Structure and expression of the promoter for the R4/ALK5 human type I transforming growth factor-beta receptor: regulation by TGF-beta

Brain type of creatine kinase induces doxorubicin resistance via TGF-β signaling in MDA-MB-231 breast cancer cells

Brain type of creatine kinase (CKB) regulates energy homeostasis by reversibly transferring phosphate groups between phosphocreatine and ATP at sites of high energy demand. Several types of cancer cells exhibit upregulated CKB expression, but the function of CKB in cancer cells remains unclear. In this study, we investigated the function of CKB in breast cancer by overexpressing CKB in MDA-MB-231 cells. The overexpression of CKB did not affect cell growth rate, cell cycle distribution, ATP level or key mediators of aerobic glycolysis and lactate dehydrogenase isoform levels. Meanwhile, CKB overexpression did increase resistance to doxorubicin. TGF-β-induced Smad phosphorylation and Smad-dependent transcriptional activity were significantly up-regulated by CKB expression without changes in inhibitory Smad protein levels. Moreover, treatment with TGF-β considerably enhanced cell viability during doxorubicin treatment and decreased doxorubicin-induced apoptosis in CKB-expressing MDA-MB-231 cells compared to control cells. These results suggest that CKB attenuates doxorubicin-induced apoptosis and potentiates resistance to doxorubicin by enhancing TGF-β signaling in MDA-MB-231 cells.

Berberine inhibits epithelial-mesenchymal transition and promotes apoptosis of tumour-associated fibroblast-induced colonic epithelial cells through regulation of TGF-β signalling

Tumour-associated fibroblasts (TAFs) mediate the differentiation of adjacent stromal cells. Berberine (BBR), a monomer of traditional Chinese herbs, exhibits a potent therapeutic effect against cancer. However, the effects of BBR on the differentiation of normal colonic epithelial cells induced by TAFs have not been determined. In the present study, we selected the TAF-like myofibroblast cell line CCD-18Co. CCD-18Co-derived conditioned medium (CM) and co-culture induced epithelial-mesenchymal transition (EMT) changes in colonic epithelial HCoEpiC cells with decreased E-cadherin and increased vimentin and α-SMA expression. In addition, CCD-18Co stimulated the expression of ZEB1 and Snail and promoted motility. We used LY364947, a TGF-β receptor kinase type I (TβRI) inhibitor, and BBR. Our results showed that LY364947 and BBR inhibited these phenomena. BBR decreased the expression of ZEB1 and Snail, and this effect was concentration dependent. BBR also downregulated the expression of TβRI, TβRII, Smad2/p-Smad2 and Smad3/p-Smad3. In addition, BBR induced apoptosis in EMT-like HCoEpiC cells in a concentration-dependent manner with upregulation of Bax and downregulation of Bcl-2. However, VX-702, an inhibitor of p38 MAPK, significantly suppressed the apoptosis rate. BBR promoted the expression of p38 MAPK and phosphorylated p38 MAPK. In conclusion, berberine inhibits EMT and promotes apoptosis in TAF-induced colonic epithelial cells through mediation of the Smad-dependent and SMAD-independent TGF-β signalling pathways.

Ionizing radiation induces a motile phenotype in human carcinoma cells in vitro through hyperactivation of the TGF-beta signaling pathway

Radiotherapy, a major treatment modality against cancer, can lead to secondary malignancies but it is uncertain as to whether tumor cells that survive ionizing radiation (IR) treatment undergo epithelial-mesenchymal transition (EMT) and eventually become invasive or metastatic. Here, we have tested the hypothesis that the application of IR (10 MeV photon beams, 2-20 Gy) to lung and pancreatic carcinoma cells induces a migratory/invasive phenotype in these cells by hyperactivation of TGF-β and/or activin signaling. In accordance with this assumption, IR induced gene expression patterns and migratory responses consistent with an EMT phenotype. Moreover, in A549 cells, IR triggered the synthesis and secretion of both TGF-β1 and activin A as well as activation of intracellular TGF-β/activin signaling as evidenced by Smad phosphorylation and transcriptional activation of a TGF-β-responsive reporter gene. These responses were sensitive to SB431542, an inhibitor of type I receptors for TGF-β and activin. Likewise, specific antibody-mediated neutralization of soluble TGF-β, or dominant-negative inhibition of the TGF-β receptors, but not the activin type I receptor, alleviated IR-induced cell migration. Moreover, the TGF-β-specific approaches also blocked IR-dependent TGF-β1 secretion, Smad phosphorylation, and reporter gene activity, collectively indicating that autocrine production of TGF-β(s) and subsequent activation of TGF-β rather than activin signaling drives these changes. IR strongly sensitized cells to further increase their migration in response to recombinant TGF-β1 and this was accompanied by upregulation of TGF-β receptor expression. Our data raise the possibility that hyperactivation of TGF-β signaling during radiotherapy contributes to EMT-associated changes like metastasis, cancer stem cell formation and chemoresistance of tumor cells.

Activin Receptor-Like Kinase Receptors ALK5 and ALK1 Are Both Required for TGFβ-Induced Chondrogenic Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells

Introduction

Bone marrow-derived mesenchymal stem cells (BMSCs) are promising for cartilage regeneration because BMSCs can differentiate into cartilage tissue-producing chondrocytes. Transforming Growth Factor β (TGFβ) is crucial for inducing chondrogenic differentiation of BMSCs and is known to signal via Activin receptor-Like Kinase (ALK) receptors ALK5 and ALK1. Since the specific role of these two TGFβ receptors in chondrogenesis is unknown, we investigated whether ALK5 and ALK1 are expressed in BMSCs and whether both receptors are required for chondrogenic differentiation of BMSCs.

Materials & Methods

ALK5 and ALK1 gene expression in human BMSCs was determined with RT-qPCR. To induce chondrogenesis, human BMSCs were pellet-cultured in serum-free chondrogenic medium containing TGFβ1. Chondrogenesis was evaluated by aggrecan and collagen type IIα1 RT-qPCR analysis, and histological stainings of proteoglycans and collagen type II. To overexpress constitutively active (ca) receptors, BMSCs were transduced either with caALK5 or caALK1. Expression of ALK5 and ALK1 was downregulated by transducing BMSCs with shRNA against ALK5 or ALK1.

Results

ALK5 and ALK1 were expressed in in vitro-expanded as well as in pellet-cultured BMSCs from five donors, but mRNA levels of both TGFβ receptors did not clearly associate with chondrogenic induction. TGFβ increased ALK5 and decreased ALK1 gene expression in chondrogenically differentiating BMSC pellets. Neither caALK5 nor caALK1 overexpression induced cartilage matrix formation as efficient as that induced by TGFβ. Moreover, short hairpin-mediated downregulation of either ALK5 or ALK1 resulted in a strong inhibition of TGFβ-induced chondrogenesis.

Conclusion

ALK5 as well as ALK1 are required for TGFβ-induced chondrogenic differentiation of BMSCs, and TGFβ not only directly induces chondrogenesis, but also modulates ALK5 and ALK1 receptor signaling in BMSCs. These results imply that optimizing cartilage formation by mesenchymal stem cells will depend on activation of both receptors.

Induction of transforming growth factor beta receptors following focal ischemia in the rat brain

Transforming growth factor-βs (TGF-βs) regulate cellular proliferation, differentiation, and survival. TGF-βs bind to type I (TGF-βRI) and II receptors (TGF-βRII), which are transmembrane kinase receptors, and an accessory type III receptor (TGF-βRIII). TGF-β may utilize another type I receptor, activin-like kinase receptor (Alk1). TGF-β is neuroprotective in the middle cerebral artery occlusion (MCAO) model of stroke. Recently, we reported the expression pattern of TGF-β1-3 after MCAO. To establish how TGF-βs exert their actions following MCAO, the present study describes the induction of TGF-βRI, RII, RIII and Alk1 at 24 h, 72 h and 1 mo after transient 1 h MCAO as well as following 24 h permanent MCAO using in situ hybridization histochemistry. In intact brain, only TGF-βRI had significant expression: neurons in cortical layer IV contained TGF-βRI. At 24 h after the occlusion, no TGF-β receptors showed induction. At 72 h following MCAO, all four types of TGF-β receptors were induced in the infarct area, while TGF-βRI and RII also appeared in the penumbra. Most cells with elevated TGF-βRI mRNA levels were microglia. TGF-βRII co-localized with both microglial and endothelial markers while TGF-βRIII and Alk1 were present predominantly in endothels. All four TGF-β receptors were induced within the lesion 1 mo after the occlusion. In particular, TGF-βRIII was further induced as compared to 72 h after MCAO. At this time point, TGF-βRIII signal was predominantly not associated with blood vessels suggesting its microglial location. These data suggest that TGF-β receptors are induced after MCAO in a timely and spatially regulated fashion. TGF-β receptor expression is preceded by increased TGF-β expression. TGF-βRI and RII are likely to be co-expressed in microglial cells while Alk1, TGF-βRII, and RIII in endothels within the infarct where TGF-β1 may be their ligand. At later time points, TGF-βRIII may also appear in glial cells to potentially affect signal transduction via TGF-βRI and RII.

