Oncogene ect2 is related to regulators of small GTP-binding proteins

Prioritizing cervical cancer candidate genes using chaos game and fractal-based time series approach

Cervical cancer is one of the most severe threats to women worldwide and holds fourth rank in lethality. It is estimated that 604, 127 cervical cancer cases have been reported in 2020 globally. With advancements in high throughput technologies and bioinformatics, several cervical candidate genes have been proposed for better therapeutic strategies. In this paper, we intend to prioritize the candidate genes that are involved in cervical cancer progression through a fractal time series-based cross-correlations approach. we apply the chaos game representation theory combining a two-dimensional multifractal detrended cross-correlations approach among the known and candidate genes involved in cervical cancer progression to prioritize the candidate genes. We obtained 16 candidate genes that showed cross-correlation with known cancer genes. Functional enrichment analysis of the candidate genes shows that they involve GO terms: biological processes, cell-cell junction assembly, cell-cell junction organization, regulation of cell shape, cortical actin cytoskeleton organization, and actomyosin structure organization. KEGG pathway analysis revealed genes' role in Rap1 signaling pathway, ErbB signaling pathway, MAPK signaling pathway, PI3K-Akt signaling pathway, mTOR signaling pathway, Acute myeloid leukemia, chronic myeloid leukemia, Breast cancer, Thyroid cancer, Bladder cancer, and Gastric cancer. Further, we performed survival analysis and prioritized six genes CDH2, PAIP1, BRAF, EPB41L3, OSMR, and RUNX1 as potential candidate genes for cervical cancer that has a crucial role in tumor progression. We found that our study through this integrative approach an efficient tool and paved a new way to prioritize the candidate genes and these genes could be evaluated experimentally for potential validation. We suggest this may be useful in analyzing the nucleotide sequences and protein sequences for clustering, classification, class affiliation, etc.

Dbl family RhoGEFs in cancer: different roles and targeting strategies

Small Ras homologous guanosine triphosphatase (Rho GTPase) family proteins are highly associated with tumorigenesis and development. As intrinsic exchange activity regulators of Rho GTPases, Rho guanine nucleotide exchange factors (RhoGEFs) have been demonstrated to be closely involved in tumor development and received increasing attention. They mainly contain two families: the diffuse B-cell lymphoma (Dbl) family and the dedicator of cytokinesis (Dock) family. More and more emphasis has been paid to the Dbl family members for their abnormally high expression in various cancers and their correlation to poor prognosis. In this review, the common and distinctive structures of Dbl family members are discussed, and their roles in cancer are summarized with a focus on Ect2, Tiam1/2, P-Rex1/2, Vav1/2/3, Trio, KALRN, and LARG. Significantly, the strategies targeting Dbl family RhoGEFs are highlighted as novel therapeutic opportunities for cancer.

Guanine nucleotide exchange factors for Rho GTPases (RhoGEFs) as oncogenic effectors and strategic therapeutic targets in metastatic cancer

Metastatic cancer cells dynamically adjust their shape to adhere, invade, migrate, and expand to generate secondary tumors. Inherent to these processes is the constant assembly and disassembly of cytoskeletal supramolecular structures. The subcellular places where cytoskeletal polymers are built and reorganized are defined by the activation of Rho GTPases. These molecular switches directly respond to signaling cascades integrated by Rho guanine nucleotide exchange factors (RhoGEFs), which are sophisticated multidomain proteins that control morphological behavior of cancer and stromal cells in response to cell-cell interactions, tumor-secreted factors and actions of oncogenic proteins within the tumor microenvironment. Stromal cells, including fibroblasts, immune and endothelial cells, and even projections of neuronal cells, adjust their shapes and move into growing tumoral masses, building tumor-induced structures that eventually serve as metastatic routes. Here we review the role of RhoGEFs in metastatic cancer. They are highly diverse proteins with common catalytic modules that select among a variety of homologous Rho GTPases enabling them to load GTP, acquiring an active conformation that stimulates effectors controlling actin cytoskeleton remodeling. Therefore, due to their strategic position in oncogenic signaling cascades, and their structural diversity flanking common catalytic modules, RhoGEFs possess unique characteristics that make them conceptual targets of antimetastatic precision therapies. Preclinical proof of concept, demonstrating the antimetastatic effect of inhibiting either expression or activity of βPix (ARHGEF7), P-Rex1, Vav1, ARHGEF17, and Dock1, among others, is emerging.

Two RhoGEF isoforms with distinct localisation control furrow position during asymmetric cell division

Cytokinesis partitions cellular content between daughter cells. It relies on the formation of an acto-myosin contractile ring, whose constriction induces the ingression of the cleavage furrow between the segregated chromatids. Rho1 GTPase and its RhoGEF (Pbl) are essential for this process. However, how Rho1 is regulated to sustain furrow ingression while maintaining correct furrow position remains poorly defined. Here, we show that during asymmetric division of Drosophila neuroblasts, Rho1 is controlled by two Pbl isoforms with distinct localisation. Spindle midzone- and furrow-enriched Pbl-A focuses Rho1 at the furrow to sustain efficient ingression, while Pbl-B pan-plasma membrane localization promotes the broadening of Rho1 activity and the subsequent enrichment of myosin on the entire cortex. This enlarged zone of Rho1 activity is critical to adjust furrow position, thereby preserving correct daughter cell size asymmetry. Our work highlights how the use of isoforms with distinct localisation makes an essential process more robust.

ECT2 promotes malignant phenotypes through the activation of the AKT/mTOR pathway and cisplatin resistance in cervical cancer

Epithelial cell transforming sequence 2 (ECT2) is expressed at high levels in various malignancies and contributes to malignant phenotypes in cancers. However, ECT2 is still not fully understood regarding its function and carcinogenic mechanism in cervical cancer. This research indicated that ECT2 expression was elevated in cervical cancer based on bioinformatics analysis and clinical specimens. Experiments in vitro and in vivo confirmed that ECT2 knockdown could suppress the proliferation and metastasis of cervical carcinoma cells. In addition, we found that silencing ECT2 could enhance the sensitivity to cisplatin and promote cell apoptosis. Mechanistically, we observed that ECT2 knockdown could inhibit the AKT/mTOR pathway and activate apoptosis, while ECT2 overexpression induced the opposite effect. The relationship between ECT2 and AKT was further confirmed by immunoprecipitation and rescue experiments. We found that the ECT2 and AKT could interact to form a complex, and knockdown AKT could offset all of the effects induced by ECT2. Our study emphasized the key point of ECT2 in the reversal of cisplatin resistance, and ECT2 could become a potential therapeutic target in cervical cancer.

Increased expression of ECT2 predicts the poor prognosis of breast cancer patients

Breast cancer is the most common malignancy and the second leading cause of cancer-related death in women. Recent studies have indicated that aberrant activation of Rho GTPases relates to the malignant properties of breast cancer cells. As the guanine nucleotide exchange factor of Rho GTPases, the role of ECT2 (epithelial cell transforming 2) in breast cancer is still unclear. Tissue microarrays and multiple public databases were utilized to investigate the relationship between ECT2 level and clinical-pathological features of breast cancer patients. Kaplan Meier-plotter online tool and tissue microarray with survival information were used to investigate the predictive value for breast cancer. Here, we found increased ECT2 level was highly associated with advanced TNM stage, poor differentiation, and loss of hormone receptors of breast cancer. Gene expression profile showed that ECT2 level was closely correlated to cell-proliferation-associated pathways. Integration analysis using public databases and tissue microarray indicated that high ECT2 was an adverse prognostic factor for breast cancer patients. We believe the ECT2 level might be a valuable complement for commercially available predictors such as the 21 genes test. Furthermore, ECT2 would be a novel target for drug development for breast cancer.

Membrane compartmentalization of Ect2/Cyk4/Mklp1 and NuMA/dynein regulates cleavage furrow formation

In animal cells, spindle elongation during anaphase is temporally coupled with cleavage furrow formation. Spindle elongation during anaphase is regulated by NuMA/dynein/dynactin complexes that occupy the polar region of the cell membrane and are excluded from the equatorial membrane. How NuMA/dynein/dynactin are excluded from the equatorial membrane and the biological significance of this exclusion remains unknown. Here, we show that the centralspindlin (Cyk4/Mklp1) and its interacting partner RhoGEF Ect2 are required for NuMA/dynein/dynactin exclusion from the equatorial cell membrane. The Ect2-based (Ect2/Cyk4/Mklp1) and NuMA-based (NuMA/dynein/dynactin) complexes occupy mutually exclusive membrane surfaces during anaphase. The equatorial membrane enrichment of Ect2-based complexes is essential for NuMA/dynein/dynactin exclusion and proper spindle elongation. Conversely, NuMA-based complexes at the polar region of the cell membrane ensure spatially confined localization of Ect2-based complexes and thus RhoA. Overall, our work establishes that membrane compartmentalization of NuMA-based and Ect2-based complexes at the two distinct cell surfaces restricts dynein/dynactin and RhoA for coordinating spindle elongation with cleavage furrow formation.

