Pdcd4, a colon cancer prognostic that is regulated by a microRNA

microRNA-21-induced dissociation of PDCD4 from rictor contributes to Akt-IKKβ-mTORC1 axis to regulate renal cancer cell invasion

Renal cancer metastasis may result from oncogenic forces that contribute to the primary tumor. We have recently identified microRNA-21 as an oncogenic driver of renal cancer cells. The mechanism by which miR-21 controls renal cancer cell invasion is poorly understood. We show that miR-21 directly downregulates the proapoptotic protein PDCD4 to increase migration and invasion of ACHN and 786-O renal cancer cells as a result of phosphorylation/activation of Akt and IKKβ, which activate NFκB-dependent transcription. Constitutively active (CA) Akt or CA IKKβ blocks PDCD4-mediated inhibition and restores renal cancer cell migration and invasion. PDCD4 inhibits mTORC1 activity, which was reversed by CA IKKβ. Moreover, CA mTORC1 restores cell migration and invasion inhibited by PDCD4 and dominant negative IKKβ. Moreover, PDCD4 negatively regulates mTORC2-dependent Akt phosphorylation upstream of this cascade. We show that PDCD4 forms a complex with rictor, an exclusive component of mTORC2, and that this complex formation is reduced in renal cancer cells due to increased miR-21 expression resulting in enhanced phosphorylation of Akt. Thus our results identify a previously unrecognized signaling node where high miR-21 levels reduce rictor-PDCD4 interaction to increase phosphorylation of Akt and contribute to metastatic fitness of renal cancer cells.

The PDCD4/miR-21 pathway in medullary thyroid carcinoma

Programmed cell death 4 (PDCD4) is a tumor suppressor gene involved in tumorogenesis. MicroRNA-21 (miR-21) specifically targets PDCD4, and recent studies suggest that PDCD4 is also regulated by Akt (antiapoptotic regulator within phosphatidylinositol 3-kinase). Medullary thyroid carcinoma (MTC) is a rare neuroendocrine cancer, and disease stage at diagnosis represents the main prognostic indicator. A consecutive series of 64 MTCs was considered. REarranged during Transfection (RET) and rat sarcoma (RAS) mutation status was assessed by direct sequencing. Quantitative real-time polymerase chain reaction was used to quantify mature hsa-miR-21. PDCD4 and Ki-67 immunostaining was performed with an automated platform. Immunoblot analysis of PI3K/Akt pathway was done on thyroid tissues. MTCs were consistently associated with miR-21 up-regulation (P < .0016) and featured significant PDCD4 nuclear down-regulation. An inverse correlation emerged between miR-21 overexpression and PDCD4 down-regulation (P = .0013). At enrollment, high miR-21 levels were associated with high calcitonin levels (P = .0003), lymph node metastases (P = .001), and advanced stages (P = .0003). At the end of follow-up, high miR-21 levels were associated with biochemically persistent disease (P = .0076). At enrollment, instead, PDCD4 nuclear down-regulation was associated with high calcitonin levels (P = .04), more advanced stages of disease (P < .01), and persistent disease after the follow-up (P = .02). p-Akt was more expressed in RAS-mutated MTC than in nonmutated cancers and normal tissue. This study showed, in MTCs, that miR-21 regulates PDCD4 expression and also that the miR-21/PDCD4 pathway correlates with clinicopathological variables and prognosis. Further studies should investigate the role of miR-21 as a prognostic biomarker and the feasibility of using PDCD4-restoring strategies as a therapeutic approach to MTC.

miR-21 increases the programmed cell death 4 gene-regulated cell proliferation in head and neck squamous carcinoma cell lines

MicroRNAs (miRs) are small non-coding RNAs that regulate the translation of many genes in normal and cancer cells where they are frequently dysregulated promoting tumor progression. Several studies have illustrated the potential of manipulating miR expression in cancer research and therapy. The aim of the present study was to investigate expression patterns of a panel of miRs in head and neck squamous cell carcinoma (HNSCC) shown to be relevant in other carcinomas and to elucidate their role if dysregulated. We performed analysis of miR‑21, -200c, -138-1, -138-2, -25 and -34 expression by qRT-PCR in 6 HNSCC cell lines and computerized search for genetic targets of dysregulated miRNA-21 (miR‑21). Lipofection of mock and anti-miR-21 and determination of expression efficiencies and final programmed cell death 4 (PDCD4) expression were carried out by luciferase assay and western blotting. MTT assay was used to measure cell proliferation and flow cytometry was performed for cell cycle analysis. Expression of miR-21 was most prominently upregulated in the HNSCC cell lines, particularly in UM-SCC11B (6.45±0.25-fold, P<0.05) and UM-SCC9 (4.35±0.22-fold, P<0.05) as compared to primary epidermal keratinocytes used as control. The expression levels of the other miRs showed no difference except for miR-34 and -138-1 each in one cell line. Subsequent transfection of precursor miR-21 stimulated proliferation while anti-miR-21 inhibited proliferation of both cell lines. PDCD4 was identified with software designed for this purpose as potential target gene of miR-21. Subsequently, its role in HNSCC lines was experimentally confirmed by regulation of PDCD4 transfecting miR-21 mimics and anti-miR-21. Finally, we showed that PDCD4 is negatively regulated by miR-21 at the post-transcriptional level via binding to the 3'-untranslated region of PDCD4 mRNA. A role of upregulated miR-21 and reduced PDCD4 stimulating the proliferation was demonstrated in HNSCC lines and, in turn, transfection of anti-miR-21 upregulating PDCD4 reduced the cellular division rate. We explored miR-21 and PDCD4 expression as markers of progression and prognosis and for a potential translational value in the development of agents slowing growth of HNSCC and other carcinomas useful in palliative therapy or as a component of multi-modality treatments.

Atheroprotective pulsatile flow induces ubiquitin-proteasome-mediated degradation of programmed cell death 4 in endothelial cells

Objectives

We recently found low level of tumor suppressor programmed cell death 4 (PDCD4) associated with reduced atherosclerotic plaque area (unpublished). We investigated whether atheroprotective unidirectional pulsatile shear stress affects the expression of PDCD4 in endothelial cells.

