TGF-beta1 suppresses apoptosis via differential regulation of MAP kinases and ceramide production

The Interplay Between TGF-β Signaling and Cell Metabolism

The transforming growth factor-β (TGF-β) signaling plays a critical role in the development and tissue homeostasis in metazoans, and deregulation of TGF-β signaling leads to many pathological conditions. Mounting evidence suggests that TGF-β signaling can actively alter metabolism in diverse cell types. Furthermore, metabolic pathways, beyond simply regarded as biochemical reactions, are closely intertwined with signal transduction. Here, we discuss the role of TGF-β in glucose, lipid, amino acid, redox and polyamine metabolism with an emphasis on how TGF-β can act as a metabolic modulator and how metabolic changes can influence TGF-β signaling. We also describe how interplay between TGF-β signaling and cell metabolism regulates cellular homeostasis as well as the progression of multiple diseases, including cancer.

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.

The concomitant apoptosis and EMT underlie the fundamental functions of TGF-β

TGF-β's multipotent cellular effects and their relations are critical for TGF-β's pathophysiological functions. However, these effects may appear to be paradoxical in understanding TGF-β's functions. Apoptosis and epithelial-mesenchymal transition (EMT) are two fundamental events that are deeply linked to various physiological and disease-related processes. These two major cellular fates are subtly regulated and can be potently stimulated by TGF-β, which profoundly contribute to the biological roles of TGF-β. Moreover, these two events are also indirectly and directly correlated with TGF-β-mediated growth inhibition and are relevant to the current understanding of the roles of TGF-β in tumorigenesis and cancer progression. Although TGF-β-induced apoptosis and EMT can be singly independent cellular events, they can also be mutually exclusive but interrelated concomitant events in various cases. Thus, the modulation of apoptosis and EMT is essential for the seemingly paradoxical functions of TGF-β. However, the concomitant effect of TGF-β on apoptosis and EMT, the balance and regulated alterations of them are still been ignored or underestimated. This review focuses on the TGF-β-induced concomitant apoptosis and EMT. We aim to provide an insight in understanding their significance, balance, and modulation in TGF-β-mediated biological functions.

ECM turnover-stimulated gene delivery through collagen-mimetic peptide-plasmid integration in collagen

Gene therapies have great potential in regenerative medicine; however, clinical translation has been inhibited by low stability and limited transfection efficiencies. Herein, we incorporate collagen-mimetic peptide (CMP)-linked polyplexes in collagen scaffolds to increase DNA stability by up to 400% and enable tailorable in vivo transgene expression at 100-fold higher levels and 10-fold longer time periods. These improvements were directly linked to a sustained interaction between collagen and polyplexes that persisted during cellular remodeling, polyplex uptake, and intracellular trafficking. Specifically, incorporation of CMPs into polyethylenimine (PEI) polyplexes preserved serum-exposed polyplex-collagen activity over a period of 14days, with 4 orders-of-magnitude more intact DNA present in CMP-modified polyplex-collagen relative to unmodified polyplex-collagen after a 10day incubation under cell culture conditions. CMP-modification also altered endocytic uptake, as indicated by gene silencing studies showing a nearly 50% decrease in transgene expression in response to caveolin-1 silencing in modified samples versus only 30% in unmodified samples. Furthermore, cellular internalization studies demonstrated that polyplex-collagen association persisted within cells in CMP polyplexes, but not in unmodified polyplexes, suggesting that CMP linkage to collagen regulates intracellular transport. Moreover, experiments in an in vivo repair model showed that CMP modification enabled tailoring of transgene expression from 4 to 25days over a range of concentrations. Overall, these findings demonstrate that CMP decoration provides substantial improvements in gene retention, altered release kinetics, improved serum-stability, and improved gene activity in vivo. This versatile technique has great potential for multiple applications in regenerative medicine.

STATEMENT OF SIGNIFICANCE

In this work, we demonstrate a novel approach for stably integrating DNA into collagen scaffolds to exploit the natural process of collagen remodelling for high efficiency non-viral gene delivery. The incorporation of CMPs into DNA polyplexes, coupled with the innate affinity between CMPs and collagen, not only permitted improved control over polyplex retention and release, but also provided a series of substantial and highly unique benefits via the stable and persistent linkage between CMP-polyplexes and collagen fragments. Specifically, CMP-modification of polyplexes was demonstrated to (i) control release for nearly a month, (ii) improve vector stability under physiological-like conditions, and (iii) provide ligands able to efficiently transfer genes via endocytic collagen pathways. These unique properties overcome key barriers inhibiting non-viral gene therapy.

