Loss of PDCD4 expression in human lung cancer correlates with tumour progression and prognosis

Programmed cell death-4 deficiency prevents diet-induced obesity, adipose tissue inflammation, and insulin resistance

Programmed cell death-4 (PDCD4), a selective protein translation inhibitor, has shown proinflammatory effect in some inflammatory diseases, but its roles in obesity remain unestablished. This study aims to investigate the effects of PDCD4 on obesity, inflammation, and insulin resistance. Surprisingly, high-fat diet (HFD)-fed PDCD4-deficient (PDCD4(-/-)) mice exhibited an absolutely lean phenotype together with improved insulin sensitivity. Compared with wild-type obese mice, HFD-fed PDCD4(-/-) mice showed higher energy expenditure, lower epididymal fat weight, and reduced macrophage infiltration inflammatory cytokine secretion in white adipose tissue (WAT). Alleviated hepatic steatosis along with decreased plasma levels of triglyceride and cholesterol was also observed in these mice. Importantly, PDCD4 appeared to disturb lipid metabolism via inhibiting the expression of liver X receptor (LXR)-α, a master modulator of lipid homeostasis, which was elevated in HFD-fed PDCD4(-/-) mice accompanied by upregulation of its target genes and relieved endoplasmic reticulum stress in WAT. These data demonstrate that PDCD4 deficiency protects mice against diet-induced obesity, WAT inflammation, and insulin resistance through restoring the expression of LXR-α, thereby proposing PDCD4 as a potential target for treating obesity-associated diseases.

Downregulation of programmed cell death 4 (PDCD4) in tumorigenesis and progression of human digestive tract cancers

Nowadays, digestive tract cancers become the commonest neoplasia and one of the leading causes of cancer deaths worldwide. The development of diagnosis and therapy is urgently required. Programmed cell death 4 (PDCD4), a new tumor suppressor, has been documented to be a potential diagnostic tool and treatment target for neoplasia due to the inhabitation of tumor promotion/progression and metastasis. However, its role in human digestive tract cancers is few available up to now. In this study, we examined the expression of PDCD4 in human digestive tract cancers (61 gastric cancer, 65 colorectal cancer, and 69 pancreatic cancer patients) by Western blot analysis, reverse transcription (RT)-PCR, and immunohistochemistry. Western blot, RT-PCR, and immunohistochemistry examination showed that expressions of PDCD4 were significantly lower in cancers specimens than in noncancerous tissues. Among the different differentiated cancer tissues, PDCD4 expression was significantly lower in moderately or poorly differentiated cancers than in well-differentiated cancers (p < 0.05). Our findings suggested that PDCD4 might be a potentially valuable molecular target in diagnosis and therapy for human digestive tract cancers.

Both STAT1 and STAT3 are favourable prognostic determinants in colorectal carcinoma

BACKGROUND

Aberrant activities of Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathways have been implicated in the development and spread of various cancer entities, among them colorectal carcinoma (CRC). Transcription factors STAT3 and STAT1, both downstream effectors of interleukin (IL)-6 and its receptor, are involved in growth and developmental control of CRC cells. Constituents of the signalling network around IL-6 and STAT activation are discussed as potential biomarkers and therapeutic targets in CRC.

METHODS

By immunohistochemical analysis of a tissue microarray covering >400 CRC biopsies, the expression and activity status of STAT1, STAT3 as well as of IL-6 and the IL-6 receptor α-chain was determined. The outcome was correlated with clinical information and patients' survival data. Colorectal carcinoma biopsies were also analysed for specific DNA-binding activity of STATs.

RESULTS

Statistical analysis showed tendential associations between individual STATs, IL-6/IL-6 receptor-α and clinicopathological parameters. The study revealed a significant correlation of high STAT1 activity with longer patient overall survival. Surprisingly, strong STAT3 expression in surgical specimens was correlated with an increase in median overall survival by about 30 months. Statistical analysis revealed that high expression levels of STAT1 and STAT3 were associated. This finding was backed up by biochemical data that showed simultaneous STAT1 and STAT3 DNA-binding activity in randomly selected CRC biopsies.

CONCLUSION

By multivariate data analysis, we could show that STAT3 expression and activity constitutes an independent favourable prognostic marker for CRC.

Target proteomic profiling of frozen pancreatic CD24+ adenocarcinoma tissues by immuno-laser capture microdissection and nano-LC-MS/MS

Cellular heterogeneity of solid tumors represents a common problem in mass spectrometry (MS)-based analysis of tissue specimens. Combining immuno-laser capture microdissection (iLCM) and mass spectrometry (MS) provides a means to study proteins that are specific for pure cell subpopulations in complex tissues. CD24, as a cell surface marker for detecting pancreatic cancer stem cells (CSCs), is directly correlated with the development and metastasis of pancreatic cancer. Herein, we describe an in-depth proteomic profiling of frozen pancreatic CD24(+) adenocarcinoma cells from early stage tumors using iLCM and LC-MS/MS and a comparison with CD24(-) cells dissected from patient-matched adjacent normal tissues. Approximately 40 nL of tissue was procured from each specimen and subjected to tandem MS analysis in triplicate. A total of 2665 proteins were identified, with 375 proteins in common that were significantly differentially expressed in CD24(+) versus CD24(-) cells by at least a 2-fold change. The major groups of the differentially overexpressed proteins are involved in promoting tumor cell migration and invasion, immune escape, and tumor progression. Three selected candidates relevant to mediating immune escape, CD59, CD70, and CD74, and a tumor promoter, TGFBI, were further validated by immunohistochemistry analysis on tissue microarrays. These proteins showed significantly increased expression in a large group of clinical pancreatic adenocarcinomas but were negative in all normal pancreas samples. The significant coexpression of these proteins with CD24 suggests that they may play important roles in the progression of pancreatic cancer and could serve as promising prognosis markers and novel therapeutic targets for this deadly disease.

Tumor suppressor gene PDCD4 negatively regulates autophagy by inhibiting the expression of autophagy-related gene ATG5

PDCD4 (programmed cell death protein 4), a suppressor of gene transcription and translation, plays a crucial inhibitory role in several types of human tumors. However, its underlying mechanisms remain unclear. Autophagy, an evolutionarily conserved catabolic process, maintains cellular homeostasis under stress conditions such as starvation and plays a crucial role in tumor initiation and progression. We report here that PDCD4 inhibits autophagy in multiple cell types both in vitro and in vivo, which in turn contributes to its tumor suppressor activity. Importantly, PDCD4 inhibits the expression of an essential autophagy related gene, ATG5 and the formation of an ATG12-ATG5 complex, and its ma3 domains are required for PDCD4-mediated inhibition of autophagy. Unlike most tumor suppressors that act as positive or dual regulators of autophagy, our findings indicate that PDCD4 negatively regulates autophagy by targeting ATG5, which provides a novel mechanism of tumor suppression.

Distinct roles of different fragments of PDCD4 in regulating the metastatic behavior of B16 melanoma cells

Melanoma is an aggressive cutaneous malignancy. In this study, we demonstrated that the levels of the programmed cell death 4 (PDCD4) protein and mRNA were lower in tumor tissues compared with normal tissues. In order to further investigate the effects of PDCD4 and its fragments in B16 melanoma cells, we established B16 clones with expression of different PDCD4 fragments. Intact PDCD4, PDCD4∆164‑469 and PDCD4∆327-440 expression, respectively, decreased proliferation and migration and increased apoptosis in B16 cells in vitro. We found that intact PDCD4, PDCD4∆164-469 or PDCD4∆327-440 can inhibit the activity of MMP-2 and the expression of CXCR4. However, PDCD4∆164-275 showed no effects on B16 cells. These results may prove helpful for the development of novel therapies for melanoma treatment.

