Calmodulin differentially modulates Smad1 and Smad2 signaling

Drug tolerant persister cell plasticity in cancer: A revolutionary strategy for more effective anticancer therapies

Non-genetic mechanisms have recently emerged as important drivers of anticancer drug resistance. Among these, the drug tolerant persister (DTP) cell phenotype is attracting more and more attention and giving a predominant non-genetic role in cancer therapy resistance. The DTP phenotype is characterized by a quiescent or slow-cell-cycle reversible state of the cancer cell subpopulation and inert specialization to stimuli, which tolerates anticancer drug exposure to some extent through the interaction of multiple underlying mechanisms and recovering growth and proliferation after drug withdrawal, ultimately leading to treatment resistance and cancer recurrence. Therefore, targeting DTP cells is anticipated to provide new treatment opportunities for cancer patients, although our current knowledge of these DTP cells in treatment resistance remains limited. In this review, we provide a comprehensive overview of the formation characteristics and underlying drug tolerant mechanisms of DTP cells, investigate the potential drugs for DTP (including preclinical drugs, novel use for old drugs, and natural products) based on different medicine models, and discuss the necessity and feasibility of anti-DTP therapy, related application forms, and future issues that will need to be addressed to advance this emerging field towards clinical applications. Nonetheless, understanding the novel functions of DTP cells may enable us to develop new more effective anticancer therapy and improve clinical outcomes for cancer patients.

Response of mesenchymal stem cells to surface topography of scaffolds and the underlying mechanisms

Mesenchymal stem/stromal cells (MSCs) serve as essential components of regenerative medicine. Their destiny is influenced by the interaction of the cells with the external environment. In addition to the biochemical cues in a microenvironment, physical cues of the topography of the surrounding materials such as the extracellular matrix emerge as a crucial regulator of stem cell destiny and function. With recent advances in technologies of materials production and surface modification, surfaces with micro/nanotopographical characteristics can be fabricated to mimic the micro/nanoscale mechanical stimuli of the extracellular matrix environment and regulate the biological behavior of cells. Understanding the interaction of cells with the topography of a surface is conducive to the control of stem cell fate for application in regenerative medicine. However, the mechanisms by which topography affects the biological behavior of stem cells have not been fully elucidated. This review will present the effects of surface topography at the nano/micrometer scale on stem cell adhesion, morphology, proliferation, migration, and differentiation. It also focuses on discussing current theories about the sensing and recognition of surface topology cues, the transduction of the extracellular cues into plasma, and the final activation of related signaling pathways and downstream gene expression in MSCs. These insights will provide a theoretical basis for the future design of biomaterial scaffolds for application in regenerative medicine and tissue engineering.

Mesenchymal stromal cells in tumor microenvironment remodeling of BCR-ABL negative myeloproliferative diseases

Chronic myeloproliferative neoplasms encompass the BCR-ABL1-negative neoplasms polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). These are characterized by calreticulin (CALR), myeloproliferative leukemia virus proto-oncogene (MPL) and the tyrosine kinase Janus kinase 2 (JAK2) mutations, eventually establishing a hyperinflammatory tumor microenvironment (TME). Several reports have come to describe how constitutive activation of JAK-STAT and NFκB signaling pathways lead to uncontrolled myeloproliferation and pro-inflammatory cytokines secretion. In such a highly oxidative TME, the balance between Hematopoietic Stem Cells (HSCs) and Mesenchymal Stromal Cells (MSCs) has a crucial role in MPN development. For this reason, we sought to review the current literature concerning the interplay between HSCs and MSCs. The latter have been reported to play an outstanding role in establishing of the typical bone marrow (BM) fibrotic TME as a consequence of the upregulation of different fibrosis-associated genes including PDGF- β upon their exposure to the hyperoxidative TME characterizing MPNs. Therefore, MSCs might turn to be valuable candidates for niche-targeted targeting the synthesis of cytokines and oxidative stress in association with drugs eradicating the hematopoietic clone.

The role of Ca2+ /Calcineurin/NFAT signalling pathway in osteoblastogenesis

The bone remodelling process is closely related to bone health. Osteoblasts and osteoclasts participate in the bone remodelling process under the regulation of various factors inside and outside. Excessive activation of osteoclasts or lack of function of osteoblasts will cause occurrence and development of multiple bone‐related diseases. Ca²⁺/Calcineurin/NFAT signalling pathway regulates the growth and development of many types of cells, such as cardiomyocyte differentiation, angiogenesis, chondrogenesis, myogenesis, bone development and regeneration, etc. Some evidences indicate that this signalling pathway plays an extremely important role in bone formation and bone pathophysiologic changes. This review discusses the role of Ca²⁺/Calcineurin/NFAT signalling pathway in the process of osteogenic differentiation, as well as the influence of regulating each component in this signalling pathway on the differentiation and function of osteoblasts, whereby the relationship between Ca²⁺/Calcineurin/NFAT signalling pathway and osteoblastogenesis could be deeper understood.

Temperature and insulin signaling regulate body size in Hydra by the Wnt and TGF-beta pathways

How multicellular organisms assess and control their size is a fundamental question in biology, yet the molecular and genetic mechanisms that control organ or organism size remain largely unsolved. The freshwater polyp Hydra demonstrates a high capacity to adapt its body size to different temperatures. Here we identify the molecular mechanisms controlling this phenotypic plasticity and show that temperature-induced cell number changes are controlled by Wnt- and TGF-β signaling. Further we show that insulin-like peptide receptor (INSR) and forkhead box protein O (FoxO) are important genetic drivers of size determination controlling the same developmental regulators. Thus, environmental and genetic factors directly affect developmental mechanisms in which cell number is the strongest determinant of body size. These findings identify the basic mechanisms as to how size is regulated on an organismic level and how phenotypic plasticity is integrated into conserved developmental pathways in an evolutionary informative model organism.

