.JPG?ad=18503&adview=true)
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Cell and Tumor Biology |
1 Laboratory of GI Developmental Biology, Departments of Surgery and Medicine & Lombardi Cancer Center, Georgetown University; 2 Department of Veterans Affairs Medical Center, Washington, District of Columbia; Departments of 3 Medicine and 4 Pathology, University of Pennsylvania, Presbyterian Medical Center; 5 Albert Einstein Medical Center and 6 Fels Institute for Cancer Research and Molecular Biology, Temple University, Philadelphia, Pennsylvania
Requests for reprints: Lopa Mishra, Laboratory of GI Developmental Biology, Departments of Medicine and Surgery, Lombardi Cancer Center and Georgetown University, Med/Dent Building, NW 210-12, 3900 Reservoir Road, Northwest, Washington, DC 20007. Phone: 202-687-5707; Fax: 202-687-0992; E-mail: gutresearch{at}yahoo.com.
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
TGF-ß ligand binding results in phosphorylation at Gly-Ser (GS) in the cytoplasmic tail domain of TßRI by TßRII, activation of Smad2, and Smad3 phosphorylation at the COOH-terminal serines (7, 8). Subsequent heteromeric complex formation with the L3 loop region phosphoserine-binding pockets of Smad4 facilitates nuclear translocation and TGF-ß target gene activation (9–11). Adaptor proteins are required for functional specificity and Smad modulation. In previous studies, we have shown that ELF, a ß-spectrin, is a crucial adaptor protein in TGF-ß signaling and is required for Smad3 and Smad4 localization and signaling (12, 13). This finding was interesting because ß-spectrins are major dynamic scaffold molecules involved in generating functionally distinct membrane protein domains, conferring cell polarity and regulating endocytic traffic (14, 15).
Originally described for its transforming capability, TGF-ß is also a growth inhibitor in epithelial tissues as it is both a suppressor and promoter of tumorigenesis. It has been suggested that nearly all colon cancers, pancreatic cancers, and gastric carcinomas have mutations inactivating some component of TGF-ß signaling from TßRII frameshift mutations with microsatellite instability to mutations in Smad4, Smad2, or an as yet untested component of the TGF-ß signaling pathway (16–19). Genetic studies in mice have provided strong models and further evidence for the role of TGF-ß in tumor suppression in early stages. Tgf-ß–/–/Rag2–/– mutant mice that live to adulthood rapidly develop colon cancer by 5 months of age, preceded by precancerous lesions with inflammation and hyperplasia (20). Smad4 deficiency in the Apc
716 mouse increases adenoma size and promotes cancer progression (2) and Smad4+/– mutant mice develop gastric polyps and carcinomas (17).
To understand the role of ELF in Smad4 tumor suppression, we intercrossed elf+/– mutant mice with Smad4+/– mutant mice and determined a genetic basis for ELF/Smad4 interaction in early colorectal cancers. It was possible that, in addition to its involvement in TGF-ß signaling, ELF, as a ß-spectrin, could be important in conferring cell polarity and maintaining cell architecture. Support for this hypothesis comes from embryonic day 11.5 (E11.5) elf–/– mutant embryos that display a profoundly abnormal gut phenotype, with flattened gut epithelial cells and loss of villi. We then investigated the abnormal gut phenotype and determined that the distribution of cell polarization markers dependent upon ß-spectrin, such as E-cadherin, Na+-K+-ATPase, and microtubule associated protein-2 (MAP-2), was altered. We found that the cellular polarization through abnormal distribution of proteins, such as Na+-K+-ATPase, could be restored by ELF expression in elf–/– mutant cells. However, alterations in MAP-2 expression were not associated with aberrant expression of tubulin or microtubule function. Finally, we extrapolated our findings of abnormal cellular architecture and early colon cancer suppression to human studies. A strikingly reduced expression of ELF alone was seen in Dukes' B1 stage tissues (P < 0.05) and with a concomitant loss of Smad4 expression in advanced colon cancers (Dukes' D stage, P < 0.05). Our results indicate that ELF maintains cellular polarization by localization of a specific subset of proteins and is involved in preservation of cell architecture, the disruption of which may be a key to early colon cancer development.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Confocal laser scanning immunofluorescence microscopy. Colocalization studies were done with antibodies against ELF and Smad4 on normal gastric tissues, wild-type mouse gastric antral cells, or mouse embryonic fibroblasts (MEF). Monoclonal mouse and polyclonal goat and rabbit primary antibodies were visualized with tetramethyl rhodamine isothiocyanate–conjugated goat secondary rabbit IgG or FITC-conjugated goat anti-mouse IgG or cyanine (Cy5). The samples were analyzed with a Bio-Rad Radiance 2000 confocal microscope (Bio-Rad, Cambridge, MA) with an ILT model 5470 K laser (Ion Laser Technology, Salt Lake City, UT). Digital images were analyzed using Metamorph (Universal Imaging, Downingtown, PA) and figures were prepared using Adobe Photoshop.
