Mitogen-activated protein kinases promote WNT/beta-catenin signaling via phosphorylation of LRP6

Multiple myeloma: signaling pathways and targeted therapy

Multiple myeloma (MM) is the second most common hematological malignancy of plasma cells, characterized by osteolytic bone lesions, anemia, hypercalcemia, renal failure, and the accumulation of malignant plasma cells. The pathogenesis of MM involves the interaction between MM cells and the bone marrow microenvironment through soluble cytokines and cell adhesion molecules, which activate various signaling pathways such as PI3K/AKT/mTOR, RAS/MAPK, JAK/STAT, Wnt/β-catenin, and NF-κB pathways. Aberrant activation of these pathways contributes to the proliferation, survival, migration, and drug resistance of myeloma cells, making them attractive targets for therapeutic intervention. Currently, approved drugs targeting these signaling pathways in MM are limited, with many inhibitors and inducers still in preclinical or clinical research stages. Therapeutic options for MM include non-targeted drugs like alkylating agents, corticosteroids, immunomodulatory drugs, proteasome inhibitors, and histone deacetylase inhibitors. Additionally, targeted drugs such as monoclonal antibodies, chimeric antigen receptor T cells, bispecific T-cell engagers, and bispecific antibodies are being used in MM treatment. Despite significant advancements in MM treatment, the disease remains incurable, emphasizing the need for the development of novel or combined targeted therapies based on emerging theoretical knowledge, technologies, and platforms. In this review, we highlight the key role of signaling pathways in the malignant progression and treatment of MM, exploring advances in targeted therapy and potential treatments to offer further insights for improving MM management and outcomes.

PI15, a novel secreted WNT-signaling antagonist, regulates chondrocyte differentiation

PURPOSE/AIM OF STUDY

During the development of the vertebrate skeleton, the progressive differentiation and maturation of chondrocytes from mesenchymal progenitors is precisely coordinated by multiple secreted factors and signaling pathways. The WNT signaling pathway has been demonstrated to play a major role in chondrogenesis. However, the identification of secreted factors that fine-tune WNT activity has remained elusive. Here, in this study, we have identified PI15 (peptidase inhibitor 15, protease Inhibitor 15, SugarCrisp), a member of the CAP (cysteine rich secretory proteins, antigen 5, and pathogenesis related 1 proteins) protein superfamily, as a novel secreted WNT antagonist dynamically upregulated during chondrocyte differentiation.

MATERIALS AND METHODS

ATDC5 cells, C3H10T1/2 micromass cultures and primary chondrocyte cells were used as in vitro models of chondrogenesis. PI15 levels were stably depleted or overexpressed by viral shRNA or expression vectors. Chondrogenesis was evaluated by qPCR gene expression analysis and Alcian blue staining. Protein interactions were determined by coimmunoprecipitation assays.

RESULTS AND CONCLUSIONS

shRNA-mediated knockdown of PI15 in ATDC5 cells, C3H10T1/2 cells or primary chondrocytes inhibits chondrogenesis, whereas the overexpression of PI15 strongly enhances chondrogenic potential. Mechanistically, PI15 binds to the LRP6 WNT co-receptor and blocks WNT-induced LRP6 phosphorylation, thus repressing WNT-induced transcriptional activity and alleviating the inhibitory effect of WNT signaling on chondrogenesis. Altogether, our findings suggest that PI15 acts as a key regulator of chondrogenesis and unveils a mechanism through which chondrocyte-derived molecules can modulate WNT activity as differentiation proceeds, thereby creating a positive feedback loop that further drives differentiation.

Role of CELF2 in ferroptosis: Potential targets for cancer therapy (Review)

Ferroptosis is a novel form of regulated cellular necrosis that plays a critical role in promoting cancer progression and developing drug resistance. The main characteristic of ferroptosis is iron‑dependent lipid peroxidation caused by excess intracellular levels of reactive oxygen species. CUGBP ELAV‑like family number 2 (CELF2) is an RNA‑binding protein that is downregulated in various types of cancer and is associated with poor patient prognoses. CELF2 can directly bind mRNA to a variety of ferroptosis control factors; however, direct evidence of the regulatory role of CELF2 in ferroptosis is currently limited. The aim of the present review was to summarise the findings of previous studies on CELF2 and its role in regulating cellular redox homeostasis. The present review may provide insight into the possible mechanisms through which CELF2 affects ferroptosis and to provide recommendations for future studies.

Lactoferrin alleviates cyclophosphamide induced-nephropathy through suppressing the orchestration between Wnt4/β-catenin and ERK1/2/NF-κB signaling and modulating klotho and Nrf2/HO-1 pathway

AIMS

Cyclophosphamide is an alkylating agent with vast arrays of therapeutic activity. Currently, its medical use is limited due to its numerous adverse events, including nephrotoxicity. This study aimed to follow the molecular mechanisms behind the potential renoprotective action of lactoferrin (LF) against cyclophosphamide (CP)-induced renal injury.

MATERIALS AND METHODS

For fulfillment of our aim, Spragw-Dwaly rats were orally administrated LF (300 mg/kg) for seven consecutive days, followed by a single intraperitoneal injection of CP (150 mg/kg).

KEY FINDINGS

Treatment of CP-injured rats with LF significantly reduced the elevated creatinine and blood urea nitrogen (BUN), markedly upregulated Nrf2/HO-1 signaling with consequent increase in renal total antioxidant capacity (TAC) and decrease in renal malondialdehyde (MDA) level. Furthermore, LF treatment significantly reduced the elevated renal p-ERK1/2 expression, tumor necrosis factor-α (TNFα), interleukin-6 (IL-6), nuclear factor-kappa B (NF-κB) levels in CP-treated animals. Interestingly, LF treatment downregulated Wnt4/β-catenin signaling and increased both renal klotho gene expression and serum klotho level. Furthermore, LF treatment reduced apoptosis in kidney tissue via suppressing GSK-3β expression and modulating caspase-3 and Bcl2 levels. Histopathological examination of kidney tissue confirmed the protective effect of LF against CP-induced renal injury.

SIGNIFICANCE

The present findings document the renoprotective effect of LF against CP-induced nephropathy, which may be mediated via suppressing ERK1/2/ NF-κB and Wnt4/β-catenin trajectories and enhancing klotho expression and Nrf2/HO-1 signaling.

Upregulation of β-catenin due to loss of miR-139 contributes to motor neuron death in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the loss of motor neurons (MNs). There are no effective treatments and patients usually die within 2-5 years of diagnosis. Emerging commonalities between familial and sporadic cases of this complex multifactorial disorder include disruption to RNA processing and cytoplasmic inclusion bodies containing TDP-43 and/or FUS protein aggregates. Both TDP-43 and FUS have been implicated in RNA processing functions, including microRNA biogenesis, transcription, and splicing. In this study, we explore the misexpression of microRNAs in an iPSC-based disease model of FUS ALS. We identify the downregulation of miR-139, an MN-enriched microRNA, in FUS and sporadic ALS MN. We discover that miR-139 downregulation leads to the activation of canonical WNT signaling and demonstrate that the WNT transcriptional mediator β-catenin is a major driver of MN degeneration in ALS. Our results highlight the importance of homeostatic RNA networks in ALS.

The role of the Wnt signalling pathway in the energy metabolism of bone remodelling

OBJECTIVES

Bone remodelling is necessary to repair old and impaired bone caused by aging and its effects. Injury in the process of bone remodelling generally leads to the development of various bone diseases. Energy metabolism plays crucial roles in bone cell formation and function, the disorder of which will disrupt the balance between bone formation and bone resorption.

MATERIALS AND METHODS

Here, we review the intrinsic interactions between bone remodelling and energy metabolism and the role of the Wnt signalling pathway.

RESULTS

We found a close interplay between metabolic pathways and bone homeostasis, demonstrating that bone plays an important role in the regulation of energy balance. We also discovered that Wnt signalling is associated with multiple biological processes regulating energy metabolism in bone cells.

CONCLUSIONS

Thus, targeted regulation of Wnt signalling and the recovery of the energy metabolism function of bone cells are key means for the treatment of metabolic bone diseases.

