TIF1γ and SMAD4 regulation in colorectal cancer: impact on cell proliferation and liver metastasis

We investigated the effects of transcriptional intermediary factor 1γ (TIF1γ) and SMAD4 on the proliferation and liver metastasis of colorectal cancer (CRC) cells through knockdown of TIF1γ and/or SMAD4 and knockdown of TIF1γ and/or restoration of SMAD4 expression. Furthermore, we examined TIF1γ and SMAD4 expression in human primary CRC and corresponding liver metastatic CRC specimens. TIF1γ promoted but SMAD4 inhibited the proliferation of CRC cells by competitively binding to activated SMAD2/SMAD3 complexes and then reversely regulating c-Myc, p21, p27, and cyclinA2 levels. Surprisingly, both TIF1γ and SMAD4 reduced the liver metastasis of all studied CRC cell lines via inhibition of MEK/ERK pathway-mediated COX-2, Nm23, uPA, and MMP9 expression. In patients with advanced CRC, reduced TIF1γ or SMAD4 expression was correlated with increased invasion and liver metastasis and was a significant, independent risk factor for recurrence and survival after radical resection. Patients with advanced CRC with reduced TIF1γ or SAMD4 expression had higher recurrence rates and shorter overall survival. TIF1γ and SMAD4 competitively exert contrasting effects on cell proliferation but act complementarily to suppress the liver metastasis of CRC via MEK/ERK pathway inhibition. Thus, reduced TIF1γ or SMAD4 expression in advanced CRC predicts earlier liver metastasis and poor prognosis.

Oncostatin M/Oncostatin M Receptor Signal Induces Radiation-Induced Heart Fibrosis by Regulating SMAD4 in Fibroblast

PURPOSE

Radiation-induced heart fibrosis (RIHF) is a severe consequence of radiation-induced heart damage (RIHD) leading to impaired cardiac function. The involvement of oncostatin M (OSM) and its receptor (OSMR) in RIHD remains unclear. This study aimed to investigate the specific mechanism of OSM/OSMR in RIHF/RIHD.

METHODS AND MATERIALS

RNA sequencing was performed on heart tissues from a RIHD mouse model. OSM levels were assessed in serum samples obtained from patients receiving thoracic radiation therapy (RT), as well as in RIHF mouse heart tissues and serum using enzyme-linked immunosorbent assay. Fiber activation was evaluated through costimulation of primary cardiac fibroblasts and NIH3T3 cells with RT and OSM, using Western blotting, immunofluorescence, and quantitative Polymerase Chain Reaction (qPCR). Adeno-associated virus serotype 9-mediated overexpression or silencing of OSM specifically in the heart was performed in vivo to assess cardiac fibrosis levels by transthoracic echocardiography and pathologic examination. The regulatory mechanism of OSM on the transcription level of SMAD4 was further explored in vitro using mass spectrometric analysis, chromatin immunoprecipitation-qPCR, and DNA pull-down.

RESULTS

OSM levels were elevated in the serum of patients after thoracic RT as well as in RIHF mouse cardiac endothelial cells and mouse serum. The OSM rate (post-RT/pre-RT) and the heart exposure dose in RT patients showed a positive correlation. Silencing OSMR in RIHF mice reduced fibrosis, while OSMR overexpression increased fibrotic responses. Furthermore, increased OSM promoted histone acetylation (H3K27ac) in the SMAD4 promoter region, influencing SMAD4 transcription and subsequently enhancing fibrotic response.

CONCLUSIONS

The findings demonstrated that OSM/OSMR signaling promotes SMAD4 transcription in cardiac fibroblasts through H3K27 hyperacetylation, thereby promoting radiation-induced cardiac fibrosis and manifestations of RIHD.

5-Azacytidine- and retinoic-acid-induced reprogramming of DCCs into dormancy suppresses metastasis via restored TGF-β-SMAD4 signaling

Disseminated cancer cells (DCCs) in secondary organs can remain dormant for years to decades before reactivating into overt metastasis. Microenvironmental signals leading to cancer cell chromatin remodeling and transcriptional reprogramming appear to control onset and escape from dormancy. Here, we reveal that the therapeutic combination of the DNA methylation inhibitor 5-azacytidine (AZA) and the retinoic acid receptor ligands all-trans retinoic acid (atRA) or AM80, an RARα-specific agonist, promotes stable dormancy in cancer cells. Treatment of head and neck squamous cell carcinoma (HNSCC) or breast cancer cells with AZA+atRA induces a SMAD2/3/4-dependent transcriptional program that restores transforming growth factor β (TGF-β)-signaling and anti-proliferative function. Significantly, either combination, AZA+atRA or AZA+AM80, strongly suppresses HNSCC lung metastasis formation by inducing and maintaining solitary DCCs in a SMAD4+/NR2F1+ non-proliferative state. Notably, SMAD4 knockdown is sufficient to drive resistance to AZA+atRA-induced dormancy. We conclude that therapeutic doses of AZA and RAR agonists may induce and/or maintain dormancy and significantly limit metastasis development.

AR cooperates with SMAD4 to maintain skeletal muscle homeostasis

Androgens and androgen-related molecules exert a plethora of functions across different tissues, mainly through binding to the transcription factor androgen receptor (AR). Despite widespread therapeutic use and misuse of androgens as potent anabolic agents, the molecular mechanisms of this effect on skeletal muscle are currently unknown. Muscle mass in adulthood is mainly regulated by the bone morphogenetic protein (BMP) axis of the transforming growth factor (TGF)-β pathway via recruitment of mothers against decapentaplegic homolog 4 (SMAD4) protein. Here we show that, upon activation, AR forms a transcriptional complex with SMAD4 to orchestrate a muscle hypertrophy programme by modulating SMAD4 chromatin binding dynamics and enhancing its transactivation activity. We challenged this mechanism of action using spinal and bulbar muscular atrophy (SBMA) as a model of study. This adult-onset neuromuscular disease is caused by a polyglutamine expansion (polyQ) in AR and is characterized by progressive muscle weakness and atrophy secondary to a combination of lower motor neuron degeneration and primary muscle atrophy. Here we found that the presence of an elongated polyQ tract impairs AR cooperativity with SMAD4, leading to an inability to mount an effective anti-atrophy gene expression programme in skeletal muscle in response to denervation. Furthermore, adeno-associated virus, serotype 9 (AAV9)-mediated muscle-restricted delivery of BMP7 is able to rescue the muscle atrophy in SBMA mice, supporting the development of treatments able to fine-tune AR-SMAD4 transcriptional cooperativity as a promising target for SBMA and other conditions associated with muscle loss.

Based on bioinformatics analysis lncrna SNHG5 modulates the function of vascular smooth muscle cells through mir-205-5p/SMAD4 in abdominal aortic aneurysm

Objective

The aim of this study was to explore expression profiles of long noncoding RNA (lncRNA)‐messenger RNA (mRNA) in abdominal aortic aneurysm (AAA) patients. Further, we explored the mechanisms by which lncRNA SNHG5 modulates the function of vascular smooth muscle cells (VSMC) in AAA.

Methods

Human gene expression profile GSE57691 dataset, was retrieved from Gene Expression Omnibus database. The dataset included gene expression array data of 49 AAA patients and 10 control aortic specimens from organ donors. To explore the main roles of the biological network, differentially expressed lncRNA and mRNAs in the aortic aneurysm (AAA) and normal aortic specimens were determined. Differentially expressed lncRNA and mRNAs were then used to construct a competing endogenous RNA (ceRNA) network using Cytoscape software, and the five key lncRNA were identified. SNHG5 which was significantly downregulated in the AAA was chosen and analysis showed that it regulates mir‐205‐5p and SMAD4 by binding to mir‐205‐5p. Double luciferase reporter gene assays, RNA immunoprecipitation, and RNA knockdown studies were used to establish the relationship between SNHG5 and mir‐205‐5p. Apoptosis rate was determined using flow cytometry, whereas cell proliferation was evaluated using Edu, and 24 well Transwell assay. Western blot analysis was used to determine protein expression levels.