Interphase microtubule disassembly is a signaling cue that drives cell rounding at mitotic entry

At mitotic entry, reorganization of the actomyosin cortex prompts cells to round-up. Proteins of the ezrin, radixin, and moesin family (ERM) play essential roles in this process by linking actomyosin forces to the plasma membrane. Yet, the cell-cycle signal that activates ERMs at mitotic entry is unknown. By screening a compound library using newly developed biosensors, we discovered that drugs that disassemble microtubules promote ERM activation. We further demonstrated that disassembly of interphase microtubules at mitotic entry directs ERM activation and metaphase cell rounding through GEF-H1, a Rho-GEF inhibited by microtubule binding, RhoA, and its kinase effector SLK. We finally demonstrated that GEF-H1 and Ect2, another Rho-GEF previously identified to control actomyosin forces, act together to drive activation of ERMs and cell rounding in metaphase. In summary, we report microtubule disassembly as a cell-cycle signal that controls a signaling network ensuring that actomyosin forces are efficiently integrated at the plasma membrane to promote cell rounding at mitotic entry.

Rationally designed cationic amphiphilic peptides for selective gene delivery to cancer cells

Gene therapy has gained increasing attention as an alternative to pharmacotherapy for treatment of various diseases. The extracellular and intracellular barriers to gene delivery necessitate the use of gene vectors which has led to the development of myriads of gene delivery systems. However, many of these gene delivery systems have pitfalls such as low biocompatibility, low loading efficiency, low transfection efficiency, lack of tissue selectivity and high production costs. Herein, we report the development of a new series of short cationic amphiphilic peptides with anticancer activity for selective delivery of small interfering RNA (siRNA) and antisense oligodeoxynucleotides (ODNs) to cancer cells. The peptides consist of alternating dyads of hydrophobic (isoleucine (I) or leucine (L)) and hydrophilic (arginine (R) or lysine (L)) amino acids. The peptides exhibited higher preference for transfection of HCT 116 colorectal cancer cells compared to human dermal fibroblasts (HDFs) and induced higher level of gene silencing in the cancer cells. The nucleic acid complexation and transfection efficiency of the peptides was a function of their secondary structure, their hydrophobicity and their C-terminal amino acid. The peptides containing L in their hydrophobic domain formed stronger complexes with siRNA and successfully delivered it to the cancer cells but were unable to release their cargo inside the cells and therefore could not induce any gene silencing. On the contrary, the peptides containing I in their hydrophobic domain were able to release their associated siRNA and induce considerable gene silencing in cancer cells. The peptides exhibited higher selectivity for colorectal cancer cells and induced less gene silencing in fibroblasts compared to the lipid-based commercial transfection reagent DharmaFECT™ 1. The results from this study can serve as a tool for rational design of new peptide-based gene vectors for high selective gene delivery to cancer cells.

Aberrant Expression and Subcellular Localization of ECT2 Drives Colorectal Cancer Progression and Growth

ECT2 is an activator of RHO GTPases that is essential for cytokinesis. In addition, ECT2 was identified as an oncoprotein when expressed ectopically in NIH/3T3 fibroblasts. However, oncogenic activation of ECT2 resulted from N-terminal truncation, and such truncated ECT2 proteins have not been found in patients with cancer. In this study, we observed elevated expression of full-length ECT2 protein in preneoplastic colon adenomas, driven by increased ECT2 mRNA abundance and associated with APC tumor-suppressor loss. Elevated ECT2 levels were detected in the cytoplasm and nucleus of colorectal cancer tissue, suggesting cytoplasmic mislocalization as one mechanism of early oncogenic ECT2 activation. Importantly, elevated nuclear ECT2 correlated with poorly differentiated tumors, and a low cytoplasmic:nuclear ratio of ECT2 protein correlated with poor patient survival, suggesting that nuclear and cytoplasmic ECT2 play distinct roles in colorectal cancer. Depletion of ECT2 reduced anchorage-independent cancer cell growth and invasion independent of its function in cytokinesis, and loss of Ect2 extended survival in a Kras G12D Apc-null colon cancer mouse model. Expression of ECT2 variants with impaired nuclear localization or guanine nucleotide exchange catalytic activity failed to restore cancer cell growth or invasion, indicating that active, nuclear ECT2 is required to support tumor progression. Nuclear ECT2 promoted ribosomal DNA transcription and ribosome biogenesis in colorectal cancer. These results support a driver role for both cytoplasmic and nuclear ECT2 overexpression in colorectal cancer and emphasize the critical role of precise subcellular localization in dictating ECT2 function in neoplastic cells. SIGNIFICANCE: ECT2 overexpression and mislocalization support its role as a driver in colon cancer that is independent from its function in normal cell cytokinesis.

Epithelial cell transforming 2 is regulated by Yes-associated protein 1 and mediates pancreatic cancer progression and metastasis

Pancreatic ductal adenocarcinoma (PDAC) is highly metastatic and represents one of the deadliest forms of human cancers. Previous studies showed that activation of Yes-associated protein 1 (YAP1) plays a key role in malignant transformation in the pancreas. In this study, we found that YAP1 regulates the expression of epithelial cell transforming 2 (ECT2), a guanine nucleotide exchange factor for Rho-like GTPases. By immunohistochemistry analysis of human tissues, we show that ECT2 is highly expressed in primary PDAC and liver metastasis but not in normal pancreas. These correlations were also observed in a mouse model of PDAC, where pancreatic transformation is driven by mutants of Kras and Trp53. Notably, nuclear ECT2 is upregulated in the transition from preneoplastic lesions to PDAC. High levels of YAP1 or ECT2 expression correlates with the poor overall survival rate of patients with PDAC. We further demonstrate that ECT2 is required for pancreatic cancer cell proliferation and migration in vitro. Finally, using a syngeneic orthotopic xenograft mouse model for pancreatic cancer, we found that ablation of ECT2 expression reduces pancreatic cancer growth and dissemination to the liver. These findings highlight the critical role of ECT2 in promoting pancreatic cancer growth and metastasis and provides insights into the development of novel methods for early detection and treatment.NEW & NOTEWORTHY Pancreatic ductal adenocarcinoma is one of the deadliest forms of human cancers. In this study, we identified a novel signaling mechanism involved in PDAC progression and metastasis. Yes-associated protein 1 mediates the expression of epithelial cell transforming 2, which is elevated in PDAC and correlates with poor survival. Epithelial cell transforming 2 is required for PDAC growth and metastasis. This study provides insights into the development of novel methods for early detection and treatment of PDAC.

ECT2 promotes lung adenocarcinoma progression through extracellular matrix dynamics and focal adhesion signaling

Lung adenocarcinoma (LAC) is the most prevalent form of lung cancer. Epithelial cell transforming sequence 2 (ECT2) is a guanine nucleotide exchange factor that has been implicated in oncogenic and malignant phenotypes of LAC. Here, we identified an oncogenic role of ECT2 in the extracellular matrix (ECM) dynamics of LAC cells. We showed that suppression of ECT2 decreased adhesion and spreading of LAC cells on ECM components. Morphologically, ECT2-depleted cells exhibited a rounded shape and cytoskeletal changes. Examination of transcriptional changes by RNA sequencing revealed a total of 1569 and 828 genes whose expressions were altered (absolute fold change and a difference of >2 fold) in response to suppression of ECT2 in two LAC cells (Calu-3 and NCI-H2342), respectively, along with 298 genes that were common to both cell lines. Functional enrichment analysis of common genes demonstrated a significant enrichment of focal adhesions. In accord with this observation, we found that ECT2 suppression decreased the expression level of proteins involved in focal adhesion signaling including focal adhesion kinase (FAK), Crk, integrin β1, paxillin, and p130Cas. FAK knockdown leads to impaired cell proliferation, adhesion, and spreading of LAC cells. Moreover, in LAC cells, ECT2 binds to and stabilizes FAK and is associated with the formation of the focal adhesions. Our findings provide new insights into the underlying role of ECT2 in cell-ECM dynamics during LAC progression and suggest that ECT2 could be a promising therapeutic avenue for lung cancer.

Effect of Ect2 Expression on the Growth of Triple-Negative Breast Cancer Cells with Paclitaxel Intervention

Object

To identify the expression levels of ECT2 (epithelial cell transforming sequence 2) in triple-negative breast cancer (TNBC) before and after administration of paclitaxel (PTX) and explore the interaction between ECT2 and PTX in breast cancer treatment.

