Involvement of cell-cell interactions in the rapid stimulation of Cas tyrosine phosphorylation and Src kinase activity by transforming growth factor-beta 1

c-Src Suppresses Dendritic Cell Antitumor Activity via T Cell Ig and Mucin Protein-3 Receptor

The enhanced expression of T cell Ig and mucin protein-3 (TIM-3) on tumor-associated dendritic cells (DCs) attenuates antitumor effects of DNA vaccines. To identify a potential target (or targets) for reducing TIM-3 expression on tumor-associated DCs, we explored the molecular mechanisms regulating TIM-3 expression. In this study, we have identified a novel signaling pathway (c-Src→Bruton's tyrosine kinase→transcription factors Ets1, Ets2, USF1, and USF2) necessary for TIM-3 upregulation on DCs. Both IL-10 and TGF-β, which are produced in the tumor microenvironment, upregulated TIM-3 expression on DCs via this pathway. Suppressed expression of c-Src or downstream Bruton's tyrosine kinase, Ets1, Ets2, USF1, or USF2 blocked IL-10- and TGF-β-induced TIM-3 upregulation on DCs. Notably, in vivo knockdown of c-Src in mice reduced TIM-3 expression on tumor-associated DCs. Furthermore, adoptive transfer of c-Src-silenced DCs in mouse tumors enhanced the in vivo antitumor effects of immunostimulatory CpG DNA; however, TIM-3 overexpression in c-Src-silenced DCs blocked this effect. Collectively, our data reveal the molecular mechanism regulating TIM-3 expression in DCs and identify c-Src as a target for improving the efficacy of nucleic acid-mediated anticancer therapy.

AFAP1 Is a Novel Downstream Mediator of TGF-β1 for CCN2 Induction in Osteoblasts

Background

CCN2 acts as an anabolic growth factor to regulate osteoblast differentiation and function. CCN2 is induced by TGF-β1 and acts as a mediator of TGF-β1 induced matrix production in osteoblasts and Src is required for CCN2 induction by TGF-β1; however, the molecular mechanisms that control CCN2 induction in osteoblasts are poorly understood. AFAP1 binds activated forms of Src and can direct the activation of Src in certain cell types, however a role for AFAP1 downstream of TGF-β1 or in osteoblats is undefined. In this study, we investigated the role of AFAP1 for CCN2 induction by TGF-β1 in primary osteoblasts.

Results

We demonstrated that AFAP1 expression in osteoblasts occurs in a biphasic pattern with maximal expression levels occurring during osteoblast proliferation (~day 3), reduced expression during matrix production/maturation (~day 14–21), an a further increase in expression during mineralization (~day 21). AFAP1 expression is induced by TGF-β1 treatment in osteoblasts during days 7, 14 and 21. In osteoblasts, AFAP1 binds to Src and is required for Src activation by TGF-β1 and CCN2 promoter activity and protein induction by TGF-β1 treatment was impaired using AFAP1 siRNA, indicating the requirement of AFAP1 for CCN2 induction by TGF-β1. We also demonstrated that TGF-β1 induction of extracellular matrix protein collagen XIIa occurs in an AFAP1 dependent fashion.

Conclusions

This study demonstrates that AFAP1 is an essential downstream signaling component of TGF-β1 for Src activation, CCN2 induction and collagen XIIa in osteoblasts.

XB130-A Novel Adaptor Protein: Gene, Function, and Roles in Tumorigenesis

Several adaptor proteins have previously been shown to play an important role in the promotion of tumourigenesis. XB130 (AFAP1L2) is an adaptor protein involved in many cellular functions, such as cell survival, cell proliferation, migration, and gene and miRNA expression. XB130's functional domains and motifs enable its interaction with a multitude of proteins involved in several different signaling pathways. As a tyrosine kinase substrate, tyrosine phosphorylated XB130 associates with the p85 α regulatory subunit of phosphoinositol-3-kinase (PI3K) and subsequently affects Akt activity and its downstream signalling. Tumourigenesis studies show that downregulation of XB130 expression by RNAi inhibits tumor growth in mouse xenograft models. Furthermore, XB130 affects tumor oncogenicity by regulating the expression of specific tumour suppressing miRNAs. The expression level and pattern of XB130 has been studied in various human tumors, such as thyroid, esophageal, and gastric cancers, as well as, soft tissue tumors. Studies show the significant effects of XB130 in tumourigenesis and suggest its potential as a diagnostic biomarker and therapeutic target for cancer treatments.

Apigenin inhibits TGF-β-induced VEGF expression in human prostate carcinoma cells via a Smad2/3- and Src-dependent mechanism

Cancer progression relies on establishment of the blood supply necessary for tumor growth and ultimately metastasis. Prostate cancer mortality is primarily attributed to development of metastases rather than primary, organ-confined disease. Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis in prostate tissue. Our previous studies have demonstrated that the chemopreventive bioflavonoid apigenin inhibited hypoxia-induced elevation of VEGF production at low oxygen conditions characteristic for solid tumors. Low oxygen (hypoxia) and transforming growth factor-β (TGF-β) are two major factors responsible for increased VEGF secretion. In the present study, experiments were performed to investigate the inhibitory effect of apigenin on TGF-β-induced VEGF production and the mechanisms underlying this action. Our results demonstrate that VEGF expression is induced by TGF-β1 in human prostate cancer PC3-M and LNCaP C4-2B cells, and treatment with apigenin markedly decreased VEGF production. Additionally, apigenin inhibited TGF-β1-induced phosphorylation and nuclear translocation of Smad2 and Smad3. Further experiments demonstrated that specific transient knockdown of Smad2 or Smad3 blunted apigenin's effect on VEGF expression. We also found that apigenin inhibited Src, FAK, and Akt phosphorylation in PC3-M and LNCaP C4-2B cells. Furthermore, constitutively active Src reversed the inhibitory effect of apigenin on VEGF expression and Smad2/3 phosphorylation. Taken together, our results suggest that apigenin inhibits prostate carcinogenesis by modulating TGF-β-activated pathways linked to cancer progression and metastases, in particular the Smad2/3 and Src/FAK/Akt pathways. These findings provide new insights into molecular pathways targeted by apigenin, and reveal a novel molecular mechanism underlying the antiangiogenic potential of apigenin.

p130Cas, Crk-associated substrate plays essential roles in liver development by regulating sinusoidal endothelial cell fenestration

p130Cas, Crk-associated substrate (Cas), is an adaptor/scaffold protein that plays a central role in actin cytoskeletal reorganization. We previously showed that mice in which Cas was deleted (Cas(-/-)) died in utero because of early cardiovascular maldevelopment. To further investigate the in vivo roles of Cas, we generated mice with a hypomorphic Cas allele lacking the exon 2-derived region (Cas(Deltaex2/Deltaex2)), which encodes Src homology domain 3 (SH3) of Cas. Cas(Deltaex2/Deltaex2) mice again died as embryos, but they particularly showed progressive liver degeneration with hepatocyte apoptosis. Because Cas expression in the liver is preferentially detected in sinusoidal endothelial cells (SECs), the observed hepatocyte apoptosis was most likely ascribable to impaired function of SECs. To address this possibility, we stably introduced a Cas mutant lacking the SH3 domain (Cas DeltaSH3) into an SEC line (NP31). Intriguingly, the introduction of Cas DeltaSH3 induced a loss of fenestrae, the characteristic cell-penetrating pores in SECs that serve as a critical route for supplying oxygen and nutrients to hepatocytes. The disappearance of fenestrae in Cas DeltaSH3-expressing cells was associated with an attenuation of actin stress fiber formation, a marked reduction in tyrosine phosphorylation of Cas, and defective binding of Cas to CrkII.