Results

The five differentially expressed lncRNAs were significantly correlated with 34 microRNAs and 112 mRNAs. mRNAs in the ceRNA network are implicated in protein binding, signal transduction, DNA and RNA transcription, development, and cell differentiation. SNHG5 was downregulated in the AAA and acts as a molecular sponge for mir‐205. Downregulation of SNHG5 induces expression of mir‐205‐5p. Increased mir‐205‐5p expression level inhibits SMAD4 production, thus inhibiting proliferation and migration and promotes apoptosis of smooth muscle cells.

Conclusion

Bioinformatics were used to explore molecular mechanism of AAA progression. The findings of this study show that lncRNA SNHG5 regulates proliferation and apoptosis of VSMC cells through modulation of the mir‐205‐5p/SMAD4 axis. Therefore, SNHG5 is a potential therapeutic target for AAA disease.

Autism Spectrum Disorder and Psychiatric Comorbidity in a Patient with Myhre Syndrome

Myhre syndrome (MS) is a connective tissue disorder with multisystem involvement with or without intellectual disability. In most cases SMAD4 mutations are reported. To date, 55 individuals have been molecularly confirmed. Autism has been proposed among associate clinical features of MS but no standardized diagnosis was available in previous cases. We report a case of a 25-year-old man with a pathogenic heterozygous SMAD4 missense mutation affecting residue Arg⁴⁹⁶ (SMAD4:p.Arg496Cys). Clinical findings are consistent with MS, commorbid with affective disorder and High Functioning Autism Spectrum Disorder confirmed by a standardized assessment procedure. The thorough clinical assessment of cases with syndromes such as MS can extend our knowledge on both the phenotypic characteristics of the syndrome and the genetic basis of autism.

Pyloric gland adenoma: a histologic, immunohistochemical and molecular genetic study of 23 cases

Pyloric gland adenoma is a rare neoplasm with a gastric epithelial differentiation. We report 23 cases of pyloric gland adenoma in older persons, with a mean age of 74 years (range 52 - 87 years). They occurred in the esophagus (3 cases), corporal gastric mucosa (7 cases), duodenum (10 cases), gallbladder (2 cases), and choledochus (one case). Histologically, they were characterized by closely packed pyloric gland-type tubules with a monolayer of cuboidal to low columnar epithelial cells containing basally located round nuclei, and a superficial layer of tall, columnar, foveolar-type epithelium. Immunohistochemically, most tumor glands expressed pyloric gland mucin MUC6, whereas MUC5AC was positive in superficial gastric foveolar epithelium, and in a minority of glands. In addition, scattered neuroendocrine cells positive for chromogranin A and/or synaptophysin were seen in all cases. In 3 cases (two cases in the gallbladder and one case in the esophagus), areas of intestinal metaplasia with CK20, CDX2, and MUC2 positivity were found. Focal low-grade dysplasia was found in five cases (21.7%), and diffuse high-grade dysplasia was seen in one adenoma (4.4%), i.e., 6 of 23 PGAs (26.1%) showed dysplastic features. In one esophageal case, an invasive adenocarcinoma was diagnosed. Scattered p53 positive cells were found in all cases. Their number was higher in lesions with low-grade dysplasia and it was substantially increased in adenoma with high-grade dysplasia and in adenocarcinoma. Our molecular genetic results indicate that pyloric gland adenomas neoplastic nature is associated with p53 accumulation, mutations in oncogenes GNAS, KRAS, CTTNB1 and tumor suppressor genes SMAD4, and TP53. Pyloric gland adenoma can evolve into dysplasia and adenocarcinoma.

[Expression of Smad4 and Smad7 of BMP signaling pathway in oral squamous cell carcinoma]

PURPOSE

To observe the changes of the expressions of Smad4 and Smad7 in oral squamous cell carcinoma and adjacent normal tissue, and to investigate the effects of Smad4 and Smad7 on occurrence and development of oral squamous cell carcinoma (OSCC).

METHODS

Seventy-two cases with OSCC which were pathologically confirmed were included in the study. Cancer tissue and adjacent normal tissue were taken to make slices. SP immunohistochemical method was used to detect the expression of Smad4 and Smad7 in oral squamous cell carcinoma and adjacent normal tissue. SPSS11.5 software package was used for statistical analysis.

RESULTS

The positive expression rate of Smad4 protein was 69.44% in adjacent normal tissues, and it was 45.83% in oral squamous cell carcinoma(P<0.05). The positive expression rate of Smad4 was lower when the degree of differentiation decreased; The positive expression rate of Smad4 with lymph node metastasis was 22.50%, while it was 65.63% without lymph node metastasis(P<0.05). The positive expression rate of Smad7 protein in adjacent normal tissues was 19.44%, and it was 83.33% (P<0.05) in oral squamous cell carcinoma, the positive expression rate of Smad7 was higher when the degree of differentiation decreased. The positive expression rate of Smad7 with lymph node metastasis was 92.50%, while it was 68.75%(P<0.05) without lymph node metastasis.

CONCLUSIONS

The expression of Smad4 is significantly reduced in cancer tissues and the expression is lower when the degree of differentiation decreased; the expression rate of Smad4 with lymph node metastasis is lower compared with those without lymph node metastasis. Smad7 has the opposite effect. Loss of expression of Smad4 may contribute to the development and metastasis of oral squamous cell carcinoma. Over-expression of Smad7 may promote the development and metastasis of oral squamous cell carcinoma. The inhibition of BMP/Smads signaling pathway may result in the occurrence and development of oral squamous cell carcinoma continually. Supported by Science and Technology Development Plan (2010GSF10239) of Shandong Province and Science and Technology Special Project of Shandong Province (2012G0021852).

Alteration of Smad3 signaling in ischemic rabbit dermal ulcer wounds

Impaired reepithelialization is a hallmark of chronic, ischemic wounds; however, the pathogenesis of the delayed reepithelialization in these wounds remains poorly understood. Transforming growth factor beta is involved in both the normal and hypoxic wound-healing response and exogenous overexpression of Smad3, which has been known to accelerate reepithelialization. Recently, it was shown in the rabbit ear dermal ulcer model that Ad-Smad3 injection enhanced reepithelialization and granulation tissue formation suggesting a positive effect of Smad3 on wound healing. However, little is known about the role of Smad3 in the ischemic wound healing process. In this study, we examined the effect of Smad3 in an ischemic wound model. Ad-Smad3 or Ad-LacZ (10(8) pfu/wound) was injected into either ear of white New Zealand rabbits. Twenty-four hours later, these ears were rendered ischemic using an established model, and four 7 mm full-thickness punch wounds were made on each ear. Histological evaluation showed a significant increase in reepithelialization parameters in Ad-Smad3-transfected wounds (p<0.01). In contrast, granulation tissue parameters were not affected by Smad3 in ischemia. Smad4 and Smad7 mRNA-expression was not affected by Smad3 overexpression. Connective tissue growth factor protein was up-regulated under ischemic conditions but was unaffected by Smad3 transfection in both ischemic and nonischemic wounds. Our results suggest an enhancing effect of Smad3 on reepithelialization in an ischemic wound model that, in turn, might provide novel therapeutic options. Furthermore, the lack of alteration of Smad-dependent intermediates by Smad3 overexpression suggests the activation of Smad-independent pathways in ischemia.

[Historical background and recent advance in BMP research]

In 1971, Uurist gave the name bone morphogenetic protein (BMP) to the factor in bone matrix, which retains the activity to induce ectopic bone formation. After that, BMP research has rapidly developed by achieving BMP purification, BMP cloning, and identification of BMP receptors and signal transuding molecules (Smads). In this review, I overview the historical background and recent advance in BMP research.

