Prognostic significance of the expression of Smad4 and Smad7 in human gastric carcinomas

Y. H. Kim1,4, H. S. Lee2,4, H.-J. Lee1, K. Hur4, W. H. Kim2,4, Y.-J. Bang3,4, S.-J. Kim5, K. U. Lee1, K. J. Choe1 and H.-K. Yang1,4,*

1 Department of Surgery, 2 Department of Pathology, 3 National Research Laboratory for Cancer Epigenetics, 4 Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea; 5 Laboratory of Cell Regulation and Carcinogenesis, National Cancer Institute, Bethesda, MD, USA

Received 30 August 2003; revised 26 November 2003; accepted 22 December 2003


    ABSTRACT
 Top
 ABSTRACT
 Introduction
 Materials and methods
 Results
 Discussion
 REFERENCES
 
Background:

Transforming growth factor-ß (TGF-ß) modulates the growth and function of many cells, including those with malignant transformation. Smad proteins have been identified as major components in the intracellular signaling of TGF-ß family members.

Patients and methods:

To clarify the correlations between clinicopathologic profiles and the patient’s survival, the expression of common mediator Smad (Smad4) and inhibitory Smad (Smad7) were evaluated immunohistochemically in 304 consecutive gastric carcinomas using the tissue array method.

Results:

Positive Smad4 expression was observed in 266 (87.5%) tumors and positive Smad7 expression in 98 (32.2%) tumors. The prognosis of patients with a Smad4-positive tumor was significantly better than that of the patients with a negative tumor. The survival rate was significantly higher in patients with negative Smad7 expression than those with positive Smad7 expression. In subgroup analysis according to TNM (tumour–node–metastasis) stage, both Smad4 and Smad7 showed most significant prognostic differences in stage I gastric cancer patients. Multivariate analysis indicated that tumor size, depth of invasion, lymph node metastasis and Smad7 expression were independent prognostic factors.

Conclusion:

Enhanced expression of the TGF-ß signaling inhibitor Smad7 may present one of the novel mechanisms of TGF-ß resistance in human gastric carcinomas.

Key words: gastric carcinoma, prognostic factor, Smad4, Smad7, transforming growth factor-ß


    Introduction
 Top
 ABSTRACT
 Introduction
 Materials and methods
 Results
 Discussion
 REFERENCES
 
Deregulated transforming growth factor-ß (TGF-ß) family signaling has been implicated in various human diseases, including auto-immune diseases, vascular disorders and cancer [1]. Recent studies have revealed that Smad proteins, discovered through genetic studies in Drosophila and Caenorhabditis elegans, are pivotal intracellular mediators of TGF-ß family members [2, 3]. The Smad family can be divided into three distinct subfamilies: receptor-regulated Smads (R-Smads: Smad1, -2, -3, -5 and -8), common mediator Smads (Co-Smads: Smad4) and inhibitory Smads (I-Smads: Smad6 and -7) [4, 5]. The demonstration that TGF-ß has antiproliferative effects in a variety of cell types has led to the hypothesis that inactivation of the TGF-ß signaling pathway contributes to tumor development or progression [6]. Recently, disruption of the TGF-ß pathway in cancer has been demonstrated at the level of the Smad signal transducers.

The gene encoding Smad4 was originally cloned as a tumor suppressor gene on chromosome 18q21, which is frequently deleted or mutated in pancreatic carcinomas. Hence, its original name was DPC4 (deleted in pancreatic carcinoma locus 4) [7]. Smad4 is also mutated in a significant proportion of colorectal tumors and less frequently in breast, ovarian, head and neck, prostatic and esophageal cancers [812]. Recent studies of human clinical samples have suggested that decreased expression of Smad4 or LOH (loss of heterozygosity) at 18q21 may be associated with a more aggressive phenotype in gastric, esophageal and pancreatic cancers, and intrahepatic cholangiocarcinoma [1316]. Xiangming et al. have previously reported that reduced expression of Smad4 was related to the depth of tumor invasion and reduced Smad4 expression was an unfavorable prognostic factor for advanced gastric cancer [17].

