A role for ezrin in a neglected metastatic tumor function

Mapping Cell-in-Cell Structures in Oral Squamous Cell Carcinoma

Cell-in-cell (CIC) structures contribute to tumor aggressiveness and poor prognosis in oral squamous cell carcinoma (OSCC). In vitro 3D models may contribute to the understanding of the underlying molecular mechanisms of these events. We employed a spheroid model to study the CIC structures in OSCC. Spheroids were obtained from OSCC (HSC3) and cancer-associated fibroblast (CAF) lines using the Nanoshuttle-PLTM bioprinting system (Greiner Bio-One). Spheroid form, size, and reproducibility were evaluated over time (EvosTM XL; ImageJ version 1.8). Slides were assembled, stained (hematoxylin and eosin), and scanned (Axio Imager Z2/VSLIDE) using the OlyVIA System (Olympus Life Science) and ImageJ software (NIH) for cellular morphology and tumor zone formation (hypoxia and/or proliferative zones) analysis. CIC occurrence, complexity, and morphology were assessed considering the spheroid regions. Well-formed spheroids were observed within 6 h of incubation, showing the morphological aspects of the tumor microenvironment, such as hypoxic (core) and proliferative zone (periphery) formation. CIC structures were found in both homotypic and heterotypic groups, predominantly in the proliferative zone of the mixed HSC3/CAF spheroids. "Complex cannibalism" events were also noted. These results showcase the potential of this model in further studies on CIC morphology, formation, and relationship with tumor prognosis.

Cell-in-cell: a potential biomarker of prognosis and a novel mechanism of drug resistance in cancer

The cell-in-cell (CIC) phenomenon has received increasing attention over recent years because of its wide existence in multiple cancer tissues. The mechanism of CIC formation is considerably complex as it involves interactions between two cells. Although the molecular mechanisms of CIC formation have been extensively investigated, the process of CIC formation remains ambiguous. Currently, CIC is classified into four subtypes based on different cell types and inducing factors, and the underlying mechanisms for each subtype are distinct. Here, we investigated the subtypes of CIC and their major mechanisms involved in cancer development. To determine the clinical significance of CIC, we reviewed several clinical studies on CIC and found that CIC could serve as a diagnostic and prognostic biomarker. The implications of CIC on the clinical management of cancers also remain largely unknown. To clarify this aspect, in the present review, we highlight the findings of recent investigations on the causal link between CIC and cancer treatment. We also indicate the existing issues that need to be resolved urgently to provide a potential direction for future research on CIC.

Ez-Metastasizing: The Crucial Roles of Ezrin in Metastasis

Ezrin is the cytoskeletal organizer and functions in the modulation of membrane-cytoskeleton interaction, maintenance of cell shape and structure, and regulation of cell-cell adhesion and movement, as well as cell survival. Ezrin plays a critical role in regulating tumor metastasis through interaction with other binding proteins. Notably, Ezrin has been reported to interact with immune cells, allowing tumor cells to escape immune attack in metastasis. Here, we review the main functions of Ezrin, the mechanisms through which it acts, its role in tumor metastasis, and its potential as a therapeutic target.

TM9SF4 is an F-actin disassembly factor that promotes tumor progression and metastasis

F-actin dynamics is crucial for many fundamental properties of cancer cells, from cell-substrate adhesion to migration, invasion and metastasis. However, the regulatory mechanisms of actin dynamics are still incompletely understood. In this study, we demonstrate the function of a protein named TM9SF4 in regulating actin dynamics and controlling cancer cell motility and metastasis. We show that an N-terminal fragment (NTF) cleaved from TM9SF4 can directly bind to F-actin to induce actin oxidation at Cys374, consequently enhancing cofilin-mediated F-actin disassembly. Knockdown of TM9SF4 reduces cell migration and invasion in ovarian cancer cells A2780, SKOV3 and several high grade serous ovarian cancer lines (HGSOCs). In vivo, knockdown of TM9SF4 completely abolishes the tumor growth and metastasis in athymic nude mice. These data provide mechanistic insights into TM9SF4-mediated regulation of actin dynamics in ovarian cancer cells.

