Programmed Cell Death Protein 4 (PDCD4) Acts As a Tumor Suppressor in Neuroendocrine Tumor Cells

The Role and Interactions of Programmed Cell Death 4 and its Regulation by microRNA in Transformed Cells of the Gastrointestinal Tract

Data from GLOBOCAN 2020 estimates that there were 19.3 million new cases of cancer and 10.0 million cancer-related deaths in 2020 and that this is predicted to increase by 47% in 2040. The combined burden of cancers of the gastrointestinal (GI) tract, including oesophageal-, gastric- and colorectal cancers, resulted in 22.6% of the cancer-related deaths in 2020 and 18.7% of new diagnosed cases. Understanding the aetiology of GI tract cancers should have a major impact on future therapies and lessen this substantial burden of disease. Many cancers of the GI tract have suppression of the tumour suppressor Programmed Cell Death 4 (PDCD4) and this has been linked to the expression of microRNAs which bind to the untranslated region of PDCD4 mRNA and either inhibit translation or target the mRNA for degradation. This review highlights the properties of PDCD4 and documents the evidence for the regulation of PDCD4 expression by microRNAs in cancers of the GI tract.

A Role for Adipocytes and Adipose Stem Cells in the Breast Tumor Microenvironment and Regenerative Medicine

Obesity rates are climbing, representing a confounding and contributing factor to many disease states, including cancer. With respect to breast cancer, obesity plays a prominent role in the etiology of this disease, with certain subtypes such as triple-negative breast cancer having a strong correlation between obesity and poor outcomes. Therefore, it is critical to examine the obesity-related alterations to the normal stroma and the tumor microenvironment (TME). Adipocytes and adipose stem cells (ASCs) are major components of breast tissue stroma that have essential functions in both physiological and pathological states, including energy storage and metabolic homeostasis, physical support of breast epithelial cells, and directing inflammatory and wound healing responses through secreted factors. However, these processes can become dysregulated in both metabolic disorders, such as obesity and also in the context of breast cancer. Given the well-established obesity-neoplasia axis, it is critical to understand how interactions between different cell types in the tumor microenvironment, including adipocytes and ASCs, govern carcinogenesis, tumorigenesis, and ultimately metastasis. ASCs and adipocytes have multifactorial roles in cancer progression; however, due to the plastic nature of these cells, they also have a role in regenerative medicine, making them promising tools for tissue engineering. At the physiological level, the interactions between obesity and breast cancer have been examined; here, we will delineate the mechanisms that regulate ASCs and adipocytes in these different contexts through interactions between cancer cells, immune cells, and other cell types present in the tumor microenvironment. We will define the current state of understanding of how adipocytes and ASCs contribute to tumor progression through their role in the tumor microenvironment and how this is altered in the context of obesity. We will also introduce recent developments in utilizing adipocytes and ASCs in novel approaches to breast reconstruction and regenerative medicine.

MicroRNA-421-targeted PDCD4 regulates breast cancer cell proliferation

MicroRNAs (miRNAs) are expressed aberrantly in various types of cancer, and negatively regulate the expression of target genes which may be useful in therapeutic strategies in several biological processes. In the present study, the expression levels and the effects of miRNA (miR)-421 in breast cancer tissues and MCF-7 and MDA-MB-231 cells were evaluated to elucidate therapeutic targets in breast cancer cells. The putative targets of miR-421 were predicted by bioinformatics approaches, and the expression levels of miR-421 were measured in MCF-7 and MDA-MB-231 cells by reverse transcription-quantitative polymerase chain reaction analysis following miR-421 knockdown. The rates of cell proliferation, migration capacity, invasiveness and apoptosis were determined in miR-421 inhibitor-transfected MCF-7 and MDA-MB-231 cells. The expression levels of target proteins regulated by miR-421 in MCF-7 and MDA-MB-231 cells were analyzed by western blot analysis. miR-421 was increased significantly in breast cancer tissues and cells, and was regulated by miR-421 antisense oligonucleotides. The knockdown of miR-421 in MCF-7 and MDA-MB-231 cells decreased cell proliferation, migration capacity and invasiveness, and promoted apoptosis compared with control groups. The expression of target protein programmed cell death 4 (PDCD4) were decreased in MCF-7 and MDA-MB-231 cells transfected with miR-421 inhibitors. These results suggested a correlation between miR-421 and PDCD4, and physiological functions of breast cancer cells, suggesting that miR-421 may be a potential strategy in the therapy of breast cancer.

Current Status and Perspectives Regarding LNA-Anti-miR Oligonucleotides and microRNA miR-21 Inhibitors as a Potential Therapeutic Option in Treatment of Colorectal Cancer

Colorectal cancer (CRC) is among the leading causes of cancer-related death, principally due to its metastatic spread and multifactorial chemoresistance. The therapeutic failure can also be explained by inter- or intra-tumor genetic heterogeneity and tumor stromal content. Thus, the identification of novel prognostic biomarkers and therapeutic options are warranted in the management of CRC patients. There are data showing that microRNA-21 is elevated in different types of cancer, particularly colon adenocarcinoma and that this is association with a poor prognosis. This suggests that microRNA-21 may be of value as a potential therapeutic target. Furthermore, locked nucleic acid (LNA)-modified oligonucleotides have recently emerged as a therapeutic option for targeting dysregulated miRNAs in cancer therapy, through antisense-based gene silencing. Further work is required to identify innovative anticancer drugs that improve the current therapy either through novel combinatorial approaches or with better efficacy than conventional drugs. We aimed to provide an overview of the preclinical and clinical studies targeting key dysregulated signaling pathways in CRC as well as the therapeutic application of LNA-modified oligonucleotides, and miR inhibitors in the treatment of CRC patients. J. Cell. Biochem. 118: 4129-4140, 2017. © 2017 Wiley Periodicals, Inc.