Prognostic significance of PDCD4 expression in human salivary adenoid cystic carcinoma

Programmed cell death 4 (PDCD4) has been recognized as a tumor suppressor gene that may inhibit neoplastic transformation and tumor promotion/progression. It was demonstrated that PDCD4 expression was associated with prognosis of multiple types of tumors and cancers. However, PDCD4 expression in salivary adenoid cystic carcinoma (ACC) has not been studied. We analyzed PDCD4 protein level by immunohistochemistry in 96 cases of ACC and found that PDCD4 expression was downregulated in 64.6 % (62/96) of tumor samples compared with adjacent nontumor salivary gland tissues. Moreover, decreased PDCD4 expression was significantly associated with clinical stage of the disease (P < 0.01). Analyses of overall survival and disease-specific survival by Kaplan-Meier method revealed that poor prognosis of ACC patients was associated with decreased PDCD4 expression (χ (2) = 5.971, P = 0.013; χ (2) = 4.274, P = 0.029). Furthermore, multivariate Cox model analysis demonstrated that PDCD4 expression was an independent risk factor for ACC (P < 0.05). Thus, our study suggested, for the first time, that PDCD4 expression might have an essential role in the progression of ACC.

Throwing a monkey wrench in the motor: targeting DExH/D box proteins with small molecule inhibitors

DExH/D box proteins are molecular motors that utilize the energy derived from NTP hydrolysis to perform work - from helicases that remodel RNA to RNPases that alter RNA-protein complexes. Members of this class of proteins are uniquely placed along the RNA information highway to regulate the flow of genetic information. They have been implicated in a number of nodal points encompassing nuclear, cytoplasmic, and organellar RNA-based processes. The identification and characterization of three unique natural products that selectively inhibit the activity of eukaryotic initiation factor (eIF)4A (DDX2) has provided proof-of-principle that the activity of DExH/D box family members can be selectively targeted. Extending these achievements to other DExH/D box proteins is an important future challenge for drugging this family of proteins. This article is part of a Special Issue entitled: The Biology of RNA helicases - Modulation for life.

MicroRNAs and Glucocorticoid-Induced Apoptosis in Lymphoid Malignancies

The initial response of lymphoid malignancies to glucocorticoids (GCs) is a critical parameter predicting successful treatment. Although being known as a strong inducer of apoptosis in lymphoid cells for almost a century, the signaling pathways regulating the susceptibility of the cells to GCs are only partly revealed. There is still a need to develop clinical tests that can predict the outcome of GC therapy. In this paper, I discuss important parameters modulating the pro-apoptotic effects of GCs, with a specific emphasis on the microRNA world comprised of small players with big impacts. The journey through the multifaceted complexity of GC-induced apoptosis brings forth explanations for the differential treatment response and raises potential strategies for overcoming drug resistance.

Tumor suppressor protein Pdcd4 interacts with Daxx and modulates the stability of Daxx and the Hipk2-dependent phosphorylation of p53 at serine 46

The tumor suppressor protein Pdcd4 is a nuclear/cytoplasmic shuttling protein that has been implicated in the development of several types of human cancer. In the nucleus, Pdcd4 affects the transcription of specific genes by modulating the activity of several transcription factors. We have identified the Daxx protein as a novel interaction partner of Pdcd4. Daxx is a scaffold protein with roles in diverse processes, including transcriptional regulation, DNA-damage signaling, apoptosis and chromatin remodeling. We show that the interaction of both proteins is mediated by the N-terminal domain of Pdcd4 and the central part of Daxx, and that binding to Pdcd4 stimulates the degradation of Daxx, presumably by disrupting the interaction of Daxx with the de-ubiquitinylating enzyme Hausp. Daxx has previously been shown to serve as a scaffold for protein kinase Hipk2 and tumor suppressor protein p53 and to stimulate the phosphorylation of p53 at serine 46 (Ser-46) in response to genotoxic stress. We show that Pdcd4 also disrupts the Daxx–Hipk2 interaction and inhibits the phosphorylation of p53. We also show that ultraviolet irradiation decreases the expression of Pdcd4. Taken together, our results support a model in which Pdcd4 serves to suppress the phosphorylation of p53 in the absence of DNA damage, while the suppressive effect of Pdcd4 is abrogated after DNA damage owing to the decrease of Pdcd4. Overall, our data demonstrate that Pdcd4 is a novel modulator of Daxx function and provide evidence for a role of Pdcd4 in restraining p53 activity in unstressed cells.

PDCD4 functions as a suppressor for pT2a and pT2b stage gastric cancer

Gastric cancer is one of the leading causes of cancer‑related mortality worldwide. Loss of programmed cell death 4 (PDCD4) expression has been detected in gastric cancer. However, the effects of PDCD4 on pT2 stage gastric cancer remain unclear. The aim of this study was to identify the relationship between PDCD4 expression and clinicopathological features of patients with pT2 stage gastric cancer. In the present study, 122 pT2 stage gastric cancer specimens were subclassified as pT2a and pT2b stage. The levels of PDCD4 mRNA and protein in gastric cancer tissues were lower compared to that in normal tissues as detected by real‑time PCR and western blot analysis, respectively. In addition, both PDCD4 mRNA and protein in pT2b stage gastric cancer were lower when compared to that in pT2a stage gastric cancer. Finally, we used immuno-histochemistry to determine the protein expression and analyzed the relationship between PDCD4 expression and the clinicopathological features of pT2 stage gastric cancer patients. Cumulative survival rate of patients with PDCD4 expression was significantly higher compared to the patients without PDCD4 expression. PDCD4 expression in gastric cancer can be employed to indicate a favorable prognosis for the disease outcome.

PDCD4/miR-21 dysregulation in inflammatory bowel disease-associated carcinogenesis

Inflammatory bowel diseases (IBDs; both ulcerative colitis [UC] and Crohn's colitis [CC]) are well-established predisposing pathological conditions for colorectal cancer (CRC) development. In IBDs, both the endoscopy and the histology assessment of CRC precursors (i.e., dysplasia, also defined as intraepithelial neoplasia) are associated with low interobserver consistency, and no reliable dysplasia-specific biomarker is available. The programmed cell death 4 (PDCD4) tumor suppressor gene is involved in sporadic colorectal oncogenesis, but scanty information is available on its involvement in IBD-associated colorectal oncogenesis. One hundred twenty tissue samples representative of active and inactive IBD and of flat dysplasia were obtained from 30 cases of UC and 30 of CC who undergone colectomy. Twenty additional biopsy samples obtained from patients with irritable bowel syndrome acted as normal controls. PDCD4 expression was assessed by immunohistochemistry; the expression of miR-21 (a major PDCD4 regulator) was investigated by quantitative real-time PCR and in situ hybridization in different series of a hundred samples. Tissue specimens from both controls and inactive IBD consistently featured strong PDCD4 nuclear immunostain; conversely, lower PDCD4 nuclear expression was featured by both active IBD and IBD-associated dysplastic lesions. Significant PDCD4 down-regulation distinguished IBD-associated dysplasia (p < 0.001) versus active IBD. In both active IBD and dysplasia, PDCD4 down-regulation was significantly associated with miR-21 up-regulation. PDCD4 nuclear down-regulation (which parallels miR-21 up-regulation) is involved in the molecular pathway of IBD-associated carcinogenesis. PDCD4 nuclear expression may be usefully applied as ancillary maker in the histological assessment of IBD-associated dysplastic lesions.

