Cancer Research Landon Prizes for Basic and Translational Cancer Research AACR Conference on Molecular Diagnostics - 2008
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
Cancer Research 67, 1589-1593, February 15, 2007. doi: 10.1158/0008-5472.CAN-06-2472
© 2007 American Association for Cancer Research
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Huang, J.
Right arrow Articles by Xu, X.-c.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Huang, J.
Right arrow Articles by Xu, X.-c.

Cell, Tumor, and Stem Cell Biology

Tumor-Suppressive Effect of Retinoid Receptor–Induced Gene-1 (RRIG1) in Esophageal Cancer

Jie Huang1, Zheng D. Liang1, Tsung-Teh Wu2, Ashraful Hoque1, Hongli Chen1, Yan Jiang3, Hongfu Zhang3 and Xiao-chun Xu1,3

Departments of 1 Clinical Cancer Prevention and 2 Pathology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas and 3 Department of Pathology, Anhui Medical University, Hefei, China

Requests for reprints: Xiao-chun Xu, Department of Clinical Cancer Prevention, The University of Texas M.D. Anderson Cancer Center, Unit 1360, 1515 Holcombe Boulevard, Houston, TX 77030. Phone: 713-745-2940; Fax: 713-563-5747; E-mail: xxu{at}mdanderson.org.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
We previously showed that induction of retinoid receptor–induced gene-1 (RRIG1) expression inhibited RhoA activation and tumor cell colony formation, invasion, and proliferation, and these effects are associated with the suppression of extracellular signal-regulated protein kinases 1 and 2 phosphorylation and cyclooxygenase-2 expression. To further elucidate its role in tumor cell growth, gene expression, and tumorigenesis, we determined RRIG1 expression in breast and esophageal tissue specimens and then stably transfected RRIG1 into a TE-8 esophageal squamous cell carcinoma (SCC) cell line. We found that RRIG1 was expressed in normal mammary glands (10 of 10) but not all ductal carcinoma in situ [11 of 19 (57.9%), P = 0.018] and invasive cancer [14 of 30 (46.7%), P = 0.0023] tissues. Similarly, RRIG1 was expressed in normal esophageal epithelium (22 of 22) but not all dysplastic [6 of 43 (14%), P = 0.0001] and SCC [50 of 122 (41%), P = 0.0001] tissues. Furthermore, RRIG1 expression correlated positively with tumor differentiation but inversely with lymph node metastasis of esophageal SCC. Finally, the stable transfection of RRIG1 inhibited esophageal SCC cell growth and the expression of extracellular signal-regulated protein kinases 1 and 2 and cell cycle–related genes (e.g., cyclin D1, phosphorylated Rb, and E2F). RRIG1-transfected sublines also inhibited tumor development in nude mice. The results of this study indicate that RRIG1 plays a role in suppressing tumorigenesis. [Cancer Res 2007;67(4):1589–93]


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Various lines of evidence have shown that retinoic acid receptor-ß2 (RAR-ß2) is a tumor suppressor gene, and that loss of RAR-ß2 expression alters its downstream signaling pathway (for reviews, see refs. 1, 2). For example, the expression of RAR-ß2 is frequently and progressively lost in various premalignant and malignant human cells and tissues (3–6). The loss of RAR-ß2 expression is associated with malignant transformation in different epithelial cells (for reviews, see refs. 1, 2) and with a poor prognosis in patients with neuroblastoma (7). Tobacco smoke or benzo(a)pyrene diol epoxide (BPDE; a carcinogen present in tobacco smoke and environment pollution) suppressed RAR-ß2 expression in esophageal cancer cells (8, 9), and they induced the methylation of the RAR-ß2 gene promoter (9, 10). RAR-ß2 suppressed breast cancer cell metastases in a mouse xenograft model (11). Conversely, the restoration of RAR-ß2 expression inhibited the growth of various cancers, induced tumor cells to undergo apoptosis, and suppressed cancer development in vitro and in vivo (for reviews, see refs. 1, 2). We showed that, on the molecular level, RAR-ß2 suppressed the expression of the epidermal growth factor receptor, activating protein-1, and cyclooxygenase-2 (COX-2) and the phosphorylation of extracellular signal-regulated protein kinases 1 and 2 (Erk1/2; ref. 9). However, four isoforms of RAR-ß have been found in mice (ß1, ß2, ß3, and ß4) and three isoforms in humans (ß1, ß2, and ß4; ref. 12). More isoforms (i.e., RAR-ß5 and RAR-ß1') have recently been identified in human cancer cells (13, 14). Different RAR-ß isoforms have different affinities to RA and possess different biological functions in the cells (i.e., the RAR-ß2 protein is a tumor suppressor, whereas RAR-ß4 has oncogenic properties; refs. 15–17); thus, these make it difficult for us to understand the biological functions of retinoids in vivo.