Profiling of metastatic small intestine neuroendocrine tumors reveals characteristic miRNAs detectable in plasma

Background

Current diagnostic and prognostic blood-based biomarkers for neuroendocrine tumors are limited. MiRNAs have tumor-specific expression patterns, are relatively stable, and can be measured in patient blood specimens. We performed a multi-stage study to identify and validate characteristic circulating miRNAs in patients with metastatic small intestine neuroendocrine tumors, and to assess associations between miRNA levels and survival.

Methods

Using a 742-miRNA panel, we identified candidate miRNAs similarly expressed in 19 small intestine neuroendocrine tumors and matched plasma samples. We refined our panel in an independent cohort of plasma samples from 40 patients with metastatic small intestine NET and 40 controls, and then validated this panel in a second, large cohort of 120 patients with metastatic small intestine NET and 120 independent controls.

Results

miRNA profiling of 19 matched small intestine neuroendocrine tumors and matched plasma samples revealed 31 candidate miRNAs similarly expressed in both tissue and plasma. We evaluated expression of these 31 candidate miRNAs in 40 independent cases and 40 normal controls, and identified 4 miRNAs (miR-21-5p, miR-22-3p, miR-29b-3p, and miR-150-5p) that were differently expressed in cases and controls (p<0.05). We validated these 4 miRNAs in a separate, larger panel of 120 cases and 120 controls. We confirmed that high circulating levels of miR-22-3p (p<0.0001), high levels of miR 21-5p, and low levels of miR-150-5p (p=0.027) were associated with the presence of metastatic small intestine NET. While levels of 29b-3p were lower in cases than in controls in both the initial cohort and the validation cohort, the difference in the validation cohort did not reach statistical significance. We further found that high levels of circulating miR-21-5p, high levels of circulating miR-22-3p and low levels of circulating miR-150-5p were each independently associated with shorter overall survival. A combined analysis using all three markers was highly prognostic for survival (HR 0.47, 95% CI 0.27-0.82).

Conclusions

Our study suggests that elevated circulating levels of miR-21-5p and miR-22-3p and low levels of miR-150-5p are characteristic in patients with metastatic small intestine neuroendocrine tumors, and further suggests that levels of these miRNAs are associated with overall survival. These observations provide the basis for further validation studies, as well as studies to assess the biological function of these miRNAs in small intestine neuroendocrine tumors.

Inhibition of microRNA-21 via locked nucleic acid-anti-miR suppressed metastatic features of colorectal cancer cells through modulation of programmed cell death 4

Colorectal cancer is among the most lethal of malignancies, due to its propensity to metastatic spread and multifactorial-chemoresistance. The latter property supports the need to identify novel therapeutic approaches for the treatment of colorectal cancer. MicroRNAs are endogenous non-coding small RNA molecules that function as post-transcriptional regulators of gene expression. Recently, programmed cell death 4 has been identified as a protein that increases during apoptosis. This gene is among the potential targets of miR-21 (OncomiR). Locked nucleic acid-modified oligonucleotides have recently emerged as a potential therapeutic option for targeting microRNAs. The aim of this study was to explore the functional role of locked nucleic acid-anti-miR-21 in the LS174T cell line in vitro and in vivo models. LS174T cells were treated with locked nucleic acid-anti-miR-21 for 24, 48, and 72 h in vitro. The expression of miR-21 and PDCD4 at messenger RNA (mRNA) level was evaluated by quantitative real-time polymerase chain reaction, while the protein level of PDCD4 was determined by Western blotting. Cell migratory behavior and the cluster-forming ability of cells were assessed before and after therapy. The disseminated tumor cells were assessed in the chick chorioallantoic membrane model by Alu quantitative polymerase chain reaction. Locked nucleic acid-anti-miR-21 was transfected successfully into the LS174T cells and inhibited the expression of miR-21. Locked nucleic acid-anti-miR-21 inhibited the migration and the number of cells forming clusters. Moreover, we found that locked nucleic acid-anti-miR-21 transfection was associated with a significant reduction in metastatic properties as assessed by the in ovo model. Our findings demonstrated the novel therapeutic potential of locked nucleic acid-anti-miR-21 in colon adenocarcinoma with high miR-21 expression.

Brain in situ hybridization maps as a source for reverse-engineering transcriptional regulatory networks: Alzheimer's disease insights

Microarray data have been a valuable resource for identifying transcriptional regulatory relationships among genes. As an example, brain region-specific transcriptional regulatory events have the potential of providing etiological insights into Alzheimer Disease (AD). However, there is often a paucity of suitable brain-region specific expression data obtained via microarrays or other high throughput means. The Allen Brain Atlas in situ hybridization (ISH) data sets (Jones et al., 2009) represent a potentially valuable alternative source of high-throughput brain region-specific gene expression data for such purposes. In this study, Allen Brain Atlas mouse ISH data in the hippocampal fields were extracted, focusing on 508 genes relevant to neurodegeneration. Transcriptional regulatory networks were learned using three high-performing network inference algorithms. Only 17% of regulatory edges from a network reverse-engineered based on brain region-specific ISH data were also found in a network constructed upon gene expression correlations in mouse whole brain microarrays, thus showing the specificity of gene expression within brain sub-regions. Furthermore, the ISH data-based networks were used to identify instructive transcriptional regulatory relationships. Ncor2, Sp3 and Usf2 form a unique three-party regulatory motif, potentially affecting memory formation pathways. Nfe2l1, Egr1 and Usf2 emerge among regulators of genes involved in AD (e.g. Dhcr24, Aplp2, Tia1, Pdrx1, Vdac1, and Syn2). Further, Nfe2l1, Egr1 and Usf2 are sensitive to dietary factors and could be among links between dietary influences and genes in the AD etiology. Thus, this approach of harnessing brain region-specific ISH data represents a rare opportunity for gleaning unique etiological insights for diseases such as AD.

