During development and in the context of different morphogenetic events, epithelial cells undergo a process called epithelial to mesenchymal transition or transdifferentiation (EMT). In this process, the cells lose their epithelial characteristics, including their polarity and specialized cell-cell contacts, and acquire a migratory behavior, allowing them to move away from their epithelial cell community and to integrate into surrounding tissue, even at remote locations. EMT illustrates the differentiation plasticity during development and is complemented by another process, called mesenchymal to epithelial transition (MET). While being an integral process during development, EMT is also recapitulated under pathological conditions, prominently in fibrosis and in invasion and metastasis of carcinomas. Accordingly, EMT is considered as an important step in tumor progression. TGF-beta signaling has been shown to play an important role in EMT. In fact, adding TGF-beta to epithelial cells in culture is a convenient way to induce EMT in various epithelial cells. Although much less characterized, epithelial plasticity can also be regulated by TGF-beta-related bone morphogenetic proteins (BMPs), and BMPs have been shown to induce EMT or MET depending on the developmental context. In this review, we will discuss the induction of EMT in response to TGF-beta, and focus on the underlying signaling and transcription mechanisms.
Transforming growth factor-beta utilizes a multitude of intracellular signaling pathways in addition to Smads to regulate a wide array of cellular functions. These non-canonical, non-Smad pathways are activated directly by ligand-occupied receptors to reinforce, attenuate, or otherwise modulate downstream cellular responses. These non-Smad pathways include various branches of MAP kinase pathways, Rho-like GTPase signaling pathways, and phosphati-dylinositol-3- kinase/AKT pathways. This review focuses on recent advances in the understanding of the molecular and biochemical mechanisms of non-Smad pathways. In addition, functions of these non-Smad pathways are also discussed.
Transforming growth factor-beta (TGF-beta)/bone morphogenic protein ( BMP) signaling is involved in the vast majority of cellular processes and is fundamentally important during the entire life of all metazoans. Deregulation of TGF-beta/BMP activity almost invariably leads to developmental defects and/or diseases, including cancer. The proper functioning of the TGF-beta/BMP pathway depends on its constitutive and extensive communication with other signaling pathways, leading to synergistic or antagonistic effects and eventually desirable biological outcomes. The nature of such signaling cross-talk is overwhelmingly complex and highly context-dependent. Here we review the different modes of cross-talk between TGF-beta/BMP and the signaling pathways of Mitogen-activated protein kinase, phosphatidylinositol-3 kinase/Akt, Wnt, Hedgehog, Notch, and the interleukin/interferon-gamma/tumor necrosis factor-alpha cytokines, with an emphasis on the underlying molecular mechanisms.
The TGF beta signaling pathway is conserved from flies to humans and has been shown to regulate such diverse processes as cell proliferation, differentiation, motility, adhesion, organization, and programmed cell death. Both in vitro and in vivo experiments suggest that TGF beta can utilize these varied programs to promote cancer metastasis through its effects on the tumor microenvironment, enhanced invasive properties, and inhibition of immune cell function. Recent clinical evidence demonstrating a link between TGF beta signaling and cancer progression is fostering interest in this signaling pathway as a therapeutic target. Anti-TGF beta therapies are currently being developed and tested in preclinical studies. However, targeting TGF beta carries a substantial risk as this pathway is implicated in multiple homeostatic processes and is also known to have tumor-suppressor functions. Additionally, clinical and experimental results show that TGF beta has diverse and often conflicting roles in tumor progression even within the same tumor types. The development of TGF beta inhibitors for clinical use will require a deeper understanding of TGF beta signaling, its consequences, and the contexts in which it acts.
CD4 T helper （Th） cells play critical roles in adaptive immune responses. They recruit and activate other immune cells including B cells, CD8 T cells, macrophages, mast cells, neutrophils, eosinophils and basophils. Based on their functions, their pattern of cytokine secretion and their expression of specific transcription factors, Th cells, differentiated from naive CD4 T cells, are classified into four major lineages, Thl, Th2, Th17 and T regulatory （Treg） cells, although other Th lineages may exist. Subsets of the same lineage may express different effector cytokines, reside at different locations or give rise to cells with different fates, whereas cells from different lineages may secrete common cytokines, such as IL-2, IL-9 and IL-10, resulting in massive heterogeneity of the Th cell population. In addition, the pattern of cytokine secretion may switch from that of one lineage toward another under certain circumstances, suggesting that Th cells are plastic. Tregs are also more heterogeneous and plastic than were originally thought. In this review, we summarize recent reports on heterogeneity and plasticity of Th cells, and discuss potential mechanisms and implications of such features that Th cells display.