Membrane Potential Depolarization Alters Calcium Flux and Phosphate Signaling During Osteogenic Differentiation of Human Mesenchymal Stem Cells

Background: Membrane potential (Vmem) changes accompany important events in embryonic development and organ regeneration. Recent studies have pointed to its function as a potent regulator of cell proliferation, differentiation, migration, and tissue regeneration. We have previously reported that Vmem depolarization and hyperpolarization control the osteogenic (OS) differentiation potential of human mesenchymal stem cells (hMSCs). Materials and Methods: In this study, we sought to understand the mechanism(s) underlying voltage regulation of hMSC differentiation. We investigated the role of calcium and phosphate ion flux in the depolarization response of OS-differentiating hMSCs, as these ions are the two major inorganic components of the bone mineral matrix and are indicative of mature osteoblast function. Results: Our results suggest that inorganic phosphate levels play a larger role than calcium flux in mediating hMSC response to depolarization and that the expression of stanniocalcin 1 (STC1), a protein that regulates calcium and phosphate homeostasis in osteoblasts, is functionally required for the depolarization response during the early stages of differentiation. Conclusion: Depolarization alters hMSC differentiation through a phosphate signaling pathway involving STC1. This study enriches our mechanistic understanding of hMSC response to endogenous voltage cues.

Annotation of nerve cord transcriptome in earthworm Eisenia fetida

In annelid worms, the nerve cord serves as a crucial organ to control the sensory and behavioral physiology. The inadequate genome resource of earthworms has prioritized the comprehensive analysis of their transcriptome dataset to monitor the genes express in the nerve cord and predict their role in the neurotransmission and sensory perception of the species. The present study focuses on identifying the potential transcripts and predicting their functional features by annotating the transcriptome dataset of nerve cord tissues prepared by Gong et al., 2010 from the earthworm Eisenia fetida. Totally 9762 transcripts were successfully annotated against the NCBI nr database using the BLASTX algorithm and among them 7680 transcripts were assigned to a total of 44,354 GO terms. The conserve domain analysis indicated the over representation of P-loop NTPase domain and calcium binding EF-hand domain. The COG functional annotation classified 5860 transcript sequences into 25 functional categories. Further, 4502 contig sequences were found to map with 124 KEGG pathways. The annotated contig dataset exhibited 22 crucial neuropeptides having considerable matches to the marine annelid Platynereis dumerilii, suggesting their possible role in neurotransmission and neuromodulation. In addition, 108 human stem cell marker homologs were identified including the crucial epigenetic regulators, transcriptional repressors and cell cycle regulators, which may contribute to the neuronal and segmental regeneration. The complete functional annotation of this nerve cord transcriptome can be further utilized to interpret genetic and molecular mechanisms associated with neuronal development, nervous system regeneration and nerve cord function.

FuncPatch: a web server for the fast Bayesian inference of conserved functional patches in protein 3D structures

MOTIVATION

A number of statistical phylogenetic methods have been developed to infer conserved functional sites or regions in proteins. Many methods, e.g. Rate4Site, apply the standard phylogenetic models to infer site-specific substitution rates and totally ignore the spatial correlation of substitution rates in protein tertiary structures, which may reduce their power to identify conserved functional patches in protein tertiary structures when the sequences used in the analysis are highly similar. The 3D sliding window method has been proposed to infer conserved functional patches in protein tertiary structures, but the window size, which reflects the strength of the spatial correlation, must be predefined and is not inferred from data. We recently developed GP4Rate to solve these problems under the Bayesian framework. Unfortunately, GP4Rate is computationally slow. Here, we present an intuitive web server, FuncPatch, to perform a fast approximate Bayesian inference of conserved functional patches in protein tertiary structures.

RESULTS

Both simulations and four case studies based on empirical data suggest that FuncPatch is a good approximation to GP4Rate. However, FuncPatch is orders of magnitudes faster than GP4Rate. In addition, simulations suggest that FuncPatch is potentially a useful tool complementary to Rate4Site, but the 3D sliding window method is less powerful than FuncPatch and Rate4Site. The functional patches predicted by FuncPatch in the four case studies are supported by experimental evidence, which corroborates the usefulness of FuncPatch.

AVAILABILITY AND IMPLEMENTATION

The software FuncPatch is freely available at the web site, http://info.mcmaster.ca/yifei/FuncPatch

CONTACT

golding@mcmaster.ca

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

The transcriptional repressor activity of ASYMMETRIC LEAVES1 is inhibited by direct interaction with calmodulin in Arabidopsis

Calmodulin (CaM), a key Ca2+ sensor, regulates diverse cellular processes by modulating the activity of a variety of enzymes and proteins. However, little is known about the biological function of CaM in plant development. In this study, an ASYMMETRIC LEAVES1 (AS1) transcription factor was isolated as a CaM-binding protein. AS1 contains two putative CaM-binding domains (CaMBDs) at the N-terminus. Using domain mapping analysis, both predicted domains were identified as authentic Ca2+ -dependent CaMBDs. We identified three hydrophobic amino acid residues for CaM binding, Trp49 in CaMBDI, and Trp81 and Phe103 in CaMBDII. The interactions of AS1 with CaM were verified in yeast and plant cells. Based on electrophoretic mobility shift assays, CaM inhibited the DNA-binding activity of the AS1/AS2 complex to two cis-regulatory motifs in the KNAT1 promoter. Furthermore, CaM relieved the suppression of KNAT1 transcription by AS1 not only in transient expression assays of protoplasts but also by the overexpression of a CaM-binding negative form of AS1 in as1 mutant plant. Our study suggests that CaM, a calcium sensor, can be involved in the transcriptional control of meristem cell-specific genes by the inhibition of AS1 under the condition of higher levels of Ca2+ in plants.

Interplay between electrical activity and bone morphogenetic protein signaling regulates spinal neuron differentiation

A gradient of bone morphogenetic proteins (BMPs) along the dorsoventral axis of the spinal cord is necessary for the specification of dorsal neurons. Concurrently, a gradient of calcium-mediated electrical activity is present in the developing spinal cord but in an opposing ventrodorsal direction. Whether BMPs and electrical activity interact in embryonic spinal neurons remains unknown. We show that BMP decreases electrical activity by enhancing p38 MAPK-mediated negative modulation of voltage-gated sodium channels. In turn, electrical activity affects the phosphorylation status and nuclear level of activated Smads, the canonical components of BMP signaling. This interaction between calcium spike activity and BMP signaling regulates the specification of the dorsal commissural spinal neuron phenotype. The present study identifies an unexpected interplay between BMPs and electrical activity that is critical for decoding the morphogen gradient during spinal neuron differentiation.

