Differentially expressed protein Pdcd4 inhibits tumor promoter-induced neoplastic transformation

Quercetin inhibits Cr(VI)-induced malignant cell transformation by targeting miR-21-PDCD4 signaling pathway

Hexavalent chromium [Cr(VI)] is an important human carcinogen associated with pulmonary diseases and lung cancer. Inhibition of Cr(VI)-induced carcinogenesis by a dietary antioxidant is a novel approach. Quercetin is one of the most abundant dietary flavonoids widely present in many fruits and vegetables, possesses potent antioxidant and anticancer properties. MicroRNA-21 (miR-21) is a key oncomiR significantly elevated in the majority of human cancers that exerts its oncogenic activity by targeting the tumor suppressor gene programmed cell death 4 (PDCD4). The present study examined the effect of quercetin on the inhibition of Cr(VI)-induced malignant cell transformation and the role of miR-21-PDCD4 signaling involved. Our results showed that quercetin decreased ROS generation induced by Cr(VI) exposure in BEAS-2B cells. Chronic Cr(VI) exposure induced malignant cell transformation, increased miR-21 expression and caused inhibition of PDCD4, which were significantly inhibited by the treatment of quercetin in a dose dependent manner. Nude mice injected with BEAS-2B cells chronically exposed to Cr(VI) in the presence of quercetin showed reduced tumor incidence compared to Cr(VI) alone treated group. Stable knockdown of miR-21 and overexpression of PDCD4 or catalase in BEAS-2B cells suppressed Cr(VI)-induced malignant transformation and tumorigenesis. Taken together, these results demonstrate that quercetin is able to protect BEAS-2B cells from Cr(VI)-induced carcinogenesis by targeting miR-21-PDCD4 signaling.

New Concepts in Cancer Biomarkers: Circulating miRNAs in Liquid Biopsies

The effective and efficient management of cancer patients relies upon early diagnosis and/or the monitoring of treatment, something that is often difficult to achieve using standard tissue biopsy techniques. Biological fluids such as blood hold great possibilities as a source of non-invasive cancer biomarkers that can act as surrogate markers to biopsy-based sampling. The non-invasive nature of these “liquid biopsies” ultimately means that cancer detection may be earlier and that the ability to monitor disease progression and/or treatment response represents a paradigm shift in the treatment of cancer patients. Below, we review one of the most promising classes of circulating cancer biomarkers: microRNAs (miRNAs). In particular, we will consider their history, the controversy surrounding their origin and biology, and, most importantly, the hurdles that remain to be overcome if they are really to become part of future clinical practice.

Regulation of the tumour suppressor PDCD4 by miR-499 and miR-21 in oropharyngeal cancers

BACKGROUND

The rates of oropharyngeal cancers such as tonsil cancers are increasing. The tumour suppressor protein Programmed Cell Death Protein 4 (PDCD4) has been implicated in the development of various human cancers and small RNAs such as microRNAs (miRNAs) can regulate its expression. However the exact regulation of PDCD4 by multiple miRNAs in oropharyngeal squamous cell carcinoma (SCC) is not well understood.

RESULTS

Using two independent oropharyngeal SCC cohorts with a focus on the tonsillar region, we identified a miRNA profile differentiating SCC tissue from normal. Both miR-21 and miR-499 were highly expressed in tonsil SCC tissues displaying a loss of PDCD4. Interestingly, expression of the miRNA machinery, Dicer1, Drosha, DDX5 (Dead Box Helicase 5) and DGCR8 (DiGeorge Syndrome Critical Region Gene 8) were all elevated by greater than 2 fold in the tonsil SCC tissue. The 3'UTR of PDCD4 contains three binding-sites for miR-499 and one for miR-21. Using a wild-type and truncated 3'UTR of PDCD4, we demonstrated that the initial suppression of PDCD4 was mediated by miR-21 whilst sustained suppression was mediated by miR-499. Moreover the single miR-21 site was able to elicit the same magnitude of suppression as the three miR-499 sites.

CONCLUSION

This study describes the regulation of PDCD4 specifically in tonsil SCC by miR-499 and miR-21 and has documented the loss of PDCD4 in tonsil SCCs. These findings highlight the complex interplay between miRNAs and tumour suppressor gene regulation and suggest that PDCD4 loss may be an important step in tonsillar carcinogenesis.

Hypermethylation and Expression Silencing of PDCD4 Gene in Hepatocellular Carcinoma: A Consort Study

Programmed cell death 4 (PDCD4) is a novel tumor suppressor, which is involved in the initiation and progression of cancers. However, the role of PDCD4 in hepatocellular carcinoma (HCC) has not been reported. The aim of this study was to investigate the molecular mechanism and clinical significance of PDCD4 inactivation in HCC.The mRNA levels of PDCD4 in HCC tissues and adjacent nontumor tissues were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). Bisulfite sequencing PCR was performed to determine the methylation status of PDCD4 promoter. Furthermore, the mRNA expression level and the methylated level of PDCD4 were analyzed with the clinical and pathological characteristics.qRT-PCR analysis showed that PDCD4 mRNA levels in tumor tissues were significantly decreased compared with that in adjacent nontumor tissues. The methylation rate of PDCD4 promoter was significantly higher in HCC tissues than that in adjacent nontumor tissues. PDCD4 mRNA levels and promoter methylation levels were both statistically correlated with metastasis and the degree of differentiation in HCC. In addition, the correlation between PDCD4 hypermethylation, mRNA levels, and overall survival (OS) was statistically significant.Our results indicated that PDCD4 may be a novel candidate of tumor suppressor gene in HCC, and that promoter hypermethylation is an important mechanism for its downregulation and is also a good predictor of OS for HCC.

Cell Density-Dependent Upregulation of PDCD4 in Keratinocytes and Its Implications for Epidermal Homeostasis and Repair

Programmed cell death 4 (PDCD4) is one multi-functional tumor suppressor inhibiting neoplastic transformation and tumor invasion. The role of PDCD4 in tumorigenesis has attracted more attention and has been systematically elucidated in cutaneous tumors. However, the normal biological function of PDCD4 in skin is still unclear. In this study, for the first time, we find that tumor suppressor PDCD4 is uniquely induced in a cell density-dependent manner in keratinocytes. To determine the potential role of PDCD4 in keratinocyte cell biology, we show that knockdown of PDCD4 by siRNAs can promote cell proliferation in lower cell density and partially impair contact inhibition in confluent HaCaT cells, indicating that PDCD4 serves as an important regulator of keratinocytes proliferation and contact inhibition in vitro. Further, knockdown of PDCD4 can induce upregulation of cyclin D1, one key regulator of the cell cycle. Furthermore, the expression patterns of PDCD4 in normal skin, different hair cycles and the process of wound healing are described in detail in vivo, which suggest a steady-state regulatory role of PDCD4 in epidermal homeostasis and wound healing. These findings provide a novel molecular mechanism for keratinocytes’ biology and indicate that PDCD4 plays a role in epidermal homeostasis.