Hsa-miR-143-3p inhibits Wnt-β-catenin and MAPK signaling in human corneal epithelial stem cells

Our previous study demonstrated hsa-miR-143-3p as one of the highly expressed miRNAs in enriched corneal epithelial stem cells (CESCs). Hence this study aims to elucidate the regulatory role of hsa-miR-143-3p in the maintenance of stemness in CESCs. The target genes of hsa-miR-143-3p were predicted and subjected to pathway analysis to select the targets for functional studies. Primary cultured limbal epithelial cells were transfected with hsa-miR-143-3p mimic, inhibitor or scrambled sequence using Lipofectamine 3000. The transfected cells were analysed for (i) colony forming potential, (ii) expression of stem cell (SC) markers/ transcription factors (ABCG2, NANOG, OCT4, KLF4, ΔNp63), (iii) differentiation marker (Cx43), (iv) predicted five targets of hsa-miR-143-3p (DVL3, MAPK1, MAPK14, KRAS and KAT6A), (v) MAPK signaling regulators and (vi) Wnt-β-catenin signaling regulators by qPCR, immunofluorescence staining and/or Western blotting. High expression of hsa-miR-143-3p increased the colony forming potential (10.04 ± 1.35%, p < 0.001) with the ability to form holoclone-like colonies in comparison to control (3.33 ± 0.71%). The mimic treated cells had increased expression of SC markers but reduced expression of Cx43 and hsa-miR-143-3p targets involved in Wnt-β-catenin and MAPK signaling pathways. The expression of β-catenin, active β-catenin and ERK2 in hsa-miR-143-3p inhibitor transfected cells were higher than the control cells and the localized nuclear expression indicated the activation of Wnt and MAPK signaling. Thus, the probable association of hsa-miR-143-3p in the maintenance of CESCs through inhibition of Wnt and MAPK signaling pathways was thus indicated.

Activation of Functional Somatic Stem Cells Promotes Endogenous Tissue Regeneration

Periodontal ligament derived stem cells (PDLSCs) are capable of differentiating into multiple cell types and inducing a promising immunomodulation for tissue regeneration and disease treatment. However, it is still challenging to develop a practical approach to activate endogenous stem cells for tissue self-healing and regeneration. In this study, transcriptome analysis reveals that resveratrol promotes PDLSC stemness through activation of stem cell, osteoprogenitor, and chondroprogenitor markers. Self-renewal and multipotent differentiation abilities are also improved in resveratrol-treated PDLSCs. In addition, immunomodulation of PDLSCs is dramatically increased after resveratrol treatment. Mechanistically, we show that resveratrol activates ERK/WNT crosstalk through elevation of olfactory and growth factor signaling pathways to upregulate the expression levels of RUNX2 and FASL for osteogenesis and immunomodulation, respectively. By using a periodontitis animal model, administration of resveratrol partially rescues bone loss through activation of endogenous somatic stem cells and inhibition of inflammatory T-cell infiltration. Taken together, our findings identify a novel pharmacological approach to achieve autotherapies for endogenous tissue regeneration.

Role of p38 MAP kinase in cancer stem cells and metastasis

Therapeutic resistance and metastatic progression are responsible for the majority of cancer mortalities. In particular, the development of resistance is a significant barrier to the efficacy of cancer treatments such as chemotherapy, radiotherapy, targeted therapies, and immunotherapies. Cancer stem cells (CSCs) underlie treatment resistance and metastasis. p38 mitogen-activated protein kinase (p38 MAPK) is downstream of several CSC-specific signaling pathways, and it plays an important role in CSC development and maintenance and contributes to metastasis and chemoresistance. Therefore, the development of therapeutic approaches targeting p38 can sensitize tumors to chemotherapy and prevent metastatic progression.

R-spondin 3 deletion induces Erk phosphorylation to enhance Wnt signaling and promote bone formation in the appendicular skeleton

Activation of Wnt signaling leads to high bone density. The R-spondin family of four secreted glycoproteins (Rspo1-4) amplifies Wnt signaling. In humans, RSPO3 variants are strongly associated with bone density. Here, we investigated the role of Rspo3 in skeletal homeostasis in mice. Using a comprehensive set of mouse genetic and mechanistic studies, we show that in the appendicular skeleton, Rspo3 haplo-insufficiency and Rspo3 targeted deletion in Runx2⁺ osteoprogenitors lead to an increase in trabecular bone mass, with increased number of osteoblasts and bone formation. In contrast and highlighting the complexity of Wnt signaling in the regulation of skeletal homeostasis, we show that Rspo3 deletion in osteoprogenitors results in the opposite phenotype in the axial skeleton, i.e., low vertebral trabecular bone mass. Mechanistically, Rspo3 deficiency impairs the inhibitory effect of Dkk1 on Wnt signaling activation and bone mass. We demonstrate that Rspo3 deficiency leads to activation of Erk signaling which in turn, stabilizes β-catenin and Wnt signaling activation. Our data demonstrate that Rspo3 haplo-insufficiency/deficiency boosts canonical Wnt signaling by activating Erk signaling, to favor osteoblastogenesis, bone formation, and bone mass.

Roles of Non-Canonical Wnt Signalling Pathways in Bone Biology

The Wnt signalling pathway is one of the central signalling pathways in bone development, homeostasis and regulation of bone mineral density. It consists of numerous Wnt ligands, receptors and co-receptors, which ensure tight spatiotemporal regulation of Wnt signalling pathway activity and thus tight regulation of bone tissue homeostasis. This enables maintenance of optimal mineral density, tissue healing and adaptation to changes in bone loading. While the role of the canonical/β-catenin Wnt signalling pathway in bone homeostasis is relatively well researched, Wnt ligands can also activate several non-canonical, β-catenin independent signalling pathways with important effects on bone tissue. In this review, we will provide a thorough overview of the current knowledge on different non-canonical Wnt signalling pathways involved in bone biology, focusing especially on the pathways that affect bone cell differentiation, maturation and function, processes involved in bone tissue structure regulation. We will describe the role of the two most known non-canonical pathways (Wnt/planar cell polarity pathways and Wnt/Ca2+ pathway), as well as other signalling pathways with a strong role in bone biology that communicate with the Wnt signalling pathway through non-canonical Wnt signalling. Our goal is to bring additional attention to these still not well researched but important pathways in the regulation of bone biology in the hope of prompting additional research in the area of non-canonical Wnt signalling pathways.

Regulation of the Low-Density Lipoprotein Receptor-Related Protein LRP6 and Its Association With Disease: Wnt/β-Catenin Signaling and Beyond

Wnt signaling plays crucial roles in development and tissue homeostasis, and its dysregulation leads to various diseases, notably cancer. Wnt/β-catenin signaling is initiated when the glycoprotein Wnt binds to and forms a ternary complex with the Frizzled and low-density lipoprotein receptor-related protein 5/6 (LRP5/6). Despite being identified as a Wnt co-receptor over 20 years ago, the molecular mechanisms governing how LRP6 senses Wnt and transduces downstream signaling cascades are still being deciphered. Due to its role as one of the main Wnt signaling components, the dysregulation or mutation of LRP6 is implicated in several diseases such as cancer, neurodegeneration, metabolic syndrome and skeletal disease. Herein, we will review how LRP6 is activated by Wnt stimulation and explore the various regulatory mechanisms involved. The participation of LRP6 in other signaling pathways will also be discussed. Finally, the relationship between LRP6 dysregulation and disease will be examined in detail.

A CRISPR knockout screen reveals new regulators of canonical Wnt signaling

The Wnt signaling pathways play fundamental roles during both development and adult homeostasis. Aberrant activation of the canonical Wnt signal transduction pathway is involved in many diseases including cancer, and is especially implicated in the development and progression of colorectal cancer. Although extensively studied, new genes, mechanisms and regulatory modulators involved in Wnt signaling activation or silencing are still being discovered. Here we applied a genome-scale CRISPR-Cas9 knockout (KO) screen based on Wnt signaling induced cell survival to reveal new inhibitors of the oncogenic, canonical Wnt pathway. We have identified several potential Wnt signaling inhibitors and have characterized the effects of the initiation factor DExH-box protein 29 (DHX29) on the Wnt cascade. We show that KO of DHX29 activates the Wnt pathway leading to upregulation of the Wnt target gene cyclin-D1, while overexpression of DHX29 inhibits the pathway. Together, our data indicate that DHX29 may function as a new canonical Wnt signaling tumor suppressor and demonstrates that this screening approach can be used as a strategy for rapid identification of novel Wnt signaling modulators.