Methods

Lentiviral (LV) packaging ECT2 overexpression and interference plasmids were constructed for in vitro assays. The effects of ECT2 expression on the TNBC cell line (HCC1806), particularly its roles in the proliferation, invasion, migration and apoptosis and cell cycle, were evaluated using the CCK-8 and other methods before and after PTX treatment. In nude mouse xenograft settings were performed to detect cell apoptosis and Ki-67 expression levels by TUNEL and immunohistochemical staining, respectively.

Results

In the vitro assays, before and after the PTX treatment, comparison of the LV-ECT2 and sh-ECT2 groups and the remaining three groups (control, LV-NC, sh-NC) showed statistically significant differences in terms of cell proliferation, invasion and migration and apoptosis and changes in the cell cycle. In the vivo assays, the control, LV-ECT2 and sh-ECT2 groups markedly outweighed the corresponding PTX-treated groups. The LV-ECT2, PTX, sh-ECT2 and sh-ECT2-PTX were all significantly different from the control group in terms of body weight and tumour size changes. Cell apoptosis occurred in the PTX, sh-ECT2 and sh-ECT2-PTX groups. About the Ki-67 proliferation index, the PTX, LV-ECT2-PTX, sh-ECT2 and sh-ECT2-PTX groups were significantly different from the control group.

Conclusion

ECT2, which is a major driving factor in the growth of breast cancer cells, plays an important role in regulating TNBC growth. PTX therapy had significantly improved efficacy after silencing ECT2. This finding indicates that the inhibition of ECT2 expression may facilitate the treatment of breast cancer as a new regimen and provide a theoretical basis for the development of new targeted drugs as a replacement for PTX in breast cancer treatment.

Animal Cell Cytokinesis: The Rho-Dependent Actomyosin-Anilloseptin Contractile Ring as a Membrane Microdomain Gathering, Compressing, and Sorting Machine

Cytokinesis is the last step of cell division that partitions the cellular organelles and cytoplasm of one cell into two. In animal cells, cytokinesis requires Rho-GTPase-dependent assembly of F-actin and myosin II (actomyosin) to form an equatorial contractile ring (CR) that bisects the cell. Despite 50 years of research, the precise mechanisms of CR assembly, tension generation and closure remain elusive. This hypothesis article considers a holistic view of the CR that, in addition to actomyosin, includes another Rho-dependent cytoskeletal sub-network containing the scaffold protein, Anillin, and septin filaments (collectively termed anillo-septin). We synthesize evidence from our prior work in Drosophila S2 cells that actomyosin and anillo-septin form separable networks that are independently anchored to the plasma membrane. This latter realization leads to a simple conceptual model in which CR assembly and closure depend upon the micro-management of the membrane microdomains to which actomyosin and anillo-septin sub-networks are attached. During CR assembly, actomyosin contractility gathers and compresses its underlying membrane microdomain attachment sites. These microdomains resist this compression, which builds tension. During CR closure, membrane microdomains are transferred from the actomyosin sub-network to the anillo-septin sub-network, with which they flow out of the CR as it advances. This relative outflow of membrane microdomains regulates tension, reduces the circumference of the CR and promotes actomyosin disassembly all at the same time. According to this hypothesis, the metazoan CR can be viewed as a membrane microdomain gathering, compressing and sorting machine that intrinsically buffers its own tension through coordination of actomyosin contractility and anillo-septin-membrane relative outflow, all controlled by Rho. Central to this model is the abandonment of the dogmatic view that the plasma membrane is always readily deformable by the underlying cytoskeleton. Rather, the membrane resists compression to build tension. The notion that the CR might generate tension through resistance to compression of its own membrane microdomain attachment sites, can account for numerous otherwise puzzling observations and warrants further investigation using multiple systems and methods.

A feedforward circuit shaped by ECT2 and USP7 contributes to breast carcinogenesis

Rationale: A number of guanine nucleotide exchange factors (GEFs) including epithelial cell transforming factor ECT2 are believed to drive carcinogenesis through activating distinct oncogenic GTPases. Yet, whether GEF-independent activity of ECT2 also plays a role in tumorigenesis remains unclear. Methods: Immunohistochemical (IHC) staining, colony formation and xenograft assays were used to examine the role of ECT2 in breast carcinogenesis. Co-immunoprecipitation, immunofluorescent stainings, in vivo deubiquitination and in vitro deubiquitination experiments were performed to examine the physical and functional interaction between ECT2 and ubiquitin-specific protease USP7. High-throughput RNA sequencing, quantitative reverse transcription-PCR and Western blotting were employed to investigate the biological significance of the interplay between ECT2 and USP7. Results: We report that ECT2 plays a tumor-promoting role in breast cancer, and GEF activity-deficient ECT2 is able to alleviate ECT2 depletion associated growth defects in breast cancer cells. Mechanistically, we demonstrated that ECT2 physically interacts with ubiquitin-specific protease USP7 and functionally facilitates USP7 intermolecular self-association, -deubiquitination and -stabilization in a GEF activity-independent manner. USP7 in turn, deubiquitinates and stabilizes ECT2, resulting in a feedforward regulatory circuit that ultimately sustains the expression of oncogenic protein MDM2. Conclusion: Our study uncovers a GEF-independent role of ECT2 in promoting survival of breast cancer cells, provides a molecular insight for the reciprocal regulation of ECT2 and USP7, and supports the pursuit of ECT2/USP7 as potential targets for breast cancer intervention.

RAS and RHO family GTPase mutations in cancer: twin sons of different mothers?

The RAS and RHO family comprise two major branches of the RAS superfamily of small GTPases. These proteins function as regulated molecular switches and control cytoplasmic signaling networks that regulate a diversity of cellular processes, including cell proliferation and cell migration. In the early 1980s, mutationally activated RAS genes encoding KRAS, HRAS and NRAS were discovered in human cancer and now comprise the most frequently mutated oncogene family in cancer. Only recently, exome sequencing studies identified cancer-associated alterations in two RHO family GTPases, RAC1 and RHOA. RAS and RHO proteins share significant identity in their amino acid sequences, protein structure and biochemistry. Cancer-associated RAS mutant proteins harbor missense mutations that are found primarily at one of three mutational hotspots (G12, G13 and Q61) and have been identified as gain-of-function oncogenic alterations. Although these residues are conserved in RHO family proteins, the gain-of-function mutations found in RAC1 are found primarily at a distinct hotspot. Unexpectedly, the cancer-associated mutations found with RHOA are located at different hotspots than those found with RAS. Furthermore, since the RHOA mutations suggested a loss-of-function phenotype, it has been unclear whether RHOA functions as an oncogene or tumor suppressor in cancer development. Finally, whereas RAS mutations are found in a broad spectrum of cancer types, RHOA and RAC1 mutations occur in a highly restricted range of cancer types. In this review, we focus on RHOA missense mutations found in cancer and their role in driving tumorigenesis, with comparisons to cancer-associated mutations in RAC1 and RAS GTPases.

Protein kinase Cι promotes UBF1-ECT2 binding on ribosomal DNA to drive rRNA synthesis and transformed growth of non-small-cell lung cancer cells

Epithelial cell-transforming sequence 2 (ECT2) is a guanine nucleotide exchange factor for Rho GTPases that is overexpressed in many cancers and involved in signal transduction pathways that promote cancer cell proliferation, invasion, and tumorigenesis. Recently, we demonstrated that a significant pool of ECT2 localizes to the nucleolus of non-small-cell lung cancer (NSCLC) cells, where it binds the transcription factor upstream binding factor 1 (UBF1) on the promoter regions of ribosomal DNA (rDNA) and activates rDNA transcription, transformed cell growth, and tumor formation. Here, we investigated the mechanism by which ECT2 engages UBF1 on rDNA promoters. Results from ECT2 mutagenesis indicated that the tandem BRCT domain of ECT2 mediates binding to UBF1. Biochemical and MS-based analyses revealed that protein kinase Cι (PKCι) directly phosphorylates UBF1 at Ser-412, thereby generating a phosphopeptide-binding epitope that binds the ECT2 BRCT domain. Lentiviral shRNA knockdown and reconstitution experiments revealed that both a functional ECT2 BRCT domain and the UBF1 Ser-412 phosphorylation site are required for UBF1-mediated ECT2 recruitment to rDNA, elevated rRNA synthesis, and transformed growth. Our findings provide critical molecular insight into ECT2-mediated regulation of rDNA transcription in cancer cells and offer a rationale for therapeutic targeting of UBF1- and ECT2-stimulated rDNA transcription for the management of NSCLC.

