Down-regulation of X-linked inhibitor of apoptosis synergistically enhanced peroxisome proliferator-activated receptor γ ligand-induced growth inhibition in colon cancer

Constructing a novel competing Endogenous RNAs network based on NR3C1 and X-linked inhibitor of apoptosis protein genes reveals potential prognostic biomarkers in colorectal cancer

Background:

Long noncoding RNAs (lncRNAs) have been recognized as the main modulatory molecules in various cancers and perform as competing endogenous RNAs (ceRNAs). The nuclear hormone receptor superfamily of ligand-activated transcription factors (NR3C1) regulates numerous proliferative and metabolic processes such as tumorigenesis and metabolic diseases. Furthermore, X-linked inhibitor of apoptosis protein (XIAP) belongs to a family of the inhibitors of apoptosis proteins, is located downstream of the glucocorticoid receptor (GR or NR3C1) pathway, and cooperates with GR to suppress apoptosis. However, the underlying mechanisms of NR3C1 and XIAP in colorectal cancer (CRC) remain mainly unclear. This research aims to clarify the potential RNA biomarkers and to construct a novel ceRNA network in CRC.

Materials and Methods:

Multistep bioinformatics methods such as Lnc2cancer and miRDB databases were applied to identify candidate lncRNAs and miRNAs. The interaction energy between lncRNAs, NR3C1, and XIAP genes was analyzed by the LncRRIsearch database. Plus, microRNAs and lncRNA were evaluated via the Diana tools database to select microRNAs with the most binding scores. Quantitative reverse transcription–polymerase chain reaction (QRT-PCR) was applied to verify RNA molecules’ expression levels and their association with the clinicopathological factors in 30 CRC tissues compared to 30 adjacent tissues.

Results:

QRT-PCR showed upregulation of KCNQ1OT1, NR3C1, and XIAP and downregulation of miR-421. The ceRNA network was constructed with 17 lncRNAs, 2 mRNAs, and 42 miRNAs. Thus, we explained the potential interactions between KCNQ1OT1 and miR-421 with NR3C1 and XIAP genes.

Conclusion:

Our study represents potential prognostic biomarkers and a new ceRNA network for further study in CRC.

15-deoxy-δ12,14-prostaglandin j2 inhibits osteolytic breast cancer bone metastasis and estrogen deficiency-induced bone loss

Breast cancer is the major cause of cancer death in women worldwide. The most common site of metastasis is bone. Bone metastases obstruct the normal bone remodeling process and aberrantly enhance osteoclast-mediated bone resorption, which results in osteolytic lesions. 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is an endogenous ligand of peroxisome proliferator-activated receptor gamma (PPARγ) that has anti-inflammatory and antitumor activity at micromolar concentrations through PPARγ-dependent and/or PPARγ-independent pathways. We investigated the inhibitory activity of 15d-PGJ₂ on the bone loss that is associated with breast cancer bone metastasis and estrogen deficiency caused by cancer treatment. 15d-PGJ₂ dose-dependently inhibited viability, migration, invasion, and parathyroid hormone-related protein (PTHrP) production in MDA-MB-231 breast cancer cells. 15d-PGJ₂ suppressed receptor activator of nuclear factor kappa-B ligand (RANKL) mRNA levels and normalized osteoprotegerin (OPG) mRNA levels in hFOB1.19 osteoblastic cells treated with culture medium from MDA-MB-231 cells or PTHrP, which decreased the RANKL/OPG ratio. 15d-PGJ₂ blocked RANKL-induced osteoclastogenesis and inhibited the formation of resorption pits by decreasing the activities of cathepsin K and matrix metalloproteinases, which are secreted by mature osteoclasts. 15d-PGJ₂ exerted its effects on breast cancer and bone cells via PPARγ-independent pathways. In Balb/c nu/nu mice that received an intracardiac injection of MDA-MB-231 cells, subcutaneously injected 15d-PGJ₂ substantially decreased metastatic progression, cancer cell-mediated bone destruction in femora, tibiae, and mandibles, and serum PTHrP levels. 15d-PGJ₂ prevented the destruction of femoral trabecular structures in estrogen-deprived ICR mice as measured by bone morphometric parameters and serum biochemical data. Therefore, 15d-PGJ₂ may be beneficial for the prevention and treatment of breast cancer-associated bone diseases.