Apoptotic cells represent a dynamic stem cell niche governing proliferation and tissue regeneration

Stem cells (SCs) play a key role in homeostasis and repair. While many studies have focused on SC self-renewal and differentiation, little is known regarding the molecular mechanism regulating SC elimination and compensation upon loss. Here, we report that Caspase-9 deletion in hair follicle SCs (HFSCs) attenuates the apoptotic cascade, resulting in significant temporal delays. Surprisingly, Casp9-deficient HFSCs accumulate high levels of cleaved caspase-3 and are improperly cleared due to an essential caspase-3/caspase-9 feedforward loop. These SCs are retained in an apoptotic-engaged state, serving as mitogenic signaling centers by continuously releasing Wnt3 and instructing proliferation. Investigating the underlying mechanism, we reveal a caspase-3/Dusp8/p38 module responsible for Wnt3 induction, which operates in both normal and Casp9-deleted HFSCs. Notably, Casp9-deleted mice display accelerated wound repair and de novo hair follicle regeneration. Taken together, we demonstrate that apoptotic cells represent a dynamic SC niche, from which emanating signals drive SC proliferation and tissue regeneration.

Urokinase-type plasminogen activator-mediated crosstalk between N-cadherin and β-catenin promotes wound healing

Urokinase-type plasminogen activator (uPA; encoded by Plau) is a serine proteinase that, in the central nervous system, induces astrocytic activation. β-Catenin is a protein that links the cytoplasmic tail of cadherins to the actin cytoskeleton, thus securing the formation of cadherin-mediated cell adhesion complexes. Disruption of cell-cell contacts leads to the detachment of β-catenin from cadherins, and β-catenin is then degraded by the proteasome following its phosphorylation by GSK3β. Here, we show that astrocytes release uPA following a scratch injury, and that this uPA promotes wound healing via a plasminogen-independent mechanism. We found that uPA induces the detachment of β-catenin from the cytoplasmic tail of N-cadherin (NCAD; also known as CDH2) by triggering its phosphorylation at Tyr654. Surprisingly, this is not followed by degradation of β-catenin because uPA also induces the phosphorylation of the low density lipoprotein receptor-related protein 6 (LRP6) at Ser1490, which then blocks the kinase activity of GSK3β. Our work indicates that the ensuing cytoplasmic accumulation of β-catenin is followed by its nuclear translocation and β-catenin-triggered transcription of the receptor for uPA (Plaur), which in turn is required for uPA to induce astrocytic wound healing.

LRP5 and LRP6 in Wnt Signaling: Similarity and Divergence

The canonical Wnt/β-catenin signaling plays a fundamental role in regulating embryonic development, injury repair and the pathogenesis of human diseases. In vertebrates, low density lipoprotein receptor-related proteins 5 and 6 (LRP5 and LRP6), the single-pass transmembrane proteins, act as coreceptors of Wnt ligands and are indispensable for Wnt signal transduction. LRP5 and LRP6 are highly homologous and widely co-expressed in embryonic and adult tissues, and they share similar function in mediating Wnt signaling. However, they also exhibit distinct characteristics by interacting with different protein partners. As such, each of them possesses its own unique functions. In this review, we systematically discuss the similarity and divergence of LRP5 and LRP6 in mediating Wnt and other signaling in the context of kidney diseases. A better understanding of the precise role of LRP5 and LRP6 may afford us to identify and refine therapeutic targets for the treatment of a variety of human diseases.

Targeting the crosstalk between canonical Wnt/β-catenin and inflammatory signaling cascades: A novel strategy for cancer prevention and therapy

Emerging scientific evidence indicates that inflammation is a critical component of tumor promotion and progression. Most cancers originate from sites of chronic irritation, infections and inflammation, underscoring that the tumor microenvironment is largely orchestrated by inflammatory cells and pro-inflammatory molecules. These inflammatory components are intimately involved in neoplastic processes which foster proliferation, survival, invasion, and migration, making inflammation the primary target for cancer prevention and treatment. The influence of inflammation and the immune system on the progression and development of cancer has recently gained immense interest. The Wnt/β-catenin signaling pathway, an evolutionarily conserved signaling strategy, has a critical role in regulating tissue development. It has been implicated as a major player in cancer development and progression with its regulatory role on inflammatory cascades. Many naturally-occurring and small synthetic molecules endowed with inherent anti-inflammatory properties inhibit this aberrant signaling pathway, making them a promising class of compounds in the fight against inflammatory cancers. This article analyzes available scientific evidence and suggests a crosslink between Wnt/β-catenin signaling and inflammatory pathways in inflammatory cancers, especially breast, gastrointestinal, endometrial, and ovarian cancer. We also highlight emerging experimental findings that numerous anti-inflammatory synthetic and natural compounds target the crosslink between Wnt/β-catenin pathway and inflammatory cascades to achieve cancer prevention and intervention. Current challenges, limitations, and future directions of research are also discussed.

Microenvironmental regulation of intestinal stem cells in the inflamed intestine

The rapid renewal of intestinal epithelium during homeostasis requires balanced proliferation and differentiation of intestinal stem cells (ISCs) at the base of crypt. Upon intestinal inflammation, the vigorous expansion of surviving ISCs is responsible for epithelial repair. However, it is not well depicted how ISCs adapt to the inflammatory conditions within intestinal tissue and support epithelial repair. In the intestinal inflammation, niche cells around ISCs along with their secreted niche factors can facilitate the regeneration of ISCs via niche signals. Additionally, the growth of ISCs can respond to inflammatory cells, inflammatory cytokines, and inflammatory signals. Understanding the adaptive mechanism of ISCs in supporting intestinal epithelial regeneration during inflammation is a focus on the treatment for patients with intestinal inflammation. Here, we aim to present an overview of how ISCs adapt to the acute inflammation to support intestinal repair, with a focus on the roles and interaction of niche signals.

Aberrant cytoplasmic localization of ARID1B activates ERK signaling and promotes oncogenesis

The ARID1B (BAF250b) subunit of the human SWI/SNF chromatin remodeling complex is a canonical nuclear tumor suppressor. We employed in silico prediction, intracellular fluorescence and cellular fractionation-based subcellular localization analyses to identify the ARID1B nuclear localization signal (NLS). A cytoplasm-restricted ARID1B-NLS mutant was significantly compromised in its canonical transcription activation and tumor suppressive functions, as expected. Surprisingly however, cytoplasmic localization appeared to induce a gain of oncogenic function for ARID1B, as evidenced from several cell line- and mouse xenograft-based assays. Mechanistically, cytoplasm-localized ARID1B could bind c-RAF (RAF1) and PPP1CA causing stimulation of RAF-ERK signaling and β-catenin (CTNNB1) transcription activity. ARID1B harboring NLS mutations derived from tumor samples also exhibited aberrant cytoplasmic localization and acquired a neo-morphic oncogenic function via activation of RAF-ERK signaling. Furthermore, immunohistochemistry on a tissue microarray revealed significant correlation of ARID1B cytoplasmic localization with increased levels of active forms of ERK1 and ERK2 (also known as MAPK3 and MAPK1) and of β-catenin, as well as with advanced tumor stage and lymph node positivity in human primary pancreatic tumor tissues. ARID1B therefore promotes oncogenesis through cytoplasm-based gain-of-function mechanisms in addition to dysregulation in the nucleus.This article has an associated First Person interview with the first author of the paper.

LRPs in WNT Signalling

The WNT/β-catenin signalling pathway is a rich and complex network of cellular proteins that orchestrates diverse short-range cell-to-cell communication in metazoans and is essential for both embryonic development and adult homeostasis. Due to its fundamental importance in controlling cell behaviour at multiple levels, its deregulation is associated with a wide range of diseases in humans and identification of drugs targeting the pathway has attracted strong interest in the pharmaceutical sector. Transduction of WNT signals across the plasma membrane of cells involves a staggering degree of complexity and variety with respect to ligand-receptor, receptor-receptor and receptor-co-receptor interactions (Niehrs, Nat Rev Mol Cell Biol 13:767-779, 2012). Although the low-density-lipoprotein-receptor-related-protein (LRP) family is best known for its role in binding and endocytosis of lipoproteins, specific members appear to have additional roles in cellular communication. Indeed, for WNT/β-catenin signalling one apparently universal requirement is the presence of either LRP5 or LRP6 in combination with one of the ten Frizzled (FZD) WNT receptors (FZD_1-10). In the 20 years since their discovery as WNT/FZD co-receptors, research on the LRP family has contributed greatly to our understanding of WNT signalling and LRPs have emerged as central players in WNT/β-catenin signalling. LRP5/6 are highly similar and represent the least redundant class of WNT receptor that transduce WNT/β-catenin signalling from a wide range of different WNT and FZD subtypes. This apparent simplicity however belies the complex arrangement of binding sites in the extracellular domain (ECD) of LRP5/6, which regulate interaction not only with WNTs but also with several inhibitors of WNT signalling. This chapter provides a historical overview, chronologically charting this remarkable progress in the field during the last 20 years of research on LRPs and their role in WNT/-catenin signalling. A more focused overview of the structural, functional and mechanistic aspects of LRP biology is also provided, together with the implications this has for pharmacological targeting of this notoriously intractable pathway.