Smad3 signalling plays an important role in keloid pathogenesis via epithelial-mesenchymal interactions

Smad signalling plays important roles in developmental and cancer biology as well as in fibropathogenesis. Its role in keloid biology is not known. Epithelial-mesenchymal interactions, originally described in normal skin, have recently been established to play a significant role in keloid pathogenesis, and demonstrate the important influence of keratinocyte paracrine factor signalling on fibroblast behaviour. The present study investigated the role of downstream Smad cascade induction in this interaction. Normal fibroblasts (NF) and keloid fibroblasts (KF) were co-cultured in serum-free medium with normal keratinocytes (NK) or keloid keratinocytes (KK) for 5 days, after which fibroblast cell lysates were subjected to western blot and immunoprecipitation analysis to quantify the levels of Smad and Smad2/3/4 binding complex. In another set of experiments, wild-type (wt), Smad2-null (Smad2-/-) and Smad3-null (Smad3-/-) mouse embryonic fibroblasts (MEF) were assayed for cell proliferation and collagen production after serum-free co-culture with KK or exposure to conditioned media collected from serum-free KK/KF co-culture. Compared to normal skin, keloids expressed high basal levels of TGFbetaR1 and TGFbetaR2, Smad2, 3 and 4 and phospho-Smad2. Upregulation of TGFbetaR1 and TGFbetaR2, Smad3 and p-Smad2 was observed in KF co-cultured with KK, together with enhanced Smad3 phosphorylation and Smad2/3/4 binding complex production. When MEF-wt, MEF-Smad2-/- or MEF-Smad3-/- were co-cultured with KK or exposed to KK/KF co-culture conditioned media, enhanced proliferation and collagen production were seen in MEF-wt and MEF-Smad2-/- but not in MEF-Smad3-/- cells. The activation of Smad signalling, importantly that of Smad3, appears to be one facet of the complex epithelial-mesenchymal interactions in keloid pathogenesis, resulting in active KF proliferation and collagen-ECM production in co-culture with KK. This finding suggests the suppression of Smad signalling as a novel approach in keloid therapy.

Vessels' morphology in SMAD4 and BMPR1A-related juvenile polyposis

Juvenile polyposis syndrome is a hamartomatous intestinal polyposis associated with malignant changes in 20% of patients at an early age. Germline mutations mostly involve two genes, SMAD4 and BMPR1, with no strong evidence of phenotype-genotype correlation, which could be predictive of the specific long-term evolution. In contrast, PTEN mutations are more commonly associated with Cowden and related diseases. Forty-two unrelated patients affected by juvenile polyposis syndrome were analyzed for germline alterations in the BMPR1A and SMAD4 genes, and for clinical and histological features. Deleterious mutations were found in 14/42 (33%) patients: 5 in BMPR1A and 9 in SMAD4. Low-grade adenomas were present in both SMAD4 and BMPR1A mutation carriers; only patients with SMAD4 mutations harbored carcinoma lesions (5/9). Malformative vessels were present in all SMAD4 related polyps when the mutation involved codons prior to position 423. No gastric polyps were observed in BMPR1A mutation carriers. SMAD4 germline mutations are responsible for a more aggressive digestive phenotype in patients with juvenile polyposis. The presence of malformative vessels within the stromal component might be a useful tool to drive the subsequent genetic and clinical management.

Smad4 dependency defines two classes of transforming growth factor {beta} (TGF-{beta}) target genes and distinguishes TGF-{beta}-induced epithelial-mesenchymal transition from its antiproliferative and migratory responses

In response to transforming growth factor beta (TGF-beta), Smad4 forms complexes with activated Smad2 and Smad3, which accumulate in the nucleus, where they both positively and negatively regulate TGF-beta target genes. Mutation or deletion of Smad4 is found in about 50% of pancreatic tumors and in about 15% of colorectal tumors. As Smad4 is a central component of the TGF-beta/Smad pathway, we have determined whether Smad4 is absolutely required for all TGF-beta responses, to evaluate the effect of its loss during human tumor development. We have generated cell lines from the immortalized human keratinocyte cell line HaCaT or the pancreatic tumor cell line Colo-357, which stably express a tetracyline-inducible small interfering RNA targeted against Smad4. In response to tetracycline, Smad4 expression is effectively silenced. Large-scale microarray analysis identifies two populations of TGF-beta target genes that are distinguished by their dependency on Smad4. Some genes absolutely require Smad4 for their regulation, while others do not. Functional analysis also indicates a differential Smad4 requirement for TGF-beta-induced functions; TGF-beta-induced cell cycle arrest and migration, but not epithelial-mesenchymal transition, are abolished after silencing of Smad4. Altogether our results suggest that loss of Smad4 might promote TGF-beta-mediated tumorigenesis by abolishing tumor-suppressive functions of TGF-beta while maintaining some tumor-promoting TGF-beta responses.

Smad4 is required for the normal organization of the cartilage growth plate

Smad4 is the central intracellular mediator of transforming growth factor-beta (TGF-beta) signals. To study the role of Smad4 in skeletal development, we introduced a conditional mutation of the gene in chondrocytes using Cre--loxP system. We showed that Smad4 was expressed strongly in prehypertrophic and hypertrophic chondrocytes. The abrogation of Smad4 in chondrocytes resulted in dwarfism with a severely disorganized growth plate characterized by expanded resting zone of chondrocytes, reduced chondrocyte proliferation, accelerated hypertrophic differentiation, increased apoptosis and ectopic bone collars in perichondrium. Meanwhile, Smad4 mutant mice exhibited decreased expression of molecules in Indian hedgehog/parathyroid hormone-related protein (Ihh/PTHrP) signaling. The cultured mutant metatarsal bones failed to response to TGF-beta1, while the hypertrophic differentiation was largely inhibited by Sonic hedgehog (Shh). This indicated that Ihh/PTHrP inhibited the hypertrophic differentiation of chondrocytes independent of the Smad4-mediated TGF-beta signals. All these data provided the first genetic evidence demonstrating that Smad4-mediated TGF-beta signals inhibit the chondrocyte hypertrophic differentiation, and are required for maintaining the normal organization of chondrocytes in the growth plate.

Hepatitis C virus core variants isolated from liver tumor but not from adjacent non-tumor tissue interact with Smad3 and inhibit the TGF-beta pathway

Hepatitis C virus (HCV) is a major risk factor for human hepatocellular carcinoma (HCC) but the mechanisms underlying HCV-induced carcinogenesis are still poorly understood. We have hypothesized that viral variants, selected during long-term infection, might contribute to cellular transformation. To address this issue, we have investigated the effect of natural HCV core variants isolated from liver tumors (T), or their non-tumor (NT) counterparts, on the tumor growth factor-beta (TGF-beta) pathway, a major regulator of cellular proliferation, differentiation and apoptosis. We have found a significant reduction in TGF-beta reporter gene activity with the expression of core sequences isolated from liver tumors. In contrast, moderate or no effects were observed with non-tumor mutants or a core reference sequence. The molecular mechanisms have been characterized and involved the inhibition, by tumor-derived cores, of the DNA-binding activity of the Smad3/4 transcription factors complex. This inhibition occurs through a direct interaction between the central domain (amino acids 59-126) of tumor-derived core and the MH1 DNA-binding domain of Smad3, thus preventing its binding to DNA. We have therefore identified a new cell-signaling pathway targeted by HCV core and inhibited by tumor-derived core sequences. These results suggest that during chronic infection, there is selection of viral variants that may promote cell transformation by providing, to clonally expanding cells, resistance to TGF-beta antiproliferative effects.

Coexpression of matrix metalloproteinase-7 (MMP-7) and epidermal growth factor (EGF) receptor in colorectal cancer: an EGF receptor tyrosine kinase inhibitor is effective against MMP-7-expressing cancer cells

PURPOSE

Matrix metalloproteinase-7 (MMP-7) plays an important role in carcinoma invasion and metastasis of cancer. Recent studies focus on diverse roles of MMP-7, other than as a protease, during cancer progression. MMP-7 activates the epidermal growth factor (EGF) receptor by releasing an EGF ligand, tumor growth factor (TGF)-alpha.

EXPERIMENTAL DESIGN

We examined expression of MMP-7 and EGF receptor in an immunohistochemical study of 40 colorectal cancer (CRC) cases. To determine the relationship between the EGF receptor and MMP-7, with a potential curative application, we compared the antitumor activity of the EGF receptor tyrosine kinase inhibitor (gefitinib) between MMP-7 transfectant, KYSE150 and HT29, and control cells.