Quantitative Proteomic Analysis of Enriched Nuclear Fractions from BK Polyomavirus-Infected Primary Renal Proximal Tubule Epithelial Cells

Polyomaviruses are a family of small DNA viruses that are associated with a number of severe human diseases, particularly in immunocompromised individuals. The detailed virus-host interactions during lytic polyomavirus infection are not fully understood. Here, we report the first nuclear proteomic study with BK polyomavirus (BKPyV) in a primary renal proximal tubule epithelial cell culture system using stable isotope labeling by amino acids in cell culture (SILAC) proteomic profiling coupled with liquid chromatography-tandem mass spectrometry. We demonstrated the feasibility of SILAC labeling in these primary cells and subsequently performed reciprocal labeling-infection experiments to identify proteins that are altered by BKPyV infection. Our analyses revealed specific proteins that are significantly up- or down-regulated in the infected nuclear proteome. The genes encoding many of these proteins were not identified in a previous microarray study, suggesting that differential regulation of these proteins may be independent of transcriptional control. Western blotting experiments verified the SILAC proteomic findings. Finally, pathway and network analyses indicated that the host cell DNA damage response signaling and DNA repair pathways are among the cellular processes most affected at the protein level during polyomavirus infection. Our study provides a comprehensive view of the host nuclear proteomic changes during polyomavirus lytic infection and suggests potential novel host factors required for a productive polyomavirus infection.

Comparative phosphoproteomic analysis of intestinal phosphorylated proteins in active versus aestivating sea cucumbers

The sea cucumber Apostichopus japonicus is becoming an excellent model marine invertebrate for studies of environmentally-induced aestivation. Reversible protein phosphorylation as a regulatory mechanism in aestivation is known for some terrestrial aestivators but has never before been documented in sea cucumbers. The present study provides a global quantitative analysis of the role of reversible phosphorylation in sea cucumber aestivation by using tandem mass tag (TMT) labeling followed by an IMAC enrichment strategy to map aestivation-responsive changes in the phosphoproteome of sea cucumber intestine. We identified 2295 unique phosphosites derived from 1283 phosphoproteins and, of these, 211 hyperphosphorylated and 65 hypophosphorylated phosphoproteins were identified in intestine during deep aestivation compared with the active state based on the following criterion: quantitative ratios over 1.5 or less than 0.67 with corrected p-value <0.05. Six major functional classes of proteins exhibited changes in their phosphorylation status during aestivation: (1) protein synthesis, (2) transcriptional regulators, (3) kinases, (4) signaling, (5) transporter, (6) DNA binding. These data on the global involvement of phosphorylation in sea cucumber aestivation significantly improve our understanding of the regulatory mechanisms involved in metabolic arrest when marine invertebrates face environmental stress and provide substantial candidate phosphorylated proteins that could be important for identifying functionally adaptive variation in marine invertebrates.

SIGNIFICANCE

Sea cucumber Apostichopus japonicus is an excellent model organism for studies of environmentally-induced aestivation by a marine invertebrate. The present study provides the first quantitative phosphoproteomic analysis of sea cucumber aestivation using isobaric tag based TMT labeling followed by an IMAC enrichment strategy. These data on the global involvement of phosphorylation in sea cucumber aestivation significantly improve our understanding of the regulatory mechanism involved in metabolic arrest when marine invertebrates face environmental stress and provide substantial candidate phosphorylated proteins that could be important for identifying functionally adaptive variation in marine invertebrates. This study also demonstrates the usefulness of the TMT-based quantitative phosphoproteomics approach to explore the survival responses of a non-model marine invertebrate species to seasonal changes in its environment.

Down-regulation of programmed cell death 4 (PDCD4) is associated with aromatase inhibitor resistance and a poor prognosis in estrogen receptor-positive breast cancer

Progression or recurrence due to resistance to aromatase inhibitors (AIs) is a significant clinical problem for a considerable number of patients with breast cancer. Programmed cell death 4 (PDCD4), a tumor suppressor protein, is targeted for degradation during tumor progression. In the current study, we aimed to examine PDCD4 expression and regulation in AI-resistant breast cancer cells, and its association with survival in patients with estrogen receptor (ER)-positive breast cancer. We determined PDCD4 expression levels in AI-resistant breast cancer cell lines and ER-positive breast cancer tumors, investigated the regulation of PDCD4 in AI-resistant breast cancer cell lines, and carried out a Kaplan-Meier survival analysis in two independent cohorts that included a total of 420 patients with ER-positive breast cancer. We found that PDCD4 expression was down-regulated in AI-resistant breast cancer cells, and this down-regulation was inversely correlated with activation of HER2 signaling. Moreover, lower expression of PDCD4 was significantly associated with HER2 positive status in ER-positive breast tumors. Down-regulation of PDCD4 was mediated through up-regulation of HER2 via the mitogen-activated protein kinase (MAPK), protein kinase B (PKB/AKT), and miR-21 in AI-resistant breast cancer cells. MiR-21 inhibitor and the ER down-regulator fulvestrant induced PDCD4 expression and decreased cell proliferation in AI-resistant breast cancer cells. Furthermore, forced overexpression of PDCD4 resensitized AI-resistant cells to AI or hormone deprivation. Finally, we identified that down-regulation of PDCD4 was associated with a lower rate of disease-free survival in patients with ER-positive breast cancer and high histologic grade of breast tumors. In summary, our study shows that expression of PDCD4 is down-regulated by HER2 signaling in AI-resistant breast cancer. Down-regulation of PDCD4 is associated with AI resistance and a poor prognosis in patients with ER-positive breast cancer.