Generation of mouse embryo–derived fibroblasts. Mouse embryo–derived fibroblasts harboring the null allele elf as well as wild-type, Elf knockout (elf–/–), and elf wild-type (elf+/+) MEFs were derived as previously described (13). Briefly, embryos E14.5 were tritrurated in 0.25% trypsin/1 mmol/L EDTA and genotyped as previously described. The lines were propagated in DMEM supplemented with 10% fetal bovine serum, 100 units/mL penicillin, and 50 µg/mL streptomycin to establish wild-type and elf–/– fibroblasts that were cultured over multiple passages to obtain sufficient cells to perform the experiments. The fibroblasts used for the experiments were at passages 3 to 25. Three different elf–/– and wild-type fibroblast lines were tested in different experiments and the results obtained were also independent of passage number. Representative data are shown.
Histology and immunohistochemical staining. Colon carcinomas detected in mutant mice were fixed in 10% neutral buffered formalin and paraffin-embedded, and later, H&E staining was used to confirm histologic characterization. An indirect immunoperoxidase procedure was used for immunohistochemical localization of ELF and Smad4 proteins in colorectal cancer tissue samples. Serial, sagittal sections of colorectal cancer tissues were immersed in xylene to remove paraffin, then dehydrated in graded alcohol, and rinsed in 1x PBS. Endogenous peroxide was quenched using 3% hydrogen peroxide (Sigma, St. Louis, MO). Nonspecific binding sites were blocked using 1 mL PBS containing 5% goat serum and 1 mg/mL bovine serum albumin (BSA). The sections were incubated overnight at 4°C in a humidor with primary antibodies, monoclonal antibody to Smad4 linker region (Zymed, San Francisco, CA), and peptide-specific antibody to ELF (13) diluted to 2.5 to 5 µg/mL in 1x PBS containing 1 mg/mL BSA. Primary antibodies to Na+-K+-ATPase, vimentin, E-cadherin, and ankyrin (Santa Cruz Biotechnology, Santa Cruz, CA) were used to for cell polarization studies. In addition, to examine cell proliferation and apoptosis in mouse colon tissues, primary antibodies of anti-p-histone H3 (Ser10), a mitosis maker (Upstate, Charlottesville, VA), and anti-active caspase 3 (Promega, Madison, WI) were used. All further steps were carried out at room temperature. Four 5-minute rinses with 1x PBS followed each successive step. The sections were then incubated with peroxidase-conjugated secondary antibodies (Jackson Immunoresearch Laboratories, West Grove, PA) as previously described (13). The secondary antibody was diluted in 1x PBS containing 1% goat serum. After rinses, 200 to 500 µL of the insoluble peroxidase substrate 3,3'-diaminobenzidine (Sigma) was added to cover the entire tissue on the slide, and we monitored color development under the microscope. After rinsing in distilled water for 2 minutes, we counterstained with modified Harris hematoxylin solution (Sigma) for 1 minute followed by a rinse in distilled water for 3 minutes. Sections were dehydrated by passage through graded alcohol concentrations and finally xylene. Coverslips were mounted using DPX (Sigma) before observation.