The inhibitory Smads, Smad6 and Smad7, have been shown to bind to the TGF-ß type I receptor, precluding the phosphorylation of the receptor-regulated Smads and, consequently, interfering with TGF-ß signaling [18]. It has been reported previously that Smad7 is overexpressed in pancreatic cancer, suggesting that this is a mechanism of repression of the TGF-ß-signaling pathway [19]. More recently, the position of the gene for Smad7 has been assigned to the region 18q21, identical to Smad4, by in situ hybridization and mapped between Smad2 and Smad4 genes with a 4-Mb gene cluster [20, 21]. However, little is known about the roles of Smad7 in gastric carcinoma.

The purpose of this study was to investigate the expression of Smad4 and Smad7 proteins and their prognostic significance in human gastric carcinoma.


    Materials and methods
 Top
 ABSTRACT
 Introduction
 Materials and methods
 Results
 Discussion
 REFERENCES
 
Patients
A total of 304 gastric carcinoma patients who had undergone gastrectomy at Seoul National University Hospital from 1 January 1995 to 30 June 1995 were included in this study. None of the patients had received prior chemotherapy or irradiation therapy. All patients had histologically proven adenocarcinoma of the stomach. The clinicopathologic findings were determined according to the criteria established by the Japanese General Rules for Gastric Cancer Study. There were 203 male patients and 101 female patients, and their ages ranged from 21 to 80 years (mean 54.8 years). The clinicopathological characteristics of the patients are given in Table 1. Among them, most patients underwent gastrectomy with UICC [International Union Against Cancer (Union Internationale Contre le Cancer)] R0 category [n = 286 (92.8%)], followed by R2 [n = 16 (5.3%)] and R1 categories [n = 6 (2.0%)]. We selected the following 12 prognostic factors for evaluation: age, sex, tumor size, tumor location, Lauren histology, differentiation, depth of invasion, lymph node metastasis, distant metastasis, stage, lymphatic invasion and vascular invasion. Survival data were available for all patients and obtained from patient records and the Population Registry in Korea. During follow-up, 110 (36.2%) patients died of gastric cancer. The overall 5-year survival rate was 62.6% and the median follow-up was 67 months (range 1–72 months).


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Table 1. The relationship between Smad4 or Smad7 expression and clinicopathologic findings in gastric carcinomas
 
Tissue array methods
Core tissue biopsies (2 mm in diameter) were taken from individual paraffin-embedded gastric tumors (donor blocks) and arranged in a new recipient paraffin block (tissue array block) using a trephine apparatus (Superbiochips Laboratories, Seoul, Korea). Each tissue array block contained up to 60 cases, allowing six array blocks to contain the total 304 cases. An adequate case was defined as tumor occupying >10% of core area. Each block contained an internal control consisting of non-neoplastic gastric mucosa. Sections of 4 µm were cut from each tissue array block, deparaffinized and dehydrated.

Immunohistochemistry
Immunohistochemical staining against Smad4 [1:100; B-8, sc-7966 (Santa Cruz Biotechnology, Santa Cruz, CA)] and Smad7 [1:100; H-79, sc-11392 (Santa Cruz Biotechnology)] was performed using a streptavidin peroxidase procedure. After deparaffinization and rehydration, tissue sections were treated three times with microwaves in 0.01 M citrate buffer (pH 6.0) for 5 min each time. The sections were then immersed in methanol containing 0.3% hydrogen peroxidase for 6 min to block the endogenous peroxidase activity, and incubated in 2.5% blocking serum to reduce non-specific binding. After incubation with primary antibodies, the sections were incubated with biotinylated anti-rabbit IgG and avitin–biotin peroxidase (Vector Laboratories, Burlingame, CA), and visualized using diaminobenzidine tetrahydrochloride. Two antibodies among various commercially available antibodies were selected after the test procedure using a human control slide for immunohistochemistry (Superbiochips Laboratories).