Tacrolimus abrogates TGF-β1-induced type I collagen production in normal human fibroblasts through suppressing p38MAPK signalling pathway: implications on treatment of chronic atopic dermatitis lesions

BACKGROUND

Atopic dermatitis (AD) is a commonly encountered inflammatory skin disease. Although acute lesions of acute AD are characterized by intense inflammation, the hallmarks of chronic AD lesions include lichenified fibrosis and thickening of the upper dermis. The increased expression of transforming growth factor beta 1 (TGF-β1), a well-known fibrogenic cytokine, is observed in chronic AD lesions. Tacrolimus (FK506) ointment has been reported to be effective for treating AD as well as some TGF-β1-induced fibrotic diseases.

OBJECTIVES

To evaluate the effect of tacrolimus on TGF-β1-stimulated cultured normal human dermal fibroblasts and explore the potential signalling pathways involved.

METHODS

Fibroblasts cultured from healthy adult human foreskins were treated with TGF-β1 with or without tacrolimus. The impact on cell viability and proliferation were assessed by [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) assay and BrdU incorporation assay respectively. Reverse transcription-polymerase chain reaction (RT-PCR), quantitative real-time PCR, enzyme-linked immunosorbent assay (ELISA) and western blotting were performed to evaluate the relevant expressions of mRNA or proteins in fibroblasts.

RESULTS

Our results revealed that the increased expressions of transforming growth factor-β receptor I (TGF-βRI) and TGF-βRII in TGF-β1-treated fibroblasts were suppressed by tacrolimus treatment. In addition, tacrolimus significantly inhibited fibroblast proliferation enhanced by TGF-β1. TGF-β1 increased type I collagen production, and this enhancing effect was suppressed by tacrolimus. The down-regulation of MMP-1 and up-regulation of TIMP-1 induced by TGF-β1 were reversed by tacrolimus. The increase in phosphorylated p38 mitogen-activated protein kinase (p38MAPK) expression stimulated by TGF-β1 was down-regulated by tacrolimus. Moreover, the fibroblasts treated with p38MAPK inhibitor significantly reduced type I collagen expression induced by TGF-β1.

CONCLUSIONS

The present results demonstrated that tacrolimus significantly inhibited physiological functions of fibroblasts enhanced by TGF-β1 in vitro. Clinically, we propose that topical tacrolimus may not only reduce AD recurrence but also ameliorate dermal fibrosis often seen in chronic AD lesions.

The BHLH transcription factor DEC1 plays an important role in the epithelial-mesenchymal transition of pancreatic cancer

DEC1 (BHLHE40/Stra13/Sharp2) is a basic helix-loop-helix (bHLH) transcription factor that is involved in the regulation of apoptosis and cell proliferation and the response to hypoxia. Epithelial-mesenchymal transition (EMT) is an important step leading to invasion and migration of various tumor cells, and TGF-β treatment has been shown to induce cancer cells to undergo EMT. However, the significance of DEC1 in TGF-β-induced EMT remains unknown. We examined the role of DEC1 in EMT of PANC-1 cells, a human pancreatic cancer cell line. As a result, we found that DEC1 was upregulated by TGF-β in PANC-1 cells, and regulated the expression and the levels of nuclear, cytoplasmic or membrane localization of EMT-related factors, including phosphorylated Smad3 (pSmad3), snail, claudin-4 and N-cadherin. In the presence of TGF-β, DEC1 knockdown by siRNA inhibited morphological changes during EMT processes, while TGF-β induced PANC-1 cells to taken on a spindle-shaped morphology. Furthermore, a combination treatment of DEC1 expression with TGF-β was closely linked to the migration and invasion of PANC-1 cells. Immunohistochemically, DEC1 and pSmad3 were detected within pancreatic cancer tissues, whereas claudin-4 expression was weaker in the cancer tissues compared with the adjacent non-cancer pancreatic tissues. These findings suggest that DEC1 plays an important role in the regulation of these EMT-related factors in pancreatic cancer.

Off-target effects dominate a large-scale RNAi screen for modulators of the TGF-β pathway and reveal microRNA regulation of TGFBR2

BACKGROUND

RNA interference (RNAi) screens have been used to identify novel components of signal-transduction pathways in a variety of organisms. We performed a small interfering (si)RNA screen for novel members of the transforming growth factor (TGF)-β pathway in a human keratinocyte cell line. The TGF-β pathway is integral to mammalian cell proliferation and survival, and aberrant TGF-β responses have been strongly implicated in cancer.

RESULTS

We assayed how strongly single siRNAs targeting each of 6,000 genes affect the nuclear translocation of a green fluorescent protein (GFP)-SMAD2 reporter fusion protein. Surprisingly, we found no novel TGF-β pathway members, but we did find dominant off-target effects. All siRNA hits, whatever their intended direct target, reduced the mRNA levels of two known upstream pathway components, the TGF-β receptors 1 and 2 (TGFBR1 and TGFBR2), via micro (mi)RNA-like off-target effects. The scale of these off-target effects was remarkable, with at least 1% of the sequences in the unbiased siRNA library having measurable off-target effects on one of these two genes. It seems that relatively minor reductions of message levels via off-target effects can have dominant effects on an assay, if the pathway output is very dose-sensitive to levels of particular pathway components. In search of mechanistic details, we identified multiple miRNA-like sequence characteristics that correlated with the off-target effects. Based on these results, we identified miR-20a, miR-34a and miR-373 as miRNAs that inhibit TGFBR2 expression.

CONCLUSIONS

Our findings point to potential improvements for miRNA/siRNA target prediction methods, and suggest that the type II TGF-β receptor is regulated by multiple miRNAs. We also conclude that the risk of obtaining misleading results in siRNA screens using large libraries with single-assay readout is substantial. Control and rescue experiments are essential in the interpretation of such screens, and improvements to the methods to reduce or predict RNAi off-target effects would be beneficial.

Modulation of transforming growth factor beta signalling pathway genes by transforming growth factor beta in human osteoarthritic chondrocytes: involvement of Sp1 in both early and late response cells to transforming growth factor beta

Introduction

Transforming growth factor beta (TGFβ) plays a central role in morphogenesis, growth, and cell differentiation. This cytokine is particularly important in cartilage where it regulates cell proliferation and extracellular matrix synthesis. While the action of TGFβ on chondrocyte metabolism has been extensively catalogued, the modulation of specific genes that function as mediators of TGFβ signalling is poorly defined. In the current study, elements of the Smad component of the TGFβ intracellular signalling system and TGFβ receptors were characterised in human chondrocytes upon TGFβ1 treatment.

Methods

Human articular chondrocytes were incubated with TGFβ1. Then, mRNA and protein levels of TGFβ receptors and Smads were analysed by RT-PCR and western blot analysis. The role of specific protein 1 (Sp1) was investigated by gain and loss of function (inhibitor, siRNA, expression vector).

Results

We showed that TGFβ1 regulates mRNA levels of its own receptors, and of Smad3 and Smad7. It modulates TGFβ receptors post-transcriptionally by affecting their mRNA stability, but does not change the Smad-3 and Smad-7 mRNA half-life span, suggesting a potential transcriptional effect on these genes. Moreover, the transcriptional factor Sp1, which is downregulated by TGFβ1, is involved in the repression of both TGFβ receptors but not in the modulation of Smad3 and Smad7. Interestingly, Sp1 ectopic expression permitted also to maintain a similar expression pattern to early response to TGFβ at 24 hours of treatment. It restored the induction of Sox9 and COL2A1 and blocked the late response (repression of aggrecan, induction of COL1A1 and COL10A1).

Conclusions

These data help to better understand the negative feedback loop in the TGFβ signalling system, and enlighten an interesting role of Sp1 to regulate TGFβ response.

Characterization of the human Activin-A receptor type II-like kinase 1 (ACVRL1) promoter and its regulation by Sp1

Background

Activin receptor-like kinase 1 (ALK1) is a Transforming Growth Factor-β (TGF-β) receptor type I, mainly expressed in endothelial cells that plays a pivotal role in vascular remodelling and angiogenesis. Mutations in the ALK1 gene (ACVRL1) give rise to Hereditary Haemorrhagic Telangiectasia, a dominant autosomal vascular dysplasia caused by a haploinsufficiency mechanism. In spite of its patho-physiological relevance, little is known about the transcriptional regulation of ACVRL1. Here, we have studied the different origins of ACVRL1 transcription, we have analyzed in silico its 5'-proximal promoter sequence and we have characterized the role of Sp1 in the transcriptional regulation of ACVRL1.