High expression of miR-21 and miR-155 predicts recurrence and unfavourable survival in non-small cell lung cancer

We synthesised the evidence of microRNAs as prognostic biomarkers in lung cancer. Studies were identified by searching PubMed, Embase and Web of Science until March 2012. Descriptive characteristics for studies were described and an additional meta-analysis for two specific microRNAs (miR-21 and miR-155) which were studied extensively was performed. Pooled hazard ratios (HRs) and their corresponding 95% confidence intervals (CIs) were calculated. The median study size was 88 patients (interquartile range [IQR]=53-193) and the median HR in the studies that reported statistically significant results was 2.855 (IQR=2.01-5.035). For the studies evaluating miR-21's association with clinical outcomes, the pooled HR suggested that high expression of miR-21 has a negative impact on overall survival (OS) in non-small cell lung cancer (NSCLC) (HR=2.32[1.17-4.62], P<0.05) and recurrence-free survival (RFS)/cancer-specific survival (CSS) in lung adenocarcinoma (HR=2.43[1.67-3.54], P<0.001). As for miR-155, the pooled HR for OS was 2.09 (95%CI: 0.68-6.41, P>0.05) which was not statistically significant, but for RFS/CSS was 1.42 (95% CI: 1.10-1.83, P=0.007). These results indicate that microRNAs show promising associations with prognosis in lung cancer; moreover, specific microRNAs such as miR-21 and miR-155 can predict recurrence and poor survival in NSCLC.

The DEAD-box helicase eIF4A: paradigm or the odd one out?

DEAD-box helicases catalyze the ATP-dependent unwinding of RNA duplexes. They share a helicase core formed by two RecA-like domains that carries a set of conserved motifs contributing to ATP binding and hydrolysis, RNA binding and duplex unwinding. The translation initiation factor eIF4A is the founding member of the DEAD-box protein family, and one of the few examples of DEAD-box proteins that consist of a helicase core only. It is an RNA-stimulated ATPase and a non-processive helicase that unwinds short RNA duplexes. In the catalytic cycle, a series of conformational changes couples the nucleotide cycle to RNA unwinding. eIF4A has been considered a paradigm for DEAD-box proteins, and studies of its function have revealed the governing principles underlying the DEAD-box helicase mechanism. However, as an isolated helicase core, eIF4A is rather the exception, not the rule. Most helicase modules in other DEAD-box proteins are modified, some by insertions into the RecA-like domains, and the majority by N- and C-terminal appendages. While the basic catalytic function resides within the helicase core, its modulation by insertions, additional domains or a network of interaction partners generates the diversity of DEAD-box protein functions in the cell. This review summarizes the current knowledge on eIF4A and its regulation, and discusses to what extent eIF4A serves as a model DEAD-box protein.

AKT Activation by Pdcd4 Knockdown Up-Regulates Cyclin D1 Expression and Promotes Cell Proliferation

Programmed cell death 4 (Pdcd4), a novel tumor suppressor, inhibits neoplastic transformation and tumor invasion. In this study, the authors found that knockdown of Pdcd4 promoted cell proliferation and up-regulated cyclin D1 expression. Previously, the authors demonstrated that Pdcd4 knockdown activated NF-κB-dependent transcription. Mutations of NF-κB binding sites on the cyclin D1 promoter attenuated the cyclin D1 promoter activity induced by Pdcd4 knockdown. In addition, knockdown of NF-κB/IκB kinase (IKK) α or IKKβ, the kinase regulating NF-κB activation, inhibited cyclin D1 promoter activity and cyclin D1 expression, indicating that up-regulation of cyclin D1 by Pdcd4 knockdown is contributed, at least in part, by NF-κB activation. To investigate the mechanism of how Pdcd4 knockdown activates NF-κB, the authors found that the levels of AKT phosphorylation and AKT kinase activity were increased in the Pdcd4 knockdown cells. Conversely, ectopic expression of Pdcd4 inhibited AKT phosphorylation and cyclin D1 expression, suggesting that Pdcd4 regulates AKT activity and cyclin D1 expression. Furthermore, knockdown of AKT in the Pdcd4 knockdown cells inhibited IKK phosphorylation, NF-κB activation, cyclin D1 promoter activity, and cyclin D1 expression as well as cell proliferation. Taken together, these findings suggest that activation of NF-κB by Pdcd4 knockdown through AKT contributes to the elevated expression of cyclin D1, thus providing new insights into how loss of Pdcd4 expression promotes tumor development.

Heterogeneous nuclear ribonucleoprotein C1/C2 controls the metastatic potential of glioblastoma by regulating PDCD4

MicroRNAs (miRNAs) have been implicated in the pathogenesis and progression of brain tumors. miR-21 is one of the most highly overexpressed miRNAs in glioblastoma multiforme (GBM), and its level of expression correlates with the tumor grade. Programmed cell death 4 (PDCD4) is a well-known miR-21 target and is frequently downregulated in glioblastomas in accordance with increased miR-21 expression. Downregulation of miR-21 or overexpression of PDCD4 can inhibit metastasis. Here, we investigate the role of heterogeneous nuclear ribonucleoprotein C1/C2 (hnRNPC) in the metastatic potential of the glioblastoma cell line T98G. hnRNPC bound directly to primary miR-21 (pri-miR-21) and promoted miR-21 expression in T98G cells. Silencing of hnRNPC lowered miR-21 levels, in turn increasing the expression of PDCD4, suppressing Akt and p70S6K activation, and inhibiting migratory and invasive activities. Silencing of hnRNPC reduced cell proliferation and enhanced etoposide-induced apoptosis. In support of a role for hnRNPC in the invasiveness of GBM, highly aggressive U87MG cells showed higher hnRNPC expression levels and hnRNPC abundance in tissue arrays and also showed elevated levels as a function of brain tumor grade. Taken together, our data indicate that hnRNPC controls the aggressiveness of GBM cells through the regulation of PDCD4, underscoring the potential usefulness of hnRNPC as a prognostic and therapeutic marker of GBM.

NF-κB and the link between inflammation and cancer

The nuclear factor-κB (NF-κB) transcription factor family has been considered the central mediator of the inflammatory process and a key participant in innate and adaptive immune responses. Coincident with the molecular cloning of NF-κB/RelA and identification of its kinship to the v-Rel oncogene, it was anticipated that NF-κB itself would be involved in cancer development. Oncogenic activating mutations in NF-κB genes are rare and have been identified only in some lymphoid malignancies, while most NF-κB activating mutations in lymphoid malignancies occur in upstream signaling components that feed into NF-κB. NF-κB activation is also prevalent in carcinomas, in which NF-κB activation is mainly driven by inflammatory cytokines within the tumor microenvironment. Importantly, however, in all malignancies, NF-κB acts in a cell type-specific manner: activating survival genes within cancer cells and inflammation-promoting genes in components of the tumor microenvironment. Yet, the complex biological functions of NF-κB have made its therapeutic targeting a challenge.

RNA helicases in infection and disease

RNA helicases unwind their RNA substrates in an ATP-dependent reaction, and are central to all cellular processes involving RNA. They have important roles in viral life cycles, where RNA helicases are either virus-encoded or recruited from the host. Vertebrate RNA helicases sense viral infections, and trigger the innate antiviral immune response. RNA helicases have been implicated in protozoic, bacterial and fungal infections. They are also linked to neurological disorders, cancer, and aging processes.   Genome-wide studies continue to identify helicase genes that change their expression patterns after infection or disease outbreak, but the mechanism of RNA helicase action has been defined for only a few diseases. RNA helicases are prognostic and diagnostic markers and suitable drug targets, predominantly for antiviral and anti-cancer therapies. This review summarizes the current knowledge on RNA helicases in infection and disease, and their growing potential as drug targets.