RESULTS

We found a statistically significant correlation (P = 0.04) between MMP-7 and activated (phosphorylated) EGF receptor expression, both being positive in six (15%) cases. Gefitinib reduced the cell number ratio more for MMP-7 transfectant than mock cells, and the proportion of apoptotic cells was 1.5 times higher in MMP-7 transfectant than mock cells by annexin/propidium iodide staining. This was mediated by activation of a TGF-beta signal as confirmed by the abundant expression of TGF-beta protein, the cytoplasmic to nuclear translocation of Smad4 protein by the administration of gefitinib, and the quantitative assay of the plasminogen activator inhibitor-1 promoter/luciferase construction.

CONCLUSIONS

We propose that there are some cancers with up-regulated MMP-7 expression that leads to the activation of apoptotic activity of TGF-beta, which is susceptible to treatment with EGF receptor tyrosine kinase inhibitor.

TGF beta-induced focal complex formation in epithelial cells is mediated by activated ERK and JNK MAP kinases and is independent of Smad4

Advanced malignancies often exhibit increased concentrations of transforming growth factor-beta (TGF beta), which has been suggested to promote invasion and metastasis. While inhibition of epithelial cell proliferation in response to TGF beta is mainly mediated by the well-characterised Smad pathway, the molecular mechanism leading to TGF beta-induced invasiveness and metastasis are largely unknown. To elucidate these mechanisms, we compared TGF beta1 signalling in MCF-7 and the Smad4-negative MDA-MB-468 breast cancer cells. Both cell lines react to TGF beta1 treatment with decreased subcortical actin and increased numbers of focal contacts. TGF beta1-induced cell migration was strongly dependent on the activation of extracellular signal-regulated kinase (ERK) and Jun N-terminal kinase (JNK). These mitogen-activated protein kinases were phosphorylated in response to TGF beta and subsequently translocated into focal contacts. Inhibition of the TGF beta type I receptor ALK5 slightly reduced phosphorylation of ERK in MCF-7 cells, but neither inhibited phosphorylation of ERK in MDA-MB-468 cells nor TGF beta1-induced migration of both cell lines. In contrast, ALK5 inhibition effectively blocked Smad2 phosphorylation. In addition to ERK and JNK, the monomeric GTPase RhoA was activated by TGF beta1 and necessary for TGF beta-induced migration. Taken together, our study identifies a role of ERK and JNK activation and association of activated MAPKs with focal complexes in TGF beta1-induced cell migration in epithelial cells. These TGF beta-dependent processes were mediated independently of Smad4.

TGF-beta signaling in T cells: roles in lymphoid and epithelial neoplasia

Transforming growth factor-beta (TGF-beta) plays an essential role in regulating the homeostasis of cells in the lymphoid lineage. TGF-beta signaling is not required for normal thymopoiesis, but is essential for regulating the expansion, activation, and effector function of the mature CD4+ and CD8+ T cells in the peripheral lymphoid organs and target tissues. Recent studies in both mice and humans have elucidated an important and complex role for TGF-beta in regulatory T-cell biology. Disruption of TGF-beta signaling in T cells impairs the maintenance of regulatory T cells, results in the expansion of activated effector T cells, and is associated with the production of cytokines that have major effects on cells in their environment. While autoimmunity and inflammation are the principal phenotypes associated with the abrogation of TGF-beta signaling in T cells in mice, emerging evidence now also directly links Smad-dependent TGF-beta signaling in T cells to the suppression of epithelial neoplasia. The TGF-beta receptor-activated Smad3 plays a critical role in mediating many of the inhibitory effects of TGF-beta signaling in T cells, and has now been established as an important suppressor of leukemogenesis. These studies are increasing our awareness of the many complex mechanisms through which TGF-beta signaling controls the pathogenesis of cancer.

SMAD4 Levels and Response to 5-Fluorouracil in Colorectal Cancer

We have recently reported that low tumor levels of SMAD4, a key mediator of transforming growth factor-beta superfamily signaling, can predict the probability of recurrence in patients with Dukes C colorectal cancer who had surgery as the only form of treatment. However, standard treatment for Dukes C colorectal cancer patients currently involves the administration of 5-fluorouracil (5-FU)-based adjuvant chemotherapy after surgery. Approximately 30% to 40% of these patients present with recurrence and die within 5 years, and there is great need for markers capable of predicting poor prognosis after the combined surgery/adjuvant treatment. In this study, we evaluate the prognostic value of SMAD4 in patients treated with surgery and 5-FU-based adjuvant therapy. We used immunohistochemistry and quantitative real-time reverse transcription-PCR to measure the levels of SMAD4 protein and mRNA expression in the primary tumors and a number of lymph node metastases from a series of 75 Dukes C colorectal cancer patients with at least 6 years of follow-up. Patients with tumors expressing low levels of SMAD4 protein or mRNA showed significantly shorted disease-free and overall survival than patients with high tumor levels of SMAD4. The median survival of patients with low SMAD4 protein or mRNA tumor levels was 1.4 and 1.2 years, respectively, whereas patients with high SMAD4 tumor level had a median survival of >9.3 years. In addition, the protein and mRNA levels of SMAD4 in lymph node metastases was significantly lower than in primary tumors (P = 0.006). In contrast, allelic imbalance in chromosome 18q21 was of no prognostic significance in these patients. In conclusion, low SMAD4 tumor levels identified a subset of patients with poor prognosis following surgery and 5-FU-based adjuvant therapy; therefore, these patients could be good candidates to receive combined treatment with additional chemotherapeutic agents such as CPT-11 and/or oxaliplatin.

ALK5 and Smad4 are involved in TGF-beta1-induced pulmonary endothelial permeability

The ability of inflammatory cytokine TGF-beta1 to alter endothelial cell phenotype suggests its role in the regulation of vascular endothelial cell permeability. We demonstrate that depletion of TGF-beta1 receptor ALK5 and regulatory protein Smad4, but not ALK1 receptor attenuates TGF-beta1-induced permeability increase and significantly inhibits TGF-beta1-induced EC contraction manifested by actin stress fiber formation and increased MLC and MYPT1 phosphorylation. Consistent with these results, EC treatment with SB 431542, an inhibitor of ALK5 but not ALK1 receptor, significantly attenuates TGF-beta1-induced permeability. Thus, our data demonstrate for the first time direct link between TGF-beta1-mediated activation of ALK5/Smad and EC barrier dysfunction.

Tsc-22 enhances TGF-beta signaling by associating with Smad4 and induces erythroid cell differentiation

Tsc-22 was isolated as a TGF-beta-inducible gene by differential screening of the mouse osteoblastic cell cDNA library [J Biol Chem 267 (1992) 10219]. tsc-22 mRNA is expressed in almost all organs of mice and humans and its expression is induced in a variety of cell lines by many different factors including TGF-beta, phorbol ester, serum, and progestin. tsc-22 encodes a 18-kd protein that contains a leucine zipper motif and a Tsc-box. The leucine zipper motif of the Tsc-22 protein does not have a basic DNA binding motif and when the protein was fused to a heterologous DNA binding domain, it showed various transcription-modulating activities ranging from activation to repression [J Biol Chem 274 (1999) 27439, Biochem Biophys Res Commun 278 (2000) 659]. Although these results suggest that the Tsc-22 protein functions as a transcriptional regulator recruiting various coactivators or repressors, its mechanism is not known. In this study, we examined whether Tsc-22 modulates the TGF-beta-dependant signaling pathway and found that Tsc-22 binds to and modulate the transcriptional activity of Smad3 and Smad4. Its effect on cellular differentiation was also examined.

Single small-interfering RNA expression vector for silencing multiple transforming growth factor-beta pathway components

Although RNA interference (RNAi) is a popular technique, no method for simultaneous silencing of multiple targets by small-hairpin RNA (shRNA)-expressing RNAi vectors has yet been established. Although gene silencing can be achieved by synthetic small-interfering RNA (siRNA) duplexes, the approach is transient and largely dependent on the transfection efficiency of the host cell. We offer a solution: a simple, restriction enzyme-generated stable RNAi technique that can efficiently silence multiple targets with a single RNAi vector and a single selection marker. In this study, we succeeded in simultaneous stable knockdown of transforming growth factor beta (TGF-beta) pathway-related Smads--Smad2, Smad3 and Smad4--at the cellular level. We observed distinct phenotypic changes in TGF-beta-dependent cellular functions such as invasion, wound healing and apoptosis. This method is best suited for an analysis of complex signal transduction pathways in which silencing of a single gene cannot account for the whole process.

