Wnt/β-catenin signaling in mouse embryonic stem cells, we identified a compound, ID-8, that could support Wnt-induced human embryonic stem cell proliferation and survival without differentiation. Dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) is the target of the small molecule ID-8. Its role in human pluripotent cell renewal was confirmed by DYRK knockdown in human embryonic stem cells. Using Wnt and the DYRK inhibitor ID-8, we have developed a novel and simple chemically defined xeno-free culture system that allows for long-term expansion of human pluripotent stem cells without FGF or TGFβ activation. These culture conditions do not include xenobiotic supplements, serum, serum replacement, or albumin. Using this culture system, we have shown that several human pluripotent cell lines maintained pluripotency (>20 passages) and a normal karyotype and still retained the ability to differentiate into derivatives of all three germ layers. This Wnt-dependent culture system should provide a platform for complete replacement of growth factors with chemical compounds.
No preview · Article · Nov 2012 · STEM CELLS TRANSLATIONAL MEDICINE