CONCLUSION

Cas plays pivotal roles in liver development through the reorganization of the actin cytoskeleton and formation of fenestrae in SECs.

Src is a major signaling component for CTGF induction by TGF-beta1 in osteoblasts

Connective tissue growth factor (CTGF/CCN2) is induced by transforming growth factor beta1 (TGF-beta1) where it acts as a downstream mediator of TGF-beta1 induced matrix production in osteoblasts. We have shown the requirement of Src, Erk, and Smad signaling for CTGF induction by TGF-beta1 in osteoblasts; however, the potential interaction among these signaling pathways remains undetermined. In this study we demonstrate that TGF-beta1 activates Src kinase in ROS17/2.8 cells and that treatment with the Src family kinase inhibitor PP2 prevents Src activation and CTGF induction by TGF-beta1. Additionally, inhibiting Src activation prevented Erk activation, Smads 2 and 3 activation and nuclear translocation by TGF-beta1, demonstrating that Src is an essential upstream signaling partner of both Erk and Smads in osteoblasts. MAPKs such as Erk can modulate the Smad pathway directly by mediating the phosphorylation of Smads or indirectly through activation/inactivation of required nuclear co-activators that mediate Smad DNA binding. When we treated cells with the Erk inhibitor, PD98059, it inhibited TGF-beta1-induced CTGF protein expression but had no effect on Src activation, Smad activation or Smad nuclear translocation. However PD98059 impaired transcriptional complex formation on the Smad binding element (SBE) of the CTGF promoter, demonstrating that Erk activation was required for SBE transactivation. These data demonstrate that Src is an essential upstream signaling transducer of Erk and Smad signaling with respect to TGF-beta1 in osteoblasts and that Smads and Erk function independently but are both essential for forming a transcriptionally active complex on the CTGF promoter in osteoblasts.

PAI-1 mediates the TGF-beta1+EGF-induced "scatter" response in transformed human keratinocytes

Cooperative interactions between growth factor signaling pathways are important elements in carcinoma progression. A model system combining transforming growth factor-beta1 (TGF-beta1) and EGF was developed to investigate mechanisms underlying induced epithelial-to-mesenchymal transition (EMT) in ras-transformed human (HaCaT II-4) keratinocytes. Dual stimulation with TGF-beta1+EGF resulted in keratinocyte "plasticity" and pronounced colony dispersal. The most highly expressed transcript, identified by mRNA profiling, encoded plasminogen activator inhibitor-1 (PAI-1; SERPINE1). PAI-1 negatively regulates plasmin-dependent matrix degradation, preserving a stromal scaffold permissive for keratinocyte motility. Mitogen-activated extracellular kinase (MEK)/extracellular signal-regulated kinase (ERK) and p38 signaling were required for maximal PAI-1 upregulation and TGF-beta1+EGF-stimulated cell locomotion, as pharmacologic disruption of MEK/p38 activity ablated both responses. Moreover, PAI-1 knockdown alone effectively inhibited TGF-beta1+EGF-dependent cell scattering, indicating a functional role for this SERPIN in the dual-growth factor model of induced motility. Moreover, EGFR signaling blockade or EGFR knockdown attenuated TGF-beta1-induced PAI-1 expression, implicating EGFR transactivation in TGF-beta1-stimulated PAI-1 expression, and reduced colony dispersal in TGF-beta1+EGF-treated cultures. Identification of such cooperative signaling networks and their effect on specific invasion-promoting target genes, such as PAI-1, may lead to the development of pathway-specific therapeutics that affect late-stage events in human tumor progression.

Targeting the transforming growth factor-beta signaling pathway in human cancer

The transforming growth factor-ss (TGF-beta) signaling pathway plays a pivotal role in diverse cellular processes. TGF-beta switches its role from a tumor suppressor in normal or dysplastic cells to a tumor promoter in advanced cancers. It is widely believed that the Smad-dependent pathway is involved in TGF-beta tumor-suppressive functions, whereas activation of Smad-independent pathways, coupled with the loss of tumor-suppressor functions of TGF-beta, is important for its pro-oncogenic functions. TGF-beta signaling has been considered a useful therapeutic target. The discovery of oncogenic actions of TGF-beta has generated a great deal of enthusiasm for developing TGF-beta signaling inhibitors for the treatment of cancer. The challenge is to identify the group of patients where targeted tumors are not only refractory to TGF-beta-induced tumor suppressor functions but also responsive to the tumor-promoting effects of TGF-beta. TGF-beta pathway inhibitors, including small and large molecules, have now entered clinical trials. Preclinical studies with these inhibitors have shown promise in a variety of different tumor models. Here, we focus on the mechanisms of signaling and specific targets of the TGF-beta pathway that are critical effectors of tumor progression and invasion. This report also examines the therapeutic intervention of TGF-ss signaling in human cancers.

PAI-1 Regulates the Invasive Phenotype in Human Cutaneous Squamous Cell Carcinoma

The emergence of highly aggressive subtypes of human cutaneous squamous cell carcinoma (SCC) often reflects increased autocrine/paracrine TGF-beta synthesis and epidermal growth factor receptor (EGFR) amplification. Cooperative TGF-beta/EGFR signaling promotes cell migration and induces expression of both proteases and protease inhibitors that regulate stromal remodeling resulting in the acquisition of an invasive phenotype. In one physiologically relevant model of human cutaneous SCC progression, TGF-beta1+EGF stimulation increases the production of several matrix metalloproteinases (MMPs), among the most prominent of which is MMP-10-an MMP known to be elevated in SCC in situ. Activation of stromal plasminogen appears to be critical in triggering downstream MMP activity. Paradoxically, PAI-1, the major physiological inhibitor of plasmin generation, is also upregulated under these conditions and is an early event in progression of incipient epidermal SCC. One testable hypothesis proposes that TGF-beta1+EGF-dependent MMP-10 elevation directs focalized matrix remodeling events that promote epithelial cell plasticity and tissue invasion. Increased PAI-1 expression serves to temporally and spatially modulate plasmin-initiated pericellular proteolysis, further facilitating epithelial invasive potential. Defining the complex signaling and transcriptional mechanisms that maintain this delicate balance is critical to developing targeted therapeutics for the treatment of human cutaneous malignancies.