Effect of wound type on Smad 2 and 4 translocation

PURPOSE

In a prior study, it was reported that both TGF-beta receptors type-I and -II are upregulated after wounding, suggesting that TGF-beta signaling may play a role in corneal epithelial repair. The Smad proteins, which translocate into the nucleus after activation of the TGF-beta receptors, are key factors in the major TGF-beta signaling pathway. The present study was undertaken to examine whether Smads 2 and 4 translocate into the nucleus during wound repair and whether the wound type affects the extent of translocation.

METHODS

Either a 3-mm superficial keratectomy or epithelial debridement was performed on adult Sprague-Dawley rats. The eyes were allowed to heal from 4 hours to 2 weeks. Indirect immunofluorescence was performed with anti-Smads 2 and 4, anti-laminin, a marker of basement membrane, and anti-alphavbeta6 integrin, which has been implicated in TGF-beta activation. In addition, the effect of the p38MAPK inhibitor SB202190 on healing rates of debridement and keratectomy wounds was determined in organ culture.

RESULTS

In unwounded tissue, Smad 2 was cytoplasmic. By 4 hours after keratectomy, nuclear localization was visible in a few epithelial basal cells at the leading edge of the wound. The number of basal cells expressing nuclear Smad 2 in the wound area increased with time, peaking at 48 hours (95%). However, in the debridement model, Smad 2 localization remained primarily cytoplasmic. Smad 4 showed similar localization. In both wound models, p38MAPK inhibitor slowed epithelial migration, and alphavbeta6 integrin appeared to be upregulated with localization primarily observed in the basal cells migrating over the wound area.

CONCLUSIONS

The presence of the basement membrane appears to have an effect on the extent and duration of translocation of the Smad 2 and 4 proteins during corneal epithelial wound repair. The Smad pathway does not appear to be essential for migration; rather, it may play a role in resynthesis of the basement membrane.

Context-dependent neuronal differentiation and germ layer induction of Smad4-/- and Cripto-/- embryonic stem cells

Activation of transforming growth factor-beta (TGF-beta) receptors typically elicits mesodermal development, whereas inhibition of this pathway induces neural fates. In vitro differentiated mouse embryonic stem (ES) cells with deletion of the TGF-beta pathway-related factors Smad4 or Cripto exhibited increased numbers of neurons. Cripto-/- ES cells developed into neuroecto-/epidermal cell types, while Smad4-/- cells also displayed mesodermal differentiation. ES cell differentiation into catecholaminergic neurons showed that these ES cells retained their ability to develop into dopaminergic and serotonergic neurons with typical expression patterns of midbrain and hindbrain genes. In vivo, transplanted ES cells to the mouse striatum became small neuronal grafts, or large grafts with cell types from all germ layers independent of their ES cell genotype. This demonstrates that Smad4-/- and Cripto-/- ES cells favor a neural fate in vitro, but also express the mesodermal phenotype, implying that deletion of either Smad4 or Cripto is not sufficient to block nonneuronal tissue formation.

SMAD4 as a prognostic marker in colorectal cancer

More than 50% of patients with Dukes C colorectal cancer have disease recurrence and die within 5 years after surgical removal of their primary tumor. It is currently not possible to distinguish patients with good and bad prognosis. SMAD4 is an important tumor suppressor gene that mediates transforming growth factor-beta superfamily signaling and is located in chromosome 18q21, a region with frequent genetic losses in these tumors. Allelic imbalance in 18q has been linked to poor prognosis in a subset of colorectal cancer patients. Therefore, we generated a tissue microarray containing triplicate tumor samples from 86 Dukes C patients and used immunohistochemistry to assess the relative expression level of SMAD4 and its value as a prognostic marker. In addition, SMAD4 was screened for mutations and two polymorphic microsatellite markers were used to assess the presence of allelic imbalance in these tumors. Patients with tumors expressing high SMAD4 levels had significantly better overall (P < 0.025) and disease-free (P < 0.013) survival than patients with low levels. This identifies SMAD4 as a prognostic marker for Dukes C colorectal cancer. Although all tumors with absent SMAD4 staining showed allelic imbalance in 18q21, tumors with 18q21 allelic imbalance as a group showed no difference in SMAD4 levels compared with tumors without allelic imbalance, suggesting that additional mechanisms of SMAD4 down-regulation exist. In addition, although SMAD4 mutations were found in five tumors, they were not associated with shorter survival. In conclusion, the level of expression of SMAD4 was found to be a more sensitive marker than 18q21 allelic imbalance and SMAD4 mutations, which were of no prognostic significance for these patients.

Linking Smads and transcriptional activation

TGF-beta1 (transforming growth factor-beta1) is the prototypical member of a large family of pleiotropic cytokines that regulate diverse biological processes during development and adult tissue homoeostasis. TGF-beta signals via membrane bound serine/threonine kinase receptors which transmit their signals via the intracellular signalling molecules Smad2, Smad3 and Smad4. These Smads contain conserved MH1 and MH2 domains separated by a flexible linker domain. Smad2 and Smad3 act as kinase substrates for the receptors, and, following phosphorylation, they form complexes with Smad4 and translocate to the nucleus. These Smad complexes regulate gene expression and ultimately determine the biological response to TGF-beta. In this issue of the Biochemical Journal, Wang et al. have shown that, like Smad4, the linker domain of Smad3 contains a Smad transcriptional activation domain. This is capable of recruiting the p300 transcriptional co-activator and is required for Smad3-dependent transcriptional activation. This study raises interesting questions about the nature and regulation of Smad-regulated gene activation and elevates the status of the linker domain to rival that of the much-lauded MH1 and MH2 domains.

Differences in Smad4 expression in human papillomavirus type 16-positive and human papillomavirus type 16-negative head and neck squamous cell carcinoma

The SMADs are a group of interrelated proteins that mediate transforming growth factor beta (TGF-beta) signaling. Upon TGF-beta binding the TGF-beta type I receptor phosphorylates Smad2 and Smad3, which then complex with Smad4 and translocate to the nucleus, with subsequent activation of target genes. Disruption of TGF-beta signaling is thought to contribute to the development of head and neck squamous cell carcinomas (HNSCC). Alterations in the function of the DPC4/Smad4 tumor suppressor gene have been found to inactivate TGF-beta signaling in several tumor types. For example, DPC4/Smad4 is lost or mutated in colorectal, pancreatic, and esophageal cancers. In addition, DPC4/Smad4 transcriptional activity and TGF-beta ability to inhibit DNA synthesis is blocked by the E7 protein of the human papillomavirus type 16 (HPV16) in cervical carcinoma cell lines. HPV16 infection is a risk factor for the development of a subset of HNSCC. This study was undertaken to investigate a potential correlation between expression of components of the TGF-beta signaling pathway and HPV16 status in HNSCC tumors. We examined the expression of TGF-beta signaling proteins Smad2, Smad2-P, and Smad4 by immunohistochemistry in 27 HPV16-negative and 16 HPV16-positive HNSCCs. We compared the expression patterns and assessed their relationship to HPV16 status. No significant differences were detected between HPV16-positive and HPV16-negative tumors in the expression of Smad2 and Smad2-P. Smad4 expression, however, was decreased in 56% of the HPV16-positive tumors and in 39% of HPV16-negative tumors. This difference was statistically significant (P = 0.01) suggesting that loss of Smad4 expression may be involved in HPV16-induced carcinogenesis of HNSCC.

