The role of the Smad3 protein in phorbol ester-induced promoter expression

FisR activates σ54 -dependent transcription of sulfide-oxidizing genes in Cupriavidus pinatubonensis JMP134

Some heterotrophic bacteria are able to oxidize sulfide (H₂ S, HS^- and S^2- ) to sulfite and thiosulfate via polysulfide. The genes coding for the oxidation enzymes in Cupriavidus pinatubonensis JMP134 have recently been identified; however, their regulation is unknown. A regulator gene is adjacent to the operon of the sulfide-oxidizing genes, encoding a σ⁵⁴ -dependent transcription factor (FisR) with three domains: an R domain, an AAA+ domain and a DNA-binding domain. Here it is reported that the regulator responds to the presence of sulfide and activates the sulfide-oxidizing genes. FisR binds to its cognate operator at -114 to -135 bp of the transcription start of the operon. When polysulfide reacts with the R domain of FisR through the three conserved cysteine residues (C53, C64 and C71), FisR activates the expression of the operon. FisR is highly sensitive to polysulfide, activating σ⁵⁴ -dependent transcription of sulfide-oxidizing genes for sulfide removal. Further, sequence analysis indicates that FisR-type regulators are relatively common for controlling sulfide-oxidizing genes under sulfide stress in the Proteobacteria.

Dynamic transcription factor activity profiling in 2D and 3D cell cultures

Live-cell assays to measure cellular function performed within 3D cultures have the potential to elucidate the underlying processes behind disease progression and tissue formation. Cells cultured in 3D interact and remodel their microenvironment and can develop into complex structures. We have developed a transcription factor (TF) activity array that uses bioluminescence imaging (BLI) of lentiviral delivered luminescent reporter constructs that allows for the non-invasive imaging of TF activity in both 2D and 3D culture. Imaging can be applied repeatedly throughout culture to capture dynamic TF activity, though appropriate normalization is necessary. We investigated in-well normalization using Gaussia or Renilla luciferase, and external well normalization using firefly luciferase. Gaussia and Renilla luciferase were each unable to provide consistent normalization for long-term measurement of TF activity. However, external well normalization provided low variability and accounted for changes in cellular dynamics. Using external normalization, dynamic TF activities were quantified for five TFs. The array captured expected changes in TF activity to stimuli, however the array also provided dynamic profiles within 2D and 3D that have not been previously characterized. The development of the technology to dynamically track TF activity within cells cultured in both 2D and 3D can provide greater understanding of complex cellular processes.

Cross-talk between IFN-alpha and TGF-beta1 signaling pathways in preneoplastic rat liver

Interferon-gamma/transforming growth factor-beta (IFN-gamma/TGF-beta) pathways have opposite effects on diverse cellular functions. However, little is known about interactions between IFN-alpha/TGF-beta. In previous studies, we showed that IFN-alpha2b increases TGF-beta(1) production and secretion in hepatocytes from preneoplastic rat livers. Here, the interaction between IFN-alpha/TGF-beta(1) pathways was explored. We observed a positive cross-talk between IFN-alpha and TGF-beta(1) signaling, with activation of both pathways. p300 protein levels in hepatocytes from preneoplastic livers were enough to interact with both activated Stat1 and Smad2/3. Besides, Smad7 was not directly related with TGF-beta(1) and IFN-alpha signals. Interestingly, we reported the novel finding that the autocrine TGF-beta(1) up-regulates TGF-betaRII at protein and mRNA levels. In conclusion, the intracellular signals triggered by IFN-alpha2b and by autocrine TGF-beta(1) are integrated at the nuclear level, where activated Stat1 and Smad2/3 are capable of interact with p300, present in no restrictive cellular amounts.

Twisted gastrulation (Tsg) is regulated by Tob and enhances TGF-beta signaling in activated T lymphocytes

Quiescent T cells express Tob, an APRO gene family member, which functions as a transcriptional regulator. Subtractive hybridization identified Twisted gastrulation (Tsg) as one of the genes suppressed by Tob. Tsg is a secreted protein that interacts with Drosophila decapentaplegic (Dpp) and its vertebrate orthologs BMP2/4 and regulates morphogenetic effects in embryos. Here, we report the expression and function of Tsg in human T cells. Tsg mRNA was almost undetectable in unstimulated T cells and was up-regulated after activation by TCR/CD3 and either CD28, IL-2, or PMA. Tsg protein had no effect on responses of primary T cells to TCR/CD3 stimulation but had a potent inhibitory effect on proliferation and cytokine production of primed alloreactive CD4+ cells. Surprisingly, Tsg did not affect phosphorylation of the BMP-specific Smad1 but induced phosphorylation of the TGF-beta-specific Smad2 and mediated DNA binding on Smad3/4 consensus-binding sites, suggesting that it acted downstream of TGF-beta. In vitro association assays revealed a direct interaction of Tsg and TGF-beta proteins. Thus, Tsg functions as an agonist synergizing with TGF-beta to inhibit T-cell activation. Modulation of Tsg signaling may represent a novel target for molecular intervention toward control of aberrant T-cell responses during ongoing graft-versus-host disease (GVHD) and autoimmune diseases.