Crk and CrkL adaptor proteins: networks for physiological and pathological signaling

The Crk adaptor proteins (Crk and CrkL) constitute an integral part of a network of essential signal transduction pathways in humans and other organisms that act as major convergence points in tyrosine kinase signaling. Crk proteins integrate signals from a wide variety of sources, including growth factors, extracellular matrix molecules, bacterial pathogens, and apoptotic cells. Mounting evidence indicates that dysregulation of Crk proteins is associated with human diseases, including cancer and susceptibility to pathogen infections. Recent structural work has identified new and unusual insights into the regulation of Crk proteins, providing a rationale for how Crk can sense diverse signals and produce a myriad of biological responses.

Molecular requirements for induction of CTGF expression by TGF-beta1 in primary osteoblasts

Connective tissue growth factor (CTGF/CCN2) is a cysteine rich, extracellular matrix protein that acts as an anabolic growth factor to regulate osteoblast differentiation and function. In osteoblasts, CTGF is induced by TGF-beta1 where it acts as a downstream mediator of TGF-beta1 induced matrix production. The molecular mechanisms that control CTGF induction by TGF-beta1 in osteoblasts are not known. To assess the role of individual Smads in mediating the induction of CTGF by TGF-beta1, we used specific Smad siRNAs to block Smad expression. These studies demonstrated that Smads 3 and 4, but not Smad 2, are required for TGF-beta1 induced CTGF promoter activity and expression in osteoblasts. Since the activation of MAPKs (Erk, Jnk and p38) by TGF-beta1 is cell type specific, we were interested in determining the role of individual MAPKs in TGF-beta1 induction of CTGF promoter activity and expression. Using dominant negative (DN) mutants for Erk, Jnk and p38, we demonstrated that the expression of DN-Erk caused a significant inhibition of TGF-beta1 induced CTGF promoter activity. In contrast, the expression of DN-p38 or DN-Jnk failed to inhibit activation of CTGF promoter activity. To confirm the vital role of Erk, we used the Erk inhibitor (PD98059) to block its activation, demonstrating that it prevented TGF-beta1 activation of the CTGF promoter and up-regulation of CTGF expression in osteoblasts. Since Src can also act as a downstream signaling effector for TGF-beta in some cell types, we determined its role in TGF-beta1 induction of CTGF in osteoblasts. Treatment of osteoblasts with a Src family kinase inhibitor, PP2, or the expression of two independent kinase-dead Src mutant constructs caused significant inhibition of TGF-beta1 induced CTGF promoter activity and expression. Additionally, blocking Src activation prevented Erk activation by TGF-beta1 demonstrating a role for Src as an upstream mediator of Erk in regulating CTGF expression in osteoblasts. To investigate the involvement of the TGF-beta1 response element (TRE) and the SMAD binding element (SBE) in CTGF induction, we cloned the rat CTGF proximal promoter (-787 to +1) containing the TRE and SBE motifs into a pGL3-Luciferase reporter construct. Using a combination of CTGF promoter deletion constructs and site-directed mutants, we demonstrated the unique requirement of both the TRE and SBE for CTGF induction by TGF-beta1 in osteoblasts. Electro-mobility shift assays using specific probes containing the TRE, SBE or both showed TGF-beta1 inducible complexes that can be ablated by mutation of the respective motif, confirming their requirement for TGF-beta1 induced CTGF promoter activity. In conclusion, these studies demonstrate that CTGF induction by TGF-beta1 in osteoblasts involves Smads 3 and 4, the Erk and Src signaling pathways, and requires both the TRE and SBE motifs in the CTGF proximal promoter.

Ligand release-independent transactivation of epidermal growth factor receptor by transforming growth factor-beta involves multiple signaling pathways

Many of the signaling responses induced by transforming growth factor-beta (TGF-beta) are mediated by Smad proteins, but there is evidence that it can also signal independently of Smads. Here, we provide evidence that multiple signal pathways induced by TGF-beta1-including Src family tyrosine kinases (SFKs), generation of reactive oxygen species (ROS), de novo protein synthesis and E-cadherin-dependent cell-cell interactions-transactivate the epidermal growth factor receptor (EGFR), which in turn regulates expression of c-Fos and c-Jun. Immunoprecipitation and immunofluorescence staining showed that EGFR was phosphorylated on tyrosine in response to TGF-beta1. EGFR transactivation required the activation of SFKs and the production of ROS via NADPH oxidase, but was not dependent on metalloproteases or the release of EGF-like ligands. In addition, the production of ROS was dependent on signaling by specific SFKs as well as de novo protein synthesis. Stable transfection of E-cadherin into MDA-MB-231 cells as well as E-cadherin-blocking assays revealed that E-cadherin-mediated cell-cell interactions were also essential for EGFR transactivation. Finally, EGFR transactivation was involved in the expression of c-Fos and c-Jun via the extracellular signal-regulated kinase signaling cascade. Taken together our data suggest that ligand release-independent transactivation of EGFR may diversify early TGF-beta signaling and represent a novel pathway leading to TGF-beta-mediated gene expression.

XB130, a Novel Adaptor Protein for Signal Transduction

Adaptor proteins are important mediators in signal transduction. In the present study, we report the cloning and characterization of a novel adaptor protein, XB130. This gene is located on human chromosome 10q25.3 and encodes a protein of 818 amino acids. It contains several Src homology (SH)2- and SH3-binding motifs, two pleckstrin homology domains, a coiled-coil region, and a number of potential tyrosine or serine/threonine phosphorylation sites. Endogenous XB130 interacts with c-Src tyrosine kinase. Their co-expression in COS-7 cells resulted in activation of c-Src and elevated tyrosine phosphorylation of multiple proteins, including XB130 itself. XB130 expression in HEK293 cells enhanced serum response element- and AP-1-dependent transcriptional activation mediated by c-Src. XB130DeltaN, an N-terminal deletion mutant lacking a putative SH3-binding motif and several putative SH2-binding sites, reduced its ability to mediate Src signal transduction. Down-regulation of endogenous XB130 with siRNA reduced c-Src activity, IL-8 production, EGF-induced phosphorylation of Akt and GSK3beta, and altered cell cycles in human lung epithelial cells. These data suggest that XB130 as an adaptor may play an important role in the regulation of signal transduction and cellular functions.

Vanadate-induced activation of cytosolic phospholipase A2α in L929 cells: Roles of tyrosine kinase, protein kinase C, and extracellular signal-regulated kinase

Orthovanadate (Na3VO4), which acts as an inhibitor of protein tyrosine phosphatases, has a various pharmacological effects including the release of arachidonic acid (AA) from cells. We investigated roles of alpha-type cytosolic phospholipase A2 (cPLA2alpha), Src family kinases (Src) and protein kinase C (PKC) in the release of AA induced by Na3VO4 from a murine fibroblast cell line, L929. C12 cells, a variant of L929 that lacks expression of cPLA2alpha, were used along with a clone of C12 cells that are stably expressing cPLA2alpha (C12-cPLA2alpha cells). In the presence of a Ca2+ ionophore (10 microM A23187), 5 and 10mM Na3VO4 synergistically stimulated AA release from L929 and C12-cPLA2alpha cells, and to a much lesser extent from control C12 cells. The release of AA by Na3VO4/A23187 was inhibited by a selective cPLA2alpha inhibitor (3 microM pyrrophenone). The release of AA by Na3VO4/A23187 was significantly inhibited by a PKC inhibitor (10 microM GF109203X), in PKC-depleted cells, by a Src inhibitor (2 microM PP2) and by an inhibitor of extracellular signal-regulated kinase 1/2 (ERK1/2) kinase (10 microM U0126). The phosphorylation of ERK1/2 was stimulated by Na3VO4, and the response was significantly decreased by inhibitors of Src, PKC and ERK1/2 kinase. Our data show that Na3VO4 stimulates AA release largely via cPLA2alpha activation in Ca2+-dependent manner, and the cross-talk between Src and PKC and the ERK-dependent pathways are involved in Na3VO4-induced AA release from L929 cells.

