Transforming growth factor-beta 1 induces apoptosis independently of p53 and selectively reduces expression of Bcl-2 in multipotent hematopoietic cells

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Roles of TGF-β in cancer hallmarks and emerging onco-therapeutic design

Transforming growth factor-beta (TGF-β) is a double-edged sword in cancer treatment because of its pivotal yet complex and roles played during cancer initiation/development. Current anti-cancer strategies involving TGF-β largely view TGF-β as an onco-therapeutic target that not only substantially hinders its full utilisation for cancer control, but also considerably restricts innovations in this field. Thereby, how to take advantages of therapeutically favourable properties of TGF-β for cancer management represents an interesting and less investigated problem. Here, by categorising cancer hallmarks into four critical transition events and one enabling characteristic controlling cancer initiation and progression, and delineating TGF-β complexities according to these cancer traits, we identify the suppressive role of TGF-β in tumour initiation and early-stage progression and its promotive functionalities in cancer metastasis as well as other cancer hallmarks. We also propose the feasibility and possible scenarios of combining cold atmospheric plasma (CAP) with onco-therapeutics utilising TGF-β for cancer control given the intrinsic properties of CAP against cancer hallmarks.

Transcriptional signatures of the BCL2 family for individualized acute myeloid leukaemia treatment

Background

Although anti-apoptotic proteins of the B-cell lymphoma-2 (BCL2) family have been utilized as therapeutic targets in acute myeloid leukaemia (AML), their complicated regulatory networks make individualized therapy difficult. This study aimed to discover the transcriptional signatures of BCL2 family genes that reflect regulatory dynamics, which can guide individualized therapeutic strategies.

Methods

From three AML RNA-seq cohorts (BeatAML, LeuceGene, and TCGA; n = 451, 437, and 179, respectively), we constructed the BCL2 family signatures (BFSigs) by applying an innovative gene-set selection method reflecting biological knowledge followed by non-negative matrix factorization (NMF). To demonstrate the significance of the BFSigs, we conducted modelling to predict response to BCL2 family inhibitors, clustering, and functional enrichment analysis. Cross-platform validity of BFSigs was also confirmed using NanoString technology in a separate cohort of 47 patients.

Results

We established BFSigs labeled as the BCL2, MCL1/BCL2, and BFL1/MCL1 signatures that identify key anti-apoptotic proteins. Unsupervised clustering based on BFSig information consistently classified AML patients into three robust subtypes across different AML cohorts, implying the existence of biological entities revealed by the BFSig approach. Interestingly, each subtype has distinct enrichment patterns of major cancer pathways, including MAPK and mTORC1, which propose subtype-specific combination treatment with apoptosis modulating drugs. The BFSig-based classifier also predicted response to venetoclax with remarkable performance (area under the ROC curve, AUROC = 0.874), which was well-validated in an independent cohort (AUROC = 0.950). Lastly, we successfully confirmed the validity of BFSigs using NanoString technology.

Conclusions

This study proposes BFSigs as a biomarker for the effective selection of apoptosis targeting treatments and cancer pathways to co-target in AML.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-022-01115-w.

Determining the function of LvSmad3 on Litopenaeus vannamei in response to acute low temperature stress

Smad3 is a key mediator of the canonical TGF-β signaling pathway and plays an important role in TGF-β1-mediated transcriptional regulation. However, the function of Smad3 in crustaceans such as shrimp, is still poorly understood and needs to be further explored. We characterized Litopenaeus vannamei Smad3 (LvSmad3) and its biological functions were investigated in response low temperature stress. Full-length LvSmad3 cDNA was 2341bp and contained an open reading frame (ORF) of 1326 bp that encoded a 441 amino acid long protein, with a predicted molecular mass of 48.35 kDa. Phylogenetic analysis revealed that LvSmad3 has a high degree of similarity with other known species. LvSmad3 mRNA was detected in all the tested tissues and highest transcription occurred mostly in gills. Further research showed that suppressing the expression of Smad3 could reduce ROS production, DNA damage and the apoptosis rate in shrimp hemocyte under low temperature compared with the dsGFP group. Thus, we speculated that Smad3 could promote the apoptosis of hemocytes. We confirmed that Smad3 could inhibit apoptosis in the hepatopancreas by suppressing the expression of pro-apoptotic genes. Taken together, the silencing of Smad3 can reduce ROS production induced by low temperature stress, weaken the damage to hemocytes and the hepatopancreas by inhibit the apoptosis.

The Role of TGF-β Signaling Pathways in Cancer and Its Potential as a Therapeutic Target

The transforming growth factor-β (TGF-β) signaling pathway mediates various biological functions, and its dysregulation is closely related to the occurrence of malignant tumors. However, the role of TGF-β signaling in tumorigenesis and development is complex and contradictory. On the one hand, TGF-β signaling can exert antitumor effects by inhibiting proliferation or inducing apoptosis of cancer cells. On the other hand, TGF-β signaling may mediate oncogene effects by promoting metastasis, angiogenesis, and immune escape. This review summarizes the recent findings on molecular mechanisms of TGF-β signaling. Specifically, this review evaluates TGF-β's therapeutic potential as a target by the following perspectives: ligands, receptors, and downstream signaling. We hope this review can trigger new ideas to improve the current clinical strategies to treat tumors related to the TGF-β signaling pathway.

Role of Cell Death in Cellular Processes During Odontogenesis

The development of a tooth germ in a precise size, shape, and position in the jaw, involves meticulous regulation of cell proliferation and cell death. Apoptosis, as the most common type of programmed cell death during embryonic development, plays a number of key roles during odontogenesis, ranging from the budding of the oral epithelium during tooth initiation, to later tooth germ morphogenesis and removal of enamel knot signaling center. Here, we summarize recent knowledge about the distribution and function of apoptotic cells during odontogenesis in several vertebrate lineages, with a special focus on amniotes (mammals and reptiles). We discuss the regulatory roles that apoptosis plays on various cellular processes during odontogenesis. We also review apoptosis-associated molecular signaling during tooth development, including its relationship with the autophagic pathway. Lastly, we cover apoptotic pathway disruption, and alterations in apoptotic cell distribution in transgenic mouse models. These studies foster a deeper understanding how apoptotic cells affect cellular processes during normal odontogenesis, and how they contribute to dental disorders, which could lead to new avenues of treatment in the future.

Anti-pyroptotic function of TGF-β is suppressed by a synthetic dsRNA analogue in triple negative breast cancer cells

Development of innovative therapeutic modalities would address an unmet clinical need in the treatment of triple negative breast cancer (TNBC). Activation of retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) such as melanoma differentiation-associated gene 5 (MDA5) and RIG-I in cancer cells is suggested to suppress tumor progression by inducing cell death. Transfection of polyI:C, a conventionally used synthetic double-stranded RNA (dsRNA) analogue that activates RLRs, has been evaluated in clinical trials. However, detailed mechanisms of tumor suppression by RLRs, especially interactions with other signaling pathways, remain elusive. Here, we showed that transfection of polyI:C suppressed transforming growth factor-β (TGF-β) signaling in a MDA5- and RIG-I-dependent manner. We found that suppression of TGF-β signaling by polyI:C promoted cancer cell death, which was attenuated by forced expression of constitutively active Smad3. More detailed analysis suggested that cell death by polyI:C transfection exhibited characteristics of pyroptosis, which is distinct from apoptosis. Therapeutic efficacy of polyI:C transfection was also demonstrated using a mouse model. These results indicated that intratumor administration of polyI:C and related dsRNA analogues may be promising treatments for TNBC through inhibition of the anti-pyroptotic function of TGF-β.