Methods and Results

En face co-immunostaining of the mouse aortic arch revealed a low level of PDCD4 in endothelial cells undergoing pulsatile shear stress. Application of unidirectional pulsatile shear stress to human umbilical vein endothelial cells (HUVECs) decreased PDCD4 protein but not mRNA level. Immunoprecipitation revealed that pulsatile shear stress induced the coupling of ubiquitin with PDCD4 expression. The phosphatidyl inositol 3-kinase (PI3K)/Akt pathway was involved in this ubiquitin-proteasome–mediated degradation of PDCD4. Gain of function and loss of function experiments showed that PDCD4 induced turnover (proliferation and apoptosis) of HUVECs. Low PDCD4 level was associated with reduced proliferation but not apoptosis or phosphorylation of endothelial nitric oxide synthase caused by pulsatile shear stress to help maintain the homeostasis of endothelial cells.

Conclusions

Pulsatile shear stress induces ubiquitin-proteasome–mediated degradation of PDCD4 via a PI3K/Akt pathway in HUVECs. PDCD4 induces turnover (proliferation and apoptosis) of HUVECs. Low PDCD4 level is associated with reduced proliferation for maintenance of HUVEC homeostasis under pulsatile shear stress.

Differential effects of PDCD4 depletion on protein synthesis in myoblast and myotubes

BACKGROUND

Reduced muscle mass is a hallmark of metabolic diseases like diabetes and cancer. The mammalian (mechanistic) target of rapamycin complex 1/S6 kinase 1 (mTORC1/S6K1) pathway is critical to the regulation of muscle protein synthesis and mass but its mechanism of action is not completely understood.

RESULTS

Using L6 myotubes, we characterized the regulation of programmed cell death 4 (PDCD4), a recently described substrate of S6K1. The abundance, but not Ser67 phosphorylation, of PDCD4 was sensitive to amino acid and serum deprivation: values in starved cells were 4.5X of control (P < 0.001). Refeeding had opposite effects. Growth factors, compared to amino acids, appeared more critical in regulating PDCD4 abundance. Furthermore, inhibition of mTORC1 or the proteasome prevented the refeeding-associated decrease in PDCD4 abundance. Amino acid and serum deprivation significantly increased PDCD4 binding to eIF4A (P < 0.05); this was reversed during refeeding. PDCD4 depletion by RNA interference had no significant effect on phenylalanine incorporation into myotube mixed proteins in control cells but further suppressed (30%) this measure in nutrient-deprived cells (P < 0.0005). This was not observed in myoblasts. In starved myotubes, PDCD4 depletion further reduced the association of eIF4G with eIF4E.

CONCLUSION

Our data suggest that in myotubes, PDCD4 abundance is sensitive to nutritional manipulation in an mTORC1 and proteasome depended manner. Furthermore, the role of PDCD4 in regulating protein synthesis appears dependent on the developmental state of the cell.

mTOR-dependent transcriptional repression of Pdcd4 tumor suppressor in lung cancer cells

Programmed cell death 4 (Pdcd4) tumor suppressor is frequently lost in tumors of various origins including lung cancer, and its loss contributes to tumor progression. However molecular mechanisms underlying Pdcd4 suppression in lung cancer cells remain largely unexplored. Here we investigated molecular mechanisms of Pdcd4 suppression in lung cancer cells. Besides enhanced mTOR-dependent proteasomal degradation of Pdcd4 protein, we found that Pdcd4 transcription is negatively regulated by mTOR signaling, and localized cis-acting element in Pdcd4 promoter responsible for this effect. In conclusion, we described a novel molecular mechanism of Pdcd4 suppression in cancer cells consisting from mTOR signaling-dependent transcriptional repression of Pdcd4.

Control of a tumor suppressor PDCD4: Degradation mechanisms of the protein in hepatocellular carcinoma cells

In this study, we demonstrate that EGF inhibits the TGF-β1-induced apoptosis of Huh7 cells. TGF-β1 up-regulates the expression of PDCD4 causing apoptosis, by stimulating the synthesis of PDCD4 mRNA via the Smad signaling pathway. TGF-β1 also inhibits the activation of S6 kinase 1 which phosphorylates the serine 67 residue of PDCD4 and leads to the phosphorylation of serine 71 and serine 76 in the β-TRCP binding sequence. This phosphorylation sequence causes the protein to be degraded in the ubiquitin-proteasome system. EGF activates S6 kinase 1 via the PI3K-Akt-mTOR signaling pathway and stimulates the degradation of PDCD4. EGF also suppresses PDCD4 mRNA levels. As the mTOR inhibitor rapamycin up-regulated PDCD4 mRNA levels, the PI3K-Akt-mTOR signaling pathway may control the transcription of the PDCD4 gene as well as the degradation of the protein. TPA also inhibited the TGF-β1-induced apoptosis of Huh7 cells, stimulating the degradation of the PDCD4-protein. Analyses using PDCD4 mutants with changes of serines 67, 71 and 76 to alanine revealed that the phosphorylation of serine 67 is not essential for the TPA-induced suppression of the protein. The mitogens could not suppress the PDCD4-mutant proteins with changes of serine 71 and/or serine 76 to alanine, however, indicating that phosphorylations at these residues are necessary for the proteasome-mediated degradation of PDCD4. The phosphor-mimic S71/D and S76/D mutants were able to be degraded in the ubiquitin-proteasome system unlike the mutants with changes of serine to alanine. The expression of S71/D mutant was suppressed with EGF but that of S76/D mutant was not indicating that at least partly the phosphorylation of both sites was mediated by different enzymes.

MicroRNAs targeting EGFR signalling pathway in colorectal cancer

MicroRNAs (miRNAs) are short, 18-25-nucleotide long, non-coding single-stranded RNAs, which are capable to regulate gene expression on post-transcriptional level through binding to their target protein-encoding mRNAs. miRNAs regulate individual components of multiple oncogenic pathways. One of them is epidermal growth factor receptor (EGFR) signalling pathway that regulates cell proliferation, differentiation, migration, angiogenesis and apoptosis. All these processes are deregulated in colorectal cancer (CRC). Moreover, EGFR has been validated as the therapeutic target in CRC, and monoclonal antibodies cetuximab and panitumumab are used in the therapy of patients with metastatic CRC. Because of the extensive involvement of miRNAs in the regulation of EGFR signalling, it seems they could also serve as promising predictive biomarkers to anti-EGFR therapy. In this review, we summarize current knowledge about miRNAs targeting EGFR signalling pathway, their functioning in CRC pathogenesis and potential usage as biomarkers.