Synergistic effects of IAP inhibitor LCL161 and paclitaxel on hepatocellular carcinoma cells

Inhibitor of Apoptosis Proteins (IAPs) are key regulators of apoptosis in hepatocellular carcinoma (HCC) and their expression is negatively correlated with patient survival. LCL161 is a small molecule inhibitor of IAPs that has potent antitumour activity in a range of solid tumours. In HCC, response to LCL161 therapy has shown to be mediated by Bcl-2 expression. In this study, we aim to determine whether LCL161 has any therapeutic potential in HCC. Protein expression was determined by Western blot. Cell proliferation was determined by Cell Proliferation ELISA and BrdU colorimetric assays. Apoptosis was determined by Annexin V assay. Cell cycle analysis was performed by staining cells with propidium iodide and analysed in a FACScan. Automated Cell Counter and phase contrast microscopy were used to determine the cell viability. We have found that LCL161 targets (cIAP1, cIAP2 and XIAP) were up-regulated in HCC tumours. Both high Bcl-2 expressing HuH7 cells and low Bcl-2 expressing SNU423 cells showed strong resistance to LCL161 therapy with significant effects on both apoptosis and cell viability only evident at LCL161 concentrations of ⩾100μM. At these doses there was significant inhibition of IAP targets, however there was also significant inhibition of off-target proteins including pERK and pJNK suggesting apoptosis caused by drug toxicity. However, when used in combination with paclitaxel in HuH7 and SNU423 cells, LCL161 had significant antiproliferative effects at doses as low as 2μM and this was independent of Bcl-2 expression. Thus, LCL161 may be a useful agent in combination with paclitaxel to treat liver tumours.

Silencing of Jagged1 inhibits cell growth and invasion in colorectal cancer

Dysregulated Notch signaling has a critical role in the tumorigenesis. Jagged1, a Notch ligand, is overexpressed in various human cancers. Recent studies revealed the involvement of Jagged1 in colorectal cancer (CRC) development. These basic studies provide a promising potential for inhibition of the Notch pathway for the treatment of CRC. Herein, we aimed to investigate the consequences of targeting Jagged1 using shRNA on CRC both in vitro and in vivo to test their potential to inhibit this key element for CRC treatment. We found that downregulation of Jagged1 with lentiviral Jagged1-shRNA resulted in decreased colon cancer cell viability in vitro, most likely mediated through reduced cell proliferation. Importantly, Jagged1 knockdown induced G₀/G₁ phase cell cycle arrest, with reduced Cyclin D1, Cyclin E and c-Myc expression. Silencing of Jagged1 reduced the migration and invasive capacity of the colon cancer cells in vitro. Furthermore, colon cancer cells with knockdown of Jagged1 had much slower growth rate than control cells in a xenograft mouse model in vivo, with a marked downregulation of cell proliferation markers (PCNA, Ki-67, and c-Myc) and metastasis markers (MMP-2 and MMP-9). These findings rationalize a mechanistic approach to CRC treatment based on Jagged1-targeted therapeutic development.