Pannexin 3 functions as an ER Ca(2+) channel, hemichannel, and gap junction to promote osteoblast differentiation

Pannexin 3 functions as an essential protein for Ca²⁺ and ATP transport and cell–cell communication during osteoblast differentiation

The pannexin proteins represent a new gap junction family. However, the cellular functions of pannexins remain largely unknown. Here, we demonstrate that pannexin 3 (Panx3) promotes differentiation of osteoblasts and ex vivo growth of metatarsals. Panx3 expression was induced during osteogenic differentiation of C2C12 cells and primary calvarial cells, and suppression of this endogenous expression inhibited differentiation. Panx3 functioned as a unique Ca²⁺ channel in the endoplasmic reticulum (ER), which was activated by purinergic receptor/phosphoinositide 3-kinase (PI3K)/Akt signaling, followed by activation of calmodulin signaling for differentiation. Panx3 also formed hemichannels that allowed release of ATP into the extracellular space and activation of purinergic receptors with the subsequent activation of PI3K–Akt signaling. Panx3 also formed gap junctions and propagated Ca²⁺ waves between cells. Blocking the Panx3 Ca²⁺ channel and gap junction activities inhibited osteoblast differentiation. Thus, Panx3 appears to be a new regulator that promotes osteoblast differentiation by functioning as an ER Ca²⁺ channel and a hemichannel, and by forming gap junctions.

Thapsigargin-induced Ca2+ increase inhibits TGFβ1-mediated Smad2 transcriptional responses via Ca2+/calmodulin-dependent protein kinase II

Transforming growth factor β (TGFβ) signalling plays important roles in a variety of tissues and cell types. Impaired TGFβ signalling contributes to several pathologies, including cancer, fibrosis as well as neurodegenerative diseases. TGFβ receptor type I-mediated phosphorylation of Smad2, the formation of the Smad2-Smad4 complex and translocation to the nucleus are critical steps of the TGFβ signalling pathway. Here, we demonstrate that thapsigargin-mediated increase of intracellular Ca(2+) concentrations inhibited TGFβ1-induced Smad2 transcriptional activity in the oligodendroglial cell line OLI-neu. We provide evidence that thapsigargin treatment dramatically reduced the nuclear translocation of Smad2 after TGFβ1 treatment but had no effect on its phosphorylation at Ser465/467. Moreover, using Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibitors and a constitutively active CaMKII mutant, we provide evidence that the observed inhibition of TGFβ signalling in OLI-neu cells was strongly dependent on Ca(2+)-mediated CaMKII activation. In summary, this study clearly shows that the TGFβ1-induced Smad2 nuclear translocation is negatively regulated by intracellular Ca(2+) in OLI-neu cells and that increased intracellular Ca(2+) concentrations block Smad2-mediated transcription of TGFβ target genes. These results underline the importance of intracellular Ca(2+) for the regulation of TGFβ signalling.

Functional interaction between Smad3 and S100A4 (metastatin-1) for TGF-beta-mediated cancer cell invasiveness

TGF-beta (transforming growth factor-beta) induces a cytostatic response in most normal cell types. In cancer cells, however, it often promotes metastasis, and its high expression is correlated with poor prognosis. In the present study, we show that S100A4, a metastasis-associated protein, also called metastatin-1, can physically and functionally interact with Smad3, an important mediator of TGF-beta signalling. In agreement with its known property, S100A4 binds to Smad3 in a Ca2+-dependent manner. The S100A4-binding site is located in the N-terminal region of Smad3. S100A4 can potentiate transcriptional activity of Smad3 and the related Smad2. When exogenously expressed in MCF10CA1a.cl1, an MCF10-derived breast cancer cell line, S100A4 increases TGF-beta-induced MMP-9 (matrix metalloproteinase-9) expression. On the other hand, depletion of S100A4 by siRNA (small interfering RNA) from the MDA-MB231 cell line results in attenuation of MMP-9 induction by TGF-beta. Consistent with these observations, S100A4 increases cell invasion ability induced by TGF-beta in MCF10CA1a.cl1 cells, and depletion of the protein in MDA-MB-231 cells inhibits it. Because expression of both S100A4 and TGF-beta is highly elevated in many types of malignant tumours, S100A4 and Smad3 may co-operatively increase metastatic activity of some types of cancer cells.

TRPM7-mediated Ca2+ signals confer fibrogenesis in human atrial fibrillation

RATIONALE

Cardiac fibrosis contributes to pathogenesis of atrial fibrillation (AF), which is the most commonly sustained arrhythmia and a major cause of morbidity and mortality. Although it has been suggested that Ca(2+) signals are involved in fibrosis promotion, the molecular basis of Ca(2+) signaling mechanisms and how Ca(2+) signals contribute to fibrogenesis remain unknown.

OBJECTIVE

To determine the molecular mechanisms of Ca(2+)-permeable channel(s) in human atrial fibroblasts, and to investigate how Ca(2+) signals contribute to fibrogenesis in human AF.

METHODS AND RESULTS

We demonstrate that the transient receptor potential (TRP) melastatin related 7 (TRPM7) is the molecular basis of the major Ca(2+)-permeable channel in human atrial fibroblasts. Endogenous TRPM7 currents in atrial fibroblasts resemble the biophysical and pharmacological properties of heterologous expressed TRPM7. Knocking down TRPM7 by small hairpin RNA largely eliminates TRPM7 current and Ca(2+) influx in atrial fibroblasts. More importantly, atrial fibroblasts from AF patients show a striking upregulation of both TRPM7 currents and Ca(2+) influx and are more prone to myofibroblast differentiation, presumably attributable to the enhanced expression of TRPM7. TRPM7 small hairpin RNA markedly reduced basal AF fibroblast differentiation. Transforming growth factor (TGF)-beta1, the major stimulator of atrial fibrosis, requires TRPM7-mediated Ca(2+) signal for its effect on fibroblast proliferation and differentiation. Furthermore, TGF-beta1-induced differentiation of cultured human atrial fibroblasts is well correlated with an increase of TRPM7 expression induced by TGF-beta1.