Proteomic Profiling of Paclitaxel Treated Cells Identifies a Novel Mechanism of Drug Resistance Mediated by PDCD4

Paclitaxel (PTX) is a widely used chemotherapeutic drug effective against numerous cancers. To elucidate cellular pathways targeted by PTX and identify novel mechanisms of PTX resistance, we used a SILAC based quantitative proteomic approach to evaluate global changes of cellular protein abundance in HeLa cells. We identified 347 proteins involved in a number of biological processes including spindle assembly, mitotic exit, and extracellular adhesion whose abundance changes upon PTX treatment. Notably, the tumor suppressor PDCD4 involved in translation suppression was down-regulated by PTX. We demonstrated that PDCD4 is a cell-cycle regulated protein and that changes in its abundance are sufficient to alter PTX sensitivity in multiple human cancer cell lines. Immunoprecipitation of PDCD4-RNA complexes and RT-PCR revealed that PDCD4 mediated PTX sensitivity acts through its interaction with mRNA of UBE2S, a ubiquitin K11 linkage conjugating enzyme critical for mitotic exit. Lastly, high levels of PDCD4 in lung cancer tissues are positively correlated with the longer overall survival time of the examined lung cancer patients with PTX involved adjuvant therapy. Therefore, our proteomic screen for paclitaxel targets not only provided novel insight into the cellular resistance to paclitaxel via the PDCD4-mitotic exit regulation axis, but also offered a predictive biomarker for paclitaxel-based personalized chemotherapy in the treatment of lung cancer.

MicroRNA-330-3p functions as an oncogene in human esophageal cancer by targeting programmed cell death 4

MicroRNAs comprise a family of small non-coding RNA molecules that have emerged as key post-transcriptional regulators of gene expression. Aberrant miRNA expression has been linked to various human tumors. This study was aimed to identify novel miRNAs involved in the carcinogenesis of esophageal squamous cell carcinoma (ESCC) and their potential functions. We performed miRNA microarray and found that miR-330-3p was highly expressed in ESCC tumor tissues. qRT-PCR further confirmed the result in other 35 pairs of ESCC tumor tissues and ESCC cell lines. Ectopic expression of miR-330-3p significantly promoted ESCC cell proliferation, survival, migration, invasion in vitro and stimulated tumor formation in nude mice. Knockdown of miR-330-3p leaded to the opposite effects. The luciferase assay confirmed that miR-330-3p directly interacted with the PDCD4 mRNA 3' un-translated region (UTR). Moreover, expression of PDCD4 was inversely associated with miR-330-3p in ESCC tissues. Silencing of PDCD4 significantly promoted cell growth, cell migration, invasion and inhibited cisplatin-induced apoptosis in ESCC cells. This study suggested that miR-330-3p might play an oncogenic role in the development of ESCC partially via suppression of PDCD4 expression.

Inhibition of p70S6K1 Activation by Pdcd4 Overcomes the Resistance to an IGF-1R/IR Inhibitor in Colon Carcinoma Cells

Agents targeting insulin-like growth factor 1 receptor (IGF-1R) are being actively examined in clinical trials. Although there has been some initial success of single-agent targeting IGF-1R, attempts in later studies failed because of resistance. This study aimed to understand the effects of programmed cell death 4 (Pdcd4) on the chemosensitivity of the IGF-1R inhibitor OSI-906 in colorectal cancer cells and the mechanism underlying this impact. Using OSI-906-resistant and -sensitive colorectal cancer cells, we found that the Pdcd4 level directly correlates with cell chemosensitivity to OSI-906. In addition, tumors derived from Pdcd4 knockdown cells resist the growth inhibitory effect of OSI-906 in a colorectal cancer xenograft mouse model. Moreover, Pdcd4 enhances the antiproliferative effect of OSI-906 in resistant cells through suppression of p70S6K1 activation. Knockdown of p70S6K1, but not p70S6K2, significantly increases the chemosensitivity of OSI-906 in cultured colorectal cancer cells. Furthermore, the combination of OSI-906 and PF-4708671, a p70S6K1 inhibitor, efficiently suppresses the growth of OSI-906-resistant colon tumor cells in vitro and in vivo. Taken together, activation of p70S6K1 that is inhibited by Pdcd4 is essential for resistance to the IGF-1R inhibitor in colon tumor cells, and the combinational treatment of OSI-906 and PF-4708671 results in enhanced antiproliferation effects in colorectal cancer cells in vitro and in vivo, providing a novel venue to overcome the resistance to the IGF-1R inhibitor in treating colorectal cancer.

The total synthesis of (−)-cryptocaryol A

A stereoselective total synthesis of (−)-cryptocaryol A (1) is described. Key features of the 17-step route include the use of three boron-mediated aldol reaction–reduction sequences to control all stereocenters and an Ando modification of the Horner–Wadsworth–Emmons olefination that permitted the installation of the Z double bond of the α-pyrone ring.

Post-transcriptional regulation of programmed cell death 4 (PDCD4) mRNA by the RNA-binding proteins human antigen R (HuR) and T-cell intracellular antigen 1 (TIA1)

Post-transcriptional processing of mRNA transcripts plays a critical role in establishing the gene expression profile of a cell. Such processing events are mediated by a host of factors, including RNA-binding proteins and microRNAs. A number of critical cellular pathways are subject to regulation at multiple levels that allow fine-tuning of key biological responses. Programmed cell death 4 (PDCD4) is a tumor suppressor and an important modulator of mRNA translation that is regulated by a number of mechanisms, most notably as a target of the oncomiR, miR-21. Here, we provide evidence for post-transcriptional regulation of PDCD4 by the RNA-binding proteins, HuR and TIA1. Complementary approaches reveal binding of both HuR and TIA1 to the PDCD4 transcript. Consistent with a model where RNA-binding proteins modulate the PDCD4 transcript, knockdown of HuR and/or TIA1 results in a significant decrease in steady-state PDCD4 mRNA and protein levels. However, fractionation experiments suggest that the mode of regulation of the PDCD4 transcript likely differs in the cytoplasm and the nucleus as the pool of PDCD4 mRNA present in the cytoplasm is more stable than the nuclear pool of PDCD4 transcript. We observe a competitive mode of binding between HuR and TIA1 on the PDCD4 transcript in the cytoplasm, suggesting that these two factors dynamically interact with one another as well as the PDCD4 transcript to maintain tight control of PDCD4 levels. Overall, this study reveals an additional set of regulatory interactions that modulate the expression of PDCD4, a key pro-apoptotic factor, and also reveals new insights into how HuR and TIA1 functions are integrated to achieve such regulation.