Microarray analysis identification of key pathways and interaction network of differential gene expressions during osteogenic differentiation

BACKGROUND

Adult bone marrow-derived mesenchymal stem cells (BM-MSCs) are multipotent stem cells that can differentiate into three lineages. They are suitable sources for cell-based therapy and regenerative medicine applications. This study aims to evaluate the hub genes and key pathways of differentially expressed genes (DEGs) related to osteogenesis by bioinformatics analysis in three different days. The DEGs were derived from the three different days compared with day 0.

RESULTS

Gene expression profiles of GSE37558 were obtained from the Gene Expression Omnibus (GEO) database. A total of 4076 DEGs were acquired on days 8, 12, and 25. Gene ontology (GO) enrichment analysis showed that the non-canonical Wnt signaling pathway and lipopolysaccharide (LPS)-mediated signaling pathway were commonly upregulated DEGs for all 3 days. KEGG pathway analysis indicated that the PI3K-Akt and focal adhesion were also commonly upregulated DEGs for all 3 days. Ten hub genes were identified by CytoHubba on days 8, 12, and 25. Then, we focused on the association of these hub genes with the Wnt pathways that had been enriched from the protein-protein interaction (PPI) by the Cytoscape plugin MCODE.

CONCLUSIONS

These findings suggested further insights into the roles of the PI3K/AKT and Wnt pathways and their association with osteogenesis. In addition, the stem cell microenvironment via growth factors, extracellular matrix (ECM), IGF1, IGF2, LPS, and Wnt most likely affect osteogenesis by PI3K/AKT.

12-O-Tetradecanoylphorbol-13-acetate increases cardiomyogenesis through PKC/ERK signaling

12-O-Tetradecanoylphorbol-13-acetate (TPA) is the most widely used diacylglycerol (DAG) mimetic agent and inducer of protein kinase C (PKC)-mediated cellular response in biomedical studies. TPA has been proposed as a pluripotent cell differentiation factor, but results obtained have been inconsistent. In the present study we show that TPA can be applied as a cardiomyogenesis-promoting factor for the differentiation of mouse embryonic stem (mES) cells in vitro. The mechanism of TPA action is mediated by the induction of extracellular signal-regulated kinase (ERK) activity and the subsequent phosphorylation of GATA4 transcription factor. Interestingly, general mitogens (FGF, EGF, VEGF and serum) or canonical WNT signalling did not mimic the effect of TPA. Moreover, on the basis of our results, we postulate that a TPA-sensitive population of cardiac progenitor cells exists at a certain time point (after days 6–8 of the differentiation protocol) and that the proposed treatment can be used to increase the multiplication of ES cell-derived cardiomyocytes.

Erk and MAPK signaling is essential for intestinal development through Wnt pathway modulation

Homeostasis of intestinal stem cells (ISCs) is maintained by the orchestration of niche factors and intrinsic signaling networks. Here, we have found that deletion of Erk1 and Erk2 (Erk1/2) in intestinal epithelial cells at embryonic stages resulted in an unexpected increase in cell proliferation and migration, expansion of ISCs, and formation of polyp-like structures, leading to postnatal death. Deficiency of epithelial Erk1/2 results in defects in secretory cell differentiation as well as impaired mesenchymal cell proliferation and maturation. Deletion of Erk1/2 strongly activated Wnt signaling through both cell-autonomous and non-autonomous mechanisms. In epithelial cells, Erk1/2 depletion resulted in loss of feedback regulation, leading to Ras/Raf cascade activation that transactivated Akt activity to stimulate the mTor and Wnt/β-catenin pathways. Moreover, Erk1/2 deficiency reduced the levels of Indian hedgehog and the expression of downstream pathway components, including mesenchymal Bmp4 - a Wnt suppressor in intestines. Inhibition of mTor signaling by rapamycin partially rescued Erk1/2 depletion-induced intestinal defects and significantly prolonged the lifespan of mutant mice. These data demonstrate that Erk/Mapk signaling functions as a key modulator of Wnt signaling through coordination of epithelial-mesenchymal interactions during intestinal development.

Aberrantly activated Wnt/β-catenin pathway co-receptors LRP5 and LRP6 regulate osteoblast differentiation in the developing coronal sutures of an Apert syndrome (Fgfr2S252W /+ ) mouse model

BACKGROUND

Apert syndrome is an autosomal, dominant inherited disorder characterized by craniosynostosis and syndactyly caused by gain-of-function mutations in the fibroblast growth factor receptor 2 (FGFR2) gene. Wnt/β-catenin signaling plays critical roles in regulating the skeletal development. Here, we analyzed the role of this pathway in the developing coronal sutures (CS) of a murine Apert syndrome model (Fgfr2^S252W/+ ).

RESULTS

We observed aberrantly increased mRNA expression of Lrp5 and Lrp6 in CS of Fgfr2^S252W/+ mice, whereas both wild type (WT) and Fgfr2^S252W/+ mice showed similar expression of other Wnt/β-catenin-related genes, such as Wnt3, Wnt3a, Fzd4, Fzd6, Axin2, and Dkk1 as evidenced by in situ hybridization. Significantly increased Lrp5 and Lrp6 mRNA expression was observed by quantitative PCR analysis of cultured cells isolated from CS of Fgfr2^S252W/+ mice. Phospho-LRP5, phospho-LRP6, and non-phospho-β-catenin were upregulated in Fgfr2^S252W/+ CS compared with that in WT CS. Short-interfering RNA targeting Lrp5 and Lrp6 significantly reduced runt-related transcription factor 2, collagen type 1 alpha 1, and osteocalcin mRNA expression, and alkaline phosphatase activity in cultured cells.

CONCLUSIONS

The Wnt/β-catenin pathway was activated in the CS of Fgfr2^S252W/+ mice during craniofacial development, suggesting the involvement of the Wnt/β-catenin pathway in the pathogenesis of CS synostosis in Fgfr2^S252W/+ mice.

Low-density lipoprotein receptor-related protein 6-mediated signaling pathways and associated cardiovascular diseases: diagnostic and therapeutic opportunities

Low-density lipoprotein receptor-related protein 6 (LRP6) is a member of the low-density lipoprotein receptors (LDLRs) family and accumulating evidence points to the critical role of LRP6 in cardiovascular health and homeostasis. In addition to presenting the well-appreciated roles in canonical signaling regulating blood pressure, blood glucose, lipid metabolism, atherosclerosis, cardiac valve disease, cardiac development, Alzheimer's disease and tumorigenesis, LRP6 also inhibits non-canonical Wnt signals that promote arterial smooth muscle cell proliferation and vascular calcification. Noticeably, the role of LRP6 is displayed in cardiometabolic disease, an increasingly important clinical burden with aging and obesity. The prospect for cardiovascular diseases treatment via targeting LRP6-mediated signaling pathways may improve central blood pressure and lipid metabolism, and reduce neointima formation and myocardial ischemia-reperfusion injury. Thus, a deep and comprehensive understanding of LRP6 structure, function and signaling pathways will contribute to clinical diagnosis, therapy and new drug development for LRP6-related cardiovascular diseases.

A Role for the WNT Co-Receptor LRP6 in Pathogenesis and Therapy of Epithelial Cancers

The WNT/β-catenin signaling pathway controls stem and progenitor cell proliferation, survival and differentiation in epithelial tissues. Aberrant stimulation of this pathway is therefore frequently observed in cancers from epithelial origin. For instance, colorectal and hepatic cancers display activating mutations in the CTNNB1 gene encoding β-catenin, or inactivating APC and AXIN gene mutations. However, these mutations are uncommon in breast and pancreatic cancers despite nuclear β-catenin localization, indicative of pathway activation. Notably, the low-density lipoprotein receptor-related protein 6 (LRP6), an indispensable co-receptor for WNT, is frequently overexpressed in colorectal, liver, breast and pancreatic adenocarcinomas in association with increased WNT/β -catenin signaling. Moreover, LRP6 is hyperphosphorylated in KRAS-mutated cells and in patient-derived colorectal tumours. Polymorphisms in the LRP6 gene are also associated with different susceptibility to developing specific types of lung, bladder and colorectal cancers. Additionally, recent observations suggest that LRP6 dysfunction may be involved in carcinogenesis. Indeed, reducing LRP6 expression and/or activity inhibits cancer cell proliferation and delays tumour growth in vivo. This review summarizes current knowledge regarding the biological function and regulation of LRP6 in the development of epithelial cancers—especially colorectal, liver, breast and pancreatic cancers.