Cell polarity assays. Antibodies to Na+-K+-ATPase, vimentin, E-cadherin, and tubulin were used for immunohistologic characterization of the gut in elf–/– and wild-type mice as described above. In transient transfection assays, elf–/– and wild-type MEFs were seeded at a density of 2 x 105 cells/well in six-well dishes. They were then transfected with a construct that contains the full-length of elf or vector DNA alone (3 µg of DNA per well). For localization studies, transfections with pEYFP-Mem (encoding GAP-43, which contains a signal for posttranslational palmitoylation of cysteines 3 and 4 that targets membranes), pEYFP-Nuc (encoding a gene with three copies of the nuclear localization signal of the SV40 large antigen fused at its COOH terminus), and pECFP-Golgi (encoding the NH2-terminal human ß-1,4-galactosyltransferase that helps in targeting the fusion protein to the trans-medial region of the Golgi apparatus) were used. Transfected cells were washed 2x with DMEM after 12 to 18 hours and then treated with 5 µg/mL TGF-ß and incubated for an additional 24 hours. All experiments were repeated at least thrice and similar results were obtained each time. Cells were then fixed and analyzed by confocal microscopy as above.
Luciferase assays. Elf–/– and elf+/+ MEFs were plated 1 day before transfection, in 12-well plates, at a density of 1.5 x 105 to 2.5 x 105 cells per well in DMEM medium (10% fetal bovine serum, 1% P/S, 1% L-glutamine). For TGF-ß response assays, the cells were transfected with p3TP-lux (1.5 µg) in controls and in cells treated with placitaxel (a microtubule-stabilizing agent; Sigma) or nocodazole (a microtubule-disrupting agent; Sigma). The cells were subsequently incubated for 18 hours with or without TGF-ß1 (100 pmol/L). In mutant rescue assays, the elf+/+ and elf–/– cells were transfected with a construct that contains the full-length of elf or vector DNA alone and subsequently treated with TGF-ß1 (100 pmol/L). Protein normalized luciferase activity in cell lysates was measured in a TD-20/20 Luminometer (Turner Designs, Sunnyvale, CA) by using substrate prepared in accordance with Promega luciferase assay system. All assays were carried out in duplicate or triplicate.
TGF-ß–responsive regions of the human PAI-1 promoter contain DNA elements homologous to the consensus binding site for the transcription factor AP1. The p3TP-Lux luciferase reporter is a well-described and widely used artificial promoter construct that was empirically designed to have maximal responsiveness to TGF-ß. Interestingly, using a variety of TGF-ß–dependent luciferase gene reporters, it has been found that only Smad3 can directly interact with Smad binding elements found in the promoters of many TGF-ß–responsive genes. Thus, Smad3 activates transcription of the 3TP-Lux, a reporter that contains elements of the PAI-l promoter. Functional effects of reduced Smad3 expression are seen in our model as reduced basal and TGF-ß1–stimulated levels of luciferase expression using the TGF-ß1–responsive reporter construct 3TP-Lux in the elf null-phenotype cells compared with control cells.
Cancer specimens. Formalin-fixed and paraffin-embedded colorectal cancer and colon specimens were obtained from the Department of Pathology, University of Pennsylvania Medical Center-Presbyterian. Twenty-one colorectal cancers collected from patients with varying grades and stages of colorectal cancer, identified by the Dukes' classification, were analyzed for ELF and Smad4 expression. All the specimens were collected after colectomy. Tissues were collected randomly at various zones of cancer manifestation, including the rectum, and the ascending, transverse, descending, and sigmoid colon. Tumor grade was determined by histology and markers, such as carcinoembryonic antigen (CEA; Table 1). In staging the tumors, Dukes' classification B1, C1, and D stages represent dysplasia, adenomas, and invasive carcinomas, respectively. Two independent blinded pathologists evaluated the tumors used in the study. The control samples of normal colon tissue used in the present investigation were taken from the borders of the surgical specimens.
