Crk-associated substrate lymphocyte type regulates transforming growth factor-beta signaling by inhibiting Smad6 and Smad7

The role of quiescent thymic progenitors in TAL/LMO2-induced T-ALL chemotolerance

Relapse in T-cell acute lymphoblastic leukemia (T-ALL) may signify the persistence of leukemia-initiating cells (L-ICs). Ectopic TAL1/LMO expression defines the largest subset of T-ALL, but its role in leukemic transformation and its impact on relapse-driving L-ICs remain poorly understood. In TAL1/LMO mouse models, double negative-3 (DN3; CD4-CD8-CD25+CD44-) thymic progenitors harbored L-ICs. However, only a subset of DN3 leukemic cells exhibited L-IC activity, and studies linking L-ICs and chemotolerance are needed. To investigate L-IC heterogeneity, we used mouse models and applied single-cell RNA-sequencing and nucleosome labeling techniques in vivo. We identified a DN3 subpopulation with a cell cycle-restricted profile and heightened TAL1/LMO2 activity, that expressed genes associated with stemness and quiescence. This dormant DN3 subset progressively expanded throughout leukemogenesis, displaying intrinsic chemotolerance and enrichment in genes linked to minimal residual disease. Examination of TAL/LMO patient samples revealed a similar pattern in CD7+CD1a- thymic progenitors, previously recognized for their L-IC activity, demonstrating cell cycle restriction and chemotolerance. Our findings substantiate the emergence of dormant, chemotolerant L-ICs during leukemogenesis, and demonstrate that Tal1 and Lmo2 cooperate to promote DN3 quiescence during the transformation process. This study provides a deeper understanding of TAL1/LMO-induced T-ALL and its clinical implications in therapy failure.

Feedback regulation of TGF-β signaling

Transforming growth factor beta (TGF-β) is a multi-functional polypeptide that plays a critical role in regulating a broad range of cellular functions and physiological processes. Signaling is initiated when TGF-β ligands bind to two types of cell membrane receptors with intrinsic Ser/Thr kinase activity and transmitted by the intracellular Smad proteins, which act as transcription factors to regulate gene expression in the nucleus. Although it is relatively simple and straight-forward, this TGF-β/Smad pathway is regulated by various feedback loops at different levels, including the ligand, the receptor, Smads and transcription, and is thus fine-tuned in terms of signaling robustness, duration, specificity, and plasticity. The precise control gives rise to versatile and context-dependent pathophysiological functions. In this review, we firstly give an overview of TGF-β signaling, and then discuss how each step of TGF-β signaling is finely controlled by distinct modes of feedback mechanisms, involving both protein regulators and miRNAs.

BKI1 Regulates Plant Architecture through Coordinated Inhibition of the Brassinosteroid and ERECTA Signaling Pathways in Arabidopsis

Hundreds of leucine-rich repeat receptor-like kinases (LRR-RLKs) play indispensable roles in a wide range of plant developmental and physiological processes. The mechanisms controlling LRR-RLKs at a basal and inactive status are essential but rarely studied. BKI1 is the only reported inhibitor of receptor kinases in Arabidopsis, which negatively regulates BRI1 in the brassinosteroid pathway. In this study, we found that BKI1 can also interact with another important LRR-RLK, ERECTA (ER). Phenotypic analysis showed that BKI1 and ER together regulate plant architecture, including pedicel orientation, which is a newly reported phenotype in the BR- and ER-mediated developmental processes. Gene expression analysis revealed that BKI1 regulates a subset of ER-responsive genes. Kinase assays demonstrated that BKI1 inhibits ER kinase activity. In addition, the release of BKI1 inhibition on ER signaling relies largely on BRI1 activation. Our data provide significant insights into the regulation and activation of RLKs and suggest that BKI1 functions as a common suppressor of the BRI1 and ER signaling pathways.