For statistical analysis, the results of immunostaining were considered to be positive if ≥10% of the neoplastic cells were stained. Previous studies in which immunolabeling patterns have been correlated with Smad4 gene status have shown that both focal and diffusely positive labelings correlate with an intact Smad gene, whereas complete loss of labeling correlates with inactivation of the Smad gene [22]. On the contrary, there have been few studies dealing with the definite level of Smad7 positivity in immunohistochemical staining, so we applied the previously reported methodology on Smad7 positivity in immunohistochemical staining [23]. For purposes of data analysis, both focal and diffusely positive lesions were considered to show intact Smad expression (positive), and only complete loss of labeling was considered to show loss of Smad expression (negative).

Statistical analysis
The association of factors was evaluated using the chi-square test. The significance of differences among means was determined by the Mann–Whitney U-test. Survival rates were calculated using the Kaplan–Meier method and analyzed using the Log-rank test. A multivariate analysis was performed using the Cox proportional hazards model. The significance level was set at 5% for all analyses. All statistical analyses were conducted using the SPSS 10.0 statistical software program (SPSS, Chicago, IL).


    Results
 Top
 ABSTRACT
 Introduction
 Materials and methods
 Results
 Discussion
 REFERENCES
 
Immunohistochemical staining for Smad4 and Smad7
Smad4 protein was consistently expressed in a nuclear location (Figure 1A and B). Smad4 was homogeneously stained in normal cells but the rates of Smad4 expression were reduced in gastric cancer tissues. Smad7 protein was stained mainly in the cytoplasm of cancer cells (Figure 1C and D). Smad7 overexpression was observed in gastric cancer tissues, whereas no expression was observed in normal tissues.



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Figure 1. Immunohistochemical staining for Smad4 and Smad7 in gastric carcinoma tissues. (A) Positive expression of Smad4 (x40). (B) Smad4 was consistently expressed in the nuclear location (x200). (C) Positive expression of Smad7 (x40). (D) Smad7 was stained mainly in the cytoplasm of cancer cells (x200).

 
Relationship between Smad4 or Smad7 expression and clinicopathologic findings
Positive Smad4 and Smad7 expression was observed in 266 (87.5%) and 98 (32.2%) tumors, respectively. The correlation between Smad4 or Smad7 expression and the clinicopathologic findings are shown in Table 1. The rate of positive Smad4 expression was higher in female patients, smaller tumor sizes, undifferentiated tumors and diffuse tumor type than in male patients, larger tumor sizes, differentiated tumors and intestinal tumor type (P <0.05). However, the rate of Smad4-positive expression decreased as tumors invaded deeper layers or in tumors with more advanced stages (P <0.05). The rate of Smad7-positive expression was significantly higher in the patients with differentiated tumors or intestinal type of tumors than in those with undifferentiated tumors or diffuse tumor type (P <0.05). There was no significant correlation between Smad7 expression and sex, tumor size, vascular invasion, lymphatic invasion, depth of invasion, lymph node metastasis or clinical stage.

Correlation between Smad4 or Smad7 expression and survival rate
The 5-year survival rate was 64.4% in patients with Smad4-positive tumors and 49.8% in patients with Smad4-negative tumors. Accordingly, the prognosis for patients with a Smad4-positive tumor was significantly better than for patients with a negative tumor (P = 0.017). In subgroup analysis according to TNM (tumour–node–metastasis) stage [24], the survival rate of patients with a Smad4-positive tumor was significantly higher than that of patients with a Smad4-negative tumor with stage I (93.3% versus 77.9%; P = 0.037) and IV (21.6% versus 0%; P = 0.05), but there were no statistical significances in the tumors with stage II (65.3% versus 87.5%) and III (40.7% versus 45.5%) (Figure 2). Moreover, the 5-year survival rate of patients with tumors in which Smad7 expression was positive was 52.2%, whereas the survival rate of patients with tumors in which Smad7 expression was negative was 67.5%. The survival rate was significantly higher in patients with negative Smad7 expression than in patients with positive Smad7 expression (P = 0.011). In subgroup analysis according to TNM stage, the survival rate of patients with a Smad7-negative tumor was significantly higher than that of patients with a Smad7-positive tumor with stage I (95.6% versus 84.1%, P = 0.025) and III (50.0% versus 26.1%, P = 0.05), but there were no statistical significances in the tumors with stage II (66.6% versus 72.2%) and IV (17.2% versus 16.7%) (Figure 3).