Human pluripotent stem cells represent a potentially unlimited source of functional pancreatic endocrine lineage cells. Here we report a highly efficient approach to induce human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells to differentiate into mature insulin-producing cells in a chemical-defined culture system. The differentiated human ES cells obtained by this approach comprised nearly 25% insulin-positive cells as assayed by flow cytometry analysis, which released insulin/C-peptide in response to glucose stimuli in a manner comparable to that of adult human islets. Most of these insulin-producing cells co-expressed mature beta cell-specific markers such as NKX6-1 and PDX1, indicating a similar gene expression pattern to adult islet beta cells in vivo. In this study, we also demonstrated that EGF facilitates the expansion of PDX1-positive pancreatic progenitors. Moreover, our protocol also succeeded in efficiently inducing human iPS cells to differentiate into insulin-producing cells. Therefore, this work not only provides a new model to study the mechanism of human pancreatic specialization and maturation in vitro, but also enhances the possibility of utilizing patient-specific iPS cells for the treatment of diabetes.
Human induced pluripotent stem （iPS） cells are similar to embryonic stem （ES） cells, and can proliferate intensively and differentiate into a variety of cell types. However, the hepatic differentiation of human iPS cells has not yet been reported. In this report, human iPS cells were induced to differentiate into hepatic cells by a stepwise protocol. The expression of liver cell markers and liver-related functions of the human iPS cell-derived cells were monitored and compared with that of differentiated human ES cells and primary human hepatocytes. Approximately 60% of the differentiated human iPS cells at day 7 expressed hepatic markers alpha fetoprotein and Alb. The differentiated cells at day 21 exhibited liver cell functions including albumin Asecretion, glycogen synthesis, urea production and inducible cytochrome P450 activity. The expression of hepatic markers and fiver-related functions of the iPS cellderived hepatic ceils were comparable to that of the human ES cell-derived hepatic cells. These results show that human iPS cells, which are similar to human ES cells, can be efficiently induced to differentiate into hepatocyte-like cells.
The discovery of intrinsically disordered proteins (IDP) (i.e., biologically active proteins that do not possess stable secondary and/or tertiary structures) came as an unexpected surprise, as the existence of such proteins is in contradiction to the traditional "sequence -> structure -> function" paradigm. Accurate prediction of a protein's predisposition to be intrinsically disordered is a necessary prerequisite for the further understanding of principles and mechanisms of protein folding and function, and is a key for the elaboration of a new structural and functional hierarchy of proteins. Therefore, prediction of IDPs has attracted the attention of many researchers, and a number of prediction tools have been developed. Predictions of disorder, in turn, are playing major roles in directing laboratory experiments that are leading to the discovery of ever more disordered proteins, and thereby leading to a positive feedback loop in the investigation of these proteins. In this review of algorithms for intrinsic disorder prediction, the basic concepts of various prediction methods for IDPs are summarized, the strengths and shortcomings of many of the methods are analyzed, and the difficulties and directions of future development of IDP prediction techniques are discussed.
Transforming growth factor (TGF)-beta s and their family members, including bone morphogenetic proteins (BMPs), Nodal and activins, have been implicated in the development and maintenance of various organs, in which stem cells play important roles. Stem cells are characterized by their ability to self-renew and to generate differentiated cells of a particular tissue, and are classified into embryonic and somatic stem cells. Embryonic stem (ES) cells self-renew indefinitely and contribute to derivatives of all three primary germ layers. In contrast, somatic stem cells, which can be identified in various adult organs, exhibit limited abilities for self-renewal and differentiation in most cases. The multi-lineage differentiation capacity of ES cells and somatic stem cells has opened possibilities for cell replacement therapies for genetic, malignant and degenerative diseases. In order to utilize stem cells for therapeutic applications, it is essential to understand the extrinsic and intrinsic factors regulating self-renewal and differentiation of stem cells. More recently, induced pluripotent stem (iPS) cells have been generated from mouse and human fibroblasts that resemble ES cells via ectopic expression of four transcription factors. iPS cells may have an advantage in regenerative medicine, since they overcome the immunogenicity and ethical controversy of ES cells. Moreover, recent studies have highlighted the involvement of cancer stem cells during the formation and progression of various types of cancers, including leukemia, glioma, and breast cancer. Here, we illustrate the roles of TGF-beta family members in the maintenance and differentiation of ES cells, somatic stem cells, and cancer stem cells.