Ilomastat contributes to the survival of mouse after irradiation via promoting the recovery of hematopoietic system

Ilomastat, a broad-spectrum inhibitor of matrix metalloproteinases (MMPs), has drawn attentions for its function in alleviating radiation damage. However, the detailed mechanisms of Ilomastat’s protection from animal model remain not fully clear. In this study, the C57BL/6 mice were pre-administrated with Ilomastat or vihicle for 2 h, and then total body of mice were exposed to 6 Gy of γ-rays. The protective effect of Ilomastat on the hematopoietic system in the irradiated mice were investigated. We found that pretreatment with Ilomastat significantly reduced the level of TGF-β1 and TNF-α, and elevated the number of bone marrow (BM) mononuclear cells in the irradiated mice. Ilomastat pretreatment also increased the fraction of BM hematopoietic progenitor cells (HPCs) and hematopoietic stem cells (HSCs) at day 30 after irradiation, and protected the spleen of mouse from irradiation. These results suggest that Ilomastat promotes the recovery of hematopoietic injury in the irradiated mice, and thus contributes to the survival of mouse after irradiation.

E3 Ubiquitin Ligases: Key Regulators of TGFβ Signaling in Cancer Progression

Transforming growth factor β (TGFβ) is a secreted growth and differentiation factor that influences vital cellular processes like proliferation, adhesion, motility, and apoptosis. Regulation of the TGFβ signaling pathway is of key importance to maintain tissue homeostasis. Perturbation of this signaling pathway has been implicated in a plethora of diseases, including cancer. The effect of TGFβ is dependent on cellular context, and TGFβ can perform both anti- and pro-oncogenic roles. TGFβ acts by binding to specific cell surface TGFβ type I and type II transmembrane receptors that are endowed with serine/threonine kinase activity. Upon ligand-induced receptor phosphorylation, SMAD proteins and other intracellular effectors become activated and mediate biological responses. The levels, localization, and function of TGFβ signaling mediators, regulators, and effectors are highly dynamic and regulated by a myriad of post-translational modifications. One such crucial modification is ubiquitination. The ubiquitin modification is also a mechanism by which crosstalk with other signaling pathways is achieved. Crucial effector components of the ubiquitination cascade include the very diverse family of E3 ubiquitin ligases. This review summarizes the diverse roles of E3 ligases that act on TGFβ receptor and intracellular signaling components. E3 ligases regulate TGFβ signaling both positively and negatively by regulating degradation of receptors and various signaling intermediates. We also highlight the function of E3 ligases in connection with TGFβ's dual role during tumorigenesis. We conclude with a perspective on the emerging possibility of defining E3 ligases as drug targets and how they may be used to selectively target TGFβ-induced pro-oncogenic responses.

TGF-β1 fucosylation enhances the autophagy and mitophagy via PI3K/Akt and Ras-Raf-MEK-ERK in ovarian carcinoma

Transforming growth factor-β, a cell secretion factor of the TGF-β superfamily, is involved in the regulation of cell proliferation, differentiation, cytoskeleton formation, migration, invasion and other biological behaviors. Autophagy and mitophagy play an important role in tumor progression by regulating self-digestion, and degradation and reuse of cells and mitochondria. In this study, changes in autophagy and mitophagy processes in ovarian cancer cells under TGF-β1 treatment were detected via Western blot and immunofluorescence, as well as the role of fucosylation modification. Changes in mitochondrial membrane potential in response to TGF-β1 and fucosylation were detected via immunofluorescence. The effects of TGF-β1 and its fucosylation on autophagic flux were further determined by transient transfection of cells with Ad-mRFP-GFP-LC3 adenovirus. TGF-β1 clearly promoted autophagy and mitophagy in ovarian cancer cells. TGF-β1 fucosylation stimulated these regulatory effects on ovarian cancer cells via modulation of PI3K/Akt and Ras-Raf-MEK-ERK pathways through TAK1. Our collective data support the physiological significance of TGF-β1 and provide a novel direction for targeted therapy for ovarian cancer.

Effect of Genistein in Comparison with Trichostatin A on Reactivation of DNMTs Genes in Hepatocellular Carcinoma

Background and Aims: DNA methylation and histone modification are epigenetic modifications essential for normal function of mammalian cells. The processes are mediated by biochemical interactions between DNA methyltransferases (DNMTs) and histone deacetylases. Promoter hypermethylation and deacetylation of tumor suppressor genes play major roles in cancer induction, through transcriptional silencing of these genes. DNA hypermethylation is carried out by a family of DNMTs including DNMT1, DNMT3a and DNMT3b. In hepatocellular carcinoma, a significant positive correlation between over-expression of these genes and cancer induction has been reported. The DNA demethylating agent genistein (GE) has been demonstrated to reduce different cancers. Previously, we reported that GE can induce apoptosis and inhibit proliferation in hepatocellular carcinoma PLC/PRF5 and HepG2 cell lines. Besides, histone deacetylase inhibitors, such as trichostatin A (TSA), were successfully used to inhibit cancer cell growth. The present study was designed to assess the effect of GE in comparison with TSA on DNMT1, DNMT3a and DNMT3b gene expression, cell growth inhibition and apoptosis induction in the HepG2 cell line. Methods: Cells were seeded and treated with various doses of GE and TSA. The MTT assay, flow cytometry assay, and real-time RT-PCR were used to determine viability, apoptosis, and DNMT1, DNMT3a and DNMT3b gene expression respectively. Results: Both agents inhibited cell growth, induced apoptosis and reactivated DNMT1, DNMT3a and DNMT3b gene expression. Furthermore, TSA demonstrated a significantly greater apoptotic effect than the other agent, whereas GE improved gene expression more significantly than TSA. Conclusions: Our findings suggest that GE and TSA can significantly inhibit cell growth, induce apoptosis and restore DNMT1, DNMT3a and DNMT3b gene reactivation.

Dichotomous roles of TGF-β in human cancer

Transforming growth factor-β (TGF-β) mediates numerous biological processes, including embryonic development and the maintenance of cellular homeostasis in a context-dependent manner. Consistent with its central role in maintaining cellular homeostasis, inhibition of TGF-β signaling results in disruption of normal homeostatic processes and subsequent carcinogenesis, defining the TGF-β signaling pathway as a tumor suppressor. However, once carcinogenesis is initiated, the TGF-β signaling pathway promotes cancer progression. This dichotomous function of the TGF-β signaling pathway is mediated through altering effects on both the cancer cells, by inducing apoptosis and inhibiting proliferation, and the tumor microenvironment, by promoting angiogenesis and inhibiting immunosurveillance. Current studies support inhibition of TGF-β signaling either alone, or in conjunction with anti-angiogenic therapy or immunotherapy as a promising strategy for the treatment of human cancers.

C-phycocyanin suppresses transforming growth factor-β1-induced epithelial mesenchymal transition in human epithelial cells

BACKGROUND

Epithelial mesenchymal transition (EMT) is a process through which epithelial cells undergo multiple biochemical changes, causing them to differentiate into a mesenchymal-cell phenotype. This process has been shown to contribute to the development of fibrotic diseases. C-phycocyanin (C-PC) is a phycobiliprotein extracted from Spirulina platensis. This study was done to investigate the effect of C-PC on transforming growth factor-β1 (TGF-β1)-induced EMT and an EMT associated proliferation in human epithelial cell lines.

METHODS

Human adenocarcinoma cell line, A549 and breast cancer cell line, MCF-7 were treated with TGF-β1, and EMT-related genes expression, cell proliferation and cell cycle arrest were examined.

RESULTS

C-PC suppressed the EMT as assessed by reduced expression of vimentin, type-1-collagen and fibronectin, and increased E-cadherin expression in TGF-β1 treated cells. Further, TGF-β1 treatment induced cell cycle arrest in S and G2/M phase in A549 cells. However, TGF-β1-mediated cell cycle arrest was significantly reversed by combined treatment with C-PC.

CONCLUSIONS

The overall data suggested that C-PC suppresses TGF- β1-induced EMT and warrants further in vivo studies for future evaluation of C-PC as a potential antifibrotic agent.