Molecular mechanism of adaphostin-mediated G1 arrest in prostate cancer (PC-3) cells: signaling events mediated by hepatocyte growth factor receptor, c-Met, and p38 MAPK pathways

Adaphostin (NSC680410), a small molecule congener of tyrphostin AG957, has been demonstrated previously to have significant anti-proliferative effects in several leukemia models. However, this effect of adaphostin in adherent cells/solid tumor models has not been examined. In this study, we investigated the anti-proliferative effects of adaphostin in the human prostate cancer cell line PC-3. Specifically, we explored the potential molecular mechanism(s) by which adaphostin elicits its anti-proliferative effect(s). We demonstrate that adaphostin inhibits the proliferation of PC-3 cells by inducing a G(1) phase cell cycle arrest. This adaphostin-induced G(1) arrest was associated with an increase in the expression of p21 and p27 and a decrease in the expression of G(1)-specific cyclins (cyclin A, D1, and D3) and cyclin-dependent kinases 4 and 6. Consequently, a dramatic decrease in the phosphorylation of retinoblastoma protein was also observed. Additionally, we found that adaphostin treatment induced a decrease in the phosphorylation of nucleophosmin, a major nuclear phosphoprotein, and that this decreased phosphorylation was a result of the p21- and p27-mediated inactivation of cyclin E-cyclin-dependent kinase 2 complex kinase activity. Furthermore, we have determined that the adaphostin-mediated cell cycle arrest of PC-3 cells is dependent upon activation of the p38 MAPK. We also demonstrate that the hepatocyte growth factor receptor-c-Met is involved in the adaphostin-mediated signaling events that regulate p38 MAPK. Taken together, these results identify for the first time a signaling cascade of adaphostin-mediated G(1) phase-specific cell cycle arrest in PC-3 cells. These findings suggest that the tyrphostin member has a broader spectrum of activity than originally predicted.

Hydrogen peroxide-induced arachidonic acid release in L929 cells; roles of Src, protein kinase C and cytosolic phospholipase A2α

Hydrogen peroxide (H(2)O(2)) stimulates the release of arachidonic acid from cells, but the signaling mechanism(s) involved remains to be elucidated. We investigated the roles of alpha-type cytosolic phospholipase A(2) (cPLA(2)alpha), Src family kinases (Src) and protein kinase C (PKC) in the release of arachidonic acid from L929 cells (a murine fibroblast cell line), C12 cells (a variant of L929 that lacks cPLA(2)alpha) and a stable clone of C12 cells expressing cPLA(2)alpha (C12-cPLA(2)alpha cells). In the presence of 10 muM A23187, 100 nM phorbol myristate acetate (PMA) and 1 mM H(2)O(2) synergistically stimulated arachidonic acid release from L929 cells and C12-cPLA(2)alpha cells, and to a much lesser extent from C12 cells. The reagents alone and co-treatment with PMA and H(2)O(2) without A23187 had marginal effects. No arachidonic acid was released by PMA/A23187 or H(2)O(2)/A23187 in CaCl(2)-free buffer and the release was inhibited by a selective cPLA(2)alpha inhibitor (3 microM pyrrophenone). Addition of 10 microM H(2)O(2), which did not stimulate arachidonic acid release with A23187, enhanced the response to PMA/A23187. The release induced by PMA/A23187 and by H(2)O(2)/A23187 was significantly inhibited by a PKC inhibitor (10 microM GF109203X) and in PKC-depleted cells, and by a Src inhibitor (2 microM PP2). The phosphorylation of extracellular signal-regulated kinase 1/2 induced by PMA/A23187 and H(2)O(2)/A23187 was significantly decreased by inhibitors of PKC and Src. These findings suggest that H(2)O(2) with Ca(2+) stimulates arachidonic acid release via cPLA(2)alpha in a Src- and PKC-dependent manner in L929 cells. The role of cross-talk between Src and PKC in arachidonic acid release is discussed.

Transforming growth factor beta induces rosettes of podosomes in primary aortic endothelial cells

Cytoskeletal rearrangements are central to endothelial cell physiology and are controlled by soluble factors, matrix proteins, cell-cell interactions, and mechanical forces. We previously reported that aortic endothelial cells can rearrange their cytoskeletons into complex actin-based structures called podosomes when a constitutively active mutant of Cdc42 is expressed. We now report that transforming growth factor beta (TGF-beta) promotes podosome formation in primary aortic endothelial cells. TGF-beta-induced podosomes assembled together into large ring- or crescent-shaped structures. Their formation was dependent on protein synthesis and required functional Src, phosphatidylinositide 3-kinase, Cdc42, RhoA, and Smad signaling. MT1-MMP and metalloprotease 9 (MMP9), both upregulated by TGF-beta, were detected at sites of podosome formation, and MT1-MMP was found to be involved in the local degradation of extracellular matrix proteins beneath the podosomes and required for the invasion of collagen gels by endothelial cells. We propose that TGF-beta plays an important role in endothelial cell physiology by inducing the formation of podosomal structures endowed with metalloprotease activity that may contribute to arterial remodeling.

TGF-beta 1-induced PAI-1 expression is E box/USF-dependent and requires EGFR signaling

Transforming growth factor-beta1 (TGF-beta1) transcriptionally regulates the expression of genes that encode specific proteins (e.g., plasminogen activator inhibitor-1; PAI-1) important in stromal remodeling and cellular invasion. Definition of molecular events underlying TGF-beta1-initiated PAI-1 transcription, therefore, may lead to the identification of new therapeutic targets for diseases associated with elevated PAI-1 synthesis (e.g., tissue fibrosis, vascular disorders, tumor progression). An intact upstream stimulatory factor (USF)-binding E box motif (5'-(-165)CACGTG(-160)-3') at the HRE-2 site in the rat PAI-1 gene was required for PAI-1 transcription in TGF-beta1-treated cells. Mutation of the CA dinucleotide to TC at position -165/-164 in a reporter construct driven by 764 bp of PAI-1 promoter sequence decreased TGF-beta1-dependent CAT activity by >80% indicating the necessity for a consensus hexanucleotide E box motif in induced expression. The same CA --> TC substitution eliminated USF binding to an 18-bp HRE-2 DNA target highlighting the importance of site occupancy to transcriptional activation. Transfection of a dominant-negative USF construct, moreover, completely inhibited formation of USF/HRE-2 probe complexes, attenuated PAI-1 promoter-driven luciferase activity and reduced the response of the endogenous PAI-1 gene to TGF-beta1 (to that approximating quiescent controls). Maximal immediate-early PAI-1 induction upon exposure to TGF-beta1 required EGFR, p21ras, MEK and pp60(c-src) signaling as pharmacologic or dominant-negative inhibition of any of the four intermediates (EGFR, p21ras, MEK, pp60(c-src)) virtually eliminated TGF-beta1-augmented PAI-1 levels. U0126 titering experiments, furthermore, revealed that the same MEK inhibitor concentration that blocked the TGF-beta1 increase in ERK1/2 phosphorylation (20 microM) also effectively attenuated the PAI-1 inductive response suggesting a requirement for stimulated ERK signaling in TGF-beta1-mediated PAI-1 expression. These data suggest a model whereby TGF-beta1 activates a complex signaling cascade to affect PAI-1 gene control and involves USF occupancy of a critical E box motif at the HRE-2 site in the PAI-1 gene.