Transforming growth factor (TGF)-beta family members are multifunctional cytokines that elicit their effects on cells, including endothelial and mural cells, via specific type I and type II serine/threonine kinase receptors and intracellular Smad transcription factors. Knock-out mouse models for TGF-beta family signaling pathway components have revealed their critical importance in proper yolk sac angiogenesis. Genetic studies in humans have linked mutations in these signaling components to specific cardiovascular syndromes such as hereditary hemorrhagic telangiectasia, primary pulmonary hypertension and Marfan syndrome. In this review, we present recent advances in our understanding of the role of TGF-beta receptor signaling in vascular biology and disease, and discuss how this may be applied therapy.
MicroRNAs (miRNAs) are endogenous, small, non-coding RNAs, which are capable of silencing gene expression at the post-transcriptional level. In this study, we report that miR-205 is significantly underexpressed in breast tumor compared to the matched normal breast tissue. Similarly, breast cancer cell lines, including MCF-7 and MDA-MB231, express a lower level miR-205 than the non-malignant MCF-10A cells. Of interest, ectopic expression of miR-205 significantly inhibits cell proliferation and anchorage independent growth, as well as cell invasion. Furthermore, miR-205 was shown to suppress lung metastasis in an animal model. Finally, western blot combined with the luciferase reporter assays demonstrate that ErbB3 and vascular endothelial growth factor A (VEGF-A) are direct targets for miR-205, and this miR-205-mediated suppression is likely through the direct interaction with the putative miR-205 binding site in the 3'-untranslated region (3'-UTR) of ErbB3 and VEGF-A. Together, these results suggest that miR-205 is a tumor suppressor in breast cancer.
The nuclear factor-kappa B (NF-kappa B) transcription factor plays a critical role in diverse cellular processes associated with proliferation, cell death, development, as well as innate and adaptive immune responses. NF-kappa B is normally sequestered in the cytoplasm by a family of inhibitory proteins known as inhibitors of NF-kappa B (I kappa Bs). The signal pathways leading to the liberation and nuclear accumulation of NF-kappa B, which can be activated by a wide variety of stimuli, have been extensively studied in the past two decades. After gaining access to the nucleus, NF-kappa B must be actively regulated to execute its fundamental function as a transcription factor. Recent studies have highlighted the importance of nuclear signaling in the regulation of NF-kappa B transcriptional activity. A non-Rel subunit of NF-kappa B, ribosomal protein S3 (RPS3), and numerous other nuclear regulators of NF-kappa B, including Akirin, Nurr1, SIRT6, and others, have recently been identified, unveiling novel and exciting layers of regulatory specificity for NF-kappa B in the nucleus. Further insights into the nuclear events that govern NF-kappa B function will deepen our understanding of the elegant control of its transcriptional activity and better inform the potential rational design of therapeutics for NF-kappa B-associated diseases.
NAC family genes encode plant-specific transcription factors involved in diverse biological processes. In this study, the Arabidopsis NAC gene ATAF1 was found to be induced by drought, high-salinity, abscisic acid (ABA), methyl jasmonate, mechanical wounding, and Botrytis cinerea infection. Significant induction of ATAF1 was found in an ABA-deficient mutant aba2 subjected to drought or high salinity, revealing an ABA-independent mechanism of expression. Arabidopsis ATAF1-overexpression lines displayed many altered phenotypes, including dwarfism and short primary roots. Furthermore, in vivo experiments indicate that ATAF1 is a bona fide regulator modulating plant responses to many abiotic stresses and necrotrophic-pathogen infection. Overexpression of ATAF1 in Arabidopsis increased plant sensitivity to ABA, salt, and oxidative stresses. Especially, ATAF1 overexpression plants, but not mutant lines, showed remarkably enhanced plant tolerance to drought. Additionally, ATAF1 overexpression enhanced plant susceptibility to the necrotrophic pathogen B. cinerea, but did not alter disease symptoms caused by avirulent or virulent strains of P. syringae pv tomato DC3000. Transgenic plants overexpressing ATAF1 were hypersensitive to oxidative stress, suggesting that reactive oxygen intermediates may be related to ATAF1-mediated signaling in response to both pathogen and abiotic stresses.