CONCLUSIONS

Our results establish that TRPM7 is the major Ca(2+)-permeable channel in human atrial fibroblasts and likely plays an essential role in TGF-beta1-elicited fibrogenesis in human AF.

Effects of ATP on the intracellular calcium level in the osteoblastic TBR31-2 cell line

We investigated the effects of extracellular ATP on TBR31-2 cells established from the bone marrow of transgenic mice harboring the temperature-sensitive simian virus (SV) 40 T-antigen gene. These cells showed the capacity to differentiate toward osteoblasts and could be enhanced by bone morphogenetic protein (BMP)-2, an inducer of osteoblasts. The intracellular calcium ion level ([Ca(2+)](i)) in differentiating TBR31-2 cells was measured by fluorescence confocal microscopic imaging using the Ca(2+)-sensitive probe, Calcium Green 1/AM. P2 receptor agonists, such as ATP (1 microM), uridine 5'-triphosphate (1 microM), and ADP (1 microM), significantly increased the [Ca(2+)](i) of TBR31-2 cells in 2-d and 5-d cultures, but a potent P2X receptor agonist, alpha,beta-methylene ATP (10 microM), did not increase [Ca(2+)](i). The increase in [Ca(2+)](i) induced by ATP in the 2-d culture tended to be higher than in the 5-d culture. The increase in [Ca(2+)](i) of both cultures was inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid, a P2 receptor antagonist. However, in an external Ca(2+)-free condition ATP-induced increase in [Ca(2+)](i) was unchanged at either stage. U73122, phospholipase C inhibitor and Thapsigargin, a calcium-pump inhibitor, significantly inhibited the increase in [Ca(2+)](i) at both stages. Reverse transcription-polymerase chain reaction analysis showed that the expression of P2Y receptor mRNA was higher in the 2-d culture than in the 5-d culture. These results indicate that ATP induces the increase in [Ca(2+)](i) from the calcium store through activating P2Y receptors in TBR31-2 cells and that the 2-d culture can respond to ATP more than the 5-d culture due to the higher expression of P2Y receptors. This suggests that the physiological role of ATP in osteoblasts is altered during differentiation.

NFATc is required for TGFbeta-mediated transcriptional regulation of fibronectin

Calcineurin is an important regulator of extracellular matrix (ECM) accumulation in the kidney but functions in a cell-specific manner. Previously, we identified a novel role for calcineurin in mesangial cells where calcineurin activity is required for TGFbeta-mediated induction of fibronectin expression. In this study, we examined the role of the calcineurin substrate NFATc in transcriptional regulation of fibronectin. First, inhibition of calcineurin blocks TGFbeta induction of the fibronectin promoter. Moreover, expression of constitutively active calcineurin in mesangial cells is sufficient to increase fibronectin transcription. Next, inhibition of the calcineurin substrate NFATc1 blocked TGFbeta-mediated activation of the fibronectin promoter. Finally, stable expression of a dominant-negative NFATc protein reduced transcriptional activation of the promoter and inhibited TGFbeta-mediated fibronectin expression. In conclusion, TGFbeta activation of calcineurin in mesangial cells results in regulation of ECM accumulation at least in part by direct transcriptional activity of NFATc on the fibronectin promoter.

Hereditary gingival fibromatosis: characteristics and novel putative pathogenic mechanisms

Hereditary gingival fibromatosis (HGF) is a rare condition that can occur as an isolated disease or as part of a syndrome or chromosomal abnormality. In severe cases, the gingival enlargement may cover the crowns of teeth and cause severe functional and esthetic concerns. Histological and cell culture studies have uncovered some of the molecular and cellular changes associated with HGF. However, the pathogenesis of the disease is still largely unknown. Recent studies about the genetic characteristics of HGF have provided novel clues about the potential pathogenic mechanisms. In particular, mutation in the son-of-sevenless (SOS-1) gene has been associated with one form of the disease. However, HGF displays genetic heterogeneity, and mutations in other genes are also likely involved. This review outlines the current knowledge about the histological, cellular, and genetic characteristics of HGF. In addition, the potential role of the SOS-1 molecule and related novel intracellular signaling pathways in the pathogenesis of HGF will be discussed.

Effects of calcium ion-implantation of titanium on bone cell functionin vitro

The modification of titanium (Ti) surfaces by ion-implantation has previously been reported to enhance osseointegration in vivo. However, the mechanisms underlying the apparently improved biocompatibility of these novel implant materials are unknown. The aim of this study is, therefore, to determine the precise effects of calcium ion-implanted Ti on the functional activity of bone cells in vitro. Flow cytometry (FCM) and the reverse transcriptase polymerase chain reaction (RT-PCR) were used to measure the response of bone-derived cells to key bone-associated components, including alkaline phosphatase (ALP), bone morphogenetic protein receptor-1B (BMPR-1B), bone sialoprotein (BSP), osteonectin (ON), and osteopontin (OPN). FCM analysis showed that BMPR-1B, BSP and particularly OPN were significantly up-regulated in MG-63 cells cultured on Ca-implanted Ti compared with control nonimplanted Ti. Moreover, the effects of this novel Ca-Ti surface were found to be mediated, at least partly, via gene activation, since RT-PCR demonstrated the presence of notably elevated levels of OPN mRNA transcripts in the MG-63 cells. These findings thus show that Ti surfaces implanted with Ca ions can enhance the expression of certain bone-associated components in vitro, and suggest that this effect could be the cause of the potential benefit of this material on bone in vivo.

