Activin A induces phosphorylation of Smad2 but not complex formation of Smad2 with Smad4 in human colon cancer cell line HT-29

Western blotting coupled with immunoprecipitation showed that activin A treatment induced phosphorylation of Smad2 but not complex formation of Smad2/4 in human colon cancer-derived HT-29 cells. Because HT-29 cells expressed neither Smad4 mRNA nor Smad4 protein, it is suggested that deletion of Smad4 leads to a defect of formation of Smad2/4 complex upon activin A stimulation in HT-29 cells.

Proteomic analysis of the TGF-beta signaling pathway in pancreatic carcinoma cells using stable RNA interference to silence Smad4 expression

Smad4 is a tumor-suppressor gene that is lost or mutated in 50% of pancreatic carcinomas. Smad4 is also an intracellular transmitter of transforming growth factor-beta (TGF-beta) signals. Although its tumor-suppressor function is presumed to reside in its capacity to mediate TGF-beta-induced growth inhibition, there seems to be a Smad4-independent TGF-beta signaling pathway. Here, we succeeded in establishing Smad4 knockdown (S4KD) pancreatic cancer cell lines using stable RNA interference. Smad4 protein expression and TGF-beta-Smad4 signaling were impaired in S4KD cells, and we compared the proteomic changes with TGF-beta stimulation using two-dimensional gel electrophoresis (2-DE) and mass spectrometry. We identified five proteins that were up-regulated and seven proteins that were down-regulated; 10 of them were novel targets for TGF-beta. These proteins function in processes such as cytoskeletal regulation, cell cycle, and oxidative stress. Introducing siRNA-mediated gene silencing into proteomics revealed a novel TGF-beta signal pathway that did not involve Smad4.

Biologically Different Subgroups of Invasive Ductal Carcinoma of the Pancreas

PURPOSE

Among invasive ductal carcinomas of the pancreas (IDCP), there is a morphologically characteristic subgroup accompanied by abundant intraductal carcinoma components (ICCs). With the aim of determining whether ICC-rich IDCP are biologically different from ICC-poor IDCP, the expression status of Dpc4 protein was analyzed.

EXPERIMENTAL DESIGN

A total of 43 IDCP was subdivided into two groups: (a). ICC-rich IDCP (ICCs area occupies >or=10% of the entire tumorous area); and (b). ICC-poor IDCP (with <10% of ICCs area). A total of 10 invasive carcinomas derived from intraductal papillary-mucinous neoplasms (ICs from IPMNs) were also analyzed. Each invasive and intraductal carcinoma area was then evaluated for Dpc4 protein status by immunohistochemistry.

RESULTS

In a total of 43 IDCP, there were 23 ICC-rich IDCP and 20 ICC-poor IDCP. Dpc4-positive immunostaining was observed in the invasive carcinoma component of ICC-rich IDCP, ICC-poor IDCP, and ICs from IPMN in 18 of 23 (78%), 4 of 20 (20%), and 7 of 10 (70%) cases, respectively. In the intraductal component, positive staining for Dpc4 was found in 20 of 23 (87%), 3 of 7 (41%), and 8 of 10 (80%) cases, respectively. Dpc4 expression was found in both the invasive and ICC components of ICC-rich IDCP, similar to that found in IC derived from IPMN, whereas the expression of Dpc4 was largely diminished in ICC-poor IDCP.

CONCLUSIONS

Morphologically distinct subgroups of invasive ductal carcinomas of the pancreas, namely ICC-rich IDCP and ICC-poor IDCP, are also biologically distinguishable as revealed by the differential expression of Dpc4.

[Growth suppression of colon cancer cells in vitro by DPC4 gene expression and its mechanism]

OBJECTIVE

To study the effect of DPC4 gene expression on the growth of colon cancer cells and its mechanism.

METHODS

Expression plasmid pcDNA3.1-DPC4 was constructed and transfected into the colon cancer cell line SW620 by use of lipofectamine gene transfer technique. DPC4 protein expression was detected by Western blot and immunocytochemistry. The effect of DPC4 gene on the growth of SW620 cells was monitored by population doubling time (PDT) and cloning efficiency. The influence of DPC4 expression on p21WAF1 transcription was investigated by RT-PCR to detect p21WAF1 mRNA.