Chronic exposure to chewing tobacco selects for overexpression of stearoyl-CoA desaturase in normal oral keratinocytes

Chewing tobacco is a common practice in certain socio-economic sections of southern Asia, particularly in the Indian subcontinent and has been well associated with head and neck squamous cell carcinoma. The molecular mechanisms of chewing tobacco which leads to malignancy remains unclear. In large majority of studies, short-term exposure to tobacco has been evaluated. From a biological perspective, however, long-term (chronic) exposure to tobacco mimics the pathogenesis of oral cancer more closely. We developed a cell line model to investigate the chronic effects of chewing tobacco. Chronic exposure to tobacco resulted in higher cellular proliferation and invasive ability of the normal oral keratinocytes (OKF6/TERT1). We carried out quantitative proteomic analysis of OKF6/TERT1 cells chronically treated with chewing tobacco compared to the untreated cells. We identified a total of 3,636 proteins among which expression of 408 proteins were found to be significantly altered. Among the overexpressed proteins, stearoyl-CoA desaturase (SCD) was found to be 2.6-fold overexpressed in the tobacco treated cells. Silencing/inhibition of SCD using its specific siRNA or inhibitor led to a decrease in cellular proliferation, invasion and colony forming ability of not only the tobacco treated cells but also in a panel of head and neck cancer cell lines. These findings suggest that chronic exposure to chewing tobacco induced carcinogenesis in non-malignant oral epithelial cells and SCD plays an essential role in this process. The current study provides evidence that SCD can act as a potential therapeutic target in head and neck squamous cell carcinoma, especially in patients who are users of tobacco.

Selective Hyaluronan-CD44 Signaling Promotes miRNA-21 Expression and Interacts with Vitamin D Function during Cutaneous Squamous Cell Carcinomas Progression Following UV Irradiation

Hyaluronan (HA), the major extracellular matrix component, is often anchored to CD44, a family of structurally/functionally important cell surface receptors. Recent results indicate that UV irradiation (UVR)-induced cutaneous squamous cell carcinomas (SCC) overexpress a variety of CD44 variant isoforms (CD44v), with different CD44v isoforms appear to confer malignant SCC properties. UVR also stimulates HA degradation in epidermal keratinocytes. Both large HA polymers and their UVR-induced catabolic products (small HA) selectively activate CD44-mediated cellular signaling in normal keratinocytes and SCC cells, with all of the downstream processes being mediated by RhoGTPases (e.g., Rac1 and Rho). Importantly, we found that the hormonally active form of vitamin D 1,25(OH)2D3 not only prevents the UVR-induced small HA activation of abnormal keratinocyte behavior and SCC progression, but also enhances large HA stimulation of normal keratinocyte activities and epidermal function(s). The aim of this hypothesis and theory article is to question whether matrix HA and its UVR-induced catabolic products (e.g., large and small HA) can selectively activate CD44-mediated cellular signaling such as GTPase (Rac and RhA) activation. We suggested that large HA-CD44 interaction promotes Rac-signaling and normal keratinocyte differentiation (lipid synthesis), DNA repair, and keratinocyte survival function. Conversely, small HA-CD44 interaction stimulates RhoA activation, NFκB/Stat-3 signaling, and miR-21 production, resulting in inflammation and proliferation as well as SCC progression. We also question whether vitamin D treatment displays any effect on small HA-CD44v-mediated RhoA signaling, inflammation, and SCC progression, as well as large HA-CD44-mediated differentiation, DNA repair, keratinocyte survival, and normal keratinocyte function. In addition, we discussed that the topical application of signaling perturbation agents (e.g., Y27623, a ROK inhibitor) may be used to treat certain skin diseases displaying upregulation of keratinocyte proliferation such as psoriasis and actinic keratoses in order to correct the imbalance between Rac and RhoA signaling during various UV irradiation-induced skin diseases in patients. Finally, we proposed that matrix HA/CD44-signaling strategies and matrix HA (HAS vs. HAL or HAS → HAL)-based therapeutic approaches (together with vitamin D) may be used for the treatment of patients suffering a number of UV irradiation-induced skin diseases (e.g., inflammation, skin cancer, and chronic non-healing wounds).

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

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

Regulatory effects of programmed cell death 4 (PDCD4) protein in interferon (IFN)-stimulated gene expression and generation of type I IFN responses

The precise mechanisms by which the activation of interferon (IFN) receptors (IFNRs) ultimately controls mRNA translation of specific target genes to induce IFN-dependent biological responses remain ill defined. We provide evidence that IFN-α induces phosphorylation of programmed cell death 4 (PDCD4) protein on Ser67. This IFN-α-dependent phosphorylation is mediated by either the p70 S6 kinase (S6K) or the p90 ribosomal protein S6K (RSK) in a cell-type-specific manner. IFN-dependent phosphorylation of PDCD4 results in downregulation of PDCD4 protein levels as the phosphorylated form of PDCD4 interacts with the ubiquitin ligase β-TRCP (β-transducin repeat-containing protein) and undergoes degradation. This process facilitates IFN-induced eukaryotic translation initiation factor 4A (eIF4A) activity and binding to translation initiation factor eIF4G to promote mRNA translation. Our data establish that PDCD4 degradation ultimately facilitates expression of several ISG protein products that play important roles in the generation of IFN responses, including IFN-stimulated gene 15 (ISG15), p21(WAF1/CIP1), and Schlafen 5 (SLFN5). Moreover, engagement of the RSK/PDCD4 pathway by the type I IFNR is required for the suppressive effects of IFN-α on normal CD34(+) hematopoietic precursors and for antileukemic effects in vitro. Altogether, these findings provide evidence for a unique function of PDCD4 in the type I IFN system and indicate a key regulatory role for this protein in mRNA translation of ISGs and control of IFN responses.