MicroRNA Regulation of the Small Rho GTPase Regulators-Complexities and Opportunities in Targeting Cancer Metastasis

The small Rho GTPases regulate important cellular processes that affect cancer metastasis, such as cell survival and proliferation, actin dynamics, adhesion, migration, invasion and transcriptional activation. The Rho GTPases function as molecular switches cycling between an active GTP-bound and inactive guanosine diphosphate (GDP)-bound conformation. It is known that Rho GTPase activities are mainly regulated by guanine nucleotide exchange factors (RhoGEFs), GTPase-activating proteins (RhoGAPs), GDP dissociation inhibitors (RhoGDIs) and guanine nucleotide exchange modifiers (GEMs). These Rho GTPase regulators are often dysregulated in cancer; however, the underlying mechanisms are not well understood. MicroRNAs (miRNAs), a large family of small non-coding RNAs that negatively regulate protein-coding gene expression, have been shown to play important roles in cancer metastasis. Recent studies showed that miRNAs are capable of directly targeting RhoGAPs, RhoGEFs, and RhoGDIs, and regulate the activities of Rho GTPases. This not only provides new evidence for the critical role of miRNA dysregulation in cancer metastasis, it also reveals novel mechanisms for Rho GTPase regulation. This review summarizes recent exciting findings showing that miRNAs play important roles in regulating Rho GTPase regulators (RhoGEFs, RhoGAPs, RhoGDIs), thus affecting Rho GTPase activities and cancer metastasis. The potential opportunities and challenges for targeting miRNAs and Rho GTPase regulators in treating cancer metastasis are also discussed. A comprehensive list of the currently validated miRNA-targeting of small Rho GTPase regulators is presented as a reference resource.

ECT2/PSMD14/PTTG1 axis promotes the proliferation of glioma through stabilizing E2F1

BACKGROUND

Epithelial cell transformation sequence 2 (ECT2) is upregulated in glioma and promotes glioma cell proliferation. A preliminary experiment showed a positive correlation between ECT2 and pituitary tumor-transforming gene 1 (PTTG1). The aim of this study was to explore how ECT2 affects PTTG1 to influence the proliferation of glioma cells.

METHODS

The expression of ECT2 in glioma was detected by western blot and reverse transcription PCR. The effect of ECT2 on glioma proliferation was examined using cell proliferation-related assays and in vivo experiments. The effect of ECT2 on the stability of E2F transcription factor 1 (E2F1) and the expression of PTTG1 were examined by western blot, co-immunoprecipitation, and in vivo ubiquitination assays.

RESULTS

ECT2 was upregulated in gliomas and was negatively correlated with prognosis; its downregulation inhibited glioma cell proliferation. Furthermore, ECT2 regulated PTTG1 expression by affecting the stability of E2F1, thereby affecting the glioma cell proliferation. In addition, the deubiquitinating enzyme proteasome 26S subunit, non-ATPase 14 (PSMD14) affected the degradation of E2F1 and regulated the stability of E2F1. Interestingly, ECT2 regulated the expression of PSMD14.

CONCLUSION

In this study, we clarify a new mechanism by which ECT2 regulates the expression of PTTG1 and thus affects the proliferation of glioma cells: ECT2 influences the stability of E2F1 by regulating the expression of the deubiquitinating enzyme PSMD14, thereby affecting the expression of PTTG1. Intensive and extensive understanding of the mechanism of ECT2 in glioma proliferation may provide an opportunity for the development of new molecular therapeutic targets for glioma treatment.

StarD13: a potential star target for tumor therapeutics

StarD13 is a tumor suppressor and a GTPase activating protein (GAP) for Rho GTPases. Thus, StarD13 regulates cell survival pathways and induces apoptosis in a p53-dependent and independent manners. In tumors, StarD13 is either downregulated or completely inhibited, depending on the tumor type. As such, and through the dysregulation of Rho GTPases, this affects adhesion dynamics, actin dynamics, and leads to an increase or a decrease in tumor metastasis depending on the tumor grade and type. Being a key regulatory protein, StarD13 is a potential promising candidate for therapeutic approaches. This paper reviews the key characteristics of this protein and its role in tumor malignancies.

Structure and regulation of human epithelial cell transforming 2 protein

Epithelial cell transforming 2 (Ect2) protein activates Rho GTPases and controls cytokinesis and many other cellular processes. Dysregulation of Ect2 is associated with various cancers. Here, we report the crystal structure of human Ect2 and complementary mechanistic analyses. The data show the C-terminal PH domain of Ect2 folds back and blocks the canonical RhoA-binding site at the catalytic center of the DH domain, providing a mechanism of Ect2 autoinhibition. Ect2 is activated by binding of GTP-bound RhoA to the PH domain, which suggests an allosteric mechanism of Ect2 activation and a positive-feedback loop reinforcing RhoA signaling. This bimodal RhoA binding of Ect2 is unusual and was confirmed with Förster resonance energy transfer (FRET) and hydrogen-deuterium exchange mass spectrometry (HDX-MS) analyses. Several recurrent cancer-associated mutations map to the catalytic and regulatory interfaces, and dysregulate Ect2 in vitro and in vivo. Together, our findings provide mechanistic insights into Ect2 regulation in normal cells and under disease conditions.

Clinicopathological and prognostic significance of epithelial cell transforming sequence 2 expression in cancers: a systematic review and meta-analysis

Numerous studies have investigated the prognostic significance of ECT2 (epithelial cell transforming sequence 2) expression in patients with cancer. Nevertheless, conflicting results have been obtained. We thus performed a meta-analysis to systematically assess the prognostic significance of ECT2 in cancer. Electronic databases (PubMed and EMBASE) were searched for eligible studies. Hazard ratios (HR) and odds ratios (OR) with 95% confidence intervals (CIs) were used to estimate effect sizes. A total of 5,305 patients from 19 articles and 21 studies were included. The pooled results revealed that high ECT2 expression was correlated with advanced TNM stage (OR = 2.17; 95% CI: 1.42-3.32), positive lymph node metastasis (OR = 2.98; 95% CI: 2.28-3.89), distant metastasis (OR = 2.25; 95% CI: 1.03-4.92), and poor tumour differentiation (OR = 2.25; 95% CI: 1.03-4.92). More importantly, high ECT2 expression was significantly associated with poor overall survival (HR = 2.26; 95% CI, 1.84-2.78) and recurrence-free survival (HR = 1.52; 95% CI, 1.24-1.86). Our results suggested that ECT2 is a promising prognostic indicator and therapeutic target for cancer.

Epithelial cell transforming sequence 2 expression is associated with the progression of laryngeal squamous cell carcinoma

Epithelial cell transforming sequence 2 (ECT2) is a guanine nucleotide exchange factor and its expression is associated with the development of malignant tumor types. However, to the best of our knowledge, there is no information on the role of ECT2 in the development and progression of laryngeal squamous cell carcinoma (LSCC). The present study aimed at investigating the expression pattern and potential role of ECT2 in the development and progression of LSCC. The expression of ECT2 in 81 pairs of LSCC and adjacent non-tumor tissues was characterized by immunohistochemistry and reverse transcription-quantitative polymerase chain reaction. ECT2 expression was upregulated in LSCC tissues and associated significantly with poor differentiation, higher stages, lymph node metastasis and poor survival in the sample population. The relative expression levels of ECT2 mRNA transcripts were correlated with the intensity of anti-ECT2 staining in 25 ECT2+LSCC specimens selected randomly. These results indicated that ECT2 expression was crucial for the progression of LSCC and may serve as a biomarker for the diagnosis and prognosis of LSCC.

Cytoplasmic expression of epithelial cell transforming sequence 2 in lung adenocarcinoma and its implications for malignant progression

Epithelial cell transforming sequence 2 (ECT2), a guanine nucleotide exchange factor, is predominantly localized in the nucleus of non-transformed cells and functions to regulate cytokinesis. ECT2 is also localized in the cytoplasm of cancer cells. Aberrant cytoplasmic expression of ECT2 is thought to drive tumor growth and invasion. In this study, we investigated the cytoplasmic expression of ECT2 and its prognostic and biological significance in lung adenocarcinoma. Western blotting of cellular fractions from the nucleus and cytoplasm was performed to determine the subcellular localization of ECT2 in lung adenocarcinoma cell lines. The cytoplasmic expression of ECT2 in 167 lung adenocarcinomas was evaluated by immunohistochemistry and its clinical significance was examined using Kaplan-Meier curves and Cox regression analysis. Scraping cytology specimens of 13 fresh lung adenocarcinomas were used to assess the subcellular localization of ECT2 and its phosphorylation at Thr790 (P-ECT2(T790)). We found that ECT2 was localized in both the nucleus and cytoplasm of lung adenocarcinoma cell lines and tumor tissues. Cytoplasmic expression of ECT2 was detected by immunohistochemistry in 83 (50%) of the lung adenocarcinomas, and was found to increase during cancer progression. It was expressed in 30 (29%) small adenocarcinomas ( ≤ 2 cm in diameter) and 53 (82%) advanced adenocarcinomas ( > 2 cm in diameter). Cytoplasmic positivity for ECT2 was associated with a poor outcome in terms of both disease-free and overall survival (both P < 0.001), and was an independent prognostic factor for overall survival (P = 0.025). Immunocytochemical staining for P-ECT2(T790) demonstrated cytoplasmic and membrane positivity in Calu-3 cells and scraping cytology specimens. Positive P-ECT2(T790) staining was correlated with cytoplasmic ECT2 expression in 6 of 13 scraped cytology specimens tested. In conclusion, our findings indicate that cytoplasmic ECT2 expression could promote the malignant progression of lung adenocarcinoma and may represent a potent therapeutic target for patients with lung adenocarcinoma.