RESULTS

Successful expression of DPC4 protein was detected in the transfected SW620 cells. Compared with the control cells, PDT (74 h) of the DPC4 expressing cells was prolonged and the cloning efficiency (21%) decreased. In addition, the mRNA level of p21(WAF1) in DPC4 transfected cells was increased.

CONCLUSIONS

Overexpression of DPC4 gene inhibits the growth of colon cancer in vitro, and induction of p21(WAF1) expression may be an important functional aspect of DPC4.

Smad expression in human atherosclerotic lesions: evidence for impaired TGF-beta/Smad signaling in smooth muscle cells of fibrofatty lesions

OBJECTIVE

Transforming growth factor-beta (TGF-beta) has been implicated in the pathogenesis of human atherosclerosis but its actions during lesion progression are poorly understood. Smad2, Smad3, and Smad4 proteins are signaling molecules by which TGF-beta modulates gene transcription. Our objective was to define the actions of TGF-beta during lesion progression in humans by examining the expression of Smads in relation to TGF-beta-mediated responses.

METHODS AND RESULTS

Immunohistochemistry and reverse-transcription polymerase chain reaction demonstrated Smad2, Smad3, and Smad4 expression in macrophages of fibrofatty lesions and their upregulation after differentiation of monocytes to macrophages. The major Smad splice variants expressed by the macrophages were those that are transcriptionally most active. Macrophages also expressed cyclin inhibitors whose expression is induced via Smad proteins. The cytoplasmic location of p21(Waf1) suggests it may protect macrophages from apoptosis. Smooth muscle cells (SMCs) within the fibrofatty lesions did not express the Smad proteins or the cyclin inhibitors. SMCs of fibrous plaques expressed all 3 Smad proteins.

CONCLUSIONS

In human atherosclerotic lesions, the actions of TGF-beta appear restricted to SMCs in fibrous plaques and macrophages in fatty streaks/fibrofatty lesions. The lack of key TGF-beta signaling components in SMCs of fibrofatty lesions indicates impaired ability of these cells to initiate TGF-beta-mediated Smad-dependent transcriptional responses.

Inhibitor of DNA binding/differentiation helix-loop-helix proteins mediate bone morphogenetic protein-induced osteoblast differentiation of mesenchymal stem cells

Bone morphogenetic proteins (BMPs) belong to the TGF-beta superfamily and play an important role in development and in many cellular processes. We have found that BMP-2, BMP-6, and BMP-9 induce the most potent osteogenic differentiation of mesenchymal stem cells. Expression profiling analysis has revealed that the Inhibitors of DNA binding/differentiation (Id)-1, Id-2, and Id-3 are among the most significantly up-regulated genes upon BMP-2, BMP-6, or BMP-9 stimulation. Here, we sought to determine the functional role of these Id proteins in BMP-induced osteoblast differentiation. We demonstrated that the expression of Id-1, Id-2, and Id-3 genes was significantly induced at the early stage of BMP-9 stimulation and returned to basal levels at 3 days after stimulation. RNA interference-mediated knockdown of Id expression significantly diminished the BMP-9-induced osteogenic differentiation of mesenchymal progenitor cells. Surprisingly, a constitutive overexpression of these Id genes also inhibited osteoblast differentiation initiated by BMP-9. Furthermore, we demonstrated that BMP-9-regulated Id expression is Smad4-dependent. Overexpression of the three Id genes was shown to promote cell proliferation that was coupled with an inhibition of osteogenic differentiation. Thus, our findings suggest that the Id helix-loop-helix proteins may play an important role in promoting the proliferation of early osteoblast progenitor cells and that Id expression must be down-regulated during the terminal differentiation of committed osteoblasts, suggesting that a balanced regulation of Id expression may be critical to BMP-induced osteoblast lineage-specific differentiation of mesenchymal stem cells.

Loss of BMP2, Smad8, and Smad4 expression in prostate cancer progression

BACKGROUND

The role of the bone morphogenetic protein (BMP) pathway in prostate cancer (PC) is unclear. This study aimed to characterize aspects of the BMP pathway in PC by assessing BMP2, Smad8, and Smad4 expression in normal, hyperplastic, and malignant prostate tissue, and to correlate findings with progression to PC.