F-actin dynamics influence cancer cell motility. Here the authors show that TM9SF4 facilitates the cofilin-induced disassembly of F-actin to promote cancer cell migration and metastasis.

Cell-in-Cell Events in Oral Squamous Cell Carcinoma

For over a century, cells within other cells have been detected by pathologists as common histopathological findings in tumors, being generally identified as “cell-in-cell” structures. Despite their characteristic morphology, these structures can originate from various processes, such as cannibalism, entosis and emperipolesis. However, only in the last few decades has more attention been given to these events due to their importance in tumor development. In cancers such as oral squamous cell carcinoma, cell-in-cell events have been linked to aggressiveness, metastasis, and therapeutic resistance. This review aims to summarize relevant information about the occurrence of various cell-in-cell phenomena in the context of oral squamous cell carcinoma, addressing their causes and consequences in cancer. The lack of a standard terminology in diagnosing these events makes it difficult to classify the existing cases and to map the behavior and impacts of these structures. Despite being frequently reported in oral squamous cell carcinoma and other cancers, their impacts on carcinogenesis aren’t fully understood. Cell-in-cell formation is seen as a survival mechanism in the face of a lack of nutritional availability, an acid microenvironment and potential harm from immune cell defense. In this deadly form of competition, cells that engulf other cells establish themselves as winners, taking over as the predominant and more malignant cell population. Understanding the link between these structures and more aggressive behavior in oral squamous cell carcinoma is of paramount importance for their incorporation as part of a therapeutic strategy.

Ezrin Modulates the Cell Surface Expression of Programmed Cell Death Ligand-1 in Human Cervical Adenocarcinoma Cells

Cancer cells employ programmed cell death ligand-1 (PD-L1), an immune checkpoint protein that binds to programmed cell death-1 (PD-1) and is highly expressed in various cancers, including cervical carcinoma, to abolish T-cell-mediated immunosurveillance. Despite a key role of PD-L1 in various cancer cell types, the regulatory mechanism for PD-L1 expression is largely unknown. Understanding this mechanism could provide a novel strategy for cervical cancer therapy. Here, we investigated the influence of ezrin/radixin/moesin (ERM) family scaffold proteins, crosslinking the actin cytoskeleton and certain plasma membrane proteins, on the expression of PD-L1 in HeLa cells. Our results showed that all proteins were expressed at mRNA and protein levels and that all ERM proteins were highly colocalized with PD-L1 in the plasma membrane. Interestingly, immunoprecipitation assay results demonstrated that PD-L1 interacted with ERM as well as actin cytoskeleton proteins. Furthermore, gene silencing of ezrin, but not radixin and moesin, remarkably decreased the protein expression of PD-L1 without affecting its mRNA expression. In conclusion, ezrin may function as a scaffold protein for PD-L1; regulate PD-L1 protein expression, possibly via post-translational modification in HeLa cells; and serve as a potential therapeutic target for cervical cancer, improving the current immune checkpoint blockade therapy.

Subcellular distribution of ezrin/radixin/moesin and their roles in the cell surface localization and transport function of P-glycoprotein in human colon adenocarcinoma LS180 cells

The ezrin/radixin/moesin (ERM) family proteins act as linkers between the actin cytoskeleton and P-glycoprotein (P-gp) and regulate the plasma membrane localization and functionality of the latter in various cancer cells. Notably, P-gp overexpression in the plasma membrane of cancer cells is a principal factor responsible for multidrug resistance and drug-induced mutagenesis. However, it remains unknown whether the ERM proteins contribute to the plasma membrane localization and transport function of P-gp in human colorectal cancer cells in which the subcellular localization of ERM has yet to be determined. This study aimed to determine the gene expression patterns and subcellular localization of ERM and P-gp and investigate the role of ERM proteins in the plasma membrane localization and transport function of P-gp using the human colon adenocarcinoma cell line LS180. Using real-time reverse transcription polymerase chain reaction and immunofluorescence analyses, we showed higher levels of ezrin and moesin mRNAs than those of radixin mRNA in these cells and preferential distribution of all three ERM proteins on the plasma membrane. The ERM proteins were highly colocalized with P-gp. Additionally, we show that the knockdown of ezrin, but not of radixin and moesin, by RNA interference significantly decreased the cell surface expression of P-gp in LS180 cells without affecting the mRNA expression of P-gp. Furthermore, gene silencing of ezrin substantially increased the intracellular accumulation of rhodamine123, a typical P-gp substrate, with no alterations in the plasma membrane permeability of Evans blue, a passive transport marker. In conclusion, ezrin may primarily regulate the cell surface localization and transport function of P-gp as a scaffold protein without influencing the transcriptional activity of P-gp in LS180 cells. These findings should be relevant for treating colorectal cancer, which is the second leading cause of cancer-related deaths in males and females combined.