MicroRNAs: molecular features and role in cancer

microRNAs (miRNAs) are small noncoding endogenously produced RNAs that play key roles in controlling the expression of many cellular proteins. Once they are recruited and incorporated into a ribonucleoprotein complex miRISC, they can target specific mRNAs in a miRNA sequence-dependent process and interfere in the translation into proteins of the targeted mRNAs via several mechanisms. Consequently, miRNAs can regulate many cellular pathways and processes. Dysregulation of their physiological roles may largely contribute to disease. In particular, in cancer, miRNAs can be involved in the deregulation of the expression of important genes that play key roles in tumorigenesis, tumor development, and angiogenesis and have oncogenic or tumor suppressor roles. This review focuses on the biogenesis and maturation of miRNAs, their mechanisms of gene regulation, and the way their expression is deregulated in cancer. The involvement of miRNAs in several oncogenic pathways such as angiogenesis and apoptosis, and in the inter-cellular dialog mediated by miRNA-loaded exosomes as well as the development of new therapeutical strategies based on miRNAs will be discussed.

Tumor suppressor PDCD4 represses internal ribosome entry site-mediated translation of antiapoptotic proteins and is regulated by S6 kinase 2

Apoptosis can be regulated by extracellular signals that are communicated by peptides such as fibroblast growth factor 2 (FGF-2) that have important roles in tumor cell proliferation. The prosurvival effects of FGF-2 are transduced by the activation of the ribosomal protein S6 kinase 2 (S6K2), which increases the expression of the antiapoptotic proteins X chromosome-linked Inhibitor of Apoptosis (XIAP) and Bcl-x(L). We now show that the FGF-2-S6K2 prosurvival signaling is mediated by the tumor suppressor programmed cell death 4 (PDCD4). We demonstrate that PDCD4 specifically binds to the internal ribosome entry site (IRES) elements of both the XIAP and Bcl-x(L) messenger RNAs and represses their translation by inhibiting the formation of the 48S translation initiation complex. Phosphorylation of PDCD4 by activated S6K2 leads to the degradation of PDCD4 and thus the subsequent derepression of XIAP and Bcl-x(L) translation. Our results identify PDCD4 as a specific repressor of the IRES-dependent translation of cellular mRNAs (such as XIAP and Bcl-x(L)) that mediate FGF-2-S6K2 prosurvival signaling and provide further insight into the role of PDCD4 in tumor suppression.

Clinical significance of programmed cell death 4 expression in malignant progression of human nasal inverted papillomas

Programmed cell death 4 (PDCD4) is a novel tumor suppressor gene that can inhibit tumor neoplastic transformation and progression in cultured cells and gene knock-out mouse models. Lost or decreased PDCD4 expression has been associated with progression and prognosis of multiple types of human tumors. However, the expression and clinical significance of PDCD4 in nasal inverted papillomas (NIPs) has not been investigated. We compared PDCD4 expression in 64 samples of NIPs, 23 of associated squamous cell carcinomas (SCCs), and 19 normal nasal samples at mRNA and protein levels by RT-PCR, western blot analysis, and immunohistochemistry. PDCD4 mRNA expression was reduced in 52% of NIP frozen samples (13/25), and the protein level was diminished in 56.3% of samples (36/64) as compared with 19 normal nasal samples, which expressed high levels of PDCD4 mRNA and protein. Furthermore, altered expression of PDCD4 was associated with the clinicopathological features Krouse stage and dysplasia. Importantly, we found a strong negative correlation of PDCD4 expression and Ki-67 labeling index in NIPs (r=-0.6645, p<0.001). In addition, the 3 tissue-sample groups significantly differed in PDCD4 expression and Ki-67 labeling index. Thus, PDCD4 expression may play a key role in pre-cancerous lesions of human NIPs and may help predict malignant progression from benign nasal tumors to associated SCC.

Promoter cloning and characterization of the human programmed cell death protein 4 (pdcd4) gene: evidence for ZBP-89 and Sp-binding motifs as essential Pdcd4 regulators

Pdcd4 (programmed cell death protein 4) is an important novel tumour suppressor inhibiting transformation, translation, invasion and intravasation, and its expression is down-regulated in several cancers. However, little is known about the transcriptional regulation and the promoter of this important tumour suppressor. So far the following is the first comprehensive study to describe the regulation of Pdcd4 transcription by ZBP-89 (zinc-finger-binding protein 89), besides characterizing the gene promoter. We identified the transcriptional start sites of the human pdcd4 promoter, a functional CCAAT-box, and the basal promoter region. Within this basal region, computer-based analysis revealed several potential binding sites for ZBPs, especially for Sp (specificity protein) family members and ZBP-89. We identified four Sp1/Sp3/Sp4-binding elements to be indispensable for basal promoter activity. However, overexpression of Sp1 and Sp3 was not sufficient to enhance Pdcd4 protein expression. Analysis in different solid cancer cell lines showed a significant correlation between pdcd4 and zbp-89 mRNA amounts. In contrast with Sp transcription factors, overexpression of ZBP-89 led to an enhanced expression of Pdcd4 mRNA and protein. Additionally, specific knockdown of ZBP-89 resulted in a decreased pdcd4 gene expression. Reporter gene analysis showed a significant up-regulation of basal promoter activity by co-transfection with ZBP-89, which could be abolished by mithramycin treatment. Predicted binding of ZBP-89 to the basal promoter was confirmed by EMSA (electrophoretic mobility-shift assay) data and supershift analysis for ZBP-89. Taken together, data for the first time implicate ZBP-89 as a regulator of Pdcd4 by binding to the basal promoter either alone or by interacting with Sp family members.

Tumour suppressive function and modulation of programmed cell death 4 (PDCD4) in ovarian cancer

Background

Programmed cell death 4 (PDCD4), originally identified as the neoplastic transformation inhibitor, was attenuated in various cancer types. Our previous study demonstrated a continuous down-regulation of PDCD4 expression in the sequence of normal-borderline-malignant ovarian tissue samples and a significant correlation of PDCD4 expression with disease-free survival. The objective of the current study was to further investigate the function and modulation of PDCD4 in ovarian cancer cells.

Principal Findings

We demonstrated that ectopic PDCD4 expression significantly inhibited cell proliferation by inducing cell cycle arrest at G₁ stage and up-regulation of cell cycle inhibitors of p27 and p21. Cell migration and invasion were also inhibited by PDCD4. PDCD4 over-expressing cells exhibited elevated phosphatase and tensin homolog (PTEN) and inhibited protein kinase B (p-Akt). In addition, the expression of PDCD4 was up-regulated and it was exported to the cytoplasm upon serum withdrawal treatment, but it was rapidly depleted via proteasomal degradation upon serum re-administration. Treatment of a phosphoinositide 3-kinase (PI3K) inhibitor prevented the degradation of PDCD4, indicating the involvement of PI3K-Akt pathway in the modulation of PDCD4.

Conclusion

PDCD4 may play a critical function in arresting cell cycle progression at key checkpoint, thus inhibiting cell proliferation, as well as suppressing tumour metastasis. The PI3K-Akt pathway was implied to be involved in the regulation of PDCD4 degradation in ovarian cancer cells. In response to the stress condition, endogenous PDCD4 was able to shuttle between cell compartments to perform its diverted functions.

PDCD4 expression inversely correlated with miR-21 levels in gastric cancers

PURPOSE

The specific aim of this study was to investigate whether the PDCD4 gene is involved in the development and progression of gastric cancer.

METHODS

We examined the genetic and epigenetic alterations of the PDCD4 gene as well as the expression of PDCD4 protein in gastric cancers. The mRNA expression of PDCD4 and miRNA-21 expression were also analyzed using quantitative real-time RT-PCR.

RESULTS

Loss or reduced PDCD4 expression was observed in 79 (36.7%) of 215 gastric cancer specimens. Statistically, altered PDCD4 expression was not associated with the clinicopathological parameters, including tumor differentiation, location, lymph node metastasis and overall survival (P > 0.05). miRNA-21 overexpression was frequently detected in gastric cancers (31 of 46, 67.4%), and there was a significant inverse correlation between miRNA-21 and PDCD4 protein expression (P = 0.029), but not between miRNA-21 and PDCD4 mRNA expression. In genetic analysis, no mutation was detected in the coding region of the PDCD4 gene, and promoter hypermethylation was found in 24 (36.4%) of the 66 gastric cancer samples.