Calcium/calmodulin signaling controls osteoblast growth and differentiation

Ca2+ is a ubiquitous intracellular messenger responsible for controlling numerous cellular processes including fertilization, mitosis, neuronal transmission, contraction and relaxation of muscles, gene transcription, and cell death. At rest, the cytoplasmic Ca2+ concentration [Ca2+]i is approximately 100 nM, but this level rises to 500-1,000 nM upon activation. In osteoblasts, the elevation of [Ca2+]i is a result of an increase in the release of Ca2+ from endoplasmic reticulum and/or extracellular Ca2+ influx through voltage gated Ca2+ channels. Many of the cellular effects of Ca2+ are mediated by the Ca2+ binding protein, calmodulin (CaM). Upon binding up to four calcium ions, CaM undergoes a conformational change, which enables it to bind to specific proteins eliciting a specific response. Calmodulin kinase II (CaMKII) is a major target of the Ca(2+)/CaM second messenger system. Once bound to Ca(2+)/CaM, the multimeric CaMKII is released from its autoinhibitory status and maximally activated, which then leads to an intraholoenzyme autophosphorylation reaction. Calcineurin (Cn) is another major target protein that is activated by Ca(2+)/CaM. Cn is a serine-threonine phosphatase that consists of a heterodimeric protein complex composed of a catalytic subunit (CnA) and a regulatory subunit (CnB). Upon activation, Cn directly binds to, and dephosphorylates nuclear factor of activated T cells (NFAT) transcription factors within the cytoplasm allowing them to translocate to the nucleus and participate in the regulation of gene expression. This review will examine the potential mechanisms by which calcium, CaM, CaMKII, and Cn/NFAT control osteoblast proliferation and differentiation.

gamma-Sarcoglycan deficiency increases cell contractility, apoptosis and MAPK pathway activation but does not affect adhesion

The functions of gamma-sarcoglycan (gammaSG) in normal myotubes are largely unknown, however gammaSG is known to assemble into a key membrane complex with dystroglycan and its deficiency is one known cause of limb-girdle muscular dystrophy. Previous findings of apoptosis from gammaSG-deficient mice are extended here to cell culture where apoptosis is seen to increase more than tenfold in gammaSG-deficient myotubes compared with normal cells. The deficient myotubes also exhibit an increased contractile prestress that results in greater shortening and widening when the cells are either lightly detached or self-detached. However, micropipette-forced peeling of single myotubes revealed no significant difference in cell adhesion. Consistent with a more contractile phenotype, acto-myosin striations were more prominent in gammaSG-deficient myotubes than in normal cells. An initial phosphoscreen of more than 12 signaling proteins revealed a number of differences between normal and gammaSG(-/-) muscle, both before and after stretching. MAPK-pathway proteins displayed the largest changes in activation, although significant phosphorylation also appeared for other proteins linked to hypertension. We conclude that gammaSG normally moderates contractile prestress in skeletal muscle, and we propose a role for gammaSG in membrane-based signaling of the effects of prestress and sarcomerogenesis.

Gonadotropin releasing hormone analogue (GnRHa) alters the expression and activation of Smad in human endometrial epithelial and stromal cells

Gonadotropin releasing hormone analogues (GnRHa) are often used to regress endometriosis implants and prevent premature luteinizing hormone surges in women undergoing controlled ovarian stimulation. In addition to GnRH central action, the expression of GnRH and receptors in the endometrium implies an autocrine/paracrine role for GnRH and an additional site of action for GnRHa. To further examine the direct action of GnRH (Leuprolide acetate) in the endometrium, we determined the effect of GnRH on endometrial stromal (ESC) and endometrial surface epithelial (HES) cells expression and activation of Smads (Smad3, -4 and -7), intracellular signals activated by transforming growth factor beta (TGF-beta), a key cytokine expressed in the endometrium. The results show that GnRH (0.1 microM) increased the expression of inhibitory Smad7 mRNA in HES with a limited effect on ESC, while moderately increasing the common Smad4 and Smad7 protein levels in these cells (P < 0.05). GnRH in a dose--(0.01 to 10 microM) and time--(5 to 30 min) dependent manner decreased the rate of Smad3 activation (phospho-Smad3, pSmad3), and altered Smad3 cellular distribution in both cell types. Pretreatment with Antide (GnRH antagonist) resulted in further suppression of Smad3 induced by GnRH, with Antide inhibition of pSmad3 in ESC. Furthermore, co-treatment of the cells with GnRH + TGF-beta, or pretreatment with TGF-beta type II receptor antisense to block TGF-beta autocrine/paracrine action, in part inhibited TGF-beta activated Smad3. In conclusion, the results indicate that GnRH acts directly on the endometrial cells altering the expression and activation of Smads, a mechanism that could lead to interruption of TGF-beta receptor signaling mediated through this pathway in the endometrium.

Identification of novel protein-protein interactions using a versatile mammalian tandem affinity purification expression system

Identification of protein-protein interactions is essential for elucidating the biochemical mechanism of signal transduction. Purification and identification of individual proteins in mammalian cells have been difficult, however, due to the sheer complexity of protein mixtures obtained from cellular extracts. Recently, a tandem affinity purification (TAP) method has been developed as a tool that allows rapid purification of native protein complexes expressed at their natural level in engineered yeast cells. To adapt this method to mammalian cells, we have created a TAP tag retroviral expression vector to allow stable expression of the TAP-tagged protein at close to physiological levels. To demonstrate the utility of this vector, we have fused a TAP tag, consisting of a protein A tag, a cleavage site for the tobacco etch virus (TEV) protease, and the FLAG epitope, to the N terminus of human SMAD3 and SMAD4. We have stably expressed these proteins in mammalian cells at desirable levels by retroviral gene transfer and purified native SMAD3 protein complexes from cell lysates. The combination of two different affinity tags greatly reduced the number of nonspecific proteins in the mixture. We have identified HSP70 as a specific interacting protein of SMAD3. We demonstrated that SMAD3, but not SMAD1, binds HSP70 in vivo, validating the TAP purification approach. This method is applicable to virtually any protein and provides an efficient way to purify unknown proteins to homogeneity from the complex mixtures found in mammalian cell lysates in preparation for identification by mass spectrometry.