On the origin of cancer metastasis

Metastasis involves the spread of cancer cells from the primary tumor to surrounding tissues and to distant organs and is the primary cause of cancer morbidity and mortality. In order to complete the metastatic cascade, cancer cells must detach from the primary tumor, intravasate into the circulatory and lymphatic systems, evade immune attack, extravasate at distant capillary beds, and invade and proliferate in distant organs. Currently, several hypotheses have been advanced to explain the origin of cancer metastasis. These involve an epithelial mesenchymal transition, an accumulation of mutations in stem cells, a macrophage facilitation process, and a macrophage origin involving either transformation or fusion hybridization with neoplastic cells. Many of the properties of metastatic cancer cells are also seen in normal macrophages. A macrophage origin of metastasis can also explain the long-standing "seed and soil" hypothesis and the absence of metastasis in plant cancers. The view of metastasis as a macrophage metabolic disease can provide novel insight for therapeutic management.

FLT3-driven redox-modulation of Ezrin regulates leukaemic cell migration

The concept of reactive oxygen species (ROS) being produced via the activation of specific oncogenes provides a basis for generating genomic instability and pro-survival signalling in tumour cells. The purpose of this study was to identify downstream targets of NADPH oxidase (Nox)-derived ROS signalling in acute myeloid leukaemia cells, by performing a proteomic analysis utilizing two-dimensional phosphotyrosine immunoblotting. The majority of the targets identified were cytoskeletal-associated proteins including Ezrin, a known regulator of the cytoskeleton, which was examined further. The study demonstrated that inhibition of Nox enzymes, using diphenyleneiodonium chloride in the acute myeloid leukaemia cell line MOLM-13, resulted in a decrease in Ezrin tyrosine phosphorylation and also triggered a shift in Ezrin sub-cellular localization as detected by immunofluorescence. The change in Ezrin localization coincided with altered cell morphology, observed using scanning electron microscopy and a decreased ability to migrate through a polycarbonate transwell membrane. Similar effects were observed upon inhibition of the oncogenic receptor tyrosine kinase FLT3 using the staurosporine derivate PKC412, implicating a role for FLT3 as an upstream regulator of Ezrin. Our results indicate that FLT3 drives production of ROS by Nox, which stimulates changes in Ezrin tyrosine phosphorylation and localization via redox regulation of Src. Furthermore, inhibition of FLT3 signalling leads to alterations in MOLM-13 cell morphology and has a significant influence on cell motility.

Ezrin overexpression predicts the poor prognosis of gastric adenocarcinoma

Background

Ezrin is a cytoskeletal protein that is involved in tumor growth and invasion. It has been suggested that Ezrin expression plays an important role in tumor metastasis. This study is aimed to investigate the clinicopathological significance of Ezrin overexpression in gastric adenocarcinomas.

Methods

Ezrin protein expression was examined by immunohistochemistry in 26 normal gastric mucosa, 32 dysplasia, and 277 gastric adenocarcinomas. The relationship between Ezrin expression and the clinicopathological features of gastric cancers was analyzed. In addition, a gastric cancer cell line, MKN-1, was also used for immunofluorescence staining to evaluate the distribution of Ezrin protein.

Results

Ezrin protein located in the cytoplasm and/or membrane in the migrating gastric cancer cells, and it mainly concentrated at the protrusion site; however, only cytoplasmic distribution was observed in the non-migrating cancer cells by immunofluorescence staining. The positive rate of Ezrin protein expression was significantly higher in gastric adenocarcinoma and dysplasia compared with that in the normal gastric mucosa. Moreover, expression frequency of Ezrin protein increased significantly in lymph node metastasis and late clinical stages. Consistently, strong expression of Ezrin was significantly correlated with poor prognosis of gastric cancer.