METHODS

Radical prostatectomy (RP) specimens from 74 patients with clinically localized PC (median follow-up 51 months, range 15-152), 44 benign prostatic hypertrophy (BPH) lesions, and 4 normal prostates (NPs) were assessed for BMP2, Smad8, and Smad4 expression using immunohistochemistry.

RESULTS

Both BMP2 (P < 0.001) and nuclear Smad4 (P < 0.0001) expression were significantly decreased in PC compared to benign prostate tissue. Nuclear Smad8 was present in normal/benign prostate tissue but absent in PC and adjacent hyperplasia. Furthermore, loss of BMP2 (P < 0.001) and decreased nuclear Smad4 (P = 0.05) expression correlated with increasing Gleason score.

CONCLUSIONS

These data suggest that decreased BMP2, nuclear smad8 and nuclear Smad4 expression are associated with the progression to PC, and in particular loss of BMP2 and Smad4 are related to progression to a more aggressive phenotype.

Repression of endogenous Smad7 by Ski

The Ski protein has been proposed to serve as a corepressor for Smad4 to maintain a transforming growth factor-beta (TGF-beta)-responsive promoter at a repressed, basal level. However, there have been no reports so far that it indeed acts on a natural promoter. We have previously cloned the human Smad7 promoter and shown that it contains the 8-base pair palindromic Smad-binding element (SBE) necessary for TGF-beta induction. In this report, we have characterized the negative regulation of Smad7 promoter basal activity by Ski. We show that Ski inhibits the Smad7 promoter basal activity in a SBE-dependent manner. Mutation of the SBE abrogates the inhibitory effect of Ski on the Smad7 promoter. Moreover, mutation of the SBE increases the Smad7 promoter basal activity. Using the chromatin immunoprecipitation assay, we further show that Ski together with Smad4 binds to the endogenous Smad7 promoter. Finally, we show that RNAi knockdown of Ski increases Smad7 reporter gene activity in transient transfection assays as well as elevating the endogenous level of Smad7 mRNA. Taken together, our results provide the first evidence that Ski is indeed a corepressor for Smad4, which can inhibit a natural TGF-beta responsive gene at the basal state.

[Effects of TGF beta 1 on the cell cycle of irradiated human lung fibroblasts and its signal transduction mechanism]

AIM

To investigate the effects of TGF beta 1 on the proliferative activity and cell cycle of normal and gamma ray-irradiated human lung fibroblasts (HLFs).

METHODS

HLFs were cultured and irradiated with 3Gy gamma rays and then stimulated by TGF beta 1 at 0.01, 0.1, 1 and 10 microg/L. The proliferative activity and cell cycle were detected by MTT colorimetry and FACS. Furthermore, the expressions of signal proteins Smad3/4 in HLFs were observed by immunohistochemical staining and FACS.

RESULTS

TGF beta 1 of 10 microg/L could promote the proliferation of HLFs, with the number of cells in S phase increased. It also could enhance the expression of Smad3 protein and promote the nuclear translocation of Smad4 protein.

CONCLUSION

A given dose of TGF beta 1 can promote the proliferation of gamma rays-irradiated HLFs by regulating their cell cycle in which the activation of Smad pathway may play a role.

TGF‐β signaling and the fibrotic response

The cause of fibrotic diseases, pathologies characterized by excessive production, deposition, and contraction of extracellular matrix, is unknown. To understand the molecular basis of fibrotic disease, it is essential to appreciate how matrix deposition is normally controlled and how this process is dysregulated in fibrogenesis. This review discusses the current state of knowledge concerning interactions among the profibrotic proteins transforming growth factor-beta (TGF-beta), connective tissue growth factor (CTGF, CCN2), and ED-A fibronectin (ED-A FN) and the antifibrotic proteins tumor necrosis factor-alpha (TNF-alpha) and gamma-interferon (IFN-gamma).

Microcystic tubulopapillary carcinoma of the pancreas: a new tumor entity?