PDCD4 as a predictor of sensitivity to neoadjuvant chemoradiotherapy in locally advanced rectal cancer patients

OBJECTIVE

The purpose of this study was to examine the role of programmed cell death 4 (PDCD4) expression in predicting tumor response to neoadjuvant chemoradiotherapy and outcomes for patients with locally advanced rectal cancer.

METHODS

Clinicopathological factors and expression of PDCD4 were evaluated in 92 patients with LARC treated with nCRT. After the completion of therapy, 4 cases achieved clinical complete response (cCR), and thus the remaining 88 patients underwent a standardized total mesorectal excision procedure. There were 38 patients (41.3%) with a good response (TRG 3-4) and 54 (58.7%) with a poor one (TRG 0-2).

RESULTS

Immunohistochemical staining analyses showed that patients with high expression of PDCD4 were more sensitive to nCRT than those with low PDCD4 expression (P=0.02). High PDCD4 expression before nCRT and good response (TRG3-4) were significantly associated with improved 5-year disease-free survival and 5-year overall survival (P<0.05). Multivariate analysis demonstrated that the pretreatment PDCD4 expression was an independent prognostic factor.

CONCLUSION

Our study demonstrated that high expression of PDCD4 protein is a useful predictive factor for good tumor response to nCRT and good outcomes in patients with LARC.

MicroRNA-183 promotes proliferation and invasion in oesophageal squamous cell carcinoma by targeting programmed cell death 4

BACKGROUND

Dysregulated microRNAs (miRNAs) can serve as oncogenes or suppressors and are associated with many cancers, including oesophageal squamous cell carcinoma (ESCC).

METHODS

An alignment miRNA array was used to identify differentially expressed miRNAs in ESCC tissues. The expression of miR-183 and programmed cell death 4 (PDCD4) in oesophageal tissues from ESCC and early oesophageal carcinoma patients was examined by quantitative reverse transcriptase PCR and western blotting. A luciferase assay was performed to confirm miR-183 target genes. The effects of miR-183 on ESCC cells and the associated mechanisms were established by in vitro experiments.

RESULTS

We identified 51 upregulated miRNAs and 17 downregulated miRNAs in our array, and miR-183 was one of the most upregulated miRNAs. An inverse correlation between miR-183 and PDCD4 levels was found in ESCC tissues. Upregulated expression of miR-183 was not correlated with tumour stage or lymphatic metastasis in ESCC patients. The luciferase assay confirmed that miR-183 directly interacted with the PDCD4 mRNA 3'-untranslated region in ESCC cells. Overexpression of miR-183 led to decreased PDCD4 protein levels and promoted ESCC cell proliferation and invasion. Inhibition of the PI3K/Akt signalling pathway increased PDCD4 protein levels and decreased miR-183 expression in ESCC cells.

CONCLUSIONS

MiR-183 promotes ESCC cell proliferation and invasion by directly targeting PDCD4, which suggests that it is involved in the pathogenesis of ESCC.

Inflammation and MiR-21 pathways functionally interact to downregulate PDCD4 in colorectal cancer

Inflammation plays a direct role in colorectal cancer (CRC) progression; however the molecular mechanisms responsible for this effect are unclear. The inflammation induced cyclooxygenase 2 (COX-2) enzyme required for the production of Prostaglandin E2 (PGE₂), can promote colorectal cancer by decreasing expression of the tumour suppressor gene Programmed Cell Death 4 (PDCD4). As PDCD4 is also a direct target of the oncogene microRNA-21 (miR-21) we investigated the relationship between the COX-2 and miR-21 pathways in colorectal cancer progression. Gene expression profile in tumour and paired normal mucosa from 45 CRC patients demonstrated that up-regulation of COX-2 and miR-21 in tumour tissue correlates with worse Dukes' stage. In vitro studies in colonic adenocarcinoma cells revealed that treatment with the selective COX-2 inhibitor NS398 significantly decreased miR-21 levels (p = 0.0067) and increased PDCD4 protein levels (p<0.001), whilst treatment with PGE₂ up-regulated miR-21 expression (p = 0.019) and down-regulated PDCD4 protein (p<0.05). These findings indicate that miR-21 is a component of the COX-2 inflammation pathway and that this pathway promotes worsening of disease stage in colorectal cancer by inducing accumulation of PGE₂ and increasing expression of miR-21 with consequent downregulation of the tumour suppressor gene PDCD4.

The role of IRES trans-acting factors in carcinogenesis

Regulation of protein expression through RNA metabolism is a key aspect of cellular homeostasis. Upon specific cellular stresses, distinct transcripts are selectively controlled to modify protein output in order to quickly and appropriately respond to stress. Reprogramming of the translation machinery is one node of this strict control that typically consists of an attenuation of the global, cap-dependent translation and accompanying switch to alternative mechanisms of translation initiation, such as internal ribosome entry site (IRES)-mediated initiation. In cancer, many aspects of the RNA metabolism are frequently misregulated to provide cancer cells with a growth and survival advantage. This includes changes in the expression and function of RNA binding proteins termed IRES trans-acting factors (ITAFs) that are central to IRES translation. In this review, we will examine select emerging, as well as established, ITAFs with important roles in cancer initiation and progression, and in particular their role in IRES-mediated translation. This article is part of a Special Issue entitled: Translation and Cancer.

Challenges and opportunities of microRNAs in lymphomas

MicroRNAs (miRNAs) are small non-coding RNAs that control the expression of many target messenger RNAs (mRNAs) involved in normal cell functions (differentiation, proliferation and apoptosis). Consequently their aberrant expression and/or functions are related to pathogenesis of many human diseases including cancers. Haematopoiesis is a highly regulated process controlled by a complex network of molecular mechanisms that simultaneously regulate commitment, differentiation, proliferation, and apoptosis of hematopoietic stem cells (HSC). Alterations on this network could affect the normal haematopoiesis, leading to the development of haematological malignancies such as lymphomas. The incidence of lymphomas is rising and a significant proportion of patients are refractory to standard therapies. Accurate diagnosis, prognosis and therapy still require additional markers to be used for diagnostic and prognostic purpose and evaluation of clinical outcome. The dysregulated expression or function of miRNAs in various types of lymphomas has been associated with lymphoma pathogenesis. Indeed, many recent findings suggest that almost all lymphomas seem to have a distinct and specific miRNA profile and some miRNAs are related to therapy resistance or have a distinct kinetics during therapy. MiRNAs are easily detectable in fresh or paraffin-embedded diagnostic tissue and serum where they are highly stable and quantifiable within the diagnostic laboratory at each consultation. Accordingly they could be specific biomarkers for lymphoma diagnosis, as well as useful for evaluating prognosis or disease response to the therapy, especially for evaluation of early relapse detection and for greatly assisting clinical decisions making. Here we summarize the current knowledge on the role of miRNAs in normal and aberrant lymphopoiesis in order to highlight their clinical value as specific diagnosis and prognosis markers of lymphoid malignancies or for prediction of therapy response. Finally, we discuss their controversial therapeutic role and future applications in therapy by modulating miRNA.