Evidence for antagonism of BMP-4 signals by MAP kinase during Xenopus axis determination and neural specification

We have previously shown that mitogen-activated protein (MAP) kinase activity is required for neural specification in Xenopus. In mammalian cells, the BMP-4 effector Smad1 is inhibited by phosphorylation at MAP kinase sites (Kretzschmar et al., 1997). To test the hypothesis that MAP kinase inhibits the BMP-4/Smad1 pathway during early Xenopus development, we have generated a Smad1 mutant lacking the MAP kinase phosphorylation sites (M4A-Smad1) and compared the effects of wild-type (WT)- and M4A-Smad1 on axial pattern and neural specification in Xenopus embryos. Although overexpression of either WT- or M4A-Smad1 produced ventralized embryos, at each mRNA concentration, M4A-Smad1 had a greater ventralizing effect than WT-Smad1. Interestingly, overexpression of either form of Smad1 in ventral blastomeres disrupted posterior pattern and morphogenesis; again, more severe defects were produced by expression of M4A-Smad1 than by equal amounts of WT-Smad1. Ectodermal expression of M4A-Smad1 disrupted expression of the anterior neural gene otx2 in vivo and inhibited neural specification in response to endogenous signals in mesoderm-ectoderm recombinates. In contrast, overexpression of WT-Smad1 at identical levels had little effect on either neural specification or otx2 expression. Comparisons of protein levels following overexpression of either WT- or M4A-Smad1 indicate that WT-Smad1 may be slightly more stable than M4A-Smad1; thus, differences in stability cannot account for the increased effectiveness of M4A-Smad1. Our results demonstrate that mutations disrupting the MAPK phosphorylation sites act collectively as a gain-of-function mutation in Smad1 and that inhibitory phosphorylation of Smad1 may be a significant mechanism for the regulation of BMP-4/Smad1 signals during Xenopus development.

New intracellular components of bone morphogenetic protein/Smad signaling cascades

Bone morphogenetic proteins (BMPs) regulate many processes in the embryo, including cell type specification, patterning, apoptosis, and epithelial-mesenchymal interaction. They also act in soft and hard tissues in adult life. Their signals are transduced from the plasma membrane to the nucleus through a limited number of Smad proteins. The list of Smad-interacting proteins is however growing and it is clear that these partners determine the outcome of the signal. We summarize the present status in BMP/Smad signaling, with emphasis on recently identified Smad partners and how these proteins may cooperate in the regulation of the expression of BMP target genes.

Two major Smad pathways in TGF-beta superfamily signalling

Members of the transforming growth factor-beta (TGF-beta) superfamily bind to two different serine/threonine kinase receptors, i.e. type I and type II receptors. Upon ligand binding, type I receptors specifically activate intracellular Smad proteins. R-Smads are direct substrates of type I receptors; Smads 2 and 3 are specifically activated by activin/nodal and TGF-beta type I receptors, whereas Smads 1, 5 and 8 are activated by BMP type I receptors. Nearly 30 proteins have been identified as members of the TGF-beta superfamily in mammals, and can be classified based on whether they activate activin/TGF-beta-specific R-Smads (AR-Smads) or BMP-specific R-Smads (BR-Smads). R-Smads form complexes with Co-Smads and translocate into the nucleus, where they regulate the transcription of target genes. AR-Smads bind to various proteins, including transcription factors and transcriptional co-activators or co-repressors, whereas BR-Smads interact with other proteins less efficiently than AR-Smads. Id proteins are induced by BR-Smads, and play important roles in exhibiting some biological effects of BMPs. Understanding the mechanisms of TGF-beta superfamily signalling is thus important for the development of new ways to treat various clinical diseases in which TGF-beta superfamily signalling is involved.

An allelic series of mutations in Smad2 and Smad4 identified in a genotype-based screen of N-ethyl-N- nitrosourea-mutagenized mouse embryonic stem cells

Using selectable genes as proof of principle, a new high-throughput genotype-based mutation screen in mouse embryonic stem (ES) cells was developed [Chen et al. (2002) Nat. Genet. 24, 314-317]. If expanded to nonselectable genes, this approach would allow one to proceed quickly from sequence to whole-animal phenotypes. Here data are presented showing that a screen of a cryopreserved library of clonal, germ line competent, N-ethyl-N-nitrosurea (ENU) mutagenized ES cells can identify a large series of allelic mutations in Smad2 and Smad4, two nonselectable genes of the transforming growth factor beta superfamily of signaling molecules. Whole animal phenotypic analyses of some of these alleles provided evidence for novel developmental processes mediated by these components of transforming growth factor beta signaling, demonstrating the utility of non-null alleles created by chemical mutagens. The accurately assessed mutation load of the ES cell library indicates that it is a valuable resource for developing mouse lines for genetic and functional studies. This methodology can conceptually be applied for the generation of an allelic series of subtle mutations at any locus of interest in the mouse.

Interleukin-4 regulates connective tissue growth factor expression in human lung fibroblasts

Transforming growth factor-beta (TGF-beta) and interleukin-4 (IL-4) have fibrogenic properties and induce extracellular matrix production in a variety of lung diseases. Connective tissue growth factor (CTGF) is a matrix signaling molecule stimulated by TGF-beta that in part mediates alpha1(I) collagen mRNA expression. In these studies, the regulation of CTGF expression by IL-4 in human lung fibroblasts was examined. Following 6 h of stimulation with IL-4, basal CTGF mRNA levels were unchanged as assessed by Northern blot analysis. However, IL-4 attenuated the TGF-beta-stimulated induction of CTGF mRNA expression by 50%. This effect was selective because IL-4 did not affect fibronectin or alpha1(I) collagen mRNA expression induced by TGF-beta. Experiments employing the transcriptional inhibitor actinomycin D suggest that IL-4 did not affect the stability of the CTGF mRNA. Transient transfection assays with 3TP-Lux, a luciferase gene controlled by a TGF-beta inducible promoter, and with a CTGF promoter construct indicate that IL-4 interfered with the TGF-beta-induced transcriptional activation of the CTGF gene.

Modulation of Smad2-mediated signaling by extracellular signal-regulated kinase

Components of the transforming growth factor-beta and mitogen-activated protein kinase pathways interact in controlling cell growth and differentiation. We show that phosphorylation of Smad2, a mediator of the activin/transforming growth factor-beta signal, by activated extracellular signal-regulated kinase 1 (ERK1) increases the amount of Smad2 protein and leads to enhanced transcriptional activity. Epidermal growth factor increased phosphorylation of Smad2 in COS7 cells, and Smad2-dependent transcription in a mink lung epithelial cell line, L17, was enhanced by co-transfection of a constitutively active MEK1. In addition, transfection of Smad2 mutants lacking ERK sites resulted in reduced transcription, whereas mutants that mimicked ERK phosphorylation stimulated transcription. The amount of Smad2 protein was increased by transfection with a constitutively active MEK1 and reduced by co-transfection with the ERK phosphatase, HVH2. The elevation of Smad2 protein levels was because of increased half-life and resulted in increased complex formation with Smad4. A site of ERK-dependent phosphorylation on Smad2 was located to Thr(8), a site that overlaps with the calmodulin binding region. We show that calmodulin inhibits Smad2 phosphorylation by ERK1, and overexpressing calmodulin, or stimulating calmodulin activity with ionomycin, reduces Smad2 levels. These findings suggest that the ERK pathway positively regulates Smad2 signaling by phosphorylating Smad2 and that negative regulation of Smad2 signaling by calmodulin is achieved in part by inhibiting this phosphorylation.