An unusual pancreatic tumor with microcystic and tubulopapillary features was observed in a 53-year-old woman. The tumor presented as a large, focally cystic mass in the head of the pancreas, which compressed the surrounding structures. The histological and immunohistochemical analysis revealed a neoplasm that could not be assigned to any of the known pancreatic tumor types. At the molecular level, the tumor showed inactivation of the DPC4/SMAD4 gene, deletion of exon 1 of the p16(INK4A) gene and a point mutation at codon 34 (GGA>AGA) of beta-catenin. Transcriptional profiling analyses and subsequent correspondence cluster analysis demonstrated that the transcriptional profile of the tumor differed distinctly from that of ductal adenocarcinomas, pancreatic cystic tumors and normal pancreatic tissues. These data suggest that the neoplasm most likely represents a new pancreatic tumor entity, which we would like to refer to as microcystic tubulopapillary tumor.

Tumor suppressor Smad4 mediates downregulation of the anti-adhesive invasion-promoting matricellular protein SPARC: Landscaping activity of Smad4 as revealed by a“secretome” analysis

We have demonstrated previously that restoration of Smad4 expression in Smad4-deficient SW480 human colon carcinoma cells was adequate to suppress tumorigenicity and invasive potential, whereas cell growth in vitro was not affected. Here we show that Smad4-positive and Smad4-negative SW480 cells deposit extracellular matrices in tissue culture which are functionally different with respect to their adhesiveness. We present a "differential secretomics analysis" as the most direct approach to identify the underlying alterations. The protein composition of conditioned media produced by Smad4-positive and Smad4-negative SW480 cells was compared by two-dimensional (2-D) gel electrophoresis. A major group of protein spots was detected in media derived from Smad4-negative cells, only, which were identified as "secreted protein, acidic and rich in cysteins" (SPARC) by mass spectrometry. SPARC expression in SW480 cells was suppressed by Smad4 at the level of transcription. SPARC is a glycoprotein of the extracellular matrix, characterized as an anti-adhesive and invasion-promoting protein. Differential secretomics appeared as a powerful method to identify a novel Smad4 target gene, which may be one of the players involved in reduced adhesiveness of extracellular matrices and thus consistent with Smad4's emerging role as an invasion suppressor.

[Obstruction of TGF-beta1 signal transduction by anti-Smad4 gene can therapy experimental liver fibrosis in the rat]

OBJECTIVE

To study the therapeutic effects to block the TGF-beta1 (transforming growth factor beta1) signal transduction by antisense Smad4 gene on experimental fibrotic liver.

METHODS

Using the rat model of liver fibrosis induced by Carbon Tetrachloride (CCl4)/ethanol, we transfected antisense Smad4 gene mediated by adenovirus via portal vein infusion into the liver, and observed the expression of Smad4 by Retro-Polymerase Chain Reaction (RT-PCR) and Western Blot. We also investigated the pathologic features and collagen expression.

RESULTS

In the non-therapeutic cirrhotic liver, the expression of Smad4 mRNA was significantly increased than normal liver, and so was the collagen I. After antisense Smad4 gene being transfected, the expression of Smad4 mRNA and that of collagen I in the therapeutic liver was significantly decreased, compared with the non-therapeutic cirrhotic liver. The fibrous degree of therapeutic liver was also reduced compared with the non-therapeutic fibrous liver.

CONCLUSION

These results indicate that because antisense Smad4 gene could block TGF-beta1 signal transduction by reducing the expression of Smad4, so it could inhibit the production of extracellular matrix (ECM) and improve hepatic fibrosis.

Regulation of Smad4 Sumoylation and Transforming Growth Factor-β Signaling by Protein Inhibitor of Activated STAT1

The tumor suppressor, Smad4/DPC4, is a common signal transducer in transforming growth factor-beta (TGF-beta) signaling. In this study, we demonstrated that the protein inhibitor of activated STAT1 (PIAS1) regulates the signaling potential of Smad4 through a sumoylation-dependent mechanism. PIAS1 was shown to be an E3 ligase for Smad4 sumoylation in vitro and in vivo. PIAS1 physically interacted with Smad4 in a TGF-beta-inducible manner. A minimal SUMO E3 ligase domain and Smad4-binding domain were defined on PIAS1 protein. The RING finger domain of PIAS1 was essential for its E3 ligase function. Although PIAS1 enhanced the Smad4-dependent transcriptional activation of TGF-beta signaling, a mutant lacking the RING domain inhibited the sumoylation of Smad4 in a dominant negative manner and, as a result, abolished the transcriptional response of TGF-beta. These data demonstrate that PIAS1 protein positively modulates TGF-beta responses as a SUMO E3 ligase for Smad4.