p38MAPK mediates benzyl isothiocyanate-induced p21WAF1 expression in vascular smooth muscle cells via the regulation of Sp1

It has recently been reported that the transcription factors involved in p21WAF1 activation by certain signaling factors may vary in different cell types. However, the role and importance of the signaling pathway in the transcriptional regulation of p21WAF1 on vascular smooth muscle cells (VSMC) in response to benzyl isothiocyanate (BITC) has been unclear. In this report, we demonstrate that BITC induces the p21WAF1 expression at the transcriptional level. This increase in p21WAF1 gene expression was due to p38MAPK-dependent activation of the p21WAF1 promoter by BITC. Transcription factor Sp1 binding site was identified as the cis-element for the activation of p21WAF1 promoter by BITC, as determined by deletion and mutation analysis. In addition, gel shift and supershift assays demonstrated that this BITC-responsive element binds specifically to the transcription factor Sp1. Treatment with SB203580, an inhibitor of the p38MAPK, significantly downregulated transactivation of BITC-induced Sp1. Finally, the transient expression of VSMC with dominant negative p38MAPK plasmid suppressed BITC-stimulated Sp1 activity. In conclusion, we report that the transcription factor Sp1 involved in the p38MAPK-mediated control of p21WAF1 regulation on VSMC in response to BITC has now been identified.

Phosphorylation of AML1/RUNX1 regulates its degradation and nuclear matrix association

The acute myeloid leukemia 1 (AML1) transcription factors are key regulators of hematopoietic differentiation. Cellular AML1c protein is found in the nucleus and can be separated into two fractions, one soluble in buffers containing salt and nonionic detergent and the other insoluble and tightly bound to the nuclear matrix. We find that the AML1c protein is modified by both phosphorylation and ubiquitination. Our studies show that the majority of the ubiquitinated AML1c is associated with the insoluble nuclear matrix. Treatment of cells with the proteasome inhibitor PS341 (Velcade, Bortezomib) increases the levels of ubiquitinated AML1c. Mutation of the four phosphorylation sites necessary for transcriptional regulation (serine 276, serine 293, serine 303, and threonine 300) mimics the effects of the proteasome inhibitor, increasing the levels of ubiquitinated, matrix-bound AML1c. We find that the soluble and insoluble forms of AML1c are degraded at a similar rate. However, mutation of these four serine/threonine residues statistically increases the half-life of the matrix-associated AML1c. Thus, phosphorylation of AML1c on specific serine/threonine residues controls both transcriptional activity and rate of degradation.

Oxidation of Titanium, RGD Peptide Attachment, and Matrix Mineralization of Rat Bone Marrow Stromal Cells

The aim of this study was to compare the efficacy of attachment of arginine-glycine-aspartic acid (RGD) peptide to titanium surfaces oxidized by different methods. Titanium surfaces were treated as follows: (1) treatment A: passivation in nitric acid, (2) treatment B: heated in air at 400°C for 1 hour, (3) treatment C: immersed in 8.8 M H2O2/0.1 M HCl at 80°C for 30 minutes, and (4) treatment D: treated as in treatment C and then heated at 400°C for 1 hour. RGD was attached to titanium samples treated as in treatments A through D. The quantity of attached RGD was determined by an enzyme-linked immunoabsorbent assay. Mineralization of a rat bone marrow stromal cell (RMSC) culture on the titanium surfaces after 21 days was determined y atomic absorption spectroscopy. The treatments were ranked according to quantity of RGD attached as C, A, B, and D. Twenty-one days after RMSC culture, the degree of mineralization was significantly higher for treatment C than for treatments A, B, and D and for controls. The efficacy of RGD attachment varies with the oxidation treatment given to titanium. Oxidation in H2O2/0.1 M HCl at 80°C provided the best overall surface for RGD attachment as well as calcified matrix formation of RMSCs.