Activins, inhibins, and follistatins: from endocrinology to signaling. A paradigm for the new millennium

It has been 70 years since the name inhibin was used to describe a gonadal factor that negatively regulated pituitary hormone secretion. The majority of this period was required to achieve purification and definitive characterization of inhibin, an event closely followed by identification and characterization of activin and follistatin (FS). In contrast, the last 15-20 years saw a virtual explosion of information regarding the biochemistry, physiology, and biosynthesis of these proteins, as well as identification of activin receptors, and a unique mechanism for FS action-the nearly irreversible binding and neutralization of activin. Many of these discoveries have been previously summarized; therefore, this review will cover the period from the mid 1990s to present, with particular emphasis on emerging themes and recent advances. As the field has matured, recent efforts have focused more on human studies, so the endocrinology of inhibin, activin, and FS in the human is summarized first. Another area receiving significant recent attention is local actions of activin and its regulation by both FS and inhibin. Because activin and FS are produced in many tissues, we chose to focus on a few particular examples with the most extensive experimental support, the pituitary and the developing follicle, although nonreproductive actions of activin and FS are also discussed. At the cellular level, it now seems that activin acts largely as an autocrine and/or paracrine growth factor, similar to other members of the transforming growh factor beta superfamily. As we discuss in the next section, its actions are regulated extracellularly by both inhibin and FS. In the final section, intracellular mediators and modulators of activin signaling are reviewed in detail. Many of these are shared with other transforming growh factor beta superfamily members as well as unrelated molecules, and in a number of cases, their physiological relevance to activin signal propagation remains to be elucidated. Nevertheless, taken together, recent findings suggest that it may be more appropriate to consider a new paradigm for inhibin, activin, and FS in which activin signaling is regulated extracellularly by both inhibin and FS whereas a number of intracellular proteins act to modulate cellular responses to these activin signals. It is therefore the balance between activin and all of its modulators, rather than the actions of any one component, that determines the final biological outcome. As technology and model systems become more sophisticated in the next few years, it should become possible to test this concept directly to more clearly define the role of activin, inhibin, and FS in reproductive physiology.

Modulation of the Ras/Raf/MEK/ERK pathway by Ca(2+), and calmodulin

Ras activation induces a variety of cellular responses that depend on the specific activated effector, the intensity and amplitude of its activation, and the cellular type. Transient activation followed by a sustained but low signal of the Ras/Raf/MEK/ERK pathway is a common feature of cell proliferation in many systems. On the contrary, sustained, high activation is linked with either senescence or apoptosis in fibroblasts and to differentiation in neurones and PC12 cells. The temporal regulation of the pathway is relevant and not only depends on the specific receptor activated but also on the presence of diverse modulators of the pathway. We review here evidence showing that calcium (Ca(2+)) and calmodulin (CaM) are able to regulate the Ras/Raf/MEK/ERK pathway. CaM-binding proteins (CaMBPs) as Ras-GRF and CaM-dependent protein kinase IV (CaMKIV) positively modulate ERK1/2 activation induced by either NGF or membrane depolarisation in neurones. In fibroblasts, CaM binding to EGF receptor and K-Ras(B) may be involved in the downregulation of the pathway after its activation, allowing a proliferative signalling.

TGF-beta-induced Ca(2+) influx involves the type III IP(3) receptor and regulates actin cytoskeleton

Ca(2+) influx has been postulated to modulate the signaling pathway of transforming growth factor-beta (TGF-beta); however, the underlying mechanism and functional significance of TGF-beta-induced stimulation of Ca(2+) influx are unclear. We show here that TGF-beta stimulates Ca(2+) influx in mesangial cells without Ca(2+) release. The influx of Ca(2+) is prevented by pharmacological inhibitors of inositol 1,4,5-trisphosphate receptors (IP(3)R) as well as specific antibodies to type III IP(3)R (IP(3)RIII) but not to type I IP(3)R (IP(3)RI). TGF-beta enhances plasma membrane localization of IP(3)RIII, whereas the sarcoplasmic-endoplasmic reticulum Ca(2+)-ATPase (SERCA) preferentially translocates to the nucleus. Untreated mesangial cells exhibit actin filamentous protrusions on the cell surface, and treatment with TGF-beta dramatically reduces this pattern. The alterations in the actin cytoskeleton by TGF-beta are dependent on TGF-beta-induced Ca(2+) influx. These studies identify a novel pathway by which TGF-beta regulates Ca(2+) influx and induces cytoskeletal alterations.

Calmodulin-dependent protein kinase IV mediated antagonism of BMP signaling regulates lineage and survival of hematopoietic progenitors

In the current study, we show that bone morphogenetic proteins (BMPs) play a role in hematopoiesis that is independent of their function in specifying ventral mesodermal fate. When BMP activity is upregulated or inhibited in Xenopus embryos hematopoietic precursors are specified properly but few mature erythrocytes are generated. Distinct cellular defects underlie this loss of erythrocytes: inhibition of BMP activity induces erythroid precursors to undergo apoptotic cell death, whereas constitutive activation of BMPs causes an increase in commitment of hematopoietic progenitors to myeloid differentiation and a concomitant decrease in erythrocytes that is not due to enhanced apoptosis. These blood defects are observed even when BMP activity is misregulated solely in non-hematopoietic (ectodermal) cells, demonstrating that BMPs generate extrinsic signals that regulate hematopoiesis independent of mesodermal patterning. Further analysis revealed that endogenous calmodulin-dependent protein kinase IV (CaM KIV) is required to negatively modulate hematopoietic functions of BMPs downstream of receptor activation. Our data are consistent with a model in which CaM KIV inhibits BMP signals by activating a substrate, possibly cAMP-response element-binding protein (CREB), that recruits limiting amounts of CREB binding protein (CBP) away from transcriptional complexes functioning downstream of BMPs.

