Xiuli Bi

Genetic deficiency of decorin causes intestinal tumor formation through disruption of intestinal cell maturation

Decorin is a member of the small leucine-rich proteoglycan gene family and plays an important role in suppressing cancer cell growth and metastasis. To elucidate the importance of decorin in intestinal carcinogenesis, a decorin-deficient (Dcn(-/-)) mouse model was employed. We found that targeted inactivation of decorin was sufficient to cause intestinal tumor formation with 30% of the Dcn(-/-) mice developing intestinal tumors with no other chemical or genetic initiation. Moreover, a high-risk diet amplified and accelerated the tumors initiated by decorin deficiency. Further, tumorigenesis in Dcn(-/-) mice was associated with disruption of intestinal maturation, including decreased cell differentiation and increased proliferation, which were linked to the downregulation of p21(WAF1/cip1), p27(kip1), intestinal trefoil factor and E-cadherin and to the upregulation of beta-catenin signaling. In addition, we found that decorin was highly expressed in the differentiated area of human normal colonic mucosa, but was dramatically reduced in paired colorectal cancer tissues. Taken together, our data demonstrate that decorin acts as a tumor suppressor gene and plays an important role in the maintenance of cell maturation and therefore homeostasis in the intestinal tract.

Decorin-mediated inhibition of colorectal cancer growth and migration is associated with E-cadherin in vitro and in mice

Previous studies have shown that decorin expression is significantly reduced in colorectal cancer tissues and cancer cells, and genetic deletion of the decorin gene is sufficient to cause intestinal tumor formation in mice, resulting from a downregulation of p21, p27(kip1) and E-cadherin and an upregulation of β-catenin signaling [Bi,X. et al. (2008) Genetic deficiency of decorin causes intestinal tumor formation through disruption of intestinal cell maturation. Carcinogenesis, 29, 1435-1440]. However, the regulation of E-cadherin by decorin and its implication in cancer formation and metastasis is largely unknown. Using a decorin knockout mouse model (Dcn(-/-) mice) and manipulated expression of decorin in human colorectal cancer cells, we found that E-cadherin, a protein that regulates cell-cell adhesion, epithelial-mesenchymal transition and metastasis, was almost completely lost in Dcn(-/-) mouse intestine, and loss of decorin and E-cadherin accelerated colon cancer cell growth and invasion in Dcn(-/-) mice. However, increasing decorin expression in colorectal cancer cells attenuated cancer cell malignancy, including inhibition of cancer cell proliferation, promotion of apoptosis and importantly, attenuation of cancer cell migration. All these changes were linked to the regulation of E-cadherin by decorin. Moreover, overexpression of decorin upregulated E-cadherin through increasing of E-cadherin protein stability as E-cadherin messenger RNA and promoter activity were not affected. Co-immunoprecipitation assay showed a physical binding between decorin and E-cadherin proteins. Taken together, our results provide direct evidence that decorin-mediated inhibition of colorectal cancer growth and migration are through the interaction with and stabilization of E-cadherin.

Transcriptional Regulation and Biological Functions of Selenium-Binding Protein 1 in Colorectal Cancer In Vitro and in Nude Mouse Xenografts

Background It has been shown that selenium-binding protein 1 (SBP1) is significantly downregulated in different human cancers. Its regulation and function have not yet been established. Methodology and Principal Findings We show that the SBP1 promoter is hypermethylated in colon cancer tissues and human colon cancer cells. Treatment with 5′-Aza-2′-deoxycytidine leads to demethylation of the SBP1 promoter and to an increase of SBP1 promoter activity, rescues SBP1 mRNA and protein expression in human colon cancer cells. Additionally, overexpression of SBP1 sensitizes colon cancer cells to H2O2-induced apoptosis, inhibits cancer cell migration in vitro and inhibits tumor growth in nude mice. Conclusion and Significance These data demonstrate that SBP1 has tumor suppressor functions that are inhibited in colorectal cancer through epigenetic silencing.