Distinct progression pathways involving the dysfunction of DUSP6/MKP-3 in pancreatic intraepithelial neoplasia and intraductal papillary-mucinous neoplasms of the pancreas

DUSP6/MKP-3 is identified as a candidate tumor suppressor gene for pancreatic cancer. The aim of this study was to elucidate the roles of DUSP6 in the pancreatic carcinogenesis through the pancreatic intraepithelial neoplasia and/or intraductal papillary-mucinous neoplasms, both of which are considered to be precursor lesions of invasive carcinoma of the pancreas, by comparing with involvements of other major tumor suppressive pathways. Expressions of DUSP6, CDKN2A, TP53, and SMAD4 were investigated by immunohistochemistry in a total of 206 lesions of dysplastic ductal precursors and carcinomas retrieved from 52 pancreata with invasive ductal carcinomas and 51 of those with intraductal papillary-mucinous neoplasms. The intensity of staining was evaluated in lesions at different atypical grades and statistically compared among them. Mutations of KRAS2 were analyzed by methods of the allele-specific oligonucleotide hybridization and nucleotide sequencing. In pancreata with invasive ductal carcinomas, expressions of DUSP6 were abrogated exclusively in the invasive carcinoma cells in contrast to its fairly preserved expressions in pancreatic intraepithelial neoplasia. In pancreata with intraductal papillary-mucinous neoplasms, abrogated expressions of DUSP6 were observed in a relatively small fraction of intraductal adenoma/borderlines and intraductal carcinomas. Most of the intraductal adenoma/borderline lesions with abrogation of DUSP6 harbored mutations of KRAS2. None of the molecules was associated with each other in any grade of lesions. Morphological variations of papillae of the intraductal papillary-mucinous neoplasms were evaluated and analyzed for their associations with abrogations of the molecules, which resulted in finding of no significant associations. Our results suggest that the abrogation of DUSP6 is associated exclusively with progression from pancreatic intraepithelial neoplasia to the invasive ductal carcinoma while it is potentially associated with initiation of intraductal papillary-mucinous neoplasms with mutated KRAS2, which is independent of other major tumor suppressive pathways in both types of neoplasms.

Smad4 expression in gastric adenoma and adenocarcinoma: frequent loss of expression in diffuse type of gastric adenocarcinoma

Smads are signal transducers for the members of the TGF-beta superfamily. Of these Smads, Smad4 is essential for TGF-beta signaling. The purpose of this study was to elucidate Smad4 expression and localization in 65 gastric adenomas, 49 intestinal-type and 39 diffuse type of gastric adenocarcinomas (including 12 cases of fresh frozen tissue) using Real-time RT-PCR and immunohistochemistry. Real-time RT-PCR showed that intestinal type gastric adenocarcinomas have higher Smad4 mRNA expression than diffuse type gastric adenocarcinomas. Immunohistochemical stain for Smad4 revealed that expression of Smad4 was significantly lower in diffuse-type gastric adenocarcinoma than intestinal-type gastric adenocarcinomas. Also, higher Smad4 protein expression in intestinal type gastric adenocarcinomas than overall gastric adenoma was noted. The rate of reduced Smad4 expression was higher in advanced gastric cancer than early gastric cancer. These results suggest that Smad4 might play different roles in human gastric carcinogenesis, especially between intestinal type and diffuse type of gastric adenocarcinoma.

Regulation of GDF-8 signaling by the p38 MAPK

Growth differentiation factor-8 (GDF-8), a member of the TGF-beta superfamily, is a negative regulator of skeletal muscle growth, which functions through activation of the Smad proteins. We found that GDF-8 can activate the p38 mitogen-activated protein kinase (MAPK) through the TGF-beta-activated kinase 1 (TAK1), and this appeared to be independent of Smad signaling. GDF-8-induced transcriptional activation was inhibited by expression of dominant negative MKK6 or treatment with the p38 inhibitor SB203580, while overexpression of wild-type forms of either MKK6 or p38 augmented GDF-8-induced transcriptional activity. In addition, ATF-2, a known transcription factor target of p38, was found to be phosphorylated on GDF-8 stimulation and was detected in a complex with Smad3/Smad4 upon GDF-8 treatment. Furthermore, we found that the p38 MAPK played an important role in GDF-8-induced inhibition of proliferation and upregulation of the cyclin kinase inhibitor p21. Together, these results highlight a functional link between the p38 MAPK and GDF-8-activated Smad pathways, and identify a critical role for the p38 MAPK in GDF-8's function as a negative regulator of muscle growth.

Transforming growth factor-beta suppresses nonmetastatic colon cancer through Smad4 and adaptor protein ELF at an early stage of tumorigenesis

Although transforming growth factor-beta (TGF-beta) is both a suppressor and promoter of tumorigenesis, its contribution to early tumor suppression and staging remains largely unknown. In search of the mechanism of early tumor suppression, we identified the adaptor protein ELF, a beta-spectrin from stem/progenitor cells committed to foregut lineage. ELF activates and modulates Smad4 activation of TGF-beta to confer cell polarity, to maintain cell architecture, and to inhibit epithelial-to-mesenchymal transition. Analysis of development of colon cancer in (adult) elf+/-/Smad4+/-, elf+/-, Smad4+/-, and gut epithelial cells from elf-/- mutant mouse embryos pinpoints the defect to hyperplasia/adenoma transition. Further analysis of the role of ELF in human colorectal cancer confirms reduced expression of ELF in Dukes' B1 stage tissues (P < 0.05) and of Smad4 in advanced colon cancers (P < 0.05). This study indicates that by modulating Smad 4, ELF has a key role in TGF-beta signaling in the suppression of early colon cancer.

Analysis of SMAD4/DPC4 gene alterations in multiploid colorectal carcinomas

BACKGROUND

Although recent animal studies have shown that SMAD4/DPC4 gene alterations are essential for late-stage intestinal tumorigenesis, the role of SMAD4/DPC4 gene alterations in primary human colorectal carcinomas is not fully understood. Therefore, we attempted to clarify the role of the SMAD4/DPC4 gene during tumor progression of colorectal carcinoma.

METHODS

Differences in allelic imbalance (AI) and mutations of the SMAD4/DPC4 gene between diploid and aneuploid populations were analyzed for 30 sporadic DNA multiploid colorectal carcinomas (used as a tumor progression model and defined as the coexistence of diploid and aneuploid cells within the same tumor). The crypt isolation technique was coupled with DNA cytometric sorting and a polymerase chain reaction assay. In addition, hypermethylation of the promoter region was examined to clarify whether inactivation of gene expression occurred.

RESULTS

Although a SMAD4/DPC4 gene AI was detected in only 5 of 27 informative diploid populations, 25 of 27 aneuploid populations had a SMAD4/DPC4 gene AI. Mutation of the SMAD4/DPC4 gene was detected in only one aneuploid population of multiploid colorectal carcinomas, but not in the corresponding diploid population. In total, 20 available multiploid carcinomas were selected for methylation analysis, and no evidence of hypermethylation of the promoter region was found.

CONCLUSIONS

We suggest that, although mutation of the SMAD4/DPC4 gene and hypermethylation of the promoter region are infrequent events in colorectal tumorigenesis, AI at the SMAD4/DPC4 gene locus may play a key role in the progression of colorectal carcinomas.

Differential proteome analysis of conditioned media to detect Smad4 regulated secreted biomarkers in colon cancer

Smad4 is a tumor suppressor gene primarily involved in carcinogenesis of the pancreas and colon. The functional inactivation of Smad4 is a late step genetically. In pancreatic carcinogenesis, loss of Smad4 marks the transition to invasive growth. In colorectal cancers, the frequency of Smad4 inactivation is markedly increased in metastatic cancers. We have established cell biological models, re-expressing Smad4 in deficient human cancer cells, in which we could show that Smad4 is adequate to suppress tumor growth through suppression of angiogenic and invasive properties. Thus, pairs of Smad4-re-expressing and Smad4-deficient cells are prone to model the progression from premalignant stages to carcinomas in the carcinogenic process and may provide access to Smad4 targets of high clinical relevance. We present here a "differential secretome analysis", comparing all the proteins released in vitro from the Smad4-deficient and Smad4-re-expressing SW480 human colon carcinoma cells. The differential secretome catalog comprises more than 25 proteins including proteases and protease inhibitors, as well as established tumor biomarkers. In conclusion, this approach proved to be a sensitive tool to specifically detect Smad4 targets relevant for tumor-stroma interactions. It is also able to reflect complex alterations of cellular physiology. Moreover, the results support our hypothesis that human tumor markers detectable in serum may be identified through differential secretome analyses.