|
2 test was used to test the hypothesis that the coefficient of each variable was equal to 0. Tissue sample sets of immunohistochemical data were compared with assess the significance. A P value <0.05 was required for statistical significance, and all tests were two-sided. All tests were done with SPSS 10.1 software (SPSS, Inc., Chicago, IL). |
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
|
Loss of polarity in elf–/– gut epithelial cells. We first investigated abnormalities in intestinal epithelial cell morphology in the elf–/– mutant embryos, then analyzed the role of ELF/TGF-ß in organelle formation and gut epithelial cell polarity. H&E-stained sections showed gut epithelial cells to be severely flattened with loss of villi in E11.5 elf–/– mutant embryos. Further visualization of plasma membrane, Golgi, and nuclei by transfection of pEYFP-Mem, pECFP-Golgi, and pEYFP-Nuc (Clontech, Palo Alto, CA) into elf–/– mutant MEFs revealed all three to be normal.7 Strikingly, we observed a marked distortion in expression patterns of Na+-K+-ATPase, MAP-2, and actin with increased vimentin, decreased E-cadherin, but normal ankyrin B and G expression in the elf–/– and decreased E-cadherin expression in the elf+/–/Smad4+/– gut epithelial cells (Figs. 1F-K and S2). Na+-K+-ATPase labeling showed irregular and punctate intracellular localization, and it seemed absent at the apical (brush border) plasma membrane in the elf+/–/Smad4+/– colonic mucosa and aberrantly localized in elf–/– cells (Fig. 3C and E) compared with normal, wild-type control, as well as Smad4+/– colonic mucosa (Fig. 3A, B, and D).
|
Microtubules have been shown to modulate TGF-ß–induced Smad signaling (22). We noted an aberrant expression of MAP-2 in elf–/– mutant embryonic and in the elf+/–/Smad4+/– colonic mucosa adult gut tissue (Fig. 4B and E) compared with normal wild-type embryonic and adult elf control tissues (Fig. 4A and C). Interestingly, both ß-spectrin and MAP-2 have been shown to be important for microtubule bundling and function (23, 24). To exclude abnormalities in microtubule function as a cause of the observed phenotype seen in elf–/– mutant embryos, we analyzed microtubule distribution and function in wild-type and elf–/– mutant MEFs and in embryos. Immunofluorescence confocal microscopy determined that the subcellular distribution of ß-tubulin is unaltered in the mutant embryos.7 Furthermore, neither a microtubule-stabilizing agent (placitaxel) nor a microtubule-disrupting agent (such as nocodazole) corrected TGF-ß signaling in elf–/– mutant fibroblasts (Fig. 4F). Lack of response to TGF-ß stimulation in mutant cells suggests that microtubule modulation of Smads may be less relevant and secondary to ELF spectrins. This was further supported by transient transfection of the reporter construct p3TP-Lux, into wild-type and elf–/– cultured MEFs. When we treated transfected wild-type MEFs with TGF-ß1, the luciferase activity induced was seven to eight times that of elf–/– MEFs (Fig. 3H). However, in MEFs derived from elf–/– mouse embryos, TGF-ß1–dependent induction of p3TP-Lux was abolished, as it was in vector controls, which indicated that the TGF-ß1 response needs ELF (Fig. 3H). In mutant rescue assays, restoration of elf in elf–/–-cultured MEFs dramatically induced a 7- to 8-fold increase in luciferase activity, almost as in the wild type (elf+/+).
|
0.05) of the basal crypts (Tables 1 and 2). The lamina propria separating the crypts with loose connective tissue, capillaries, and strands of smooth muscle did not label strongly for ELF. Labeling for ELF in colorectal cancer tissue samples showed reduction or loss of expression in aberrant crypt foci (Fig. 5B and C). In Dukes' B1, an early stage of cancer, ELF expression was reduced and abnormal compared with that of controls, which suggested a down-regulation of this gene in early neoplasia (Fig. 5B; Table 2). Abnormal ELF expression was also observed in the epithelial outpockets from the basal crypts that form adenomatous polyclonal polyps, an obligatory step for tumor progression. In adenomas, 14.2% showed moderate labeling and 23.8% showed intense labeling; almost 57.1% exhibited disruption of ELF. About 24% and 15% of carcinomas showed moderate and intense labeling for ELF, respectively (P 0.05). ELF expression was strikingly absent in 9 of 10 B1 and 2 of 4 C1 cancers (Fig. 5B and C; Tables 1 and 2). Aberrant or reduced ELF expression or loss of it was observed in almost all B1 colon cancers. In C1 and D1 late-stage tumors, we observed loss of expression in the crypt epithelial cells and a simultaneous positive labeling in the stromal tissue.
|
|
0.05; Tables 1 and 2). In these normal samples, labeling was mostly in the cytoplasm.