P144, a Transforming Growth Factor beta inhibitor peptide, generates antitumoral effects and modifies SMAD7 and SKI levels in human glioblastoma cell lines

Glioblastoma (GBM) is the most prevalent malignant primary brain tumor, accounting for 60-70% of all gliomas. Current median patient survival time is 14-16 months after diagnosis. Numerous efforts in therapy have not significantly altered the nearly uniform lethality of this malignancy. The Transforming Growth Factor beta (TGF-β) signaling pathway plays a key role in GBM and is implicated in proliferation, invasion and therapy resistance. Several inhibitors of the TGF-β pathway have entered clinical trials or are under development. In this work, the therapeutic potential of P144, a TGF-β inhibitor peptide, was analyzed. P144 decreased proliferation, migration, invasiveness, and tumorigenicity in vitro, whereas apoptosis and anoikis were significantly increased for GBM cell lines. SMAD2 phosphorylation was reduced, together with a downregulation of SKI and an upregulation of SMAD7 at both transcriptional and translational levels. Additionally, P144 was able to impair tumor growth and increase survival in an in vivo flank model. Our findings suggest a potential effect of P144 in vitro and in vivo that is mediated by regulation of transcriptional target genes of the TGF-β pathway, suggesting a therapeutic potential of P144 for GBM treatment.

Conditional ablation of TGF-β signaling inhibits tumor progression and invasion in an induced mouse bladder cancer model

The role of transforming growth factor-β (TGF-β) signaling in cancer progression is still under debate. To determine the function of TGF-β signaling in bladder cancer progression, we conditionally knocked out the Tgfbr2 in mouse model after a N-butyl-N-4-hydroxybutyl Nitrosamine induced bladder carcinogenesis. We found the ablation of TGF-β signaling could inhibit the cancer cell proliferation, cancer stem cell population and EMT, hence suppressed the invasive cancer progression, which is similar with the result of TGF-β receptor I inhibitor treatment. These findings recognize the roles and mechanisms of TGF-β signaling in bladder cancer progression in vivo for the first time.

TGF-β1 promotes bovine mammary fibroblast proliferation through the ERK 1/2 signalling pathway

The abnormal proliferation of bovine mammary fibroblasts (BMFBs) impairs mammary gland development and lactation. Severe manifestations develop into breast fibrosis, leading to the culling of cows and causing serious losses to the dairy industry. Transforming growth factor β1 (TGF-β1) is an important modulator of cell proliferation and extracellular matrix formation; however, limited information is available on BMFBs. In this study, a convenient and stable culture method for BMFBs was established. Treatment with 5 ng/mL of TGF-β1 significantly promoted the proliferation of BMFBs and accelerated the cell cycle. TGF-β1 stimulation for up to 12 h significantly increased the relative ERK1/2 mRNA expression and enhanced the protein expression of p-ERK1/2 and cyclin D1. Conversely, the ERK1/2 inhibitor PD98059 blocked these TGF-β1 effects. Further exploration using a mouse model showed that TGF-β1 significantly increased the proportion of fibroblasts and accelerating the cell transition from the G1 to G2/M phases. In addition, TGF-β1 enhanced the expression of fibrosis markers, α-SMA and I Collagen, which could be blocked efficiently by the PD98059 in mouse mammary gland. Finally, immunofluorescence analysis confirmed that TGF-β1 promoted fibroblast proliferation in healthy dairy cows after normal long-term dietary corn straw roughage supplementation. It is suggested that the diet may promote mammary fibroblast proliferation by raising the level of TGF-β1. Our study provides new insights into how nutrition causes undesirable changes in mammary gland structure.

mTOR inhibition by rapamycin increases ceramide synthesis by promoting transforming growth factor-β1/Smad signaling in the skin

Although mammalian target of rapamycin (mTOR) mediates a wide variety of biological functions, little information is available on the effect of mTOR on the functions of skin cells. In this study, we investigated effects of mTOR inhibition by rapamycin on ceramide synthesis in the skin of rats and human keratinocytes and its regulatory mechanisms. The phosphorylation of p70 S6 kinase, which indicates mTOR activation, was induced in the skin of rats fed a high-fat diet, but this abnormality was reversed by supplementation with rapamycin. Ceramide levels and the mRNA levels of serine palmitoyltransferase (SPT) and transforming growth factor (TGF)-β1 were suppressed in the skin of rats fed high-fat diets, but this abnormality was reversed by supplementation with rapamycin. TGF-β1-induced SPT mRNA expression was blocked by SB525334, an inhibitor of TGF-β1-induced Smad2/3 nuclear localization, in human keratinocytes. Rapamycin-induced SPT mRNA expression was blocked by an anti-TGF-β1 antibody or SB525334 in human keratinocytes. These results show that mTOR inhibition by rapamycin increases ceramide synthesis by promoting TGF-β1/Smad signaling in the skin.