Conclusion

The detection of Ezrin expression can be used as the marker for early diagnosis and prognosis of gastric adenocarcinoma.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2303598677653946

Clinical significance of expression of Ezrin and HER2 proteins in gastric cancer

AIM: To investigate the expression of Ezrin and human epidermal growth factor receptor 2 (HER2) proteins in normal gastric mucosa and gastric cancer tissues and to analyze their correlation with tumor invasion and metastasis.

METHODS: Immunohistochemistry was performed to detect Ezrin and HER2 protein expression using tissue microarray (TMA) containing paraffin-embedded normal gastric mucosa and gastric cancer tissue samples. Of 485 primary gastric adenocarcinoma samples detected, 19 had well differentiated caner, 235 had moderately differentiated cancer, and 231 had poorly differentiated cancer; 353 had lymph node metastasis; 166 had TNM stage I to II cancer, 319 had stage III to IV cancer. Forty paraffin-embedded tissue blocks of normal gastric epithelium were used as controls.

RESULTS: Ezrin and HER2 protein expression in gastric cancer was significantly higher than in normal gastric mucosa. Ezrin and HER2 protein expression was closely associated with Lauren's histological type and tumor differentiation (χ² = 17.625, 20.386, both P = 0.000; χ² = 9.474, P = 0.009, χ² = 13.377, P = 0.010). Ezrin protein expression was also closely associated with Japanese histological type, TNM stage, depth of invasion and lymph node metastasis (χ² = 37.542, 12.237, 21.194, 9.868; P = 0.000, 0.002, 0.002, 0.007). The expression of Ezrin was positively correlated to that of HER2 in gastric cancer (r = 0.129, P = 0.004).

CONCLUSION: Ezrin protein may be a useful marker for predicting the invasion and metastasis of gastric cancer. Combined detection of expression of Ezrin and HER2 proteins can help predict prognosis and devise individualized treatment in patients with gastric cancer.

Cell cannibalism and cancer

Cellular cannibalism, defined as a large cell enclosing a slightly smaller one within its cytoplasm. In this review, we discussed the morphology, possible mechanism, and the cytological significance of cannibalism in relation to malignancy. Cannibalism is a completely different entity than phagocytosis, entosis, and emeriopoliosis. It is an important morphologic feature to distinguish benign from malignant lesions. Cannibalism has been described in various cancers such as, bladder cancer, breast cancer, lung cancer, etc, and this is related with the aggressiveness of the malignancy.

Identification of novel molecular targets for endometrial cancer using a drill-down LC-MS/MS approach with iTRAQ

Background

The number of patients with endometrial carcinoma (EmCa) with advanced stage or high histological grade is increasing and prognosis has not improved for over the last decade. There is an urgent need for the discovery of novel molecular targets for diagnosis, prognosis and treatment of EmCa, which will have the potential to improve the clinical strategy and outcome of this disease.

Methodology and Results

We used a “drill-down” proteomics approach to facilitate the identification of novel molecular targets for diagnosis, prognosis and/or therapeutic intervention for EmCa. Based on peptide ions identified and their retention times in the first LC-MS/MS analysis, an exclusion list was generated for subsequent iterations. A total of 1529 proteins have been identified below the Proteinpilot® 5% error threshold from the seven sets of iTRAQ experiments performed. On average, the second iteration added 78% new peptides to those identified after the first run, while the third iteration added 36% additional peptides. Of the 1529 proteins identified, only 40 satisfied our criteria for significant differential expression in EmCa in comparison to normal proliferative tissues. These proteins included metabolic enzymes (pyruvate kinase M2 and lactate dehydrogenase A); calcium binding proteins (S100A6, calcyphosine and calumenin), and proteins involved in regulating inflammation, proliferation and invasion (annexin A1, interleukin enhancer-binding factor 3, alpha-1-antitrypsin, macrophage capping protein and cathepsin B). Network analyses revealed regulation of these molecular targets by c-myc, Her2/neu and TNF alpha, suggesting intervention with these pathways may be a promising strategy for the development of novel molecular targeted therapies for EmCa.