Induction of miR-21-PDCD4 signaling by UVB in JB6 cells involves ROS-mediated MAPK pathways

Ultraviolet (UV) irradiation plays a major role in the development of human skin cancer. The present study examined the alterations of miR-21-PDCD4 signaling in a mouse epidermal cell line (JB6 P(+)) post exposure to UVB irradiation. The results showed that (1) UVB caused PDCD4 inhibition in JB6 cells; (2) exposure of cells to UVB caused a significant increase of miR-21, the upstream regulator of PDCD4, expression; (3) both inhibition of ERKs with U0126 and inhibition of p38 with SB203580 significantly reversed UVB-induced PDCD4 inhibition; (4) ROS scavenger, N-acetyl-l-cysteine reversed the inhibitory effect of UVB on PDCD4 expression. The above results suggested that UVB induced PDCD4 inhibition, which may be mediated through ROS, especially endogenous H2O2 and p38 and ERKs phosphorylation. Unraveling the complex mechanisms associated with these events may provide insights into the initiation and progression of UVB-induced carcinogenesis.

Modifying chemotherapy response by targeted inhibition of eukaryotic initiation factor 4A

Translation is regulated predominantly at the initiation phase by several signal transduction pathways that are often usurped in human cancers, including the PI3K/Akt/mTOR axis. mTOR exerts unique administration over translation by regulating assembly of eukaryotic initiation factor (eIF) 4F, a heterotrimeric complex responsible for recruiting 40S ribosomes (and associated factors) to mRNA 5′ cap structures. Hence, there is much interest in targeted therapies that block eIF4F activity to assess the consequences on tumor cell growth and chemotherapy response. We report here that hippuristanol (Hipp), a translation initiation inhibitor that selectively inhibits the eIF4F RNA helicase subunit, eIF4A, resensitizes Eμ-Myc lymphomas to DNA damaging agents, including those that overexpress eIF4E—a modifier of rapamycin responsiveness. As Mcl-1 levels are significantly affected by Hipp, combining its use with the Bcl-2 family inhibitor, ABT-737, leads to a potent synergistic response in triggering cell death in mouse and human lymphoma and leukemia cells. Suppression of eIF4AI using RNA interference also synergized with ABT-737 in murine lymphomas, highlighting eIF4AI as a therapeutic target for modulating tumor cell response to chemotherapy.

Aldose reductase inhibition suppresses colon cancer cell viability by modulating microRNA-21 mediated programmed cell death 4 (PDCD4) expression

Inhibition of polyol pathway enzyme aldose reductase (AR) has been shown to prevent colon cancer cells growth in culture and in nude mice xenografts. However, the role of AR in the mediation of growth factor-induced colon cancer cells growth is not well understood. In this study, we have investigated how AR inhibition prevents tumour growth via regulation of microRNA (miR)-21-mediated programmed cell death 4 (PDCD4) expression in colon cancer cells in in vitro and in vivo. Treatment of colon cancer cells (HT29, SW480 and Caco-2) with epidermal growth factor (EGF) caused increased expression of miR-21 and inhibition of AR prevented it. Further, AR inhibition also increased PDCD4, a putative target of miR-21 in human colon cancer cells. Inhibition of AR also prevented EGF-induced phosphorylation of PDCD4. Treatment of HT29 cells with AR inhibitor, fidarestat, prevented the EGF-induced phosphorylation of mammalian target of rapamycin (mTOR), regulatory associated protein of mTOR (Raptor), eukaryotic initiation factor 4E (eIF4E), p70 S6 kinase (S6K) and eukaryotic initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) and increased the phosphorylation of 5' adenosine monophosphate-activated protein kinase (AMPK). Similarly, in nude mice xenograft tissues, PDCD4 and 4E-BP1 levels were significantly higher in AR inhibitor-treated mice compared to controls. Collectively, these results indicate that AR inhibition prevents growth factor-induced colon cancer growth by down-regulating miR-21 expression and increasing PDCD4 levels through the reactive oxygen species (ROS)/AMPK/mTOR/AP1/4E-BP1 pathway.

miRNA: The nemesis of gastric cancer (Review)

microRNAs (miRNAs) are a group of small non-coding RNAs that are ~22 (18 to 25) nucleotides (nt) long and have been associated with a variety of diseases, including cancer. Increasing evidence indicates that miRNAs are essential in the development, diagnosis, treatment and prognosis of a variety of tumors. The utility of miRNAs as biomarkers for diagnosis and of target molecules for the treatment of cancers is increasingly being recognized. With the discovery of circulating miRNAs, a non-invasive approach for the diagnosis and treatment of cancer has been identified. This review summarizes the role of miRNAs in the development of different tumors, as well as a variety of other biological events. Moreover, this review focuses on analyzing the function and mechanism of gastric cancer-related miRNAs and investigates the importance of circulating miRNAs in gastric cancer, as well as their origin. Finally, this review lists a number of the problems that must be solved prior to miRNAs being used as reliable non-invasive tools for the diagnosis, treatment and prognosis of gastric cancer.

MicroRNA-21 regulates the migration and invasion of a stem-like population in hepatocellular carcinoma

Due to invasion and intrahepatic metastasis, the prognosis for patients with hepatocellular carcinoma (HCC) is poor. However, the mechanisms underlying these processes of HCC remain unclear. Cancer stem cells may be involved in early systemic dissemination and metastasis formation and side population (SP) cells isolated from diverse cancer cells possess stem cell-like properties. However, the mechanisms involved in migration and invasion of cancer stem cells are not well understood. In this study, we identified and isolated populations of SP cells from HCC cell lines using flow cyto-metry. SP cells showed higher levels of migration and invasion capability. Higher expression of miR-21 was observed in SP cells. Silencing of miR-21 led to a reduction in the migration and invasion of these cells and overexpression of miR-21 can increase in cell migration and invasion. Overexpression of miR-21 did not cause degradation of PTEN or RECK or PDCD4 mRNA but drastically inhibited its protein expression. Consistent with these results, silencing miR-21 increased the levels of PTEN, RECK and PDCD4 protein, respectively. The role of silencing miR-21 was partially attenuated by silencing of PTEN or RECK or PDCD4 mRNA. The results of this study revealed the aberrant expression of miR-21 in SP cells and showed that miR-21 regulates the expression of multiple target proteins that are associated with tumor dissemination. MiR-21 is a pro-metastatic miRNA in SP cells and raises the possibility that therapy of HCC may be improved by pharmaceutical strategies directed towards miR-21.

microRNAs as pharmacological targets in cancer

The survival rate of cancer patients has increased considerably in the last 20 years owing to significant efforts made in prevention, early detection protocols, combined chemotherapy regimens, targeted therapies, refined radiotherapy and cancer vaccines. However, metastasis and acquired resistance to current therapies represent two major challenges for achieving long-term cure. Therefore, new treatment strategies must be developed. One promising alternative is epigenetic-based therapies, of which miRNAs are at the forefront. MicroRNAs are endogenous small non-coding RNAs, often deregulated in cancer, which regulate gene expression by specific binding to the 3'-UTR of target genes. They are excellent candidates for therapy since miRNAs can regulate multiple targets of the same or different pathways, thereby minimizing the risk of resistance development or compensatory mechanisms. In this review, the mechanisms that lead to miRNA deregulation in cancer, their feasibility as therapeutic tools and the different strategies for the pharmacological manipulation of miRNAs in preclinical animal models are discussed.