Neuropilin-1 Is an Important Niche Component and Exerts Context-Dependent Effects on Hematopoietic Stem Cells

Marrow adipocytes pose a significant problem in post-transplant regeneration of hematopoiesis owing to their negative effects on regeneration of hematopoiesis. However, the precise mechanism operative in this negative regulation is not clear. In this study, we show that marrow adipocytes express neuropilin-1 (NRP1) as a function of differentiation and inhibit regeneration of hematopoiesis by three principal mechanisms: one, by inducing apoptosis in hematopoietic stem/progenitor cells (HSPCs) through the death receptor-mediated pathway; two, by downregulating CXCR4 expression on the HSPCs through ligand-mediated internalization; and three, by secreting copious amounts of transforming growth factor β1 (TGFβ1), a known inhibitor of hematopoiesis. Silencing of NRP1 in these adipocytes rescued the apoptosis of cocultured HSPCs and boosted the CXCR4 surface expression on them, showing an active role of NRP1 in these processes. However, such silencing had no effect on TGFβ1 secretion and consequent inhibition of hematopoiesis by them, showing that secretion of TGFβ1 by adipocytes is independent of NRP1 expression by them. Surprisingly, mesenchymal stromal cells modified with NRP1 supported expansion of HSPCs having enhanced functionality, suggesting that NRP1 exerts a context-dependent effect on hematopoiesis. Our data demonstrate that NRP1 is an important niche component and exerts context-dependent effects on HSPCs. Based on these data, we speculate that antibody- or peptide-mediated blocking of NRP1-HSC interactions coupled with a pharmacological inhibition of TGFβ1 signaling may help in combating the negative regulation of post-transplant regeneration of hematopoiesis in a more effective manner.

Smad4 controls bone homeostasis through regulation of osteoblast/osteocyte viability

Regulation of osteoblast and osteocyte viability is essential for bone homeostasis. Smad4, a major transducer of bone morphogenetic protein and transforming growth factor-β signaling pathways, regulates apoptosis in various cell types through a mitochondrial pathway. However, it remains poorly understood whether Smad4 is necessary for the regulation of osteoblast and osteocyte viability. In this study, we analyzed Smad4Δ(Os) mice, in which Smad4 was subjected to tissue-specific disruption under the control of the 2.3-kb Col1a1 promoter, to understand the functional significance of Smad4 in regulating osteoblast/osteocyte viability during bone formation and remodeling. Smad4Δ(Os) mice showed a significant increase in osteoblast number and osteocyte density in the trabecular and cortical regions of the femur, whereas osteoclast activity was significantly decreased. The proliferation of osteoblasts/osteocytes did not alter, as shown by measuring 5'-bromo-2'deoxyuridine incorporation. By contrast, the percentage of TUNEL-positive cells decreased, together with a decrease in the Bax/Bcl-2 ratio and in the proteolytic cleavage of caspase 3, in Smad4Δ(Os) mice. Apoptosis in isolated calvaria cells from Smad4Δ(Os) mice decreased after differentiation, which was consistent with the results of the TUNEL assay and western blotting in Smad4Δ(Os) mice. Conversely, osteoblast cells overexpressing Smad4 showed increased apoptosis. In an apoptosis induction model of Smad4Δ(Os) mice, osteoblasts/osteocytes were more resistant to apoptosis than were control cells, and, consequently, bone remodeling was attenuated. These findings indicate that Smad4 has a significant role in regulating osteoblast/osteocyte viability and therefore controls bone homeostasis.

TGRL Lipolysis Products Induce Stress Protein ATF3 via the TGF-β Receptor Pathway in Human Aortic Endothelial Cells

Studies have suggested a link between the transforming growth factor beta 1 (TGF-β1) signaling cascade and the stress-inducible activating transcription factor 3 (ATF3). We have demonstrated that triglyceride-rich lipoproteins (TGRL) lipolysis products activate MAP kinase stress associated JNK/c-Jun pathways resulting in up-regulation of ATF3, pro-inflammatory genes and induction of apoptosis in human aortic endothelial cells. Here we demonstrate increased release of active TGF-β at 15 min, phosphorylation of Smad2 and translocation of co-Smad4 from cytosol to nucleus after a 1.5 h treatment with lipolysis products. Activation and translocation of Smad2 and 4 was blocked by addition of SB431542 (10 μM), a specific inhibitor of TGF-β-activin receptor ALKs 4, 5, 7. Both ALK receptor inhibition and anti TGF-β1 antibody prevented lipolysis product induced up-regulation of ATF3 mRNA and protein. ALK inhibition prevented lipolysis product-induced nuclear accumulation of ATF3. ALKs 4, 5, 7 inhibition also prevented phosphorylation of c-Jun and TGRL lipolysis product-induced p53 and caspase-3 protein expression. These findings demonstrate that TGRL lipolysis products cause release of active TGF-β and lipolysis product-induced apoptosis is dependent on TGF-β signaling. Furthermore, signaling through the stress associated JNK/c-Jun pathway is dependent on TGF-β signaling suggesting that TGF-β signaling is necessary for nuclear accumulation of the ATF3/cJun transcription complex and induction of pro-inflammatory responses.

The Retinoblastoma Tumor Suppressor Protein (pRb)/E2 Promoter Binding Factor 1 (E2F1) Pathway as a Novel Mediator of TGFβ-induced Autophagy

TGFβ is a multifunctional cytokine that regulates cell proliferation, cell immortalization, and cell death, acting as a key homeostatic mediator in various cell types and tissues. Autophagy is a programmed mechanism that plays a pivotal role in controlling cell fate and, consequently, many physiological and pathological processes, including carcinogenesis. Although autophagy is often considered a pro-survival mechanism that renders cells viable in stressful conditions and thus might promote tumor growth, emerging evidence suggests that autophagy is also a tumor suppressor pathway. The relationship between TGFβ signaling and autophagy is context-dependent and remains unclear. TGFβ-mediated activation of autophagy has recently been suggested to contribute to the growth inhibitory effect of TGFβ in hepatocarcinoma cells. In the present study, we define a novel process of TGFβ-mediated autophagy in cancer cell lines of various origins. We found that autophagosome initiation and maturation by TGFβ is dependent on the retinoblastoma tumor suppressor protein/E2 promoter binding factor (pRb/E2F1) pathway, which we have previously established as a critical signaling axis leading to various TGFβ tumor suppressive effects. We further determined that TGFβ induces pRb/E2F1-dependent transcriptional activation of several autophagy-related genes. Together, our findings reveal that TGFβ induces autophagy through the pRb/E2F1 pathway and transcriptional activation of autophagy-related genes and further highlight the central relevance of the pRb/E2F1 pathway downstream of TGFβ signaling in tumor suppression.

TGF-β cascade regulation by PPP1 and its interactors -impact on prostate cancer development and therapy

Protein phosphorylation is a key mechanism by which normal and cancer cells regulate their main transduction pathways. Protein kinases and phosphatases are precisely orchestrated to achieve the (de)phosphorylation of candidate proteins. Indeed, cellular health is dependent on the fine-tune of phosphorylation systems, which when deregulated lead to cancer. Transforming growth factor beta (TGF-β) pathway involvement in the genesis of prostate cancer has long been established. Many of its members were shown to be hypo- or hyperphosphorylated during the process of malignancy. A major phosphatase that is responsible for the vast majority of the serine/threonine dephosphorylation is the phosphoprotein phosphatase 1 (PPP1). PPP1 has been associated with the dephosphorylation of several proteins involved in the TGF-β cascade. This review will discuss the role of PPP1 in the regulation of several TGF-β signalling members and how the subversion of this pathway is related to prostate cancer development. Furthermore, current challenges on the protein phosphatases field as new targets to cancer therapy will be addressed.