Conclusions

Our analyses revealed the significance of drill-down proteomics approach in combination with iTRAQ to overcome some of the limitations of current proteomics strategies. This study led to the identification of a number of novel molecular targets having therapeutic potential for targeted molecular therapies for endometrial carcinoma.

Perspectives on the mesenchymal origin of metastatic cancer

Emerging evidence suggests that many metastatic cancers arise from cells of the myeloid/macrophage lineage regardless of the primary tissue of origin. A myeloid origin of metastatic cancer stands apart from origins involving clonal evolution or epithelial-mesenchymal transitions. Evidence is reviewed demonstrating that numerous human cancers express multiple properties of macrophages including phagocytosis, fusogenicity, and gene/protein expression. It is unlikely that the macrophage properties expressed in metastatic cancers arise from sporadic random mutations in epithelial cells, but rather from damage to an already existing mesenchymal cell, e.g., a myeloid/macrophage-type cell. Such cells would naturally embody the capacity to express the multiple behaviors of metastatic cells. The view of metastasis as a myeloid/macrophage disease will impact future cancer research and anti-metastatic therapies.

WWOX gene and gene product: tumor suppression through specific protein interactions

The WWOX gene, an archetypal fragile gene, encompasses a chromosomal fragile site at 16q23.2, and encodes the approximately 46-kDa Wwox protein, with WW domains that interact with a growing list of interesting proteins. If the function of a protein is defined by the company it keeps, then Wwox is involved in numerous important signal pathways for bone and germ-cell development, cellular and animal growth and death, transcriptional control and suppression of cancer development. Because alterations to genes at fragile sites are exquisitely sensitive to replication stress-induced DNA damage, there has been an ongoing scientific discussion questioning whether such gene expression alterations provide a selective advantage for clonal expansion of neoplastic cells, and a parallel discussion on why important genes would be present at sites that are susceptible to inactivation. We offer some answers through a description of known WWOX functions.

The Janus-faced role of ezrin in "linking" cells to either normal or metastatic phenotype

In the majority of eukaryotic cells, the ezrin, radixin and moesin (ERM) proteins are involved in many physiologic functions including regulation of actin cytoskeleton, control of cell shape, adhesion, motility and modulation of signal transduction pathways. In a previous study, we used a dominant negative ezrin-mutant to address ezrin involvement in remodeling of actin cytoskeleton and subsequently we depicted ezrin key role in melanoma cell migration and progression. Herein, we highlight recent advances on ezrin involvement in the metastatic phenomenon, including also some more neglected ezrin-related functions. Novel molecular processes driven by ezrin activation include: phagocytosis, acquisition of resistance to chemotherapeutics and triggering of programmed cell death signals. Recent data support an integrated role of ezrin also in development of tumor malignancy. On one hand, ezrin may be responsible of deranged execution of specific known functions such as adhesion and motility and on the other, it may also participate to unique metastatic determinants, through the establishment of aberrant linkages with tumor-related proteins. For instance, ezrin misslocalization, absence or deranged activity has started to be correlated with tumor progression in many tumors of different species, including humans. Concomitantly, ezrin may act simultaneously as a regulatory or deregulatory chaperon in both normal and tumor cells. It is still to be established whether this Janus-faced feature of ezrin is due to some unknown transforming Zelig-like property or to the fact that a tumor-associated molecule preferentially links to ezrin thus distracting it from its normal connections. However, the contribution of ezrin functional deregulation to the acquisition of the metastatic phenotype appears clear and ezrin or ezrin aberrant associations may represent good candidates for future anti-tumor therapies.

RNAi-mediated silencing of ezrin gene reverses malignant behavior of human gastric cancer cell line SGC-7901

OBJECTIVE

To investigate the effects of ezrin targeting gene of RNA interference (RNAi) on human gastric cancer cell line SGC-7901 in vitro.

METHODS

The highly metastatic human gastric cancer cell line SGC-7901 transfected with a small interfering (siRNA) lentivirus vector was selected for this research study. Expressions of ezrin mRNA and ezrin protein in the SGC-7901 cells were detected using RT-PCR and Western blot. Cell apoptosis was observed using flow cytometry. Transwell invasion and the cell adhesion test were used to verify the effect of RNAi on ezrin expression in the human gastric cancer cell line SGC-7901 in vitro.