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

Background

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

Principal Findings

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

Conclusion

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

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.

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

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

Identification of novel phosphorylation modification sites in human proteins that originated after the human-chimpanzee divergence

MOTIVATION

Phosphorylation modifications of specific protein residues are involved in a wide range of biological processes such as modulation of intracellular signal networks. Here, we present the development and application of a bioinformatics procedure for systematic identification of human-specific phosphorylation sites in proteins that may have occurred after the human-chimpanzee divergence.

RESULTS

We collected annotated human phosphorylation sites and compared each site to orthologous mammalian proteins across taxa including chimpanzee, orangutan, rhesus macaque, marmoset, mouse, dog, cow, elephant, opossum and platypus. We identified 37 human-specific gains of annotated phosphorylation sites in 35 proteins: 22 serines, 12 threonines and 3 tyrosines. The novel phosphorylation sites are situated in highly conserved segments of the protein. Proteins with novel phosphorylation sites are involved in crucial biological processes such as cell division (AURKB, CASC5, MKI67 and PDCD4) and chromatin remodeling (HIRA, HIRIP3, HIST1H1T, NAP1L4 and LRWD1). Modified phosphorylatable residues produce novel target sites for protein kinases such as cyclin-dependent kinases and casein kinases, possibly resulting in rewiring and fine-tuning of phosphorylation regulatory networks. The potential human-specific phosphorylation sites identified in this study are useful as candidates for functional analysis to identify novel phenotypes in humans.

CONTACT

hahny@cau.ac.kr

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Clinicopathological and prognostic value of microRNA-21 and microRNA-155 in colorectal cancer

OBJECTIVE

The clinical significance of microRNA-21 (miR-21) and miR-155 in colorectal cancer (CRC) patients remains elusive. In this study, we established the prognostic value of miR-21 and miR-155 using clinical samples from CRC patients. Furthermore, relationships between these microRNAs and target genes (PDCD4 and TP53INP1 mRNAs) were examined.

METHODS

miR-21 and miR-155 expression was assessed in tumor tissue and in adjacent normal tissue of 156 CRC patients by TaqMan MicroRNA assays, and PDCD4 and TP53INP1 mRNA levels were measured by quantitative real-time reverse transcriptase PCR (RT-PCR).

RESULTS

High miR-21 expression was significantly associated with venous invasion, liver metastasis and tumor stage, and high miR-155 expression was significantly correlated with lymph node metastases. The overall (OS) and disease-free survival (DFS) rates of patients with high miR-21 expression were significantly worse than those of patients with low miR-21 expression. The OS and DFS of patients with high miR-155 expression were also significantly worse than those in patients with low miR-155 expression. miR-21 and miR-155 expression levels in CRC tissue were independent prognostic factors for OS and DFS. Significant inverse correlations were demonstrated between miR-21 and PDCD4 mRNA, and miR-155 and TP53INP1 mRNA.

CONCLUSION

Increases in miR-21 and miR-155 expression may represent effective biomarkers for the prediction of a poor prognosis.

Pdcd4 repression of lysyl oxidase inhibits hypoxia-induced breast cancer cell invasion

Metastasis to bone, liver and lungs is the primary cause of death in breast cancer patients. Our studies have revealed that the novel tumor suppressor Pdcd4 inhibits breast cancer cell migration and invasion in vitro. Loss of Pdcd4 in human nonmetastatic breast cancer cells increased the expression of lysyl oxidase (LOX) mRNA. LOX is a hypoxia-inducible amine oxidase, the activity of which enhances breast cancer cell invasion in vitro and in vivo. Specific inhibition of LOX activity by beta-aminopropionitrile or small interfering RNA decreased the invasiveness of T47D and MCF7 breast cancer cells attenuated for Pdcd4 function. Most significantly, loss of Pdcd4 augments hypoxia induction of LOX as well. Conversely, overexpression of Pdcd4 significantly reversed the hypoxia induction of LOX expression in T47D cells attenuated for Pdcd4. However, Pdcd4 did not affect hypoxia-inducible factor-1 (HIF-1) protein expression or HIF-1-responsive element-luciferase activity in response to hypoxia, suggesting that Pdcd4 regulation of LOX occurs through an HIF-independent mechanism. Nevertheless, the loss of Pdcd4 early in cancer progression may have an important role in the increased sensitivity of cancer cells to hypoxia through increased LOX activity and concomitant enhanced invasiveness.

Pathologic research update of colorectal neuroendocrine tumors

Colorectal neuroendocrine tumors (NETs) originate from neuroendocrine cells in the intestinal tract, and represent a small area within oncology, but one which has provided increasing new data during the past years. Although the World Health Organization has determined clinical and histological features to predict prognosis for such tumors, they may not be valid on an individual basis. We aim to give an overview of the recent findings with regard to pathology, molecular genetics and diagnosis of NETs.