Src Activation Is Not Necessary for Transforming Growth Factor (TGF)-β-mediated Epithelial to Mesenchymal Transitions (EMT) in Mammary Epithelial Cells

Epithelial to mesenchymal transitions (EMTs) are key events during embryonic development and cancer progression. It has been proposed that Src plays a major role in some EMT models, as shown by the overexpression of viral Src (v-Src) in epithelial cells. It is clear that Src family kinases can regulate the integrity of both adherens junctions and focal adhesions; however, their significance in EMT, especially in the physiological context, remains to be elucidated. Here we showed that Src is activated in transforming growth factor-beta1 (TGF-beta1)-mediated EMT in mammary epithelial cells and that the Src family kinase inhibitor, PP1, prevents EMT. However, neither a more specific Src family kinase inhibitor, SU6656, nor a dominant-negative Src inhibited TGF-beta1-mediated EMT, leading us to speculate that Src activation is not an essential component of TGF-beta1-mediated EMT. Unexpectedly, PP1 prevented Smad2/3 activation by TGF-beta1, whereas SU6656 did not. Most interestingly, an in vitro kinase assay showed that PP1 strongly inhibited the TGF-beta receptor type I, and to a lesser extent, the TGF-beta receptor type II. Taken together, our data indicated that PP1 interferes with TGF-beta1-mediated EMT not by inhibiting Src family kinases but by inhibiting the Smad pathway via a direct inhibition of TGF-beta receptor kinase activity.

Reactive oxygen species production via NADPH oxidase mediates TGF-beta-induced cytoskeletal alterations in endothelial cells

Cytoskeletal alterations in endothelial cells have been linked to nitric oxide generation and cell-cell interactions. Transforming growth factor (TGF)-beta has been described to affect cytoskeletal rearrangement in numerous cell types; however, the underlying pathway is unclear. In the present study, we found that human umbilical vein endothelial cells (HUVEC) have marked cytoskeletal alterations with short-term TGF-beta treatment resulting in filipodia formation and F-actin assembly. The cytoskeletal alterations were blocked by the novel TGF-beta type I receptor/ALK5 kinase inhibitor (SB-505124) but not by the p38 kinase inhibitor (SB-203580). TGF-beta also induced marked stimulation of reactive oxygen species (ROS) within 5 min of TGF-beta exposure. TGF-beta stimulation of ROS was mediated by the NAPDH oxidase homolog Nox4 as DPI, an inhibitor of NADPH oxidase, and dominant-negative Nox4 adenovirus blocked ROS production. Finally, inhibition of ROS with ROS scavengers or dominant-negative Nox4 blocked the TGF-beta effect on cytoskeleton changes in endothelial cells. In conclusion, our studies show for the first time that TGF-beta-induced ROS production in human endothelial cells is via Nox4 and that TGF-beta alteration of cytoskeleton in HUVEC is mediated via a Nox4-dependent pathway.

TGF-beta3 regulates anchoring junction dynamics in the seminiferous epithelium of the rat testis via the Ras/ERK signaling pathway: An in vivo study

Recent studies have shown that transforming growth factor (TGF)-beta3 regulates blood-testis barrier (BTB) dynamics in vivo, plausibly by determining the steady-state levels of occludin and zonula occludens-1 (ZO-1) at the BTB site via the p38 MAP kinase signaling pathway. Since BTB is composed of coexisting TJs and basal ectoplasmic specializations [ES, a testis-specific adherens junction (AJ) type] in the seminiferous epithelium of the rat testis, we sought to examine if TGF-beta3 would also regulate anchoring junction dynamics. Using an in vivo model in which rats were treated with AF-2364 [1-(2,4-dichlorobenzyl)-indazole-3-carbohydrazide] to perturb Sertoli-germ cell AJs without affecting the integrity of TJs at the BTB, it was noted that the event of germ cell loss from the epithelium was associated with a transient surge in TGF-beta3. Furthermore, it was also associated with a surge in the protein levels of Ras, p-ERK, and the intrinsic activity of ERK, illustrating TGF-beta3 apparently regulates Sertoli-germ cell ES function via the Ras/MEK/ERK signaling pathway. Indeed, pretreatment of rats with TbetaRII/Fc chimera, a TGF-beta antagonist, or U0126, a specific MEK inhibitor, could significantly delay and partially block the disruptive effects of AF-2364 in depleting germ cells from the epithelium. While the protein levels of the cadherin/catenin complex were significantly induced during AF-2364-mediated germ cell loss, perhaps being used to retain germ cells in the epithelium, this increase failed to reverse the loss of adhesion function between Sertoli and germ cells because of a loss of protein-protein interactions between cadherins and catenins. Collectively, these results illustrate that the testis has a novel mechanism in place in which an agent that primarily disrupts TJs can induce secondary loss of AJ function, leading to germ cell loss from the seminiferous epithelium. Yet an agent that selectively disrupts AJs (e.g., AF-2364) can limit its effects exclusively at the Sertoli-germ cell adhesive site without perturbing the Sertoli-Sertoli TJs.

TGF-beta1-mediated activations of c-Src and Rac1 modulate levels of cyclins and p27(Kip1) CDK inhibitor in hepatoma cells replated on fibronectin

Integrin-mediated cell adhesion transduces signals to regulate actin cytoskeleton and cell proliferation. While understanding how integrin signals cross-talk with the TGF-beta1 pathways, we observed lamellipodia formation and cyclin regulation in Hep3B cells, following TGF-beta1 treatment. To answer if integrin signaling via actin organization might regulate cell cycle progression after TGF-beta1 treatment, we analyzed cross-talk between the two receptor-mediated pathways in hepatoma cells on specific ECMs. We found that basal and TGF-beta1-mediated activation of c-Src and Rac1, expression of cyclins E and A, and suppression of p27Kip1 were significant in cells replated on fibronectin, but not in cells on collagen I, indicating a different integrin-mediated cellular response to TGF-beta1 treatment. Levels of tyrosine phosphorylation and actin-enriched lamellipodia on fibronectin were also more prominent than in cells on collagen I. Studies using pharmacological inhibitors or transient transfections revealed that the preferential TGF-beta1 effects in cells on fibronectin required c-Src family kinase activity. These observations suggest that a specific cross-talk between TGF-beta1 and fibronectin-binding integrin signal pathways leads to the activation of c-Src/Rac1/actin-organization, leading to changes in cell cycle regulator levels in hepatoma cells. Therefore, this study represents another mechanism to regulate cell cycle regulators when integrin signaling is collaborative with TGF-beta1 pathways.