Phorbol ester treatment of K562 cells regulates the transcriptional activity of AML1c through phosphorylation

We find that phorbol ester (PE) treatment of K562 cells greatly stimulates promoters (T cell receptor beta, myeloperoxidase, macrophage colony-stimulating factor receptor, and granulocyte macrophage colony-stimulating factor receptor) containing AML1 transcription factor binding sites. This stimulation of AML1c transcriptional activity is mediated by direct phosphorylation of the AML1c molecule on multiple phosphorylation sites. Eleven AML1c (S/T)P sites in the transcriptional activating domain are phosphorylated at a basal level in untreated K562 cells; treatment of the K562 cells with PE results in increased phosphorylation at five of these sites (serines 276, 293, 303, 462, and threonine 300). Mutation of these five sites to alanine inhibits PE-induced transcriptional activity; mutation of the sites to an acidic amino acid, aspartic acid, stimulates constitutive activity. Single mutations in four amino acids or double mutations (serines 276 and 293 or threonine 300 and serine 303) have little effect on AML1c transcriptional activity. Inhibitor assays suggest that the ERK family of protein kinases is activated by PEs to phosphorylate the (S/T)P sites within the AML1c molecule and markedly enhance the transcriptional activity of AML1c.

Synergistic activation of CREB-mediated transcription by forskolin and phorbol ester requires PKC and depends on the glutamine-rich Q2 transactivation domain

Recruitment of a RNA polymerase II complex by the glutamine-rich Q2 domain of cAMP response element-binding protein (CREB) allows basal transcriptional activity, while recruitment of CBP/p300 through signal-induced phosphorylation of the kinase-inducible domain at serine-133 enhances CREB-dependent transcription. Here we demonstrate that co-administration of forskolin and phorbol ester TPA to NIH3T3 cells provoked a dose-dependent increase in phosphoserine-133. CREB- and Q2-dependent transcription, as well as transcription by other glutamine-rich transcription factors, but not by transcription factors lacking glutamine-rich regions, augmented synergistically in the presence of both stimuli. Synergistic activation was abograted by specific inhibition of protein kinase C (PKC), but not of PKA. Co-stimulation increased the basal activity of a minimal, CREB-independent promoter. Therefore, Q2, which directly interacts with the RNA polymerase II initiation complex, may transmit the increased basal promoter activity provoked by these stimuli to CREB, thereby contributing to synergistic activation of CREB-mediated transcription. This synergism may have important implications on glutamine-rich transcription factor-target genes.

Imperatorin inhibits HIV-1 replication through an Sp1-dependent pathway

Coumarins and structurally related compounds have been recently shown to present anti-human immunodeficiency virus, type 1 (HIV-1) activity. Among them, the dietary furanocoumarin imperatorin is present in citrus fruits, in culinary herbs, and in some medicinal plants. In this study we report that imperatorin inhibits either vesicular stomatitis virus-pseudotyped or gp160-enveloped recombinant HIV-1 infection in several T cell lines and in HeLa cells. These recombinant viruses express luciferase as a marker of viral replication. Imperatorin did not inhibit the reverse transcription nor the integration steps in the viral cell cycle. Using several 5' long terminal repeat-HIV-1 constructs where critical response elements were either deleted or mutated, we found that the transcription factor Sp1 is critical for the inhibitory activity of imperatorin induced by both phorbol 12-myristate 13-acetate and HIV-1 Tat. Moreover in transient transfections imperatorin specifically inhibited phorbol 12-myristate 13-acetate-induced transcriptional activity of the Gal4-Sp1 fusion protein. Since Sp1 is also implicated in cell cycle progression we further studied the effect of imperatorin on cyclin D1 gene transcription and protein expression and in HeLa cell cycle progression. We found that imperatorin strongly inhibited cyclin D1 expression and arrested the cells at the G(1) phase of the cell cycle. These results highlight the potential of Sp1 transcription factor as a target for natural anti-HIV-1 compounds such as furanocoumarins that might have a potential therapeutic role in the management of AIDS.