Identification of Nedd9 as a TGF-β-Smad2/3 Target Gene Involved in RANKL-Induced Osteoclastogenesis by Comprehensive Analysis

TGF-ß is a multifunctional cytokine that is involved in cell proliferation, differentiation and function. We previously reported an essential role of the TGF-ß -Smad2/3 pathways in RANKL-induced osteoclastogenesis. Using chromatin immunoprecipitation followed by sequencing, we comprehensively identified Smad2/3 target genes in bone marrow macrophages. These genes were enriched in the gene population upregulated by TGF-ß and downregulated by RANKL. Recent studies have revealed that histone modifications, such as trimethylation of histone H3 lysine 4 (H3K4me3) and lysine 27 (H3K27me3), critically regulate key developmental steps. We identified Nedd9 as a Smad2/3 target gene whose histone modification pattern was converted from H3K4me3(+)/H3K4me27(+) to H3K4me3(+)/H3K4me27(-) by TGF-ß. Nedd9 expression was increased by TGF-ß and suppressed by RANKL. Overexpression of Nedd9 partially rescued an inhibitory effect of a TGF-ß inhibitor, while gene silencing of Nedd9 suppressed RANKL-induced osteoclastogenesis. RANKL-induced osteoclastogenesis were reduced and stimulatory effects of TGF-ß on RANKL-induced osteoclastogenesis were partially abrogated in cells from Nedd9-deficient mice although knockout mice did not show abnormal skeletal phenotypes. These results suggest that Nedd9 is a Smad2/3 target gene implicated in RANKL-induced osteoclastogenesis.

Preclinical and clinical studies of the NEDD9 scaffold protein in cancer and other diseases

Cancer progression requires a significant reprogramming of cellular signaling to support the essential tumor-specific processes that include hyperproliferation, invasion (for solid tumors) and survival of metastatic colonies. NEDD9 (also known as CasL and HEF1) encodes a multi-domain scaffolding protein that assembles signaling complexes regulating multiple cellular processes relevant to cancer. These include responsiveness to signals emanating from the T and B cell receptors, integrins, chemokine receptors, and receptor tyrosine kinases, as well as cytoplasmic oncogenes such as BCR-ABL and FAK- and SRC-family kinases. Downstream, NEDD9 regulation of partners including CRKL, WAVE, PI3K/AKT, ERK, E-cadherin, Aurora-A (AURKA), HDAC6, and others allow NEDD9 to influence functions as pleiotropic as migration, invasion, survival, ciliary resorption, and mitosis. In this review, we summarize a growing body of preclinical and clinical data that indicate that while NEDD9 is itself non-oncogenic, changes in expression of NEDD9 (most commonly elevation of expression) are common features of tumors, and directly impact tumor aggressiveness, metastasis, and response to at least some targeted agents inhibiting NEDD9-interacting proteins. These data strongly support the relevance of further development of NEDD9 as a biomarker for therapeutic resistance. Finally, we briefly discuss emerging evidence supporting involvement of NEDD9 in additional pathological conditions, including stroke and polycystic kidney disease.

The role of Cas-L/NEDD9 as a regulator of collagen-induced arthritis in a murine model

Cas-L/NEDD9 is a cytoplasmic docking protein downstream of β1 integrin-mediated signaling pathway and is essential for cellular migration and β1 integrin-mediated costimulation of T cells. We previously found that increased number of Cas-L positive leukocytes migrated into the inflamed joints of HTLV-I tax transgenic mice which spontaneously develop polyarthritis, suggesting a role of Cas-L in rheumatoid arthritis (RA) pathophysiology. Our current study expanded these findings on the role of Cas-L/NEDD9 in the development of RA by analyzing the pathophysiological changes in a Nedd9(-/-) mouse collagen-induced arthritis (CIA) model. Nedd9(-/-) mice exhibited a decrease in arthritis severity as compared to Nedd9(+/+) mice. In addition, as being conducted bone marrow transplantation experiments with a CIA model, Nedd9(-/-)→Nedd9(+/+) transplant showed a decrease in the incidence and severity score of arthritis, compared to those of Nedd9(+/+)→Nedd9(-/-) transplant. For analysis of serum levels of various cytokines, IL-1β, IL-6, IL-17, TNF-α, IFN-γ and anti-collagen antibody were decreased, while IL-4 and IL-10 levels were increased, in Nedd9(-/-) mice as compared to those in Nedd9(+/+) mice. Furthermore, collagen-mediated cellular responses of lymphocytes isolated from spleen or affected lymph nodes of Nedd9(-/-) mice were reduced. Our results strongly suggest that Cas-L/NEDD9 plays a pivotal role in the pathophysiology of CIA, and that Cas-L/NEDD9 may be a potential molecular target for the treatment of RA.