Comparative analysis of cell adhesion molecules, cell cycle regulatory proteins, mismatch repair genes, cyclooxygenase-2, and DPC4 in carcinomas arising in inflammatory bowel disease and sporadic colon cancer

Colon carcinoma arising in inflammatory bowel disease often exhibits aggressive behavior compared to sporadic carcinomas. The rationale for the different biological behaviors of these two groups of tumors is not fully understood. In this study, we have examined carcinomas arising in inflammatory bowel disease (IBD) and sporadic carcinomas (SCA) for molecular differences that may provide clues for the behavioral disparity of these tumors. Thirty-eight colon carcinomas (12 from ulcerative colitis, 5 from Crohn's disease, and 21 SCA) were analyzed by immunohistochemistry for cell adhesion molecules (E-cadherin, beta-catenin, CD44), cell cycle regulatory proteins (cyclin D1, p27, p21), mismatch repair proteins (hMLH1, hMSH2), cyclooxygenase-2 and DPC4. Carcinomas arising in IBD showed significant decrease in expression of cell adhesion molecules, the cell cycle inhibitor protein, p21, and increased expression of cyclooxygenase-2 compared to sporadic carcinomas. No differences were observed in the expression of cell cycle regulatory proteins p27, cyclin D1, DPC4 and mismatch repair proteins between these two groups of tumors. Decreased expression of p21 as well as adhesion molecules may provide increased impetus for the aggressive behavior of tumors arising in inflammatory bowel disease.

Infrequent alteration of the DPC4 tumor suppressor gene in renal cell carcinoma

The aim of this study was to investigate the alterations in the DPC4 tumor suppressor gene in renal cell carcinoma (RCC). The study included 32 tumor specimens from Croatian patients with a diagnosis of RCC. Loss of heterozygosity (LOH) was investigated using three specific oligonucleotide primers for the three DPC4 polymorphic markers. Our investigation of mutations in the DPC4 gene was focused on exons 2, 8, 10 and 11. These exons belong to the mad homology domains 1 (exon 2) and 2 (exons 8-11). The presence of previously documented mutation in exons 2 (codon 100), 8 (codon 358), 10 (codon 412), and 11 (codon 493) was investigated by restriction fragment length polymorphism (RFLP) analysis, as a first screening method. Finally, the study was extended to search for any other type of mutation in the four selected exons by single strand conformation polymorphism (SSCP) assay. To increase heterozygosity, all 32 tumor specimens were tested with primers for three polymorphic markers. A total of 30 (94%) were heterozygous (informative). LOH at any of these markers was only revealed in four (13%) of the 30 informative samples. No tumor samples were positive for mutation in the four investigated exons analyzed by RFLP. In addition, no samples showed other types of mutation in denaturing conditions. Genetic alterations were shown only in a minority of patients, probably because mutation analysis of the DPC4 gene has only been partially covered by our work. It seems that exon 2 (belonging to the MH1 domain) and exons 8, 10, 11 (belonging to the MH2 domain) are not altered in RCC. This investigation must be extended on other exons of DPC4 for a better understanding a role of this gene in renal cell carcinoma.

Expression of Smad2 and Smad4, transforming growth factor-beta signal transducers in rat endometrium during the estrous cycle, pre-, and peri-implantation

SMADs are intracellular signaling molecules that transmit signals elicited by members of transforming growth factor-beta (TGF-beta) superfamily. To decipher the mechanism of TGF-beta signaling during the estrous cycle and implantation, we performed in situ hybridization to investigate the expression patterns of mRNAs for Smad2 and Smad4 in rat endometrium during the estrous cycle and on Days 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, and 6.5 of pregnancy. Intense epithelial expression of Smad2 mRNA at diestrus and proestrus was reduced at estrus and metaestrus, while Smad4 maintained its constitutive expression during the estrous cycle. During pre-implantation, both Smads were accumulated in the luminal epithelium and the glandular epithelium. Contrary to the dramatic Smad4 expression, Smad2 was highly down-regulated on Day 2.5 and was increased on Day 3.5. During peri-implantation, both Smads were expressed in the luminal epithelium, subepithelial stroma, and the primary decidual zone. Smad4 was down-modulated on Day 5.5. These results suggest that (a) both Smads are involved in the tissue remodeling of cycling and pregnant rat uteri; (b) TGF-beta signaling functions mainly in the epithelium during pre-implantation and Smad2 is involved in the endometrial switch from the neutral phase to the receptive phase; (c) TGF-beta signaling is down-regulated at the time when trophoblast invasion begins and both Smads are involved in the formation of the primary decidual zone.