MEK inhibitors activate Wnt signalling and induce stem cell plasticity in colorectal cancer

In colorectal cancer (CRC), aberrant Wnt signalling is essential for tumorigenesis and maintenance of cancer stem cells. However, how other oncogenic pathways converge on Wnt signalling to modulate stem cell homeostasis in CRC currently remains poorly understood. Using large-scale compound screens in CRC, we identify MEK1/2 inhibitors as potent activators of Wnt/β-catenin signalling. Targeting MEK increases Wnt activity in different CRC cell lines and murine intestine in vivo. Truncating mutations of APC generated by CRISPR/Cas9 strongly synergize with MEK inhibitors in enhancing Wnt responses in isogenic CRC models. Mechanistically, we demonstrate that MEK inhibition induces a rapid downregulation of AXIN1. Using patient-derived CRC organoids, we show that MEK inhibition leads to increased Wnt activity, elevated LGR5 levels and enrichment of gene signatures associated with stemness and cancer relapse. Our study demonstrates that clinically used MEK inhibitors inadvertently induce stem cell plasticity, revealing an unknown side effect of RAS pathway inhibition.

MEK inhibitors activate Wnt signalling and induce stem cell plasticity in colorectal cancer

In colorectal cancer (CRC), aberrant Wnt signalling is essential for tumorigenesis and maintenance of cancer stem cells. However, how other oncogenic pathways converge on Wnt signalling to modulate stem cell homeostasis in CRC currently remains poorly understood. Using large-scale compound screens in CRC, we identify MEK1/2 inhibitors as potent activators of Wnt/β-catenin signalling. Targeting MEK increases Wnt activity in different CRC cell lines and murine intestine in vivo. Truncating mutations of APC generated by CRISPR/Cas9 strongly synergize with MEK inhibitors in enhancing Wnt responses in isogenic CRC models. Mechanistically, we demonstrate that MEK inhibition induces a rapid downregulation of AXIN1. Using patient-derived CRC organoids, we show that MEK inhibition leads to increased Wnt activity, elevated LGR5 levels and enrichment of gene signatures associated with stemness and cancer relapse. Our study demonstrates that clinically used MEK inhibitors inadvertently induce stem cell plasticity, revealing an unknown side effect of RAS pathway inhibition.

Wnt signaling is necessary for colorectal cancer tumorigenesis and stem cell maintenance. Here, the authors identify MEK1/2 inhibitors as potent activators of Wnt/β-catenin signalling and show that clinically approved MEK inhibitors inadvertently induce stem cell plasticity in colorectal cancer

Lgr5-overexpressing mesenchymal stem cells augment fracture healing through regulation of Wnt/ERK signaling pathways and mitochondrial dynamics

Fracture remains one of the most common traumatic conditions in orthopedic surgery. The use of mesenchymal stem cells (MSCs) to augment fracture repair is promising. Leucine-rich repeat-containing GPCR 5 (Lgr5), a transmembrane protein, has been identified as a novel adult stem cell marker in various organs and tissues. However, the roles of Lgr5 in MSCs are not fully understood. In this study, we investigated cellular functions of Lgr5 in MSCs and its potential implications in treating fracture. Lgr5-overexpressing MSCs (MSC^Lgr5) were established in murine SV40 promoter-driven luciferase reporter MSC line through virus transfection. Results of real-time quantitative PCR and Western blot analysis confirmed the increased expression of Lgr5 in MSC^Lgr5. MSC^Lgr5 exhibited increased osteogenic capacity, which may result from elevated expression of β-catenin and phosphorylated ERK1/2 within the nuclear region of cells. In contrast, inhibition of Lgr5 expression decreased the osteogenic differentiation ability of MSCs, accompanied with increased mitochondrial fragmentation and reduced expression of β-catenin. Local transplantation of MSC^Lgr5 at fracture sites accelerated fracture healing via enhanced osteogenesis and angiogenesis. MSC^Lgr5 stimulated the tube formation capacity of HUVECs in a Matrigel coculture system in vitro significantly. Taken together, results suggest that Lgr5 is implicated in the cellular processes of osteogenic differentiation of MSCs through regulation of Wnt and ERK signaling pathways and mitochondrial dynamics in fusion and fission. Inhibition of Lgr5 expression induced increased mitochondrial fragmentation and suppression of osteogenesis. MSC^Lgr5 exhibited enhanced therapeutic efficacy for fracture healing, which may serve as a superior cell source for bone tissue repair.-Lin, W., Xu, L., Pan, Q., Lin, S., Feng, L., Wang, B., Chen, S., Li, Y., Wang, H., Li, Y., Wang, Y., Lee, W. Y. W., Sun, D., Li, G. Lgr5-overexpressing mesenchymal stem cells augment fracture healing through regulation of Wnt/ERK signaling pathways and mitochondrial dynamics.

Functional link between plasma membrane spatiotemporal dynamics, cancer biology, and dietary membrane-altering agents

The cell plasma membrane serves as a nexus integrating extra- and intracellular components, which together enable many of the fundamental cellular signaling processes that sustain life. In order to perform this key function, plasma membrane components assemble into well-defined domains exhibiting distinct biochemical and biophysical properties that modulate various signaling events. Dysregulation of these highly dynamic membrane domains can promote oncogenic signaling. Recently, it has been demonstrated that select membrane-targeted dietary bioactives (MTDBs) have the ability to remodel plasma membrane domains and subsequently reduce cancer risk. In this review, we focus on the importance of plasma membrane domain structural and signaling functionalities as well as how loss of membrane homeostasis can drive aberrant signaling. Additionally, we discuss the intricacies associated with the investigation of these membrane domain features and their associations with cancer biology. Lastly, we describe the current literature focusing on MTDBs, including mechanisms of chemoprevention and therapeutics in order to establish a functional link between these membrane-altering biomolecules, tuning of plasma membrane hierarchal organization, and their implications in cancer prevention.

Craniofacial, orofacial and dental disorders: the role of the RAS/ERK pathway

Deviations from the precisely coordinated programme of human head development can lead to craniofacial and orofacial malformations often including a variety of dental abnormalities too. Although the aetiology is still unknown in many cases, during the last decades different intracellular signalling pathways have been genetically linked to specific disorders. Among these pathways, the RAS/extracellular signal-regulated kinase (ERK) signalling cascade is the focus of this review since it encompasses a large group of genes that when mutated cause some of the most common and severe developmental anomalies in humans. We present the components of the RAS/ERK pathway implicated in craniofacial and orodental disorders through a series of human and animal studies. We attempt to unravel the specific molecular targets downstream of ERK that act on particular cell types and regulate key steps in the associated developmental processes. Finally we point to ambiguities in our current knowledge that need to be clarified before RAS/ERK-targeting therapeutic approaches can be implemented.

KIAA1199 is a secreted molecule that enhances osteoblastic stem cell migration and recruitment

Factors mediating mobilization of osteoblastic stem and progenitor cells from their bone marrow niche to be recruited to bone formation sites during bone remodeling are poorly known. We have studied secreted factors present in the bone marrow microenvironment and identified KIAA1199 (also known as CEMIP, cell migration inducing hyaluronan binding protein) in human bone biopsies as highly expressed in osteoprogenitor reversal cells (Rv.C) recruited to the eroded surfaces (ES), which are the future bone formation sites. In vitro, KIAA1199 did not affect the proliferation of human osteoblastic stem cells (also known as human bone marrow skeletal or stromal stem cells, hMSCs); but it enhanced cell migration as determined by scratch assay and trans-well migration assay. KIAA1199 deficient hMSCs (KIAA1199down) exhibited significant changes in cell size, cell length, ratio of cell width to length and cell roundness, together with reduction of polymerization actin (F-actin) and changes in phos-CFL1 (cofflin1), phos-LIMK1 (LIM domain kinase 1) and DSTN (destrin), key factors regulating actin cytoskeletal dynamics and cell motility. Moreover, KIAA1199down hMSC exhibited impaired Wnt signaling in TCF-reporter assay and decreased expression of Wnt target genes and these effects were rescued by KIAA1199 treatment. Finally, KIAA1199 regulated the activation of P38 kinase and its associated changes in Wnt-signaling. Thus, KIAA1199 is a mobilizing factor that interacts with P38 and Wnt signaling, and induces changes in actin cytoskeleton, as a mechanism mediating recruitment of hMSC to bone formation sites.