SCF(beta-TrCP1) controls Smad4 protein stability in pancreatic cancer cells

Smad4, also known as deleted in pancreatic carcinoma locus 4 (DPC4), is a critical co-factor in signal transduction pathways activated by transforming growth factor (TGF)-beta-related ligands that regulate cell growth and differentiation. Mutations in Smad4/DPC4 have been identified in approximately 50% of pancreatic adenocarcinomas. Here we report that SCF(beta-TrCP1), a ubiquitin (E3) ligase, is a critical determinant for Smad4 protein degradation in pancreatic cancer cells. We found that F-box protein beta-TrCP1 in this E3 ligase interacted with Smad4 and that SCF(beta-TrCP1) inhibited TGF-beta biological activity in pancreatic cancer cells by decreasing Smad4 stability. Very low Smad4 protein levels in human pancreatic ductal adenocarcinoma cells were observed by immunohistochemistry. By analyzing pancreatic tumor-derived Smad4 mutants, we found that most point-mutated Smad4 proteins, except those within or very close to a mutation cluster region, exhibited higher interaction affinity with beta-TrCP1 and significantly elevated protein ubiquitination by SCF(beta-TrCP1). Furthermore, AsPC-1 and Caco-2, two cancer cell lines harboring Smad4 point mutations, exhibited rapid Smad4 protein degradation due to the effect of SCF(beta-TrCP1). Both Smad4 levels and TGF-beta signaling were elevated by retrovirus-delivered beta-TrCP1 siRNA in pancreatic cancer cells. Therefore, inhibition of Smad4-specific E3 ligase might be a target for therapeutic intervention in pancreatic cancer.

Germ-layer specification and control of cell growth by Ectodermin, a Smad4 ubiquitin ligase

TGF-beta signaling is essential for development and proliferative homeostasis. During embryogenesis, maternal determinants act in concert with TGF-beta signals to form mesoderm and endoderm. In contrast, ectoderm specification requires the TGF-beta response to be attenuated, although the mechanisms by which this is achieved remain unknown. In a functional screen for ectoderm determinants, we have identified Ectodermin (Ecto). In Xenopus embryos, Ecto is essential for the specification of the ectoderm and acts by restricting the mesoderm-inducing activity of TGF-beta signals to the mesoderm and favoring neural induction. Ecto is a RING-type ubiquitin ligase for Smad4, a TGF-beta signal transducer. Depletion of Ecto in human cells enforces TGF-beta-induced cytostasis and, moreover, plays a causal role in limiting the antimitogenic effects of Smad4 in tumor cells. We propose that Ectodermin is a key switch in the control of TGF-beta gene responses during early embryonic development and cell proliferation.

Ubiquitin-mediated degradation a mechanism for fine-tuning TGF-beta signaling

Effects of the cytokine TGF-beta can be dampened by E3 ubiquitin ligases that target specific Smads, the TGF-beta signal transducers, for proteolytic destruction. Two papers in this issue of Cell highlight the importance of this mechanism in regulating the in vivo effects of TGF-beta. The first paper identifies and characterizes a novel Smad4 ubiquitin ligase, and the second paper redefines the role of a previously identified Smad1 ubiquitin ligase, Smurf-1 (Dupont et al., 2005; Yamashita et al., 2005).

Specific interaction between Smad1 and CHIP: a surface plasmon resonance study

The TGF-beta superfamily signaling pathway regulates many important biological processes, including cell growth, differentiation and embryonic pattern formation. Smad1, a member of this signaling pathway that functions downstream of serine/threonine kinase receptors, has ability to interact with carboxyl terminus of Hsc70-interacting protein (CHIP), which is an E3 ubiquitin ligase in other cases. It has been reported that Smurf1, a member of the Hect family E3 ubiquitin ligases, can target Smad1 to 26S proteasome for degradation. In this paper, we studied the interaction of Smad1 and CHIP by combination of surface plasmon resonance and supported monolayer approach. The specific binding of Smad1 to CHIP indicates that the degradation of Smad1 may also be mediated by CHIP, and CHIP may play an essential role in the TGF-beta signaling pathway.

A complex pattern of mutations and abnormal splicing of Smad4 is present in thyroid tumours

Sensitivity to transforming growth factor-beta is impaired in thyroid tumours. Similar to Mad -- Mother Against Decapentaplegic-(Smad)4 is frequently altered in cancers, but its involvement in this system is unknown. We analysed 56 thyroid tumours of various histotypes for Smad4 mutations by PCR-SSCP and sequencing, linking them to Smad4 reactivity as examined by immunohistochemistry (IHC), and 29 of them also for abnormalities in RNA expression due to alternative splicing. In all, 15/56 cases (27%), both benign and malignant lesions, harbour alterations of Smad4 coding sequence. We found several novel intragenic mutations (13 missense, two silent, one frameshift and one large insertion-deletion), with high incidence in the linker region. A subset of mutated tumours failed to express Smad4 protein by IHC. We have also detected four alternatively spliced tumour-associated Smad4 isoforms, lacking portions of the linker region, and three more due to unreported internal exon-exon rearrangements. Smad4 is both frequently mutated and deregulated by aberrant splicing in thyroid tumours and these alterations may contribute as an early event to thyroid tumorigenesis.

CUTL1 is a target of TGF(beta) signaling that enhances cancer cell motility and invasiveness

CUTL1, also known as CDP, Cut, or Cux-1, is a homeodomain transcriptional regulator known to be involved in development and cell cycle progression. Here we report that CUTL1 activity is associated with increased migration and invasiveness in numerous tumor cell lines, both in vitro and in vivo. Furthermore, we identify CUTL1 as a transcriptional target of transforming growth factor beta and a mediator of its promigratory effects. CUTL1 activates a transcriptional program regulating genes involved in cell motility, invasion, and extracellular matrix composition. CUTL1 expression is significantly increased in high-grade carcinomas and is inversely correlated with survival in breast cancer. This suggests that CUTL1 plays a central role in coordinating a gene expression program associated with cell motility and tumor progression.

Degradation of the Tumor Suppressor Smad4 by WW and HECT Domain Ubiquitin Ligases

Smad4 mediates signaling by the transforming growth factor-beta (TGF-beta) superfamily of cytokines. Smad signaling is negatively regulated by inhibitory (I) Smads and ubiquitin-mediated processes. Known mechanisms of proteasomal degradation of Smads depend on the direct interaction of specific E3 ligases with Smads. Alternatively, I-Smads elicit degradation of the TGF-beta receptor by recruiting the WW and HECT domain E3 ligases, Smurfs, WWP1, or NEDD4-2. We describe an equivalent mechanism of degradation of Smad4 by the above E3 ligases, via formation of ternary complexes between Smad4 and Smurfs, mediated by R-Smads (Smad2) or I-Smads (Smad6/7), acting as adaptors. Smurfs, which otherwise cannot directly bind to Smad4, mediated poly-ubiquitination of Smad4 in the presence of Smad6 or Smad7. Smad4 co-localized with Smad7 and Smurf1 primarily in the cytoplasm and in peripheral cell protrusions. Smad2 or Smad7 mutants defective in Smad4 interaction failed to induce Smurf1-mediated down-regulation of Smad4. A Smad4 mutant defective in Smad2 or Smad7 interaction could not be effectively down-regulated by Smurf1. We propose that Smad4 is targeted for degradation by multiple ubiquitin ligases that can simultaneously act on R-Smads and signaling receptors. Such mechanisms of down-regulation of TGF-beta signaling may be critical for proper physiological response to this pathway.

Smad signal and TGFβ induced apoptosis in human lymphoma cells

Transforming growth factor beta1 (TGF beta1) has antiproliferative and/or apoptotic effect on lymphoid cells. In certain lymphomas exogenous TGF beta1 is able to induce apoptosis, however many lymphoid malignancies are resistant to the endogenous TGF beta1 production. We studied the expression and the activity of TGF beta1 signalling components in B cell lymphoma cell lines (e.g. HT 58 cells) and in isolated human peripheral mononuclear cells (PBMCs) from healthy individual's and B-CLL patient's blood. We found that all signal transducer Smads (Smad2,-3; Smad4) and at least one of the inhibitory Smads (Smad6,-7) were expressed in non-treated lymphoma cells, but the inhibitory Smads did not in normal/control PBMCs. However, after TGF beta1 treatment Smad6 disappeared, while the expression of Smad7 increased in HT 58 cells. The activity of Smad signals was proved by phosphorylation of Smad2, nuclear translocation of Smad2/3, and the increased expression of Smad-dependent gene, TIEG in TGF beta1 treated lymphoma cells. These results showed that Smad signaling is available in certain different human lymphoma cells, however ISmads expression could inhibit the signal transmission. This findings indicates that the lost sensitivity of lymphoma cells toward a physiological regulatory factor could be reversed.