MicroRNA-183 inhibits apoptosis and promotes proliferation and invasion of gastric cancer cells by targeting PDCD4

MicroRNA plays an important role in multiple processes of cancer development. Aberrant expression of miR-183 has been frequently reported in a variety of cancer types; however, the roles and mechanisms of miR-183 in gastric cancer are largely unknown. Here, we report that miR-183 is significantly up-regulated in human gastric tumor tissues compared to the adjacent normal tissues. Up-regulation of miR-183 is associated with advanced clinical stage, positive lymph node, deep stromal invasion, and distant metastasis in gastric cancer patients. We further demonstrated that miR-183 promotes gastric cancer cell growth in vitro by inhibition of apoptosis. Moreover, overexpression of miR-183 enhances gastric cancer cell migration and invasion. Mechanistically, we demonstrated that overexpression of miR-183 decreased, and inhibition of miR-183 increased the expression of PDCD4, a tumor suppressor, at both mRNA and protein levels. Taken together, our results suggest that miR-183 may modulate progression and metastatic potential of gastric cancer through inhibition of PDCD4 expression. miR-183 could serve as a potential biomarker for gastric cancer progression and a novel therapeutic target for gastric cancer treatment.

Programmed cell death 4 and microRNA 21 inverse expression is maintained in cells and exosomes from ovarian serous carcinoma effusions

BACKGROUND

Ovarian serous carcinoma (OSC) is a fatal gynecologic malignancy usually presenting with bilateral localization and malignant peritoneal effusion. Programmed cell death 4 (PDCD4) is a tumor suppressor gene whose expression is directly controlled by microRNA-21 (miR-21). Exosomes are small cell-derived vesicles that participate in intercellular communication, delivering their cargo of molecules to specific cells. Exosomes are involved in several physiological and pathological processes including oncogenesis, immunomodulation, angiogenesis, and metastasis. The current study analyzed the expression of PDCD4 and miR-21 in resected OSC specimens and in cells and exosomes from OSC peritoneal effusions.

METHODS

PDCD4 was immunohistochemically examined in 14 normal ovaries, 14 serous cystadenoma (CA), and 14 OSC cases. Quantitative reverse transcriptase-polymerase chain reaction analysis of PDCD4 and miR-21 expression was performed in CA and OSC cases and in cells and exosomes obtained from 10 OSC and 10 nonneoplastic peritoneal effusions. miR-21 was also evaluated by in situ hybridization.

RESULTS

Immunohistochemistry demonstrated a gradual PDCD4 loss from normal ovaries to CA and OSC specimens. Quantitative reverse transcriptase-polymerase chain reaction displayed higher PDCD4 messenger RNA levels in CA specimens compared with OSC cases and highlighted miR-21 overexpression in OSC specimens. In situ hybridization detected miR-21 only in OSC cells. This PDCD4 and miR-21 inverse expression was also noted in cells and exosomes from OSC peritoneal effusions compared with nonneoplastic effusions.

CONCLUSIONS

PDCD4 and miR-21 are involved in OSC oncogenesis. The transfer of miR-21 by exosomes could promote oncogenic transformation in target cells distant from the primary tumor without direct colonization by cancer cells and could be used as a diagnostic tool.

Enhanced arginine methylation of programmed cell death 4 protein during nutrient deprivation promotes tumor cell viability

The role of programmed cell death 4 (PDCD4) in tumor biology is context-dependent. PDCD4 is described as a tumor suppressor, but its coexpression with protein arginine methyltransferase 5 (PRMT5) promotes accelerated tumor growth. Here, we report that PDCD4 is methylated during nutrient deprivation. Methylation occurs because of increased stability of PDCD4 protein as well as increased activity of PRMT5 toward PDCD4. During nutrient deprivation, levels of methylated PDCD4 promote cell viability, which is dependent on an enhanced interaction with eIF4A. Upon recovery from nutrient deprivation, levels of methylated PDCD4 are regulated by phosphorylation, which controls both the localization and stability of methylated PDCD4. This study reveals that, in response to particular environmental cues, the role of PDCD4 is up-regulated and is advantageous for cell viability. These findings suggest that the methylated form of PDCD4 promotes tumor viability during nutrient deprivation, ultimately allowing the tumor to grow more aggressively.

A novel mechanism for the control of translation of specific mRNAs by tumor suppressor protein Pdcd4: inhibition of translation elongation

The tumor suppressor gene Pdcd4 (programmed cell death gene 4) has drawn considerable attention because its downregulation is involved in the development of several types of cancer. Because Pdcd4 interacts with the translation initiation factor eIF4A and inhibits its helicase activity, Pdcd4 has been implicated in the translational suppression of cellular mRNAs containing structured 5'-untranslated regions. However, Pdcd4's role in translation regulation is still poorly understood, because only very few physiological Pdcd4 target mRNAs are known. By using a Pdcd4-deficient clone of the chicken B-cell line DT40, we have discovered that the mRNA of the A-myb proto-oncogene is a novel Pdcd4 target RNA whose translation is suppressed by Pdcd4. Interestingly, the inhibitory effect of Pdcd4 is independent of the Pdcd4-eIF4A interaction, but is dependent on an RNA-binding domain at the N terminus of Pdcd4 and on sequences located within the coding region of A-myb mRNA, indicating that Pdcd4 suppresses A-myb translation by a novel mechanism. Our data show that the Pdcd4 RNA-binding domain preferentially recognizes an RNA secondary structure element formed by the part of the A-myb coding region that mediates Pdcd4-dependent suppression. Previously, we have shown that Pdcd4 also suppresses the translation of the c-myb mRNA by a similar mechanism involving binding of Pdcd4 to RNA secondary structure formed by the c-myb coding region. Surprisingly, our data show that Pdcd4 exerts its inhibitory activity only when the target region of Pdcd4 in A-myb and c-myb mRNA is itself translated, consistent with a mechanism in which Pdcd4 suppresses translation by interfering with translation elongation. Taken together, our work reveals a novel mechanism by which Pdcd4 affects the translational of cellular RNAs. Furthermore, as c-myb and A-myb are members of the Myb proto-oncogene family whose deregulation has been implicated in tumorigenesis, inhibiting their translation might contribute to the tumor-suppressive activity of Pdcd4.