Transcription factor Sp1 mediates p38MAPK-dependent activation of the p21WAF1 gene promoter in vascular smooth muscle cells by pyrrolidine dithiocarbamate

Previously, we demonstrated that pyrrolidine dithiocarbamate (PDTC) induced G1 cell cycle arrest in vascular smooth muscle cells (VSMC) through inducing p21WAF1 expression. It has recently been reported that the transcription factors involved in p21WAF1 activation by certain signaling factors may vary in different cell types. However, little is known concerning the molecular mechanisms by which PDTC induces p21WAF1 gene expression in VSMC. In this report, we demonstrate that PDTC induces the p21WAF1 expression at the mRNA level. This increase in p21WAF1 gene expression was due to p38MAPK-dependent activation of the p21WAF1 promoter by PDTC. Transcription factor Sp1 binding site was identified as the cis-element for the activation of p21WAF1 promoter by PDTC, as determined by deletion and mutation analysis. In addition, gel shift and supershift assays demonstrated that this PDTC-responsive element binds specifically to the transcription factor Sp1. Treatment with SB203580, an inhibitor of the p38MAPK, significantly down-regulated transactivation of PDTC-induced Sp1. Finally, the transient expression of VSMC with dominant negative p38MAPK plasmid suppressed PDTC-stimulated Sp1 activity. In conclusion, we report the novel finding that transcription factor Sp1 that is involved in the p38MAPK-mediated control of p21WAF1 regulation on VSMC in response to PDTC has now been identified.

Expressions of inhibitory Smads, Smad6 and Smad7, are differentially regulated by TPA in human lung fibroblast cells

Smad6 and Smad7 are inhibitory Smads (I-Smads) with differential inhibitory effects on the regulation of the cellular signalings induced by TGF-beta superfamily. Here, we show that phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) down-regulates Smad6 mRNA expression and up-regulates Smad7 mRNA expression in IMR-90, a human lung fibroblast cell line. These regulations of I-Smads by TPA were suppressed by one PKC inhibitor (Gö6983), but not by another (Gö6976). TPA treatment had little effect on the phosphorylation of novel PKCs (PKCdelta and PKCepsilon), but specifically induced PKCmu phosphorylation, and this effect was inhibited by Gö6983, but not by Gö6976. Additionally, Gö6983 but not Gö6976 inhibited ERK- and JNK-phosphorylation as well as Smad7 promoter activity induced by TPA. MEK inhibitor U0126 inhibited the down-regulation of Smad6 mRNA expression but not the up-regulation of Smad7 mRNA expression. In contrast, JNK inhibitor SP600125 had no such effects. Luciferase reporter analysis revealed that TPA did not induce NF-kappaB activation. In addition, TPA up-regulated Smad7 expression in the presence of NF-kappaB inhibitor TLCK. These findings indicate that TPA down-regulates Smad6 expression presumably via PKCmu-ERK-dependent pathway and up-regulates Smad7 expression via PKCmu-dependent mechanism(s) which need no MAPK and NF-kappaB activation.

Role of protein kinase C and the Sp1-p53 complex in activation of p21(WAF-1) expression by 12-O-tetradecanoylphorbol-13-acetate in human T cells

Previous reports have shown that, in certain cell types, p21(WAF-1), which plays a central role in cell proliferation, can be activated by HTLV-I Tax protein and by TPA. Tax and TPA are also known to stimulate HTLV-I gene expression. Since cell proliferation has a major impact on HTLV-I replication, it was of interest to investigate their effect on p21(WAF-1) in human T cells, which are the main target of HTLV-I in human infection. This study demonstrates that p21(WAF-1) is activated in such cells by both factors, each acting through a different mechanism that does not influence the other. The effect of TPA is shown to require PKC activity. Notably, however, examination of different PKC isoforms revealed that PKC-alpha and PKC-epsilon stimulated p21(WAF-1) expression, whereas PKC-eta was rather inhibitory and PKC-beta1 and beta2 were ineffective. All these isoforms were found to be activated by TPA in the employed T cells, but this apparent paradox was resolved by the observation that when coexpressed together in these cells, the stimulatory PKCs override the inhibitory isoform. Further experiments demonstrated that the PKC-induced p21(WAF-1) activation was mediated by binding of Sp1-p53 complex to the second most upstream of the six Sp1 recognition sites present in its promoter and that this effect did not require the cooperation of an p53-binding site.