Overexpression of ECT2 is a strong poor prognostic factor in ER(+) breast cancer

Epithelial cell transforming sequence 2 (ECT2) is a guanine nucleotide exchange factor encoded by the ECT2 gene, which is located on the 3q26.31 chromosomal region and is directly associated with the occurrence of cancers. The aim of the present study was to examine the expression and prognostic importance of ECT2 in various breast cancer subtypes using the online tools, Gene Expression Profiling Interactive Analysis, Kaplan-Meier-plotter and bc-GenExMiner. ECT2 mRNA expression was significantly different in oestrogen receptor ER(+) breast cancer; overexpression of ECT2 was associated with poor prognosis in ER⁺ breast cancer. The mRNA expression levels of ECT2 were increased in basal-like breast cancer and triple negative breast cancer, but were not significant for prognostic prediction. We identified ECT2-correlated genes and their corresponding Gene Ontology (GO) enrichment terms. The results revealed that GO: 0005524 (protein binding) had the greatest number of correlated genes and also contained ECT2. This suggested that overexpression of ECT2 may be a significant prognostic factor for poor outcome in ER⁺ breast cancer; however, the precise role of ECT2 in breast cancer requires further investigation.

Targeting mitosis exit: A brake for cancer cell proliferation

The transition from mitosis to interphase, referred to as mitotic exit, is a critical mitotic process which involves activation and inactivation of multiple mitotic kinases and counteracting protein phosphatases. Loss of mitotic exit checkpoints is a common feature of cancer cells, leading to mitotic dysregulation and confers cancer cells with oncogenic characteristics, such as aberrant proliferation and microtubule-targeting agent (MTA) resistance. Since MTA resistance results from cancer cells prematurely exiting mitosis (mitotic slippage), blocking mitotic exit is believed to be a promising anticancer strategy. Moreover, based on this theory, simultaneous inhibition of mitotic exit and additional cell cycle phases would likely achieve synergistic antitumor effects. In this review, we divide the molecular regulators of mitotic exit into four categories based on their different regulatory functions: 1) the anaphase-promoting complex/cyclosome (APC/C, a ubiquitin ligase), 2) cyclin B, 3) mitotic kinases and phosphatases, 4) kinesins and microtubule-binding proteins. We also review the regulators of mitotic exit and propose prospective anticancer strategies targeting mitotic exit, including their strengths and possible challenges to their use.

Cytokinesis defects and cancer

Whole-genome and centrosome duplication as a consequence of cytokinesis failure can drive tumorigenesis in experimental model systems. However, whether cytokinesis failure is in fact an important cause of human cancers has remained unclear. In this Review, we summarize evidence that whole-genome-doubling events are frequently observed in human cancers and discuss the contribution that cytokinesis defects can make to tumorigenesis. We provide an overview of the potential causes of cytokinesis failure and discuss how tetraploid cells that are generated through cytokinesis defects are used in cancer as a transitory state on the route to aneuploidy. Finally, we discuss how cytokinesis defects can facilitate genetic diversification within the tumour to promote cancer development and could constitute the path of least resistance in tumour evolution.

Quantitative phosphoproteomic analysis identifies novel functional pathways of tumor suppressor DLC1 in estrogen receptor positive breast cancer

Deleted in Liver Cancer-1 (DLC1), a member of the RhoGAP family of proteins, functions as a tumor suppressor in several cancers including breast cancer. However, its clinical relevance is unclear in breast cancer. In this study, expression of DLC1 was correlated with prognosis using publicly available breast cancer gene expression datasets and quantitative Reverse Transcription PCR in cohorts of Estrogen Receptor-positive (ER+) breast cancer. Low expression of DLC1 correlates with poor prognosis in patients with ER+ breast cancer with further decrease in metastatic lesions. The Cancer Genome Atlas (TCGA) data showed that down regulation of DLC1 is not due to methylation or mutations. To seek further insights in understanding the role of DLC1 in ER+ breast cancer, we stably overexpressed DLC1-full-length (DLC1-FL) in T-47D breast cancer cells; this inhibited cell colony formation significantly in vitro compared to its control counterpart. Label-free global proteomic and TiO2 phosphopeptide enrichment assays (ProteomeXchange identifier PXD008220) showed that 205 and 122 phosphopeptides were unique to DLC1-FL cells and T-47D-control cells, respectively, whereas 6,726 were quantified by phosphoproteomics analysis in both conditions. The top three significant clusters of differentially phosphopeptides identified by DAVID pathway analysis represent cell-cell adhesion, mRNA processing and splicing, and transcription regulation. Phosphoproteomics analysis documented an inverse relation between DLC1 expression and several phosphopeptides including epithelial cell transforming sequence 2 (ECT2). Decreased phosphorylation of ECT2 at the residue T359, critical for its active conformational change, was validated by western blot. In addition, the ECT2 T359-containing phosphopeptide was detected in both basal and luminal patient-derived breast cancers breast cancer phosphoproteomics data on the Clinical Proteomic Tumor Analysis Consortium (CPTAC) Assay portal. Together, for the first time, this implicates ECT2 phosphorylation in breast cancer, which has been proposed as a therapeutic target in lung cancer. In conclusion, this data suggests that low expression of DLC1 is associated with poor prognosis. Targeting ECT2 phosphopeptides could provide a promising mechanism for controlling poor prognosis seen in DLC1low ER+ breast cancer.

Progression and prognostic value of ECT2 in non-small-cell lung cancer and its correlation with PCNA

Purpose

Epithelial cell transforming sequence 2 (ECT2) is a guanine nucleotide exchange factor, which is involved in cell division regulation and cell cycle modulation. Recent evidence indicates that ECT2 is overexpressed in many human cancers. However, the exact prognostic value of ECT2 in lung cancer has not been elucidated.

Patients and methods

In the current study, we performed correlation and prognosis analyses using public databases and conducted immunohistochemical staining in tissue microarrays, using samples from 204 lung cancer patients with survival data.

Results

We found that the expression of ECT2 was markedly increased in lung cancer tissues compared with normal tissues. Moreover, we demonstrated that the expression of ECT2 was related to tumor cell differentiation degree, TNM stage, lymph node metastasis, and prognosis in non-small-cell lung cancer (NSCLC). A correlation analysis indicated that ECT2 levels were significantly correlated with proliferating cell nuclear antigen (PCNA) levels in NSCLC. Furthermore, Kaplan–Meier analyses revealed that high ECT2 expression was associated with unfavorable overall survival (OS) and progression-free survival (PFS) in NSCLC patients.

Conclusion

Taken together, these results indicate that the overexpression of ECT2 contributes to tumor invasion and progression, suggesting that ECT2 is a potential prognostic marker for NSCLC patients.

The Role of Mitotic Cell-Substrate Adhesion Re-modeling in Animal Cell Division

Animal cells undergo a dramatic series of shape changes as they divide, which depend on re-modeling of cell-substrate adhesions. Here, we show that while focal adhesion complexes are disassembled during mitotic rounding, integrins remain in place. These integrin-rich contacts connect mitotic cells to the underlying substrate throughout mitosis, guide polarized cell migration following mitotic exit, and are functionally important, since adherent cells undergo division failure when removed from the substrate. Further, the ability of cells to re-spread along pre-existing adhesive contacts is essential for division in cells compromised in their ability to construct a RhoGEF-dependent (Ect2) actomyosin ring. As a result, following Ect2 depletion, cells fail to divide on small adhesive islands but successfully divide on larger patterns, as the connection between daughter cells narrows and severs as they migrate away from one another. In this way, regulated re-modeling of cell-substrate adhesions during mitotic rounding aids division in animal cells.

MiR-223-3p targets ECT2 to regulate cell cycle and apoptosis in gastric cancer cells

AIM

To explore the role of miRNA-223-3p and epithelial cell transforming sequence 2 oncogene (ECT2) in cell cycle and apoptosis of gastric cancer (GC) cells and to analyze their correlation with clinicopathological characteristics.