The role of peroxisome proliferator-activated receptors in colorectal cancer

Colorectal cancer is one of the most common cancers in the world. Dietary fat intake is a major risk factor for colorectal cancer. Some nuclear hormone receptors play an important role in regulating nutrient metabolism and energy homeostasis. Among these receptors, special attention has been focused on the role of peroxisome proliferator-activated receptors (PPARs) in colorectal cancer, because PPARs are involved in regulation of lipid and carbohydrate metabolism. PPARs are ligand-activated intracellular transcription factors. The PPAR subfamily consists of three subtypes encoded by distinct genes named PPARα, PPARβ/δ, and PPARγ. PPARγ is the most extensively studied subtype of PPARs. Even though many investigators have studied the expression and clinical implications of PPARs in colorectal cancer, there are still many controversies about the role of PPARs in colorectal cancer. In this paper, the recent progresses in understanding the role of PPARs in colorectal cancer are summarized.

Role of PCDH10 and its hypermethylation in human gastric cancer

Epigenetic changes of genomic DNA are involved in the development and progression of many cancers. Aberrant methylation of CpG islands in the promoter regions of certain tumor-suppressor genes (TSG) is frequently observed in cancer cells. Protocadherin 10 (PCDH10), a member of the cadherin superfamily, is a recently identified putative TSG. PCDH10 is frequently silenced in many solid tumors. However, the role of PCDH10 in gastric cancer is largely unknown. In this study, we examined the expression and methylation status of PCDH10 in gastric cancer cells and tissues by real time PCR and methylation-specific PCR (MSP), and then investigated the biological function of PCDH10. We found that the expression of PCDH10 was markedly reduced in gastric cancer cells and tissues. The reduced expression correlated with hypermethylation of this gene in its promoter region, as demonstrated by MSP and bisulfite genomic sequencing (BGS) analysis. In addition, pharmacological demethylation using 5-Aza restored the expression of PCDH10 in gastric cancer cells. Over-expression of PCDH10 in gastric cancer cells suppressed cell proliferation and migration, but did not cause marked apoptosis. Over-expression of PCDH10 also suppressed growth of xenograft tumors in nude mice. Thus, PCDH10 functions as a TSG in gastric cancer, and might be a useful target for cancer therapy.

Peroxisome proliferator-activated receptor γ and colorectal cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and ligand-activated transcription factors. PPARγ plays an important role in adipocyte differentiation, lipid storage and energy dissipation in adipose tissue, and is involved in the control of inflammatory reactions as well as in glucose metabolism through the improvement of insulin sensitivity. Growing evidence has demonstrated that activation of PPARγ has an antineoplastic effect in tumors, including colorectal cancer. High expression of PPARγ is detected in human colon cancer cell lines and adenocarcinoma. This review describes the molecular mechanisms by which PPARγ regulates tumorigenesis in colorectal cancer, and examines current clinical trials evaluating PPARγ agonists as therapeutic agents for colorectal cancer.

Modulation of mammary cancer cell migration by 15-deoxy-delta(12,14)-prostaglandin J(2): implications for anti-metastatic therapy

Recently, a number of steps in the progression of metastatic disease have been shown to be regulated by redox signalling. Electrophilic lipids affect redox signalling through the post-translational modification of critical cysteine residues in proteins. However, the therapeutic potential as well as the precise mechanisms of action of electrophilic lipids in cancer cells is poorly understood. In the present study, we investigate the effect of the electrophilic prostaglandin 15d-PGJ2 (15-deoxy-Delta12,14-prostaglandin J2) on metastatic properties of breast cancer cells. 15d-PGJ2 was shown to decrease migration, stimulate focal-adhesion disassembly and cause extensive F-actin (filamentous actin) reorganization at low concentrations (0.03-0.3 microM). Importantly, these effects seem to be independent of PPARgamma (peroxisome-proliferator-activated receptor gamma) and modification of actin or Keap1 (Kelch-like ECH-associated protein 1), which are known protein targets of 15d-PGJ2 at higher concentrations. Interestingly, the p38 inhibitor SB203580 was able to prevent both 15d-PGJ2-induced F-actin reorganization and focal-adhesion disassembly. Taken together, the results of the present study suggest that electrophiles such as 15d-PGJ2 are potential anti-metastatic agents which exhibit specificity for migration and adhesion pathways at low concentrations where there are no observed effects on Keap1 or cytotoxicity.