Results

We have performed a 5'Rapid Amplification of cDNA Ends (5'RACE) of ACVRL1 transcripts, finding two new transcriptional origins, upstream of the one previously described, that give rise to a new exon undiscovered to date. The 5'-proximal promoter region of ACVRL1 (-1,035/+210) was analyzed in silico, finding that it lacks TATA/CAAT boxes, but contains a remarkably high number of GC-rich Sp1 consensus sites. In cells lacking Sp1, ACVRL1 promoter reporters did not present any significant transcriptional activity, whereas increasing concentrations of Sp1 triggered a dose-dependent stimulation of its transcription. Moreover, silencing Sp1 in HEK293T cells resulted in a marked decrease of ACVRL1 transcriptional activity. Chromatin immunoprecipitation assays demonstrated multiple Sp1 binding sites along the proximal promoter region of ACVRL1 in endothelial cells. Furthermore, demethylation of CpG islands, led to an increase in ACVRL1 transcription, whereas in vitro hypermethylation resulted in the abolishment of Sp1-dependent transcriptional activation of ACVRL1.

Conclusions

Our results describe two new transcriptional start sites in ACVRL1 gene, and indicate that Sp1 is a key regulator of ACVRL1 transcription, providing new insights into the molecular mechanisms that contribute to the expression of ACVRL1 gene. Moreover, our data show that the methylation status of CpG islands markedly modulates the Sp1 regulation of ACVRL1 gene transcriptional activity.

Mechanisms of decreased expression of transforming growth factor-beta receptor type I at late stages of HPV16-mediated transformation

Transforming growth factor-beta (TGF-beta) signaling is disrupted in many cancers, including cervical cancer, leading to TGF-beta resistance. Although initially sensitive, human papillomavirus type 16 (HPV16) immortalized human keratinocytes (HKc/HPV16) become increasingly resistant to the growth inhibitory effects of TGF-beta during in vitro progression to a differentiation resistant phenotype (HKc/DR). We have previously shown that loss of TGF-beta sensitivity in HKc/DR is attributed to decreased expression of TGF-beta receptor type I (TGF-beta RI), while the levels of TGF-beta receptor type II (TGF-beta RII) remain unchanged. The present study explored molecular mechanisms leading to reduced TGF-beta RI expression in HKc/DR. Using TGF-beta RI and TGF-beta RII promoter reporter constructs, we determined that acute expression of the HPV16 oncogenes E6 and E7 decreased the promoter activity of TGF-beta RI and TGF-beta RII by about 50%. However, promoter activity of TGF-beta RI is decreased to a greater extent than TGF-beta RII as HKc/HPV16 progress to HKc/DR. Reduced TGF-beta RI expression in HKc/DR was found not to be linked to mutations within the TGF-beta RI promoter or to promoter methylation. Electrophoretic mobility shift and supershift assays using probes encompassing Sp1 binding sites in the TGF-beta RI promoter found no changes between HKc/HPV16 and HKc/DR in binding of the transcription factors Sp1 or Sp3 to the probes. Also, Western blots determined that protein levels of Sp1 and Sp3 remain relatively unchanged between HKc/HPV16 and HKc/DR. Overall, these results demonstrate that mutations in or hypermethylation of the TGF-beta RI promoter, along with altered levels of Sp1 or Sp3, are not responsible for the reduced expression of TGF-beta RI we observe in HKc/DR. Rather the HPV16 oncogenes E6 and E7 themselves exhibit an inhibitory effect on TGF-beta receptor promoter activity.

Autocrine TGF-beta signaling in the pathogenesis of systemic sclerosis

Excessive extracellular matrix deposition in the skin, lung, and other organs is a hallmark of systemic sclerosis (SSc). Fibroblasts isolated from sclerotic lesions in patients with SSc and cultured in vitro are characterized by increased synthesis of collagen and other extracellular matrix components, consistent with the disease phenotype. Thus, cultured scleroderma fibroblasts serve as a principal experimental model for studying the mechanisms involved in extracellular matrix overproduction in SSc. The pathogenesis of SSc is still poorly understood, but increasing evidence suggests that transforming growth factor-beta (TGF-beta) is a key mediator of tissue fibrosis as a consequence of extracellular matrix accumulation in the pathology of SSc. TGF-beta regulates diverse biological activities including cell growth, cell death or apoptosis, cell differentiation, and extracellular matrix synthesis. TGF-beta is known to induce the expression of extracellular matrix proteins in mesenchymal cells and to stimulate the production of protease inhibitors that prevent enzymatic breakdown of the extracellular matrix. This review focuses on the possible role of autocrine TGF-beta signaling in the pathogenesis of SSc.

Epidermal growth factor up-regulates transforming growth factor-beta receptor type II in human dermal fibroblasts via p38 mitogen-activated protein kinase pathway

TGF-beta receptors (TbetaRs) are serine/threonine kinase receptors that bind to TGF-beta and propagate intracellular signaling through Smad proteins. TbetaRs are repressed in some human cancers and expressed at high levels in several fibrotic diseases. We demonstrated that epidermal growth factor (EGF) up-regulates type II TGF-beta receptor (TbetaRII) expression in human dermal fibroblasts. EGF-mediated induction of TbetaRII expression was inhibited by the treatment of fibroblasts with a specific p38 mitogen-activated protein kinase (MAPK) inhibitor, SB203580, whereas MEK inhibitor PD98059 did not block the up-regulation of TbetaRII by EGF. EGF induced the TbetaRII promoter activity, and this induction was significantly blocked by SB203580, but not by PD98059. The overexpression of the dominant negative form of p38alpha or p38beta significantly reduced the induction of TbetaRII promoter activity by EGF. These results indicate that the EGF-mediated induction of TbetaRII expression involves the p38 MAPK signaling pathway. The EGF-mediated induction of TbetaRII expression may participate in a synergistic interplay between EGF and TGF-beta signaling pathway.

Extracellular matrix proteoglycans control the fate of bone marrow stromal cells

Extracellular matrix glycoproteins and proteoglycans bind a variety of growth factors and cytokines thereby regulating matrix assembly as well as bone formation. However, little is known about the mechanisms by which extracellular matrix molecules modulate osteogenic stem cells and bone formation. Using mice deficient in two members of the small leucine-rich proteoglycans, biglycan and decorin, we uncovered a role for these two extracellular matrix proteoglycans in modulating bone formation from bone marrow stromal cells. Our studies showed that the absence of the critical transforming growth factor-beta (TGF-beta)-binding proteoglycans, biglycan and decorin, prevents TGF-beta from proper sequestration within the extracellular matrix. The excess TGF-beta directly binds to its receptors on bone marrow stromal cells and overactivates its signaling transduction pathway. Overall, the predominant effect of the increased TGF-beta signaling in bgn/dcn-deficient bone marrow stromal cells is a "switch in fate" from growth to apoptosis, leading to decreased numbers of osteoprogenitor cells and subsequently reduced bone formation. Thus, biglycan and decorin appear to be essential for maintaining an appropriate number of mature osteoblasts by modulating the proliferation and survival of bone marrow stromal cells. These findings underscore the importance of the micro-environment in controlling the fate of adult stem cells and reveal a novel cellular and molecular basis for the physiological and pathological control of bone mass.

Alteration of the TGF-β/SMAD pathway in intrinsically and UV-induced skin aging

In an effort to characterize transforming growth factor (TGF-beta) signaling and to determine its association with the aging and photoaging processes, we directly compared the expressions of TGF-beta/SMAD in intrinsically aged and photoaged human skin in vivo. By using an RNase protection assay and by immunohistochemistry, we found that the expression levels of TbetaRII mRNA and protein in the epidermis of the forearm (sun-exposed) of the elderly were significantly lower than that of the upper-inner arm (sun-protected) skin of the same individual. In the epidermis, the expressions of Smad7 mRNA in both the intrinsically aged and photoaged skin of the elderly were higher than in the sun-protected skin of the young, and this was elevated in the photoaged epidermis. Decreased pSmad2 immunoreactivity was observed in the epidermis of photoaged forearm skin versus matched intrinsically aged skin. This decrease was also found in the epidermis of upper-inner arm skin of the elderly versus the young. These results suggest that the UV-induced down-regulation of TbetaRII and the concerted over-expression of Smad7 may trigger the inhibition of the TGF-beta-induced phosphorylation of Smad2.