Sorafenib/MEK inhibitor combination inhibits tumor growth and the Wnt/β‑catenin pathway in xenograft models of hepatocellular carcinoma

Mutations affecting the Wnt/β‑catenin pathway have been identified in 26‑40% of hepatocellular carcinoma (HCC) cases. Aberrant activation of this pathway leads to uncontrolled cell proliferation and survival. Thus, identifying Wnt/β‑catenin pathway inhibitors may benefit a subset of patients with HCC. In the present study, the effects of sorafenib and a MEK inhibitor on tumor growth and Wnt/β‑catenin signaling in HCC models were evaluated. A β‑catenin mutant and β‑catenin wild‑type HCC models were treated once daily with i) 10 mg/kg sorafenib, ii) 15 mg/kg refametinib (or 25 mg/kg selumetinib), or iii) sorafenib/refametinib. Western blotting was employed to determine changes in biomarkers relevant to Wnt/β‑catenin signaling. Apoptosis, cell proliferation and β‑catenin localization were analyzed by immunohistochemistry. Sorafenib/refametinib markedly inhibited tumor growth and cell proliferation, and caused cell death in naïve and sorafenib‑resistant HCC models. Despite similar total β‑catenin levels, significant reductions in phosphorylated (p)‑RanBP3 Ser58, p‑β‑catenin Tyr142, active β‑catenin and β‑catenin target genes were observed in sorafenib/refametinib‑treated tumors. Greater levels of β‑catenin in sorafenib/refametinib‑treated tumors were accumulated at the membrane, as compared with in the control. In vitro, sorafenib/refametinib inhibited the Wnt/β‑catenin pathway and suppressed Wnt‑3A‑induced p‑low‑density lipoprotein receptor‑related protein 6 Ser1490, p‑RanBP3 Ser58 and p‑β‑catenin Tyr142 in HCC cells. Combination of sorafenib and refametinib inhibits the growth of naïve and sorafenib resistant HCC tumors in association with active suppression of β‑catenin signaling regardless of β‑catenin mutational status. Thus, the sorafenib/MEK inhibitor combination may represent an alternative treatment for patients with HCC whose tumors develop resistance to sorafenib therapy.

Learning time-varying information flow from single-cell epithelial to mesenchymal transition data

Cellular regulatory networks are not static, but continuously reconfigure in response to stimuli via alterations in protein abundance and confirmation. However, typical computational approaches treat them as static interaction networks derived from a single time point. Here, we provide methods for learning the dynamic modulation of relationships between proteins from static single-cell data. We demonstrate our approach using TGFß induced epithelial-to-mesenchymal transition (EMT) in murine breast cancer cell line, profiled with mass cytometry. We take advantage of the asynchronous rate of transition to EMT in the data and derive a pseudotime EMT trajectory. We propose methods for visualizing and quantifying time-varying edge behavior over the trajectory, and a metric of edge dynamism to predict the effect of drug perturbations on EMT.

MMP-12-Induced Pro-osteogenic Responses in Human Aortic Valve Interstitial Cells

BACKGROUND

Calcific aortic valve disease (CAVD) is an age-related and slowly progressive valvular disorder. Overexpression of matrix metalloproteinase 12 (MMP-12) has been found in atherosclerosis, stiffed vascular tissue, and calcified aortic valves. We hypothesized that MMP-12 may induce the pro-osteogenic responses in human aortic valve interstitial cells (AVICs).

METHODS

Human AVICs were isolated from normal and calcified aortic valves. Cells were treated with MMP-12. The pro-osteogenic marker Runt-related transcription factor 2 (RUNX-2), bone morphogenetic protein 2 (BMP-2), and alkaline phosphatase (ALP), as well as MMP-12-associated signaling molecules, were analyzed.

RESULTS

Human calcified aortic valves expressed significantly higher MMP-12 than normal human aortic valves. MMP-12-induced the expression of RUNX-2, BMP-2, ALP, and calcium deposit formation. Suppression of MMP-12 by its inhibitor decreased the expression of RUNX-2, BMP-2, and ALP. MMP-12-induced osteogenic responses were associated with higher levels of phosphorylation of p38 mitogen-activated protein kinases (MAPK), low density lipoprotein-related protein 6 (LRP-6), and β-catenin signaling molecules. Calcified aortic valves exhibited markedly higher levels of LRP-6 and β-catenin levels. Inhibition of either p38 MAPK or LRP-6 attenuated MMP-12-induced expression of RUNX-2, BMP-2, and ALP. Suppression of p38 MAPK abrogated MMP-12-induced activation of LRP-6 and β-catenin signaling pathways.

CONCLUSIONS

MMP-12 induces pro-osteogenic responses in AVICs by activation of p38 MAPK-mediated LRP-6 and β-catenin signaling pathways. The study revealed that the potential role of MMP-12 in the pathogenesis of CAVD and therapeutically targeting MMP-12 may suppress the development of CAVD.

Tumor promoter TPA activates Wnt/β-catenin signaling in a casein kinase 1-dependent manner

The phorbol ester 12-O-tetra-decanoylphorbol-13-acetate (TPA) is a well-known tumor promoter in two-stage mouse skin carcinogenesis, but the exact mechanism by which TPA promotes tumorigenesis remains elusive. This study discovered that TPA could stabilize CK1ε, enhance its kinase activity, and induce phosphorylation of LRP6, resulting in the formation of CK1ε–LRP6–axin1 complex, which may bypass the requirement of Wnt–Fzd–Dvl complex. TPA also increased the interaction between β-catenin and TCF4E in a CK1ε/δ-dependent way, and finally led to activation of the Wnt/β-catenin pathway. Our findings reveal a pathway by which TPA activates the Wnt/β-catenin signaling cascade. This pathway may represent a common mechanism for the tumor-promoting activity of some carcinogenic agents.

The tumor promoter 12-O-tetra-decanoylphorbol-13-acetate (TPA) has been defined by its ability to promote tumorigenesis on carcinogen-initiated mouse skin. Activation of Wnt/β-catenin signaling has a decisive role in mouse skin carcinogenesis, but it remains unclear how TPA activates Wnt/β-catenin signaling in mouse skin carcinogenesis. Here, we found that TPA could enhance Wnt/β-catenin signaling in a casein kinase 1 (CK1) ε/δ-dependent manner. TPA stabilized CK1ε and enhanced its kinase activity. TPA further induced the phosphorylation of LRP6 at Thr1479 and Ser1490 and the formation of a CK1ε–LRP6–axin1 complex, leading to an increase in cytosolic β-catenin. Moreover, TPA increased the association of β-catenin with TCF4E in a CK1ε/δ-dependent way, resulting in the activation of Wnt target genes. Consistently, treatment with a selective CK1ε/δ inhibitor SR3029 suppressed TPA-induced skin tumor formation in vivo, probably through blocking Wnt/β-catenin signaling. Taken together, our study has identified a pathway by which TPA activates Wnt/β-catenin signaling.

Phosphorylation of low density lipoprotein receptor-related protein 6 is involved in receptor for advanced glycation end product-mediated β-catenin stabilization in a toluene diisocyanate-induced asthma model

BACKGROUND

We have previously demonstrated that the receptor for advanced glycation end products (RAGE)/β-catenin axis plays a vital role in regulating airway inflammation and airway remodeling in a toluene diisocyanate (TDI)-induced murine asthma model. However, the exact mechanism of β-catenin activation remains unclear. Given that phosphorylation of the low-density lipoprotein receptor-related protein 6 (Lrp6) is a key step in mediating β-catenin stabilization in canonical wnt/β-catenin signaling, we explored the possible relationship between RAGE and Lrp6 in regulating β-catenin stabilization in TDI-induced asthma.

METHODS

In this study, a TDI-induced murine asthma model was generated, and mice were treated with a specific inhibitor of RAGE. In vitro, the human bronchial epithelial cell line 16HBE was treated with TDI-human serum albumin (TDI-HSA). RAGE overexpression or knockdown cells were also constructed and assessed.