CONCLUSIONS

Our data suggest that overexpression of miRNA-21 and reduced or loss of PDCD4 expression may play a role in the development and progression of gastric cancers.

Association of microRNA-21 expression with its targets, PDCD4 and TIMP3, in pancreatic ductal adenocarcinoma

Since the discovery of small non-coding RNAs, the analyses of microRNA (miRNA) expression patterns in human cancer have provided new insights into cancer biology. miRNA-21 has been suggested to be one of the miRNAs that have an important role in the development or biological behavior of a variety of malignancies, including pancreatic cancer. This study was conducted to evaluate the relationship between the expression of miRNA-21 and that of its molecular targets, programmed cell death 4 (PDCD4) and tissue inhibitor of metalloproteinase (TIMP3), in pancreatic ductal adenocarcinoma. The study included 65 pancreatic ductal adenocarcinomas and 5 normal pancreatic tissue specimens for comparison. The miRNA expression profiling of five selected pancreatic ductal adenocarcinomas and five normal pancreatic specimens was performed using a microarray platform, and was evaluated by a hierarchical clustering analysis. The miRNA most highly expressed in pancreatic ductal adenocarcinomas (ie, miRNA-21) was further assessed by quantitative real-time reverse transcription PCR (RT-PCR) assays in the 65 pancreatic ductal adenocarcinoma cases. The expression pattern of its molecular targets (eg, PDCD4 and TIMP3) in pancreatic ductal adenocarcinoma was examined immunohistochemically. In the microarray analyses, 28 miRNAs were upregulated in pancreatic ductal adenocarcinoma compared with normal pancreatic tissue, whereas 48 miRNAs were downregulated. miRNA-21 was the most significantly overexpressed miRNA in the pancreatic ductal adenocarcinomas analyzed, and was also highly expressed in 75% of the 65 pancreatic ductal adenocarcinomas examined by real-time RT-PCR. High miRNA-21 expression was correlated with a worse prognosis in the pancreatic ductal adenocarcinoma patients (P=0.045). The immunohistochemical expression patterns of PDCD4 (reduced nuclear staining pattern) and TIMP3 (downregulated expression) were significantly associated with both the upregulated miR-21 expression (P<0.05) and the poor survival of the patients (P<0.001 and P=0.001, respectively). Our data suggest that an overexpression of miRNA-21 is, therefore, associated with the biological behavior of pancreatic ductal adenocarcinoma via the downregulation of the expression of tumor suppressors, PDCD4 and TIMP3, thus resulting in tumor progression and the adverse clinical course of pancreatic ductal adenocarcinoma.

Down-regulation of PDCD4 expression is an independent predictor of poor prognosis in human renal cell carcinoma patients

OBJECTIVES

The tumor suppressor gene entitled programmed cell death 4 (PDCD4) encodes a protein that inhibits neoplastic transformation and invasion. The aim of this study was to investigate the expression of PDCD4 and its prognostic roles in human renal cell carcinoma (RCC).

MATERIALS AND METHODS

A total of 32 paired fresh tumor specimens and adjacent non-cancerous renal tissue from RCC patients by western blot to detect the difference of PDCD4 expression in tumor tissues and non-cancerous tissues. 66 RCC paraffin-embedded specimens and 18 normal renal tissues were analyzed by immunohistochemistry to investigate the association of PDCD4 expression with RCC clinicopathological features.

RESULTS

PDCD4 expression was significantly decreased in RCC compared with normal renal tissues (P = 0.03), and it was found to be significantly associated with RCC metastasis (P = 0.007), tumor T-stage (P = 0.022) and tumor grade (P = 0.015). The mean overall survival was significantly decreased in the low PDCD4 group compared to the high PDCD4 group (low PDCD4: mean overall survival 41.9 months, high PDCD4: mean overall survival 52.9 months, P = 0.008).

CONCLUSION

PDCD4 expression strongly correlated to RCC stage, tumor grade, tumor metastasis and tumor-related death. PDCD4 expression was also appears to be a marker in RCC prognosis.

Expression of programmed cell death protein 4 (PDCD4) and miR-21 in urothelial carcinoma

BACKGROUND

We investigated the role of the programmed cell death 4 (PDCD4) tumor suppressor gene in specimens of transitional cell carcinoma and of healthy individuals.

METHODS

PDCD4 immunohistochemical expression was investigated in 294 cases in histologically proven transitional cell carcinoma in different tumorous stages (28 controls, 122 non-muscle invasive urothelial carcinoma, stages Tis-T1, 119 invasive transitional cell carcinoma stages T2-T4 and 25 metastases). MiR-21 expression, an important PDCD4 regulator, was assessed with real-time PCR analysis and showed inverse correlation to tissue PDCD4 expression.

RESULTS

Nuclear and cytoplasmatic PDCD4 immunostaining decreased significantly with histopathological progression of the tumor (p<0001). Controls showed strong nuclear and cytoplasmatic immunohistochemical staining. MiR-21 up regulation in tissue corresponded to PDCD4 suppression.

CONCLUSIONS

These data support a decisive role for PDCD4 down regulation in transitional cell carcinoma and confirm miR-21 as a negative regulator for PDCD4. Additionally, PDCD4 immunohistochemical staining turns out to be a possible diagnostic marker for transitional cell carcinoma.

Association of Tumor Suppressor Protein Pdcd4 With Ribosomes Is Mediated by Protein-Protein and Protein-RNA Interactions

The Pdcd4 (programmed cell death gene 4) gene has been implicated as a novel tumor suppressor gene in the development of several types of human cancer. The Pdcd4 protein is believed to act as a translation suppressor of mRNAs containing structured 5' UTRs. Pdcd4 contains 2 copies of so-called MA3 domains that mediate tight interactions with the translation initiation factor eIF4A, resulting in the inhibition of the eIF4A helicase activity. The N-terminal part of Pdcd4, which has been less well characterized, binds RNA in vitro, but as yet, it has not been clear whether RNA binding by Pdcd4 plays a role in vivo. Here, the authors have identified 2 highly conserved clusters of basic amino acid residues that are essential for the RNA binding activity of Pdcd4. They also show that a substantial fraction of Pdcd4 is present, together with small ribosomal subunits, in translation preinitiation complexes. Using mutants that disrupt RNA binding or the Pdcd4-eIF4A interaction, they demonstrate that the ribosomal association of Pdcd4 is dependent on its RNA binding activity as well as on its ability to interact with eIF4A. Their work provides the first direct evidence for an essential role of the Pdcd4 RNA binding activity in vivo and suggests that RNA binding is required for recruiting Pdcd4 to the translation machinery.

Programmed cell death 4 (Pdcd4) expression in colorectal adenocarcinoma: Association with clinical stage

The aim of this study was to examine the role of Programmed cell death 4 (Pdcd4) in colorectal adenocarcinoma (CRA). Pdcd4 expression was observed in both the nucleus and cytoplasm in colorectal adenocarcinoma, whereas Pdcd4 was expressed in the nucleus in normal colonic epithelial cells. Loss or weak expression of Pdcd4 was identified in 44 cases (40.7%) of cancer cells. Pdcd4 expression was associated with an increase in the nodal and clinical stage (p=0.022 and p=0.016, respectively). Nuclear staining was identified in 66 cases (61.15%), with no correlation with clinicopathological factors. Conversely, cytoplasmic staining for Pdcd4 was observed in 45 cases (41.7%), and increased according to nodal and clinical stage (p=0.011 and p=0.009, respectively), indicating that aberrant Pdcd4 expression leads to tumor progression. However, Pdcd4 expression was not correlated to disease-free survival time. This study demonstrated that during the tumorigenesis of CRA, loss of nuclear Pdcd4 expression occurs, and during tumor progression, aberrant cytoplasmic expression is present, suggesting a higher clinical stage. Although loss of Pdcd4 was not significantly correlated with survival time, as the prognosis of colorectal cancer varies depending on clinical stage including invasion depth, nodal status and metastatic status, cytoplasmic Pdcd4 expression may be a favorable prognostic marker in CRA.