Involvement of EGF receptor and c-Src in the survival signals induced by TGF-β1 in hepatocytes

Transforming growth factor beta1 (TGF-beta1) belongs to a family of polypeptide factors, whose cytostatic and apoptotic functions help restrain the growth of mammalian cells. Although solid data established the role of TGF-beta's as suppressor factors in tumorigenic processes, in the context of an advanced stage of disease, TGF-beta's could also play a pro-oncogenic role. We have previously shown that TGF-beta1 induces both pro- and anti-apoptotic signals in foetal rat hepatocytes. In this work, we have focused on its anti-apoptotic mechanism. We show that TGF-beta1 activates the epidermal growth factor receptor (EGFR) and phosphorylates c-Src. EGFR is required for Akt activation. Blocking EGFR signalling amplifies the apoptotic response to TGF-beta1. TGF-beta1 induced a rapid activation of the tumour necrosis factor-alpha-converting enzyme (TACE/ADAM (a disintegrin and metalloprotease) 17). Inhibitors of TACE considerably attenuated Akt activation, which suggests that TGF-beta1 activates EGF signalling in hepatocytes by promoting shedding of EGF-like ligands. The activation of c-Src by TGF-beta1 is EGFR dependent and is required for full Akt phosphorylation and cell survival. Inhibition of EGFR does not block the epithelial-mesenchymal transition (EMT) induced by TGF-beta1 in hepatocytes, which indicates that activation of EGFR plays an essential role in impairing apoptosis, but it is dispensable for the EMT process.

Inactivation of TGFbeta signaling in neural crest stem cells leads to multiple defects reminiscent of DiGeorge syndrome

Specific inactivation of TGFbeta signaling in neural crest stem cells (NCSCs) results in cardiovascular defects and thymic, parathyroid, and craniofacial anomalies. All these malformations characterize DiGeorge syndrome, the most common microdeletion syndrome in humans. Consistent with a role of TGFbeta in promoting non-neural lineages in NCSCs, mutant neural crest cells migrate into the pharyngeal apparatus but are unable to acquire non-neural cell fates. Moreover, in neural crest cells, TGFbeta signaling is both sufficient and required for phosphorylation of CrkL, a signal adaptor protein implicated in the development of DiGeorge syndrome. Thus, TGFbeta signal modulation in neural crest differentiation might play a crucial role in the etiology of DiGeorge syndrome.

Transforming growth factor-beta1-dependent activation of Smad2/3 and up-regulation of PAI-1 expression is negatively regulated by Src in SKOV-3 human ovarian cancer cells

The net balance between urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type-1 (PAI-1) has been implicated in tumor cell invasion and metastasis. To elucidate the mechanism of the transforming growth factor-beta1 (TGF-beta1)-dependent up-regulation of PAI-1 expression, we investigated which signaling pathway transduced by TGF-beta1 is responsible for this effect. Here, we show (1) nontoxic concentrations of TGF-beta1 up-regulates uPA expression in HRA and SKOV-3 human ovarian cancer cells, (2) TGF-beta1 activates Smads (phosphorylation of Smad2 and nuclear translocation of Smad3) and subsequently up-regulates PAI-1 expression in HRA cells, whereas TGF-beta1 neither activates Smads nor up-regulates PAI-1 in SKOV-3 cells, (3) pharmacological Src inhibitor PP2 or antisense (AS) c-Src oligodeoxynucleotide (ODN) treatment significantly induces TGF-beta1-dependent activation of Smads, leading to PAI-1 synthesis, compared with controls, in SKOV-3 cells, (4) combination of TGF-beta1 and PP2, which activates PAI-1 expression and reduces uPA expression in SKOV-3, results in decreased invasiveness, (5) pharmacological inhibitors for mitogen-activated protein kinase (MAPK) (PD98059) and phosphoinositide-3-kinase (PI3K) (LY294002 and wortmannin) or AS-PI3K ODN transfection do not affect TGF-beta1-induced Smad signaling and up-regulation of PAI-1 expression in SKOV-3 cells pretreated with PP2, and (6) the induction of PAI-1 protein was partially inhibited by an inhibitor of Sp1-DNA binding, mithramycin, implicating, at least in part, Sp1 in the regulation of this gene by TGF-beta1. In conclusion, TGF-beta1-dependent activation of Smad2/3, leading to PAI-1 synthesis, may be negatively regulated by Src, but not its downstream targets MAPK and PI3K in SKOV-3 cells. These data also reflect the complex biological effect of uPA-PAI-1 system.

Plasminogen activator inhibitor type-1 gene expression and induced migration in TGF-β1-stimulated smooth muscle cells is pp60c-src/MEK-dependent

Transforming growth factor-beta1 (TGF-beta1) stimulates expression of plasminogen activator inhibitor type-1 (PAI-1), a serine protease inhibitor (SERPIN) important in the control of stromal barrier proteolysis and cell-to-matrix adhesion. Pharmacologic agents that target MEK (PD98059, U0126) or src family (PP1) kinases attenuated TGF-beta1-dependent PAI-1 transcription in R22 aortic smooth muscle cells. Pretreatment with PP1 at concentrations that inhibited TGF-beta1-dependent PAI-1 expression also blocked ERK1/2 activation/nuclear accumulation suggesting that the required src kinase activity is upstream of ERK1/2 in the TGF-beta1-initiated signaling cascade. The IC(50) of the PP1-sensitive kinase, furthermore, specifically implied involvement of pp60(c-src) in PAI-1 induction. Indeed, addition of TGF-beta1 to quiescent R22 cells resulted in a 3-fold increase in pp60(c-src) autophosphorylation and kinase activity. Transfection of a dominant-negative pp60(c-src) construct, moreover, reduced TGF-beta1-induced PAI-1 expression levels to that of unstimulated controls or PP1-pretreated cells. A >/=170 kDa protein that co-immunoprecipitated with TGF-beta1-activated pp60(c-src) was also phosphorylated transiently in response to TGF-beta1. TGF-beta1 is known to transactivate the 170 kDa EGF receptor (EGFR) by autocrine HB-EGF or TGF-alpha mechanisms suggesting involvement of EGFR activation in certain TGF-beta1-initiated responses. Incubation of quiescent R22 cells with the EGFR-specific inhibitor AG1478 prior to growth factor (EGF or TGF-beta1) addition effectively blocked EGFR activation as determined by direct visualization of receptor internalization. AG1478 suppressed (in a dose-dependent fashion) EGF-induced PAI-1 protein levels and, at a final concentration of 2.5 muM, virtually eliminated EGF-dependent PAI-1 synthesis. More importantly, AG1478 similarly repressed inducible PAI-1 levels in TGF-beta1-stimulated R22 cultures. PP1, PD98059, and U0126 also inhibited TGF-beta1-dependent cell motility at concentrations that significantly attenuated PAI-1 expression. Consistent with the AG1478-associated reductions in EGF- and TGF-beta1-stimulated PAI-1 expression, pretreatment of R22 cell cultures with AG1478 effectively suppressed growth factor-stimulated cell motility. These data indicate that two major phenotypic characteristics of TGF-beta1-exposure (i.e., transcription of specific target genes [e.g., PAI-1], increased cell motility) are linked in the R22 vascular smooth muscle cell system, require pp60(c-src) kinase activity and MEK signaling and involve activation of an AG1478-sensitive (likely EGFR-dependent) pathway.

Imatinib mesylate inhibits the profibrogenic activity of TGF-beta and prevents bleomycin-mediated lung fibrosis

Idiopathic pulmonary fibrosis is a progressive and fatal fibrotic disease of the lungs with unclear etiology. Prior efforts to treat idiopathic pulmonary fibrosis that focused on anti-inflammatory therapy have not proven to be effective. Recent insight suggests that the pathogenesis is mediated through foci of dysregulated fibroblasts driven by profibrotic cytokine signaling. TGF-beta and PDGF are 2 of the most potent of these cytokines. In the current study, we investigated the role of TGF-beta-induced fibrosis mediated by activation of the Abelson (Abl) tyrosine kinase. Our data indicate that fibroblasts respond to TGF-beta by stimulating c-Abl kinase activity independently of Smad2/3 phosphorylation or PDGFR activation. Moreover, inhibition of c-Abl by imatinib prevented TGF-beta-induced ECM gene expression, morphologic transformation, and cell proliferation independently of any effect on Smad signaling. Further, using a mouse model of bleomycin-induced pulmonary fibrosis, we found a significant inhibition of lung fibrosis by imatinib. Thus, Abl family members represent common targets for the modulation of profibrotic cytokine signaling.

Tyrosine phosphorylation-dependent PI 3 kinase/Akt signal transduction regulates TGFbeta-induced fibronectin expression in mesangial cells

TGFbeta stimulates expression of fibronectin in various cells, including mesangial cells. The mechanism by which TGFbeta exerts this effect is not fully understood. We investigated the involvement of tyrosine phosphorylation and the phosphatidylinositol (PI) 3 kinase/Akt signalling pathway in this process. TGFbeta increased tyrosine phosphorylation, resulting in activation of PI 3 kinase in mesangial cells. Inhibition of tyrosine phosphorylation blocked TGFbeta-induced fibronectin expression. Inhibition of PI 3 kinase activity also prevented fibronectin expression induced by TGFbeta. Furthermore, expression of constitutively active PI 3 kinase by adenovirus-mediated gene transfer increased fibronectin expression similar to TGFbeta. TGFbeta stimulated Akt serine threonine kinase in a tyrosine kinase- and PI 3 kinase-dependent manner. Inhibition of TGFbeta-induced Akt activity by adenovirus-mediated expression of a dominant-negative mutant of Akt abolished expression of fibronectin. Dominant-negative PI 3 kinase or dominant-negative Akt inhibited TGFbeta-induced fibronectin transcription. In contrast, and similarly to TGFbeta, expression of constitutively active PI 3 kinase or constitutively active Akt increased transcription of fibronectin, confirming a prominent role of these kinases in expression of fibronectin. These data provide the evidence that activation of TGFbeta receptor serine threonine kinase stimulates the PI 3 kinase/Akt pathway in a tyrosine phosphorylation-dependent manner and define a role for the same signal transduction pathway in TGFbeta-induced fibronectin expression.

TGF-beta1 (transforming growth factor-beta1)-mediated adhesion of gastric carcinoma cells involves a decrease in Ras/ERKs (extracellular-signal-regulated kinases) cascade activity dependent on c-Src activity

Signalling by integrin-mediated cell anchorage to extracellular matrix proteins is co-operative with other receptor-mediated signalling pathways to regulate cell adhesion, spreading, proliferation, survival, migration, differentiation and gene expression. It was observed that an anchorage-independent gastric carcinoma cell line (SNU16) became adherent on TGF-beta1 (transforming growth factor beta1) treatment. To understand how a signal cross-talk between integrin and TGF-beta1 pathways forms the basis for TGF-beta1 effects, cell adhesion and signalling activities were studied using an adherent subline (SNU16Ad, an adherent variant cell line derived from SNU16) derived from the SNU16 cells. SNU16 and SNU16Ad cells, but not integrin alpha5-expressing SNU16 cells, showed an increase in adhesion on extracellular matrix proteins after TGF-beta1 treatment. This increase was shown to be mediated by an integrin alpha3 subunit, which was up-regulated in adherent SNU16Ad cells and in TGF-beta1-treated SNU16 cells, compared with the parental SNU16 cells. After TGF-beta1 treatment of SNU16Ad cells on fibronectin, Tyr-416 phosphorylation of c-Src was increased, but Ras-GTP loading and ERK1/ERK2 (extracellular-signal-regulated kinases 1 and 2) activity were decreased, which showed a dependence on c-Src family kinase activity. Studies on adhesion and signalling activities using pharmacological inhibitors or by transient-transfection approaches showed that inhibition of ERK1/ERK2 activity increased TGF-beta1-mediated cell adhesion slightly, but not the basal cell adhesion significantly, and that c-Src family kinase activity and decrease in Ras/ERKs cascade activity were required for the TGF-beta1 effects. Altogether, the present study indicates that TGF-beta1 treatment causes anchorage-independent gastric carcinoma cells to adhere by an increase in integrin alpha3 level and a c-Src family kinase activity-dependent decrease in Ras/ERKs cascade activity.

Endoglin controls cell migration and composition of focal adhesions: function of the cytosolic domain

Mutations in the human endoglin gene result in hereditary hemorrhagic telangiectasia type 1, a vascular disorder characterized by multisystemic vascular dysplasia, arteriovenous malformations, and focal dilatation of postcapillary venules. Previous studies have implicated endoglin in the inhibition of cell migration in vivo and in vitro. In the course of studies to address the relationship of the conserved cytosolic domain to endoglin function, we identified zyxin, a LIM domain protein that is concentrated at focal adhesions, as an interactor with endoglin in human umbilical vein vascular endothelial cells. This interaction is localized within the 47-amino acid carboxyl-terminal cytosolic domain of endoglin, and maps within zyxin residues 326-572. The endoglin-zyxin interaction was found to be largely mediated by the third LIM domain of zyxin, and is specific for endoglin because the homologous cytosolic domain of the transforming growth factor-beta type III receptor, betaglycan, fails to interact with zyxin. Expression of endoglin is associated with reduction of zyxin, as well as its interacting proteins p130(cas) and CrkII, from a focal adhesion protein fraction, and this reduction is correlated with inhibition of cell migration. We also show that endoglin-dependent: (i) inhibition of cell migration, (ii) reduction of focal adhesion-associated p130(cas)/CrkII protein levels, (iii) tyrosine phosphorylation of p130(cas), and (iv) focal adhesion-associated endoglin levels are mediated by the cytosolic domain of endoglin. These results suggest a novel mechanism of endoglin function involving its interaction with LIM domain-containing proteins, and associated adapter proteins, affecting sites of focal adhesion.

Transforming growth factor-beta activates both pro-apoptotic and survival signals in fetal rat hepatocytes

Transforming growth factor-beta (TGF-beta) induces apoptosis in fetal rat hepatocytes. However, a subpopulation of these cells survives concomitant with changes in morphology and phenotype, reminiscent of an epithelial mesenchymal transition (EMT) [Exp. Cell Res. 252 (1999) 281-291]. In this work, we have isolated the subpopulation that survives to TGF-beta-induced apoptosis, showing that these cells maintain the response to TGF-beta in terms of Smads activation and growth inhibition. Analyses of the intracellular signals that could impair the apoptotic effects of TGF-beta have indicated that the phosphatidylinositol 3-kinase (PI 3-K)/Akt pathway is activated in these resistant cells. Experiments in fetal rat hepatocytes have shown that TGF-beta is able to transiently activate PI 3-K/Akt by a mechanism independent of protein synthesis but dependent on a tyrosine kinase activity. Pro-apoptotic signals, such as oxidative stress and caspases, contribute to the loss of Akt at later times. Inhibiting PI 3-K sensitizes fetal hepatocytes (FH) to the apoptosis induced by TGF-beta and causes spontaneous death in the resistant cells. In conclusion, TGF-beta, as it is known for other cytokines, could be inducing pro-apoptotic and survival signals in hepatocytes, the balance among them will decide cell fate.

Transforming growth factor-beta1-dependent urokinase up-regulation and promotion of invasion are involved in Src-MAPK-dependent signaling in human ovarian cancer cells

Urokinase-type plasminogen activator (uPA) has been implicated in tumor cell invasion and metastasis. We reported previously that transforming growth factor (TGF)-beta1 induces a dose- and time-dependent up-regulation of uPA mRNA and protein in highly invasive human ovarian cancer cell line HRA, leading to invasion. To further elucidate the mechanism of the invasive effect of TGF-beta1, we investigated which signaling pathway transduced by TGF-beta1 is responsible for this effect. Here, we show that 1) nontoxic concentrations of TGF-beta1 activated Src kinase; 2) TGF-beta1 rapidly phosphorylates ERK1/2 and Akt, but not p38; 3) pharmacological Src inhibitor PP2 or antisense (AS) c-Src oligodeoxynucleotide (ODN) treatment reduced TGF-beta1-induced phosphorylation of ERK1/2 and Akt by 85-90% compared with controls; 4) pharmacological inhibition of MAPK by PD98059 abrogated TGF-beta1-mediated Akt stimulation, whereas TGF-beta1-induced ERK1/2 stimulation was not inhibited by PI3K inhibitor LY294002 or AS-PI3K ODN transfection; 5) up-regulation of uPA mRNA in response to TGF-beta1 was almost totally blocked by PP2 and PD98059 and partially ( approximately 55%) by LY294002; 6) TGF-beta1-induced uPA mRNA up-regulation was inhibited by treatment with AS ODNs to c-Src or PI3K by 90 or 60%, respectively, compared with control ODN treatment; and 7) blockade of the release of the transcription factor NF-kappaB by pyrrolidinedithiocarbamate reduced the TGF-beta1-induced activation of the uPA gene by approximately 65%. In addition, curcumin, a blocker of the transcriptional factor AP-1, partially (35%) canceled this effect. Taken together, these data support a role for TGF-beta1 activation of two distinct pathways (Src-MAPK-PI3K-NF-kappaB-dependent and Src-MAPK-AP-1-dependent) for TGF-beta1-dependent uPA up-regulation and promotion of invasion.

Transforming growth factor-β1 stimulated protein kinase B serine-473 and focal adhesion kinase tyrosine phosphorylation dependent on cell adhesion in human hepatocellular carcinoma SMMC-7721 cells

Transforming growth factor-beta1 (TGF-beta1) is a potent growth inhibitor and apoptosis inducer for most normal cells. However, tumor cells are commonly nevertheless sensitive to the tumor-suppressing effects of TGF-beta1. In this paper, we focus on the effects of TGF-beta1 on two important anti-apoptotic protein kinases, protein kinase B (PKB), and focal adhesion kinase (FAK), in SMMC-7721 cells. We found that PKB-Ser-473 phosphorylation was apparently up-regulated by TGF-beta1. In the meantime, PKB-Thr-308 phosphorylation was slightly up-regulated by TGF-beta1. TGF-beta1 could also enhance FAK-Tyr phosphorylation. We observed that integrin-linked kinase (ILK) was also up-regulated by TGF-beta1 in good accordance with PKB-Ser-473 phosphorylation. We first found that TGF-beta1 could stimulate PKB-Ser-473 phosphorylation possibly via up-regulating ILK expression. Furthermore, we also failed to detect PKB-Ser-473 and FAK-Tyr phosphorylation with various concentrations of TGF-beta1 treatment when cells were kept in suspension. The above results indicate that PKB-Ser-473 and FAK-Tyr phosphorylation stimulated by TGF-beta1 are both dependent on cell adhesion.

Epithelial–mesenchymal transitions in development and pathologies

The epithelial-mesenchymal transition (EMT) is a fundamental process governing morphogenesis in multicellular organisms. This process is also reactivated in a variety of diseases including fibrosis and in the progression of carcinoma. The molecular mechanisms of EMT were primarily studied in epithelial cell lines, leading to the discovery of transduction pathways involved in the loss of epithelial cell polarity and the acquisition of a variety of mesenchymal phenotypic traits. Similar mechanisms have also been uncovered in vivo in different species, showing that EMT is controlled by remarkably well-conserved mechanisms. Current studies further emphasise the critical importance of EMT and provide a better molecular and functional definition of mesenchymal cells and how they emerged >500 million years ago as a key event in evolution.

alpha1B-Adrenergic receptor phosphorylation and desensitization induced by transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) induced alpha(1B)-adrenergic receptor phosphorylation in Rat-1 fibroblasts stably expressing these adrenoceptors. This effect of TGF-beta was rapid, reaching a maximum within 30 min and decreasing thereafter, and concentration-dependent (EC(50) 0.3 pM). The phosphoinositide 3-kinase inhibitors wortmannin and LY294002, and the protein kinase C inhibitors staurosporine, Ro 318220 and bisindolylmaleimide, blocked the effect of this growth factor. alpha(1B)-Adrenergic receptor phosphorylation was associated with desensitization, as indicated by a reduction in the adrenergic-mediated production of [(3)H]inositol phosphates. Phosphorylation of alpha(1B)-adrenergic receptors by TGF-beta was also observed in Cos-1 cells transfected with the receptor. Co-transfection of the dominant-negative mutant of the regulatory subunit of phosphoinositide 3-kinase (Deltap85) inhibited the phosphorylation of alpha(1B)-adrenergic receptors induced by TGF-beta. Our results indicate that activation of TGF-beta receptors induces alpha(1B)-adrenergic receptor phosphorylation and desensitization. The data suggest that phosphoinositide 3-kinase and protein kinase C play key roles in this effect of TGF-beta.