Functional and physical interaction between the selenium-binding protein 1 (SBP1) and the glutathione peroxidase 1 selenoprotein

Selenium-binding protein (SBP) 1 is present in reduced levels in several cancer types as compared with normal tissues, and lower levels are associated with poor clinical prognosis. Another selenium-containing protein, glutathione peroxidase 1 (GPX1), has been associated with cancer risk and development. The interaction between these representatives of different classes of selenoproteins was investigated. Increasing SBP1 levels in either human colorectal or breast cancer cells by transfection of an expression construct resulted in the reduction of GPX1 enzyme activity. Increased expression of GPX1 in the same cell types resulted in the transcriptional and translational repression of SBP1, as evidenced by the reduction of SBP1 messenger RNA and protein and the inhibition of transcription measured using an SBP1 reporter construct. The opposing effects of SBP1 and GPX1 on each other were also observed when GPX1 was increased by supplementing the media of these tissue culture cells with selenium, and the effect of selenium on SBP1 was shown to be GPX1 dependent. Decreasing or increasing GPX1 levels in colonic epithelial cells of mice fed a selenium-deficient, -adequate or -supplemented diet resulted in the opposing effect on SBP1 levels. These data are explained in part by the demonstration that SBP1 and GPX1 form a physical association, as determined by coimmunoprecipitation and fluorescence resonance energy transfer assay. The results presented establish an interaction between two distinct selenium-containing proteins that may enhance the understanding of the mechanisms by which selenium and selenoproteins affect carcinogenesis in humans.

Sulindac suppresses β-catenin expression in human cancer cells

Sulindac has been reported to be effective in suppressing tumor growth through the induction of p21WAF1/cip1 in human, animal models of colon cancer and colon cancer cells. In this study, we treated human breast cancer cell line MCF-7 and lung cancer cell line A549 as well as colon cancer cell line SW620 with sulindac to observe the effects of sulindac in other tissue sites. In all cell lines, proliferation was significantly inhibited by sulindac after 24 and 72 h of treatment. Apoptosis was induced by sulindac in both lung cancer cells and colon cancer cells but was not induced in breast cancer cells. Western blots showed that p21 protein level were induced by sulindac in lung cancer cells and colon cancer cells, but not in breast cancer cells. However, the suppression of beta-catenin, a key mediator of Wnt signaling pathway, was seen in all three cell lines with sulindac administration. Further studies revealed that transcriptional activities of beta-catenin were significantly inhibited by sulindac and that the inhibition was sulindac dosage-dependent. The transcriptional targets of beta-catenin, c-myc, cyclin D1 and cdk 4 were also dramatically downregulated. In conclusion, our data demonstrated that the efficacy of sulindac in the inhibition of cell proliferation (rather than the induction of apoptosis) might be through the suppression of beta-catenin pathway in human cancer cells.

Black Raspberries Inhibit Intestinal Tumorigenesis in Apc1638+/− and Muc2−/− Mouse Models of Colorectal Cancer

Freeze-dried black raspberries (BRB) produce chemopreventive effects in a rat model of colon carcinogenesis; however, the mechanisms of inhibition were not determined. Herein, we used two mouse models of human colorectal cancer to determine if dietary BRBs would inhibit colorectal tumor development and to investigate the underlying mechanisms. We found that a 12-week feeding of BRBs significantly inhibited intestinal tumor formation in both models; reducing tumor incidence by 45% and tumor multiplicity by 60% in Apc1638+/− mice and tumor incidence and multiplicity by 50% in Muc2−/− mice. Mechanistic studies revealed that BRBs inhibit tumor development in Apc1638+/− mice by suppressing β-catenin signaling and in Muc2−/− mice by reducing chronic inflammation. Intestinal cell proliferation was inhibited by BRBs in both animal models; however, the extent of mucus cell differentiation was not changed in either model. Collectively, our data suggest that BRBs are highly effective in preventing intestinal tumor development in both Apc1638+/− and Muc2−/− mice through targeting multiple signaling pathways. Cancer Prev Res; 3(11); 1443–50. ©2010 AACR.

Anticancer activity of Panax notoginseng extract 20(S)-25-OCH3-PPD: targetting β-catenin signalling.

1 The Wnt/β‐catenin pathway plays a critical role in carcinogenesis and so agents that target Wnt/β‐catenin may have potential in cancer prevention and therapy. The aim of the present study was to evaluate the anticancer activity of the novel natural product dammarane‐type triterpene sapogenin (20(S)‐25‐OCH3‐PPD; PPD25) isolated from the leaves of Panax notoginseng. 2 The anticancer activity of PPD25 was evaluated in three colon cancer cell lines and in one lung cancer cell line. The effects of PPD25 to inhibit proliferation and to induce apoptosis were evaluated. In addition, the potential mechanisms underlying the effects of PPD25 were investigated. 3 It was found that the addition of 5 or 25 µmol/L PPD25 to the culture medium significantly inhibited cell proliferation and induced apoptosis in all four cancer cell lines. Mechanistic studies revealed that PPD25 significantly reduced the expression of β‐catenin, a key mediator in the Wnt pathway, as well as transcriptional targets of β‐catenin, namely c‐myc, cyclin D1, cdk4 and T cell factor (TCF)‐4. In addition, β‐catenin/TCF transcriptional activity was significantly suppressed by PPD25. 4 The data demonstrate that the PPD25 exerts its anticancer effect by targetting β‐catenin signalling, suggesting that PPD25 may have potential as a chemotherapeutic and/or chemopreventive agent for colon and lung cancer.