Prostate cancer cells with stem cell characteristics were identified in human prostate cancer cell lines by their ability to form from single cells self-renewing prostaspheres in non-adherent cultures. Prostaspheres exhibited heterogeneous expression of proliferation, differentiation and stem cell-associated makers CD44, ABCG2 and CD133. Treatment with WNT inhibitors reduced both prostasphere size and self-renewal. In contrast, addition of Wnt3a caused increased prostasphere size and self-renewal, which was associated with a significant increase in nuclear beta-catenin, keratin 18, CD133 and CD44 expression. As a high proportion of LNCaP and C4-2B cancer cells express androgen receptor we determined the effect of the androgen receptor antagonist bicalutamide. Androgen receptor inhibition reduced prostasphere size and expression of PSA, but did not inhibit prostasphere formation. These effects are consistent with the androgen-independent self-renewal of cells with stem cell characteristics and the androgen-dependent proliferation of transit amplifying cells. As the canonical WNT signaling effector b-catenin can also associate with the androgen receptor, we propose a model for tumour propagation involving a balance between WNT and androgen receptor activity. That would affect the self-renewal of a cancer cell with stem cell characteristics and drive transit amplifying cell proliferation and differentiation. In conclusion, we provide evidence that WNT activity regulates the self-renewal of prostate cancer cells with stem cell characteristics independently of androgen receptor activity. Inhibition of WNT signaling therefore has the potential to reduce the self-renewal of prostate cancer cells with stem cell characteristics and improve the therapeutic outcome.
Members of the transforming growth factor-beta ( TGF-beta) family control a broad range of cellular responses in metazoan organisms via autocrine, paracrine, and endocrine modes. Thus, aberrant TGF-beta signaling can play a key role in the pathogenesis of several diseases, including cancer. TGF-beta signaling pathways are activated by a short phospho-cascade, from receptor phosphorylation to the subsequent phosphorylation and activation of downstream signal transducers called R-Smads. R-Smad phosphorylation state determines Smad complex assembly/disassembly, nuclear import/export, transcriptional activity and stability, and is thus the most critical event in TGF-beta signaling. Dephosphorylation of R-Smads by specific phosphatases prevents or terminates TGF-beta signaling, highlighting the need to consider Smad (de) phosphorylation as a tightly controlled and dynamic event. This article illustrates the essential roles of reversible phosphorylation in controlling the strength and duration of TGF-beta signaling and the ensuing physiological responses.
Alterations in oxidative phosphorylation resulting from mitochondrial dysfunction have long been hypothesized to be involved in tumorigenesis. Mitochondria have recently been shown to play an important role in regulating both programmed cell death and cell proliferation. Furthermore, mitochondrial DNA (mtDNA) mutations have been found in various cancer cells. However, the role of these mtDNA mutations in tumorigenesis remains largely unknown. This review focuses on basic mitochondrial genetics, mtDNA mutations and consequential mitochondrial dysfunction associated with cancer. The potential molecular mechanisms, mediating the pathogenesis from mtDNA mutations and mitochondrial dysfunction to tumorigenesis are also discussed.
Neural stem cells (NSCs) are present not only during the embryonic development but also in the adult brain of all mammalian species, including humans. Stem cell niche architecture in vivo enables adult NSCs to continuously generate functional neurons in specific brain regions throughout life. The adult neurogenesis process is subject to dynamic regulation by various physiological, pathological and pharmacological stimuli. Multipotent adult NSCs also appear to be intrinsically plastic, amenable to genetic programing during normal differentiation, and to epigenetic reprograming during de-differentiation into pluripotency. Increasing evidence suggests that adult NSCs significantly contribute to specialized neural functions under physiological and pathological conditions. Fully understanding the biology of adult NSCs will provide crucial insights into both the etiology and potential therapeutic interventions of major brain disorders. Here, we review recent progress on adult NSCs of the mammalian central nervous system, including topics on their identity, niche, function, plasticity, and emerging roles in cancer and regenerative medicine.
Transforming growth factor-beta (TGF-beta) signaling is tightly regulated to ensure its proper physiological functions in different cells and tissues. Like other cell surface receptors, TGF-beta receptors are internalized into the cell, and this process plays an important regulatory role in TGF-beta signaling. It is well documented that TGF-beta receptors are endocytosed via clathrin-coated vesicles as TGF-beta endocytosis can be blocked by potassium depletion and the GTPase-deficient dynamin K44A mutant. TGF-beta receptors may also enter cells via cholesterol-rich membrane microdomain lipid rafts/caveolae and are found in caveolin-1-positive vesicles. Although receptor endocytosis is not essential for TGF-beta signaling, clathrin-mediated endocytosis has been shown to promote TGF-beta-induced Smad activation and transcriptional responses. Lipid rafts/caveolae are widely regarded as signaling centers for G protein-coupled receptors and tyrosine kinase receptors, but they are indicated to facilitate the degradation of TGF-beta receptors and therefore turnoff of TGF-beta signaling. This review summarizes current understanding of TGF-beta receptor endocytosis, the possible mechanisms underlying this process, and the role of endocytosis in modulation of TGF-beta signaling.