Albumin-binding and tumor vasculature determine the antitumor effect of 15-deoxy-Delta-(12,14)-prostaglandin-J(2) in vivo

15-Deoxy-Delta(12,14)-prostaglandin-J(2) (15d-PGJ(2)), a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, induces cell death in tumor cells in vitro; however, no study showed its in vivo effect on tumors. Here, we report that 15d-PGJ(2) shows antitumor effects in vivo in mice. However, its effects correlate with tumor uptake of albumin, to which it reversibly binds. 15d-PGJ(2) induces cell death in B16F10 melanoma and C26 colon carcinoma cells in vitro. These effects were not elicited through PPARgamma-dependent pathways because an irreversible PPARgamma antagonist GW9662 did not inhibit these effects. Caspase- and nuclear factor kappaB- (NF-kappaB) dependent pathways were found to be involved as determined with caspase-3/7 fluorescent assay and NF-kappaB containing plasmid transfection assay, respectively. Noticeably, 15d-PGJ(2) had significantly stronger effects in C26 cells compared with B16 cells in all assays. However, in vivo, there was no effect on C26 tumors, yet it significantly inhibited the B16 tumor growth in mice by 75%. We found that 15d-PGJ(2) rapidly bound to albumin and in vivo albumin greatly distributed to B16 tumors compared with C26 tumors, shown with gamma-camera imaging and immunohistochemical staining. Albumin accumulation can be attributed to the large blood vessel diameter in B16 tumors and an enhanced permeability and retention effect. These findings suggest that 15d-PGJ(2) can be an effective therapeutic agent for cancer, although its effects seem to be limited to the tumors allowing albumin penetration.

Peroxisome proliferator-activated receptor γ and colorectal cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and ligand-activated transcription factors. PPARγ plays an important role in adipocyte differentiation, lipid storage and energy dissipation in adipose tissue, and is involved in the control of inflammatory reactions as well as in glucose metabolism through the improvement of insulin sensitivity. Growing evidence has demonstrated that activation of PPARγ has an antineoplastic effect in tumors, including colorectal cancer. High expression of PPARγ is detected in human colon cancer cell lines and adenocarcinoma. This review describes the molecular mechanisms by which PPARγ regulates tumorigenesis in colorectal cancer, and examines current clinical trials evaluating PPARγ agonists as therapeutic agents for colorectal cancer.

Mitochondrial targeting of the electrophilic lipid 15-deoxy-Delta12,14-prostaglandin J2 increases apoptotic efficacy via redox cell signalling mechanisms

Prototypical electrophiles such as the lipid 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) are well recognized for their therapeutic potential. Electrophiles modify signalling proteins in both the cytosol and mitochondrion, which results in diverse cellular responses, including cytoprotective effects and, at high doses, cell death. These findings led us to the hypothesis that targeting electrophiles to specific compartments in the cell could fine-tune their biological effects. To examine this, we synthesized a novel mitochondrially targeted analogue of 15d-PGJ2 (mito-15d-PGJ2) and tested its effects on redox cell signalling. Mito-15d-PGJ2 caused profound defects in mitochondrial bioenergetics and mitochondrial membrane depolarization when compared with 15d-PGJ2. We also found that mito-15d-PGJ2 modified different members of the electrophile-responsive proteome, was more potent at initiating intrinsic apoptotic cell death and was less effective than 15d-PGJ2 at up-regulating the expression of HO-1 (haem oxygenase-1) and glutathione. These results demonstrate the feasibility of modulating the biological effects of electrophiles by targeting the pharmacophore to mitochondria.