Solar ultraviolet irradiation reduces collagen in photoaged human skin by blocking transforming growth factor-beta type II receptor/Smad signaling

Ultraviolet (UV) irradiation from the sun reduces production of type I procollagen (COLI), the major structural protein in human skin. This reduction is a key feature of the pathophysiology of premature skin aging (photoaging). Photoaging is the most common form of skin damage and is associated with skin carcinoma. TGF-beta/Smad pathway is the major regulator of type I procollagen synthesis in human skin. We have previously reported that UV irradiation impairs transforming growth factor-beta (TGF-beta)/Smad signaling in mink lung epithelial cells. We have investigated the mechanism of UV irradiation impairment of the TGF-beta/Smad pathway and the impact of this impairment on type I procollagen production in human skin fibroblasts, the major collagen-producing cells in skin. We report here that UV irradiation impairs TGF-beta/Smad pathway in human skin by down-regulation of TGF-beta type II receptor (TbetaRII). This loss of TbetaRII occurs within 8 hours after UV irradiation and precedes down-regulation of type I procollagen expression in human skin in vivo. In human skin fibroblasts, UV-induced TbetaRII down-regulation is mediated by transcriptional repression and results in 90% reduction of specific, cell-surface binding of TGF-beta. This loss of TbetaRII prevents downstream activation of Smad2/3 by TGF-beta, thereby reducing expression of type I procollagen. Preventing loss of TbetaRII by overexpression protects against UV inhibition of type I procollagen gene expression in human skin fibroblasts. UV-induced down-regulation of TbetaRII, with attendant reduction of type I procollagen production, is a critical molecular mechanism in the pathophysiology of photoaging.

Nkx2.1 transcription factor in lung cells and a transforming growth factor-beta1 heterozygous mouse model of lung carcinogenesis

The Nkx2.1 homeobox gene and transforming growth factor-beta1 (TGF-beta1) are essential for organogenesis and differentiation of the mouse lung. NKX2.1 is a marker of human lung carcinomas, but it is not known whether this gene participates in early tumorigenesis. Addition of TGF-beta1 to TGF-beta1-responsive nontumorigenic mouse lung cells cotransfected with a NKX2.1Luc luciferase reporter and either a Sp1 or Sp3 plasmid showed a significant increase or decrease, respectively, in NKX2.1Luc transcription. Cotransfection of Sp3 and dominant-negative TGF-beta type II receptor plasmids negated the effect of Sp1. Cotransfected Sp1 plasmid with either dominant-negative Smad2 or Smad3 or Smad4 plasmids significantly decreased NKX2.1Luc transcription. Electrophoretic mobility shift assays revealed binding of Sp1 and Smad4 to the NKX2.1 promoter. With a TGF-beta1 heterozygous mouse model, Nkx2.1 mRNA and protein in lungs of TGF-beta1 heterozygous mice were significantly lower compared to wildtype (WT) littermates. Competitive reverse transcription (RT)-polymerase chain reaction (PCR) and immunostaining showed that Nkx2.1 mRNA and protein decreased significantly in adenomas and adenocarcinomas compared to normal lung tissue. Our in vitro data showed that regulation of Nkx2.1 by TGF-beta1 occurs through TGF-beta type II receptor and Smad signaling, with Sp1 and Sp3 in lung cells. Our in vivo data showed reduced Nkx2.1 in lungs of TGF-beta1 heterozygous mice compared to WT mice, that is detectable in adenomas, and that is further reduced in carcinogenesis, and that correlates with reduction of Sp1, Sp3, and Smads in lung adenocarcinomas. Our findings suggest that reduced Nkx2.1 and TGF-beta1 signaling components may contribute to tumorigenesis in the lungs of TGF-beta1 heterozygous mice.

Restoration of transforming growth factor-beta signaling through receptor RI induction by histone deacetylase activity inhibition in breast cancer cells

The loss of transforming growth factor-beta (TGF-beta) response due to the dysregulation of TGF-beta receptors type I (RI) and type II (RII) is well known for its contribution to oncogenesis. Estrogen receptor-expressing breast cancer cells are refractory to TGF-beta-mediated growth control because of the reduced expression of TGF-beta receptors. Although RII is required for the binding of TGF-beta to RI, RI is responsible for directly transducing TGF-beta signals through the Smad protein family. Treatment of estrogen receptor-expressing MCF-7L and ZR75 breast cancer cells with the histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) led to a dramatic induction of RI. Accumulation of acetylated histones H3 and H4 was observed in the SAHA-treated cells. Chromatin immunoprecipitation analysis followed by PCR with RI promoter-specific primers indicated an accumulation of acetylated histones in chromatin associated with the RI gene, suggesting that histone deacetylation was involved in the transcriptional inactivation of RI. SAHA treatment stimulated RI promoter activity through the inhibition of Sp1/Sp3-associated HDAC activity. Histone acetyltransferase p300 stimulated RI promoter activity, thus further confirming the involvement of HDAC activity in the transcriptional repression of RI. Significantly, SAHA-mediated RI regeneration restored the TGF-beta response in breast cancer cells.

Regulation of Fgf10 gene expression in the prostate: identification of transforming growth factor-beta1 and promoter elements

Fibroblast growth factor 10 (FGF10) is a mesenchymal paracrine-acting factor that plays a key role in the organogenesis of the prostate, and Fgf10 transcripts exhibit a highly restricted expression pattern within prostatic mesenchyme. To study the regulation of Fgf10 we have used organ rudiments grown in vitro as well as a primary stromal cell system derived from the ventral mesenchymal pad (VMP), a condensed area of mesenchyme known to induce prostatic organogenesis. Characterization of VMP cells (VMPCs) showed that they retained expression of AR as well as transcripts for FGF10 and TGFbeta1, -2, and -3. We propose that VMPCs are a good model of specialized mesenchyme involved in prostatic organogenesis and are distinct from general urogenital sinus mesenchyme/stroma. Treatment of VMPCs with TGFbeta1 resulted in a rapid and transient decrease in Fgf10 transcript levels, which were reduced 9-fold at 3 h. TGFbeta1 also inhibited Fgf10 expression in VMP organ rudiments grown in vitro. To further analyze Fgf10 regulation, 6 kb of mouse genomic sequence 5' to the translation start site was characterized by promoter analysis. Deletion analysis of the Fgf10 promoter in VMPCs identified a region of the promoter that mediated a significant proportion of promoter activity as well as mediating promoter down-regulation by TGFbeta1. This element was located between nucleotides -182 and -172 and contained a consensus Sp1 binding site. Taken together, our data suggest that TGFbeta1 is a regulator of Fgf10 expression in prostatic mesenchyme and that a proximal element within the Fgf10 promoter plays an important role in its regulation and expression.

Sequential Gonadotropin Treatment of Immature Mice Leads to Amplification of Transforming Growth Factor β Action, Via Upregulation of Receptor-Type 1, Smad 2 and 4, and Downregulation of Smad 6

The present study was designed to establish the cellular localization and expression of transforming growth factor beta (TGFbeta) signaling pathway components, including TGFbeta1 and beta2; TGFbeta receptors type I (TbetaRI) and II (TbetaRII); and Smads 2, 3, 4, and 6 during gonadotropin-induced follicular maturation and ovulation in the mouse ovary. Immature 21-day-old mice were sequentially treated with recombinant human FSH, 5 IU daily for 3 days, and hCG once at Day 24 of life. Immunohistochemical experiments revealed a TGFbeta1 staining in granulosa cells (GC) and theca interna cells (TIC) as well as in oocytes, whereas that of TGFbeta2 was mainly localized in oocytes and GC. Strong immunostaining for both TbetaRI and -RII was observed in the TIC and, to a lesser extent, in GC. Whereas oocytes did not exhibit any staining for TbetaRII, their TbetaRI immunostaining was strong. Smads were detected in oocytes, GC, and luteal cells and in a lesser amount in TIC; the immunostaining for Smad 4 was the strongest. Western blotting and reverse transcription-polymerase chain reaction analyses indicated that, in response to gonadotropins, TGFbeta2, TbetaRI, Smad 2 and Smad 4 mRNA and protein levels increased, while those of Smad 6 decreased in ovarian homogenates. In conclusion, these results show that, in a model of immature mouse exposed to a sequential gonadotropin treatment, FSH and LH increased the expression of the TGFbeta signaling system through the increase of TGFbeta2, TbetaRI, stimulatory Smad 2, and common Smad 4 expression, which occurred concomitantly with a decrease of the inhibitory Smad 6 expression.

Antagonistic effects of TNF-alpha on TGF-beta signaling through down-regulation of TGF-beta receptor type II in human dermal fibroblasts

Transforming growth factor-beta stimulates the production of the extracellular matrix, whereas TNF-alpha has antifibrotic activity. Understanding the molecular mechanism underlying the antagonistic activities of TNF-alpha against TGF-beta is critical in the context of tissue repair and maintenance of tissue homeostasis. In the present study, we demonstrated a novel mechanism by which TNF-alpha blocks TGF-beta-induced gene and signaling pathways in human dermal fibroblasts. We showed that TNF-alpha prevents TGF-beta-induced gene trans activation, such as alpha2(I) collagen or tissue inhibitor of metalloproteinases 1, and TGF-beta signaling pathways, such as Smad3, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinases, without inducing levels of inhibitory Smad7 in human dermal fibroblasts. TNF-alpha down-regulates the expression of type II TGF-beta receptor (TbetaRII) proteins, but not type I TGF-beta receptor (TbetaRI), in human dermal fibroblasts. However, neither TbetaRII mRNA nor TbetaRII promoter activity was decreased by TNF-alpha. TNF-alpha-mediated decrease of TbetaRII protein expression was not inhibited by the treatment of fibroblasts with either a selective inhibitor of I-kappaB-alpha phosphorylation, BAY 11-7082, or a mitogen-activated protein kinase/extracellular signal-regulated kinase inhibitor, PD98059. Calpain inhibitor I (ALLN), a protease inhibitor, inhibits TNF-alpha-mediated down-regulation of TbetaRII. We found that TNF-alpha triggered down-regulation of TbetaRII, leading to desensitization of human dermal fibroblasts toward TGF-beta. Furthermore, these events seemed to cause a dramatic down-regulation of alpha2(I) collagen and tissue inhibitor of metalloproteinases 1 in systemic sclerosis fibroblasts. These results indicated that TNF-alpha impaired the response of the cells to TGF-beta by regulating the turnover of TbetaRII.