Polyoma small T antigen triggers cell death via mitotic catastrophe

Polyoma small T antigen (PyST), an early gene product of the polyoma virus, has been shown to cause cell death in a number of mammalian cells in a protein phosphatase 2A (PP2A)-dependent manner. In the current study, using a cell line featuring regulated expression of PyST, we found that PyST arrests cells in mitosis. Live-cell and immunofluorescence studies showed that the majority of the PyST expressing cells were arrested in prometaphase with almost no cells progressing beyond metaphase. These cells exhibited defects in chromosomal congression, sister chromatid cohesion and spindle positioning, thereby resulting in the activation of the spindle assembly checkpoint. Prolonged mitotic arrest then led to cell death via mitotic catastrophe. Cell cycle inhibitors that block cells in G1/S prevented PyST-induced death. PyST-induced cell death that occurs during M is not dependent on p53 status. These data suggested, and our results confirmed, that PP2A inhibition could be used to preferentially kill cancer cells with p53 mutations that proliferate normally in the presence of cell cycle inhibitors.

Transforming growth factor‑β1 reduces apoptosis via autophagy activation in hepatic stellate cells

Autophagy is a metabolic process that is important in fibrogenesis, in which cellular components are degraded by lysosomal machinery. Transforming growth factor β1 (TGF‑β1) is a potent fibrogenic cytokine involved in liver fibrosis; however, it remains elusive whether autophagy is regulated by TGF‑β1 in this process. In the present study, the function of TGF‑β1‑mediated autophagy in the proliferation and apoptosis of hepatic stellate cells (HSCs) was investigated. A rat HSC cell line (HSC‑T6) was incubated with or without TGF‑β1 followed by bafilomycin A1, and microtubule-associated proteins 1A/1B light chain 3 (LC3) small interfering (si)RNA was used to inhibit autophagy in order to assess the association between TGF‑β1 and autophagy. HSC‑T6 cell transient transfection was accomplished with a pLVX‑AcGFP‑N1‑rLC3B‑encoding plasmid. An MTS assay and flow cytometry were utilized to detect proliferation and apoptosis of HSC‑T6 cells. Quantitative polymerase chain reaction, immunofluorescence and western blot analysis were used to detect the presence of activation markers. Proliferation was increased and apoptosis was reduced in HSC‑T6 cells treated with TGF‑β1 compared with cells subjected to serum deprivation. However, when HSC‑T6 cells were treated with bafilomycin A1 and LC3 siRNA, increased apoptosis and reduced proliferation were observed. In addition, protein and mRNA expression levels of the autophagy marker LC3 were significantly increased. GFP‑LC3 punctate markings were more prolific following TGF‑β1 treatment of HSC‑T6 cells, indicating that TGF‑β1 may rescue HSC‑T6 cells from serum deprivation and reduce apoptosis via autophagy induction. The present study elucidated the possible functions of TGF‑β1‑mediated autophagy in the pathological process of liver fibrosis.

Effects of all-trans retinoic acid on signal pathway of cyclooxygenase-2 and Smad3 in transforming growth factor-β-stimulated glomerular mesangial cells

All-trans retinoic acid (ATRA) has been used for the treatment of acute promyelocytic leukemia. It remains unclear, however, whether ATRA affects cyclooxygenase-2 (COX-2; an enzyme involved in prostaglandin production), PGE2, and thromboxane A2 (TXA2) (metabolic products of COX-2) by a transforming growth factor-β/Smad-signaling pathway, which plays important roles in mesangial-cell proliferation and renal fibrosis. In this study, the mRNA and protein of Smad3, Smad7, and COX-2 were detected by reverse transcription-polymerase chain reaction and Western blot, respectively, in mesangial cells stimulated by transforming growth factor-β (TGF-β) and treated with ATRA at various concentrations and times. The protein level of PGE2 and TXA2 was also measured by enzyme-linked immunosorbent assay. The localization of Smad3 and Smand7 was observed by confocal microscope. Cell proliferation was detected by MTT assay, while apoptosis was determined using Hoechest staining. The expression of Smad3, Smad7, and COX-2 mRNA and protein was increased by exogenous TGF-β, but inhibited by pretreatment of ATRA, in dose and time-dependent manners. In addition, the expression of Smad3 and Smad7 was significantly reduced not only by staurosporine, an inhibitor of threonine/serine protein kinases as well as smad, but also by NS-398, an inhibitor of COX-2. PGE2 and TXA2 were raised by TGF-β, but also decreased by ATRA, staurosporine, and NS-398. Moreover, ATRA reversed the translocation of Smad3 and Smad7 induced by TGF-β. Compared with the control, TGF-β also significantly enhanced proliferation and inhibited apoptosis of mesangial cells. ATRA dose-dependently inhibited TGF-β-induced cell proliferation, but had no significant effect on apoptosis in rat mesangial cells. Therefore, ATRA repressed COX-2, PGE2, and TXA2 via the TGF-β/Smad-signaling pathway and inhibited mesangial-cell proliferation, which might subsequently prevent renal fibrosis.