METHODS

The expression of ECT2 and miR-223-3p in normal gastric mucosa cells (GSE-1) and GC cells (SGC-7901 and BGC-823) was detected by real-time fluorescent quantitative PCR and Western blot. Immunohistochemistry and RT-PCR were used to examine the expression of ECT2 and miR-223-3p in GC tissues and paired adjacent normal tissues, respectively. The correlation between ECT2 and miR-223-3p expression and clinicopathological characteristics was then analyzed. After miRNA-223-3p inhibitor and mimic were used to transfect SGC-7901 cells with LipofectamineTM2000, the expression of miRNA-223-3p and ECT2 was assessed by RT-PCR and Western blot in SGC-7901 cells. After another 24 h culture, the apoptosis rate and cell cycle progression were examined by flow cytometry.

RESULTS

The expression levels of ECT2 and miR-223-3p in GC cells were significantly increased as compared with those in normal gastric mucosa cells (P < 0.05 for both). In comparison with tumor adjacent normal tissues, the expression of ECT2 and miR-223-3p in GC tissues was significantly higher (P < 0.05). The expression of ECT2 and miR-223-3p was related to histologic differentiation (P < 0.05), Lauren type (P < 0.05), and TNM stage (P < 0.01), but not with gender, age, Bormann type, or tumor size (P > 0.05). Transfection with miR-223-3p mimic up-regulated ECT2 expression, whereas transfection of miR-223-3p inhibitor downregulated the expression of ECT2. Compared with negative control cells, the apoptosis rate of SGC-7901 cells transfected with miR-223-3p inhibitor significantly increased (P < 0.05), and the percentage of G₁ phase cells also significantly increased in miR-223-3p inhibitor transfected cells (P < 0.05).

CONCLUSION

MiR-223-3p is closely related with cell cycle and apoptosis of gastric cancer cells, and it can regulate the occurrence and development of GC by influencing the expression of ECT2. ECT2 and miR-223-3p may serve as good factors to indicate the biologic behavior of GC.

Shared mechanisms regulate spatiotemporal RhoA-dependent actomyosin contractility during adhesion and cell division

Local modulation of the actin cytoskeleton is essential for the initiation and maintenance of strong homotypic adhesive interfaces between neighboring cells. The epithelial adherens junction (AJ) fulfils a central role in this process by mediating E-cadherin interactions and functioning as a signaling scaffold to control the activity of the small GTPase RhoA and subsequent actomyosin contractility. Interestingly, a number of regulatory proteins that modulate RhoA activity at the AJ also control RhoA during cytokinesis, an actomyosin-dependent process that divides the cytoplasm to generate two daughter cells at the final stages of mitosis. Recent insights have revealed that the central player in AJ stability, p120-catenin (p120), interacts with and modulates essential regulators of actomyosin contraction during cytokinesis. In cancer, loss of this modulation is a common event during tumor progression that can induce chromosomal instability and tumor progression.In this review, we will highlight the functional differences and similarities of the different RhoA-associated factors that have been linked to both the regulation of cell-cell adhesion and cytokinesis.

Overexpression of epithelial cell transforming 2 protein in colorectal carcinoma predicts a poor prognosis

Epithelial cell transforming 2 (Ect2) protein is a member of the human diffuse B-cell lymphoma family of guanine nucleotide exchange factors, which activate the Ras homolog gene family of small GTPases; however, the clinical implications of Ect2 in colorectal carcinoma (CRC) are unclear. The present study aimed to determine the relationship between Ect2 expression and prognosis in patients with CRC. Western blot analysis and immunohistochemistry assays were used to determine the expression of Ect2 in CRC and paired non-cancerous tissues from 66 patients. The correlation between Ect2 expression and clinicopathological parameters was assessed using χ² tests. Patient survival was determined using the Kaplan-Meier method and log-rank test. Cox regression was used for multivariate analysis of prognostic factors. Results demonstrated that Ect2 protein was highly expressed in human CRC samples [29/45 (64.45%)] and significantly correlated with a poor prognosis (P<0.05). Compared with normal tissues, CRC tissues demonstrated higher expression levels of Ect2 mRNA [44/66 (66.67%)]. In addition, highly-expressed Ect2 was significantly associated with recurrence (P=0.023) and invasion (P=0.008) of CRC. High Ect2 expression levels in patients were associated with poorer overall survival (OS) and disease-free survival (DFS) compared with lower expression levels of Ect2. Based on multivariate analysis, Ect2 overexpression was significantly correlated with OS and DFS (P=0.015 and 0.020, respectively). In conclusion, Ect2 overexpression is an independent and important prognostic factor for OS and DFS in patients with CRC.

Role of Epithelial Cell Transforming Sequence 2 (ECT2) in Predicting Prognosis of Osteosarcoma

Background

Osteosarcoma is a major bone malignancy in children and young adults, and it is highly heterogeneous. The clinical outcome of osteosarcoma is individual-dependent due to different genetic and pathological profiles. Although chemotherapy in combination with surgery has significantly improved the survival of localized disease, the prognostic improvement for metastatic patients is less marked. ECT2 (epithelial cell transforming sequence 2) is a transforming protein that can interact with Rho-like proteins of the Ras family and has been proven as an ontogenetic protein in cancer cell lines. We studied the clinical significance of ECT2 in osteosarcoma and explored its underlying oncogenic mechanisms.

Material/Methods

The protein expression pattern of ECT2 in osteosarcoma was investigated by immunohistochemical staining, and its association with clinicopathological characteristics was initially explored. The significance of ECT2 in predicting patient prognosis was verified by univariate and multivariate analyzes. Cellular experiments were conducted to explore underlying mechanisms of ECT2 in regulating osteosarcoma progression.

Results

High ECT2 expression was correlated with tumor metastasis and poor overall survival of osteosarcoma patients. ECT2 promotes cell invasion by modulating EMT process.

Conclusions

ECT2 is an independent prognostic factor for osteosarcoma and it can upregulate the metastatic capacity of osteosarcoma cells.

Oncogenic Ect2 signaling regulates rRNA synthesis in NSCLC

The Rho GTPase family members Rac1, Cdc42 and RhoA play key contributory roles in the transformed phenotype of human cancers. Epithelial Cell Transforming Sequence 2 (Ect2), a guanine nucleotide exchange factor (GEF) for these Rho GTPases, has also been implicated in a variety of human cancers. We have shown that Ect2 is frequently overexpressed in both major forms of non-small cell lung cancer (NSCLC), lung adenocarcinoma (LADC) and lung squamous cell carcinoma (LSCC), which together make up approximately 70% of all lung cancer diagnoses. Furthermore, we have found that Ect2 is required for multiple aspects of the transformed phenotype of NSCLC cells including transformed growth and invasion in vitro and tumorigenesis in vivo. More recently, we showed that a major mechanism by which Ect2 drives KRAS-mediated LADC transformation is by regulating rRNA (rRNA) synthesis. However, it remains unclear whether Ect2 plays a similar role in ribosome biogenesis in LSCC. Here we demonstrate that Ect2 expression correlates positively with expression of ribosome biogenesis genes and with pre-ribosomal 45S RNA abundance in primary LSCC tumors. Furthermore, we demonstrate that Ect2 functionally regulates rRNA synthesis in LSCC cells. Based on these data, we propose that inhibition of Ect2-mediated nucleolar signaling holds promise as a potential therapeutic strategy for improved treatment of both LADC and LSCC.

Early Assessment of Colorectal Cancer by Quantifying Circulating Tumor Cells in Peripheral Blood: ECT2 in Diagnosis of Colorectal Cancer

Circulating tumor cells (CTCs) in peripheral blood is an indication of poor prognosis for patients with different cancer types. However, most of the available technologies for detecting CTCs show low sensitivity and specificity. Therefore, we attempted to find an alternative marker for CTCs of colorectal cancer. We have directly extracted RNA from CTCs contained in 1.5 mL peripheral blood from 90 colorectal cancer patients and 151 healthy donors, and screened these samples for candidate marker genes by nested real-time quantitative polymerase chain reaction (PCR). From genes selected from a public database of microarray analyses, we successfully identified epithelial cell transforming sequence 2 oncogene (ECT2) as a gene that exhibits high differential expression ratios (p < 0.01). ECT2 displays good sensitivity and specificity, with an area under the curve (AUC) value of 0.821. This marker gene also has a high detection rate in patients with serum carcinoembryonic antigen (CEA) concentrations below the diagnostic threshold of 5 ng/mL. The expression of ECT2 can therefore serve as an alternative measurement that can compensate for the inadequacy of the current CEA test in the diagnosis and monitoring of colorectal cancer patients.