MiR-21 is under control of STAT5 but is dispensable for mammary development and lactation

Development of mammary alveolar epithelium during pregnancy is controlled by prolactin, through the transcription factors STAT5A/B that activate specific sets of target genes. Here we asked whether some of STAT5's functions are mediated by microRNAs. The miR-21 promoter sequence contains a bona-fide STAT5 binding site and miR-21 levels increased in HC11 mammary cells upon prolactin treatment. In vivo miR-21 was abundantly expressed in mammary epithelium at day 6 of pregnancy. Analysis of mice lacking miR-21 revealed that their mammary tissue developed normally during pregnancy and dams were able to nurse their pups. Our study demonstrated that although expression of miR-21 is under prolactin control through the transcription factors STAT5A/B its presence is dispensable for mammary development and lactation.

Effect of intensive atorvastatin therapy on periprocedural PDCD4 expression in CD4+ T lymphocytes of patients with unstable angina undergoing percutaneous coronary intervention

OBJECTIVE

To investigate the effects of intensive atorvastatin therapy on programmed cell death 4 (PDCD4) expression by CD4+ T lymphocytes in patients with unstable angina who received percutaneous coronary intervention (PCI).

METHODS

Patients with unstable angina were randomized to pretreatment with either an intensive dose (80 mg/day, n = 33) or a conventional dose (20 mg/day, n = 33) of atorvastatin. Circulating CD4+ T cells were subsequently obtained prior to PCI, and also 18-24 h after PCI, using a magnetic cell sorting system. Fluorescence-based quantitative real-time PCR was then used to measure levels of PDCD4 mRNA in the isolated CD4+ T lymphocytes, and Western blot analysis was used to detect levels of PDCD4. Serum levels of interleukin (IL)-10 and TNF-α were quantified using enzyme-linked immunosorbent assays.

RESULTS

Of the 66 patients with unstable angina that were examined, levels of PDCD4 mRNA and protein were found to dramatically decrease in patients who received an intensive dose of atorvastatin following PCI (p < 0.05). In contrast, serum levels of TNF-α significantly increased following PCI in both the intensive dose group and the conventional dose group, with the latter being higher than the former (p < 0.05). Serum IL-10 levels also markedly increased following PCI for the two groups. However, higher values were associated with the intensive dose group (p < 0.05).

CONCLUSIONS

Intensive atorvastatin treatment reduced the post-PCI myocardial inflammatory response in patients with unstable angina, possibly by inhibiting PDCD4 expression in CD4+ T lymphocytes.

Tumor suppressor PDCD4 inhibits NF-κB-dependent transcription in human glioblastoma cells by direct interaction with p65

PDCD4 is a tumor suppressor induced by apoptotic stimuli that regulates both translation and transcription. Previously, we showed that overexpression of PDCD4 leads to decreased anchorage-independent growth in glioblastoma (GBM)-derived cell lines and decreased tumor growth in a GBM xenograft model. In inflammatory cells, PDCD4 stimulates tumor necrosis factor-induced activation of the transcription factor NF-κB, an oncogenic driver in many cancer sites. However, the effect of PDCD4 on NF-κB transcriptional activity in most cancers including GBM is still unknown. We studied the effect of PDCD4 on NF-κB-dependent transcriptional activity in GBM by stably overexpressing PDCD4 in U251 and LN229 cells. Stable PDCD4 expression inhibits NF-κB transcriptional activation measured by a luciferase reporter. The molecular mechanism by which PDCD4 inhibits NF-κB transcriptional activation does not involve inhibited expression of NF-κB p65 or p50 proteins. PDCD4 does not inhibit pathways upstream of NF-κB including the activation of IKKα and IKKβ kinases or degradation of IκBα, events needed for nuclear transport of p65 and p50. PDCD4 overexpression does inhibit localization of p65 but not p50 in the nucleus. PDCD4 protein interacts preferentially with p65 protein as shown by co-immunoprecipitation and confocal imaging. PDCD4 overexpression inhibits the mRNA expression of two NF-κB target genes in a p65-dependent manner. These results suggest that PDCD4 can significantly inhibit NF-κB activity in GBM cells by a mechanism that involves direct or indirect protein-protein interaction independent of the expected mRNA-selective translational inhibition. These findings offer novel opportunities for NF-κB-targeted interventions to prevent or treat cancer.

MicroRNAs cooperatively inhibit a network of tumor suppressor genes to promote pancreatic tumor growth and progression

BACKGROUND & AIMS

There has not been a broad analysis of the combined effects of altered activities of microRNAs (miRNAs) in pancreatic ductal adenocarcinoma (PDAC) cells, and it is unclear how these might affect tumor progression or patient outcomes.

METHODS

We combined data from miRNA and messenger RNA (mRNA) expression profiles and bioinformatic analyses to identify an miRNA-mRNA regulatory network in PDAC cell lines (PANC-1 and MIA PaCa-2) and in PDAC samples from patients. We used this information to identify miRNAs that contribute most to tumorigenesis.

RESULTS

We identified 3 miRNAs (MIR21, MIR23A, and MIR27A) that acted as cooperative repressors of a network of tumor suppressor genes that included PDCD4, BTG2, and NEDD4L. Inhibition of MIR21, MIR23A, and MIR27A had synergistic effects in reducing proliferation of PDAC cells in culture and growth of xenograft tumors in mice. The level of inhibition was greater than that of inhibition of MIR21 alone. In 91 PDAC samples from patients, high levels of a combination of MIR21, MIR23A, and MIR27A were associated with shorter survival times after surgical resection.

CONCLUSIONS

In an integrated data analysis, we identified functional miRNA-mRNA interactions that contribute to growth of PDACs. These findings indicate that miRNAs act together to promote tumor progression; therapeutic strategies might require inhibition of several miRNAs.

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.