An essential role of PDCD4 in vascular smooth muscle cell apoptosis and proliferation: implications for vascular disease

It is well established that vascular smooth muscle cell (VSMC) apoptosis and proliferation are critical cellular events in a variety of human vascular diseases. However, the molecular mechanisms involved in controlling VSMC apoptosis and proliferation are still unclear. In the current study, we have found that programmed cell death 4 (PDCD4) is significantly downregulated in balloon-injured rat carotid arteries in vivo and in platelet-derived growth factor-stimulated VSMCs in vitro. Overexpression of PDCD4 via adenovirus (Ad-PDCD4) increases VSMC apoptosis in an apoptotic model induced by serum deprivation. In contrast, VSMC apoptosis is significantly decreased by knockdown of PDCD4 via its small interfering RNA. In the rat carotid arteries in vivo, VSMC apoptosis is increased by Ad-PDCD4. We have further identified that activator protein 1 is a downstream signaling molecule of PDCD4 that is associated with PDCD4-mediated effects on VSMC apoptosis. In addition, VSMC proliferation was inhibited by overexpression of PDCD4. The current study has identified, for the first time, that PDCD4 is an essential regulator of VSMC apoptosis and proliferation. The downregulation of PDCD4 expression in diseased vascular walls may be responsible for the imbalance of VSMC proliferation and apoptosis. The results indicate that PDCD4 may be a new therapeutic target in proliferative vascular diseases.

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

The novel tumor suppressor Pdcd4 inhibits neoplastic transformation, tumor progression and translation. Furthermore, we and others have recently shown that Pdcd4 suppresses invasion and intravasation, at least in part by suppressing expression of the invasion-related urokinase receptor (u-PAR) gene via the transcription factors Sp1/Sp3. Nevertheless, relatively little is known about mechanisms that regulate Pdcd4 expression in cancer. MicroRNAs (miRNAs) have been recently discovered and shown to be naturally occurring non-coding RNAs that control gene expression via specific sites within the 3'UTR of target miRNAs. This short review will focus on our recent finding that the microRNA miR-21 posttranscriptionally regulates Pdcd4, as well as invasion, intravasation, and metastasis. Furthermore, we will review the first translational and clinical results concerning the prognostic value of Pdcd4, in particular our own data that show Pdcd4 to be a novel and independent prognostic factor in colorectal cancer, and a potential supportive diagnostic tool for discriminating normal colonic tissues from benign adenomas and colorectal carcinomas.

Loss of Programmed cell death 4 (Pdcd4) associates with the progression of ovarian cancer

Background

Programmed cell death 4 (Pdcd4) is a novel tumour suppressor and originally identified as a neoplastic transformation inhibitor. The aim of this study was to investigate the expression, prognostic significance and potential function of Pdcd4 in ovarian cancer.

Results

The expression of Pdcd4 was examined in 30 normal ovarian tissues, 16 borderline and 93 malignant ovarian tissues. A continuous down regulation of Pdcd4 expression in the sequence of normal, borderline and malignant tissues was observed. The expressions of Pdcd4 in both ovarian borderline tissues and carcinomas were significantly lower than the expression in normal ovarian tissues (p < 0.001). Furthermore, patients with lower Pdcd4 expressions were found to have shorter disease-free survival (p = 0.037). The expression of Pdcd4 was also assessed by immunohistochemical analysis in 13 ovarian normal tissues and 44 carcinomas. Different subcellular localization of Pdcd4 was observed in normal compared to malignant cells. Predominant nuclear localization of Pdcd4 was found in normal ovarian tissues while ovarian carcinomas showed mainly cytoplasmic localization of Pdcd4.

Conclusion

Our study demonstrated that the loss of Pdcd4 was a common abnormality at molecular level in ovarian cancer and it might be a potential prognostic factor in ovarian cancer patients.

PDCD4 inhibits the malignant phenotype of ovarian cancer cells

Programmed cell death 4 (PDCD4) is a newly identified tumor suppressor that can inhibit activator protein (AP)-1 activation and protein translation. Our previous studies indicate that lost or reduced PDCD4 expression is associated with the progression of ovarian carcinoma. However, direct evidence that PDCD4 inhibits malignant phenotype of human cancer cells is limited. In the present study, we found that PDCD4 expression in ovarian cancer cell lines (SKOV3, 3AO, and CAOV3) inhibited significantly their proliferation and cell cycle progression, and induced apoptosis. More importantly, up-regulation of PDCD4 expression decreased the colony-forming capacity of ovarian cancer cells in vitro and tumorigenic capacity in mice. These results demonstrate that PDCD4 can suppress the malignant phenotype of ovarian cancer cells, and may represent a novel therapeutic target for the treatment of ovarian cancer.

P68 RNA helicase (DDX5) alters activity of cis- and trans-acting factors of the alternative splicing of H-Ras

Background

H-Ras pre-mRNA undergoes an alternative splicing process to render two proteins, namely p21 H-Ras and p19 H-Ras, due to either the exclusion or inclusion of the alternative intron D exon (IDX), respectively. p68 RNA helicase (p68) is known to reduce IDX inclusion.

Principal Findings

Here we show that p68 unwinds the stem-loop IDX-rasISS1 structure and prevents binding of hnRNP H to IDX-rasISS1. We also found that p68 alters the dynamic localization of SC35, a splicing factor that promotes IDX inclusion. The knockdown of hnRNP A1, FUS/TLS and hnRNP H resulted in upregulation of the expression of the gene encoding the SC35-binding protein, SFRS2IP. Finally, FUS/TLS was observed to upregulate p19 expression and to stimulate IDX inclusion, and in vivo RNAi-mediated depletion of hnRNP H decreased p19 H-Ras abundance.