Topical application of phosphatidyl-inositol-3,5-bisphosphate for acute lung injury in neonatal swine

Hypoxemic respiratory failure of the neonatal organism involves increased acid sphingomyelinase (aSMase) activity and production of ceramide, a second messenger of a pro-inflammatory pathway that promotes increased vascular permeability, surfactant alterations and alveolar epithelial apoptosis. We comparatively assessed the benefits of topical aSMase inhibition by either imipramine (Imi) or phosphatidylinositol-3,5-bisphosphate (PIP2) when administered into the airways together with surfactant (S) for fortification. In this translational study, a triple-hit acute lung injury model was used that entails repeated airway lavage, injurious ventilation and tracheal lipopolysaccharide instillation in newborn piglets subject to mechanical ventilation for 72 hrs. After randomization, we administered an air bolus (control), S, S+Imi, or S+PIP2. Only in the latter two groups we observed significantly improved oxygenation and ventilation, dynamic compliance and pulmonary oedema. S+Imi caused systemic aSMase suppression and ceramide reduction, whereas the S+PIP2 effect remained compartmentalized in the airways because of the molecule's bulky structure. The surfactant surface tensions improved by S+Imi and S+PIP2 interventions, but only to a minor extent by S alone. S+PIP2 inhibited the migration of monocyte-derived macrophages and granulocytes into airways by the reduction of CD14/CD18 expression on cell membranes and the expression of epidermal growth factors (amphiregulin and TGF-β1) and interleukin-6 as pro-fibrotic factors. Finally we observed reduced alveolar epithelial apoptosis, which was most apparent in S+PIP2 lungs. Exogenous surfactant “fortified” by PIP2, a naturally occurring surfactant component, improves lung function by topical suppression of aSMase, providing a potential treatment concept for neonates with hypoxemic respiratory failure.

Arachidonoyl-phosphatidylcholine oscillates during the cell cycle and counteracts proliferation by suppressing Akt membrane binding

The activity of protein kinase B (Akt)--a major kinase promoting cell proliferation and survival--oscillates during the cell cycle. To investigate whether membrane phospholipids may regulate Akt phosphorylation and thus activity, we monitored the lipid profile of nocodazole-synchronized mouse NIH 3T3 fibroblasts during the cell cycle by liquid chromatography electrospray ionization tandem mass spectrometry (LC-MS/MS). The proportion of sn-2-arachidonoyl-phosphatidylcholine (20:4-PC) inversely correlated with Akt activity. Increasing the cellular ratio of 20:4-PC by supplementation of 20:4-PC to the cell culture medium diminished Akt [serine (Ser)473] phosphorylation. Saturated and monounsaturated phosphatidylcholines, used as control had no effect; 20:4-PC reduced cell proliferation relative to controls, interfered with S-phase transition, and suppressed Akt downstream signaling and cyclin expression like LY294002, which is a specific inhibitor of the phosphatidylinositol-3-kinase/Akt pathway. Additive effects of 20:4-PC and LY294002 were not observed, underlining the critical role of Akt for 20:4-PC signaling; 20:4-PC suppressed Akt membrane translocation as shown by immunofluorescence microscopy but left the concentration of the anchor lipid phosphatidylinositol-3,4,5-trisphosphate unchanged. An in vitro binding assay suggests that 20:4-PC attenuates the interaction of Akt with its membrane binding site. We conclude that 20:4-PC oscillates during the cell cycle and delays cell cycle progression by inhibiting Akt membrane binding.

uPAR and cathepsin B shRNA impedes TGF-β1-driven proliferation and invasion of meningioma cells in a XIAP-dependent pathway