Inhibition of miR-21 induces biological and behavioral alterations in diffuse large B-cell lymphoma

MicroRNA-21 (miR-21) has been ascribed a key role in many cellular processes, e.g. tumorigenesis via inhibition of target gene expression. However, its role in diffuse large B-cell lymphoma (DLBCL) is still unclear, and there are no in-depth studies on the relationship between miR-21 and the cellular phenotype of DLBCL. In this study, we investigated the expression and role of miR-21 in the regulation of cell biological processes in DLBCL. Firstly, miR-21 expression was evaluated in three DLBCL cell lines by real-time quantitative reverse-transcription (qRT) polymerase chain reaction (PCR). Then, to determine the possible role of miR-21 in the biological and behavioral characteristics of DLBCL, we performed miR-21 knockdown by transfection with anti-miR-21. In addition, PDCD4 and PTEN were assessed by luciferase reporter assay, qRT-PCR, and Western blot. Our study revealed that miR-21 was significantly upregulated in activated B-cell-like DLBCL cells compared to germinal center-like DLBCL cells. We demonstrated that inhibition of miR-21 induced suppression of proliferation and invasion, as well as increased apoptosis in DLBCL. Moreover, knockdown of miR-21 increased PDCD4 and PTEN expression at the protein level but not at the mRNA level. In conclusion, miR-21 can regulate proliferation, invasion, and apoptosis, and thus it has a potential therapeutic application in DLBCL.

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.

Overexpression of microRNA-21 regulating PDCD4 during tumorigenesis of liver fluke-associated cholangiocarcinoma contributes to tumor growth and metastasis

MicroRNA, an endogenous noncoding RNA modulating gene expression, is a key molecule that by its dysregulation plays roles in inflammatory-driven carcinogenesis. This study aimed to investigate the role of oncomiR miR-21 and its target, the programmed cell death 4 (PDCD4) in tumor growth and metastasis of the liver fluke Opisthorchis viverrini-associated cholangiocarcinoma (CCA). The expression levels of miR-21 and PDCD4 were analyzed using the TaqMan miRNA expression assay and immunohistochemistry in liver tissues of both O. viverrini plus N-nitrosodimethylamine (NDMA)-treated hamsters and human CCA samples (n=23 cases). The functional assay for miR-21 was performed in CCA cell lines by the anti-miR-21 and pre-miR-21 transfection procedures. The peak of miR-21 levels were reached at 2 (hyperplastic lesions) and 6 (CCA) months of the O. viverrini plus NDMA-induced group and had a reverse response with its target PDCD4 proteins. In human CCA, miR-21 was overexpressed in tumor tissues when compared with nontumor tissues (P=0.0034) and had a negative correlation with PDCD4 protein (P=0.026). It was also found that high expression of miR-21 was significantly correlated with shorter survival (P<0.05) and lymph node metastasis (P=0.037) of CCA patients. Transient transfection of pre-miR-21 reduced the PDCD4 level and resulted in an increase of M213 CCA cell growth and wound-induced migration ability. These results indicated that miR-21 plays a role in the carcinogenesis and metastasis of O. viverrini-associated CCA by suppressing the function of PDCD4. Modulation of aberrantly expressed miR-21 may be a useful strategy to inhibit tumor cell phenotypes or improve response to chemotherapy.

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.

Apoptosis and microRNA aberrations in cancer

Carcinogenesis arises from the malfunction of genes that control cell growth and division. Therefore, the most effective method of hindering tumourigenesis is to induce the death of immortalized cancer cells. Apoptosis or programmed cell death has shown the most promises in impairing cancer growth. A variety of proteins is involved in the regulation of apoptosis and the malfunction of any these regulators may cause cell proliferation. The microRNAs have been shown to play a central role in the regulation of the cell cycle, including apoptosis. The microRNAs are involved in post-transcriptional gene suppression and have been implicated in the regulation of cell differentiation and development. Aberrations in the microRNA regulation of apoptosis lead to tumourigenesis. The present review assesses the current knowledge of apoptotic regulation in cancer and the effect of microRNA aberrations in tumourigenesis.

Erioflorin stabilizes the tumor suppressor Pdcd4 by inhibiting its interaction with the E3-ligase β-TrCP1

Loss of the tumor suppressor Pdcd4 was reported for various tumor entities and proposed as a prognostic marker in tumorigenesis. We previously characterized decreased Pdcd4 protein stability in response to mitogenic stimuli, which resulted from p70(S6K1)-dependent protein phosphorylation, β-TrCP1-mediated ubiquitination, and proteasomal destruction. Following high-throughput screening of natural product extract libraries using a luciferase-based reporter assay to monitor phosphorylation-dependent proteasomal degradation of the tumor suppressor Pdcd4, we succeeded in showing that a crude extract from Eriophyllum lanatum stabilized Pdcd4 from TPA-induced degradation. Erioflorin was identified as the active component and inhibited not only degradation of the Pdcd4-luciferase-based reporter but also of endogenous Pdcd4 at low micromolar concentrations. Mechanistically, erioflorin interfered with the interaction between the E3-ubiquitin ligase β-TrCP1 and Pdcd4 in cell culture and in in vitro binding assays, consequently decreasing ubiquitination and degradation of Pdcd4. Interestingly, while erioflorin stabilized additional β-TrCP-targets (such as IκBα and β-catenin), it did not prevent the degradation of targets of other E3-ubiquitin ligases such as p21 (a Skp2-target) and HIF-1α (a pVHL-target), implying selectivity for β-TrCP. Moreover, erioflorin inhibited the tumor-associated activity of known Pdcd4- and IκBα-regulated αtranscription factors, that is, AP-1 and NF-κB, altered cell cycle progression and suppressed proliferation of various cancer cell lines. Our studies succeeded in identifying erioflorin as a novel Pdcd4 stabilizer that inhibits the interaction of Pdcd4 with the E3-ubiquitin ligase β-TrCP1. Inhibition of E3-ligase/target-protein interactions may offer the possibility to target degradation of specific proteins only as compared to general proteasome inhibition.