Dexamethasone inhibits transforming growth factor-beta receptor (Tbeta R) messenger RNA expression in hamster preantral follicles: possible association with NF-YA

To evaluate the site(s) and mechanism(s) of glucocorticoid-inhibition of transforming growth factor (TGF) beta receptor (TbetaR) mRNA expression in ovarian cells, steady-state levels of TbetaR mRNA in hamster preantral follicles exposed to FSH or estradiol with or without dexamethasone were determined by reverse transcription polymerase chain reaction and Southern hybridization. The effect of dexamethasone on follicular DNA and steroid synthesis and the expression of NF-Y and Sp3 were also investigated. Dexamethasone differentially inhibited FSH- or estradiol-induced expression of TbetaR mRNA in preantral follicles at all stages. Dexamethasone also strongly inhibited FSH-induced but not TGFbeta2-induced follicular DNA synthesis, and the inhibition was completely reversed by TGFbeta2. However, TGFbeta2 markedly attenuated FSH + dexamethasone-stimulated progesterone and FSH-induced follicular estradiol synthesis. Both FSH and estradiol upregulated NF-YA expression, but the effect was significantly attenuated by dexamethasone. Our results suggest that suppression of NF-YA levels is one of the mechanisms whereby dexamethasone reduces hormone-induced TbetaRI and TbetaRII mRNA levels in hamster preantral follicles. Dexamethasone potentiates the effect of FSH on granulosa cell steroidogenesis, whereas TGFbeta counteracts the effect. These data indicate that glucocorticoid and TGFbeta may form an important regulatory loop to modulate FSH regulation of preantral follicular growth and differentiation.

Epidermal growth factor up-regulates expression of transforming growth factor beta receptor type II in human dermal fibroblasts by phosphoinositide 3-kinase/Akt signaling pathway: Resistance to epidermal growth factor stimulation in scleroderma fibroblasts

OBJECTIVE

Transforming growth factor beta receptors (TGFbetaRs) are known to be expressed at high levels in several fibrotic diseases, including systemic sclerosis. In the present study, we investigated the mechanism of up-regulation of TGFbetaR expression.

METHODS

The levels of expression of TGFbetaR type II (TGFbetaRII) messenger RNA (mRNA), with or without stimulation by epidermal growth factor (EGF), were evaluated by Northern blot analysis, and the protein levels were determined by immunoblotting. The transcription activity of the TGFbetaRII gene was examined with luciferase assays using the -1670/+35 TGFbetaRII promoter luciferase construct.

RESULTS

EGF up-regulates the expression of TGFbetaRII mRNA and protein in human dermal fibroblasts. Actinomycin D, an RNA synthesis inhibitor, significantly blocked the EGF-mediated up-regulation of TGFbetaRII mRNA expression, whereas cycloheximide, a protein synthesis inhibitor, did not block this up-regulation. In addition, EGF treatment did not significantly affect the TGFbetaRII mRNA half-life. EGF-mediated induction of TGFbetaRII expression was inhibited by treatment of fibroblasts with the selective phosphoinositide 3-kinase (PI 3-kinase) inhibitors wortmannin or LY294002, and Akt inhibitor also blocked EGF-induced expression of TGFbetaRII. In addition, EGF induced TGFbetaRII promoter activity, and this induction was significantly blocked by wortmannin, LY294002, or Akt inhibitor. Cotransfection with a dominant-negative mutant of p85 (the regulatory component of PI 3-kinase) or Akt significantly reduced the induction of TGFbetaRII promoter activity by EGF. Moreover, a constitutive active form of p110 (a catalytic component of PI 3-kinase) induced TGFbetaRII promoter activity. In addition, scleroderma fibroblasts expressed increased levels of TGFbetaRII but did not show further up-regulation of TGFbetaRII expression by EGF.

CONCLUSION

These results indicate that EGF-mediated induction of TGFbetaRII expression occurs at the transcription level, does not require de novo protein synthesis, and involves the PI 3-kinase/Akt signaling pathway, and that abnormal activation of EGF-mediated signaling pathways, including PI 3-kinase or Akt, might play a role in the up-regulation of TGFbetaRII in scleroderma fibroblasts.

Gene structure and expression of cg-ALR1, a type I activin-like receptor from the bivalve mollusc Crassostrea gigas

Members of the transforming growth factor beta superfamily of cell signaling polypeptides have attracted much attention because of their ability, from nematodes to mammals, to control cellular functions that in turn, regulate embryo development and tissue homeostasis (the transforming growth factors betas 95 (1990) 419). To understand the divergent evolution of the structures and functions of the transforming growth factor beta receptors (superfamily) we report here the cloning and characterization of an activin-like type I receptor gene from the oyster Crassostrea gigas (cgALR1). This 6 Kb gene encodes a 534 amino acid long protein consisting of a signal peptide, an extracellular ligand binding domain, a transmembrane region and an intracellular domain. The intracellular domain contains sequence motifs such as the GS box and EIF/V and RIKKTL boxes that are thought to be hallmarks of activin type I receptors. The protein sequence shares 67% amino acid identity with other serine/threonine kinase receptors in the most conserved kinase domain and 47-49% similarity with vertebrate type I receptors. The temporal expression pattern of cgALR1 transcripts was examined during early larval developmental stages. To gain insight into evolutionary diversification, phylogenetic analysis as well as an investigation of the genomic structure, including the promoter region of the cgALR1 gene were carried out.

Transcriptional and post-transcriptional regulation of transforming growth factor beta type II receptor expression in osteoblasts

Variations in transforming growth factor beta (TGF-beta) activity depend on the expression of specific receptors in normal as well as transformed cells. For example, in addition to mutations in TGF-beta type II receptor (TbetaRII) that abrogate normal TGF-beta function, its expression decreases during the transition from replication to extracellular matrix production, or in response to other growth regulators in bone. Therefore, to understand how TbetaRII expression is controlled, we cloned the rat TbetaRII gene promoter and defined basic aspects of its structure and activity. Among several cis-acting elements, mutations within an upstream E-box that specifically binds USF nuclear factors or a downstream Sp1 binding site significantly reduced TbetaRII promoter activity in primary cultures of fetal rat osteoblasts. Treatment with bone morphogenetic protein 2 (BMP-2), which induces further osteoblast differentiation, significantly reduced cell surface TbetaRII. However, BMP-2 did not alter TbetaRII promoter activity, steady state TbetaRII mRNA, or total TbetaRII protein, but caused an intracellular relocation of TbetaRII. Select transcriptional elements thus regulate TbetaRII gene expression, whereas post-translational events controlled by BMP-2 rapidly modify the amount of TbetaRII protein on the bone cell surface. Consequently, several processes can alter functional TbetaRII levels in order to regulate the biological effects of this important growth factor.

Increased transcriptional activities of transforming growth factor beta receptors in scleroderma fibroblasts

OBJECTIVE

To investigate the molecular mechanism of the overexpression of transforming growth factor beta receptors (TGF(beta)Rs) in dermal fibroblasts from patients with systemic sclerosis (SSc).

METHODS

Dermal fibroblasts from 7 patients with diffuse SSc of recent onset and from 7 healthy individuals were studied. The expression of TGF(beta)R type I (TGF(beta)RI), TGF(beta)RII, and type I collagen proteins in dermal fibroblasts was determined by immunoblotting. TGF(beta)RI, TGF(beta)RII, and alpha2(I) collagen messenger RNA (mRNA) were evaluated by Northern blot analysis. The transcriptional activities of the TGF(beta)RI and TGF(beta)RII genes were examined by luciferase assay.