Ect2-Dependent rRNA Synthesis Is Required for KRAS-TRP53-Driven Lung Adenocarcinoma

The guanine nucleotide exchange factor (GEF) epithelial cell transforming sequence 2 (Ect2) has been implicated in cancer. However, it is not clear how Ect2 causes transformation and whether Ect2 is necessary for tumorigenesis in vivo. Here, we demonstrate that nuclear Ect2 GEF activity is required for Kras-Trp53 lung tumorigenesis in vivo and that Ect2-mediated transformation requires Ect2-dependent rDNA transcription. Ect2 activates rRNA synthesis by binding the nucleolar transcription factor upstream binding factor 1 (UBF1) on rDNA promoters and recruiting Rac1 and its downstream effector nucleophosmin (NPM) to rDNA. Protein kinase Cι (PKCι)-mediated Ect2 phosphorylation stimulates Ect2-dependent rDNA transcription. Thus, Ect2 regulates rRNA synthesis through a PKCι-Ect2-Rac1-NPM signaling axis that is required for lung tumorigenesis.

Elevated levels of epithelial cell transforming sequence 2 predicts poor prognosis for prostate cancer

Epithelial cell transforming sequence 2 (Ect2) was originally reported as an oncogene that is involved in several types of human cancers. However, little is known about its expression and function in prostate cancer. Immunohistochemical staining for Ect2 was performed on a human tissue microarray. The staining intensity was analyzed in association with clinical pathological parameters such as Gleason score, pathological grade, clinical stage, tumor invasion, lymph node and distant metastasis. Furthermore, we repeated such analysis and investigated the prognostic value of Ect2 using the TCGA (The Cancer Genome Atlas) Dataset. Our immunohistochemical results showed that the expression levels of Ect2 protein were enhanced in human prostate cancer tissues. There existed positive correlations between the expression levels of Ect2 and several clinicopathological parameters, including advanced clinical stage, enhanced tumor invasion and lymph node metastasis. Similarly, we found that the expression levels of Ect2 were positively related to Gleason score, tumor invasion, lymph node metastasis and high distant metastasis in the TCGA Dataset. Kaplan-Meier analysis revealed that lower levels of Ect2 mRNA predicted higher overall survivals and biochemical recurrence (BCR)-free survivals in all patients or non-metastatic patients. Multivariate analysis by Cox regression showed that the expression of Ect2 could be an independent prognostic marker of poor BCR-free survivals. Therefore, levels of Ect2 may serve as a novel marker for the diagnosis or prognosis of prostate cancer.

The RNA-binding profile of Acinus, a peripheral component of the exon junction complex, reveals its role in splicing regulation

Acinus (apoptotic chromatin condensation inducer in the nucleus) is an RNA-binding protein (RBP) originally identified for its role in apoptosis. It was later found to be an auxiliary component of the exon junction complex (EJC), which is deposited at exon junctions as a consequence of pre-mRNA splicing. To uncover the cellular functions of Acinus and investigate its role in splicing, we mapped its endogenous RNA targets using the cross-linking immunoprecipitation protocol (iCLIP). We observed that Acinus binds to pre-mRNAs, associating specifically to a subset of suboptimal introns, but also to spliced mRNAs. We also confirmed the presence of Acinus as a peripheral factor of the EJC. RNA-seq was used to investigate changes in gene expression and alternative splicing following siRNA-mediated depletion of Acinus in HeLa cells. This analysis revealed that Acinus is preferentially required for the inclusion of specific alternative cassette exons and also controls the faithful splicing of a subset of introns. Moreover, a large number of splicing changes can be related to Acinus binding, suggesting a direct role of Acinus in exon and intron definition. In particular, Acinus regulates the splicing of DFFA/ICAD transcript, a major regulator of DNA fragmentation. Globally, the genome-wide identification of RNA targets of Acinus revealed its role in splicing regulation as well as its involvement in other cellular pathways, including cell cycle progression. Altogether, this study uncovers new cellular functions of an RBP transiently associated with the EJC.

Coupling changes in cell shape to chromosome segregation

Animal cells undergo dramatic changes in shape, mechanics and polarity as they progress through the different stages of cell division. These changes begin at mitotic entry, with cell-substrate adhesion remodelling, assembly of a cortical actomyosin network and osmotic swelling, which together enable cells to adopt a near spherical form even when growing in a crowded tissue environment. These shape changes, which probably aid spindle assembly and positioning, are then reversed at mitotic exit to restore the interphase cell morphology. Here, we discuss the dynamics, regulation and function of these processes, and how cell shape changes and sister chromatid segregation are coupled to ensure that the daughter cells generated through division receive their fair inheritance.

The E3-ligase E6AP Represses Breast Cancer Metastasis via Regulation of ECT2-Rho Signaling

Metastatic disease is the major cause of breast cancer-related death and despite many advances, current therapies are rarely curative. Tumor cell migration and invasion require actin cytoskeletal reorganization to endow cells with capacity to disseminate and initiate the formation of secondary tumors. However, it is still unclear how these migratory cells colonize distant tissues to form macrometastases. The E6-associated protein, E6AP, acts both as an E3 ubiquitin-protein ligase and as a coactivator of steroid hormone receptors. We report that E6AP suppresses breast cancer invasiveness, colonization, and metastasis in mice, and in breast cancer patients, loss of E6AP associates with poor prognosis, particularly for basal breast cancer. E6AP regulates actin cytoskeletal remodeling via regulation of Rho GTPases, acting as a negative regulator of ECT2, a GEF required for activation of Rho GTPases. E6AP promotes ubiquitination and proteasomal degradation of ECT2 for which high expression predicts poor prognosis in breast cancer patients. We conclude that E6AP suppresses breast cancer metastasis by regulating actin cytoskeleton remodeling through the control of ECT2 and Rho GTPase activity. These findings establish E6AP as a novel suppressor of metastasis and provide a compelling rationale for inhibition of ECT2 as a therapeutic approach for patients with metastatic breast cancer. Cancer Res; 76(14); 4236-48. ©2016 AACR.

The MAP kinase pathway coordinates crossover designation with disassembly of synaptonemal complex proteins during meiosis

Asymmetric disassembly of the synaptonemal complex (SC) is crucial for proper meiotic chromosome segregation. However, the signaling mechanisms that directly regulate this process are poorly understood. Here we show that the mammalian Rho GEF homolog, ECT-2, functions through the conserved RAS/ERK MAP kinase signaling pathway in the C. elegans germline to regulate the disassembly of SC proteins. We find that SYP-2, a SC central region component, is a potential target for MPK-1-mediated phosphorylation and that constitutively phosphorylated SYP-2 impairs the disassembly of SC proteins from chromosomal domains referred to as the long arms of the bivalents. Inactivation of MAP kinase at late pachytene is critical for timely disassembly of the SC proteins from the long arms, and is dependent on the crossover (CO) promoting factors ZHP-3/RNF212/Zip3 and COSA-1/CNTD1. We propose that the conserved MAP kinase pathway coordinates CO designation with the disassembly of SC proteins to ensure accurate chromosome segregation.

DOI:http://dx.doi.org/10.7554/eLife.12039.001

Most plants and animals, including humans, have cells that contain two copies of every chromosome, with one set inherited from each parent. However, reproductive cells (such as eggs and sperm) contain just one copy of every chromosome so that when they fuse together at fertilization, the resulting cell will have the usual two copies of each chromosome.

Embryos that have incorrect numbers of chromosome copies either fail to survive or develop disorders such as Down syndrome. Therefore, it is important that when cells divide to form new reproductive cells, their chromosomes are correctly segregated.

To end up with one copy of each chromosome, reproductive cells undergo a form of cell division called meiosis. During meiosis, pairs of chromosomes are held together by a zipper-like structure called the synaptonemal complex. While held together like this, each chromosome in the pair exchanges DNA with the other by forming junctions called crossovers. Once DNA exchange is completed, the synaptonemal complex disappears from certain regions of the chromosome.

Using a range of genetic, biochemical and cell biological approaches, Nadarajan et al. have now investigated how crossover formation and the disassembly of the synaptonemal complex are coordinated in the reproductive cells of a roundworm called Caenorhabditis elegans. This revealed that a signaling pathway called the MAP kinase pathway regulates the removal of synaptonemal complex proteins from particular sites between the paired chromosomes. Turning off this pathway’s activity is required for the timely disassembly of this complex, and depends on proteins that are involved in crossover formation.

This regulatory mechanism likely ensures that the synaptonemal complex starts to disassemble only after the physical attachments between the paired chromosomes are “locked in”, thus ensuring that reproductive cells receive the correct number of chromosomes. Given that the MAP kinase pathway regulates cell processes in many different organisms, a future challenge is to determine whether this pathway regulates the synaptonemal complex in other species as well.