Bioinformatic approaches to augment study of epithelial-to-mesenchymal transition in lung cancer

Bioinformatic approaches are intended to provide systems level insight into the complex biological processes that underlie serious diseases such as cancer. In this review we describe current bioinformatic resources, and illustrate how they have been used to study a clinically important example: epithelial-to-mesenchymal transition (EMT) in lung cancer. Lung cancer is the leading cause of cancer-related deaths and is often diagnosed at advanced stages, leading to limited therapeutic success. While EMT is essential during development and wound healing, pathological reactivation of this program by cancer cells contributes to metastasis and drug resistance, both major causes of death from lung cancer. Challenges of studying EMT include its transient nature, its molecular and phenotypic heterogeneity, and the complicated networks of rewired signaling cascades. Given the biology of lung cancer and the role of EMT, it is critical to better align the two in order to advance the impact of precision oncology. This task relies heavily on the application of bioinformatic resources. Besides summarizing recent work in this area, we use four EMT-associated genes, TGF-β (TGFB1), NEDD9/HEF1, β-catenin (CTNNB1) and E-cadherin (CDH1), as exemplars to demonstrate the current capacities and limitations of probing bioinformatic resources to inform hypothesis-driven studies with therapeutic goals.

Adaptors for disorders of the brain? The cancer signaling proteins NEDD9, CASS4, and PTK2B in Alzheimer's disease

No treatment strategies effectively limit the progression of Alzheimer's disease (AD), a common and debilitating neurodegenerative disorder. The absence of viable treatment options reflects the fact that the pathophysiology and genotypic causes of the disease are not well understood. The advent of genome-wide association studies (GWAS) has made it possible to broadly investigate genotypic alterations driving phenotypic occurrences. Recent studies have associated single nucleotide polymorphisms (SNPs) in two paralogous scaffolding proteins, NEDD9 and CASS4, and the kinase PTK2B, with susceptibility to late-onset AD (LOAD). Intriguingly, NEDD9, CASS4, and PTK2B have been much studied as interacting partners regulating oncogenesis and metastasis, and all three are known to be active in the brain during development and in cancer. However, to date, the majority of studies of these proteins have emphasized their roles in the directly cancer relevant processes of migration and survival signaling. We here discuss evidence for roles of NEDD9, CASS4 and PTK2B in additional processes, including hypoxia, vascular changes, inflammation, microtubule stabilization and calcium signaling, as potentially relevant to the pathogenesis of LOAD. Reciprocally, these functions can better inform our understanding of the action of NEDD9, CASS4 and PTK2B in cancer.

The overexpression of scaffolding protein NEDD9 promotes migration and invasion in cervical cancer via tyrosine phosphorylated FAK and SRC

NEDD9, a focal adhesion scaffolding protein, has been recently proposed to regulate invasion and metastasis in some cancer types, but unknown in cervical cancer. The aim of this study was to determine if NEDD9 was involved in the progression and metastasis of cervical cancer. The experimental results showed NEDD9 protein was overexpressed in cervical cancer compared with normal cervical epithelium tissues. Overexpression of NEDD9 was correlated with histological grading, lymph node metastasis, and FIGO stage of cervical cancer. Silencing NEDD9 resulted in tyrosine dephosphorylation of FAK and SRC oncoproteins, and decreased cell migration and invasion in the cervical carcinoma SiHa and HeLa cells. Overexpression of NEDD9 led to tyrosine phosphorylation of FAK and SRC oncoproteins, and increased cell migration and invasion. Moreover, tyrosine phosphorylation of NEDD9 was significantly decreased via suppressing tyrosine phosphorylation of FAK or SRC, suggesting a positive feedback loop of tyrosine phosphorylation between NEDD9 and FAK or SRC. In addition, our data showed that silencing NEDD9 decreased Vimentin expression and increased E-cadherin expression in cervical cancer cells, and vice versa. E-cadherin was subject to regulation of NEDD9, FAK and SRC, but altered neither tyrosine-phosphorylated nor total NEDD9. Our findings suggest that NEDD9 is overexpressed in cervical cancer tissues and cells, and overexpressed NEDD9 promotes migration and invasion in cervical carcinoma cells, probably via a positive feedback loop of tyrosine phosphorylation between NEDD9 and FAK or SRC.