Tumor suppressor protein Pdcd4 inhibits translation of p53 mRNA

The tumor suppressor protein Pdcd4 is thought to suppress translation of mRNAs containing structured 5'-UTRs by interacting with translation initiation factor eIF4A and inhibiting its helicase activity. However, natural target mRNAs regulated by Pdcd4 so far are mostly unknown. Here, we identified p53 mRNA as a translational target of Pdcd4. We found that Pdcd4 is associated with p53 mRNA and suppresses its translation. The inhibitory effect of Pdcd4 on the translation of p53 mRNA depends on the ability of Pdcd4 to interact with eIF4A and is mediated by the 5'-UTR of p53 mRNA, which is able to form a stable stem-loop structure. We show that treatment of cells with DNA-damaging agents decreases the expression of Pdcd4. This suggests that translational suppression by Pdcd4 plays a role in maintaining a low level of p53 in unstressed cells and that this suppression is abrogated due to low levels of Pdcd4 after DNA damage. Overall, our work demonstrates for the first time that Pdcd4 is directly involved in translational suppression of a natural mRNA with a 5'-structured UTR and provides novel insight into the translational control of p53 expression.

Loss of programmed cell death 4 induces apoptosis by promoting the translation of procaspase-3 mRNA

The programmed cell death 4 (Pdcd4), a translation inhibitor, plays an essential role in tumor suppression, but its role in apoptosis remains unclear. Here we show that Pdcd4 is a critical suppressor of apoptosis by inhibiting the translation of procaspase-3 mRNA. Pdcd4 protein decreased more rapidly through microRNA-mediated translational repression following apoptotic stimuli than did the activation of procaspase-3, cleavage of poly(ADP)ribose polymerase (PARP) by active caspase-3, and nuclear fragmentation. Strikingly, the loss of Pdcd4 by the specific RNA interference increased procaspase-3 expression, leading to its activation and PARP cleavage even without apoptotic stimuli, and sensitized the cells to apoptosis. Thus, our findings provide insight into a novel mechanism for Pdcd4 as a regulator of apoptosis.

MicroRNA-499-5p promotes cellular invasion and tumor metastasis in colorectal cancer by targeting FOXO4 and PDCD4

MicroRNAs (miRNAs) regulate tumor progression and invasion via direct interaction with target messenger RNAs (mRNAs). We defined miRNAs involved in cancer metastasis (metastamirs) using an established in vitro colorectal cancer (CRC) model of minimally metastatic cells (SW480 line) from a colon adenocarcinoma primary lesion and highly metastatic cells (SW620 line) from a metastatic lymph node from the same patient 1 year later. We used microarray analysis to identify miRNAs differentially expressed in SW480 and SW620 cells, focusing on miR-499-5p as a novel candidate prometastatic miRNA whose functions in cancer had not been studied. We confirmed increased miR-499-5p levels in highly invasive CRC cell lines and lymph node-positive CRC specimens. Furthermore, enhancing the expression of miR-499-5p promoted CRC cell migration and invasion in vitro and lung and liver metastasis in vivo, while silencing its expression resulted in reduced migration and invasion. Additionally, we identified FOXO4 and PDCD4 as direct and functional targets of miR-499-5p. Collectively, these findings suggested that miR-499-5p promoted metastasis of CRC cells and may be useful as a new potential therapeutic target for CRC.

An essential role of PDCD4 in progression and malignant proliferation of gastrointestinal stromal tumors

Programmed cell death 4 (PDCD4) is a tumor suppressor that can inhibit tumorigenesis by suppressing activator protein (AP)-1 activation and protein translation. Lost or decreased PDCD4 expression has been found in multiple types of human cancers, which was also associated with progression and metastasis of the tumors. However, the status and significance of PDCD4 in gastrointestinal stromal tumors have not been evaluated. In the present study, we examined the PDCD4 expression in a total of 63 gastrointestinal stromal tumor samples at both mRNA and protein levels by RT-PCR, western blot, and immunohistochemistry. We demonstrated that the expression of PDCD4 mRNA was diminished in 68% (17/25) of the tumor samples, and the level of PDCD4 protein appeared to be decreased in 66.7% (42/63) of the samples, as compared to adjacent normal gastrointestinal tissues, which expressed high levels of PDCD4 mRNA and protein. In addition, altered expression of PDCD4 was associated with clinicopathological parameters including risk group, tumor size, and mitosis. Moreover, PDCD4 expression had a negative correlation with the Ki-67 labeling index (r = -0.6059, P < 0.0001). All these results suggest that downregulation of PDCD4 expression may have an essential role in the progression and malignant proliferation of human gastrointestinal stromal tumors.

Inhibitors of translation initiation as cancer therapeutics

Deregulated translation initiation is implicated extensively in cancer initiation and progression. Several translation initiation factors cooperate with known oncogenes, are elevated in human tumors and have been implicated in drug resistance. Consequently, there is a great deal of interest in targeting this process to develop new chemotherapeutics, especially since clinical trial results have been mixed when targeting upstream pathways, such as the mammalian target of rapamycin. Several inhibitors have been characterized over the last 5 years that target the ribosome recruitment phase (eukaryotic initiation factor [eIF]4E [antisense oligonucleotides and 4EGI-1] or eIF4A [pateamine A, hippuristanol and silvestrol]), some of which demonstrate activity in preclinical cancer models. The promise of these inhibitors as chemotherapeutics highlights the importance of targeting this pathway and supports efforts aimed at identifying the most susceptible targets. In addition, the framework in which translation inhibitors would be best employed (i.e., as single agents or as adjuvant therapy) in the clinic remains to be explored systematically. Small-molecule inhibitors of translation initiation are validating the idea that protein synthesis is a legitimate target for curtailing tumor growth.

Protein arginine methyltransferase 5 accelerates tumor growth by arginine methylation of the tumor suppressor programmed cell death 4

Programmed cell death 4 (PDCD4) has been described as a tumor suppressor, with high expression correlating with better outcomes in a number of cancer types. Yet a substantial number of cancer patients with high PDCD4 in tumors have poor survival, suggesting that oncogenic pathways may inhibit or change PDCD4 function. Here, we explore the significance of PDCD4 in breast cancer and identify protein arginine methyltransferase 5 (PRMT5) as a cofactor that radically alters PDCD4 function. Specifically, we find that coexpression of PDCD4 and PRMT5 in an orthotopic model of breast cancer causes accelerated tumor growth and that this growth phenotype is dependent on both the catalytic activity of PRMT5 and a site of methylation within the N-terminal region of PDCD4. In agreement with the xenograft model, elevated PDCD4 expression was found to correlate with worse outcome within the cohort of breast cancer patients whose tumors contain higher levels of PRMT5. These results reveal a new cofactor for PDCD4 that alters its tumor suppressor functions and point to the utility of PDCD4/PRMT5 status as both a prognostic biomarker and a potential target for chemotherapy.