IL-10 -1082 SNP and IL-10 in primary CNS and vitreoretinal lymphomas

OBJECTIVES

Most primary central nervous system lymphomas (PCNSLs) and primary vitreoretinal lymphomas (PVRLs) are B-cell lymphomas that produce high levels of interleukin (IL)-10, which is linked to rapid disease progression. The IL-10 (-1082) G → A polymorphism (IL-10 SNP) is associated with improved survival in certain non-CNS lymphoma patients. PDCD4 is a tumor suppressor gene and upstream regulator of IL-10. This study examined the correlation between the IL-10 SNP, PDCD4 mRNA expression, and IL-10 expression (at transcript and protein levels) in these lymphoma cells.

MATERIALS AND METHODS

Single-nucleotide polymorphism (SNP)-typing at IL-10 (-1082) was performed after microdissecting cytospun PVRL cells from 26 specimens. Vitreal IL-10 and IL-6 levels were measured by ELISA. PCNSL cells from 52 paraffin-embedded sections were microdissected and SNP typed on genomic DNA. RT-PCR was performed to analyze expression of IL-10 and PDCD4 mRNA. IL-10 (-1082) SNP typing was performed on blood samples of 96 healthy controls. We measured IL-10 (-1082) SNP expression in 26 PVRLs and 52 PCNSLs and examined its relationship with IL-10 protein and gene expression, respectively.

RESULTS

More PVRL patients expressed one copy of the IL-10 ( -1082 )  G → A SNP with the GA genotype compared to controls. The frequencies of the three genotypes (AA, AG, GG) significantly differed in PVRL versus controls and in PCNSL versus controls. In PVRLs, the vitreal IL-10/IL-6 ratio was higher in IL-10 (-1082) AG and IL-10 (-1082) AA patients, compared to IL-10 (-1082) GG patients. IL-10 mRNA expression was higher in IL-10 (-1082) AG and IL-10 (-1082) AA PCNSLs, compared to IL-10 (-1082) GG PCNSLs. No correlation was found between IL-10 and PDCD4 expression levels in 37 PCNSL samples.

CONCLUSIONS

PVRL and PCNSL patients had similar IL-10 (-1082) A allele frequencies, but genotype distributions differed from healthy controls. The findings suggest that the IL-10 (-1082) A allele is a risk factor for higher IL-10 levels in PVRLs and PCNSLs. Higher IL-10 levels have been correlated with more aggressive disease in both PVRLs and PCNSLs, making this finding an important and potentially clinically significant observation.

MicroRNA-21 correlates with tumorigenesis in malignant peripheral nerve sheath tumor (MPNST) via programmed cell death protein 4 (PDCD4)

PURPOSE

We investigated the miRNA profile in peripheral nerve tumors and clarified the involvement of miRNA in the development and progression of MPNST in comparison with neurofibroma (NF). In addition, we attempted to seek associations between the miRNA and their potential targets in MPNST.

METHODS

Global miRNA expression profiling was investigated for clinical samples of 6 MPNSTs and 6 NFs. As detected by profiling analysis, the expressions of miR-21 in clinical samples of 12 MPNSTs, 11 NFs, and 5 normal nerves, and 3 MPNST cell lines were compared using quantitative real-time reverse transcription PCR. MPNST cell line (YST-1) was transfected with miR-21 inhibitor to study its effects on cell proliferation, caspase activity, and the expression of miR-21 targets.

RESULTS

Analysis of miRNA expression profiles in MPNST and NF revealed significantly altered expression levels of nine miRNAs, one of those, miR-21, and its putative target, programmed cell death protein 4 (PDCD4), were selected for further studies. miR-21 expression level in MPNST was significantly higher than that in NF (P < 0.05). In MPNST cells, transfection of miR-21 inhibitor significantly increased caspase activity (P < 0.01), significantly suppressed cell growth (P < 0.05), and upregulated protein level of PDCD4, indicating that miR-21 inhibitor could induce cell apoptosis of MPNST cells.

CONCLUSIONS

These results suggest that miR-21 plays an important role in MPNST tumorigenesis and progression through its target, PDCD4. MiR-21 and PDCD4 may be candidate novel therapeutic targets against the development or progression of MPNSTs.

A genome-wide association study of caffeine-related sleep disturbance: confirmation of a role for a common variant in the adenosine receptor

OBJECTIVES

To identify common genetic variants that predispose to caffeine-induced insomnia and to test whether genes whose expression changes in the presence of caffeine are enriched for association with caffeine-induced insomnia.

DESIGN

A hypothesis-free, genome-wide association study.

SETTING

Community-based sample of Australian twins from the Australian Twin Registry.

PARTICIPANTS

After removal of individuals who said that they do not drink coffee, a total of 2,402 individuals from 1,470 families in the Australian Twin Registry provided both phenotype and genotype information.

MEASUREMENTS AND RESULTS

A dichotomized scale based on whether participants reported ever or never experiencing caffeine-induced insomnia. A factor score based on responses to a number of questions regarding normal sleep habits was included as a covariate in the analysis. More than 2 million common single nucleotide polymorphisms (SNPs) were tested for association with caffeine-induced insomnia. No SNPs reached the genome-wide significance threshold. In the analysis that did not include the insomnia factor score as a covariate, the most significant SNP identified was an intronic SNP in the PRIMA1 gene (P = 1.4 × 10⁻⁶, odds ratio = 0.68 [0.53 - 0.89]). An intergenic SNP near the GBP4 gene on chromosome 1 was the most significant upon inclusion of the insomnia factor score into the model (P = 1.9 × 10⁻⁶, odds ratio = 0.70 [0.62 - 0.78]). A previously identified association with a polymorphism in the ADORA2A gene was replicated.

CONCLUSIONS

Several genes have been identified in the study as potentially influencing caffeine-induced insomnia. They will require replication in another sample. The results may have implications for understanding the biologic mechanisms underlying insomnia.

Role of microRNA-21 and programmed cell death 4 in the pathogenesis of human uterine leiomyomas

OBJECTIVE

To determine whether programmed cell death 4 (PDCD-4) is altered in autologous leiomyoma and myometrial tissues and what microRNA-21's (miR-21) role is in PDCD-4 expression, apoptosis, and translation.

DESIGN

Laboratory research.

SETTING

Academic medical center.

PATIENT(S)

Myometrial and leiomyoma tissues from patients with symptomatic leiomyomata.

INTERVENTION(S)

Tissue analysis and miR-21 knockdown in cultured immortalized myometrial (UtM) and leiomyoma (UtLM) cells.

MAIN OUTCOME MEASURE(S)

MiR-21 and PDCD-4 mRNA and protein expression.