RESULTS

Ezrin gene targeting via a RNAi-mediated lentivirus vector had obvious inhibitory effects on ezrin expression in the human gastric cancer cell line SGC-7901. The results of the RT-PCR show the obvious inhibition of ezrin mRNA expression in Eai and Ebi groups (0.22 +/- 0.01 vs 0.95 +/- 0.04, P < 0.05; 0.31 +/- 0.01 vs. 0.95 +/- 0.04, P < 0.05). Western blot analysis revealed a 72.35 +/- 3.74% reduction of the ezrin protein level after interference with the ezrin targeting gene. Moreover, the inhibition of ezrin expression clearly inhibited SGC-7901 cell migration and invasion, and improved cell adhesion as well as increased sensitivity to camptothecin-induced apoptosis.

CONCLUSION

Ezrin gene targeting by RNAi can inhibit the metastatic growth and migration of SGC-7901 human gastric cancer cells.

Proteomic analysis of chemonaive pediatric osteosarcomas and corresponding normal bone reveals multiple altered molecular targets

With a view to identify the proteins involved in transformation, metastasis or chemoresistance in pediatric osteosarcoma, we carried out a new experimental approach based on comparison of the proteomic profile of paired samples of osteosarcoma and normal bone tissues from the same patient. The proteomic profiles of five pairs of cell lines (normal vs tumoral) were obtained by two-dimensional difference gel electrophoresis. We detected 56 differential protein spots (t test, p < 0.05). Subsequent protein characterization by nano-LC-ESI-MS/MS enabled us to identify some of these proteins, 16 of which were chosen on the basis of the change of their relative abundance between osteosarcomas and paired normal bones and also because their involvement was supported by the genomic analysis. Two of the 16 proteins, Alpha-crystallin B chain (CRYAB) and ezrin (EZR1), were selected for further studies: an immunohistochemical analysis of a TMA (tissue microarray) and real-time PCR for a set of 14 osteosarcoma/normal-bone pairs. The results of this second tier of studies confirmed that there were significant increases in the amounts of CRYAB and ezrin, especially in advanced stages of the disease. Our overall conclusion is that proteomic profiling of paired samples of osteosarcoma and normal bone tissues from the same patient is a practicable and potentially powerful way of initiating and proceeding with a search for proteins and genes involved in pediatric osteosarcoma.

High level of ezrin expression in colorectal cancer tissues is closely related to tumor malignancy

AIM: To investigate the ezrin expression in normal colorectal mucosa and colorectal cancer tissues, and study the correlation between ezrin expression in colorectal cancer tissues and tumor invasion and metastasis.

METHODS: Eighty paraffin-embedded cancer tissue samples were selected from primary colorectal adenocarcinoma. Twenty-eight patients had well-differentiated, 22 had moderately differentiated and 30 had poorly differentiated adenocarcinoma. Forty-five patients and 35 patients had lymph node metastasis. Forty-five patients were of Dukes A to B stage, and 35 were of C to D stage. Another 22 paraffin-embedded tissue blocks of normal colorectal epithelium (> 5 cm away from the edge of the tumor) were selected as the control group. All patients with colorectal cancer were treated surgically and diagnosed histologically, without preoperative chemotherapy or radiotherapy. The immunohistochemistry was used to detect the ezrin expression in paraffin-embedded normal colorectal mucosa tissues and colorectal cancer tissue samples.

RESULTS: Ezrin expression in colorectal cancer was significantly higher than in normal colorectal mucosa (75.00% vs 9.09%, P < 0.01), and there was a close relationship between ezrin expression and the degree of tumor differentiation, lymph node metastasis and Dukes stage (88.46% vs 50.00%, P < 0.01; 94.28% vs 51.11%, P < 0.01; 94.28% vs 51.11%, P < 0.01).

CONCLUSION: Ezrin expression is obviously higher in colorectal cancer tissues than in normal colorectal mucosa tissues, and the high level of ezrin expression is closely related to the colorectal cancer invasion and metastasis process.