Current understanding of the role of PPARγ in gastrointestinal cancers

Numerous studies have indicated that PPARγ plays multiple roles such as in inflammation, cell cycle control, cell proliferation, apoptosis, and carcinogenesis, thus PPARγ contributes to the homeostasis. Many in vitro studies have showed that ligand-induced activation of PPARγ possess antitumor effect in many cancers including CRC. However, the role of PPARγ in gastrointestinal cancers, especially in colorectal cancer, is rather controversial. Nevertheless, some recent studies with the positive results on the possible application of PPARγ ligands, such as Bezafibrate or Rosiglitazone in gastrointestinal cancers, have suggested a potential usefulness of PPARγ agonists in cancer prevention and therapy. In this review, the authors discuss the recent developments in the role of PPARγ in gastrointestinal cancers.

Adenovirus-mediated down-regulation of X-linked inhibitor of apoptosis protein inhibits colon cancer

Our previous studies and those of others have indicated that X-linked inhibitor of apoptosis protein (XIAP) holds promise as a target gene in colon cancer gene therapy. In this study, we constructed an adenoviral vector to deliver small hairpin RNA (shRNA) against XIAP (XIAP-shRNA) into colon cancer cells and tested its therapeutic efficacy in vitro and in vivo. We first confirmed an overexpression of XIAP in colon cancer cells and human cancer tissues. We then designed XIAP-small interfering RNA (siRNA) and confirmed the knockdown effect of these siRNAs in colon cancer cells. The sequences of the effective siRNAs were converted into shRNA and then packed into replication-deficient adenoviral vectors using BLOCK-iT Adenoviral RNAi Expression System to generate Adv-XIAP-shRNA. Infection of HT29 and HCT116 cells with Adv-XIAP-shRNA led to enhanced caspase-3 activity, which was associated with increased apoptosis and reduced cell proliferation. The therapeutic effect of Adv-XIAP-shRNA was then tested in xenograft tumors in nude mice. We showed that treatment of the xenograft tumors derived from HCT116 cells with Adv-XIAP-shRNA resulted in a retardation of tumor growth, which was associated with enhanced apoptosis, increased caspase-3 activity, and reduced expression of proliferating cell nuclear antigen in the tumor tissues. Treatment of xenograft tumors with Adv-XIAP-shRNA did not affect the expressions of inflammatory cytokines in tumor-bearing mice. Thus, Adv-XIAP-shRNA-mediated down-regulation of XIAP exerts a therapeutic effect in colon cancer by promoting apoptosis and inhibiting proliferation of colon cancer cells, and the antitumor effect of Adv-XIAP-shRNA was unlikely to be related to virus-induced immune response.

Peroxisome proliferator-activated receptor-gamma contributes to the inhibitory effects of Embelin on colon carcinogenesis

Down-regulation of XIAP (X-linked inhibitor of apoptosis protein) sensitizes colon cancer cells to the anticancer effect of peroxisome proliferator-activated receptor-gamma (PPARgamma) ligands in mice. The aims of this study were to evaluate the effect of embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone), an antagonist of XIAP, on colon cancer, with a particular focus on whether PPARgamma is required for embelin to exert its effect. A dominant-negative PPARgamma was used to antagonize endogenous PPARgamma in HCT116 cells. Cells were treated with or without embelin. Cell proliferation, apoptosis, and nuclear factor-kappaB (NF-kappaB) activity were measured. For in vivo studies, 1,2-dimethylhydrazine dihydrochloride (DMH) was s.c. injected to induce colon cancer in PPARgamma(+/+) and PPARgamma(+/-) mice. Mice were fed embelin daily for 10 days before DMH injection, and continued for 30 more weeks. Embelin inhibited proliferation and induced apoptosis in HCT116 cells with marked up-regulation of PPARgamma. In addition, embelin significantly inhibited the expressions of survivin, cyclin D1, and c-Myc. These effects were partially dependent on PPARgamma. PPARgamma(+/-) mice were more susceptible to DMH-induced colon carcinogenesis than PPARgamma(+/+) mice, and embelin significantly reduced the incidence of colon cancer in PPARgamma(+/+) mice but not in PPARgamma(+/-) mice. Embelin inhibited NF-kappaB activity in PPARgamma(+/+) mice but marginally so in PPARgamma(+/-) mice. Thus, reduced expression of PPARgamma significantly sensitizes colonic tissues to the carcinogenic effect of DMH. Embelin inhibits chemical carcinogen-induced colon carcinogenesis, but this effect is partially dependent on the presence of functional PPARgamma, indicating that PPARgamma is a necessary signaling pathway involved in the antitumor activity of normal organisms.