RESULT(S)

Leiomyoma tissues robustly expressed the full-length 51 kd isoform of PDCD-4, but normal myometrial tissue had negligible expression. Consistent with autologous tissues, UtLM cells expressed elevated miR-21 and a similar pattern of PDCD-4 compared with UtM cells. Knockdown of miR-21 increased PDCD-4 levels in UtM cells and UtLM cells, indicating that it can regulate PDCD-4 expression. Loss of miR-21 also increased cleavage of caspase-3 (apoptosis marker) and increased phosphorylation of elongation factor-2 (marker of reduced translation) in both cell lines.

CONCLUSION(S)

Elevated leiomyoma miR-21 levels are predicted to decrease PDCD-4 levels, thus leiomyomas differ from other tumors where loss of PDCD-4 is associated with tumor progression. Our studies indicate regulation of PDCD-4 expression is not a primary miR-21 function in leiomyomas, but instead miR-21 is able to impact cellular apoptosis and translation, through unknown targets, in a manner consistent with its involvement in the pathophysiology of uterine fibroids.

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.

Programmed cell death 4 nuclear loss and miR-21 or activated Akt overexpression in esophageal squamous cell carcinogenesis

The programmed cell death 4 (PDCD4) tumor suppressor is down-regulated in several malignancies, and the (subcellular) expression of its protein product is modulated by both oncomiR miR-21 and protein kinase B (Akt). PDCD4 and activated Akt (phosphorylated Akt [pAkt]) expression were assessed immunohistochemically in 53 tissue samples obtained from 25 endoscopic esophageal mucosal resections performed for squamous intraepithelial neoplasia (IEN) or squamous intramucosal carcinoma (IM-SSC). In total, 33 IEN (low-grade = 15; high-grade = 15) and 20 IM-SSC specimens were considered; 50 additional tissue samples of histologically proven normal esophageal mucosa were considered as normal controls. To further validate the results achieved, miR-21 expression (as assessed by quantitative real-time polymerase chain reaction and in situ hybridization) was tested in another series of 15 normal esophageal tissue samples, 15 high-grade IEN, and 15 IM-SCCs. Normal suprabasal squamous epithelial layers consistently featured strong PDCD4 nuclear immunostaining, which was significantly lower (P < 0.001) in IEN (both low-and high-grade) and in IM-SSC. Conversely, pAkt and miR-21 expression was significantly up-regulated in the whole spectrum of preneoplastic/neoplastic lesions considered. PDCD4 down-regulation, as assessed by immunohistochemistry, is a reliable biomarker of early-stage squamous cell esophageal neoplasia, providing additional information in the histological assessment of these lesions.

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.

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.

miRNAs in precancerous lesions of the gastrointestinal tract

In spite of the well-established understanding of the phenotypic lesions occurring in the shift from native epithelia to invasive (adeno) carcinoma, the molecular typing of the precancerous changes in the gastrointestinal tract remains unreliable. In recent years, no biomarkers have aroused as much interest as the miRNAs, a class of non-coding RNA molecules that function as endogenous silencers of numerous target genes. Aberrant miRNA expression is a hallmark of human disease, including cancer. Unlike most mRNAs, miRNAs are both long-living in vivo and very stable in vitro. Such characteristics allow their testing in paraffin-embedded tissue samples, which is essential in the biological profiling of small (phenotypically characterized) preneoplastic lesions of the gastrointestinal tract (as well as in other fields of human pathology). The upcoming challenge lies in the reliable identification of disease-specific targets of dysregulated miRNAs, to enable miRNA testing in the clinical management of the secondary prevention of gastrointestinal cancer.

Alterations of microRNAs contribute to colon carcinogenesis

MicroRNAs are being evaluated as biomarkers and therapeutic targets for colon cancer. MicroRNAs have a functional role in the initiation and progression of colon cancer. Altered microRNA expression is found in tumors and their expression patterns may serve as useful cancer biomarkers. Polymorphisms in microRNAs or microRNA binding sites may modify the risk of developing cancer. As we continue to improve our understanding of the role for microRNAs in the initiation and progression of cancer, one goal is to gain insights that will allow for the development of microRNAs as biomarkers and therapeutic targets for cancer. This review provides a current understanding of the connection between microRNAs and colon cancer. We will cover evidence that global microRNA expression patterns are altered in colon tumors, that specific microRNAs have a functional role in colon carcinogenesis, that polymorphisms in microRNAs may be associated with risk of colon cancer, and the potential for using circulating microRNAs as a noninvasive biomarker for the detection of cancer.

Signaling by the matrix proteoglycan decorin controls inflammation and cancer through PDCD4 and MicroRNA-21

The mechanisms linking immune responses and inflammation with tumor development are not well understood. Here, we show that the soluble form of the extracellular matrix proteoglycan decorin controls inflammation and tumor growth through PDCD4 (programmed cell death 4) and miR-21 (microRNA-21) by two mechanisms. First, decorin acted as an endogenous ligand of Toll-like receptors 2 and 4 and stimulated production of proinflammatory molecules, including PDCD4, in macrophages. Second, decorin prevented translational repression of PDCD4 by decreasing the activity of transforming growth factor-β1 and the abundance of oncogenic miR-21, a translational inhibitor of PDCD4. Moreover, increased PDCD4 abundance led to decreased release of the anti-inflammatory cytokine interleukin-10, thereby making the cytokine profile more proinflammatory. This pathway operates in both pathogen-mediated and sterile inflammation, as shown here for sepsis and growth retardation of established tumor xenografts, respectively. Decorin was an early response gene evoked by septic inflammation, and protein concentrations of decorin were increased in the plasma of septic patients and mice. In cancer, decorin reduced the abundance of anti-inflammatory molecules and increased that of proinflammatory molecules, thereby shifting the immune response to a proinflammatory state associated with reduced tumor growth. Thus, by stimulating proinflammatory PDCD4 and decreasing the abundance of miR-21, decorin signaling boosts inflammatory activity in sepsis and suppresses tumor growth.