Phosphorylated ezrin is associated with EBV latent membrane protein 1 in nasopharyngeal carcinoma and induces cell migration

Tumor metastasis is a complex phenomenon that is the culmination of effects of numerous cellular factors. We have shown that the Epstein-Barr virus (EBV) oncoprotein, latent membrane protein 1 (LMP1), is capable of inducing a wide range of such factors in cell culture, expression of which is also elevated in the LMP1-expressing tumor, nasopharyngeal carcinoma (NPC), a highly invasive neoplasm. Recently, the membrane crosslinker protein, ezrin, has been implicated in tumor cell metastasis and malignant progression. In this study, we evaluated the possible role of LMP1 and ezrin in the pathophysiology of NPC. We show that C-terminal phosphorylation of ezrin is increased by the expression of LMP1 in nasopharyngeal (NP) cells through a protein kinase C (PKC) pathway. LMP1 enhances the organization of a ternary complex of CD44, ezrin and F-actin, which is a prerequisite for ezrin phosphorylation. In NPC tissues, the expression of phosphoezrin and LMP1 is directly correlated. Silencing of endogenously expressed ezrin suppresses LMP1-induced cell motility and invasiveness. Moreover, the inhibition of ezrin phosphorylation by PKC inhibitor suppresses migration and invasion of NP cells. These data show that the phosphorylation of ezrin and its recruitment to the cell membrane linked to F-actin and CD44 is a process required for LMP1-stimulated cell motility and invasion of NP cells.

A novel juxtamembrane domain in tumor necrosis factor receptor superfamily molecules activates Rac1 and controls neurite growth

Members of the tumor necrosis factor receptor (TNFR) superfamily control cell fate determination, including cell death and differentiation. Fas (CD95) is the prototypical "death receptor" of the TNFR superfamily and signals apoptosis through well established pathways. In the adult nervous system, Fas induces apoptosis in the context of neuropathology such as stroke or amyotrophic lateral sclerosis. However, during nervous system development, Fas promotes neurite growth and branching. The molecular mechanisms underlying Fas-induced process formation and branching have remained unknown to date. Here, we define the molecular pathway linking Fas to process growth and branching in cell lines and in developing neurons. We describe a new cytoplasmic membrane proximal domain (MPD) that is essential for Fas-induced process growth and that is conserved in members of the TNFR superfamily. We show that the Fas MPD recruits ezrin, a molecule that links transmembrane proteins to the cytoskeleton, and activates the small GTPase Rac1. Deletion of the MPD, but not the death domain, abolished Rac1 activation and process growth. Furthermore, an ezrin-derived inhibitory peptide prevented Fas-induced neurite growth in primary neurons. Our results define a new domain, topologically and functionally distinct from the death domain, which regulates neuritogenesis via recruitment of ezrin and activation of Rac1.

Treatment of colon cancer cells using the cytosine deaminase/5-fluorocytosine suicide system induces apoptosis, modulation of the proteome, and Hsp90beta phosphorylation

The bacterial cytosine deaminase (CD) gene, associated with the 5-fluorocytosine (5FC) prodrug, is one of the most widely used suicide systems in gene therapy. Introduction of the CD gene within a tumor induces, after 5FC treatment of the animal, a local production of 5-fluorouracil resulting in intratumor chemotherapy. Destruction of the gene-modified tumor is then followed by the triggering of an antitumor immune reaction resulting in the regression of distant wild-type metastasis. The global effects of 5FC on colorectal adenocarcinoma cells expressing the CD gene were analyzed using the proteomic method. Application of 5FC induced apoptosis and 19 proteins showed a significant change in 5FC-treated cells compared with control cells. The up-regulated and down-regulated proteins include cytoskeletal proteins, chaperones, and proteins involved in protein synthesis, the antioxidative network, and detoxification. Most of these proteins are involved in resistance to anticancer drugs and resistance to apoptosis. In addition, we show that the heat shock protein Hsp90beta is phosphorylated on serine 254 upon 5FC treatment. Our results suggest that activation of Hsp90beta by phosphorylation might contribute to tumor regression and tumor immunogenicity. Our findings bring new insights into the mechanism of the anticancer effects induced by CD/5FC treatment.