RESULTS

SSc fibroblasts expressed increased levels of TGF(beta)RI and TGF(beta)RII protein and mRNA, as well as increased levels of type I collagen protein and alpha2(I) collagen mRNA. Moreover, the half-lives of TGF(beta)RI and TGF(beta)RII mRNA in SSc fibroblasts did not change compared with those in control dermal fibroblasts. The promoter activities of the TGF(beta)RI and TGF(beta)RII genes were both significantly increased in SSc fibroblasts compared with those in control fibroblasts. Calphostin C, a specific inhibitor of protein kinase C (PKC), inhibited TGF(beta)RI promoter activity in SSc fibroblasts, and LY294002, an inhibitor of phosphoinositide 3-kinase (PI 3-kinase), inhibited TGF(beta)RII promoter activity in SSc fibroblasts. Moreover, calphostin C and LY294002 inhibited the up-regulation of TGF(beta)RI and TGF(beta)RII mRNA, respectively, in SSc fibroblasts.

CONCLUSION

These results suggest that increased levels of TGF(beta)Rs in SSc fibroblasts play a role in excessive collagen production, and that up-regulation of TGF(beta)R expression might occur at the transcriptional levels. PKC and/or PI 3-kinase might contribute to the up-regulation of TGF(beta)R expression in SSc fibroblasts.

Psychiatric issues in pulmonary disease

This article has attempted to provide an overview of the clinical literature regarding the psychological issues facing patients with pulmonary disease, depending on when the illness begins in the life span, because different developmental tasks are disrupted. Patients must contend with side effects of medication that may mimic or exacerbate psychiatric disorders. The main drug interactions for psychiatrists to be aware of in this patient population occur between rifampin, or theophylline and psychotropic medications. In lung transplant recipients on cyclosporine therapy, the antidepressant drug nefazadone may cause increased cyclosporine levels. Psychiatrists must be aware of the risks, benefits, and survival statistics; educate patients; and ascertain whether the patient is competent to make medical decisions regarding treatment procedures.

Distribution of TGF-beta, the TGF-beta type I receptor and the R-II receptor in peripheral nerves and mechanoreceptors; observations on changes after traumatic injury

The mechanisms governing the regeneration of denervated peripheral mechanoreceptors are similar to those of peripheral nerves. The ability to regenerate depends partly on changes of the Schwann cell phenotype. The transforming growth factor beta (TGF-beta) family have been implicated in induction of Schwann cell proliferation, production of extracellular matrix and neurotrophin synthesis as well as synthesis or repression of cell adhesion molecules. Hence, they may prove to be of importance for regenerative mechanisms in peripheral mechanoreceptors. The distribution of TGF-beta, the receptors I and II and intra-cellular second messengers, Smad 2/3 and 4 was assessed in sensory neurones, peripheral nerves and mechanoreceptors by immuno-histochemistry, immuno-electron microscopy and in situ hybridisation. TGF-beta2 mRNA and TGF-beta2-like immunoreactivity (IR) were expressed in injured small and medium sized rat sensory neurones of dorsal root ganglia. TGF-beta and receptor II mRNA and immunoreactivities (IR) were present in satellite cells. Intact and injured sensory neurones expressed receptor I mRNA and Smad 2 mRNA. TGF-beta2 mRNA was found in transected nerve stumps and in sensory mechanoreceptors. TGF-beta1, 2 and Smad 4 were also observed in inner core lamellar cells of intact and denervated cat Pacinian corpuscles. Lamellar cells of intact and denervated Meissner corpuscles were TGF-beta immunoreactive. Merkel cells were receptors I and II immunoreactive. In conclusion, cutaneous and subcutaneous mechanoreceptors differ with regard to the expression of TGF-beta isoforms and receptors.

5-azaC treatment enhances expression of transforming growth factor-beta receptors through down-regulation of Sp3

We have previously reported that Sp3 acts as a transcriptional repressor of transforming growth factor-beta receptors type I (RI) and type II (RII). We now present data suggesting that treatment of MCF-7L breast and GEO colon cancer cells with 5-aza cytidine (5-azaC) leads to down-regulation of Sp3 and the concomitant induction of RI and RII. Western blot and gel shift analyses on 5-azaC-treated MCF-7L and GEO nuclear extracts indicated reduced Sp3 protein levels and decreased binding of Sp3 protein to radiolabeled consensus Sp1 oligonucleotide. Southwestern analysis detected decreased binding of Sp3 to RI and RII promoters in 5-azaC-treated MCF-7L and GEO cells, suggesting a correlation between decreased Sp3 binding and enhanced RI and RII expression in these cells. Reverse transcription-polymerase chain reaction and nuclear run-on data from 5-azaC-treated MCF-7L and GEO cells indicated down-regulation of Sp3 mRNA as a result of decreased transcription of Sp3. We reported earlier that 5-azaC treatment induces RI and RII expression through increased Sp1 protein levels/activities in these cells. These studies demonstrate that the effect of 5-azaC involves a combination of effects on Sp1 and Sp3.

Ultraviolet irradiation blocks cellular responses to transforming growth factor-beta by down-regulating its type-II receptor and inducing Smad7

Transforming growth factor-beta (TGF-beta) is a multi-functional cytokine that regulates cell growth and differentiation. Cellular responses to TGF-beta are mediated through its cell surface receptor complex, which activates transcription factors Smad2 and Smad3. Here we report that UV irradiation of mink lung epithelial cells causes near complete inhibition of TGF-beta-induced Smad2/3-mediated gene expression. UV irradiation inhibited TGF-beta-induced phosphorylation of Smad2 and subsequent nuclear translocation and DNA binding of Smad2/3. Specific cell surface binding of TGF-beta was substantially reduced after UV irradiation. This loss of TGF-beta binding resulted from UV-induced down-regulation of TGF-beta type II receptor (T beta RII) mRNA and protein. UV irradiation significantly inhibited T beta RII promoter reporter constructs, indicating that UV reduction of T beta RII expression involved transcriptional repression. In contrast to its effects on T beta RII, UV irradiation rapidly induced Smad7 mRNA and protein. Smad7 is known to antagonize activation of Smad2/3 and thereby block TGF-beta-dependent gene expression. UV irradiation stimulated Smad7 promoter reporter constructs, indicating that increased Smad7 expression resulted, at least in part, from increased transcription. Overexpression of Smad7 protein to the level induced by UV irradiation inhibited TGF-beta-induced gene expression 30%. Maintaining T beta RII levels by overexpression of T beta RII prevented UV inhibition of TGF-beta responsiveness. Taken together, these data indicate that UV irradiation blocks cellular responsiveness to TGF-beta through two mechanisms that impair TGF-beta receptor function. The primary mechanism is down-regulation of T beta RII, and the secondary mechanism is induction of Smad7.

Sp3 is a transcriptional repressor of transforming growth factor-beta receptors

MCF-7E breast cancer cells express transforming growth factor-beta (TGF-beta) receptors RI and RII in comparison to MCF-7L cells. We present data showing that Sp3 acts as a transcriptional repressor of RI and RII in MCF-7L cells and GEO colon cancer cells. MCF-7L and GEO cells express high levels of Sp3 protein. Gel shift analysis indicated enhanced binding of Sp3 from MCF-7L cells to a consensus Sp1 oligonucleotide. Southwestern data indicated increased binding of Sp3 to RI and RII promoters in MCF-7L cells, suggesting a correlation between Sp3 binding and reduced expression of TGF-beta receptors in MCF-7L cells. Cotransfection of CMV-Sp3 cDNA with RI and RII promoter-luciferase reporter constructs decreased RI and RII promoter activities by 70% in MCF-7E and GEO cells. Southwestern analysis detected the binding of transiently expressed Sp3 to RI and RII promoters in MCF-7E cells. Significantly, ectopic Sp3 expression led to repression of RI and RII transcripts in MCF-7E cells. This report demonstrates that inappropriate overexpression of Sp3 is a mechanism that contributes to repression of TGF-beta receptors.

Smad2, Smad3 and Smad4 cooperate with Sp1 to induce p15(Ink4B) transcription in response to TGF-beta

Transforming growth factor-beta (TGF-beta) arrests growth of epithelial cells by inducing the transcription of p15(Ink4B), a cyclin-dependent kinase inhibitor. In this study, we demonstrate that p15(Ink4B) induction was mediated by a TGF-beta-induced complex of Smad2, Smad3, Smad4 and Sp1. Mutations in the Sp1- or Smad-binding sequences decreased or abolished the TGF-beta responsiveness of the p15(Ink4B) promoter. Interference with, or deficiency in, Smad2, Smad3 or Smad4 functions also reduced or abolished the TGF-beta-dependent p15(Ink4B) induction, whereas the absence of Sp1 reduced the basal and TGF-beta-induced p15(Ink4B) transcription. In the nucleoprotein complex, Smad2 interacted through its C-domain with Sp1 and enhanced the DNA binding and transcriptional activity of Sp1. Smad3 interacted indirectly with Sp1 through its association with Smad2 and/or Smad4, and bound directly to the p15(Ink4B) promoter. Finally, Smad4 interacted through its N-domain with Sp1. Our data demonstrate the physical interactions and functional cooperativity of Sp1 with a complex of Smad2, Smad3 and Smad4 in the induction of the p15(Ink4B) gene. These findings explain the tumor suppressor roles of Smad2 and Smad4 in growth arrest signaling by TGF-beta.