Regulation of large-scale chromatin unfolding by Smad4

The tumor suppressor Smad4 plays a critical role in the transforming growth factor-beta (TGF-beta signaling pathway. Smad4 is an essential component of transcriptional complexes mediating the activation of Smad-dependent target genes. However, how Smad4 regulates various chromosomal events remains unknown. Here, we report that Smad4 induces large-scale chromatin unfolding by targeting Smad4 to an amplified, lac operator-containing chromosome region in mammalian cells. This unfolding activity maps to the subdomains within the transactivation domain of Smad4. Both the N-terminal missense and the C-terminal truncated tumor-derived mutations increased the chromatin unfolding activity of Smad4. These data identify a novel function of Smad4 and suggest that regulation of large-scale chromatin unfolding by Smad4 may be responsible for cancer development.

Identification and characterization of a human smad3 splicing variant lacking part of the linker region

Smad3 is one of the signal transducers that are activated in response to transforming growth factor-beta (TGF-beta). We have identified and characterized a splicing variant of smad3. The splicing variant (smad3-Delta3) lacks exon 3 resulting in a truncated linker region. We could detect mRNA expression of smad3-Delta3 in all investigated human tissues. Real-time PCR analyses demonstrated that the fraction of smad3-Delta3 mRNA compared to normal smad3 varies between tissues. The amount of spliced mRNA was estimated to represent 0.5-5% of the normal smad3 mRNA. When smad3-Delta3 is overexpressed in a fibrosarcoma cell line, the Smad3-Delta3 is translocated to the nucleus upon TGF-beta stimulation and binds the Smad responsive element. Using a CAGA luciferase reporter system, we demonstrate that Smad3-Delta3 has transcriptional activity and we conclude that Smad3-Delta3 possesses functional transactivating properties.

Status of the DPC4 tumor suppressor gene in sporadic colon adenocarcinoma of Croatian patients: identification of a novel somatic mutation

Loss of heterozygosity (LOH) of loci on chromosome 18q occurs in a majority of colorectal cancers. The DPC4 (Smad4) tumor suppressor gene, located at 18q21.1, may be a predisposing gene for Juvenile Polyposis Syndrome. To investigate alterations of the DPC4 gene in sporadic colon adenocarcinoma, a panel of 60 tumor specimens from Croatian patients was surveyed for evidence of LOH and also for mutations within the entire DPC4 coding region (exons 1-11). Using three pairs of specific primers for the three DPC4 microsatellite repetitive sequences, we investigated the frequency of LOH. The presence of single nucleotide change at restriction sites of specific codons in exons 2, 8, 10, and 11 (which belong to the conserved region of the gene) was examined by RFLP analysis. The investigation was extended to search for any other mutation within the entire coding region of the DPC4 gene by single strand conformation polymorphism (SSCP) analysis. Our results show a high frequency of heterozygosity in 58 of 60 (97%) colon adenocarcinoma samples. LOH at any one of the three flanking markers was observed in 26 (45%) of the 58 informative cases. The loss of one allele of the DPC4 gene was negatively correlated with tumor size; more frequent in smaller tumors (<5 cm) than in larger ones. A mutation was found in exon 11 in only one tumor sample (T18), and the mutation was verified by sequencing. Sequencing demonstrated a novel mutation-a deletion in exon 11 (134-153 del TAGACGAAGTACTTCATACC) of the DPC4 gene in the MH2 domain. These data suggest that inactivation of the DPC4 gene contributes to the genesis of colorectal carcinoma through allelic loss whereas mutation in the coding region of the DPC4 gene is infrequently detected in Croatian patients with A, B or C stages of colorectal cancers.