Pdcd4 directly binds the coding region of c-myb mRNA and suppresses its translation

Pdcd4 is a novel tumor suppressor protein that functions in the nucleus and the cytoplasm, and appears to be involved in the regulation of transcription and translation. In the cytoplasm, Pdcd4 has been implicated in the suppression of translation of mRNAs containing structured 5'-untranslated regions; however, the mechanisms that recruit Pdcd4 to specific target mRNAs and the identities of these mRNAs are mostly unknown. In this study, we have identified c-myb mRNA as the first natural translational target mRNA of Pdcd4. We have found that translational suppression of c-myb mRNA by Pdcd4 is dependent on sequences located within the c-myb-coding region. Furthermore, we have found that the N-terminal domain of Pdcd4 has an important role in targeting Pdcd4 to c-myb RNA by mediating preferential RNA binding to the Pdcd4-responsive region of c-myb mRNA. Overall, our work demonstrates for the first time that Pdcd4 is directly involved in translational suppression of a natural mRNA and provides the first evidence for a key role of the RNA-binding domain in targeting Pdcd4 to a specific mRNA.

Structure of the tandem MA-3 region of Pdcd4 protein and characterization of its interactions with eIF4A and eIF4G: molecular mechanisms of a tumor suppressor

One of the key regulatory points of translation initiation is recruitment of the 43S preinitation complex to the 5' mRNA cap by the eIF4F complex (eIF4A, eIF4E, and eIF4G). The tumor suppressor protein Pdcd4 has been shown to inhibit cap-dependent translation by interacting tightly with the RNA helicase eIF4A via its tandem MA-3 domains. The NMR studies reported here reveal a fairly extensive and well defined interface between the two MA-3 domains in solution, which appears to be stabilized by a network of interdomain salt bridges and hydrogen bonds, and reveals a unique orientation of the two domains. Characterization of the stoichiometry of the Pdcd4-eIF4A complex suggests that under physiological conditions Pdcd4 binds to a single molecule of eIF4A, which involves contacts with both Pdcd4 MA-3 domains. We also show that contacts mediated by a conserved acidic patch on the middle MA-3 domain of Pdcd4 are essential for forming a tight complex with eIF4A in vivo, whereas the equivalent region of the C-terminal MA-3 domain appears to have no role in complex formation in vivo. The formation of a 1:1 eIF4A-Pdcd4 complex in solution is consistent with the reported presence in vivo of only one molecule of eIF4A in the eIF4F complex. Pdcd4 has also been reported to interact directly with the middle region of eIF4G, however, we were unable to obtain any evidence for even a weak, transient direct interaction.

Curcumin regulates miR-21 expression and inhibits invasion and metastasis in colorectal cancer

Curcumin has promising potential in cancer prevention and therapy by interacting with proteins and modifying their expression and activity, which includes transcription factors, inflammatory cytokines and factors of cell survival, proliferation and angiogenesis. miR-21 is overexpressed in many tumours, promoting progression and metastasis. In the present study, we examined the potential of curcumin to regulate miR-21, tumour growth, invasion and in vivo metastasis in colorectal cancer. In Rko and HCT116 cells, we identified two new transcriptional start sites of the miR-21 gene and delineated its promoter region. PMA stimulation induced miR-21 expression via motifs bound with AP-1 (activator protein 1) transcription factors. Curcumin treatment reduced miR-21 promoter activity and expression in a dose-dependent manner by inhibiting AP-1 binding to the promoter, and induced the expression of the tumour suppressor Pdcd4 (programmed cell death protein 4), which is a target of miR-21. Curcumin-treated Rko and HCT116 cells were arrested in the G2/M phase with increasing concentrations. Furthermore, curcumin inhibited tumour growth, invasion and in vivo metastasis in the chicken-embryo-metastasis assay [CAM (chorionallantoic membrane) assay]. Additionally, curcumin significantly inhibited miR-21 expression in primary tumours generated in vivo in the CAM assay by Rko and HCT116 cells (P<0.00006 and P<0.035 respectively). Taken together, this is the first paper to show that curcumin inhibits the transcriptional regulation of miR-21 via AP-1, suppresses cell proliferation, tumour growth, invasion and in vivo metastasis, and stabilizes the expression of the tumour suppressor Pdcd4 in colorectal cancer.

MicroRNA-21 and PDCD4 expression in colorectal cancer

INTRODUCTION

MiRNAs regulate gene expression by binding to target sites and initiating translational repression and/or mRNA degradation. Studies have shown that miR-21 exerts its oncogenic activity by targeting the PDCD4 tumour suppressor 3'-UTR. However, the mechanism of this regulation is poorly understood. In colorectal cancer, loss of PDCD4 has been reported in association with increased tumour aggressiveness and poor prognosis. The purpose of this study was to delineate the interaction between PDCD4 and its oncogenic modulator miR-21 in colorectal cancer.

METHODS

A cohort of 48 colorectal tumours, 61 normal tissues and 7 polyps were profiled for miR-21 and PDCD4 gene expression. A subset of 48 specimens (31 tumours and 17 normal tissues) were analysed for PDCD4 protein expression by immunohistochemistry.

RESULTS

A significant inverse relationship between miR-21 and PDCD4 gene expression (p < 0.001) was identified by RT-qPCR. In addition, significant reduction of PDCD4 (p < 0.001) expression and reciprocal upregulation of miR-21 (p = 0.005) in a progressive manner from tumour-polyp-normal mucosae was identified. Analysis of protein expression by IHC revealed loss of PDCD4 staining in tumour tissue. Patients with disease recurrence had higher levels of miR-21.

CONCLUSION

This study demonstrates the inverse relationship between miR-21 and PDCD4, thus suggesting that miR-21 post-transcriptionally modulates PDCD4 via mRNA degradation. Pharmacological manipulation of the miR-21/PDCD4 axis could represent a novel therapeutic strategy in the treatment of colorectal cancer.

The oncogenic and tumour suppressive roles of microRNAs in cancer and apoptosis

MicroRNAs (miRNAs) are small, non-coding, endogenous RNAs that regulate gene expression at the post-transcriptional level. MiRNAs play important roles in regulating a variety of biological process such as proliferation, differentiation and apoptosis. It has been demonstrated that miRNAs have a crucial function in oncogenesis by regulating cell proliferation and apoptosis as oncogenes or tumour suppressors. As several reports have underlined the possible contribution of miRNAs to promote or evade apoptosis, it seems that the dysregulation of miRNAs involved in apoptosis may provide a mechanism for cancer development. Given emerging evidence that points to oncogenic and tumour suppressive roles of miRNAs in cancer and apoptosis, it is thought that manipulating miRNA expression level may be a potential therapeutic strategy for curing cancer.

DSC3 expression is regulated by p53, and methylation of DSC3 DNA is a prognostic marker in human colorectal cancer

Background:

Desmocollin 3 (DSC3), a member of the cadherin superfamily and integral component of desmosomes, is involved in carcinogenesis. However, the role of DSC3 in colorectal cancer (CRC) has not yet been established.

Methods:

Desmocollin 3 expression in CRC cell lines was analysed by RT–PCR and western blotting. Methylation status of DSC3 was examined by demethylation tests, methylation-specific PCR, and bisulphite sequencing (BS). The regulatory role of p53 was investigated by transfection.

Results:

Desmocollin 3 was downregulated in CRC cells at mRNA and protein levels. Desmocollin 3 expression was restored in five out of seven cell lines after 5-aza-2′-deoxycytidine (DAC) treatment. A heterogeneous methylation pattern was detected by BS in promoter region and exon 1 of DSC3. Methylation of DSC3 genomic sequences was found in 41% (41 out of 99) of primary CRC, being associated with poor prognosis (P=0.002). Transfection of p53 alone or in combination of DAC increased the DSC3 expression. Similarly, treatment with p53 inducer adriamycin alone or in combination with DAC enhanced DSC3 expression.

Conclusions:

DNA methylation contributes to downregulation of DSC3 in CRC cell lines. Methylation status of DSC3 DNA is a prognostic marker for CRC. P53 appears to have an important role in regulating DSC3 expression.

Programmed cell death 4 (PDCD4) expression during multistep Barrett's carcinogenesis

Aim

To test the contribution of programmed cell death 4 (PDCD4) tumour suppressor gene in Barrett's carcinogenesis.