Repression of transforming growth factor-beta receptor type I promoter expression by Sp1 deficiency

In this report, we describe the mechanism of TGF-beta receptor type I (RI) repression in the GEO human colon carcinoma cells. Treatment of GEO cells with the DNA methyltransferase inhibitor, 5 azacytidine induced RI expression and restored TGF-beta response. A stably transfected RI promoter-reporter construct (RI-Luc) expressed higher activity in the 5 aza C treated GEO cells, suggesting the activation of a transactivator for RI transcription. Gel shift analysis indicated enhanced binding of proteins from the 5 aza C treated nuclear extracts to radiolabeled Sp1 oligonucleotides specifically contained in the RI promoter. Protein stability studies after cyclohexamide treatment suggested an increase in the Sp1 protein stability from the 5 aza C treated GEO cells. Further, transfection of Sp1 cDNA into untreated GEO control cells increased RI promoter activity and thus induced RI expression. 5 aza C mediated Sp1 expression in Sp1 deficient GEO colon and MCF-7 breast cancer cells also enhanced the activity of several other Sp1 dependent promoters such as TGF-beta receptor type II (RII), Cyclin A and p21/waf1/cip1. These results indicate that restoration of Sp1 in several different types of Sp1 deficient cells leads to enhanced activation of a wide range of Sp1 dependent promoters.

Development of a chronic skin defect model and a study of cytokine secretion using the model

In this study, we established a delayed healing chronic type wound model in order to investigate the etiology of chronic wound healing, including wound contraction. Establishment of the model was important for clarification of the mechanism(s) of chronic wound healing and wound contraction and for use in evaluating therapeutic efficacy. A pedicled skin flap was raised beneath the panniculus carnosus membrane on the backs of mice, and after the loose connective tissue at the base of the flap was completely removed surgically, the flap was replaced and sutured. Seven days after surgery, a full-thickness defect measuring 1.5 x 1.5 cm was made in the center of the skin flap. At that time, a defect of the same size, including the panniculus carnosus membrane, was made in another group of mice as controls, and changes with time in wound area were compared between the two groups. The exudate retained on the wound surface was collected, and various cytokines contained in the exudate were measured. In the control group, the wound rapidly contracted and almost completely epithelialized and closed 21 days after surgery. On the other hand, the wound area was significantly larger in the delayed model than in the control animals during the observation period, revealing a delay in wound contraction. Transforming growth factor-beta, interleukin-1beta, and tumor necrosis factor-alpha in the exudates from the wound of the model were significantly higher than in those of the control group, whereas interleukin-6 was low in the model. From these results, it was concluded that this model could be a useful experimental system for studies on wound contraction as well as clarifying the mechanism of so called chronic type wounds.

Loss of transforming growth factor-beta (TGF-beta) receptor type I mediates TGF-beta resistance in human papillomavirus type 16-transformed human keratinocytes at late stages of in vitro progression

Human keratinocytes (HKc) immortalized by human papillomavirus type 16 DNA (HKc/HPV16) progress toward malignancy through growth factor-independent (HKc/GFI) and differentiation-resistant stages (HKc/DR). This progression is associated with a loss of sensitivity to growth inhibition by both all-trans-retinoic acid (RA) and transforming growth factor-beta (TGF-beta). In the accompanying article (Borger et al., 2000, Virology 270, 397-407), we demonstrate that RA resistance in HKc/HPV16 arises despite functional nuclear retinoid receptors and that TGF-beta mediates growth inhibition by RA. To investigate the basis for the loss of TGF-beta sensitivity during in vitro progression of HKc/HPV16, we explored the expression of TGF-beta receptors type I and type II in independently derived HKc/HPV16 lines and their corresponding HKc/GFI and HKc/DR derivatives. While TGF-beta receptor type II mRNA levels were unchanged during progression, mRNA levels for TGF-beta receptor type I decreased dramatically as the cells became TGF-beta resistant. At the HKc/DR stage, loss of TGF-beta receptor type I mRNA, compared to low-passage cells, ranged from 55 to 87% in four HKc/HPV16 lines examined. Immunohistochemistry, using anti-TGF-beta receptor type I antibodies, confirmed a loss of TGF-beta receptor type I expression in HKc/DR. Reintroduction of the TGF-beta-receptor type I into TGF-beta-resistant HKc/DR completely restored growth inhibition by TGF-beta. Southern blot analysis of DNA extracted from normal HKc, HKc/HPV16, and HKc/DR ruled out any gross changes in the TGF-beta receptor type I gene. The activity of the TGF-beta receptor type I promoter, cloned upstream of a luciferase reporter gene, was decreased in HKc/DR, to an extent comparable to the decrease in mRNA levels for the TGF-beta receptor type I. Thus, TGF-beta resistance at late stages of HPV16-mediated transformation of HKc is the result of a loss of expression of TGF-beta receptor type I.

Positive and negative regulation of TGF-beta signaling

Cytokines of the transforming growth factor beta (TGF-beta) superfamily, including TGF-betas, activins and bone morphogenetic proteins (BMPs), bind to specific serine/threonine kinase receptors and transmit intracellular signals through Smad proteins. Upon ligand stimulation, Smads move into the nucleus and function as components of transcription complexes. TGF-beta and BMP signaling is regulated positively and negatively through various mechanisms. Positive regulation amplifies signals to a level sufficient for biological activity. Negative regulation occurs at the extracellular, membrane, cytoplasmic and nuclear levels. TGF-beta and BMP signaling is often regulated through negative feedback mechanisms, which limit the magnitude of signals and terminate signaling. Negative regulation is also important for formation of gradients of morphogens, which is crucial in developmental processes. In addition, other signaling pathways regulate TGF-beta and BMP signaling through cross-talk. Nearly 20 BMP isoforms have been identified, and their activities are regulated by various extracellular antagonists. Regulation of TGF-beta signaling might be tightly linked to tumor progression, since TGF-beta is a potent growth inhibitor in most cell types.

Molecular mechanisms of inactivation of TGF-beta receptors during carcinogenesis

Signals from the TGF-betas are mediated by the TGF-beta receptors and their substrates, the Smad proteins. Inactivation of either of the two transmembrane serine/threonine kinases called the TGF-beta type I and type II receptors is now known to underlie a wide variety of human pathologies including, especially carcinogenesis. Numerous studies have now demonstrated that the TGF-beta receptor complex and its downstream signaling intermediates constitute a tumor suppressor pathway. We review here a specific pathway of mutational inactivation of the TGF-beta type II receptor resulting from microsatellite instability and demonstrate that, by contrast, the most common mechanism of loss of expression of the TGF-beta type II receptor involves transcriptional repression. This provides a new target for therapeutic intervention.

Transcriptional repression of the transforming growth factor-beta type I receptor gene by DNA methylation results in the development of TGF-beta resistance in human gastric cancer

The transforming growth factor-beta (TGF-beta) signaling pathway subserves an essential tumor suppressor function in various cell types. A heteromeric complex composed of TGF-beta type I (RI) and type II (RII) receptors is required for TGF-beta signaling. We have identified a subset of human gastric cancer cell lines which are insensitive to TGF-beta and which express a low level of TGF-beta type I receptor mRNA relative to a gastric cancer cell line which is highly responsive to TGF-beta. Using these cells, we show that hypermethylation of a CpG island in the 5' region of the TGF-beta RI gene provides another potentially important mechanism of escape from negative growth control by TGF-beta. This hypermethylation was found in four of five human gastric cancer cell lines and five out of 40 (12.5%) primary tumors examined. In human gastric cancer cell lines, treatment with the demethylating agent, 5-aza-2'-deoxycytidine, resulted in increased expression of the TGF-beta RI gene, but not the RII gene. Transient transfection of an RI expression vector into the TGF-beta resistant SNU-601 cell line restores TGF-beta responsiveness. These findings suggest that one of the mechanisms of escape from autocrine or paracrine growth control by TGF-beta during carcinogenesis could involve aberrant methylation of CpG islands in the 5' region of the TGF-beta RI gene.

TGF-beta-1 up-regulates cyclin D1 expression in COLO-357 cells, whereas suppression of cyclin D1 levels is associated with down-regulation of the type I TGF-beta receptor

Transforming growth factor-beta1 (TGF-beta1) inhibits cell growth in susceptible cells by interacting with a family of protein kinases that control cell cycle progression. In the present study, we investigated the effects of TGF-beta1 on cyclin D1 expression and activity in COLO-357 human pancreatic cancer cells. TGF-beta1 increased cyclin D1 mRNA and protein levels. Nuclear runoff transcription and protein synthesis inhibition by cycloheximide revealed that this increase was, in part, due to increased cyclin D1 mRNA synthesis. Despite its stimulatory effects on cyclin D1 levels, TGF-beta1 inhibited cyclin D1-associated kinase activity and the growth of COLO-357 cells. Furthermore, suppression of cyclin D1 expression with a cyclin D1 antisense cDNA resulted in loss of TGF-beta1-mediated growth inhibition in association with reduced induction of cyclin D1, p21(C)(ip)(1) and plasminogen activator inhibitor-1 (PAI-1). Concomitantly, there was a marked decrease in the levels of the type I TGF-beta receptor (TbetaRI). Our findings suggest that in some cell types cyclin D1 expression may be important for TGF-beta1-mediated signaling and that cyclin D1 may be involved in the transcriptional regulation of TbetaRI.