Splicing factor SRSF3 represses the translation of programmed cell death 4 mRNA by associating with the 5'-UTR region

Serine/arginine-rich splicing factor 3 (SRSF3), a member of the serine/arginine (SR)-rich family of proteins, regulates both alternative splicing of pre-mRNA and export of mature mRNA from the nucleus. Although its role in nuclear mRNA processing is well understood, the mechanism by which it alters the fate of cytoplasmic mRNA molecules remains elusive. Here, we provide evidence that SRSF3 not only regulates the alternative splicing pattern of programmed cell death 4 (PDCD4) mRNA, but also modulates its translational efficiency in the cytoplasm by lowering translation levels. We observed a marked increase in PDCD4 mRNA in translating polysome fractions upon silencing of SRSF3, and, conversely, ectopic overexpression of SRSF3 shifted PDCD4 mRNA into non-translating ribosomal fractions. In live cells, SRSF3 colocalized with PDCD4 mRNA in P-bodies (PBs), where translationally silenced mRNAs are deposited, and this localization was abrogated upon SRSF3 silencing. Furthermore, using two different reporter systems, we showed that SRSF3 interacts directly with PDCD4 mRNA and mediates translational repression by binding to the 5'-untranslated region (5'-UTR). In summary, our data suggest that the oncogenic potential of SRSF3 might be realized, in part, through the translational repression of PDCD4 mRNA.

MiR-21 overexpression is associated with acquired resistance of EGFR-TKI in non-small cell lung cancer

BACKGROUND AND PURPOSE

With the increasing use of epidermal growth factor receptor tyrosine kinase inhibitor (EGFR TKI) in patients with advanced non-small cell lung cancer (NSCLC), its acquired resistance has become a major clinical problem. Recent studies revealed that miR-21 was involved into the resistance of cytotoxic agents. The aim of this study was to investigate its role in the acquired resistance of NSCLC to EGFR-TKI.

METHODS

EGFR-TKI-sensitive human lung adenocarcinoma cell line PC9 and the acquired resistant cell line, PC9R, were used. Lentiviral vectors were used to infect PC9 or PC9R to regulate the miR-21 expression. The expression of targeted proteins PTEN and PDCD4 was controlled by RNA interference. MicroRNA array, RT-PCR and TaqMan MicroRNA Assays were used to detect miR-21 expression. The MTT and Annexin V assays were used to determine proliferation and apoptosis. Western Blot and immunohistochemistry were used to analyze target protein expression (PTEN, PDCD4, Akt, p-Akt). We also constructed PC9R xenograft tumor model to observe the relationship between miR-21 and EGFR-TKI resistance in vivo and validated it in the clinical serum specimens of NSCLC patients treated with EGFR-TKI.

RESULT

MiR-21 was overexpressed in the EGFR-TKI resistant cell line PC9R relative to PC9. The level of miR-21 was reversely correlated with the expression of PTEN and PDCD4 and positive correlated with PI3K/Akt pathway. Inhibiting miR-21 with lentivirus vector induces apoptosis in PC9R cell line and inhibiting miR-21with ASO suppressed tumor growth in nude mice treated with EGFR-TKI. Furthermore, serum miR-21 expression in NSCLC patients treated with EGFR-TKI was significantly higher at the time of acquiring resistance than at baseline (p<0.01).

CONCLUSION

miR-21 is involved in acquired resistance of EGFR-TKI in NSCLC, which is mediated by down-regulating PTEN and PDCD4 and activating PI3K/Akt pathway.

MicroRNA-182 promotes cell growth, invasion, and chemoresistance by targeting programmed cell death 4 (PDCD4) in human ovarian carcinomas

As an important tumor suppressor, programmed cell death 4 (PDCD4) influences transcription and translation of multiple genes, and modulates different signal transduction pathways. However, the upstream regulation of this gene is largely unknown. In this study, we found that microRNA-182 (miRNA-182, miR-182) was upregulated, whereas PDCD4 was downregulated in ovarian cancer tissues and cell lines. Blocking or increase of miR-182 in ovarian cancer cell lines led to an opposite alteration of endogenous PDCD4 protein level. Using fluorescent reporter assay, we confirmed the direct and negative regulation of PDCD4 by miR-182, which was dependent on the predicted miR-182 binding site within PDCD4 3' untranslated region (3' UTR). MTT and colony formation assays suggested that miR-182 blockage suppressed, whereas miR-182 mimics enhanced viability and colony formation of ovarian cancer cells. These effects may partly be attributed to the cell cycle promotion activity of miR-182. miR-182 also contributed to migration and invasion activities of ovarian cancer cells. Furthermore, miR-182 reduced the chemosensitivity of ovarian cancer cells to CDDP and Taxol, possibly by its anti-apoptosis activity. Importantly, all the alterations of the above cellular phenotypes by blocking or enhancing of miR-182 could be alleviated by subsequent suppression or ectopic expression of its target PDCD4, respectively. We conclude that in ovarian cancer cells, miR-182 acts as an oncogenic miRNA by directly and negatively regulating PDCD4.

The unique evolution of the programmed cell death 4 protein in plants

BACKGROUND

The programmed cell death 4 (PDCD4) protein is induced in animals during apoptosis and functions to inhibit translation and tumor promoter-induced neoplastic transformation. PDCD4 is composed of two MA3 domains that share similarity with the single MA3 domain present in the eukaryotic translation initiation factor (eIF) 4G, which serves as a scaffold protein to assemble several initiation factors needed for the recruitment of the 40S ribosomal subunit to an mRNA. Although eIF4A is an ATP-dependent RNA helicase that binds the MA3 domain of eIF4G to promote translation initiation, binding of eIF4A to the MA3 domains of PDCD4 inhibits protein synthesis. Genes encoding PDCD4 are present in many lower eukaryotes and in plants, but PDCD4 in higher plants is unique in that it contains four MA3 domains and has been implicated in ethylene signaling and abiotic stress responses. Here, we examine the evolution of PDCD4 in plants.

RESULTS

In older algal lineages, PDCD4 contains two MA3 domains similar to the homolog in animals. By the appearance of early land plants, however, PDCD4 is composed of four MA3 domains which likely is the result of a duplication of the two MA3 domain form of the protein. Evidence from fresh water algae, from which land plants evolved, suggests that the duplication event occurred prior to the colonization of land. PDCD4 in more recently evolved chlorophytes also contains four MA3 domains but this may have resulted from an independent duplication event. Expansion and divergence of the PDCD4 gene family occurred during land plant evolution with the appearance of a distinct gene member following the evolution of basal angiosperms.