MicroRNA-21 suppression impedes medulloblastoma cell migration

Medulloblastoma (MB), the most common malignant brain tumour in children, is characterised by a high risk of leptomeningeal dissemination. But little is known about the molecular mechanisms that promote cancer cell migration in MB. Aberrant expression of miR-21 is recognised to be causatively linked to metastasis in a variety of human neoplasms including brain tumours; however its function in MB is still unknown. In this study we investigated the expression level and the role of miR-21 in MB cell migration. miR-21 was found to be up-regulated, compared to normal cerebellum, in 29/29 MB primary samples and 6/6 MB-derived cell lines. Inverse correlation was observed between miR-21 expression and the metastasis suppressor PDCD4, while miR-21 repression increased the release of PDCD4 protein, suggesting negative regulation of PDCD4 by miR-21 in MB cells. Anti-miR-21 decreased protein expression of the tumour cell invasion mediators MAP4K1 and JNK, which are also known to be negatively regulated by PDCD4, and down-regulated integrin protein that is essential for MB leptomeningeal dissemination. Moreover miR-21 knockdown in MB cells increased the expression of two eminent negative modulators of cancer cell migration, E-Cadherin and TIMP2 proteins that are known to be positively regulated by PDCD4. Finally and importantly, suppression of miR-21 decreased the motility of MB cells and reduced their migration across basement membranes in vitro. Together, these compelling data propose miR-21 pathway as a novel mechanism impacting MB cell dissemination and raises the possibility that curability of selected MB may be improved by pharmaceutical strategies directed towards microRNA-21.

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.

Downregulation of Pdcd4 by mir-21 facilitates glioblastoma proliferation in vivo

MicroRNAs (miRNAs) are small, noncoding RNAs that play a critical role in developmental and physiological processes and are implicated in the pathogenesis of several human diseases, including cancer. They function by regulating target gene expression post-transcriptionally. In this study, we examined the role of oncogenic mir-21 in the pathogenesis of glioblastoma, the most aggressive form of primary brain tumor. We have previously reported that mir-21 is expressed at higher levels in primary glioblastoma-tissue and glioblastoma-derived cell lines than in normal brain tissue. We demonstrate that downregulation of mir-21 in glioblastoma-derived cell lines results in increased expression of its target, programmed cell death 4 (Pdcd4), a known tumor-suppressor gene. In addition, our data indicate that either downregulation of mir-21 or overexpression of its target, Pdcd4, in glioblastoma-derived cell lines leads to decreased proliferation, increased apoptosis, and decreased colony formation in soft agar. Using a glioblastoma xenograft model in immune-deficient nude mice, we observe that glioblastoma-derived cell lines in which mir-21 levels are downregulated or Pdcd4 is over-expressed exhibit decreased tumor formation and growth. Significantly, tumors grow when the glioblastoma-derived cell lines are transfected with anti-mir-21 and siRNA to Pdcd4, confirming that the tumor growth is specifically regulated by Pdcd4. These critical in vivo findings demonstrate an important functional linkage between mir-21 and Pdcd4 and further elucidate the molecular mechanisms by which the known high level of mir-21 expression in glioblastoma can attribute to tumorigenesis--namely, inhibition of Pdcd4 and its tumor-suppressive functions.

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.

A strategy for full interrogation of prognostic gene expression patterns: exploring the biology of diffuse large B cell lymphoma

BACKGROUND

Gene expression profiling yields quantitative data on gene expression used to create prognostic models that accurately predict patient outcome in diffuse large B cell lymphoma (DLBCL). Often, data are analyzed with genes classified by whether they fall above or below the median expression level. We sought to determine whether examining multiple cut-points might be a more powerful technique to investigate the association of gene expression with outcome.

METHODOLOGY/PRINCIPAL FINDINGS

We explored gene expression profiling data using variable cut-point analysis for 36 genes with reported prognostic value in DLBCL. We plotted two-group survival logrank test statistics against corresponding cut-points of the gene expression levels and smooth estimates of the hazard ratio of death versus gene expression levels. To facilitate comparisons we also standardized the expression of each of the genes by the fraction of patients that would be identified by any cut-point. A multiple comparison adjusted permutation p-value identified 3 different patterns of significance: 1) genes with significant cut-point points below the median, whose loss is associated with poor outcome (e.g. HLA-DR); 2) genes with significant cut-points above the median, whose over-expression is associated with poor outcome (e.g. CCND2); and 3) genes with significant cut-points on either side of the median, (e.g. extracellular molecules such as FN1).

CONCLUSIONS/SIGNIFICANCE

Variable cut-point analysis with permutation p-value calculation can be used to identify significant genes that would not otherwise be identified with median cut-points and may suggest biological patterns of gene effects.

Inflammation-induced loss of Pdcd4 is mediated by phosphorylation-dependent degradation

The tumor suppressor programmed cell death 4 (Pdcd4) is lost in various tumor tissues. Loss of Pdcd4 has been associated with increased tumorigenic potential and tumor progression. While various mechanisms of Pdcd4 regulation have been described, the effect of an inflammatory tumor microenvironment on Pdcd4 protein expression has not been characterized so far. In the present study, we aimed to elucidate the molecular mechanisms of Pdcd4 protein regulation in tumor cells under inflammatory conditions. 12-O-tetradecanoylphorbol 13-acetate-induced differentiation of human U937 monocytes increased the expression and secretion of inflammatory cytokines such as tumor necrosis factor α, interleukin (IL)-6 and IL-8. Exposure to conditioned medium (CM) of these activated macrophages markedly decreased Pdcd4 protein expression in various tumor cells. Similarly, indirect coculture with such activated U937 monocyte-derived macrophages resulted in the loss of Pdcd4 protein in tumor cells. Decreased Pdcd4 protein levels were attributable to enhanced proteasomal degradation, diminishing Pdcd4 protein half-life. Proteasomal degradation required activation of phosphatidylinositol-3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling. Since macrophage-CM sufficed to induce Pdcd4 degradation, Pdcd4 downregulation was determined to be an indirect unidirectional effect of the macrophages on the tumor cells. Pdcd4 protein expression was also attenuated in vivo in mouse colon tissue in response to dextran sodium sulfate-induced colitis. In summary, we characterized PI3K-mTOR-dependent proteasome-mediated Pdcd4 degradation in tumor cells in the inflammatory tumor microenvironment. Consequently, stabilization of Pdcd4 protein could provide a promising novel avenue for therapeutics targeting inflammation-associated tumors.

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.