Smad7: not only a regulator, but also a cross-talk mediator of TGF-β signalling

TGF-β (transforming growth factor-β) is a pleiotropic cytokine regulating diverse cellular processes. It signals through membrane-bound receptors, downstream Smad proteins and/or other signalling mediators. Smad7 has been well established to be a key negative regulator of TGF-β signalling. It antagonizes TGF-β signalling through multiple mechanisms in the cytoplasm and in the nucleus. Smad7 can be transcriptionally induced by TGF-β and other growth factors and serves as an important cross-talk mediator of the TGF-β signalling pathway with other signalling pathways. Accordingly, it plays pivotal roles in embryonic development and adult homoeostasis, and altered expression of Smad7 is often associated with human diseases, such as cancer, tissue fibrosis and inflammatory diseases.

The WW-HECT protein Smurf2 interacts with the Docking Protein NEDD9/HEF1 for Aurora A activation

The multi-functional adaptor protein NEDD9/HEF1/Cas-L regulates cell motility, invasion and cell cycle progression, and plays key roles in cancer progression and metastasis. NEDD9 is localized to the centrosome and is required for activation of Aurora A kinase in mitosis. Here we demonstrate that the HECT-WW protein Smurf2 physically associates with NEDD9 and is required for the stability of NEDD9 protein. Smurf2 depletion results in a marked decrease in NEDD9 protein levels, by facilitating polyubiquitination and proteasomal degradation of NEDD9. Conversely, forced overexpression of Smurf2 results in upregulation of endogenous NEDD9 protein, confirming the role for Smurf2 in NEDD9 stability. Cells with Smurf2 depletion fail to activate Aurora A at the G₂/M boundary, leading to a marked delay in mitotic entry. These observations suggest that the stable complex of Smurf2 and NEDD9 is required for timely entry into mitosis via Aurora A activation.

Dcas supports cell polarization and cell-cell adhesion complexes in development

Mammalian Cas proteins regulate cell migration, division and survival, and are often deregulated in cancer. However, the presence of four paralogous Cas family members in mammals (BCAR1/p130Cas, EFS/Sin1, NEDD9/HEF1/Cas-L, and CASS4/HEPL) has limited their analysis in development. We deleted the single Drosophila Cas gene, Dcas, to probe the developmental function of Dcas. Loss of Dcas had limited effect on embryonal development. However, we found that Dcas is an important modulator of the severity of the developmental phenotypes of mutations affecting integrins (If and mew) and their downstream effectors Fak56D or Src42A. Strikingly, embryonic lethal Fak56D-Dcas double mutant embryos had extensive cell polarity defects, including mislocalization and reduced expression of E-cadherin. Further genetic analysis established that loss of Dcas modified the embryonal lethal phenotypes of embryos with mutations in E-cadherin (Shg) or its signaling partners p120- and beta-catenin (Arm). These results support an important role for Cas proteins in cell-cell adhesion signaling in development.

Expression map of the human exome in CD34+ cells and blood cells: increased alternative splicing in cell motility and immune response genes

BACKGROUND

Hematopoietic cells are endowed with very specific biological functions, including cell motility and immune response. These specific functions are dramatically altered during hematopoietic cell differentiation, whereby undifferentiated hematopoietic stem and progenitor cells (HSPC) residing in bone marrow differentiate into platelets, red blood cells and immune cells that exit into the blood stream and eventually move into lymphoid organs or inflamed tissues. The contribution of alternative splicing (AS) to these functions has long been minimized due to incomplete knowledge on AS events in hematopoietic cells.