One piece of the puzzle might be provided by a study of the novel retinoid receptor–induced gene-1 (RRIG1), which is differentially expressed in RAR-ß2–positive and RAR-ß2–negative tumor cells (18). We previously showed that RRIG1 is a downstream gene of RAR-ß2 and regulates the effects of RAR-ß2 on cancer cell growth and gene expression. RRIG1 expression is closely associated with RAR-ß2 expression in several normal tissues but is lost in various cancers. The restoration of RRIG1 expression by transient gene transfection inhibits RhoA activation and, consequently, reduces tumor cell colony formation, invasiveness, and proliferation (18); these activities are correlated with the suppression of Erk1/2 phosphorylation and COX-2 expression. We therefore hypothesized that RRIG1 is involved in suppressing tumorigenesis. To test this hypothesis, we determined the RRIG1 expression in various tissue specimens and its association with clinical data from the patients providing the specimens and then stably transfected RRIG1 into TE-8 esophageal cancer cells to elucidate the role of the gene in vitro and in vivo in nude mice.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Tissue samples. Our institutional review board approved our protocol for the use of the patient samples in this study. Tissue specimens were obtained from the Department of Pathology, The University of Texas M.D. Anderson Cancer Center at Houston and from Anhui Medical University, Hefei, China. Briefly, we obtained 30 breast cancer specimens that also included 19 ductal carcinomas in situ and 10 normal mammary glands from M.D. Anderson Cancer Center. We also obtained 122 tissue specimens from patients with esophageal squamous cell carcinoma (SCC) and 43 specimens from patients with dysplastic esophageal lesions seen at Anhui Medical University. Of the 43 specimens of esophageal dysplastic lesions, 22 also contained normal esophageal epithelium. All samples were routinely fixed in 10% buffered formalin, embedded in paraffin, and cut into 4-µm sections. One section of each type of tissue was stained with H&E for classification.

Immunohistochemical analysis. RRIG1 and cytokeratin 1 were detected in tissue sections by using an avidin-biotin complex technique, as described previously (18). An anti-RRIG1 antibody was custom-made by Lampire Biological Laboratories (Pipersville, PA) and used at 1:500 dilution. A mouse monoclonal antibody against cytokeratin 1 (clone 34ßB4) was obtained from Enzo Diagnostics (Farmingdale, NY) and used at 1:50 dilution. Control sections were incubated with the secondary antibody (goat anti-rabbit IgG or horse anti-mouse IgG) only.

Review and scoring of sections. The stained sections were reviewed under a microscope (Olympus American, Inc., Melville, NY) and scored as negative (0), weakly positive (1), positive (2), or strongly positive (3) on the basis of their staining intensity and percentage of cells showing staining. A score of 0 or 1 was considered to represent negative staining, and a score of 2 or 3 was considered to represent positive staining. Statistical analysis was done by using the Fisher exact test or the {chi}2 test to determine the association between normal and tumor tissues. Wilcoxon matched pairs test was used to compare the expression of RRIG1 and cytokeratin 1. Ps were generated with statistical software (Statistica 4.01, StatSoft, Tulsa, OK).

Stable transfection of RRIG1. Expression vector pcDNA3.1 (Invitrogen, San Diego, CA), which contains RRIG1 cDNA, was stably transfected into TE-8 esophageal cancer cells with FuGENE6 and screened with 400 µg/mL of G418 (FuGENE6 and G418 both supplied by Roche Applied Science, Indianapolis, IN) to generate RRIG1-expressing sublines (TE8-RRIG1-S1, TE8-RRIG1-S2, and TE8-RRIG1-S3) and vector control sublines (TE8-V1 and TE8-V2). These sublines were grown in monolayers in DMEM with 10% fetal bovine serum and 400 µg/mL G418 at 37°C in a humidified atmosphere of 95% air and 5% CO2. The extent to which RRIG1 protein expression was restored was then measured by Western blotting.