RESULTS

The results showed that RAGE inhibition or RAGE knockdown decreased β-catenin nuclear accumulation and the expression of relevant β-catenin targeted genes (VEGF, MMP9, TGF-β1) in the TDI-induced murine asthma model and TDI-HSA-treated 16HBE cells, respectively. Silencing of RAGE reversed the TDI-induced increase in phospho-ERK1/2 (p-ERK) and phospho-Lrp6 (p-Lrp6) in 16HBE cells. Pretreatment with the extracellular signal-regulated kinase (ERK)1/2 inhibitor U0126 suppressed TDI-induced Lrp6 phosphorylation. Furthermore, knockdown of Lrp6 in 16HBE cells decreased β-catenin nuclear translocation and the expression of VEGF, MMP9, and TGF-β1.

CONCLUSION

These data suggested that the RAGE/ERK axis modulates Lrp6 phosphorylation, contributing to β-catenin stabilization in a TDI-induced murine model.

Genetic inhibition of PPARγ S112 phosphorylation reduces bone formation and stimulates marrow adipogenesis

A common feature of many skeletal diseases is the accumulation of marrow fat. A reciprocal relationship exists between osteogenesis and adipogenesis in bone marrow that is mediated by the relative activity of PPARγ and RUNX2 transcription factors. The ERK/MAPK pathway is an important inducer of MSC differentiation to osteoblasts and an inhibitor of adipogenesis that functions by phosphorylating RUNX2 and PPARγ. To begin to assess the importance of this regulation in vivo, we examined the consequences of blocking one arm of this pathway, PPARγ S112 phosphorylation, by evaluating the bone phenotype of PPARγ S112A mutant mice. This mutation prevents MAPK phosphorylation and inhibition of PPARγ transcriptional activity. Both male and female PPARγ S112A mice had decreased tibial and vertebral BV/TV and decreased trabecular bone relative to wild type littermates. These results were explained by a decrease in bone formation and osteoblast activity in the absence of changes in resorption. In contrast, marrow adipose tissue, adipocyte markers and serum adiponectin were all dramatically increased. Bone marrow stromal cells isolated from PPARγ S112A mice had elevated PPARγ and preferentially differentiated to adipocytes while total and phosphorylated RUNX2 and osteoblastogenesis were inhibited, indicating that the PPARγ S112A mutation affects bone in a cell autonomous manner. Changes in osteoblast/adipocyte lineage allocation in MSC cultures were also seen where CFU-OBs were reduced with a parallel increase in CFU-AD. This study emphasizes the importance of PPARγ phosphorylation in controlling bone mass and marrow adiposity and demonstrates how a regulatory mutation in PPARγ previously associated with peripheral fat metabolism can have broader effects on bone homeostasis that may in turn affect whole body energy metabolism.

Identification of a noncanonical function for ribose-5-phosphate isomerase A promotes colorectal cancer formation by stabilizing and activating β-catenin via a novel C-terminal domain

Altered metabolism is one of the hallmarks of cancers. Deregulation of ribose-5-phosphate isomerase A (RPIA) in the pentose phosphate pathway (PPP) is known to promote tumorigenesis in liver, lung, and breast tissues. Yet, the molecular mechanism of RPIA-mediated colorectal cancer (CRC) is unknown. Our study demonstrates a noncanonical function of RPIA in CRC. Data from the mRNAs of 80 patients’ CRC tissues and paired nontumor tissues and protein levels, as well as a CRC tissue array, indicate RPIA is significantly elevated in CRC. RPIA modulates cell proliferation and oncogenicity via activation of β-catenin in colon cancer cell lines. Unlike its role in PPP in which RPIA functions within the cytosol, RPIA enters the nucleus to form a complex with the adenomatous polyposis coli (APC) and β-catenin. This association protects β-catenin by preventing its phosphorylation, ubiquitination, and subsequent degradation. The C-terminus of RPIA (amino acids 290 to 311), a region distinct from its enzymatic domain, is necessary for RPIA-mediated tumorigenesis. Consistent with results in vitro, RPIA increases the expression of β-catenin and its target genes, and induces tumorigenesis in gut-specific promotor-carrying RPIA transgenic zebrafish. Together, we demonstrate a novel function of RPIA in CRC formation in which RPIA enters the nucleus and stabilizes β-catenin activity and suggests that RPIA might be a biomarker for targeted therapy and prognosis.

The pentose phosphate pathway generates NADPH, pentose, and ribose-5-phosphate by RPIA for nucleotide synthesis. Deregulation of RPIA is known to promote tumorigenesis in liver, lung, and breast tissues; however, the molecular mechanism of RPIA-mediated CRC is unknown. Here, we demonstrate a role of RPIA in CRC formation distinct from its role in these other tissues. We showed that RPIA is significantly elevated in CRC. RPIA increased cell proliferation and oncogenicity via activation of β-catenin, with RPIA entering the nucleus to form a complex with APC and β-catenin. Further investigation suggested that RPIA protects β-catenin by preventing its phosphorylation, ubiquitination, and subsequent degradation. In addition, the C-terminus of RPIA (amino acids 290 to 311), a portion of the protein not previously characterized, is necessary for RPIA-mediated tumorigenesis. Finally, we observed that transgenic expression of RPIA increases the expression of β-catenin and its target genes and induces tumorigenesis. Our findings suggest that RPIA can enter the nucleus and associate with APC/β-catenin, and suggest precise treatment of human CRC by targeting its nonenzymatic domain.

Loss of Extracellular Signal-Regulated Kinase 1/2 in the Retinal Pigment Epithelium Leads to RPE65 Decrease and Retinal Degeneration

Recent work suggested that the activity of extracellular signal-regulated kinase 1/2 (ERK1/2) is increased in the retinal pigment epithelium (RPE) of age-related macular degeneration (ARMD) patients and therefore could be an attractive therapeutic target. Notably, ERK1/2 pathway inhibitors are used in cancer therapy, with severe and noncharacterized ocular side effects. To decipher the role of ERK1/2 in RPE cells, we conditionally disrupted the Erk1 and Erk2 genes in mouse RPE. The loss of ERK1/2 activity resulted in a significant decrease in the level of RPE65 expression, a decrease in ocular retinoid levels concomitant with low visual function, and a rapid disorganization of RPE cells, ultimately leading to retinal degeneration. Our results identify the ERK1/2 pathway as a direct regulator of the visual cycle and a critical component of the viability of RPE and photoreceptor cells. Moreover, our results caution about the need for a very fine adjustment of kinase inhibition in cancer or ARMD treatment in order to avoid ocular side effects.

The connections of Wnt pathway components with cell cycle and centrosome: side effects or a hidden logic?

Wnt signaling cascade has developed together with multicellularity to orchestrate the development and homeostasis of complex structures. Wnt pathway components - such as β-catenin, Dishevelled (DVL), Lrp6, and Axin-- are often dedicated proteins that emerged in evolution together with the Wnt signaling cascade and are believed to function primarily in the Wnt cascade. It is interesting to see that in recent literature many of these proteins are connected with cellular functions that are more ancient and not limited to multicellular organisms - such as cell cycle regulation, centrosome biology, or cell division. In this review, we summarize the recent literature describing this crosstalk. Specifically, we attempt to find the answers to the following questions: Is the response to Wnt ligands regulated by the cell cycle? Is the centrosome and/or cilium required to activate the Wnt pathway? How do Wnt pathway components regulate the centrosomal cycle and cilia formation and function? We critically review the evidence that describes how these connections are regulated and how they help to integrate cell-to-cell communication with the cell and the centrosomal cycle in order to achieve a fine-tuned, physiological response.

Reduced production and uptake of lactate are essential for the ability of WNT5A signaling to inhibit breast cancer cell migration and invasion

Here we investigated the impact of WNT5A signaling on aerobic glycolysis and evaluated its effects on breast cancer cell migration/invasion. WNT5A signaling reduced migration and lactate production and caused selective down-regulation of the glycolytic enzyme phosphofructokinase platelet-type (PFKP). These events occurred in parallel with a WNT5A-induced inhibition of β-catenin signaling. Support for essential involvement of β-catenin and PFKP in lactate production and migration/invasion was obtained by siRNA knockdown of their expression. To also explore the effect of non-tumor cell-derived lactate, we added exogenous lactate to the cells and noted an increase in migration that was significantly impaired by recombinant WNT5A in parallel with a down-regulation of the lactate transporter monocarboxylate transporter 1 (MCT1). Interestingly enough, the drug-candidate Foxy5 (WNT5A-mimic hexapeptide) also inhibited breast cancer cell migration in the presence of exogenous lactate, suggesting a therapeutic potential for Foxy5 in managing breast tumors with high glycolytic activity. Overall, we demonstrated that WNT5A signaling (via a β-catenin-PFKP axis) reduces lactate production and lowers the expression of MCT1, a carrier mediating the uptake of lactate from the tumor microenvironment. These effects of WNT5A are essential for its ability to impair breast cancer migration/invasion even in an environment with elevated lactate levels.