Overexpression of transforming growth factor β1 (TGF-β1) has been linked to immune suppression, tumor angiogenesis, tumor cell migration, tumor cell survival, and tumor cell invasion in many cancers. In the present study, we found abundant expression of TGF-β1 in the microenvironment of four different pathological types of meningioma tumors. TGF-β1 induced invasion in malignant meningioma cells with an associated upregulation of urokinase-type plasminogen activator (uPA), uPAR, cathepsin B, and MMP-9, and this increase in proliferation was coupled with the expression of anti-apoptotic and pro-survival signaling molecules. In addition to the intense immunoreactivity of meningioma tumors to X-linked inhibitor to apoptosis (XIAP), its knockdown abolished the TGF-β1-induced proliferation of these cells. The stimulation of XIAP expression and the activation of pSMAD-2 is mediated by phosphatidylinositol 3-kinase (PI3K)- and MEK-dependent pathways, and the addition of anti-TGF-β1 antibodies prevented their expression with a consequent decrease in invasion. Bicistronic shRNA constructs targeting uPAR and cathepsin B (pUC) quenched TGF-β1-driven invasion and survival of meningioma cells by downregulation of XIAP and pSMAD-2 expression. Animal models with intracranial tumors showed elevated levels of TGF-β1, XIAP and pSMAD-2, and pUC treatment prevented this increased expression. Thus, targeted silencing of TGF-β1-induced signaling by pUC in meningioma would provide new treatment approaches for management of meningioma.

Deletion mutational analysis of BMRP, a pro-apoptotic protein that binds to Bcl-2

Bcl-2 is an anti-apoptotic member of the Bcl-2 family of proteins that protects cells from apoptosis induced by a large variety of stimuli. The protein BMRP (MRPL41) was identified as a Bcl-2 binding partner and shown to have pro-apoptotic activity. We have performed deletion mutational analyses to identify the domain(s) of Bcl-2 and BMRP that are involved in the Bcl-2/BMRP interaction, and the region(s) of BMRP that mediate its pro-apoptotic activity. The results of these studies indicate that both the BH4 domain of Bcl-2 and its central region encompassing its BH1, BH2, and BH3 domains are required for its interaction with BMRP. The loop region and the transmembrane domain of Bcl-2 were found to be dispensable for this interaction. The Bcl-2 deletion mutants that do not interact with BMRP were previously shown to be functionally inactive. Deletion analyses of the BMRP protein delimited the region of BMRP needed for its interaction with Bcl-2 to the amino-terminal two-thirds of the protein (amino acid residues 1-92). Further deletions at either end of the BMRP(1-92) truncated protein resulted in lack of binding to Bcl-2. Functional studies performed with BMRP deletion mutants suggest that the cell death-inducing domains of the protein reside mainly within its amino-terminal two-thirds. The region of BMRP required for the interaction with Bcl-2 is very relevant for the cell death-inducing activity of the protein, suggesting that one possible mechanism by which BMRP induces cell death is by binding to and blocking the anti-apoptotic activity of Bcl-2.

TGF-{beta}1 protects against mesangial cell apoptosis via induction of autophagy

Autophagy can lead to cell death in response to stress, but it can also act as a protective mechanism for cell survival. We show that TGF-β1 induces autophagy and protects glomerular mesangial cells from undergoing apoptosis during serum deprivation. Serum withdrawal rapidly induced autophagy within 1 h in mouse mesangial cells (MMC) as determined by increased microtubule-associated protein 1 light chain 3 (LC3) levels and punctate distribution of the autophagic vesicle-associated-form LC3-II. We demonstrate that after 1 h there was a time-dependent decrease in LC3 levels that was accompanied by induction of apoptosis, evidenced by increases in cleaved caspase 3. However, treatment with TGF-β1 resulted in induction of the autophagy protein LC3 while suppressing caspase 3 activation. TGF-β1 failed to rescue MMC from serum deprivation-induced apoptosis upon knockdown of LC3 by siRNA and in MMC from LC3 null (LC3(-/-)) mice. We show that TGF-β1 induced autophagy through TAK1 and Akt activation, and inhibition of PI3K-Akt pathway by LY294002 or dominant-negative Akt suppressed LC3 levels and enhanced caspase 3 activation. TGF-β1 also up-regulated cyclin D1 and E protein levels while down-regulating p27, thus stimulating cell cycle progression. Bafilomycin A1, but not MG132, blocked TGF-β1 down-regulation of p27, suggesting that p27 levels were regulated through autophagy. Taken together, our data indicate that TGF-β1 rescues MMC from serum deprivation-induced apoptosis via induction of autophagy through activation of the Akt pathway. The autophagic process may constitute an adaptive mechanism to glomerular injury by inhibiting apoptosis and promoting mesangial cell survival.