DOI:http://dx.doi.org/10.7554/eLife.12039.002

Mechanical forces drive neuroblast morphogenesis and are required for epidermal closure

Tissue morphogenesis requires myosin-dependent events such as cell shape changes and migration to be coordinated between cells within a tissue, and/or with cells from other tissues. However, few studies have investigated the simultaneous morphogenesis of multiple tissues in vivo. We found that during Caenorhabditis elegans ventral enclosure, when epidermal cells collectively migrate to cover the ventral surface of the embryo, the underlying neuroblasts (neuronal precursor cells) also undergo morphogenesis. We found that myosin accumulates as foci along the junction-free edges of the ventral epidermal cells to form a ring, whose closure is myosin-dependent. We also observed the accumulation of myosin foci and the adhesion junction proteins E-cadherin and α-catenin in the underlying neuroblasts. Myosin may help to reorganize a subset of neuroblasts into a rosette-like pattern, and decrease their surface area as the overlying epidermal cells constrict. Since myosin is required in the neuroblasts for ventral enclosure, we propose that mechanical forces in the neuroblasts influence constriction of the overlying epidermal cells. In support of this model, disrupting neuroblast cell division or altering their fate influences myosin localization in the overlying epidermal cells. The coordination of myosin-dependent events and forces between cells in different tissues could be a common theme for coordinating morphogenetic events during metazoan development.

The chromosome 3q26 OncCassette: A multigenic driver of human cancer

Recurrent copy number variations (CNVs) are genetic alterations commonly observed in human tumors. One of the most frequent CNVs in human tumors involves copy number gains (CNGs) at chromosome 3q26, which is estimated to occur in >20% of human tumors. The high prevalence and frequent occurrence of 3q26 CNG suggest that it drives the biology of tumors harboring this genetic alteration. The chromosomal region subject to CNG (the 3q26 amplicon) spans from chromosome 3q26 to q29, a region containing ∼200 protein-encoding genes. The large number of genes within the amplicon makes it difficult to identify relevant oncogenic target(s). Whereas a number of genes in this region have been linked to the transformed phenotype, recent studies indicate a high level of cooperativity among a subset of frequently amplified 3q26 genes. Here we use a novel bioinformatics approach to identify potential driver genes within the recurrent 3q26 amplicon in lung squamous cell carcinoma (LSCC). Our analysis reveals a set of 35 3q26 amplicon genes that are coordinately amplified and overexpressed in human LSCC tumors, and that also map to a major LSCC susceptibility locus identified on mouse chromosome 3 that is syntenic with human chromosome 3q26. Pathway analysis reveals that 21 of these genes exist within a single predicted network module. Four 3q26 genes, SOX2, ECT2, PRKCI and PI3KCA occupy the hub of this network module and serve as nodal genes around which the network is organized. Integration of available genetic, genomic, biochemical and functional data demonstrates that SOX2, ECT2, PRKCI and PIK3CA are cooperating oncogenes that function within an integrated cell signaling network that drives a highly aggressive, stem-like phenotype in LSCC tumors harboring 3q26 amplification. Based on the high level of genomic, genetic, biochemical and functional integration amongst these 4 3q26 nodal genes, we propose that they are the key oncogenic targets of the 3q26 amplicon and together define a "3q26 OncCassette" that mediates 3q26 CNG-driven tumorigenesis. Genomic analysis indicates that the 3q26 OncCassette also operates in other major tumor types that exhibit frequent 3q26 CNGs, including head and neck squamous cell carcinoma (HNSCC), ovarian serous cancer and cervical cancer. Finally, we discuss how the 3q26 OncCassette represents a tractable target for development of novel therapeutic intervention strategies that hold promise for improving treatment of 3q26-driven cancers.

Clinical significance of ECT2 expression in tissue and serum of gastric cancer patients

The ECT2 (epithelial cell transforming sequence 2) oncogene acted as a guanine nucleotide exchange factor for RhoGTPases, and regulates cytokinesis; thus, it may play a role in the pathogenesis of gastric cancer. In this study, we investigated the expression ECT2 gene in tissues and serum of gastric cancer patients to explore its clinical significance. ECT2 mRNA expression levels in tissues and serum were examined by RT-PCR, and ECT2 protein expression in tissue was evaluated by Western blot, and was further validated by immunohistochemistry and enzyme-linked immunosorbent assay at serum level. ECT2 level was significantly increased in the GC tissues and serum compared to normal control. ECT2 expression was positively correlated with the histologic differentiation, stages of TNM, and lymph node metastasis in GC (P < 0.05). Our results suggest that ECT2 plays an important role during GC progression and it may become a new diagnostic marker and therapeutic molecular target for management of GC.

Elevated expression of ECT2 predicts unfavorable prognosis in patients with colorectal cancer

Epithelial cell transforming sequence 2 (ECT2) is a well-studied guanine nucleotide exchange factor for the Rho family GTPase, which has been demonstrated as an oncogene in many types of human cancers. However, little is known about the prognostic value of ECT2 in colorectal cancer (CRC). In current study, we investigated the expression pattern and underlying clinical significance of ECT2 in CRC. ECT2 expression was detected in 345 CRC specimens by immunohistochemistry, and its correlation with clinicopathologic parameters and prognosis of CRC patients were analyzed. Data from Oncomine database and real-time PCR demonstrated that ECT2 expression was elevated in CRC compared with normal tissues. Among the clinical parameters analyzed, high expression level of ECT2 significantly associated with tumor size (P=0.020), serum CEA levels (P = 0.000) and TNM stage (P=0.027). Kaplan-Meier survival analysis showed that patients with high ECT2 expression had a remarkably shorter overall survival. Cox regression analysis revealed that ECT2 expression level was a significant and independent prognostic factor for overall survival rate of CRC patients. These data suggested that ECT2 is an unfavorable biomarker of prognosis in CRC and that ECT2 may be a potential therapeutic candidate for CRC treatment.

ECT2 regulates the Rho/ERK signalling axis to promote early recurrence in human hepatocellular carcinoma

BACKGROUND & AIMS

Early recurrence is the major obstacle for improving the outcome of patients with hepatocellular carcinoma (HCC). Therefore, identifying key molecules contributing to early HCC recurrence can enable the development of novel therapeutic strategies for the clinical management of HCC. Epithelial cell transforming sequence 2 (ECT2) has been implicated in human cancers, but its function in HCC is largely unknown.

METHODS

ECT2 expression was studied by microarrays, immunoblotting and immunohistochemistry in human HCC samples. siRNA- and lentiviral vector-mediated knockdown were employed to decipher the molecular functions of ECT2.

RESULTS

The upregulation of ECT2 is significantly associated with early recurrent HCC disease and poor survival. Knockdown of ECT2 markedly suppressed Rho GTPases activities, enhanced apoptosis, attenuated oncogenicity and reduced the metastatic ability of HCC cells. Moreover, knockdown of ECT2 or Rho also suppressed ERK activation, while the silencing of Rho or ERK led to a marked reduction in cell migration. Stable knockdown of ECT2 in vivo resulted in significant retardation of tumour growth and the suppression of ERK activation. High expression of ECT2 correlates with high ERK phosphorylation and poor survival of HCC patients. Furthermore, ECT2 enhances the expression and stability of RACGAP1, accelerating ECT2-mediated Rho activation to promote metastasis.

CONCLUSIONS

ECT2 is closely associated with the activation of the Rho/ERK signalling axis to promote early HCC recurrence. In addition, ECT2 can crosstalk with RACGAP1 to catalyse the GTP exchange involved in Rho signalling to further regulate tumour initiation and metastasis.

Annexin V-induced rat Leydig cell proliferation involves Ect2 via RhoA/ROCK signaling pathway

This study investigated the effect of annexin V on the proliferation of primary rat Leydig cells and the potential mechanism. Our results showed that annexin V promoted rat Leydig cell proliferation and cell cycle progression in a dose- and time-dependent manner. Increased level of annexin V also enhanced Ect2 protein expression. However, siRNA knockdown of Ect2 attenuated annexin V-induced proliferation of rat Leydig cells. Taken together, these data suggest that increased level of annexin V induced rat Leydig cell proliferation and cell cycle progression via Ect2. Since RhoA activity was increased following Ect2 activation, we further investigated whether Ect2 was involved in annexin V-induced proliferation via the RhoA/ROCK pathway, and the results showed that annexin V increased RhoA activity too, and this effect was abolished by the knockdown of Ect2. Moreover, inhibition of the RhoA/ROCK pathway by a ROCK inhibitor, Y27632, also attenuated annexin V-induced proliferation and cell cycle progression. We thus conclude that Ect2 is involved in annexin V-induced rat Leydig cell proliferation through the RhoA/ROCK pathway.