Methods

PDCD4 immunohistochemical expression was assessed in 88 biopsy samples obtained from histologically proven long-segment Barrett's mucosa (BM; 25 non-intestinal columnar metaplasia, 25 intestinal metaplasia (IM), 16 low-grade intraepithelial neoplasia (LG-IEN), 12 high-grade IEN (HG-IEN) and 10 Barrett's adenocarcinoma (BAc)). As controls, 25 additional samples of native oesophageal mucosa (N) were obtained from patients with dyspepsia. To further support the data, the expression levels of miR-21, an important PDCD4 expression regulator, in 14 N, 5 HG-IEN and 11 BAc samples were determined by quantitative real-time PCR analysis.

Results

PDCD4 immunostaining decreased progressively and significantly with the progression of the phenotypic changes occurring during Barrett's carcinogenesis (p<0.001). Normal basal squamous epithelial layers featured strong PDCD4 nuclear immunoreaction (mostly coexisting with weak–moderate cytoplasmic staining). Non-intestinal columnar metaplasia and intestinal metaplasia preserved a strong nuclear immunostaining; conversely, a significant decrease in PDCD4 nuclear expression was seen in dysplastic (LG-IEN and HG-IEN) and neoplastic lesions. Weak–moderate cytoplasmic immunostaining was evident in cases of LG-IEN, while HG-IEN and BAc samples showed weak cytoplasmic or no protein expression. As expected, miR-21 expression was significantly upregulated in HG-IEN and BAc samples, consistently with PDCD4 dysregulation.

Conclusions

These data support a significant role for PDCD4 downregulation in the progression of BM to BAc, and confirm miR-21 as a negative regulator of PDCD4 in vivo. Further efforts are needed to validate PDCD4 as a potential prognostic marker in patients with Barrett's oesophagus.

PDCD4 nuclear loss inversely correlates with miR-21 levels in colon carcinogenesis

Programmed cell death 4 (PDCD4) has recently been demonstrated to be a new tumor suppressor gene involved in colon carcinogenesis. PDCD4 immunohistochemical expression was assessed in 300 polypoid lesions of the colon mucosa (50 hyperplastic polyps [HP], 50 serrated adenomas [SA], 50 tubular adenomas with low-grade-intraepithelial neoplasia [LG-IEN], 50 tubular adenomas with high-grade-IEN [HG-IEN]), and in 50 colon adenocarcinomas (CRC). As normal controls, we considered 50 biopsy samples obtained from patients with irritable bowel syndrome (N). We further investigated PDCD4 messenger RNA (mRNA) levels by quantitative real-time polymerase chain reaction (PCR) in a different series of N, LG-IEN, HG-IEN, and CRC biopsy samples. miR-21 expression (an important PDCD4-expression regulator) was also determined by quantitative real-time PCR and in situ hybridization. Normal colocytes and HP featured strong PDCD4 nuclear immunostaining whereas a significantly lower PDCD4 nuclear expression was observed in dysplasia (low- and high-grade adenomas and SA) and invasive CRC. PDCD4 immunostaining and mRNA levels decreased significantly as the phenotypic changes occurring during colon carcinogenesis progressively increased (p < 0.001). As expected, miR-21 expression was significantly upregulated in preneoplastic/neoplastic samples, consistent with PDCD4 downregulation. These results consistently support the use of nuclear PDCD4 immunohistochemical downregulation as a novel biomarker for the diagnosis of dysplastic/neoplastic lesions in colon biopsy samples.

Programmed cell death 4 (PDCD4) enhances the sensitivity of gastric cancer cells to TRAIL-induced apoptosis by inhibiting the PI3K/Akt signaling pathway

OBJECTIVE

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is thought to be a promising anti-neoplastic agent because of its ability to selectively induce apoptosis in cancer cells. However, some cancer cells are resistant to TRAIL. The mechanisms underlying this resistance are unclear. The aim of this study was to explore the role of programmed cell death 4 (PDCD4) in regulating TRAIL sensitivity in gastric cancer cells.

METHODS

PDCD4 complementary DNA and PDCD4-specific short-hairpin RNA (shRNA) fragments were transfected into TRAIL-sensitive and -resistant gastric cancer cells. Expression of PDCD4 and Akt was detected via western blot. Cell survival and apoptosis were measured using 3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry (FCM) assays.

RESULTS

We found that upregulation of PDCD4 enhanced TRAIL sensitivity in gastric cancer cells. Downregulation of PDCD4 decreased TRAIL sensitivity. Inhibition of Akt by the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 induced PDCD4 activity and enhanced TRAIL sensitivity in TRAIL-resistant gastric cancer cells.

CONCLUSION

We demonstrated that PDCD4 regulates TRAIL sensitivity in gastric cancer cells by inhibiting the PI3K/Akt signaling pathway.

IGFBP7 is a p53 target gene inactivated in human lung cancer by DNA hypermethylation

Insulin-like growth factor binding protein 7 (IGFBP7) was considered a tumor suppressor gene in lung cancer. However, the mechanism responsible for the downregulation of this gene has not yet been fully understood. In this study, we analyzed the epigenetic inactivation of IGFBP7 expression in human lung cancer. We found that 14 out of 16 lung cancer cell lines showed decreased expression of IGFBP7 compared to control cells by real-time RT-PCR, and 42 out of 90 patients (46.7%) with primary lung tumor exhibited negative staining of IGFBP7 by immunohistochemistry analysis. The IGFBP7 expression could be restored by demethylation agent 5-aza-2'-deoxycytidine (DAC) in 7 cancer cell lines. Methylation status of IGFBP7 was further evaluated by bisulfite sequencing (BS) and methylation-specific-PCR (MSP). It turned out that low expression of IGFBP7 was associated with DNA methylation in lung cancer cell lines and in primary lung tumors (P=0.019). To explore the regulatory role of p53 on IGFBP7, we transfected a wild type p53 expression vector into lung cancer cell lines H1299, H2228, and H82. Forced expression of p53 increased IGFBP7 expression only in H82 harboring no IGFBP7 methylation, while transfection in combination with DAC induced the expression of IGFBP7 in H1299 and H2228, in which IGFBP7 was methylated. Additionally, treatment with p53 inducer adriamycin (ADR) alone or in combination with DAC increased the expression of IGFBP7 in the 3 cell lines. Our data suggest that IGFBP7 is inactivated in lung cancer by DNA hypermethylation in both lung cancer cell lines and primary lung tumors, and IGFBP7 might be regulated by p53 in lung cancer cells.

PDCD4 gene silencing in gliomas is associated with 5'CpG island methylation and unfavourable prognosis

Programmed cell death 4 (PDCD4) is a newly described tumour suppressor that inhibits oncogenesis by suppressing gene transcription and translation. Loss of PDCD4 expression has been found in several types of human cancers including the most common cancer of the brain, the gliomas. However, the molecular mechanisms responsible for PDCD4 gene silencing in tumour cells remain unclear. Here we report the identification of 5′CpG island methylation as the predominant cause of PDCD4 mRNA silencing in gliomas. The methylation of the PDCD4 5′CpG island was found in 47% (14/30) of glioma tissues, which was significantly associated with the loss of PDCD4 mRNA expression (γ=−1.000, P < 0.0001). Blocking methylation in glioma cells using a DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine, restored the PDCD4 gene expression, inhibited their proliferation and reduced their colony formation capacity. Longitudinal studies of a cohort of 84 patients with gliomas revealed that poor prognosis of patients with high-grade tumours were significantly associated with loss of PDCD4 expression. Thus, our current study suggests, for the first time, that PDCD4 5′CpG island methylation blocks PDCD4 expression at mRNA levels in gliomas. These results also indicate that PDCD4 reactivation might be an effective new strategy for the treatment of gliomas.