Regulation of cell proliferation, apoptosis, and carcinogenesis by activin

The aim of this review is to provide insight into the molecular mechanisms by which activin A modulates cell proliferation, apoptosis, and carcinogenesis in vitro and in vivo. Activin A, a member of the TGFbeta superfamily, has various effects on diverse biological systems, including cell growth inhibition in many cell types. However, the mechanism(s) by which activin exerts its inhibitory effects are not yet understood. This review highlights activin's effects on activin receptors and signaling pathway, modulation of activin signaling, and regulation of cell proliferation and apoptosis by activin. Based on the experiences of all the authors, we emphasized cell cycle inhibitors such as p16 and p21 and regulators of apoptosis such as p53 and members of the bcl-2 family. Aside from activin's inhibition of cell proliferation and enhancement of apoptosis, other newly developed methods for molecular studies of apoptosis by activin were briefly presented that support the role of activin as an inhibitor of carcinogenesis and cancer progression. These methods include subtractive hybridization based on covalent bonding, a simple and accurate means to determine molecular profile of as few as 20 cells based on an RNA-PCR approach, and a messenger RNA-antisense DNA interference phenomenon (D-RNAi), resulting in a long-term gene knockout effects.

The TGF-beta--Smad network: introducing bioinformatic tools

The TGF-beta superfamily is an important class of intercellular signalling molecule, including TGF-beta and bone morphogenetic proteins. Intracellular signalling cascades triggered by these molecules eventually activate transcription factors of the Smad family, which then regulate expression of their respective target genes. This article will discuss the TGF-beta--Smad signalling networks and how these processes are represented in databases of signal transduction and transcription control mechanisms. These databases can provide a well-structured overview of the subject and a basis for advanced bioinformatics analyses to interpret the function of genomic sequences or to analyse signalling networks.

Intracellular BMP signaling regulation in vertebrates: pathway or network?

Bone morphogenetic proteins (BMPs), members of the TGF-beta superfamily of secreted signaling molecules, have important functions in many biological contexts. They bind to specific serine/threonine kinase receptors, which transduce the signal to the nucleus through Smad proteins. The question of how BMPs can have such diverse effects while using the same canonical Smad pathway has recently come closer to an answer at the molecular level. Nuclear cofactors have been identified that cooperate with the Smads in regulating specific target genes depending on the cellular context. In addition, the pivotal role BMP signaling plays is underscored by the identification of factors that regulate members of this pathway at the cell surface, in the cytoplasm, and in the nucleus. Many of these factors are BMP-inducible and inhibit the BMP pathway, thus establishing negative feedback loops. Members of the BMP-Smad pathway can also physically interact with components of other signaling pathways to establish crosstalk. Finally, there is accumulating evidence that an alternative pathway involving MAP kinases can transduce BMP signals. The evidence and implications of these findings are discussed with an emphasis on early embryonic development of Xenopus and vertebrates.

Divergence and convergence of TGF-beta/BMP signaling

The transforming growth factor-beta (TGF-beta) superfamily includes more than 30 members which have a broad array of biological activities. TGF-beta superfamily ligands bind to type II and type I serine/threonine kinase receptors and transduce signals via Smad proteins. Receptor-regulated Smads (R-Smads) can be classified into two subclasses, i.e. those activated by activin and TGF-beta signaling pathways (AR-Smads), and those activated by bone morphogenetic protein (BMP) pathways (BR-Smads). The numbers of type II and type I receptors and Smad proteins are limited. Thus, signaling of the TGF-beta superfamily converges at the receptor and Smad levels. In the intracellular signaling pathways, Smads interact with various partner proteins and thereby exhibit a wide variety of biological activities. Moreover, signaling by Smads is modulated by various other signaling pathways allowing TGF-beta superfamily ligands to elicit diverse effects on target cells. Perturbations of the TGF-beta/BMP signaling pathways result in various clinical disorders including cancers, vascular diseases, and bone disorders.

Gene expression patterns in the lungs of patients with primary pulmonary hypertension: a gene microarray analysis

Primary pulmonary hypertension (PPH) is a disease of unknown etiology characterized by lumen-obliterating endothelial cell proliferation and vascular smooth muscle hypertrophy of the small precapillary pulmonary arteries. Because the vascular lesions are homogeneously distributed throughout the entire lung, we propose that a tissue fragment of the lung is representative of the whole lung. RNA extracted from the fragments is likely to provide meaningful information regarding the changes in gene expression pattern in PPH when compared with structurally normal lung tissue. We hypothesize that the lung tissue gene expression pattern of patients with PPH has a characteristic profile when compared with the gene expression pattern of structurally normal lungs and that this characteristic gene expression profile provides new insights into the pathobiology of PPH. Using oligonucleotide microarray technology, we characterized the expression pattern in the lung tissue obtained from 6 patients with primary pulmonary hypertension (PPH)-including 2 patients with the familial form of PPH (FPPH)-and from 6 patients with histologically normal lungs. For the data analysis, gene clusters were generated and the gene expression pattern differences between PPH and normal lung tissue and between PPH and FPPH lung tissue were compared. All PPH lung tissue samples showed a decreased expression of genes encoding several kinases and phosphatases, whereas several oncogenes and genes coding for ion channel proteins were upregulated in their expression. Importantly, we could distinguish by pattern comparison between sporadic PPH and FPPH, because alterations in the expression of transforming growth factor-beta receptor III, bone morphogenic protein 2, mitogen-activated protein kinase kinase 5, RACK 1, apolipoprotein C-III, and the gene encoding the laminin receptor 1 were only found in the samples from patients with sporadic PPH, but not in FPPH samples. We conclude that the microarray gene expression technique is a new and useful molecular tool that provides novel information pertinent to a better characterization and understanding of the pathobiology of the distinct clinical phenotypes of pulmonary hypertension.