The Dual Role of TGFβ in Human Cancer: From Tumor Suppression to Cancer Metastasis

The transforming growth factor-beta (TGFβ) superfamily encompasses widespread and evolutionarily conserved polypeptide growth factors that regulate and orchestrate growth and differentiation in all cell types and tissues. While they regulate asymmetric cell division and cell fate determination during early development and embryogenesis, TGFβ family members play a major regulatory role in hormonal and immune responses, cell growth, cell death and cell immortalization, bone formation, tissue remodeling and repair, and erythropoiesis throughout adult life. The biological and physiological functions of TGFβ, the founding member of this family, and its receptors are of central importance to human diseases, particularly cancer. By regulating cell growth, death, and immortalization, TGFβ signaling pathways exert tumor suppressor effects in normal cells and early carcinomas. Thus, it is not surprising that a high number of human tumors arise due to mutations or deletions in the genes coding for the various TGFβ signaling components. As tumors develop and progress, these protective and cytostatic effects of TGFβ are often lost. TGFβ signaling then switches to promote cancer progression, invasion, and tumor metastasis. The molecular mechanisms underlying this dual role of TGFβ in human cancer will be discussed in depth in this paper, and it will highlight the challenge and importance of developing novel therapeutic strategies specifically aimed at blocking the prometastatic arm of the TGFβ signaling pathway without affecting its tumor suppressive effects.

TGFβ receptor activation enhances cardiac apoptosis via SMAD activation and concomitant NO release

Transforming growth factor β (TGFβ) expression is induced in the myocardium during transition from compensated hypertrophy to heart failure. In cardiomyocytes, stimulation with TGFβ results in restricted contractile function and enhanced apoptosis. Nitric oxide (NO) also induces apoptosis and influences cardiac function. Therefore, we wanted to know whether NO is causally involved in TGFβ-induced apoptosis. In isolated ventricular cardiomyocytes of adult rat incubation with TGFβ(1) increased NO release which was inhibited by NOS inhibitor ETU but not with iNOS inhibitor (1400 W) or nNOS inhibitor (TFA). In addition, TGFβ-induced apoptosis was blocked with ETU and ODQ, but not with 1400 W or TFA. The consequent assumption that endothelial NOS is involved in TGFβ-induced NO formation and apoptosis was supported by increased phosphorylation of eNOS at serine 1177 and by the fact that TGFβ did not increase NO release in eNOS KO mice. Furthermore, TGFβ-induced apoptosis, NO formation, SMAD binding activity and SMAD2 phosphorylation were blocked by a TGFβ receptor antagonist, but only apoptosis and NO formation could be blocked with ETU. Expression of SMAD7 was increased after TGFβ stimulation and blocked with TGFβ receptor antagonist but not after blocking NO synthase with ETU.

CONCLUSION

In cardiomyocytes TGFβ-induced apoptosis is mediated via TGFβ receptor activation that concomitantly activates SMAD transcription factors and the eNOS/NO/sGC pathway. Both of these pathways are needed for apoptosis induction by TGFβ. This reveals a new pathway of cardiac NO release and identifies NO as a possible contributor to heart failure progression mediated by TGFβ.

Transforming growth factor-beta1 expression is up-regulated in maturation-stage enamel organ and may induce ameloblast apoptosis

Transforming growth factor-beta1 (TGF-beta1) regulates a variety of cellular responses that are dependent on the developmental stage and on the origins of the cell or the tissue. In mature tissues, and especially in tissues of epithelial origin, TGF-beta1 is generally considered to be a growth inhibitor that may also promote apoptosis. The ameloblast cells of the enamel organ epithelium are adjacent to and responsible for the developing enamel layer on unerupted teeth. Once the enamel layer reaches its full thickness, the tall columnar secretory-stage ameloblasts shorten, and a portion of these maturation-stage ameloblasts become apoptotic. Here we investigate whether TGF-beta1 plays a role in apoptosis of the maturation-stage ameloblasts. We demonstrate in vitro that ameloblast lineage cells are highly susceptible to TGF-beta1-mediated growth arrest and are prone to TGF-beta1-mediated cell death/apoptosis. We also demonstrate in vivo that TGF-beta1 is expressed in the maturation-stage enamel organ at significantly higher levels than in the earlier secretory-stage enamel organ. This increased expression of TGF-beta1 correlates with an increase in expression of the enamel organ immediate-early stress-response gene and with a decrease in the anti-apoptotic Bcl2 : Bax expression ratio. We conclude that TGF-beta1 may play an important role in ameloblast apoptosis during the maturation stage of enamel development.

Hematopoietic effect of fractions from the enzyme-digested colla corii asini on mice with 5-fluorouracil induced anemia

Effects of fractions A and B from enzyme-digested traditional Chinese medicine colla corii asini on mice with 5-fluorouracil-induced anemia were investigated. The purpose of this study was to further understand the hematopoietic activities and mechanisms of colla corii asini. The fractions A and B were administered to anemic mice for 12 days. After confirming the anti-anemic effect of fractions A and B, we examined the effects of fractions A and B on immature granulocyte and erythroid cell activity and plasma cytokine level. Fraction A administration at 2 g/kg and 1 g/kg and fraction B administration at 1.6 g/kg and 0.8 g/kg activated granulocyte and erythrocyte progenitor cells in bone marrow and erythrocyte progenitors in spleen, led to the recovery of white blood cell and red blood cell counts, and increased the percentage of peripheral reticulocytes in red cells. The GM-CSF and EPO production determined by examining GM-CSF mRNA and EPO mRNA in the kidney and liver of the anemic mice were also enhanced. This treatment significantly increased serum GM-CSF and EPO level and lowered serum transforming growth factor (TGF-beta) level. These results suggested that fractions A and B promoted hematopoiesis by activating immature granulocyte and erythroid cells, partly by stimulating GM-CSF and EPO secretion and suppressing TGF-beta release. Identification of a specific peptide or protein is still required for the development of a novel medicine for anemia caused by malignancy or chemotherapy.

TGF-beta signaling: a tale of two responses

Transforming growth factor-beta (TGF-beta) regulates a wide variety of cellular processes including cell growth, apoptosis, differentiation, migration, and extracellular matrix production among others. The canonical signaling pathway induced by the TGF-beta receptor complex involves the phosphorylation of Smad proteins which upon activation accumulate in the nucleus and regulate transcription. Interestingly, the cellular response to TGF-beta can be extremely variable depending on the cell type and stimulation context. TGF-beta causes epithelial cells to undergo growth arrest and apoptosis, responses which are critical to suppressing carcinogenesis, whereas it can also induce epithelial-mesenchymal transition and mediate fibroblast activation, responses implicated in promoting carcinogenesis and fibrotic diseases. However, TGF-beta induces all these responses via the same receptor complex and Smad proteins. To address this apparent paradox, during the last few years a number of additional signaling pathways have been identified which potentially regulate the different cellular responses to TGF-beta. The identification of these signaling pathways has shed light onto the mechanisms whereby Smad and non-Smad pathways collaborate to induce a particular cellular phenotype. In this article, we review TGF-beta signaling in epithelial cells and fibroblasts with a focus on understanding the mechanisms of TGF-beta versatility.

Alcohol exposure during the developmental period induces beta-endorphin neuronal death and causes alteration in the opioid control of stress axis function

Proopiomelanocortin-producing neurons in the arcuate nucleus of the hypothalamus secrete beta-endorphin (beta-EP), which controls varieties of body functions including the feedback regulation of the CRH neuronal activity in the paraventricular nucleus of the hypothalamus. Whether ethanol exposure in developing rats induces beta-EP neuronal death and alters their influence on CRH neurons in vivo has not been determined. We report here that binge-like ethanol exposures in newborn rats increased the number of apoptotic beta-EP neurons in the arcuate nucleus of the hypothalamus. We also found that immediately after ethanol treatments there was a significant reduction in the expression of proopiomelanocortin and adenylyl cyclases mRNA and an increased expression of several TGF-beta1-linked apoptotic genes in beta-EP neurons isolated by laser-captured microdissection from arcuate nuclei of young rats. Several weeks after the ethanol treatment, we detected a reduction in the number of beta-EP neuronal perikarya in arcuate nuclei and in the number of beta-EP neuronal terminals in paraventricular nuclei of the hypothalamus in the treated rats. Additionally, these rats showed increased response of the hypothalamic CRH mRNA to the lipopolysaccharide challenge. The ethanol-treated animals also showed incompetent ability to respond to exogenous beta-EP to alter the lipopolysaccharide-induced CRH mRNA levels. These data suggest that ethanol exposure during the developmental period causes beta-EP neuronal death by cellular mechanisms involving the suppression of cyclic AMP production and activation of TGF-beta1-linked apoptotic signaling and produces long-term structural and functional deficiency of beta-EP neurons in the hypothalamus.