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Figure 2. Survival rates according to the Smad4 expression. The survival rate of patients with positive Smad4 expression in the tumors was significantly higher than that of patients with negative Smad4 expression in stage I (A) and IV tumors (B), but there were no statistical significances in stage II and III tumors.

 


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Figure 3. Survival rates according to Smad7 expression. The survival rate of patients with negative Smad7 expression in tumors was significantly higher than that of patients with positive Smad7 expression in stage I (A) and III (B) tumors, but there were no statistical significances in stage II and IV tumors.

 
The factors relating to patient prognosis were evaluated by univariate and multivariate analyses. Univariate analysis showed that tumor size, Lauren histology, differentiation, depth of invasion, lymph node metastasis, distant metastasis, lymphatic invasion, vascular invasion, UICC R category, Smad4 expression and Smad7 expression were related to survival rate (P <0.05). In the multivariate Cox model, tumor size, depth of invasion, lymph node metastasis and Smad7 expression were independent prognostic factors for cancer-specific survival (Table 2).


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Table 2. Multivariate analyses for predictors of survival in gastric carcinoma patients
 
Co-expression of Smad4 and Smad7, and its prognostic significance
The numbers of tumors with Smad4/Smad7, Smad4+/Smad7, Smad4/Smad7+ and Smad4+/Smad7+ expression were 20 (6.6%), 186 (61.2%), 18 (5.9%) and 80 (26.3%), respectively. The expressions of Smad4 and Smad7 were inversely correlated with each other (P = 0.04). The 5-year survival rate for patients with Smad4+/Smad7 expression was most favorable (70.3%), while that with Smad4/Smad7+ expression was most unfavorable (38.9%), which showed a significant difference (P = 0.001). The 5-year survival rates with Smad4/Smad7 and with Smad4+/Smad7+ expression were found to lie in between (59.4% and 59.6%, respectively) (Figure 4).



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Figure 4. Survival rates according to the co-expression of Smad4 and Smad7. The 5-year survival rate for the patients with Smad4+/Smad7 expression was most favorable and that with Smad4/Smad7+ expression was most unfavorable (significant difference; P = 0.001).

 

    Discussion
 Top
 ABSTRACT
 Introduction
 Materials and methods
 Results
 Discussion
 REFERENCES
 
Downstream events in the TGF-ß signaling pathway include complex formation of Smad2 or Smad3 with Smad4, translocation of the Smad2,3/Smad4 complex to the nucleus, and eventual activation of target genes [25]. In the absence of ligand, the inhibitory Smads, Smad6 and Smad7, are localized predominantly in the nucleus [26]. Upon TGF-ß receptor activation, they accumulate in the cytoplasm and associate with the ligand-activated TGF-ß receptor complex in the cell membrane, antagonizing TGF-ß family signaling by preventing the activation of signal-transducing Smad complexes.

In this study, we examined Smad4 and Smad7 expression in gastric carcinomas to elucidate their role in tumor progression. The tissue array method was used to analyze Smad4 and Smad7 proteins in 304 consecutive gastric carcinomas. The tissue array method enabled us to analyze a large number of gastric carcinomas, and consecutive sections from the array blocks allowed different protein expressions to be analyzed from defined, almost morphologically identical, tumor regions.