Early detection of lung adenocarcinoma in sputum by a panel of microRNA markers

Adenocarcinoma is the most common type of lung cancer, the leading cause of cancer deaths in the world. Early detection is the key to improve the survival of lung adenocarcinoma patients. We have previously shown that microRNAs (miRNAs) were stably present in sputum and could be applied to diagnosis of lung cancer. The aim of our study was to develop a panel of miRNAs that can be used as highly sensitive and specific sputum markers for early detection of lung adenocarcinoma. Our study contained 3 phases: (i) marker discovery using miRNA profiling on paired normal and tumor lung tissues from 20 patients with lung adenocarcinoma; (ii) marker optimization by real-time reverse transcription-quantitative polymerase chain reaction on sputum of a case-control cohort consisting of 36 cancer patients and 36 health individuals and (iii) validation on an independent set of 64 lung cancer patients and 58 cancer-free subjects. From the surgical tissues, 7 miRNAs with significantly altered expression were identified, of which "4" were overexpressed and "3" were underexpressed in all 20 tumors. On the sputum samples of the case-control cohort, 4 (miR-21, miR-486, miR-375 and miR-200b) of the 7 miRNAs were selected, which in combination produced the best prediction in distinguishing lung adenocarcinoma patients from normal subjects with 80.6% sensitivity and 91.7% specificity. Validation of the marker panel in the independent populations confirmed the sensitivity and specificity that provided a significant improvement over any single one alone. The sputum markers demonstrated the potential of translation to laboratory settings for improving the early detection of lung adenocarcinoma.

miRNAs as biomarkers for management of patients with colorectal cancer

miRNAs serve as micromanagers, negatively regulating gene expression. Since altered miRNA expression is implicated in the pathobiology of various cancers, including colorectal cancers (CRCs), these molecules serve as potential therapeutic targets. Manipulation of miRNAs may offer an alternative therapy for chemo- and radio-resistant CRCs. For CRC patients, miRNA expression patterns can be used for diagnosis, and to predict prognosis and efficacy of therapy. This article describes the methodological approaches for miRNA measurement, their function in the pathobiology of CRCs and their potential clinical utility.

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.

The malignant phenotype-associated microRNA in gastroenteric, hepatobiliary and pancreatic carcinomas

IMPORTANCE OF THE FIELD

MicroRNA (miRNA) is a newly discovered class of small and endogenous non-coding RNAs. Many miRNAs exhibit altered expression levels in cancer, and they can affect the cancerous phenotype of malignant cells.

AREAS COVERED IN THIS REVIEW

We review the recent advances in miRNA involvement in human gastroenteric tumor and analyze the clinical and therapeutic opportunities they provide. We envisage future developments toward molecular mechanisms of miRNAs and their potential applications to cancer treatment.

WHAT THE READER WILL GAIN

MiRNAs may reasonably become novel anticancer tools. More investigations should be performed to promote the success of therapeutic-clinical use of miRNAs in cancer.

TAKE HOME MESSAGE

Future studies should focus on identification of new miRNAs and targets, the function and mechanism of miRNA-regulated cancer pathogenesis, the reliable delivery strategy and the novel type of miRNA-based therapy.

Programmed cell death 4 loss increases tumor cell invasion and is regulated by miR-21 in oral squamous cell carcinoma

BACKGROUND

The tumor suppressor Programmed Cell Death 4 (PDCD4) has been found to be under-expressed in several cancers and associated with disease progression and metastasis. There are no current studies characterizing PDCD4 expression and its clinical relevance in Oral Squamous Cell Carcinoma (OSCC). Since nodal metastasis is a major prognostic factor in OSCC, we focused on determining whether PDCD4 under-expression was associated with patient nodal status and had functional relevance in OSCC invasion. We also examined PDCD4 regulation by microRNA 21 (miR-21) in OSCC.

RESULTS

PDCD4 mRNA expression levels were assessed in 50 OSCCs and 25 normal oral tissues. PDCD4 was under-expressed in 43/50 (86%) OSCCs, with significantly reduced mRNA levels in patients with nodal metastasis (p = 0.0027), and marginally associated with T3-T4 tumor stage (p = 0.054). PDCD4 protein expression was assessed, by immunohistochemistry (IHC), in 28/50 OSCCs and adjacent normal tissues; PDCD4 protein was absent/under-expressed in 25/28 (89%) OSCCs, and marginally associated with nodal metastasis (p = 0.059). A matrigel invasion assay showed that PDCD4 expression suppressed invasion, and siRNA-mediated PDCD4 loss was associated with increased invasive potential of oral carcinoma cells. Furthermore, we showed that miR-21 levels were increased in PDCD4-negative tumors, and that PDCD4 expression may be down-regulated in OSCC by direct binding of miR-21 to the 3'UTR PDCD4 mRNA.

CONCLUSIONS

Our data show an association between the loss of PDCD4 expression, tumorigenesis and invasion in OSCC, and also identify a mechanism of PDCD4 down-regulation by microRNA-21 in oral carcinoma. PDCD4 association with nodal metastasis and invasion suggests that PDCD4 may be a clinically relevant biomarker with prognostic value in OSCC.

Downregulation of programmed cell death 4 by inflammatory conditions contributes to the generation of the tumor promoting microenvironment

Ample evidence has shown key roles of inflammation in tumor promotion and carcinogenesis, and tumor-associated macrophages are known to promote tumor growth and dissemination. Programmed cell death 4 (Pdcd4) is a novel tumor suppressor, and although various studies have revealed that the functions and expression mechanisms of Pdcd4 in tumor promotion, those in regard to inflammation remain unclear. In the present study, we examined whether inflammatory stimuli regulate Pdcd4 expression. 12-O-tetradecanoylphorbol 13-acetate (TPA) suppressed expression of pdcd4 mRNA in human monocytic cell lines (U937, THP-1). Similarly, the bacterial endotoxin lipopolysaccharide (LPS) downregulated pdcd4 level in mouse RAW264.7 and peritoneal macrophages. Furthermore, conditioned medium from LPS-stimulated RAW264.7 macrophages suppressed pdcd4 mRNA in RAW264.7 macrophages, and findings obtained with recombinant tumor necrosis factor-alpha (TNF-alpha) and TNF-alpha-specific siRNA suggested that TNF-alpha partly mediates LPS-triggered Pdcd4 downregulation via an autocrine mechanism. Specific inhibitors of phosphoinositide-3-kinase (PI3K) and c-jun N-terminus kinase (JNK) restored LPS-abolished pdcd4 mRNA. Consistently, in MCF7 mammary carcinoma cells, conditioned medium from TPA-differentiated/activated U937 cells suppressed pdcd4 mRNA. Additionally, knockdown of pdcd4 in RAW264.7 macrophages using siRNA significantly enhanced LPS-induced TNF-alpha protein production, and interferon-gamma, CC chemokine ligand (Ccl) 1, Ccl20, and interleukin-10 mRNA expression. These results suggest that Pdcd4 suppresses the induction of these inflammatory mediators. Taken together, loss of Pdcd4 in macrophages may be a critical step in establishing the inflammatory environment while that in tumor cells contributes to tumor progression.