Thalidomide induces limb deformities by perturbing the Bmp/Dkkl/Wnt signaling pathway

Thalidomide, a sedative originally used to treat morning sickness and now used to treat leprosy and multiple myeloma, is also a teratogen that induces birth defects in humans such as limb truncations and microphthalmia. However, the teratogenic mechanism of action of this drug remains obscure. Thalidomide induces limb and eye defects in the chicken embryo at an EC50 of 50 microg/kg egg wt and apoptosis in primary human embryonic fibroblasts (HEFs) at an EC50 of 8.9 microM. Using these model systems, we demonstrate by semiquantitative reverse transcriptase-polymerase chain reaction and whole-mount in situ hybridization that thalidomide-induced oxidative stress enhances signaling through bone morphogenetic proteins (Bmps). This leads to up-regulation of the Bmp target gene and Wnt antagonist Dickkopf1 (Dkk1) with subsequent inhibition of canonical Wnt/beta-catenin signaling and increased cell death as shown by trypan blue and terminal deoxynucleotidyl transferase-mediated nick end labeling staining. Thalidomide-induced cell death was dramatically reduced in HEFs and in embryonic limb buds by the use of inhibitors against Bmps, Dkk1, and Gsk3beta, a beta-catenin antagonist acting downstream of Dkk1 in the Wnt pathway. Most interestingly, blocking of Dkk1 or Gsk3beta dramatically counteracts thalidomide-induced limb truncations and microphthalmia. From this, we conclude that perturbing of Bmp/Dkk1/Wnt signaling is central to the teratogenic effects of thalidomide.

Upregulation of two BH3-only proteins, Bmf and Bim, during TGFβ-induced apoptosis

Transforming growth factor-beta (TGFbeta)-activated signalling pathways can lead to apoptosis, growth arrest or promotion of malignant behaviour, dependent on cellular context. The molecular mechanisms involved in TGFbeta-induced apoptosis remain controversial; although changes in gene expression are thought to be pivotal to the process, several different candidate apoptotic initiators and mediators have been proposed. Smad4, a critical component of the TGFbeta-induced transcriptional machinery, is shown here to be essential for induction of apoptosis. Gene expression analysis identified the proapoptotic Bcl-2 family members, Bmf and Bim, as induced by TGFbeta, dependent on both Smad4 and p38 function and the generation of reactive oxygen species. TGFbeta-induced Bmf and Bim localize to cellular membranes implicated in apoptosis. Inhibition of the TGFbeta-induced expression of both these proteins together provides significant protection of cells from apoptosis. The TGFbeta-triggered cell death programme thus involves induction of multiple BH3-only proteins during the induction of apoptosis.

Understanding cellular networks to improve hematopoietic stem cell expansion cultures

Efforts to develop culture technologies capable of eliciting robust human blood stem cell growth have met with limited success. Considering that adult stem cell cultures are complex systems, comprising multiple cell types with dynamically changing intracellular signalling environments and cellular compositions, this is not surprising. Typically treated as single-input single-output systems, adult stem cell cultures are better described as complex, non-linear, multiple-input multiple-output systems wherein the proliferation of subpopulations of cells leads to the formation of intercellular endogenously secreted protein interaction networks. Genomic and proteomic tools need to be applied to generate high-throughput (and ideally high-content) biological measurements of stem cell culture evolution. Datasets describing cellular interaction networks need to be integrated into predictive models of in vitro stem cell development. Ultimately, such models will serve as a starting point for the rational design of blood stem cell expansion bioprocesses utilizing dynamic system perturbations to achieve the preferential expansion of target cell populations.

Ethanol induces apoptotic death of developing beta-endorphin neurons via suppression of cyclic adenosine monophosphate production and activation of transforming growth factor-beta1-linked apoptotic signaling

The mechanism by which ethanol induces beta-endorphin (beta-EP) neuronal death during the developmental period was determined using fetal rat hypothalamic cells in primary cultures. The addition of ethanol to hypothalamic cell cultures stimulated apoptotic cell death of beta-EP neurons by increasing caspase-3 activity. Ethanol lowered the levels of adenylyl cyclase (AC)7 mRNA, AC8 mRNA, and/or cAMP in hypothalamic cells, whereas a cAMP analog blocked the apoptotic action of ethanol on beta-EP neurons. The AC inhibitor dideoxyadenosine (DDA) increased cell apoptosis and reduced the number of beta-EP neurons, and it potentiated the apoptotic action of ethanol on these neurons. beta-EP neurons in hypothalamic cultures showed immunoreactivity to transforming growth factor-beta1 (TGF-beta1) protein. Ethanol and DDA increased TGF-beta1 production and/or release from hypothalamic cells. A cAMP analog blocked the activation by ethanol of TGF-beta1 in these cells. TGF-beta1 increased apoptosis of beta-EP neurons, but it did not potentiate the action of ethanol or DDA actions on these neurons. TGF-beta1 neutralizing antibody blocked the apoptotic action of ethanol on beta-EP neurons. Determination of TGF-beta1-controlled cell apoptosis regulatory gene levels in hypothalamic cell cultures and in isolated beta-EP neurons indicated that ethanol, TGF-beta1, and DDA similarly alter the expression of these genes in these cells. These data suggest that ethanol increases beta-EP neuronal death during the developmental period by cellular mechanisms involving, at least partly, the suppression of cAMP production and activation of TGF-beta1-linked apoptotic signaling.

Tumor suppressor gene Runx3 sensitizes gastric cancer cells to chemotherapeutic drugs by downregulating Bcl-2, MDR-1 and MRP-1

The Runx3 gene is a member of the runt domain family transcription factors, key regulators of development and differentiation in metazoan. Recently, Runx3 was identified as a tumor suppressor gene. Loss of Runx3 was found to be associated with genesis and progression of gastric cancer. In this study, we transfected the gastric cancer cell line SGC7901 with eukaryotic expression vector of Runx3. In vitro drug sensitivity assay suggested that SGC7901/Runx3 cells were more sensitive to various chemotherapeutic drugs. Blocking Runx3 expression in immortalized stomach mucosal cells (GES-1) or gastric cancer cells (SGC7901) by Runx3-specific small interfering RNA conferred the cells resistance to chemotherapeutic drugs. Flow cytometry examination suggested that expression of Runx3 in gastric cancer cells increased the intracellular accumulation and retention of adriamycin. Semiquantitative RT-PCR and Western blot suggested that Runx3 downregulated expression of Bcl-2, MDR-1 (P-gp) and MRP-1. Binding of Runx3 to promoter sequences of Bcl-2, MDR-1 and MRP-1 gene was detected by eletrophoretic mobility shift assay (EMSA) and supershift EMSA. We cloned the MDR-1 and MRP-1 gene promoters containing Runx binding sites and constructed the luciferase reporter vectors of these 2 promoters. Luciferase reporter assay suggested that Runx3 inhibited the promoter activity of the MDR-1 and MRP-1 promoter in SGC7901 cells. Taken together, our findings suggested that overexpression of Runx3 could sensitize gastric cancer cells to chemotherapeutic drugs by downregulating the Bcl-2, MDR-1 and MRP-1.