Targeting apoptosis as an approach for gastrointestinal cancer therapy

Cancers in the gastrointestinal system account for a large proportion of malignancies and cancer-related deaths with gastric cancer and colorectal cancer being the most common ones. For those patients in whom surgical resection is not possible, other therapeutic approaches are necessary. Disordered apoptosis has been linked to cancer development and treatment resistance. Apoptosis occurs via extrinsic or intrinsic signaling each triggered and regulated by many different molecular pathways. In recent years, the selective induction of apoptosis in tumor cells has been increasingly recognized as a promising approach for cancer therapy. A detailed understanding of the molecular pathways involved in the regulation of apoptosis is essential for developing novel effective therapeutic approaches. Apoptosis can be induced by many different approaches including activating cell surface death receptors (for example, Fas, TRAIL and TNF receptors), inhibiting cell survival signaling (such as EGFR, MAPK and PI3K), altering apoptosis threshold by modulating pro-apoptotic and anti-apoptotic members of the Bcl-2 family, down-regulating anti-apoptosis proteins (such as XIAP, survivin and c-IAP2), and using other pro-apoptotic agents. In this review, the authors reviewed the currently reported apoptosis-targeting approaches in gastrointestinal cancers.

Gene expression profile in colon cancer cells with respect to XIAP expression status

BACKGROUND AND AIMS

We observed a marked synergism between peroxisome proliferator-activated receptor gamma (PPARgamma) ligands and X-linked inhibitor of apoptosis (XIAP) down-regulation in colon cancer. In the current study, we detected the gene expression profile in HCT116 cells treated with or without PPARgamma ligand troglitazone.

MATERIALS AND METHODS

HCT116-XIAP(+/+) and HCT116-XIAP(-/-) cells were treated with or without 50 microM troglitazone for 48 h. Gene expressions were detected by microarray, and selected genes were validated by reverse-transcriptase polymerase chain reaction (PCR), real-time PCR, and Western blot.

RESULTS

Relative to HCT116-XIAP(+/+) cells, 58 genes were up-regulated and 33 genes down-regulated in HCT116-XIAP(-/-) cells, all by > or =4-fold. These genes could be classified into a wide variety of functional classes, but we focused on those related to angiogenesis, apoptosis, and proliferation. Thus, two pro-apoptotic genes and one pro-proliferation gene were up-regulated in HCT116-XIAP(-/-) cells. Two pro-proliferation genes, one pro-angiogenesis gene, one anti-angiogenesis gene, and one anti-apoptosis gene were down-regulated in HCT116-XIAP(-/-) cells. Relative to HCT116-XIAP(+/+) cells treated with troglitazone, 137 genes were up-regulated, and 31 genes were down-regulated in troglitazone-treated HCT116-XIAP(-/-) cells, all by > or =4-fold. Among the up-regulated genes were two anti-angiogenesis genes, seven pro-apoptosis genes, and six anti-proliferation genes. Among the down-regulated genes were one anti-angiogenesis gene, one pro-angiogenesis gene, one anti-apoptosis gene, one anti-proliferation gene, and two pro-proliferation genes.

CONCLUSION

Down-regulation of XIAP in HCT116 cells with or without troglitazone treatment was associated with changes of gene expression that favor increased tendency of apoptosis, decreased cell proliferation, and angiogenesis potential.