We observed loss of Smad4 expression in B1, C1, and D tumors, as well as marked loss of expression in the late stages (Dukes' D cancers; Fig. 5E and F). In other types of tumors, 42.8% of adenoma had moderate staining, whereas 52.3% of carcinomas showed loss of Smad4 expression (P 0.05).
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Spectrins are key proteins involved in the support of general membrane integrity, stabilization of cell-to-cell interactions, axonal growth, and the formation of the sarcoplasmic reticulum (24, 28). They are also known to be involved in the generation of cell polarity and protein sorting (23, 29, 30). Spectrins create a multifunctional scaffold on which membrane proteins, cytoplasmic signaling molecules, and structural elements are organized in distinct domains; in this way, the general cytoarchitecture and tissue integrity of cells are maintained (24, 30).
Resistance to TGF-ß is commonly associated with late events in tumorigenesis and probably is secondary to inactivating mutations in TßRII, Smad2, or Smad4. Our recent studies that show that the disruption of TGF-ß signaling by inactivation of the adaptor protein ß-spectrin, encoded by elf (14, 31), results in Smad4 localization and activation (13). Hence, aberrations in ELF expression should also affect the otherwise normal downstream events leading to abrogation of Smad4 activity. Studies have established the role of Smad4 as a tumor suppressor, and failure of Smad4 expression has been associated with advanced stage disease, the presence of lymph node metastasis, and a significant shorter overall survival (31, 32). The essential and adaptor protein ELF, a ß-spectrin, may therefore play a similar role in suppressing gastrointestinal tumors.
Loss of ß-spectrins, such as ELF, an important protein necessary for maintaining the structural integrity of epithelial cells, may be pivotal for epithelial cell integrity and maintenance of tissue architecture in the early stages. Establishment of spatial coordinates during differentiation of polarized cells involves a positional cue from cadherins that results in targeting of ß-spectrin to a discrete plasma membrane domain (33). The spectrin tetramer is then able to capture and stabilize additional membrane interacting proteins, such as ankyrin and the basolateral Na+-K+-ATPase, to form the characteristic profile of a polarized membrane domain (34, 35). To facilitate simultaneous reception and transmission of positional information, one of the two binding sites on the tetramer for ankyrin would allow for interaction with a cell adhesion molecule for a positional clue, whereas the second ankyrin allows for acquisition of these studies indicate the requirement of ß-spectrin for this interaction. The lack of polarized distribution of the Na+-K+-ATPase in the elf ß-spectrin mutant phenotype resembles the Drosophila ß-spectrin mutant, which in turn is reminiscent of the Drosophila labial phenotype, particularly in the gut (36). Control of the homeotic gene labial is dependent upon extracellular gradients of wingless and decapentaplegic (the Drosophila homologue of TGF-ß during embryogenesis; ref. 37), which suggests that the relationship between elf and TGF-ß is important for gut epithelial cell formation and is conserved through evolution.
Here, we show that loss of ELF expression correlates with B1 colon cancers and that a strict correlation exists between ELF and Smad4 expression in the normal epithelial cells of the crypts of Leiberkühn (Fig. 5A and D). Previous coimmunoprecipitation studies indicate an interaction between ELF and Smad4 that is essential for TGF-ß–mediated gene expression in mutant mice, as well as in human gastric cancers (13).8 Smad4 expression is prominent in normal colonic crypts with typically diffuse epithelial staining. Stronger labeling is observed in the villus apex and the bottom one third of the crypts. Loss of Smad4 expression in advanced colorectal tumors substantiates earlier reports and further supports the role of Smad4 as a gastrointestinal tumor suppressor and a potential marker in colorectal cancer (38).