Apoptosis of mink lung epithelial cells by co-treatment of low-dose staurosporine and transforming growth factor-beta1 depends on the enhanced TGF-beta signaling and requires the decreased phosphorylation of PKB/Akt

We demonstrate how co-treatment of low-dose staurosporine (STS) and TGF-beta1, which alone have little effect on cell death, markedly induces apoptosis in Mv1Lu mink lung epithelial cells, but not in its clonal variant R1B cells lacking functional TGF-beta signaling. This process was associated with mitochondria-dependent apoptosis and the enhanced TGF-beta/Smad signaling in Mv1Lu cells. When R1B cells were infected with adenovirus carrying wild-type ALK5, a functional TGF-beta type I receptor gene, the apoptotic cell death was significantly restored in these cells following co-treatment of low-dose STS and TGF-beta1. Treatment of Mv1Lu cells with both low-dose STS and TGF-beta1 decreased the activity of phospho-Akt, which is involved in cell survival signal. In addition, pre-treatments of PI3 kinase inhibitors, LY294002 and wortmannin, further increased the apoptosis of MvlLu cells induced by co-treatment of low-dose STS and TGF-beta1. And overexpression of constitutively active Akt (myr-Akt) using adenoviral expression system inhibited the apoptotic cell death of Mv1Lu cells by about 50% upon co-treatment of low-dose STS and TGF-beta1. These results suggest that co-treatment of low-dose STS and TGF-beta1 induces apoptosis of mink lung epithelial cells by enhancing TGF-beta signaling and in part suppressing cytoprotective signaling.

Role of transforming growth factor Beta in human cancer

Transforming growth factor beta (TGF-beta) is a ubiquitous and essential regulator of cellular and physiologic processes including proliferation, differentiation, migration, cell survival, angiogenesis, and immunosurveillance. Alterations in the TGF-beta signaling pathway, including mutation or deletion of members of the signaling pathway and resistance to TGF-beta-mediated inhibition of proliferation are frequently observed in human cancers. Although these alterations define a tumor suppressor role for the TGF-beta pathway in human cancer, TGF-beta also mediates tumor-promoting effects, either through differential effects on tumor and stromal cells or through a fundamental alteration in the TGF-beta responsiveness of the tumor cells themselves. TGF-beta and members of the TGF-beta signaling pathway are being evaluated as prognostic or predictive markers for cancer patients. Ongoing advances in understanding the TGF-beta signaling pathway will enable targeting of this pathway for the chemoprevention and treatment of human cancers.

Mutation analysis of DKK1 and in vivo evidence of predominant p53-independent DKK1 function in gliomas

DKK1 protein belongs to a family of inhibitors of the Wnt/beta1-catenin signaling pathway. Sporadic mutations affecting almost each major player of the Wnt/beta1-catenin pathway have been described in a variety of human carcinomas. DKK1 translation can be induced by p53, thereby linking TP53 and Wnt/beta1-catenin signaling pathways. These findings raise questions in regard to human gliomas, which similar to carcinomas carry a high rate of mutations in TP53. To analyze DKK1 for its role in initiation or progression, we screened a series of 73 brain tumors for structural alterations in the entire coding sequence by single-strand conformation polymorphism and direct sequencing. While several sequence variants were detected, there were no obvious mutations affecting DKK1. Further, we analyzed the prevalence of mRNA from TP53, DKK1 and CTNNB1 and of p53 and beta1-catenin protein in a series of human gliomas with and without mutations in TP53. Transcription and expression of CTNNB1/beta1-catenin and DKK1 proved to be independent of TP53/p53. These data support in vivo function of DKK1, independent of p53, in human gliomas with no major impact on their pathogenesis.

Association between endogenous gene expression and growth regulation induced by TGF-β1 in human gastric cancer cells

AIM: To investigate the association between endogenous gene expression and growth regulation including proliferation and apoptosis induced by transforming growth factor-β1 (TGF-β1) in human gastric cancer (GC) cells.

METHODS: Reverse transcription polymerase chain reaction (RT-PCR) was performed to detect the main components of the TGF-β1/Smads signal pathway in human poorly differentiated GC cell line BGC-823. Localization of Smad proteins was also determined using immunofluorescence. Then, the BGC-823 cells were cultured in the presence or absence of TGF-β1 (10 ng/mL) for 24 and 48 h, and the effects of TGF-β1 on proliferation and apoptosis were measured by cell growth curve and flow cytometry (FCM) analysis. The ultrastructural features of BGC-823 cells with or without TGF-β1 treatment were observed under transmission electron microscope. The apoptotic cells were visualized by means of the terminal deoxynucleotidyl transferase (TdT)-mediated dTUP in situ nick end-labeling (TUNEL) method. Meanwhile, the expression levels of endogenous p15,p21 and Smad7 mRNA and the corresponding proteins in the cells were detected at 1, 2 and 3 h after culture in the presence or absence of TGF-β1 (10 ng/mL) by semi-quantitative RT-PCR and Western blot, respectively.

RESULTS: The TGF-β1/Smad signaling was found to be intact and functional in BGC-823 cells. The growth curve revealed the most evident inhibition of cell proliferation by TGF-β1 at 48 h, and FCM assay showed G1 arrest accompanied with apoptosis induced by TGF-β1. The typical morphological changes of apoptosis were observed in cells exposed to TGF-β1. The apoptosis index (AI) in TGF-β1-treated cells was significantly higher than that in the untreated controls (10.7±1.3% vs 0.32±0.06%, P<0.01). The levels of p15,p21 and Smad7 mRNA and corresponding proteins in cells were significantly up-regulated at 1 h, but gradually returned to basal levels at 3 h following TGF-β1 (10 ng/mL) treatment.

CONCLUSION: TGF-β1 affects both proliferation and apoptosis of GC cells through the regulation of p15 and p21, and induces transient expression of Smad 7 as a negative feedback modulation of TGF-β1 signal. Our results suggest a novel functional role of p21 as an accelerant of TGF-β1-mediated apoptosis in GC cells.

Global effects of BCR/ABL and TEL/PDGFRbeta expression on the proteome and phosphoproteome: identification of the Rho pathway as a target of BCR/ABL

Many leukemic oncogenes form as a consequence of gene fusions or mutation that result in the activation or overexpression of a tyrosine kinase. To identify commonalities and differences in the action of two such kinases, breakpoint cluster region (BCR)/ABL and TEL/PDGFRbeta, two-dimensional gel electrophoresis was employed to characterize their effects on the proteome. While both oncogenes affected expression of specific proteins, few common effects were observed. A number of proteins whose expression is altered by BCR/ABL, including gelsolin and stathmin, are related to cytoskeletal function whereas no such changes were seen in TEL/PDGFRbeta-transfected cells. Treatment of cells with the kinase inhibitor STI571 for 4-h reversed changes in expression of some of these cytoskeletal proteins. Correspondingly, BCR/ABL-transfected cells were less responsive to chemotactic and chemokinetic stimuli than non-transfected cells and TEL/PDGFRbeta-transfected Ba/F3 cells. Decreased motile response was reversed by a 16-h treatment with STI571. A phosphoprotein-specific gel stain was used to identify TEL/PDGFRbeta and BCR/ABL-mediated changes in the phosphoproteome. These included changes on Crkl, Ras-GAP-binding protein 1, and for BCR/ABL, cytoskeletal proteins such as tubulin, and Nedd5. Decreased phosphorylation of Rho-GTPase dissociation inhibitor (Rho GDI) was also observed in BCR/ABL-transfected cells. This results in the activation of the Rho pathway, and treatment of cells with Y27632, an inhibitor of Rho kinase, inhibited DNA synthesis in BCR/ABL-transfected Ba/F3 cells but not TEL/PDGFRbeta-expressing cells. Expression of a dominant-negative RhoA inhibited both DNA synthesis and transwell migration, demonstrating the significance of this pathway in BCR/ABL-mediated transformation.