Transcriptional activation of transforming growth factor beta1 and its receptors by the Kruppel-like factor Zf9/core promoter-binding protein and Sp1. Potential mechanisms for autocrine fibrogenesis in response to injury

We have explored the regulation of transforming growth factor beta (TGF-beta) activity in tissue repair by examining the interactions of Zf9/core promoter-binding protein, a Kruppel-like zinc finger transcription factor induced early in hepatic stellate cell (HSC) activation, with promoters for TGF-beta1 and TGF-beta receptors, types I and II. Nuclear extracts from culture-activated HSCs bound avidly by electrophoretic mobility shift assay to two tandem GC boxes within the TGF-beta1 promoter but minimally to a single GC box; these results correlated with transactivation by Zf9 of TGF-beta1 promoter-reporters. Zf9 transactivated the full-length TGF-beta1 promoter in either primary HSCs, HSC-T6 cells (an SV40-immortalized rat HSC line), Hep G2 cells, or Drosophila Schneider (S2) cells. Recombinant Zf9-GST also bound to GC box sequences within the promoters for the types I and II TGF-beta receptors. Both type I and type II TGF-beta receptor promoters were also transactivated by Zf9 in mammalian cells but not in S2 cells. In contrast, Sp1 significantly transactivated both receptor promoters in S2 cells. These results suggest that (a) Zf9/core promoter-binding protein may enhance TGF-beta activity through transactivation of both the TGF-beta1 gene and its key signaling receptors, and (b) transactivating potential of Zf9 and Sp1 toward promoters for TGF-beta1 and its receptors are not identical and depend on the cellular context.

Transfection of the type I TGF-beta receptor restores TGF-beta responsiveness in pancreatic cancer

Transforming growth factor-beta (TGF-beta) signaling is initiated following heterodimerization of the type II TGF-beta receptor (TbetaRII) with the type I TGF-beta receptor (TbetaRI). Both receptors are required for TGF-beta responsiveness. In the present study, we characterized the actions of TGF-beta1 in T3M4 human pancreatic cancer cells, which express low levels of TbetaRI and high levels of TbetaRII. Cells were transiently transfected with p3TP-Lux, a TGF-beta-responsive luciferase reporter gene construct. TGF-beta1 was without effect in parental T3M4 cells, but caused a time- and dose-dependent increase in luciferase activity in T3M4 cells co-transfected with a TbetaRI cDNA expression vector. Co-transfection of TbetaRI with a truncated Smad4 cDNA that is known to block TGF-beta-dependent signaling, abrogated the TbetaRI-induced increase in luciferase activity. Sequencing of the TbetaRI and the Smad4 genes in T3M4 cells did not reveal any mutations. These findings indicate that one mechanism for TGF-beta resistance in pancreatic cancer is due to a quantitative decrease in TbetaRI expression.

Changes in TGF-beta receptors of rat hepatocytes during primary culture and liver regeneration: increased expression of TGF-beta receptors associated with increased sensitivity to TGF-beta-mediated growth inhibition

To clarify the role of transforming growth factor-beta (TGF-beta) and its receptors in hepatocyte growth, we studied the expression of TGF-beta1 and its receptors and the sensitivity to growth inhibition by TGF-beta1 protein in rat hepatocytes derived from resting and regenerating livers. In hepatocytes derived from resting livers, mRNAs for TGF-beta type II receptor (TbetaR-II), insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-II/M-6-PR), and TGF-beta1 increased with time in primary culture. The cell surface TGF-beta receptor proteins (TbetaR-I, II, and III), examined by the receptor affinity-labeling assay using 125I-TGF-beta1, also increased, especially after 48 hr of culture. Hepatocytes were more sensitive to inhibition of DNA synthesis, when the TGF-beta1 protein was added at later times in culture, corresponding to the presence of increased TGF-beta receptors. In hepatocytes from regenerating livers after a partial hepatectomy (PH), an increase of TbetaR-I, TbetaR-II, TbetaR-III, IGF-II/M-6-PR, and TGF-beta1 mRNAs was found, compared with hepatocytes from resting livers. Similarly, using TGF-beta receptor affinity-labeling assay, hepatocytes from PH livers were found to have an increase in TbetaR-I, II, and III proteins, with a peak at 4 days post-PH, compared with hepatocytes from resting livers. When TGF-beta1 protein was added for a short period (6 or 24 hr) after cell attachment to hepatocyte cultures, it inhibited DNA synthesis more effectively in hepatocytes from regenerating compared with resting livers. Our results show that hepatocyte TGF-beta receptors and sensitivity to growth inhibition by TGF-beta1 protein change together and are modulated during liver regeneration, as well as during the conditions of primary culture.

Up-regulation of transforming growth factor (TGF)-beta receptors by TGF-beta1 in COLO-357 cells

In the present study we investigated the actions of transforming growth factor (TGF)-beta1 on gene induction and cyclin-dependent kinase inhibitors in relation to TGF-beta receptor modulation in COLO-357 pancreatic cancer cells. TGF-beta1 inhibited the growth of COLO-357 cells in a time- and dose-dependent manner and caused a rapid but transient increase in plasminogen activator inhibitor-I and insulin-like growth factor binding protein-3 mRNA levels. TGF-beta1 caused a delayed but sustained increase in the protein levels of the cyclin-dependent kinase inhibitors p15(Ink4B), p21(Cip1), and p27(Kip1) and a sustained increase in type I and II TGF-beta receptors (TbetaRI and TbetaRII) mRNA and protein levels. The protein synthesis inhibitor cycloheximide (10 microg/ml) completely blocked the TGF-beta1-mediated increase in TbetaRI and TbetaRII expression. Furthermore, a nuclear runoff transcription assay revealed that the increase in receptor mRNA levels was due to newly transcribed RNA. There was a significant increase in TbetaRI and TbetaRII mRNA levels in confluent cells in comparison to subconfluent (</=80% confluent) controls, as well as in serum- starved cells when compared with cells incubated in medium containing 10% fetal bovine serum. COLO-357 cells expressed a normal SMAD4 gene as determined by Northern blot analysis and sequencing. These results indicate that TGF-beta1 modulates a variety of functions in COLO-357 cells and up-regulates TGF-beta receptor expression via a transcriptional mechanism, which has the potential to maximize TGF-beta1-dependent antiproliferative responses.

Cloning and genomic organization of the human transforming growth factor-beta type I receptor gene

Transforming growth factor-beta (TGF beta) regulates cell cycle progression by a unique signaling mechanism that involves its binding to the type II (T beta R-II) TGF beta receptor and activation of type I (T beta R-I). Both are transmembrane serine-threonine receptor kinases. As various types of human tumor cells are often refractory to TGF beta-mediated cell cycle arrest, it is likely that the T beta R-I receptor is inactivated in many of these cases. We determined the intron-exon organization of the TGFBR1 gene. We report here that this gene is approximately 31 kb in length and consists of nine exons. The organization of the segment of the TGFBR1 gene that encodes the C-terminal portion of the serine-threonine kinase domain appears to be highly conserved between members of the R-I gene family. This information should facilitate and expedite the structural analysis of TGFBR1 in human tumors and possibly other disease states.

Multiple and essential Sp1 binding sites in the promoter for transforming growth factor-beta type I receptor

Maximal gene expression driven by the promoter for the transforming growth factor beta type I receptor (TGF-betaRI) occurs with a 1. 0-kilobase pair fragment immediately upstream of exon 1. This region lacks a typical TATA box but contains CCAAT boxes, multiple Sp1, and PEBP2/CBFalpha binding sites among other possible cis-acting elements. Alterations within two CCAAT box sequences do not mitigate reporter gene expression driven by the basal promoter, and no nuclear factor binds to oligonucleotides encompassing these sites. In contrast, other deletions or site-specific mutations reveal an essential Sp1 site in the basal promoter and several dispersed upstream Sp1 sites that contribute to maximal reporter gene expression. The proportions of transcription factors Sp1 and Sp3, and their ratios of binding to consensus elements, are maintained in bone cells at different stages of differentiation. Finally, nuclear factor that binds to PEBP2/CBFalpha-related cis-acting elements in the basal promoter sequence also occurs in osteoblasts. Our studies reveal that constitutive expression of TGF-betaRI may be determined by constitutive nuclear factor binding to Sp1 sites, whereas other elements may account for the variations in TGF-betaRI levels that parallel changes in bone cell differentiation or activity.