Detection of cell growth rate. Stable RRIG1-transfected and vector only–transfected esophageal TE-8 sublines were grown in monolayers for up to 96 h. For assaying cell viability, the cells were fixed with 10% trichloroacetic acid and stained with 0.4% sulforhodamine B in 1% acetic acid. The absorbances were determined by using an automated spectrophotometric plate reader at a single wavelength of 490 nm. The experiments were done in triplicate and repeated three times, and the data were presented as the mean ± SD of cell numbers in absorbance.

Protein extraction and Western blotting. Total cellular protein was extracted as described previously (9, 18). Samples containing 50 µg of protein from each sublines were then separated by 10% or 14% on SDS-PAGE gels and transferred electrophoretically to a Hybond-C nitrocellulose membrane (Amersham Pharmacia, Arlington Heights, IL) at 500 mA for 2 h at 4°C. The membrane was subsequently stained with 0.5% Ponceau S containing 1% acetic acid to confirm the equal loading of proteins and to verify transfer efficiency. The membranes were subjected to Western blotting by overnight incubation in a blocking solution containing 5% bovine skim milk and 0.1% Tween 20 in PBS at 4°C. The next day, the membranes were incubated with primary antibodies for 2 h at 23°C; these antibodies included anti-Erk1/2 (1:2,000 dilution), phosphorylated Erk1/2 (1:1,000), cyclin D1 (1:2,000), Rb (1:2,000), phosphorylated Rb (Ser780; 1:1,000), phosphorylated Rb (Ser795; 1:1,000), phosphorylated Rb (Ser807/811; 1:1,000), p16 (1:1,000), p15 (1:1,000), cyclin-dependent kinase 4 (CDK4; 1:2,000), CDK6 (1:2,000), p21 (1:2,000), and p27 (1:1,000; all from Cell Signaling Technology, Beverly, MA); RRIG1 (1:1,000), E2F (1:250; Santa Cruz Biotechnology, Santa Cruz, CA); or anti-ß-actin antibody (1:2,000; Sigma-Aldrich, St. Louis, MO). The membranes were washed in PBS and incubated for 1.5 h with a horse anti-mouse or a goat anti-rabbit secondary antibody (Amersham Pharmacia) diluted to 1:5,000. The membranes were subsequently incubated with an enhanced chemiluminescence solution (Amersham Pharmacia) for 1 to 2 min and then exposed to X-ray film.

Animal experiments. According to our institution-approved Animal Care and Usage protocol, five nu/nu nude mice (age 7 weeks) were injected s.c. in the right flank through a 22-gauge needle with 1 x 107 stable esophageal cancer cells mixed with 50% Matrigel (BD Biosciences, Bedford, MA) for a total volume of 200 µL per mouse. The animals were then monitored to detect tumor formation until most tumor burdens from RRIG1-transfected sublines disappeared. The tumor size, measured weekly with a Vernier caliper, was calculated as follows: length x width2. At the end of the experiments, the tumor sizes were plotted as mean ± SD.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Detection of RRIG1 expression in breast tissue specimens. The specificity of the polyclonal anti-RRIG1 antibody was previously confirmed by comparing the results of Northern and Western blotting and of in situ hybridization and immunohistochemical analyses (18). In the current study, we did immunohistochemical analysis with the anti-RRIG1 antibody to detect RRIG1 expression in breast tissue specimens. Our findings showed that RRIG1 was expressed in all tested normal mammary glands [10 of 10 cases (100%)]. However, its expression was significantly decreased in ductal carcinoma in situ tissue [11 of 19 (57.9%), P = 0.018] and invasive breast cancer tissue [14 of 30 (46.7%), P = 0.0023 by Fisher exact test] tissue (Fig. 1A ).


Figure 1
View larger version (93K):
[in this window]
[in a new window]

  		Figure 1. Expression of RRIG1 in human cancer tissues. Immunohistochemical detection of RRIG1 protein in formalin-fixed, paraffin-embedded tissue sections from (A) normal mammary gland, ductal carcinoma in situ (DCIS), and invasive cancer tissues and (B) normal, dysplastic, and neoplastic esophageal tissues. C, immunohistochemical detection of RRIG1 and cytokeratin 1 in normal esophageal tissue and well-differentiated or poorly differentiated esophageal SCC tissues.