Tumor inhibition by sodium selenite is associated with activation of c-Jun NH2-terminal kinase 1 and suppression of β-catenin signaling.

Epidemiological and clinical studies suggest that an increased intake of dietary selenium significantly reduces overall cancer risk, but the anticancer mechanism of selenium is not clear. In this study, we fed intestinal cancer mouse model. Muc2/p21 double mutant mice with a selenium‐enriched (sodium selenite) diet for 12 or 24 weeks, and found that sodium selenite significantly inhibited intestinal tumor formation in these animals (p < 0.01), which was associated with phosphorylation of JNK1 and suppression of β‐catenin and COX2. In vitro studies showed that sodium selenite promoted cell apoptosis and inhibited cell proliferation in human colon cancer cell lines HCT116 and SW620. These effects were dose‐ and time course‐dependent, and were also linked to an increase of JNK1 phosphorylation and suppression of β‐catenin signaling. Reduced JNK1 expression by small RNA interference abrogated sufficient activation of JNK1 by sodium selenite, leading to reduced inhibition of the β‐catenin signaling, resulting in reduced efficacy of inhibiting cell proliferation. Taken together, our data demonstrate that sodium selenite inhibits intestinal carcinogenesis in vivo and in vitro through activating JNK1 and suppressing β‐catenin signaling, a novel anticancer mechanism of selenium.

Anti-tumor activity of three ginsenoside derivatives in lung cancer is associated with Wnt/β-catenin signaling inhibition.

Numerous compounds isolated from Ginseng have been shown to exhibit various biological activities, including antioxidant, anti-carcinogenic, anti-mutagenic, and anti-tumor activities. Recent research has focused on the potential values of these compounds in the prevention and treatment of human cancers. The anti-tumor activity of 25-hydroxyprotopanaxadiol (25-OH-PPD), a natural compound isolated from Panax ginseng, has been established in previous study. In the current study, we investigated the anti-tumor activity of three derivatives of 25-OH-PPD, namely xl, 1c, and 8b with respect to lung cancer. All three compounds significantly inhibited the growth of the human lung cancer cells A549 and H460. Oral administration of these compounds significantly inhibited the growth of xenograft tumors in mice without affecting body weight. Further mechanistic study demonstrated that these compounds could decrease the expression levels of β-catenin and its downstream targets Cyclin D1, CDK4, and c-myc in lung cancer cells. Taken together, the results suggested that the anti-growth activity exerted by these 25-OH-PPD derivatives against lung cancer cells probably involved β-catenin-mediated signaling pathway, a finding that could have important implication for chemotherapeutic strategy aiming at the treatment of lung cancer.

GSK3β Is Involved in JNK2-Mediated β-Catenin Inhibition

Background We have recently reported that mitogen-activated protein kinase (MAPK) JNK1 downregulates β-catenin signaling and plays a critical role in regulating intestinal homeostasis and in suppressing tumor formation. This study was designed to determine whether JNK2, another MAPK, has similar and/or different functions in the regulation of β-catenin signaling. Methodology and Principal Findings We used an in vitro system with manipulation of JNK2 and β-catenin expression and found that activated JNK2 increased GSK3β activity and inhibited β-catenin expression and transcriptional activity. However, JNK2-mediated downregulation of β-catenin was blocked by the proteasome inhibitor MG132 and GSK3β inhibitor lithium chloride. Moreover, targeted mutations at GSK3β phosphorylation sites (Ser33 and Ser37) of β-catenin abrogated JNK2-mediated suppression of β-catenin. In vivo studies further revealed that JNK2 deficiency led to upregulation of β-catenin and increase of GSK3-β phosphorylation in JNK2-/- mouse intestinal epithelial cells. Additionally, physical interaction and co-localization among JNK2, β-catenin and GSK3β were observed by immunoprecipitation, mammalian two-hybridization assay and confocal microscopy, respectively. Conclusion and Significance In general, our data suggested that JNK2, like JNK1, interacts with and suppresses β-catenin signaling in vitro and in vivo, in which GSK3β plays a key role, although previous studies have shown distinct functions of JNK1 and JNK2. Our study also provides a novel insight into the crosstalk between Wnt/β-catenin and MAPK JNKs signaling.