Ets2 and protein kinase C epsilon are important regulators of parathyroid hormone-related protein expression in MCF-7 breast cancer cells

Parathyroid hormone-related protein (PTHrP) promotes the metastatic potential and proliferation of breast cancer cells, and acts anti-apoptotically. In invasive MDA-MB-231 breast cancer cells, transforming growth factor beta-regulated PTHrP synthesis is mediated by an Ets1/Smad3-dependent activation of the PTHrP P3 promoter. In the present study, we studied the regulation of PTHrP expression in non-invasive, Ets1-deficient and transforming growth factor beta-resistant MCF-7 cells. We found PMA to be a strong stimulator of P3-dependent PTHrP expression in MCF-7 cells. Mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinase (ERK) kinase 1 (MEK-1)/ERK1/2 inhibitor PD98059 interfered with this activity. Promoter studies revealed that the PMA effect depended on the Ets and stimulating protein-1 (Sp1)-binding sites. Of several Ets factors tested, Ets2, but not Ese-1, Elf-1 or Ets1, supported the PMA-dependent increase in promoter activity. PD98059 and a threonine to alanine mutation of the ERK1/2-responsive Ets2 phosphorylation site at position 72 inhibited the Ets2/PMA effect. Activated protein kinase C (PKC) epsilon could mimic PMA by stimulating the P3 promoter alone or in co-operation with Ets2 in an MEK-1/ERK1/2-dependent manner. Activated PKC alpha, although capable of co-operating with Ets2, failed to induce transcription from the P3 promoter on its own. The Ets2/PKalpha synergistic effect was neither sensitive to PD98059 nor to Thr(72)/Ala(72) mutation. PMA neither increased the expression of Sp1 nor modulated the transcriptional activity of Sp1. However, it induced the displacement of a yet unknown factor from the Sp1-binding site, which may result in Sp1 recruitment to the promoter. Our results suggest an ERK1/2-dependent Ets2/PKC epsilon synergism to be involved in PTHrP expression in MCF-7 breast cancer cells.

TPA activates p21WAF-1 promoter in human T-cells through its second most upstream Sp1 site

The p21(WAF-1) promoter contains binding sites for a number of transcription factors which mediate its activation by a variety of external signals. Moreover, it has been reported that the transcription factors involved in p21(WAF-1) activation by certain signaling factors, like the phorbol ester TPA, may vary in different cell types. We were interested in elucidating the mechanism of p21(WAF-1) activation by TPA in human T-cells, since this activation could explain the antagonistic effect of PKC on apoptosis induction in these cells noted in our previous studies. Using the Jurkat human T-cells we found that TPA activated p21(WAF-1) expression by a PKC-dependent mechanism and that out of six Sp1 binding sites residing in its promoter the second most upstream one was critically essential for this activation. Since p21(WAF-1) is known to inhibit the onset of apoptosis, its PKC-dependent activation may likely account for the PKC antagonistic effect on apoptosis induction in these cells.

Interfering with TGFbeta-induced Smad3 nuclear accumulation differentially affects TGFbeta-dependent gene expression

BACKGROUND

Transforming growth factor-beta (TGFbeta) plays an important role in late-stage carcinogenesis by stimulating invasive behavior of cancer cells, promoting neo-angiogenesis and by helping cancer cells to escape surveillance by the immune system. It also supports colonization of the bone by metastatic breast cancer cells by increasing expression of osteolytic parathyroid hormone-related protein (PTHrP). Interfering with TGFbeta signalling may thus weaken the malignant properties of cancer cells. We investigated to what extent two inhibitors, SB-202190 and SB-203580, interfere with TGFbeta-signalling in invasive MDA-MB-231 breast cancer cells. These compounds, formerly used as p38-MAPK-specific inhibitors, were recently also demonstrated to inhibit TGFbeta type I receptor kinase.

RESULTS

Our results show that these inhibitors delay the onset of TGFbeta-induced nuclear accumulation of Smad3 and reduces its amplitude. This effect was accompanied by a strong reduction in TGFbeta-responsivess of the slow-responder genes pthrp, pai-1 and upa, while the reactivity of the fast-responder gene smad7 to TGFbeta remained almost unchanged. Neither was the TGFbeta response of the fast-responder ese-1/esx gene, whose expression we found to be strongly downregulated by TGFbeta, affected by the inhibitors.

CONCLUSION

The data show that SB-202190 and SB-203580 suppress TGFbeta-dependent activation of genes that are important for the acquisition of invasive behavior, while having no effect on the expression of the natural TGFbeta inhibitor Smad7. This suggests that these compounds are potent inhibitors of malignant behavior of cancer cells.