Significance

Taken together, p68 is shown to be an essential player in the regulation of H-Ras expression as well as in a vital transduction signal pathway tied to cell proliferation and many cancer processes.

Suppression of programmed cell death 4 (PDCD4) protein expression by BCR-ABL-regulated engagement of the mTOR/p70 S6 kinase pathway

There is accumulating evidence that mammalian target of rapamycin (mTOR)-activated pathways play important roles in cell growth and survival of BCR-ABL-transformed cells. We have previously shown that the mTOR/p70 S6 kinase (p70 S6K) pathway is constitutively activated in BCR-ABL transformed cells and that inhibition of BCR-ABL kinase activity by imatinib mesylate abrogates such activation. We now provide evidence for the existence of a novel regulatory mechanism by which BCR-ABL promotes cell proliferation, involving p70 S6K-mediated suppression of expression of programmed cell death 4 (PDCD4), a tumor suppressor protein that acts as an inhibitor of cap-dependent translation by blocking the translation initiation factor eIF4A. Our data also establish that second generation BCR-ABL kinase inhibitors block activation of p70 S6K and downstream engagement of the S6 ribosomal protein in BCR-ABL transformed cells. Moreover, PDCD4 protein expression is up-regulated by inhibition of the BCR-ABL kinase in K562 cells and BaF3/BCR-ABL transfectants, suggesting a mechanism for the generation of the proapoptotic effects of such inhibitors. Knockdown of PDCD4 expression results in reversal of the suppressive effects of nilotinib and imatinib mesylate on leukemic progenitor colony formation, suggesting an important role for this protein in the generation of antileukemic responses. Altogether, our studies identify a novel mechanism by which BCR-ABL may promote leukemic cell growth, involving sequential engagement of the mTOR/p70 S6K pathway and downstream suppression of PDCD4 expression.

MicroRNA-21 (miR-21) post-transcriptionally downregulates tumor suppressor Pdcd4 and stimulates invasion, intravasation and metastasis in colorectal cancer

Tumor-suppressor Pdcd4 inhibits transformation and invasion and is downregulated in cancers. So far, it has not been studied as to whether miRNAs, suppressing target expression by binding to the 3'-UTR, regulate Pdcd4 or invasion. The present study was conducted to investigate the regulation of Pdcd4, and invasion/intra-vasation, by miRNAs. A bioinformatics search revealed a conserved target-site for miR-21 within the Pdcd4-3'-UTR at 228-249 nt. In 10 colorectal cell lines, an inverse correlation of miR-21 and Pdcd4-protein was observed. Transfection of Colo206f-cells with miR-21 significantly suppressed a luciferase-reporter containing the Pdcd4-3'-UTR, whereas transfection of RKO with anti-miR-21 increased activity of this construct. This was abolished when a construct mutated at the miR-21/nt228-249 target site was used instead. Anti-miR-21-transfected RKO cells showed an increase of Pdcd4-protein and reduced invasion. Moreover, these cells showed reduced intra-vasation and lung metastasis in a chicken-embryo-metastasis assay. In contrast, overexpression of miR-21 in Colo206f significantly reduced Pdcd4-protein amounts and increased invasion, while Pdcd4-mRNA was unaltered. Resected normal/tumor tissues of 22 colorectal cancer patients demonstrated an inverse correlation between miR-21 and Pdcd4-protein. This is the first study to show that Pdcd4 is negatively regulated by miR-21. Furthermore, it is the first report to demonstrate that miR-21 induces invasion/intravasation/metastasis.

Molecular genetics of neuroendocrine tumors

Neuroendocrine tumors can develop either sporadically or in association with familial syndromes such as multiple endocrine neoplasia type 1 (MEN1), multiple endocrine neoplasia type 2 (MEN2) or von Hippel-Lindau (VHL). A variety of genetic approaches has been utilized to dissect the underlying molecular pathogenesis of these distinctive tumors, including genome-wide screens such as comparative genomic hybridization, loss of heterozygosity and DNA microarray analysis as well as targeted investigations into specific tumor suppressor gene and oncogene candidates. The identification of the MEN1 tumor suppressor gene that underlies the MEN1 syndrome has provided important new insights into tumor pathogenesis. In addition, a number of independent approaches has converged on a pivotal role for regulators of the cell cycle. However, our understanding of the molecular biology of these tumors remains far from complete. In this review we highlight some of the key approaches, findings and implications of these genetic studies.

Tumor suppressor Pdcd4 inhibits invasion/intravasation and regulates urokinase receptor (u-PAR) gene expression via Sp-transcription factors