 
Detection of RRIG1 expression in esophageal tissue specimens. We then determined RRIG1 expression in normal, premalignant, and malignant esophageal tissue specimens by using immunohistochemical analysis. RRIG1 was expressed in all normal esophageal epithelium [22 of 22 (100%)], but its expression was reduced in dysplastic [6 of 43 (14%), P = 0.0001] and SCC [50 of 122 (41%), P = 0.0001] tissues (Fig. 1B). In adenocarcinoma of the esophagus, RRIG1 expression was also decreased to 50% (56 of 112; Fig. 1B).

Correlation of RRIG1 expression with tumor differentiation and inverse correlation with lymph node metastasis in esophageal cancer cells. In comparing the RRIG1 expression in biopsy specimens with the clinicopathologic data for the patients with esophageal cancer from whom the specimens were obtained, we found a positive, statistically significant correlation between RRIG1 expression and tumor differentiation and an inverse, statistically significant correlation between RRIG1 expression and lymph node metastasis in esophageal SCC (Table 1 ; Fig. 1C). Although we found no statistically significant correlation between RRIG1 expression and patients' gender or age, we found a marginal correlation with tumor size. To compare RRIG1 expression with tumor cell differentiation, we analyzed expression of a squamous cell differentiation marker cytokeratin 1 in the leftover tissue sections (N = 71) of esophageal cancer samples and found that cytokeratin 1 expression correlated with tumor cell differentiation. RRIG1 protein expression is closely associated with cytokeratin 1 expression (P = 0.012 by using Wilcoxon matched pairs test).


View this table:
[in this window]
[in a new window]

  		Table 1. Correlation of RRIG1 expression and clinicopathologic features of patients with esophageal SCC

 
Stable transfection of RRIG1 into esophageal SCC cells. Our previous study (18) showed that TE-8 esophageal SCC cells do not express RRIG1 mRNA or protein. Therefore, we stably transfected an RRIG1 expression vector into this cell line. Of the G418-resistant sublines that were generated, the vector control sublines TE8-V1 and TE8-V2 did not express RRIG1 protein, but the RRIG1-transfected sublines TE8-RRIG1-S1, TE8-RRIG1-S2, and TE8-RRIG1-S3 did express RRIG1 protein (Fig. 2 ). TE8-RRIG1-S1, TE8-RRIG1-S2, and TE8-RRIG1-S3 cells, compared with TE8-V1 and TE8-V2 cells, showed reduction of Erk1/2, phosphorylated Rb, cyclin D1, and E2F expression (Fig. 2), but did not show notable changes in expression of CDK4, CDK6, p16, p15, p21, or p27 (data not shown). Furthermore, the cells of RRIG1-transfected sublines had a much slower growth rate compared with TE8-V1 and TE8-V2 cells (Fig. 3 ).


Figure 2
View larger version (44K):
[in this window]
[in a new window]

  		Figure 2. RRIG1-regulated gene expression in stable clones. Stable RRIG1-transfected (TE8-RRIG1-S1, TE8-RRIG1-S2, and TE8-RRIG1-S3) and vector only–transfected TE-8 (TE8-V1 and TE8-V2) esophageal cancer sublines were grown in monolayers, and total cellular protein was extracted and subjected to Western blotting analyses to determine gene expression. NS, nonspecific band; p-Erk1/2, phosphorylated Erk1/2; t-Erk1/2, total Erk1/2; p-Rb, phosphorylated Rb.

 

Figure 3
View larger version (12K):
[in this window]
[in a new window]

  		Figure 3. Inhibition of cell growth in stable RRIG1-transfected esophageal cancer cells. Stable RRIG1-transfected and vector only–transfected TE-8 esophageal cancer sublines were grown in monolayer, and cell viability was determined by using the sulforhodamine B assay, as described in Materials and Methods. The experiments were done in triplicate and repeated three times. Points, mean of the percentage of the control; bars, SD. OD, absorbance.

 
RRIG1 suppression of tumor development in nude mice. To determine the role of RRIG1 in tumor development in nude mice, we s.c. injected TE8-V1, TE8-RRIG1-S1, TE8-RRIG1-S2, and TE8-RRIG1-S3 cells into the right flank of nu/nu nude mice (1 x 107 per mouse; five mice per group) and then monitored the mice for more than 2 months to detect tumor formation. We found that RRIG1 suppressed tumor formation in these mice (Fig. 4 ).