PRINCIPAL FINDINGS

Using Human Exon ST 1.0 microarrays, the entire exome expression profile of immature CD34+ HSPC and mature whole blood cells was mapped, compared to a collection of solid tissues and made freely available as an online exome expression atlas (Amazonia Exon! : http://amazonia.transcriptome.eu/exon.php). At a whole transcript level, HSPC strongly expressed EREG and the pluripotency marker DPPA4. Using a differential splicing index scheme (dsi), a list of 849 transcripts differentially expressed between hematopoietic cells and solid tissues was computed, that included NEDD9 and CD74. Some of these genes also underwent alternative splicing events during hematopoietic differentiation, such as INPP4B, PTPLA or COMMD6, with varied contribution of CD3+ T cells, CD19+ B cells, CD14+ or CD15+ myelomonocytic populations. Strikingly, these genes were significantly enriched for genes involved in cell motility, cell adhesion, response to wounding and immune processes.

CONCLUSION

The relevance and the precision provided by this exon expression map highlights the contribution of alternative splicing to key feature of blood cells differentiation and function.

Cell migration and metastasis markers as targets of environmental pollutants and the Aryl hydrocarbon receptor

During the last few years, several studies have pointed to a surprising link between environmental pollutants cellular signaling and important cell functions such as plasticity, adhesion and migration. This unexpected link could be related to endogenous functions of pollutants receptors that may be disrupted by environmental factors, which is supported by observations in invertebrate species. It could also reveal novel toxic end-points and mechanisms of those pollutants, such as teratogenesis and cancer metastasis that are highly relevant from a public health point of view. In the present short article, we will review our recent observations on the aryl hydrocarbon receptor and its new molecular and cellular targets. We identified HEF1/NEDD9/CAS-L, a multifunctional protein involved in integrin-based signaling as a transcriptional target of the receptor, and showed that its induction was critical for cell plasticity mediated by environmental pollutants. We will put our studies in perspective with other observations made by several groups.

Transforming growth factor beta promotes neuronal cell fate of mouse cortical and hippocampal progenitors in vitro and in vivo: identification of Nedd9 as an essential signaling component

Transforming Growth Factor β (Tgfβ) and associated signaling effectors are expressed in the forebrain, but little is known about the role of this multifunctional cytokine during forebrain development. Using hippocampal and cortical primary cell cultures of developing mouse brains, this study identified Tgfβ-regulated genes not only associated with cell cycle exit of progenitors but also with adoption of neuronal cell fate. Accordingly, we observed not only an antimitotic effect of Tgfβ on progenitors but also an increased expression of neuronal markers in Tgfβ treated cultures. This effect was dependent upon Smad4. Furthermore, in vivo loss-of-function analyses using Tgfβ2^−/−/Tgfβ3^−/− double mutant mice showed the opposite effect of increased cell proliferation and fewer neurons in the cerebral cortex and hippocampus. Gata2, Runx1, and Nedd9 were candidate genes regulated by Tgfβ and known to be involved in developmental processes of neuronal progenitors. Using siRNA-mediated knockdown, we identified Nedd9 as an essential signaling component for the Tgfβ-dependent increase in neuronal cell fate. Expression of this scaffolding protein, which is mainly described as a signaling molecule of the β1-integrin pathway, was not only induced after Tgfβ treatment but was also associated with morphological changes of the Nestin-positive progenitor pool observed upon exposure to Tgfβ.