Activation of protein kinase A (PKA) by 8-Cl-cAMP as a novel approach for antileukaemic therapy

Activation of PKA by cAMP agonists, such as 8-Cl-cAMP activation, selectively causes rapid apoptosis in v-abl transformed fibroblasts by inhibiting the Raf-1 kinase. Here we investigated whether 8-Cl-cAMP is useful for the treatment of chronic myelogenous leukaemia (CML), which is hallmarked by the expression of the p210^bcr/abl oncogene. Autologous bone marrow transplantation is a feasible alternative for patients with no suitable donor, but hampered by the risk of relapse due to the persistence of leukaemia cells in the transplant. To study the effects of 8-Cl-cAMP on primary leukaemic cells, bone marrow cells (BMCs) from eight CML patients (one at diagnosis, three in chronic and four in accelerated phase) were treated. Ex vivo treatment of BMCs obtained in chronic phase of CML with 100 μM 8-Cl-cAMP for 24–48 h led to the selective purging of Philadelphia Chromosome (Ph1 chromosome) without toxic side effects on BMCs from healthy donors as measured by colony-forming unit (CFU) assays. BMCs from patients in accelerated phase showed selective, but incomplete elimination of Ph1 chromosome positive colony forming cells. The mechanism of 8-Cl-cAMP was investigated in FDCP-mix cells transformed by p210^bcr/abl, a cell culture model for CML. The results showed that 8-Cl-cAMP reduced DNA synthesis and viability independent of Raf inhibition as Raf inhibitors had no effect. MEK inhibitors interfered with DNA synthesis, but not with viability. In summary, our results indicate that 8-Cl-cAMP could be useful to purge malignant cells from the bone marrow of patients with CML and certain other forms of leukaemias.

TIAF1 and p53 functionally interact in mediating apoptosis and silencing of TIAF1 abolishes nuclear translocation of serine 15-phosphorylated p53

TIAF1 is a TGF-beta 1-induced factor that protects L929 fibroblasts from TNF-mediated apoptosis. In contrast, overexpressed TIAF1 induces growth inhibition and apoptosis of monocytic U937 and various nonfibroblast cells. TIAF1-mediated apoptosis of U937 cells involves upregulation of p53, p21, and Smad2/4, but downregulation of ERK phosphorylation. To determine whether p53 and TIAF1 functionally interact in regulating cell death, ectopic TIAF1 and p53 were shown to induce apoptosis of U937 cells in both synergistic and antagonistic manners. At optimal levels both TIAF1 and p53 mediated apoptosis cooperatively. Also, both proteins suppressed adherence-independent growth of L929 cells. In contrast, initiation of apoptosis by overexpressed TIAF1 was blocked by low doses of p53, and vice versa. Furthermore, ectopic p53 blocked an ongoing apoptosis in U937 cells stably expressing TIAF1. Yeast two-hybrid analyses failed to demonstrate the binding of p53 with TIAF1, suggesting an unidentified protein that links the p53/TIFA1 interaction. Suppression of TIAF1 expression by siRNA could not inhibit Ser15 phosphorylation in p53 in response to UV and etoposide. However, nuclear translocation of these Ser15-phosphorylated p53 was significantly reduced in TIAF1-silenced cells. Taken together, TIAF1 and p53 functionally interact in regulating apoptosis, and TIAF1 is likely to participate in the nuclear translocation of activated p53.

Smad3 potentiates transforming growth factor beta (TGFbeta )-induced apoptosis and expression of the BH3-only protein Bim in WEHI 231 B lymphocytes

Transforming growth factor-beta (TGFbeta) is a potent growth inhibitor and inducer of apoptosis in B lymphocytes and is essential for immune regulation and maintenance of self-tolerance. Here we show that exogenous overexpression of Smad3 potentiates TGFbeta-induced apoptosis and expression of the pro-apoptotic protein Bim in WEHI 231 B lymphocytes. Overexpression of dominant-negative forms of Smad3 abrogate these TGFbeta-induced responses. We also demonstrate that TGFbeta induces Bim protein expression concomitant with its induction of apoptosis in the mouse progenitor B lymphocyte cell line, Ba/F3. Enhanced expression of Bim protein induced by TGFbeta is associated with an increased association of Bim with Bcl-2 and a concomitant loss of mitochondrial membrane potential. Furthermore, we find that the anti-apoptotic effect of the pro-survival cytokine CD40 results in the abrogation of TGFbeta-mediated Bim induction. Our data provide the first evidence of Bim expression levels that are increased by the addition of a pro-apoptotic cytokine, TGFbeta, and also suggest that the TGFbeta-specific transcription factor Smad3 plays a role in mediating Bim expression levels and apoptosis.

The involvement of diadenosine 5',5"'-P1,P4-tetraphosphate in cell cycle arrest and regulation of apoptosis

Diadenosine oligophosphates (Ap(n)A) have been proposed to function as intracellular and extracellular signaling molecules in animal cells. Here, we have examined the cellular and molecular mechanisms underlying the induction of apoptosis by diadenosine 5',5"'-P(1),P(4)-tetraphosphate (Ap(4)A). We have shown a dose-dependent apoptotic response in cells treated with Ap(4)A. Flow cytometric analysis indicated an involvement of Ap(4)A at an early stage of G1/S arrest. No difference in the amount of p21(waf1) was observed in HL60 cells treated with Ap(4)A compared to control cells. The level of retinoblastoma protein (pRb) dropped dramatically when apoptosis was extensive. The cleavage of pRb was abrogated if Ap(4)A-treated cells were incubated with general caspase inhibitor zVAD-fmk. Ap(4)A also induced a profound decrease in the level of the Bcl-2 protein. The lack of effect of Ap(4)A on CDK1 activity indicated that Ap(4)A is not involved in "aberrant mitosis". We suggest that in vivo Ap(4)A may play a significant role in tumor growth suppression by inducing apoptosis.

Estradiol reverses TGF-beta1-induced mesangial cell apoptosis by a casein kinase 2-dependent mechanism

BACKGROUND

The slower rate of progression of chronic renal disease in women than in men is explained in part by the ability of estradiol to reverse the stimulatory effect of transforming growth factor-beta1 (TGF-beta1) on collagen IV synthesis at the level of casein kinase 2 activation. Casein kinase 2 also phosphorylates and activates the pro-apoptotic protein, p53. We hypothesized that estradiol would reverse TGF-beta1-induced mesangial cell apoptosis by antagonizing the stimulatory effects of TGF-beta1 on casein kinase 2 activity, thereby preventing p53 activation.

METHODS

The effects of TGF-beta1 on mesangial cell apoptosis, p53 phosphorylation, Bax and Bcl-2 levels, caspase 9 activity, and cleavage of PARP were examined. The abilities of estradiol and a specific inhibitor of CK2 (5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole) (DRB) to modulate the effects of TGF-beta1 on these processes were also examined.

RESULTS

TGF-beta1 (2 ng/mL), which up-regulates CK2 activity, induces apoptosis in murine mesangial cells together with p53 serine389 phosphorylation, up-regulation of Bax, suppression of Bcl-2, destabilization of mitochondrial permeability transition pores, stimulation of caspase 9 activity and activation of PARP. TGF-beta1-induced p53 activation and all the intermediary steps leading to mesangial cell apoptosis were reversed by estradiol (10-9 mol/L) and by DRB, potent inhibitors of CK2 activity, but not by inhibitors of the p38 MAPK, ERK or JNK signaling cascades. In contrast, TGF-beta1 failed to induce apoptosis in p53 knockout mesangial cells.

CONCLUSIONS

Our data suggest that CK2 mediates the stimulatory effects of TGF-beta1 on mesangial cell apoptosis via a p53-dependent mechanism. The ability of estradiol to reverse TGF-beta1-induced apoptosis may contribute to the protective effects of female gender on the course of chronic renal disease.