Multiple roles of the F-box protein Slimb inDrosophilaegg chamber development

Substrate-specific degradation of proteins by the ubiquitin-proteasome pathway is a precise mechanism that controls the abundance of key cell regulators. SCF complexes are a family of E3 ubiquitin ligases that target specific proteins for destruction at the 26S-proteasome. These complexes are composed of three constant polypeptides – Skp1, Cullin1/3 and Roc1/Rbx1– and a fourth variable adapter, the F-box protein. Slimb (Slmb) is a Drosophila F-Box protein that fulfills several roles in development and cell physiology. We analyzed its participation in egg chamber development and found that slmb is required in both the follicle cells and the germline at different stages of oogenesis. We observed that in slmbsomatic clones, morphogenesis of the germarium and encapsulation of the cyst were altered, giving rise to egg chambers with extra germline cells and two oocytes. Furthermore, in slmb somatic clones, we observed ectopic Fasciclin 3 expression, suggesting a delay in follicle cell differentiation,which correlated with the occurrence of ectopic polar cells, lack of interfollicular stalks and mislocalization of the oocyte. Later in oogenesis,Slmb was required in somatic cells to specify the position, size and morphology of dorsal appendages. Mild overactivation of the Dpp pathway caused similar phenotypes that could be antagonized by simultaneous overexpression of Slmb, suggesting that Slmb might normally downregulate the Dpp pathway in follicle cells. Indeed, ectopic expression of a dad-LacZ enhancer trap revealed that the Dpp pathway was upregulated in slmb somatic clones and, consistent with this, ectopic accumulation of the co-Smad protein,Medea, was recorded. By analyzing slmb germline clones, we found that loss of Slmb provoked a reduction in E2f2 and Dp levels, which correlated with misregulation of mitotic cycles during cyst formation, abnormal nurse cell endoreplication and impairment of dumping of the nurse cell content into the oocyte.

Expression of novel markers of pancreatic ductal adenocarcinoma in pancreatic nonductal neoplasms: additional evidence of different genetic pathways

Solid pseudopapillary tumor, pancreatoblastoma, undifferentiated carcinoma with osteoclastic-like giant cells, and acinar cell carcinomas are rare pancreatic nonductal neoplasms. Compared to the significant advances in our understanding of the pathogenesis of pancreatic ductal adenocarcinomas in the last decades, the molecular mechanisms underlying pancreatic nonductal neoplasms are poorly understood. In order to elucidate their molecular pathogenesis, we constructed tissue microarrays to study the expression of some novel pancreatic ductal adenocarcinoma-associated tumor markers in these nonductal pancreatic neoplasms. We analyzed nine markers including tumor suppressor gene (14-3-3 sigma), proliferation marker (topoisomerase II alpha), epithelial markers (prostate stem cell antigen, mesothelin and cytokeratin 19), stromal markers (fascin, hsp47 and fibronectin), and gamma-synuclein whose function is not delineated. In addition, we included tumor suppressor gene DPC4 and oncogene Beta-catenin to further confirm their expression in pancreatic nonductal tumors. Our results showed that in contrast to pancreatic ductal adenocarcinomas that show loss of Dpc4 protein in 55% of cases, loss of Dpc4 expression is absent in pancreatic nonductal neoplasms. Expression of 14-3-3 sigma is frequently seen in both pancreatic nonductal neoplasms (25-100%) and ductal adenocarcinomas (89%). Aberrant nuclear expression of beta-catenin is common in pancreatic nonductal neoplasms, specifically in solid pseudopapillary tumors (88%) and pancreatoblastomas (100%) but is rarely seen in pancreatic ductal adenocarcinomas (<5%). Expression of topoisomerase II alpha is not seen in solid pseudopapillary tumors and undifferentiated carcinomas with osteoclastic-like giant cells but is focally seen in pancreatoblastomas (50%) and acinar cell carcinomas (85%). Expression of PSCA and mesothelin was observed in pancreatic nonductal neoplasms but their expression was seen less frequently (0-50%) and weaker than that in pancreatic ductal adenocarcinomas (60-100%). CK19, a marker of pancreatic ductal adenocarcinomas, is not expressed in pancreatic nonductal neoplasms. Expression of gamma-synuclein as well as stromal markers (fascin, hsp47 and fibronectin) is frequently seen in both. Our findings indicate pancreatic nonductal neoplasms have distinctive patterns of protein expression relative to pancreatic ductal adenocarcinomas and suggest that pancreatic nonductal neoplasms have different genetic pathways from the more common pancreatic ductal adenocarcinomas.

Keratocan expression of murine keratocytes is maintained on amniotic membrane by down-regulating transforming growth factor-beta signaling

Keratocytes in the corneal stroma express keratan sulfate-containing proteoglycans including cornea-specific keratocan. On plastic dishes, human, bovine, and rabbit keratocytes lose their characteristic dendritic morphology and keratocan expression when cultured in serum-containing media. Herein, we demonstrated that murine keratocytes also acquired a fibroblastic shape and lost keratocan expression after first passage when cultured on plastic in the presence of serum. In contrast, cells expanded on human amniotic membrane (AM) stromal matrix maintained a three-dimensional dendritic morphology and expressed keratocan mRNA and protein for at least 8 passages before senescence. When keratocytes were cultured on AM, the promoter activity of transforming growth factor (TGF)-beta2 and TGF-beta receptor II was down-regulated as compared with that on plastic. Furthermore, cells on AM continuously retained Smad 2 and Smad 4 in the cytoplasm and did not express alpha-smooth muscle actin, even when 10 ng/ml TGF-beta1 was added in a serum-free medium for up to 5 days. In parallel to such down-regulation of TGF-beta signaling, keratocan promoter-driven ECFP expression was observed in cells cultured either on AM in the presence of serum or on plastic containing serum treated with a neutralizing antibody to TGF-beta. Collectively, these results indicate that down-regulation of Smad-mediated TGF-beta signaling is an important mechanism for cultured keratocytes to maintain a normal phenotype while continuously expanded in a serum-containing medium. This strategy of suppressing TGF-beta signaling, achieved by AM stromal matrix in part via suppression of TGF-beta gene transcription, can be used to expand keratocytes in culture without the use of AM in the future.

Smad4 inhibits tumor growth by inducing apoptosis in estrogen receptor-alpha-positive breast cancer cells

Estrogen is a mitogen in most estrogen receptor-alpha (ERalpha)-positive breast cancers. We have found that Smad4, a common signal transducer in the transforming growth factor-beta superfamily, acts as an ERalpha transcriptional corepressor. Here, we show that Smad4 induces apoptosis in ERalpha-positive MCF-7 breast cancer cells, but not in ERalpha-negative MDA-MB-231 cells. Smad4 induced expression of short Bim isoforms (by alternative splicing) and Bax and release of cytochrome c in ERalpha-positive cells only, and expression of these apoptotic marker genes was reduced when ERalpha small interfering RNA was introduced. Notably, Smad4 was able to induce apoptosis in MDA-231 cells with acquired ERalpha expression. Furthermore, Smad4 inhibited ERalpha-positive tumor growth by inducing apoptosis in tumor xenografts in nude mice. The sizes of tumors expressing Smad4 were only one-tenth the size of those expressing green fluorescent protein, whereas in ERalpha-negative cells, Smad4 did not reduce the tumor size. Notably, Smad4 also promoted short Bim isoform and Bax expression and release of cytochrome c only in ERalpha-positive MCF-7 tumor xenografts. Bim was sufficient for induction of apoptosis, and the short form was the most potent inducer. Our results demonstrate that Smad4 induces apoptosis by regulating Bim splicing as an initial intrinsic signal in ERalpha-positive cells. Smad4-induced apoptosis in ERalpha-positive breast cancer cells may explain the invasive nature of ERalpha-negative breast tumors, thereby providing a potential target for breast cancer intervention.