Regulation of TGF-beta signaling by Smad7

Transforming growth factor (TGF)-β is a pleiotropic cytokine regulating a variety of cellular processes such as cell growth, differentiation, apoptosis, migration, cell adhesion, and immune response. In the well-understood classical TGF-β signaling pathway, TGF-β activates Smad signalling via its two cell surface receptors such as TβRII and ALK5/TβRI, leading to Smad-mediated transcriptional regulation. In addition, TGF-β may also activate other signaling pathways like mitogen-activated protein kinase, PI3K, etc. The signaling of TGF-β is finely regulated at different levels. Inhibitory Smads, including Smad6 and Smad7, are key regulators of TGF-β/bone morphogenetic protein (BMP) signaling by negative feedback loops. They can form stable complexes with activated type I receptors and thereby blocking the phosphorylation of R-Smads, or recruit ubiquitin E3 ligases, such as Smurf1/2, resulting in the ubiquitination and degradation of the activated type I receptors. Besides, these inhibitory Smad proteins also inhibit TGF-β/BMP signaling in the nucleus by interacting with transcriptional repressors, such as histone deacetylases, Hoxc-8, and CtBP, or disrupting the formation of the TGF-β-induced functional Smad-DNA complexes. Smad7 is in turn regulated by different stimuli, including TGF-β, IFN-γ, TNF-α as well as ultraviolet and TPA, and mediates the crosstalk between TGF-β and other signaling pathways. Deregulation of Smad7 expression has been associated with various human diseases, such as tissue fibrosis, inflammatory disease as well as carcinogenesis. Overexpression of Smad7 has been shown to antagonize TGF-β-mediated fibrosis, carcinogenesis, and inflammation, suggesting a therapeutic potential of Smad7 to treat these diseases.

SHP-2 inhibits tyrosine phosphorylation of Cas-L and regulates cell migration

The Src homology 2 (SH2) domain-containing protein tyrosine phosphatase, SHP-2, plays an important role in cell migration by interacting with various proteins. In this report, we demonstrated that SHP-2 inhibits tyrosine phosphorylation of Crk-associated substrate lymphocyte type (Cas-L), a docking protein which mediates cell migration, and found that SHP-2 negatively regulates migration of A549 lung adenocarcinoma cells induced by fibronectin (FN). We showed that overexpressed SHP-2 co-localizes with Cas-L at focal adhesions and that exogenous expression of SHP-2 abrogates cell migration mediated by Cas-L. SHP-2 inhibits tyrosine phosphorylation of Cas-L, and associates with Cas-L to form a complex in a tyrosine phosphorylation-dependent manner. Finally, immunoprecipitation experiments with deletion mutants revealed that both SH2 domains of SHP-2 are necessary for this association. These results suggest that SHP-2 regulates tyrosine phosphorylation of Cas-L, hence opposing the effect of kinases, and SHP-2 is a negative regulator of cell migration mediated by Cas-L.

A new central scaffold for metastasis: parsing HEF1/Cas-L/NEDD9

Greater understanding of metastasis is required to improve cancer treatment outcomes. Recently, changes in expression of the scaffold protein HEF1/CAS-L/NEDD9 were found to be a potent prometastatic stimulus in melanoma and other cancers. Mechanistic studies suggest diverse cellular roles of HEF1 and highlight its importance in the response to extracellular cues that drive invasion and metastasis. As a metastatic "hub" for signaling in cancer, HEF1 may provide a useful target for drug discovery efforts.

Molecular basis for HEF1/NEDD9/Cas-L action as a multifunctional co-ordinator of invasion, apoptosis and cell cycle

Upregulation of the scaffolding protein HEF1, also known as NEDD9 and Cas-L, has recently been identified as a pro-metastatic stimulus in a number of different solid tumors, and has also been strongly associated with pathogenesis of BCR-Abl-dependent tumors. As the evidence mounts for HEF1/NEDD9/Cas-L as a key player in metastatic cancer, it is timely to review the molecular regulation of HEF1/NEDD9/Cas-L. Most of the mortality associated with cancer arises from uncontrolled metastases, thus a better understanding of the properties of proteins specifically associated with promotion of this process may yield insights that improve cancer diagnosis and treatment. In this review, we summarize the extensive literature regarding HEF1/NEDD9/Cas-L expression and function in signaling relevant to cell attachment, migration, invasion, cell cycle, apoptosis, and oncogenic signal transduction. The complex function of HEF1/NEDD9/Cas-L revealed by this analysis leads us to propose a model in which alleviation of cell cycle checkpoints and acquired resistance to apoptosis is permissive for a HEF1/NEDD9/Cas-L-promoted pro-metastatic phenotype.