Apoptosis incidence and protein expression of p53, TGF-beta receptor II, p27Kip1, and Smad4 in benign, premalignant, and malignant human prostate

Deregulation of apoptosis is involved in prostate cancer development and progression. This study involved an immunohistochemical "profiling" of prostate tissue specimens from patients who underwent prostatectomy for localized prostate cancer, to identify apoptosis-specific alterations associated with premalignant precursor lesions. Prostate tissue was pathologically evaluated, and areas of benign acini, high-grade prostate intraepithelial neoplasia (HGPIN), and prostate cancer were identified. Immunohistochemical analysis was performed to determine the expression of p27Kip1, a key cell cycle regulator, transforming growth factor (TGF)-beta receptor II (TbetaRII), a critical signaling effector of TGF-beta; Smad4, a downstream intracellular effector of TGF-beta signaling; p53, a key apoptosis regulator; and prostate-specific antigen (PSA), a clinical marker of prostate cancer. The apoptotic index of the same cell populations was determined using the transferase-mediated digoxigenin-tagged 16-desoxy-uridine-triphosphate nick end labeling assay. Our findings indicate a significant reduction in p27Kip1 immunoreactivity in HGPIN (P<0.0001) and prostate cancer (P<0.0001) compared with the benign tissue. A significant down-regulation was detected in TbetaRII expression in HGPIN and prostate cancer compared with benign prostatic hyperplasia (BPH)(P<0.001). A significant decrease was also observed in Smad4 levels in HGPIN and prostate cancer compared with BPH (P<0.001). Evaluation of the incidence of apoptosis revealed a significant decrease in the apoptotic index among the epithelial cell populations in HGPIN and a further decrease in prostate carcinoma (P<0.01). This reduced apoptotic index correlated with a significant increase in p53 immunoreactivity in the prostatic carcinoma foci. Prostate cancer cells exhibited strong nuclear staining for p53 compared with adjacent HGPIN (P<0.05) and the benign lesions of the same prostate specimens (P<0.05). A significant reduction in PSA immunostaining was detected in HGPIN and prostate carcinoma foci compared with the benign glandular epithelia (P<0.001). These results further define deregulation of TGF-beta signaling effectors as a molecular basis for loss of apoptotic control contributing to the development of prostate tumors. Identification of apoptotic regulators in precursor premalignant lesions may have prognostic significance in disease progression as well as therapeutic value for targeting prostate cancer.

Frequent loss of RUNX3 gene expression in human bile duct and pancreatic cancer cell lines

RUNX3, a Runt domain transcription factor involved in TGF-beta signaling, is a candidate tumor-suppressor gene localized in 1p36, a region commonly deleted in a wide variety of human tumors, including those of the stomach, bile duct, and pancreas. Recently, frequent inactivation of RUNX3 has been demonstrated in human gastric carcinomas. In this study, to examine the involvement of RUNX3 abnormalities in tumorigenesis of bile duct as well as pancreatic cancers, we investigated not only the expression but also methylation status of RUNX3 in 10 human bile duct and 12 pancreatic cancer cell lines. Seven (70%) of the bile duct and nine (75%) of the pancreatic cancer cell lines exhibited no expression of RUNX3 by both Northern blot analysis and the reverse transcriptase polymerase chain reaction. All of the 16 cell lines that did not express RUNX3 also showed methylation of the promoter CpG island of the gene, whereas the six cell lines that showed RUNX3 expression were not methylated or only partially methylated in the RUNX3 promoter region. Moreover, treatment with the methylation inhibitor 5'-aza-2'-deoxycitidine activated RUNX3 mRNA expression in all of 16 cancer cell lines that originally lacked RUNX3 expression. Finally, hemizygous deletion of RUNX3, as detected by fluorescence in situ hybridization, was found in 15 of the 16 cancer cell lines that lacked RUNX3 expression. These data suggest that the inactivation of RUNX3 plays an important role in bile duct and pancreatic carcinogenesis, and that methylation is a common mechanism by which the gene is inactivated.