Figure 4
View larger version (15K):
[in this window]
[in a new window]

  		Figure 4. RRIG1 suppression of tumor formation in nude mice. Stable RRIG1-transfected and vector only–transfected TE-8 esophageal cancer sublines were s.c. injected into the right flank of five nu/nu nude mice, which were then monitored for more than 2 months to detect tumor formation. Tumor sizes, measured once a week with a vernier caliper, were calculated as follows: length x width2. Points, mean; bars, SD.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
This study suggests that RRIG1 plays a role in suppressing esophageal tumorigenesis. We found reduced RRIG1 expression in dysplastic and malignant breast and esophageal tissues and tumor-suppressive activity of RRIG1 in esophageal SCC cells. RRIG1 was expressed in normal tissues but significantly lost in premalignant and malignant tissue specimens. RRIG1 expression also correlated positively with esophageal SCC differentiation and inversely with lymph node metastasis of esophageal SCC. Furthermore, the restoration of RRIG1 expression in an esophageal SCC cell line had the antitumor effects of inhibiting tumor cell growth, suppressing the expression of Erk1/2 and cell cycle–related genes (e.g., cyclin D1, phosphorylated Rb, and E2F), and suppressing tumor development in nude mice.

Our current and previous studies clearly show that lost expression of RRIG1 is an important event in the development of human cancers, although the mechanism underlying the loss of expression of the RRIG1 gene remains unknown. With help of completion of human genome program available in Genbank, we have identified the intron-exon boundaries of the RRIG1 gene (18) and found a direct repeat of 18 putative retinoic acid response element sites, 5,160 bp upstream of the RRIG1 cDNA. A further study is needed to determine whether this direct repeat site is a functional retinoic acid response element site, which may control RRIG1 expression through its binding to RAR-ß2. Moreover, another possibility may be due to methylation of RRIG1 gene promoter, as is observed with the silencing of RAR-ß in various cancers (2, 10). Whether methylation of RRIG1 gene promoter causes lost expression of RRIG1 will be investigated after the promoter is cloned or confirmed.

This study showed that the restoration of RRIG1 expression inhibited the growth of esophageal cancer cells and suppressed the expression of Erk1/2 and cell cycle–related genes (e.g., cyclin D1, phosphorylated Rb, and E2F) as well as tumor development in nude mice. Our previous data also showed that RRIG1 mediates the effect of RAR-ß2 on tumor cell growth and gene expression (e.g., Erk1/2) and binds to RhoA, and that restoration of its expression suppresses RhoA protein activation and stress fiber formation in esophageal cancer cells (18). RRIG1 inhibited colony formation, invasion, and proliferation of esophageal cancer cells, whereas antisense RRIG1 increased RhoA activity and colony formation, invasion, and proliferation of such cells (18). Although the defined molecular mechanism that mediates RRIG1 antitumor activity is unclear, we found that RRIG1 interacts with RhoA to execute some of its biological functions. Indeed, Rho proteins can modulate gene expression, cell proliferation, and angiogenesis in addition to regulate cell morphology and migration (19). The aberrant activation of RhoA proteins has similarly been found to cause cell growth, transformation, invasion, and metastasis in experimental models of carcinogenesis and inhibition of RhoA suppressed cell proliferation, invasion, and angiogenesis in vitro and in vivo (20–24). Furthermore, the RRIG1 protein contains two putative Src homology 3 (SH3) domain-binding motifs (i.e., 63-PRAPHPP-69 and 152-LPVLSSPPTP-161; see ref. 18), both of which contain PXXP (25). Accumulated evidence indicates that genes containing SH3 domain play an important role in cell signaling, including cell differentiation, proliferation, migration, and cancer development (25). Future studies should identify RRIG1 as a novel tumor suppressor gene and unveil the underlying molecular mechanisms responsible for these RRIG1-mediated antitumor activities.

In addition, our previous studies clearly showed that RRIG1 mediates the effects of RAR-ß2 on tumor cell growth and gene expression. Thus, the cloning and identification of the RRIG1 protein provided us with a novel and useful molecular model of human carcinogenesis, at least in terms of esophageal carcinogenesis, for the following reasons: (a) BPDE, a risk factor in esophageal cancer development, suppressed RRIG expression; (b) the RAR-ß gene has several isoforms, and these isoforms have different affinities to RA and possess different biological functions in the cells (15–17), which makes us difficult in fully understanding and disassociating their biological functions in vivo; and (c) RRIG1 plays a role in the control of esophageal cancer cell growth in vitro as well as tumor development in nude mice.