FOXA2 functions as a suppressor of tumor metastasis by inhibition of epithelial-to-mesenchymal transition in human lung cancers

The forkhead box transcription factor A2 (FOXA2) is an important regulator in animal development and body homeostasis. However, whether FOXA2 is involved in transforming growth factor β1 (TGF-β1)-mediated epithelial-to-mesenchymal transition (EMT) and tumor metastasis remains unknown. The present study showed that in human lung cancer cell lines, the abundance of FOXA2 positively correlates with epithelial phenotypes and negatively correlates with the mesenchymal phenotypes of cells, and TGF-β1 treatment decreased FOXA2 protein level. Consistently, knockdown of FOXA2 promoted EMT and invasion of lung cancer cells, whereas overexpression of FOXA2 reduced the invasion and suppressed TGF-β1-induced EMT. In addition, knockdown of FOXA2 induced slug expression, and ectopic expression of FOXA2 inhibited slug transcription. Furthermore, we identified that FOXA2 can bind to slug promoter through a conserved binding site, and that the DNA-binding region and transactivation region II of FOXA2 are required for repression of the slug promoter. These data demonstrate that FOXA2 functions as a suppressor of tumor metastasis by inhibition of EMT.

Nitric oxide suppresses transforming growth factor-beta1-induced epithelial-to-mesenchymal transition and apoptosis in mouse hepatocytes

Nitric oxide (NO) is a multifunctional regulator that is implicated in various physiological and pathological processes. Here we report that administration of NO donor S-nitroso-N-acetylpenicillamine (SNAP) inhibited transforming growth factor-beta1 (TGF-beta1)-induced epithelial-to-mesenchymal transition (EMT) and apoptosis in mouse hepatocytes. Overexpression of inducible NO synthase (iNOS) by transfection of the iNOS-expressing vector, which increased NO production, also inhibited the TGF-beta1-induced EMT and apoptosis in these cells. Treatment of cells with proinflammatory mediators, including tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and interferon (IFN)-gamma, which increased the endogenous NO production, produced the same inhibitory effect. Furthermore, exogenous NO donor SNAP treatment caused a decrease in the intracellular adenosine triphosphate (ATP) levels. Consistently, depletion of intracellular ATP by mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) inhibited the TGF-beta1-induced EMT and apoptosis, suggesting that an NO-induced decrease of ATP involved in the NO-mediated inhibition of TGF-beta1-induced EMT and apoptosis. NO and FCCP also inhibited TGF-beta1-induced STAT3 activation, suggesting that signal transducer and activator of transcription 3 inactivation is involved in the NO-induced effects on TGF-beta1-induced EMT and apoptosis.

CONCLUSION

Our study indicates that NO plays an important role in the inhibition of TGF-beta1-induced EMT and apoptosis in mouse hepatocytes through the downregulation of intracellular ATP levels. The data provide an insight into the in vivo mechanisms on the function of NO during the processes of both EMT and apoptosis.

Protein phosphatase 2A regulates life and death decisions via Akt in a context-dependent manner

Here, we show how targeting protein phosphatase 2A (PP2A), a key regulator of cellular protein phosphorylation, can either induce or prevent apoptosis depending on what other signals the cell is receiving. The oncoprotein polyoma small T interacts with PP2A to regulate survival. In the presence of growth factors, small T induces apoptosis. Akt activity, which usually promotes survival, is required for this death response, because inhibitors of Akt or PI3 kinase protect cells from death. The activation of Akt under these conditions is partial, characterized by T308 phosphorylation but not S473 phosphorylation. In the absence of growth factors, small T protects from cell death. Here, small T uses PP2A to promote phosphorylation of Akt on both T308 and S473. This effect results in a different pattern of phosphorylation of Akt substrates and shifts Akt from a proapoptotic (presence of growth factors) to an antiapoptotic mode (absence of growth factors). An intriguing possibility is that Akt phosphorylation could be therapeutically disregulated to decrease the survival of cancer cells.

Synergistic activation of extracellular signal-regulated kinase in human dermal fibroblasts by human telomerase reverse transcriptase and transforming growth factor-beta1

BACKGROUND

Human telomerase reverse transcriptase (hTERT) is primarily known for its ability to elongate telomeres for maintaining chromosomal integrity and delaying cellular senescence. Recently, hTERT has emerged as having a role in promoting cellular proliferation that is independent of telomere elongation. How hTERT elicits this novel function is a fundamental question in cell biology. Understanding this question may have therapeutic implications in regenerative medicine for patients with damaged organs or tissues, cardiovascular disorders, stroke, ischemic chronic wounds, and other ischemia-reperfusion injuries. Toward this end, we treated hTERT-transfected human dermal fibroblasts (HDFs) with transforming growth factor (TGF)-beta1 and investigated the activation of extracellular signal-regulated kinase (ERK) 1/2, vital mediators of cell proliferation.