Tumor suppressor Pdcd4 has recently been shown to inhibit invasion by activating activator protein-1 (AP-1); however, little is known of the functionally significant Pdcd4-target genes. The urokinase receptor (u-PAR) promotes invasion/metastasis, and is associated with poor cancer-patient survival. The present study was conducted (1) to investigate a role for Pdcd4 in intravasation, invasion and u-PAR regulation, and (2) to describe mechanisms by which this is achieved. Fourteen cell lines showed reciprocal expression of u-PAR/Pdcd4. Resected tumor/normal tissues of 29 colorectal cancer patients demonstrated a significant inverse correlation between Pdcd4/u-PAR. siRNA-Pdcd4-transfected GEO cells significantly increased endogenous u-PAR mRNA/protein. A u-PAR-promoter-chloramphenicol acetyl transferase (CAT)-reporter was reduced in activity with increasing Pdcd4 expression in RKO. Deletion of a putative Sp-1-binding site (-402/-350) inhibited u-PAR promoter regulation by Pdcd4, this being paralleled by a reduction of Sp1 binding to this region in pdcd4-transfected cells. Pdcd4-transfected cells showed an increase in Sp3 binding to u-PAR promoter region -152/-135, the deletion of which reduces the ability of Pdcd4 to suppress u-PAR promoter activity. Surprisingly, the u-PAR-AP-1 site was not targeted by Pdcd4. Finally, RKO cells overexpressing Pdcd4 showed an inhibition of invasion/intravasation (chicken embryo metastasis assay). These data suggest Pdcd4 as a new negative regulator of intravasation, and qas the invasion-related gene u-PAR. It is the first study to implicate Pdcd4 regulation of gene expression via Sp1/Sp3.

Translational regulation of autoimmune inflammation and lymphoma genesis by programmed cell death 4

Both inflammatory diseases and cancer are associated with heightened protein translation. However, the mechanisms of translational regulation and the roles of translation factors in these diseases are not clear. Programmed cell death 4 (PDCD4) is a newly described inhibitor of protein translation. To determine the roles of PDCD4 in vivo, we generated PDCD4-deficient mice by gene targeting. We report here that mice deficient in PDCD4 develop spontaneous lymphomas and have a significantly reduced life span. Most tumors are of the B lymphoid origin with frequent metastasis to liver and kidney. However, PDCD4-deficient mice are resistant to inflammatory diseases such as autoimmune encephalomyelitis and diabetes. Mechanistic studies reveal that upon activation, PDCD4-deficient lymphocytes preferentially produce cytokines that promote oncogenesis but inhibit inflammation. These results establish that PDCD4 controls lymphoma genesis and autoimmune inflammation by selectively inhibiting protein translation in the immune system.

MicroRNA expression abnormalities in pancreatic endocrine and acinar tumors are associated with distinctive pathologic features and clinical behavior

PURPOSE

We investigated the global microRNA expression patterns in normal pancreas, pancreatic endocrine tumors and acinar carcinomas to evaluate their involvement in transformation and malignant progression of these tumor types. MicroRNAs are small noncoding RNAs that regulate gene expression by targeting specific mRNAs for degradation or translation inhibition. Recent evidence indicates that microRNAs can contribute to tumor development and progression and may have diagnostic and prognostic value in several human malignancies.

MATERIALS AND METHODS

Using a custom microarray, we studied the global microRNA expression in 12 nontumor pancreas and 44 pancreatic primary tumors, including 12 insulinomas, 28 nonfunctioning endocrine tumors, and four acinar carcinomas.

RESULTS

Our data showed that a common pattern of microRNA expression distinguishes any tumor type from normal pancreas, suggesting that this set of microRNAs might be involved in pancreatic tumorigenesis; the expression of miR-103 and miR-107, associated with lack of expression of miR-155, discriminates tumors from normal; a set of 10 microRNAs distinguishes endocrine from acinar tumors and is possibly associated with either normal endocrine differentiation or endocrine tumorigenesis; miR-204 is primarily expressed in insulinomas and correlates with immunohistochemical expression of insulin; and the overexpression of miR-21 is strongly associated with both a high Ki67 proliferation index and presence of liver metastasis.

CONCLUSION

These results suggest that alteration in microRNA expression is related to endocrine and acinar neoplastic transformation and progression of malignancy, and might prove useful in distinguishing tumors with different clinical behavior.

Luteinization of porcine preovulatory follicles leads to systematic changes in follicular gene expression

The LH surge initiates the luteinization of preovulatory follicles and causes hormonal and structural changes that ultimately lead to ovulation and the formation of corpora lutea. The objective of the study was to examine gene expression in ovarian follicles (n= 11) collected from pigs (Sus scrofa domestica) approaching estrus (estrogenic preovulatory follicle;n= 6 follicles from two sows) and in ovarian follicles collected from pigs on the second day of estrus (preovulatory follicles that were luteinized but had not ovulated;n= 5 follicles from two sows). The follicular status within each follicle was confirmed by follicular fluid analyses of estradiol and progesterone ratios. Microarrays were made from expressed sequence tags that were isolated from cDNA libraries of porcine ovary. Gene expression was measured by hybridization of fluorescently labeled cDNA (preovulatory estrogenic or -luteinized) to the microarray. Microarray analyses detected 107 and 43 genes whose expression was decreased or increased (respectively) during the transition from preovulatory estrogenic to -luteinized (P<0.01). Cells within preovulatory estrogenic follicles had a gene-expression profile of proliferative and metabolically active cells that were responding to oxidative stress. Cells within preovulatory luteinized follicles had a gene-expression profile of nonproliferative and migratory cells with angiogenic properties. Approximately, 40% of the discovered genes had unknown function.