The Smad4 gene, located at 18q21, has been found to undergo frequent alteration in pancreatic cancers [7] and LOH studies have suggested that a gene on chromosome 18q is altered frequently in intestinal-type gastric carcinomas [27]. In our study, the loss of Smad4 protein expression was also statistically significantly associated with intestinal type, and associated with male sex, larger tumor size, differentiated tumors, deep penetration, advanced clinical stage and patient survival. Xiangming et al. reported that the reduced expression of Smad4 was related to the depth of tumor invasion and that Smad4 was an independent prognostic factor. Therefore, mutation in the Smad4 gene and loss of Smad4 protein either resulted in tumorigenesis or was associated with malignancy and progression of tumors [17]. Our results also revealed that the loss of Smad4 expression was related to the deep penetration and poor survival, but Smad4 was not an independent prognostic factor in multivariate analysis in our series [28]. These different results may be attributable to the selection of patients and different cut-off positive value, or to the evaluation of the results.

Smad7 inhibits TGF-ß-induced transcriptional responses [29]. Smad7 associates with the activated TGF-ß receptor and interferes with the activation of Smad2 and Smad3 by preventing their receptor interaction and phosphorylation. It has been reported that Smad7 acts as an important molecule for regulating TGF-ß activity in human disease. Monteleone et al. reported that Smad7 was overexpressed in irritable bowel disease mucosa and purified mucosal T cells [30]. In a separate study, Kleeff et al. reported that Smad7 enhances tumorigenicity in pancreatic cancer [19]. Using in vitro and in vivo studies, they revealed that pancreatic cancer cells have redundant barriers to TGF-ß signaling that may allow the cancer cells to escape TGF-induced growth inhibition, while still allowing for the expression of metastasis-promoting genes such as PAI-1. But, until recently, whether Smad7 expression is associated with clinicopathological parameters such as tumor stage and prognosis has not been reported. In this study, Smad7 expression was significantly more frequent in intestinal type and differentiated carcinoma. The underlying etiology of this tumor heterogeneity is not well understood. The survival time analysis revealed a significant correlation between Smad7 expression and length of disease-free survival. The prognostic value of Smad7 was independent of other well established clinical prognostic factors such as depth of invasion or nodal involvement. We conclude that Smad7 plays an important role in the development of gastric carcinoma and that overexpression of Smad7 may be a significant independent prognostic indicator for clinical outcome in patients with gastric carcinoma.

In subgroup analysis according to TNM stage, although Smad4 (stage IV) and Smad7 (stage III) showed some marginal prognostic significance, both Smad4 and Smad7 showed the most significant prognostic differences only in stage I gastric cancer patients. The reason why Smad4 and Smad7 expression should be most prognostic only in stage I patients is unclear, but in case of Smad4-negative stage I gastric cancer patients, all patients were classified as having stage Ib disease (eight T2N0M0 and one T1N1M0). In the clinical setting, this result could be applied very usefully for selecting the patients who should be followed closely and considered as candidates for adjuvant treatment among patients with stage I gastric cancer.

As mentioned previously, Smad4 and Smad7 are both located on chromosome 18q21. Therefore, it would be of considerable interest to know whether gene expression of Smad4 and Smad7 were independent of each other. However, our results showed that the expression patterns of Smad4 and Smad7 were inversely correlated with each other (P = 0.04), which suggests that these two closely located genes might be expressed by a different mechanism.

As expected, comparing co-expression of Smad4 and Smad7 with survival, the 5-year survival rate for patients with Smad4+/Smad7 expression was most favorable, while that with Smad4/Smad7+ expression was most unfavorable [significant difference (P = 0.001)]. The 5-year survival rates with Smad4/Smad7 and Smad4+/Smad7+ expression were found to lie in between. Therefore, evaluating the expression profile of both Smad4 and Smad7 together could be a more useful prognostic marker for gastric cancer patients than evaluating only one expression profile of either Smad4 or Smad7.