Over the past several decades, a large body of knowledge has accumulated about the molecular alterations associated with breast and esophageal cancer development (26–28). For example, it is now known that as a tumor progresses, the normal mechanisms of cell cycle control, such as DNA repair, apoptosis, and tissue compartmentalization, increasingly break down, largely because of the silence of tumor suppressor genes and the activation of oncogenes. Our current study showed that RRIG1 expression is also reduced in breast and esophageal cancer tissues. We further found that RRIG1 expression was positively associated with esophageal cancer differentiation and inversely associated with esophageal SCC lymph node metastasis, which suggested that the lost expression of RRIG1 in breast and esophageal cancers promotes tumorigenesis and cancer progression.

Esophageal and breast cancers, when diagnosed at an advanced stage, are associated with a poor prognosis (26–29). If they are diagnosed at an early stage, these cancers are more likely to respond to therapy (29). Thus, early diagnosis of the cancers is critical. Notably, the expression of the RRIG1 protein in dysplastic lesions of breast and esophageal epithelia is less than normal, and the anti-RRIG1 antibody is quite specific in detecting this reduction (18). Therefore, RRIG1 should be further evaluated at the translational level as a potential biomarker for the early detection or the prognosis of breast and esophageal cancers.


   Acknowledgments
 
Grant support: National Cancer Institute grants R21 CA10226 and R01 CA117895 (X-C. Xu).

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.

We thank Hong Wu for his help in preparing tissue sections.


   Footnotes
 
Note: J. Huang and Z.D. Liang contributed equally to this work.