The hexosamine pathway regulates the plasminogen activator inhibitor-1 gene promoter and Sp1 transcriptional activation through protein kinase C-beta I and -delta

Increased flux through the hexosamine biosynthesis pathway (HBP) has been shown to stimulate the expression of a number of genes. We previously demonstrated in glomerular mesangial and endothelial cells that both high glucose concentrations and glucosamine activated the plasminogen activator inhibitor-1 (PAI-1) gene promoter through the transcription factor, Sp1; and that the glutamine:fructose-6-phosphate amidotransferase inhibitor, 6-diazo-5-oxonorleucine, inhibited the effect of high glucose, but not that of glucosamine. Here, we examined the role of protein kinase C (PKC) isoforms in the regulation of the PAI-1 promoter and Sp1 transcriptional activity by the HBP. In transient transfections, exposure to 2 mm glucosamine or 20 mm glucose for 4 days increased the activities of a PAI-1 promoter-luciferase reporter gene as well as the Sp1 transcriptional activation domain fused to the GAL4 DNA-binding domain cotransfected with a GAL4 promoter-luciferase reporter. Cotransfected dominant negative PKC-betaI and -delta completely blocked the induction of PAI-1 promoter transcription by both sugars, whereas only dominant negative PKC-betaI interfered with Sp1-GAL4 activation. Both glucosamine and high glucose stimulated the in vitro kinase activity of immunoprecipitated PKC-betaI and -delta. Furthermore, 6-diazo-5-oxonorleucine suppressed high glucose-induced PKC kinase activity and Sp1-GAL4 transcriptional activation. These findings demonstrate a requirement for the PKC-betaI and -delta signal transduction pathways in HBP-induced transcription.

Sp1 is a key regulator of the PDGF beta-receptor transcription

The mouse PDGF beta-receptor promoter is tightly controlled by NF-Y that binds to a CCAAT box located upstream of the initiation site [1, 2]. In this report, we show that Sp1 plays an essential role in the PDGF beta-receptor transcription. Within the upstream GC rich area there are two Sp1 binding sites located in close proximity to the CCAAT box. Deletion of the GC rich region resulted in a 50% decrease of the transcriptional activity of the promoter, and a complete loss of its responsiveness to over-expression of Sp1. There was an additive effect between NF-Y and Sp I in reporter activity when they were co-transfected together with the promoter-reporter construct. Furthermore, transfection of NF-Y failed to enhance transcriptional activity when the Sp1 binding sites were deleted from the promoter, suggesting an important role for Sp1 in this NF-Y controlled transcription. We have recently reported that c-Myc represses PDGF beta-receptor transcription through its interference with the transactivation activity of NF-Y [3]. In the case of p21(wafl/cip1) transcription, c-Myc was shown to repress its transcription by sequestering Sp1 [4]. However, we could not find any effect of Sp1 in the c-Myc-mediated repression on the PFDGF beta-receptor promoter, since the deletion of SpI binding sites could not attenuate the repression by c-Myc on the promoter activity.

Activation of Erk1/Erk2 and transiently increased p53 levels together may account for p21 expression associated with phorbol ester-induced transient growth inhibition in HepG2 cells

In HepG2 cells grown in the presence of serum, enhanced Raf-activation correlated with transient growth inhibition. The activation of Raf was increased either by the phorbol ester-induced activation of protein kinase C (PKC) or by the addition of the PKC inhibitor bisindolylmaleimide I (BIM). Either of these treatments increased the cellular levels of p21 by an Erk1/Erk2 MAP kinase cascade-dependent way, since this increase was prevented by the MEK-inhibitor PD98059. Nevertheless, the growth inhibition correlated with the transient increase of p53 levels as well. Either the activation of PKC with phorbol ester or the addition of BIM to cells growing in serum induced a rapid but transient increase of p53 levels, which preceded growth inhibition. This increase of p53 levels was probably due to the transient stabilisation of p53 and did not require the activation of Erk1/Erk2.

Involvement of MAP kinase cascades in Smad7 transcriptional regulation

Smad7 transcription is known to be regulated by TGF-beta to form a negative-feedback loop of TGF-beta-mediated biological responses. In this study, we sought to determine whether other signaling cascades, especially mitogen-activated protein (MAP) kinases, might be involved in the transcriptional regulation of Smad7. Hyperosmolarity (500 mOsm/kg H(2)O) or anisomycin (10 microg/ml) potentiated TGF-beta-induced increases of Smad7 mRNA abundance in normal rat kidney fibroblasts. SB203580 (10 microM) treatment had no effect on basal and TGF-beta-induced Smad7 mRNA abundance, and the overexpression of kinase-negative ATF2 had no effect on Smad7 promoter activity. On the other hand, overexpression of dominant-negative JNK and dominant-negative c-Jun significantly attenuated the TGF-beta-induced increases of Smad7 mRNA abundance and promoter activity, respectively. Mutations of the AP-1 element near the Smad-binding element in the rat Smad7 promoter also completely abolished TGF-beta-induced Smad7 promoter activity. These results suggested that the JNK cascade, not p38 kinase, cooperated with the Smad signaling to induce Smad7 transcription through the AP-1 element. Serum treatment (10%) attenuated the TGF-beta-induced Smad7 mRNA increase, and PD98059 (30 microM) treatment increased the basal and TGF-beta-induced Smad7 promoter activity. Gel shift analysis revealed that serum treatment decreased the amount of nuclear Smad complex that PD98059 treatment was shown to restore. These results indicated that ERK activation negatively regulated Smad7 transcription possibly by inhibiting translocation of Smad complex to nuclei. In conclusion, JNK cascade and ERK cascade are important positive and negative regulators of Smad7 transcription, respectively.

Indole-3-carbinol (I3C) induced cell growth inhibition, G1 cell cycle arrest and apoptosis in prostate cancer cells

Prostate cancer is one of the most common cancers in men and it is the second leading cause of cancer related death in men in the United States. Recent dietary and epidemiological studies have suggested the benefit of dietary intake of fruits and vegetables in lowering the incidence of prostate cancer. A diet rich in fruits and vegetables provides phytochemicals, particularly indole-3-carbinol (I3C), which may be responsible for the prevention of many types of cancer, including hormone-related cancers such as prostate. Studies to elucidate the role and the molecular mechanism(s) of action of I3C in prostate cancer, however, have not been conducted. In the current study, we investigated whether I3C had any effect against prostate cancer cells and, if so, attempts were made to identify the potential molecular mechanism(s) by which I3C elicits its biological effects on prostate cancer cells. Here we report for the first time that I3C inhibits the growth of PC-3 prostate cancer cells. Induction of G1 cell cycle arrest was also observed in PC-3 cells treated with I3C, which may be due to the observed effects of I3C in the up-regulation of p21(WAF1) and p27(Kip1) CDK inhibitors, followed by their association with cyclin D1 and E and down-regulation of CDK6 protein kinase levels and activity. The induction of p21(WAF1) appears to be transcriptionally upregulated and independent of the p53 responsive element. In addition, I3C inhibited the hyperpohosphorylation of the Retinoblastoma (Rb) protein in PC-3 cells. Induction of apoptosis was also observed in this cell line when treated with I3C, as measured by DNA laddering and poly (ADP-ribose) polymersae (PARP) cleavage. We also found an up-regulation of Bax, and down-regulation of Bcl-2 in I3C-treated cells. These effects may also be mediated by the down-regulation of NF-kappaB observed in I3C treated PC-3 cells. From these results, we conclude that I3C inhibits the growth of PC-3 prostate cancer cells by inducing G1 cell cycle arrest leading to apoptosis, and regulates the expression of apoptosis-related genes. These findings suggest that I3C may be an effective chemopreventive or therapeutic agent against prostate cancer.

The human brm protein is cleaved during apoptosis: the role of cathepsin G

The human brm (hbrm) protein (homologue of the Drosophila melanogaster brahma and Saccharomyces cervisiae SNF-2 proteins) is part of a polypeptide complex believed to regulate chromatin conformation. We have shown that the hbrm protein is cleaved in NB4 leukemic cells after induction of apoptosis by UV-irradiation, DNA damaging agents, or staurosporine. Because hbrm is found only in the nucleus, we have investigated the nature of the proteases that may regulate the degradation of this protein during apoptosis. In an in vitro assay, the hbrm protein could not be cleaved by caspase-3, -7, or -6, the "effector" caspases generally believed to carry out the cleavage of nuclear protein substrates. In contrast, we find that cathepsin G, a granule enzyme found in NB4 cells, cleaves hbrm in a pattern similar to that observed in vivo during apoptosis. In addition, a peptide inhibitor of cathepsin G blocks hbrm cleavage during apoptosis but does not block activation of caspases or cleavage of the nuclear protein polyADP ribose polymerase (PARP). Although localized in granules and in the Golgi complex in untreated cells, cathepsin G becomes diffusely distributed during apoptosis. Cleavage by cathepsin G removes a 20-kDa fragment containing a bromodomain from the carboxyl terminus of hbrm. This cleavage disrupts the association between hbrm and the nuclear matrix; the 160-kDa hbrm cleavage fragment is less tightly associated with the nuclear matrix than full-length hbrm.

Involvement of TGF-beta in inhibitory effects of negatively charged liposomes on nitric oxide production by macrophages stimulated with lps

We examined the role of TGF-beta in the inhibitory effects of negatively charged liposomes composed of phosphatidylserine (PS-liposomes) on nitric oxide (NO) production by macrophages stimulated with LPS. The expression of TGF-beta mRNA increased when mouse peritoneal macrophages were treated with PS-liposomes. The inhibitory effect of PS-liposomes on NO production was restored by treatment with anti-TGF-beta antibody. Furthermore, NO production, iNOS mRNA expression, and iNOS protein induction by LPS were inhibited by treatment of macrophages with TGF-beta as well as PS-liposomes. These results indicated that PS-liposomes down-regulate NO production by macrophages through the induction of TGF-beta and suggested that TGF-beta may suppress NO production upstream of the transcription of iNOS mRNA.

Regulation of Smad signaling by protein kinase C

Cross talk between transforming growth factor b(TGF-b) serine/threonine kinase receptor signaling and tyrosine kinase receptor signaling modulates cell responsiveness to polypeptide growth factors regulating cell proliferation, differentiation, and apoptosis. Here we provide a mechanism through which Smad-dependent TGF-b signaling is modulated by protein kinase C (PKC). PKC, for example, is activated downstream of tyrosine kinase receptors. We show that PKC directly phosphorylates receptor-regulated Smad proteins. This phosphorylation abrogates the ability of Smad3 to bind directly to DNA, which leads to subsequent inability to mediate transcriptional responses dependent on the direct binding of Smad3 to DNA. Interference with PKC regulation of Smad functions increased cell sensitivity to transformation by the tumor promoter phorbol 12-myristate 13-acetate (PMA). PKC-dependent phosphorylation of Smad3 was found also to be a key event in the PMA-dependent inactivation of TGF-b-stimulated cell death. Thus, PKC-dependent phosphorylation of Smad3 leads to down-regulation of the growth inhibitory and apoptotic action of TGF-b.

Signaling of transforming growth factor-beta family members through Smad proteins

Smads are pivotal intracellular nuclear effectors of transforming growth factor-beta (TGF-beta) family members. Ligand-induced activation of TGF-beta family receptors with intrinsic serine/threonine kinase activity trigger phosphorylation of receptor-regulated Smads (R-Smads), whereas Smad2 and Smad3 are phosphorylated by TGF-beta, and activin type I receptors, Smad1, Smad5 and Smad8, act downstream of BMP type I receptors. Activated R-Smads form heteromeric complexes with common-partner Smads (Co-Smads), e.g. Smad4, which translocate efficiently to the nucleus, where they regulate, in co-operation with other transcription factors, coactivators and corepressors, the transcription of target genes. Inhibitory Smads act in most cases in an opposite manner from R- and Co-Smads. Like other components in the TGF-beta family signaling cascade, Smad activity is intricately regulated. The multifunctional and context dependency of TGF-beta family responses are reflected in the function of Smads as signal integrators. Certain Smads are somatically mutated at high frequency in particular types of human cancers. Gene ablation of Smads in the mouse has revealed their critical roles during embryonic development. Here we review the latest advances in our understanding of the Smad mechanism of action and their in vivo functions.

Transforming growth factor-beta 1 inhibition of macrophage activation is mediated via Smad3

Activated macrophages are critical cellular participants in inflammatory disease states. Transforming growth factor (TGF)-beta1 is a growth factor with pleiotropic effects including inhibition of immune cell activation. Although the pathway of gene activation by TGF-beta1 via Smad proteins has recently been elucidated, suppression of gene expression by TGF-beta1 remains poorly understood. We found that of Smad1-Smad7, Smad3 alone was able to inhibit expression of markers of macrophage activation (inducible nitric-oxide synthase and matrix metalloproteinase-12) following lipopolysaccharide treatment in gene reporter assays. Transient and constitutive overexpression of a dominant negative Smad3 opposed the inhibitory effect of TGF-beta1. Domain swapping experiments suggest that both the Smad MH-1 and MH-2 domains are required for inhibition. Mutation of a critical amino acid residue required for DNA binding in the MH-1 of Smad3 (R74A) resulted in the loss of inhibition. Transient overexpression of p300, an interactor of the Smad MH-2 domain, partially alleviated the inhibition by TGF-beta1/Smad3, suggesting that inhibition of gene expression may be due to increased competition for limiting amounts of this coactivator. Our results have implications for the understanding of gene suppression by TGF-beta1 and for the regulation of activated macrophages by TGF-beta1.