CONCLUSIONS

The appearance of a unique form of PDCD4 in plants correlates with the appearance of components of the ethylene signaling pathway, suggesting that it may represent the adaptation of an existing protein involved in programmed cell death to one that functions in abiotic stress responses through hormone signaling.

Berberine sensitizes ovarian cancer cells to cisplatin through miR-21/PDCD4 axis

Recent studies have shown that microRNA-21 (miR-21) contributes to tumor resistance to chemotherapy. Interestingly, we have found that berberine could inhibit miR-21 expression in several cancer cell lines. In this study, we investigated whether berberine could modulate the sensitivity of ovarian cancer cells to cisplatin and explored the mechanism. The cisplatin-resistant SKOV3 cells that were incubated with berberine combined with cisplatin had a significantly lower survival than the cisplatin alone group and enhanced cisplatin-induced apoptosis. Berberine could inhibit miR-21 expression and function in ovarian cancer, as shown by an enhancement of its target PDCD4, an important tumor suppressor in ovarian cancer. The results suggested that berberine could modulate the sensitivity of cisplatin via regulating miR-21/PDCD4 axis in the ovarian cancer cells.

Briefing in family characteristics of microRNAs and their applications in cancer research

MicroRNAs (miRNAs) are endogenous, short, non-coding RNA molecules that are directly involved in the post-transcriptional regulation of gene expression. Dysregulation of miRNAs is usually associated with diseases. Since miRNAs in a family intend to have common functional characteristics, proper assignment of miRNA family becomes heuristic for better understanding of miRNA nature and their potentials in clinic. In this review, we will briefly discuss the recent progress in miRNA research, particularly its impact on protein and its clinical application in cancer research in a view of miRNA family. This article is part of a Special Issue entitled: Computational Proteomics, Systems Biology & Clinical Implications. Guest Editor: Yudong Cai.

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.

Downregulation of microRNA-182 inhibits cell growth and invasion by targeting programmed cell death 4 in human lung adenocarcinoma cells

Lung cancer is a major cause of cancer death worldwide. Programmed cell death 4 (PDCD4), an important tumor suppressor, influences transcription and translation of multiple genes and modulates different signal transduction pathways. However, the upstream regulation of this gene is largely unknown. In our study, we found that microRNA-182 (miR-182) was upregulated, whereas PDCD4 was downregulated in lung cancer cell lines. We performed methyl thiazolyl tetrazolium and colony formation assays to study the influence of miR-182 on proliferation of the lung cancer cell lines A549 and SPC-A-1. We also carried out Transwell and wound healing assays to investigate the effect of miR-182 on invasion and migration of A549 and SPC-A-1. Finally, using the luciferase reporter assay and restore assay, we demonstrated that PDCD4 is a direct target of miR-182. These results suggest that in lung adenocarcinoma cells, miR-182 plays an oncogenic role as a direct negative regulator of PDCD4.

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.

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.

Serum microRNA expression as an early marker for breast cancer risk in prospectively collected samples from the Sister Study cohort

Introduction

MicroRNAs (miRNAs) are small, non-coding, single-stranded RNAs between 18-22 nucleotides long that regulate gene expression. Expression of miRNAs is altered in tumor compared to normal tissue; there is some evidence that these changes may be reflected in the serum of cancer cases compared to healthy individuals. This has yet to be examined in a prospective study where samples are collected before diagnosis.

Methods

We used Affymetrix arrays to examine serum miRNA expression profiles in 410 participants in the Sister Study, a prospective cohort study of 50,884 women. All women in the cohort had never been diagnosed with breast cancer at the time of enrollment. We compared global miRNA expression patterns in 205 women who subsequently developed breast cancer and 205 women who remained breast cancer-free. In addition within the case group we examined the association of miRNA expression in serum with different tumor characteristics, including hormone status (ER, PR, and HER-2) and lymph node status.

Results

Overall, 414 of 1,105 of the human miRNAs on the chip were expressed above background levels in 50 or more women. When the average expression among controls was compared to cases using conditional logistic regression, 21 miRNAs were found to be differentially expressed (P≤.05). Using qRT-PCR on a small, independent sample of 5 cases and 5 controls we verified overexpression of the 3 highest expressing miRNAs among cases, miR-18a, miR-181a, and miR-222; the differences were not statistically significant in this small set. The 21 differentially expressed miRNAs are known to target at least 82 genes; using the gene list for pathway analysis we found enrichment of genes involved in cancer-related processes. In a separate case-case analyses restricted to the 21 miRNAs, we found 7 miRNAs with differential expression for women whose breast tumors differed by HER-2 expression, and 10 miRNAs with differential expression by nodal status.

Conclusions

miRNA levels in serum show a number of small differences between women who later develop cancer versus those who remain cancer-free.

The inhibitory action of PDCD4 in lipopolysaccharide/D-galactosamine-induced acute liver injury

Programmed cell death 4 (PDCD4) acts as a tumor suppressor gene, which suppresses tumor growth, infiltration and metastasis. Our previous studies demonstrated that PDCD4 had an important role in the development of ovarian cancer and glioma. Recent studies show that PDCD4 is also involved in various inflammatory diseases. However, its exact effect on inflammation remains unclear. In our current study, we explored the role of PDCD4 in acute liver injury induced by lipopolysaccharide (LPS) and D-galactosamine (D-GalN) using wild-type (WT) mice and PDCD4-deficient mice. Our results showed that liver-to-body weight ratios, as well as serum aspartate transaminase (AST) and alanine transaminase (ALT) levels were significantly increased in PDCD4-deficient mice than WT mice. Histological examination, immunohistochemical and TUNEL analysis revealed PDCD4-deficient mice had more necrotic and apoptotic hepatocytes, inflammatory cells infiltration and liver internal hemorrhage than WT mice. In addition, some inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) in the serum and liver tissues were also significantly increased in PDCD4-deficient mice. More importantly, we found that the aggravation of liver tissue injury in PDCD4-deficient mice was due to excessive mitogen-activated protein kinase and NF-κB activation, which induced the release of more inflammatory factors, and consequently resulted in higher levels of hepatocyte necrosis and apoptosis. These results indicate that PDCD4 has a protective role in LPS/D-GalN-induced acute liver injury. This finding may present new opportunities for PDCD4 to be explored as a therapeutic target in acute liver injury.

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.

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.