Received 7/ 6/06. Revised 8/23/06. Accepted 12/11/06.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Soprano DR, Qin P, Soprano KJ. Retinoic acid receptors and cancers. Annu Rev Nutr 2004;24:201–21.[CrossRef][Medline]
  2. Xu XC. Tumor-suppressive activity of retinoic acid receptor-ß in cancer. Cancer Lett. In press 2007.
  3. Xu XC, Liu X, Tahara E, Lippman SM, Lotan R. Expression and up-regulation of retinoic acid receptor-ß is associated with retinoid sensitivity and colony formation in esophageal cancer cell lines. Cancer Res 1999;59:2477–83.[Abstract/Free Full Text]
  4. Qiu H, Zhang W, El-Naggar AK, et al. Loss of retinoic acid receptor-beta expression is an early event during esophageal carcinogenesis. Am J Pathol 1999;155:1519–23.[Abstract/Free Full Text]
  5. Widschwendter M, Berger J, Daxenbichler G, et al. Loss of retinoic acid receptor beta expression in breast cancer and morphologically normal adjacent tissue but not in the normal breast tissue distant from the cancer. Cancer Res 1997;57:4158–61.[Abstract/Free Full Text]
  6. Xu XC, Sneige N, Liu X, et al. Progressive decrease in nuclear retinoic acid receptor beta messenger RNA level during breast carcinogenesis. Cancer Res 1997;57:4992–6.[Abstract/Free Full Text]
  7. Cheung B, Hocker JE, Smith SA, Norris MD, Haber M, Marshall GM. Favorable prognostic significance of high-level retinoic acid receptor beta expression in neuroblastoma mediated by effects on cell cycle regulation. Oncogene 1998;17:751–9.[CrossRef][Medline]
  8. Wang XD, Liu C, Bronson RT, Smith DE, Krinsky NI, Russell M. Retinoid signaling and activator protein-1 expression in ferrets given beta-carotene supplements and exposed to tobacco smoke. J Natl Cancer Inst 1999;91:60–6.[Abstract/Free Full Text]
  9. Song S, Lippman SM, Zou Y, Ye X, Xu X-C. Induction of cyclooxygenase-2 by benzo[a]pyrene diol epoxide through inhibition of retinoic acid receptor-ß2 expression. Oncogene 2005;24:8268–76.[CrossRef][Medline]
  10. Vuillemenot BR, Pulling LC, Palmisano WA, Hutt JA, Belinsky SA. Carcinogen exposure differentially modulates RAR-beta promoter hypermethylation, an early and frequent event in mouse lung carcinogenesis. Carcinogenesis 2004;25:623–9.[Abstract/Free Full Text]
  11. Treutin PM, Chen Li, Buetow BS, et al. Retinoic acid receptor ß2 inhibition of metastasis in mouse mammary gland xenografts. Breast Cancer Res Treat 2002;72:79–88.[CrossRef][Medline]
  12. Chambon P. A decade of molecular biology of retinoic acid receptors. FASEB J 1996;10:940–54.[Abstract]
  13. Peng X, Maruo T, Cao Y, et al. A novel RARbeta isoform directed by a distinct promoter P3 and mediated by retinoic acid in breast cancer cells. Cancer Res 2004;64:8911–8.[Abstract/Free Full Text]
  14. Petty WJ, Li N, Biddle A, et al. A novel retinoic acid receptor beta isoform and retinoid resistance in lung carcinogenesis. J Natl Cancer Inst 2005;97:1645–51.[Abstract/Free Full Text]
  15. Berard J, Gaboury L, Landers M, et al. Hyperplasia and tumours in lung, breast and other tissues in mice carrying a RAR beta 4-like transgene. EMBO J 1994;13:5570–80.[Medline]
  16. Soprano DR, Scanlon E, Shukri M, Zhang ZP, Soprano KJ. Murine RARbeta4 displays reduced transactivation activity, lower affinity for retinoic acid, and no anti-AP1 activity. J Cell Biochem 2000;77:604–14.[CrossRef][Medline]
  17. Xu XC, Lee JJ, Wu TT, Hoque A, Ajani JA, Lippman SM. Increased retinoic acid receptor-beta4 correlates in vivo with reduced retinoic acid receptor-beta2 in esophageal squamous cell carcinoma. Cancer Epidemiol Biomarkers Prev 2005;14:826–9.[Abstract/Free Full Text]
  18. Liang ZD, Lippman SM, Wu TT, Lotan R, Xu X-C. RRIG1 mediates effects of retinoic acid receptor-ß2 on tumor cell growth and gene expression through binding to and inhibition of RhoA. Cancer Res 2006;66:7111–8.[Abstract/Free Full Text]
  19. Olson MF, Ashworth A, Hall A. An essential role for Rho, Rac, and Cdc42 GTPases in cell cycle progression through G1. Science 1995;269:1270–2.[Abstract/Free Full Text]
  20. Sahai E, Marshall CJ. RHO-GTPases and cancer. Nat Rev Cancer 2002;2:133–42.[CrossRef][Medline]
  21. Vial E, Sahai E, Marshall CJ. ERK-MAPK signaling coordinately regulates activity of Rac1 and RhoA for tumor cell motility. Cancer Cell 2003;4:67–79.[CrossRef][Medline]
  22. Gomez del Pulgar T, Benitah SA, Valeron PF, Espina C, Lacal JC. Rho GTPase expression in tumourigenesis: evidence for a significant link. Bioessays 2005;27:602–13.[CrossRef][Medline]
  23. Sahai E, Marshall CJ. Differing modes of tumour cell invasion have distinct requirements for Rho/ROCK signaling and extracellular proteolysis. Nat Cell Biol 2003;5:711–9.[CrossRef][Medline]
  24. Yoshioka K, Nakamori S, Itoh K. Overexpression of small GTP-binding protein RhoA promotes invasion of tumor cells. Cancer Res 1999;59:2004–10.[Abstract/Free Full Text]
  25. Alexandropoulos K, Cheng G, Baltimore D. Proline-rich sequences that bind to Src homology 3 domains with individual specificities. Proc Natl Acad Sci U S A 1995;92:3110–4.[Abstract/Free Full Text]
  26. Mandard AM, Hainaut P, Hollstein M. Genetic steps in the development of squamous cell carcinoma of the esophagus. Mutat Res 2000;462:335–42.[CrossRef][Medline]
  27. Stoner GD, Gupta A. Etiology and chemoprevention of esophageal squamous cell carcinoma. Carcinogenesis 2001;22:1737–46.[Abstract/Free Full Text]
  28. Enzinger PC, Mayer RJ. Esophageal cancer. N Engl J Med 2003;349:2241–52.[Free Full Text]
  29. DeVita VT, Jr., Hellman S, Rosenberg SA, editors. Cancer: principles and practice of oncology. Philadelphia: Lippincott-Raven Publishers; 1997. p. 231–8, 585–608, 980–1020.




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Huang, J.
Right arrow Articles by Xu, X.-c.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Huang, J.
Right arrow Articles by Xu, X.-c.

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