MATERIALS AND METHODS

Primary HDFs were transfected with either recombinant adenovirus expressing hTERT (Ad-hTERT) or control adenovirus (Ad-NULL) and subsequently treated with TGF-beta1 (2 pg/mL). ERK 1/2 activation was determined by Western blotting using an antibody recognizing only activated ERK 1/2 that is dually phosphorylated at Thr(202) and Tyr(204). TGF-beta1, TGFbeta-RI, TGFbeta-RII, and Col1 A1 mRNA levels were analyzed by real-time PCR.

RESULTS

Ad-hTERT-transfected HDFs showed more than 7-fold up-regulation of phospho-ERK 1/2 over Ad-NULL-transfected HDFs upon TGF-beta1 treatment. The synergistic ERK 1/2 activation in Ad-hTERT-transfected HDFs occurred as early as 10 min and was sustained for at least 30 min after TGF-beta1 treatment. There were no statistically significant differences in TGF-beta1, TGFbeta-RI, TGFbeta-RII, and Col1 A1 mRNA levels between HDFs that were transfected with Ad-hTERT and those that were transfected with Ad-NULL after TGF-beta1 treatment.

CONCLUSIONS

hTERT and extremely low concentrations of TGF-beta1 (2 pg/mL) synergistically activate ERK 1/2 in HDFs by a mechanism that is independent of the autocrine TGF-beta1 loop.

TGF-beta1 and serum both stimulate contraction but differentially affect apoptosis in 3D collagen gels

Apoptosis of fibroblasts may be key for the removal of cells following repair processes. Contraction of three-dimensional collagen gels is a model of wound healing and remodeling. Here two potent inducers of contraction, TGF-β1 and fetal calf serum (FCS) were evaluated for their effect on fibroblast apoptosis in contracting collagen gels. Human fetal lung fibroblasts were cultured in floating type I collagen gels, exposed to TGF-β1 or FCS, and allowed to contract for 5 days. Apoptosis was evaluated using TUNEL and confirmed by DNA content profiling. Both TGF-β1 and serum significantly augmented collagen gel contraction. TGF-β1 also increased apoptosis assessed by TUNEL positivity and DNA content analysis. In contrast, serum did not affect apoptosis. TGF-β1 induction of apoptosis was associated with augmented expression of Bax, a pro-apoptotic member of the Bax/Bcl-2 family, inhibition of Bcl-2, an anti-apoptotic member of the same family, and inhibition of both cIAP-1 and XIAP, two inhibitors of the caspase cascade. Serum was associated with an increase in cIAP-1 and Bcl-2, anti-apoptotic proteins. Interestingly, serum was also associated with an apparent increase in Bax, a pro-apoptotic protein. Blockade of Smad3 with either siRNA or by using murine fibroblasts deficient in Smad3 resulted in a lack of TGF-β induction of augmented contraction and apoptosis. Contraction induced by different factors, therefore, may be differentially associated with apoptosis, which may be related to the persistence or resolution of the fibroblasts that accumulate following injury.

KL-6, a human MUC1 mucin, promotes proliferation and survival of lung fibroblasts

The serum level of KL-6, a MUC1 mucin, is a clinically useful marker for various interstitial lung diseases. Previous studies demonstrated that KL-6 promotes chemotaxis of human fibroblasts. However, the pathophysiological role of KL-6 remains poorly understood. Here, we further investigate the functional aspects of KL-6 in proliferation and apoptosis of lung fibroblasts. KL-6 accelerated the proliferation and inhibited the apoptosis of all human lung fibroblasts examined. An anti-KL-6 monoclonal antibody counteracted both of these effects induced by KL-6 on human lung fibroblasts. The pro-fibroproliferative and anti-apoptotic effects of KL-6 are greater than and additive to those of the maximum effective concentrations of platelet-derived growth factor, basic fibroblast growth factor, and transforming growth factor-beta. These findings indicate that increased levels of KL-6 in the epithelial lining fluid may stimulate fibrotic processes in interstitial lung diseases and raise the possibility of applying an anti-KL-6 antibody to treat interstitial lung diseases.

The modulation of apoptosis by cyclic AMP involves Akt and epidermal growth factor receptor

Adenosine 3',5'-cyclic monophosphate (cAMP) and transforming growth factor-beta are important regulators of many biological processes. In this study we investigated the effect and its potential mechanism of cAMP on transforming growth factor-beta1- and serum deprivation-induced apoptosis in Mv1Lu cells. Transforming growth factor-beta1 treatment or serum deprivation induces apoptotic response in Mv1Lu cells. Forskolin, a cAMP-elevating agent, or 8-Bromo-cAMP (8-B-cAMP), a cell permeable cAMP analogue, inhibited the cell proliferation and markedly enhanced apoptosis induced by transforming growth factor-beta1, but completely suppressed serum deprivation-induced apoptosis. Furthermore, forskolin decreased the Akt phosphorylation, and the inhibition of phosphatidylinositol-3 kinase by LY294002 sensitized Mv1Lu cells to transforming growth factor-beta1-induced apoptosis. In addition, forskolin treatment induced tyrosine phosphorylation of epidermal growth factor receptor. Inhibition of epidermal growth factor receptor by specific inhibitor PD153035 blocked the cAMP-mediated suppression of serum deprivation-induced apoptosis. The results indicate that cAMP exerts its opposite effects in transforming growth factor-beta1- and serum deprivation-induced apoptosis via a mechanism involving the modulation of signaling components of phosphatidylinositol-3-kinase/Akt and epidermal growth factor receptor in Mv1Lu cells.