TGF-beta signaling in renal disease

Since discovery over a decade ago of a role for the cytokine TGF-beta as key mediator of glomerular and tubulointerstitial pathobiology in chronic kidney diseases, studies of TGF-beta signaling in the kidney have focused on the molecular biology of fibrogenesis. In recent years, glomerular and tubular epithelial cell apoptosis and cellular transdifferentiation have been proposed as putative primary pathomechanisms that may underlie progression of renal disease. This review describes evidence in support of nonlinear models and functional roles of TGF-beta signaling in mediating apoptosis and epithelial-to-mesenchymal transdifferentiation (EMT) in chronic progressive renal disease. Emphasis is placed on cell context-dependent models of TGF-beta signaling providing a conceptual framework to consolidate seemingly distinct pathomechanisms of progression of glomerular and tubulointerstitial disease.

Bcl-2 antagonizes the combined apoptotic effect of transforming growth factor-beta and dihydrotestosterone in prostate cancer cells

BACKGROUND

We previously demonstrated that dihydrotestosterone (DHT) enhances transforming growth factor-beta (TGF-beta) -induced apoptosis in human prostate cancer cells (Endocrinology 2001;142:2419-2426).

METHODS

In this study, the ability of the apoptosis suppressor bcl-2 to directly antagonize the combined apoptotic effect of TGF-beta and DHT in the androgen-sensitive LNCaP TbetaRII prostate cancer cells was examined. The previously cloned TGF-RbetaII receptor LNCaP cells, responsive to both TGF-beta and androgens, were engineered to overexpress the bcl-2 oncoprotein and the profile of apoptosis induction was analyzed in response to TGF-beta alone (5.0 ng/ml) or in combination with DHT (1 nM).

RESULTS

Biological characterization of cloned LNCaP TbetaRII hygromycin/bcl-2 transfectants demonstrated that bcl-2 overexpression resulted in a significant inhibition of the combined TGF-beta and DHT apoptotic effect in prostate cancer cells (P < 0.01). Furthermore, molecular analysis indicated that this antagonistic effect of bcl-2 on apoptosis was due to partial suppression of TGF-beta and DHT-mediated induction of caspase-1 expression and activation in LNCaP TbetaRII-hygro/bcl-2 transfectants. These results support a potential bcl-2 interference with the TGF-beta and androgen apoptotic signaling in prostate cancer cells by means of an antagonistic effect on caspase-1 activation.

CONCLUSION

This evidence may have mechanistic significance in understanding the contribution of bcl-2 overexpression in the development of androgen-independent prostate cancer by means of conferring resistance to TGF-beta-mediated apoptosis.

Transforming growth factor-beta1 is responsible for maturation-dependent spontaneous apoptosis of cultured gastric pit cells

In this study, we established a system of high concentration serum-dependent spontaneous apoptosis of guinea pig gastric pit cells in primary culture, which seems to mimic the spontaneous apoptosis of matured gastric pit cells at gastric surface in vivo. In addition to induction of the spontaneous apoptosis, cell growth was inhibited in the presence of 10% serum compared with 0.5% serum. Transforming growth factor-beta1 (TGF-beta1), which is known to cause both apoptosis and growth inhibition in mammalian cells, was present in serum of both fetal calf and guinea pig. The addition of recombinant TGF-beta1 to the culture medium containing 0.5% fetal calf serum caused both induction of apoptosis and inhibition of cell growth. On the other hand, immunodepletion of TGF-beta1 from fetal calf serum caused inability to induce both the spontaneous apoptosis and inhibition of cell growth. These data suggest that TGF-beta1 is involved in the spontaneous apoptosis of guinea pig gastric pit cells in primary culture.

Hematopoietic cytokines, transcription factors and lineage commitment

The past two decades have witnessed significant advances in our understanding of the cellular physiology and molecular regulation of hematopoiesis. At the heart of stem cell self-renewal and lineage commitment decisions lies the relative expression levels of lineage-specific transcription factors. The expression of these transcription factors in early stem cells may be promiscuous and fluctuate, but ultimately comes under the influence of extracellular regulatory signals in the form of hematopoietic cytokines. In this review, we first summarize our current understanding of the phenotypic characterization of hematopoietic stem cells. Next, we describe key known transcription factors which govern stem cell self-renewal and lineage commitment decisions. Finally, we review data concerning the role of specific cytokines in influencing these decisions. From this review, a picture emerges in which stem cell fate decisions are governed by the integrated effects of intrinsic transcription factors and external signaling pathways initiated by regulatory cytokines.

Regulation of cell proliferation by Smad proteins

Transforming growth factor-beta (TGF-beta) family members which include TGF-betas, activins, and bone morphogenetic proteins (BMPs) regulate a broad spectrum of biological responses on a large variety of cell types. TGF-beta family members initiate their cellular responses by binding to distinct receptors with intrinsic serine/threonine kinase activity and activation of specific downstream intracellular effectors termed Smad proteins. Smads relay the signal from the cell membrane to the nucleus, where they affect the transcription of target genes. Smad activation, subcellular distribution, and stability have been found to be intricately regulated and a broad array of transcription factors have been identified as Smad partners. Important activities of TGF-beta are its potent anti-mitogenic and pro-apoptotic effects that, at least in part, are mediated via Smad proteins. Escape from TGF-beta/Smad-induced growth inhibition and apoptosis is frequently observed in tumors. Certain Smads have been found to be mutated in specific types of cancer and gene ablation of particular Smads in mice has revealed increased rate of tumorigenesis. In late stage tumors, TGF-beta has been shown to function as a tumor promoter. TGF-beta can stimulate the de-differentiation of epithelial cells to malignant invasive and metastatic fibroblastic cells. Interestingly, TGF-beta may mediate these effects directly on tumor cells via subverted Smad-dependent and/or Smad-independent pathways.

Transforming growth factor beta 1 induces apoptosis through cleavage of BAD in a Smad3-dependent mechanism in FaO hepatoma cells

Transforming growth factor beta (TGF-beta) induces apoptosis in a variety of cells. We have previously shown that TGF-beta 1 rapidly induces apoptosis in the FaO rat hepatoma cell line. We have now studied the effect of TGF-beta 1 on the expression of different members of the Bcl-2 family in these cells. We observed no detectable changes in the steady-state levels of Bcl-2, Bcl-X(L), and Bax. However, TGF-beta 1 induced caspase-dependent cleavage of BAD at its N terminus to generate a 15-kDa truncated protein. Overexpression of the 15-kDa truncated BAD protein enhanced TGF-beta 1-induced apoptosis, whereas a mutant BAD resistant to caspase 3 cleavage blocked TGF-beta 1-induced apoptosis. Overexpression of Smad3 dramatically enhanced TGF-beta 1-induced cleavage of BAD and apoptosis, whereas antisense Smad3 blocked TGF-beta 1-induced apoptosis and BAD cleavage. These results suggest that TGF-beta 1 induces apoptosis through the cleavage of BAD in a Smad3-dependent mechanism.

The Wnt antagonist Dickkopf-1 is regulated by Bmp signaling and c-Jun and modulates programmed cell death

Dickkopf-1 (Dkk-1) has been shown to be a potent inhibitor of Wnt/beta-catenin signaling in a variety of assays and organisms. In this study, we show that expression of Dkk-1 overlaps significantly with the sites of programmed cell death in normal as well as mutant vertebrate limb development, and identify several of its upstream regulators, one of which is Bmp-4. Interestingly, Bmp-4 only activates Dkk-1 when it concomitantly induces apoptosis. Moreover, Dkk-1 is heavily up-regulated by UV irradiation and several other genotoxic stimuli. We further show that normal expression of Dkk-1 is dependent on the Ap-1 family member c-Jun and that overexpression of Dkk-1 enhances Bmp-triggered apoptosis in the vertebrate limb. Taken together, our results provide evidence for an important role of Dkk-1-mediated inhibition of Wnt/beta-catenin signaling in response to different stress signals that all converge on the activation of c-Jun in vivo.