Free Radical-derived Oxysterols: Novel Adipokines Modulating Adipogenic Differentiation of Adipose Precursor Cells

CONTEXT

Increased oxidative stress in adipose tissue emerges as an inducer of obesity-linked insulin resistance. Here we tested whether free-radical derived oxysterols are formed by, and accumulate in, human adipocytes. Moreover, we asked whether increased accumulation of oxysterols characterizes the adipose cells of obese patients with type 2 diabetes (T2D) (OBT2D) compared with lean, nondiabetic controls (CTRLs). Finally, we studied the effects of the free radical-derived oxysterols on adipogenic differentiation of adipose-derived stem cells (ASCs).

MAIN OUTCOME MEASURES

Adipocytes and ASCs were isolated from sc abdominal adipose tissue biopsy in four OBT2D and four CTRL subjects. Oxysterols in adipocytes were detected by gas chromatography/mass spectrometry. The cellular and molecular effects of oxysterols were then evaluated on primary cultures of ASCs focusing on cell viability, adipogenic differentiation, and "canonical" WNT and MAPK signaling pathways.

RESULTS

7-ketocholesterol (7κ-C) and 7β-hydroxycholesterol were unambiguously detected in adipocytes, which showed higher oxysterol accumulation (P < .01) in OBT2D, as compared with CTRL individuals. Notably, the accumulation of oxysterols in adipocytes was predicted by the adipose cell size of the donor (R² = 0.582; P < .01). Challenging ASCs with free radical-derived type I (7κ-C) and type II (5,6-Secosterol) oxysterols led to a time- and concentration-dependent decrease of cell viability. Meaningfully, at a non-toxic concentration (1μM), these bioactive lipids hampered adipogenic differentiation of ASCs by sequential activation of WNT/β-catenin, p38-MAPK, ERK1/2, and JNK signaling pathways.

CONCLUSION

Free radical-derived oxysterols accumulate in the "diabetic" fat and may act as novel adipokines modulating the adipogenic potential of undifferentiated adipose precursor cells.

Adult-Onset Deletion of β-Catenin in (10kb)Dmp1-Expressing Cells Prevents Intermittent PTH-Induced Bone Gain

β-Catenin (βcat) is a major downstream signaling node in canonical Wingless-related integration site (Wnt) signaling pathway, and its activity is crucial for canonical Wnt signal transduction. Wnt signaling has recently been implicated in the osteo-anabolic response to PTH, a potent calcium-regulating factor. We investigated whether βcat is essential for the anabolic action of intermittent PTH by generating male mice with adult-onset deletion of βcat in a subpopulation of bone cells (osteocytes and late-stage osteoblasts), treating them with an anabolic regimen of PTH, and measuring the skeletal responses. Male (10kb)Dmp1-CreERt2 transgenic mice that also harbored floxed loss-of-function βcat alleles (βcat(f/f)) were induced for Cre activity using tamoxifen, then injected daily with human PTH 1-34 (30 μg/kg) or vehicle for 5 weeks. Mice in which βcat was deleted showed either total lack of bone mineral density (BMD) gain, or BMD loss, and did not respond to PTH treatment. However, bone mass measurements in the trabecular compartment of the femur and spine revealed PTH-induced bone gain whether βcat was deleted or not. PTH-stimulated increases in periosteal and cancellous bone formation rates were not impaired by βcat deletion, but resorption markers and cortical porosity were significantly increased in induced mice, particularly induced mice treated with PTH. These results suggest that βcat is required for net-positive BMD effects of PTH therapy but that the anabolic effects per se of PTH treatment might not require osteocytic/osteoblastic βcat.

JNK Signaling: Regulation and Functions Based on Complex Protein-Protein Partnerships

The c-Jun N-terminal kinases (JNKs), as members of the mitogen-activated protein kinase (MAPK) family, mediate eukaryotic cell responses to a wide range of abiotic and biotic stress insults. JNKs also regulate important physiological processes, including neuronal functions, immunological actions, and embryonic development, via their impact on gene expression, cytoskeletal protein dynamics, and cell death/survival pathways. Although the JNK pathway has been under study for >20 years, its complexity is still perplexing, with multiple protein partners of JNKs underlying the diversity of actions. Here we review the current knowledge of JNK structure and isoforms as well as the partnerships of JNKs with a range of intracellular proteins. Many of these proteins are direct substrates of the JNKs. We analyzed almost 100 of these target proteins in detail within a framework of their classification based on their regulation by JNKs. Examples of these JNK substrates include a diverse assortment of nuclear transcription factors (Jun, ATF2, Myc, Elk1), cytoplasmic proteins involved in cytoskeleton regulation (DCX, Tau, WDR62) or vesicular transport (JIP1, JIP3), cell membrane receptors (BMPR2), and mitochondrial proteins (Mcl1, Bim). In addition, because upstream signaling components impact JNK activity, we critically assessed the involvement of signaling scaffolds and the roles of feedback mechanisms in the JNK pathway. Despite a clarification of many regulatory events in JNK-dependent signaling during the past decade, many other structural and mechanistic insights are just beginning to be revealed. These advances open new opportunities to understand the role of JNK signaling in diverse physiological and pathophysiological states.

p38 MAPK Signaling in Osteoblast Differentiation

The skeleton is a highly dynamic tissue whose structure relies on the balance between bone deposition and resorption. This equilibrium, which depends on osteoblast and osteoclast functions, is controlled by multiple factors that can be modulated post-translationally. Some of the modulators are Mitogen-activated kinases (MAPKs), whose role has been studied in vivo and in vitro. p38-MAPK modifies the transactivation ability of some key transcription factors in chondrocytes, osteoblasts and osteoclasts, which affects their differentiation and function. Several commercially available inhibitors have helped to determine p38 action on these processes. Although it is frequently mentioned in the literature, this chemical approach is not always as accurate as it should be. Conditional knockouts are a useful genetic tool that could unravel the role of p38 in shaping the skeleton. In this review, we will summarize the state of the art on p38 activity during osteoblast differentiation and function, and emphasize the triggers of this MAPK.

Deletion of Na+/H+ exchanger regulatory factor 2 represses colon cancer progress by suppression of Stat3 and CD24

The Na(+)/H(+) exchanger regulatory factor (NHERF) family of proteins is scaffolds that orchestrate interaction of receptors and cellular proteins. Previous studies have shown that NHERF1 functions as a tumor suppressor. The goal of this study is to determine whether the loss of NHERF2 alters colorectal cancer (CRC) progress. We found that NHERF2 expression is elevated in advanced-stage CRC. Knockdown of NHERF2 decreased cancer cell proliferation in vitro and in a mouse xenograft tumor model. In addition, deletion of NHERF2 in Apc(Min/+) mice resulted in decreased tumor growth in Apc(Min/+) mice and increased lifespan. Blocking NHERF2 interaction with a small peptide designed to bind the second PDZ domain of NHERF2 attenuated cancer cell proliferation. Although NHERF2 is known to facilitate the effects of lysophosphatidic acid receptor 2 (LPA2), transcriptome analysis of xenograft tumors revealed that NHERF2-dependent genes largely differ from LPA2-regulated genes. Activation of β-catenin and ERK1/2 was mitigated in Apc(Min/+);Nherf2(-/-) adenomas. Moreover, Stat3 phosphorylation and CD24 expression levels were suppressed in Apc(Min/+);Nherf2(-/-) adenomas. Consistently, NHERF2 knockdown attenuated Stat3 activation and CD24 expression in colon cancer cells. Interestingly, CD24 was important in the maintenance of Stat3 phosphorylation, whereas NHERF2-dependent increase in CD24 expression was blocked by inhibition of Stat3, suggesting that NHERF2 regulates Stat3 phosphorylation through a positive feedback mechanism between Stat3 and CD24. In summary, this study identifies NHERF2 as a novel oncogenic protein and a potential target for cancer treatment. NHERF2 potentiates the oncogenic effects in part by regulation of Stat3 and CD24.