Activation of ERK and p38 kinase mediated keloid fibroblast apoptosis after flashlamp pulsed-dye laser treatment

BACKGROUND AND OBJECTIVES

Flashlamp pulsed-dye lasers (PDLs) revealed effective regression or arrest in patients with keloids in our clinical studies [Kuo YR et al., Laser Surg Med 2004;34:104-108]. In this study, we further investigated whether the induction of keloid regression seen with PDL treatment through activation in mitogen-activated protein (MAP) kinase and caspase promotes cell apoptosis and reduces fibroblast proliferation.

STUDY DESIGN/MATERIALS AND METHODS

Keloid tissues were obtained from 10 patients with intralesional or punch biopsies prior to and 7 days after PDL treatments [fluence per pulse was 10-18 J/cm2 (mean 14 J/cm2)]. Prior to and after PDL treatments, the proliferating fibroblasts in keloid tissue were immunohistochemically detected by proliferating cell nuclear antigen (PCNA) expression. The apoptotic cell was detected by terminal deoxynucleotidyl transferase dUTP-nick end labeling (TUNEL) staining and fragmented caspase-3 expression. MAP kinase activation as represented by extracellular signal-regulated kinase (ERK), p38 kinase (p38), and c-Jun N-terminal kinase (JNK) expression of keloid tissues was investigated by immunohistochemical (IHC) staining, respectively.

RESULTS

IHC staining indicated that PCNA expression of fibroblasts was significantly reduced in keloid tissue after PDL irradiation. TUNEL assay revealed lower apoptotic cells expression in the keloid tissue prior to laser treatment. Following laser treatment, apoptotic cells with relatively strong DNA damage and fragmentation were seen in all keloid biopsy samples, especially in the keloid fibroblast population. The activation of ERK and p38 MAP kinase increased significantly in keloid tissue after PDL treatment. JNK was shown to be unchanged.

CONCLUSIONS

The PDL treatment is shown to induce keloid regression through suppression of keloid fibroblast proliferation, induction of apoptosis, and upregulation of ERK and p38 MAP kinase activity.

Caspase-dependent apoptosis and -independent poly(ADP-ribose) polymerase cleavage induced by transforming growth factor beta1

Apoptosis is an important cell suicide program which involves the caspases activation and is implicated in physiological and pathological processes. Poly(ADP-ribose) polymerase (PARP) cleavage is often associated with apoptosis and has been served as one hallmark of apoptosis and caspase activation. In this study, we aimed to determine TGF-beta1-induced apoptosis and to examine the involvement of caspases and its relationship with PARP cleavage. TGF-beta1 induces strong apoptosis of AML-12 cells which can be detected by DNA fragmentation, FACS, and morphological assays. Z-VAD-fmk, a selective caspase inhibitor, partially inhibits the TGF-beta1-induced apoptosis; but has no effect on TGF-beta1-induced DNA fragmentation and PARP cleavage. However, BD-fmk, a broad-spectrum caspase inhibitor, completely suppresses TGF-beta1-induced apoptosis, but unexpectedly does not inhibit TGF-beta1-induced PARP cleavage. Furthermore, Z-VAD-fmk treatment is able to completely inhibit the daunorubicin-induced apoptosis in A-431 cells, but only slightly blocks the daunorubicin-induced PARP cleavage, whereas BD-fmk can inhibit both daunorubicin-induced apoptosis and PARP cleavage completely. In addition, we observed that both TGF-beta1-induced apoptosis and PARP degradation in AML-12 cells can be completely blocked by inhibiting the protein synthesis with cycloheximide. These results demonstrate for the first time that TGF-beta1-induced caspase-dependent apoptosis is associated with caspase-independent PARP cleavage that requires the TGF-beta1-induced synthesis of new proteins. The results indicate that caspase-3 is not a major caspase involved in TGF-beta1-induced apoptosis in AML-12 cells, and is not required for apoptosis-associated DNA fragmentation. The results also suggest that PARP cleavage may occur as an independent event that can be disassociated with cell apoptosis.