Loss of Smad4 correlates with loss of the invasion suppressor E-cadherin in advanced colorectal carcinomas

Smad4 is a tumour suppressor gene predominantly involved in gastrointestinal carcinogenesis. Loss of Smad4 is considered to be a genetically late step and occurs in up to 30% of metastatic colorectal carcinomas. Smad4, originally characterized as an intracellular transmitter of transforming growth factor-beta (TGF-beta) signals, is a transcriptional co-modulator capable of integrating cellular responses to multiple signalling cascades. Thus, there are many Smad4 target genes and they are presumably strongly context-dependent. It was recently shown that re-expression of Smad4 in Smad4-deficient SW480 human colon carcinoma cells restored epithelioid morphology and induced P-cadherin and E-cadherin transcription. The cadherins are key players in cell-cell adhesion connecting adjacent cells via the cadherin-catenin adhesion complex. Frequent loss of E-cadherin expression in human cancers has been a long-standing observation, but the underlying mechanisms are not yet fully understood. To assess the role of Smad4 in E-cadherin regulation in colorectal carcinogenesis further, the present study has analysed Smad4 and E-cadherin RNA and protein expression in colorectal carcinoma cell lines and in 51 late-stage colorectal carcinomas. In primary tumours, loss of Smad4 expression correlated highly significantly with loss of E-cadherin expression, thus providing further evidence for involvement of the tumour suppressor Smad4 in the control of expression of the tumour and invasion suppressor E-cadherin.

[Effects of anti-sense Smad4 gene on the biological characteristics of the fat-storing cell line CFSC]

OBJECTIVE

To investigate the effects of antisense Smad(4) on the biological characteristics of the fat-storing cell line CFSC.

METHODS

Fat-storing cells of line CFSC from rat with liver fibrosis were cultured and transfected with 50 MOI of recombinant adenoviral vector carrying antisense Smad(4) (AdvATSmad(4)) or the control empty adenovirus (Adv0), both produced by 293 packaging cells, respectively. Two, four, and six days after the transfection the cultured cells were collected to undergo trypan blue staining and cell counting. The growth curves were drawn. The presence of antisense Smad(4) was detected by RT-PCR and Western blotting. (3)H-TdR was added into the culture media to be co-cultured for 6 hours. Then the cells were collected to examine the (3)H-TdR incorporation rate. RT-PCR and immunohistochemistry were used to examine the expression of COL1A1 and type I collagen, kinds of extracellular matrix (ECM).

RESULTS

Compared with the control CFSC and the Adv0-transfected CFSC cells, the cell growth curve, (3)H-TdR incorporation rate, proline incorporation rate, expression of Smad(4), and expression of extracellular matrix were markedly decreased in the AdvATSmad(4)-transfected CFSCs.

CONCLUSION

The antisense Smad(4) gene inhibits the expression of Smad(4) mRNA and protein, proline incorporation and cell growth, thus down-regulating the production of ECM. Antisense Smad(4) gene may be used as a choice of gene therapy for liver fibrosis.

Smad4 Protein Stability Is Regulated by Ubiquitin Ligase SCFβ-TrCP1

Smad4 is a key intracellular mediator for the transforming growth factor-beta (TGF-beta) superfamily of growth factors and is also an important tumor suppressor. The receptor-regulated Smad (R-Smad) proteins are regulated by ubiquitin-mediated degradation, yet the precise control of Smad4 protein stability is unclear. We have identified SCF(beta-TrCP1), a ubiquitin (E3) ligase, as a critical determinant for the protein degradation of Smad4 protein. F-box protein beta-TrCP1 in this E3 ligase interacts with Smad4 both in yeast and in mammalian cells, but has no interaction with Smad2 and has weak interaction with Smad3. The beta-TrCP1/Smad3 interaction was abolished by Smad4 gene silencing, indicating the interaction is indirect and is through Smad4. Ectopic expression of SCF complex containing beta-TrCP1 is sufficient to induce the ubiquitination and degradation of Smad4. Furthermore, small interfering RNA-triggered endogenous beta-TrCP1 suppression increases the expression of Smad4 protein. Consistent with these results, cells that overexpress the SCF complex display an inhibited TGF-beta-dependent transcriptional activity and an impaired cell cycle arrest function. Thus, SCF(beta-TrCP1) abrogates TGF-beta function in vivo by decreasing Smad4 stability.