In summary, this study has demonstrated that Smad7 expression is associated with poor outcome in gastric carcinomas. These observations further underscore the importance of Smad proteins in carcinogenesis, and indicate that Smad7 expression may present one of the novel mechanisms for TGF-ß resistance in human gastric carcinoma. As both Smad4 and Smad7 showed most significant prognostic differences in stage I gastric cancer patients, Smad expression in gastric cancer could be useful in selecting the patients who should be closely followed and considered as candidates for adjuvant treatment among those with stage I gastric cancer.


    Acknowledgements
 
This study was supported by a grant from the 2002 Korean National Cancer Control Program, Ministry of Health and Welfare, Republic of Korea.


    FOOTNOTES
 
* Correspondence to: Dr H.-K. Yang, Department of Surgery and Cancer Research Institute, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul, 110-744, Korea. Tel: +82-2-760-3797; Fax: +82-2-3672-0047; E-mail: hkyang{at}plaza.snu.ac.kr Back


    REFERENCES
 Top
 ABSTRACT
 Introduction
 Materials and methods
 Results
 Discussion
 REFERENCES
 
1. Blobe GC, Schiemann WP, Lodish HF. Role of transforming growth factor ß in human disease. N Engl J Med 2000; 342: 1350–1358.[Free Full Text]

2. Derynck R, Gelbart WM, Harland RM et al. Nomenclature: vertebrate mediators of TGF ß family signals. Cell 1996; 87: 173.[ISI][Medline]

3. Savage C, Das P, Finelli AL et al. Caenorhabditis elegans genes sma-2, sma-3, and sma-4 define a conserved family of transforming growth factor beta pathway components. Proc Natl Acad Sci USA 1996; 93: 790–794.[Abstract/Free Full Text]

4. Attisano L, Wrana JL. Smads as transcriptional co-modulators. Curr Opin Cell Biol 2000; 12: 235–243.[CrossRef][ISI][Medline]

5. Massagué J, Wotton D. Transcriptional control by the TGF-ß/Smad signaling system. EMBO J 2000; 19: 1745–1754.[Abstract/Free Full Text]

6. White RL. Tumor suppressing pathways. Cell 1998; 92: 591–592.[ISI][Medline]

7. Hahn SA, Schutte M, Hoque AT et al. DPC4, a candidate tumor suppressor gene at human chromosome 18q21.1. Science 1996; 271: 350–353.[Abstract]

8. MacGrogan D, Pegram M, Slamon D, Bookstein R. Comparative mutations analysis of DPC4 (Smad4) in prostatic and colorectal carcinomas. Oncogene 1997; 15: 1111–1114.[CrossRef][ISI][Medline]

9. Schutte M, Hruban RH, Hedrick L et al. DPC4 gene in various tumor types. Cancer Res 1996; 56: 2527–2530.[Abstract]

10. Kim SK, Fan Y, Papadimitrakopoulou V et al. DPC4, a candidate tumor suppressor gene, is altered infrequently in head and neck squamous cell carcinoma. Cancer Res 1996; 56: 2519–2521.[Abstract]

11. Lei J, Zou TT, Shi YQ et al. Infrequent DPC4 gene mutation in esophageal cancer, gastric cancer and ulcerative colitis-associated neoplasms. Oncogene 1996; 13: 2459–2462.[ISI][Medline]

12. Takagi Y, Kohmura H, Futamura M et al. Somatic alterations in the DPC4 gene in human colorectal cancers in vivo. Gastroenterology 1996; 111: 1369–1372.[ISI][Medline]

13. de Manzoni G, Tomezzoli A, Di Leo A et al. Clinical significance of mutator phenotype and chrpmosome 17q and 18q allelic loss in gastric cancer. Br J Surg 2001; 88: 419–425.[CrossRef][ISI][Medline]

14. Natsugoe S, Xiangming C, Matsumoto M et al. Smad4 and transforming growth factor ß1 expression in patients with squamous cell carcinoma of the esophagus. Clin Cancer Res 2002; 8: 1838–1842.[Abstract/Free Full Text]