The basal crypt region of the colonic epithelial cells is known to harbor stem cells, which proliferate and migrate toward the villus while differentiating into cell types (39). On reaching the villus apex, cells become apoptotic and are shed into the gut lumen. These repetitive cycles of proliferation, differentiation, and shedding are events that maintain the integrity of normal colonic epithelia. Expression of ELF and Smad4 in normal colon, particularly in the basal crypt region, suggests a functional role via the TGF-ß signaling pathway. As the cells reach the midcrypt region, ELF activity is reduced along with cell differentiation. Absence of ELF expression, especially in the basal crypts of B1 and C1 tumors, suggests an inactivation of the TGF-ß signaling pathway via the abrogation of Smad4 functions. These events may modulate the differentiation signals at the stem cell compartment (basal crypt) whereby the proliferative stage is maintained and may lead to tumor formation.
Interestingly, compared with Smad4, ELF expression was significantly lost or reduced in Dukes' B1 cancers, especially in the basal crypts correlating with loss of differentiation and the onset of colonic neoplasia. With further invasiveness and metastasis of the tumors, both ELF and Smad4 expression was diminished or lost particularly in the bottom third compartment and this may serve as a prognostic factor for a poor outcome. Our findings suggest that in normal colon samples, after TGF-ß stimulation, ELF interacts with Smad4 in the cytoplasm and localizes to the nucleus for transcriptional control. Aberrant nuclear and cytoplasmic labeling of ELF in B1, C1, and D tumors also suggests mislocalization of ELF, which ablates TGF-ß–induced transcriptional response.
Indeed, ß-spectrins and ELF bind to E-cadherin via the ß-catenin (40), an important mediator of the Wnt signaling pathway (41) that has a central role in colorectal carcinoma, controlling the switch between proliferation and differentiation in intestinal epithelial cells (42). Disruption of the G1 phase of the cell cycle blocks a genetic program that is physiologically active in the proliferative compartment of colon crypts. Regulation of intracellular ß-catenin signaling through APC, originally identified from familial adenomatous polyposis patient studies, and by p53 potentially closely links the Wnt signaling to TGF-ß signaling pathways (43, 44). With this scenario, it will be interesting to delineate the cross-talk between signaling pathways that involves ELF and the key players in colorectal carcinogenesis, such as Wnt signaling. In view of the present findings, we suggest that loss of ELF potentially contributes to the events that lead to onset of colorectal cancer and ELF probably plays an important role in tumor suppressor mechanisms in colon cancer that can be recognized as a potential early marker in colorectal carcinoma.
|
Acknowledgments |
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
|
Footnotes |
|---|
Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/).
Received 12/22/04. Revised 2/23/05. Accepted 3/ 2/05.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
spectrin to polarize the Na,K ATPase in epithelial cells. J Cell Biol 2000;149:647–56.-Catenin binds directly to spectrin and facilitates spectrin-membrane assembly in vivo. J Biol Chem 2001;276:4175–81.This article has been cited by other articles:
|
|
 |
|
  E. Glasgow and L. Mishra Transforming growth factor-{beta} signaling and ubiquitinators in cancer Endocr. Relat. Cancer, March 1, 2008; 15(1): 59 - 72. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Li, J. E. Lin, I. Chervoneva, S. Schulz, S. A. Waldman, and G. M. Pitari Homeostatic Control of the Crypt-Villus Axis by the Bacterial Enterotoxin Receptor Guanylyl Cyclase C Restricts the Proliferating Compartment in Intestine Am. J. Pathol., December 1, 2007; 171(6): 1847 - 1858. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Meary, S. Metral, C. Ferreira, D. Eladari, Y. Colin, M.-C. Lecomte, and G. Nicolas A Mutant {alpha}II-spectrin Designed to Resist Calpain and Caspase Cleavage Questions the Functional Importance of This Process in Vivo J. Biol. Chem., May 11, 2007; 282(19): 14226 - 14237. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B A Onwuegbusi, A Aitchison, S-F Chin, T Kranjac, I Mills, Y Huang, P Lao-Sirieix, C Caldas, and R C Fitzgerald Impaired transforming growth factor {beta} signalling in Barrett's carcinogenesis due to frequent SMAD4 inactivation Gut, June 1, 2006; 55(6): 764 - 774. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Mishra, R. Derynck, and B. Mishra Transforming Growth Factor-{beta} Signaling in Stem Cells and Cancer Science, October 7, 2005; 310(5745): 68 - 71. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |
