Selenium-binding protein 1 as a tumor suppressor and a prognostic indicator of clinical outcome

Selenium is a trace element that plays a critical role in physiological processes and cancer prevention, whose functions may be through its effects on selenium-containing proteins. Selenium-binding protein 1 (SBP1) is a member of an unusual class of selenium-containing proteins that may function as a tumor suppressor in multiple cancer types and whose levels have been shown to be lower in cancers as compared to corresponding normal tissues. This review is intended to summarize recent advances in gaining an understanding of the significance of SBP1 in carcinogenesis, and suggest that SBP1 could be developed as a potential biomarker for cancer progression and prognosis

Selenium and sulindac are synergistic to inhibit intestinal tumorigenesis in Apc/p21 mice

Background: Both selenium and non-steroidal anti-inflammatory drug (NSAID) sulindac are effective in cancer prevention, but their effects are affected by several factors including epigenetic alterations and gene expression. The current study was designed to determine the effects of the combination of selenium and sulindac on tumor inhibition and the underlying mechanisms. Results: We fed the intestinal tumor model Apc/p21 mice with selenium- and sulindac-supplemented diet for 24 weeks, and found that the combination of selenium and sulindac significantly inhibited intestinal tumorigenesis, in terms of reducing tumor incidence by 52% and tumor multiplicities by 80% (p<0.01). Mechanistic studies revealed that the combination of selenium and sulindac led to the significant induction of the expression of p27 and p53 and JNK1 phosphorylation, and led to the suppression of β-catenin and its downstream targets. Impressively, the data also showed that demythelation on p21 promoter was associated with tumor inhibition by the combination of selenium and sulindac. Conclusions: The selenium is synergistic with sulindac to exert maximal effects on tumor inhibition. This finding provides an important chemopreventive strategy using combination of anti-cancer agents, which has a great impact on cancer prevention and has a promising translational potential

JNK2 deficiency caused upregulation of β-catenin and its downstream target CDK4, as well as upregulation of GSK3β phosphorylation in JNK2-/- mouse intestinal epithelial cells, compared to those in JNK2+/+ mice.

<p>Each lane represents one mouse. β-actin served as loading control.</p

Active JNK2 downregulated β-catenin expression and inhibited its transcriptional activity in a dose-dependent manner.

<p>(A) Activated JNK2 reduced β-catenin protein level in a dose-dependent manner. HEK293T cells were co-transfected with pcDNA3-HA-β-catenin along with different amounts of pcDNA3-Flag-MKK7-JNK2, as indicated. Forty-eight hours after transfection, cells were harvested for immunoblotting analysis to detect the alterations of HA-β-catenin and p-JNK. β-actin served as loading control. (B) Activated JNK2 inhibited β-catenin-mediated transcriptional activity of TCF in a dose-dependent manner. HEK293T cells were co-transfected with pcDNA3-HA-β-catenin, TOPFLASH, Renilla, along with different amounts of pcDNA3-Flag-MKK7-JNK2, as indicated. Forty-eight hours after transfection, cells were harvested for luciferase activity assay. Each bar represents the mean ± standard deviation (SD) for triplicated samples.</p

Active JNK2 downregulated β-catenin expression, inhibited its transcriptional activity and reduced GSK3β phosphorylation.

<p>(A) Active JNK2 suppressed β-catenin expression and GSK3β phosphorylation in HEK293T cells. HEK293T cells were transfected with pcDNA3-HA-β-catenin together with pcDNA3-Flag-MKK7-JNK1 or pcDNA3-Flag-MKK7-JNK2. Forty-eight hours after transfection, cells were harvested for immunoblotting analysis to detect the alterations of HA-β-catenin, p-JNK, p-c-Jun, phospho-Ser⁹ GSK3β, and GSK3β. β-actin served as loading control. (B) Active JNK2 reduced GSK3β phosphorylation and downregulated β-catenin expression in human lung cancer cell line A549. A549 cells were co-transfected with pcDNA3-HA-β-catenin and pcDNA3-Flag-MKK7-JNK2. Forty-eight hours after transfection, cells were harvested for immunoblotting analysis to detect the alterations of β-catenin, p-JNK, and phospho-Ser⁹ GSK3β. β-actin served as loading control. (C) Active JNK inhibited β-catenin-mediated transcriptional activity of TCF. HEK293T cells were co-transfected with pcDNA3-Flag-MKK7-JNK1 or pcDNA3-Flag-MKK7-JNK2, pcDNA3-HA-β-catenin, TOPFLASH (TOP) or FOPFLASH (FOP), and Renilla. 48 h after transfection, cells were harvested for luciferase activity assay. Each bar represents the mean ± standard deviation (SD) for triplicated samples.</p

Active JNK2-mediated β-catenin degradation occurred through the proteasome system and GSK3β.

<p>(A) HEK293T cells were co-transfected with pcDNA3-HA-β-catenin and pcDNA3-Flag-MKK7-JNK2 (lane 3 and 4) or empty vector (lane 1 and 2). Forty-four hours after transfection, 25 µM MG132 was added to the indicated samples (lane 2 and 4). Four hours later cells were harvested for immunoblotting analysis to detect the expression of HA-β-catenin and p-JNK. (B) Blocking GSK3β activity by LiCl reduced β-catenin expression inhibition by activated JNK2. pcDNA3-HA-β-catenin was transfected into HEK293T cells along with pcDNA3-Flag-MKK7-JNK2 (lane 3 and 4) or empty vector (lane 1 and 2). Thirty-six hours after transfection, half of the cultures were treated overnight with 30 mM LiCl (lane 2 and 4) and then harvested for immunoblotting analysis to detect the expression of HA-β-catenin, phospho-Ser-9 GSK3β, and p-JNK. (C) Mutant β-catenin was resistant to activated JNK2 induced degradation. Wild-type β-catenin (HA- β-catenin) (lanes 1 and 2) or various β-catenin mutants (HA-S33F β-catenin, lanes 3 and 4; HA-S33Y β-catenin, lanes 5 and 6; HA-S37A β-catenin, lanes 7 and 8) were transfected into HEK293T cells along with pcDNA3-Flag-MKK7-JNK2 (lane 2,4,6,8) or empty vector (lanes 1,3,5,7). 48 hours after transfection, cells were harvested for immunoblotting analysis to determine the protein levels of HA-β-catenin. β-actin served as loading control.</p

Activated JNK2 interacts with β-catenin and GSK3β.

<p>(A) Active JNK2 binding to β-catenin and GSK3β was analyzed by immunoprecipitation. β-catenin (HA tagged) was co-transfected with empty vector or active JNK2 (Flag tagged) into HEK293T cells. Immunoprecipitation was performed with a Flag antibody. (B) Mammalian two-hybridization assays showed a strong binding of β-catenin and JNK2 protein. The experiments were triplicated independently. (C) Active JNK2 and β-catenin co-localized in the cell nucleus and cytoplasm. Active JNK2 (Flag tagged) and pEGFP-β-catenin were co-transfected into HEK293T cells. The cells were immunostained with a Flag antibody. Co-localization (yellow fluorescence) of active JNK2 (red fluorescence) and β-catenin (green fluorescence) was detected in the nucleus and cytoplasm.</p

Quantitative identification and bioinformatics analysis of tumor tissue proteins assayed by iTRAQ.

<p><b>(A)</b> All 132 differentially accumulated proteins were classified into three groups: biological process, molecular function, and cellular component through GO analysis. <b>(B)</b> The numbers of lipid/glucose metabolism-related proteins were shown through GO analysis.</p

Hypothetic pathways of SBP1-mediated anti-cancer functions <i>in vivo</i>.

<p>SBP1-mediated anti-cancer effects may be through lipid/glucose metabolism. The possible functional regulation between SBP1 and related proteins is illustrated.</p

Quantitative identification and bioinformatics analysis of tumor tissue proteins assayed by iTRAQ.

<p><b>(A)</b> All 132 differentially accumulated proteins were classified into three groups: biological process, molecular function, and cellular component through GO analysis. <b>(B)</b> The numbers of lipid/glucose metabolism-related proteins were shown through GO analysis.</p