15. Tascilar M, Skinner HG, Rosty C et al. The Smad4 protein and prognosis of pancreatic ductal adenocarcinoma. Clin Cancer Res 2001; 7: 4115–4121.[Abstract/Free Full Text]

16. Kang YK, Kim WH, Jang JJ. Expression of G1-S modulators (p53, p16, p27, cyclin D1, Rb) and Smad4/Dpc4 in intrahepatic cholangiocarcinoma. Hum Pathol 2002; 33: 877–883.[CrossRef][ISI][Medline]

17. Xiangming C, Natsugoe S, Takao S et al. Preserved Smad4 expression in the transforming growth factor in patients with advanced gastric cancer. Clin Cancer Res 2001; 7: 277–282.[Abstract/Free Full Text]

18. Afrakhte M, Moren A, Jossan S et al. Induction of inhibitory Smad6 and Smad7 mRNA by TGF-ß family members. Biochem Biophys Res Commun 1998; 249: 505–511.[CrossRef][ISI][Medline]

19. Kleeff J, Ishiwata T, Maruyama H et al. The TGF-ß signaling inhibitor Smad7 enhances tumorigenicity in pancreatic cancer. Oncogene 1999; 18: 5363–5372.[CrossRef][ISI][Medline]

20. Roijer E, Moren A, ten Dijke P, Stenman G. Assignment of the Smad7 gene (MADH7) to human chromosome 18q21.1 by fluorescence in situ hybridization. Cytogenet Cell Genet 1998; 81: 189–190.[ISI][Medline]

21. Boulay JL, Mild G, Reuter J et al. Combined copy status of 18q21 genes in colorectal cancer shows frequent retention of SMAD7. Genes Chromosom Cancer 2001; 31: 240–247.[CrossRef][ISI][Medline]

22. Wilentz RE, Su GH, Dai JL et al. Immunohistochemical labeling for Dpc4 mirrors genetic status in pancreatic adenocarcinomas: A new marker of DPC4 inactivation. Am J Pathol 2000; 156: 37–43.[Abstract/Free Full Text]

23. Sandusky G, Berg DT, Richardson MA et al. Modulation of thrombomodulin-dependent activation of human protein C through differential expression of endothelial Smads. J Biol Chem 2002; 277: 49815–49819.[Abstract/Free Full Text]

24. Sobin LH, Wittekind CH. In Hermanek P, Sobin LH (eds): TNM Classification of Malignant Tumors (UICC. S), 6th edition. New York: Wiley-Liss 2002; 65–68.

25. Attisano L, Wrana JL. Mads and Smads in TGF ß signaling. Curr Opin Cell Biol 1998; 10: 188–194.[CrossRef][ISI][Medline]

26. Itoh S, Landstrom M, Hermansson A et al. Transforming growth factor ß1 induces nuclear export of inhibitory Smad7. J Biol Chem 1998; 273: 29195–29201.[Abstract/Free Full Text]

27. Uchino S, Tsuda H, Noguchi M et al. Frequent loss of heterozygosity at the DCC locus in gastric cancer. Cancer Res 1992; 52: 3099–3102.[Abstract]

28. Lee HS, Lee HK, Kim HS et al. Tumor suppressor gene expression correlates with gastric cancer prognosis. J Pathol 2003; 200: 39–46.[CrossRef][ISI][Medline]

29. Nakao A, Afrakhte M, Moren A et al. Identification of Smad7, a TGF-ß-inducible antagonist of TGF-ß signaling. Nature 1997; 389: 631–635.[CrossRef][ISI][Medline]

30. Monteleone G, Kumberova A, Croft NM et al. Blocking Smad7 restores TGF-ß1 signaling in chronic inflammatory bowel disease. J Clin Invest 2001; 108: 601–609.[Abstract/Free Full Text]





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