Tumorigenesis suppressor Pdcd4 down-regulates mitogen-activated protein kinase kinase kinase kinase 1 expression to suppress colon carcinoma cell invasion

Programmed cell death 4 (Pdcd4) suppresses neoplastic transformation by inhibiting the activation of c-Jun and consequently AP-1-dependent transcription. We report that Pdcd4 blocks c-Jun activation by inhibiting the expression of mitogen-activated protein kinase kinase kinase kinase 1 (MAP4K1)/hematopoietic progenitor kinase 1, a kinase upstream of Jun N-terminal kinase (JNK). cDNA microarray analysis of Pdcd4-overexpressing RKO human colon carcinoma cells revealed MAP4K1 as the sole target of Pdcd4 on the JNK activation pathway. Cotransfection of a MAP4K1 promoter-reporter with Pdcd4 demonstrated inhibition of transcription from the MAP4K1 promoter. Ectopic expression of Pdcd4 in metastatic RKO cells suppressed invasion. MAP4K1 activity is functionally significant in invasion, as overexpression of a dominant negative MAP4K1 (dnMAP4K1) mutant in RKO cells inhibited not only c-Jun activation but also invasion. Overexpression of a MAP4K1 cDNA in Pdcd4-transfected cells rescued the kinase activity of JNK. Thus, Pdcd4 suppresses tumor progression in human colon carcinoma cells by the novel mechanism of down-regulating MAP4K1 transcription, with consequent inhibition of c-Jun activation and AP-1-dependent transcription.

Anti-inflammatory effect of Lactobacillus casei on Shigella-infected human intestinal epithelial cells

Shigella invades the human intestinal mucosa, thus causing bacillary dysentery, an acute recto-colitis responsible for lethal complications, mostly in infants and toddlers. Conversely, commensal bacteria live in a mutualistic relationship with the intestinal mucosa that is characterized by homeostatic control of innate responses, thereby contributing to tolerance to the flora. Cross-talk established between commensals and the intestinal epithelium mediate this active process, the mechanisms of which remain largely uncharacterized. Probiotics such as Lactobacillus casei belong to a subclass of these commensals that modulate mucosal innate responses and possibly display anti-inflammatory properties. We analyzed whether L. casei could attenuate the pro-inflammatory signaling induced by Shigella flexneri after invasion of the epithelial lining. Cultured epithelial cells were infected with L. casei, followed by a challenge with S. flexneri. Using macroarray DNA chips, we observed that L. casei down-regulated the transcription of a number of genes encoding pro-inflammatory effectors such as cytokines and chemokines and adherence molecules induced by invasive S. flexneri. This resulted in an anti-inflammatory effect that appeared mediated by the inhibition of the NF-kappaB pathway, particularly through stabilization of I-kappaBalpha. In a time-course experiment using GeneChip hybridization analysis, the expression of many genes involved in ubiquitination and proteasome processes were modulated during L. casei treatment. Thus, L. casei has developed a sophisticated means to maintain intestinal homeostasis through a process that involves manipulation of the ubiquitin/proteasome pathway upstream of I-kappaBalpha.

The molecular genetics of gastroenteropancreatic neuroendocrine tumors

The pathobiology of neuroendocrine tumors (NETs) is hampered by the lack of scientific tools that define their mechanisms of secretion, proliferation, and metastasis; and, currently, there are no accurate means to assess tumor behavior and disease prognosis. Molecular biologic techniques and genetic analysis may facilitate the delineation of the molecular pathology of NETs and provide novel insights into their cellular mechanisms. The current status and recent advances in assessment of the molecular basis of tumorigenesis of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) were reviewed (1981-2004). The objectives of this retrospective study were to provide a cohesive overview of the current state of knowledge and to develop a molecular understanding of these rare tumor entities to facilitate the establishment of therapeutic targets and rational management strategies. Multiple differences in chromosomal aberration patterns were noted between gastrointestinal (GI) neuroendocrine and pancreatic endocrine tumors (PETs). Divergence in gene expression patterns in the development of GI carcinoids and PETs was identified, whereas examination of the PET and GI carcinoid data demonstrated only few areas of overlap in the accumulation of genetic aberrations. These data suggest that the recent World Health Organization classification of GEP-NETs may require updating. In addition, previous assumptions of tumor similarity (pancreatic vs. GI) may be unfounded when they are examined at a molecular level. On the basis of the evolution of genetic information, enteric neuroendocrine lesions (carcinoids) and PETs may need to be classified as two distinct entities rather than grouped together as the single entity "GEP-NETs."

Identification of NOM1, a nucleolar, eIF4A binding protein encoded within the chromosome 7q36 breakpoint region targeted in cases of pediatric acute myeloid leukemia

Proteins that contain the recently described MIF4G and/or MA3 domains function in translation, cell growth, proliferation, transformation, and apoptosis. Examples of MIF4G/MA3 containing proteins and their functions include eIF4G, which serves as a scaffold for assembly of factors required for translation initiation, programmed cell death protein 4 (Pdcd4) that inhibits translation and functions as a tumor suppressor, and NMD2, which is essential for nonsense-mediated mRNA decay. MIF4G and MA3 domains serve as binding sites for one or more isoforms of the eIF4A family of ATP-dependent DEAD-box RNA helicases that are required for translation and for nonsense-mediated decay. In this report, we describe the characterization of a novel MIF4G/MA3 family member called NOM1 (nucleolar protein with MIF4G domain 1) that was identified at the chromosome 7q36 breakpoint involved in 7;12 translocations associated with certain acute leukemias of childhood. NOM1, which includes a previously described EST called c7orf3, encodes a ubiquitously expressed transcript composed of 11 exons and an approximately 3 kb 3' UTR that contains several Alu repeats. The predicted NOM1 protein contains one MIF4G domain and one MA3 domain and, consistent with data obtained with other MIF4G/MA3 proteins, interacts with members of the eIF4A family of helicases. Database searches reveal that NOM1 homologs exist in several organisms and that at least two of these are essential genes. Finally, like its Saccharomyces cerevisiae homolog Sgd1p, NOM1 localizes predominantly to the nucleolus. These data demonstrate that NOM1 is a new member of the MIF4G/MA3 family of proteins and suggest that it may provide an essential function in metazoans.