Oncogenic activity of Ect2 is regulated through protein kinase C iota-mediated phosphorylation

SOXC Enhances NGN2-Mediated Reprogramming of Glioblastoma Cells Into Neuron-Like Cells by Modulating RhoA and RAC1/CDC42 Pathway Activity

BACKGROUND

Glioblastoma represents the most frequently diagnosed malignant neoplasm within the central nervous system. Human glioblastoma cells can be phenotypically reprogrammed into neuron-like cells through the forced expression of NEUROG2 and SOXC factors. NEUROG2 serves as a pioneer factor, establishing an initial framework for this transformation. However, the specific role of SOXC factors has not been fully elucidated.

METHODS

In this study, we used ChIP-seq to determine the potential target gene of NGN2. RNA-seq has been used to evaluate the transcriptional change during NGN2-SOX11-mediated neuron reprogramming. Immunofluorescence was used to determine the neuron reprogramming efficacy and cell proliferation ability. ChIP-qPCR, Co-IP, and Western Blot were performed to investigate the mechanism.

RESULTS

Our findings reveal that SOXC factors, in contrast to their previously identified function as transcriptional activators, act as transcriptional repressors. They achieve this by recruiting TRIM28 to suppress the expression of ECT2, a RhoGEF. This suppression results in the differential regulation of RhoA, RAC1, and CDC42 activities throughout the reprogramming process. We further establish that small molecules targeting RhoA and its effectors can substitute for SOXC factors in facilitating the neuronal reprogramming of glioblastoma cells.

CONCLUSION

These results underscore the pivotal role of SOXC factors' transcriptional repression and illuminate one of their specific downstream targets.

New Mechanisms Underlying Oncogenesis in Dbl Family Rho Guanine Nucleotide Exchange Factors

Transmembrane signaling is a critical process by which changes in the extracellular environment are relayed to intracellular systems that induce changes in homeostasis. One family of intracellular systems are the guanine nucleotide exchange factors (GEFs), which catalyze the exchange of GTP for GDP bound to inactive guanine nucleotide binding proteins (G proteins). The resulting active G proteins then interact with downstream targets that control cell proliferation, growth, shape, migration, adhesion, and transcription. Dysregulation of any of these processes is a hallmark of cancer. The Dbl family of GEFs activates Rho family G proteins, which, in turn, alter the actin cytoskeleton and promote gene transcription. Although they have a common catalytic mechanism exercised by their highly conserved Dbl homology (DH) domains, Dbl GEFs are regulated in diverse ways, often involving the release of autoinhibition imposed by accessory domains. Among these domains, the pleckstrin homology (PH) domain is the most commonly observed and found immediately C-terminal to the DH domain. The domain has been associated with both positive and negative regulation. Recently, some atomic structures of Dbl GEFs have been determined that reemphasize the complex and central role that the PH domain can play in orchestrating regulation of the DH domain. Here, we discuss these newer structures, put them into context by cataloging the various ways that PH domains are known to contribute to signaling across the Dbl family, and discuss how the PH domain might be exploited to achieve selective inhibition of Dbl family RhoGEFs by small-molecule therapeutics. SIGNIFICANCE STATEMENT: Dysregulation via overexpression or mutation of Dbl family Rho guanine nucleotide exchange factors (GEFs) contributes to cancer and neurodegeneration. Targeting the Dbl homology catalytic domain by small-molecule therapeutics has been challenging due to its high conservation and the lack of a discrete binding pocket. By evaluating some new autoinhibitory mechanisms in the Dbl family, we demonstrate the great diversity of roles played by the regulatory domains, in particular the PH domain, and how this holds tremendous potential for the development of selective therapeutics that modulate GEF activity.

Protein Kinase C at the Crossroad of Mutations, Cancer, Targeted Therapy and Immune Response

The frequent PKC dysregulations observed in many tumors have made these enzymes natural targets for anticancer applications. Nevertheless, this considerable interest in the development of PKC modulators has not led to the expected therapeutic benefits, likely due to the complex biological activities regulated by PKC isoenzymes, often playing ambiguous and protective functions, further driven by the occurrence of mutations. The structure, regulation and functions of PKCs have been extensively covered in other publications. Herein, we focused on PKC alterations mostly associated with complete functional loss. We also addressed the modest yet encouraging results obtained targeting PKC in selected malignancies and the more frequent negative clinical outcomes. The reported observations advocate the need for more selective molecules and a better understanding of the involved pathways. Furthermore, we underlined the most relevant immune mechanisms controlled by PKC isoforms potentially impacting the immune checkpoint inhibitor blockade-mediated immune recovery. We believe that a comprehensive examination of the molecular features of the tumor microenvironment might improve clinical outcomes by tailoring PKC modulation. This approach can be further supported by the identification of potential response biomarkers, which may indicate patients who may benefit from the manipulation of distinctive PKC isoforms.

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.

Protein kinase Cι and SRC signaling define reciprocally related subgroups of glioblastoma with distinct therapeutic vulnerabilities

We report that atypical protein kinase Cι (PKCι) is an oncogenic driver of glioblastoma (GBM). Deletion or inhibition of PKCι significantly impairs tumor growth and prolongs survival in murine GBM models. GBM cells expressing elevated PKCι signaling are sensitive to PKCι inhibitors, whereas those expressing low PKCι signaling exhibit active SRC signaling and sensitivity to SRC inhibitors. Resistance to the PKCι inhibitor auranofin is associated with activated SRC signaling and response to a SRC inhibitor, whereas resistance to a SRC inhibitor is associated with activated PKCι signaling and sensitivity to auranofin. Interestingly, PKCι- and SRC-dependent cells often co-exist in individual GBM tumors, and treatment of GBM-bearing mice with combined auranofin and SRC inhibitor prolongs survival beyond either drug alone. Thus, we identify PKCι and SRC signaling as distinct therapeutic vulnerabilities that are directly translatable into an improved treatment for GBM.

Mapping lung squamous cell carcinoma pathogenesis through in vitro and in vivo models

Lung cancer is the main cause of cancer death worldwide, with lung squamous cell carcinoma (LUSC) being the second most frequent subtype. Preclinical LUSC models recapitulating human disease pathogenesis are key for the development of early intervention approaches and improved therapies. Here, we review advances and challenges in the generation of LUSC models, from 2D and 3D cultures, to murine models. We discuss how molecular profiling of premalignant lesions and invasive LUSC has contributed to the refinement of in vitro and in vivo models, and in turn, how these systems have increased our understanding of LUSC biology and therapeutic vulnerabilities.

Epithelial cell transforming factor ECT2 is an important regulator of DNA double-strand break repair and genome stability

Proteins containing breast cancer type 1 (BRCA1) C-terminal domains play crucial roles in response to and repair of DNA damage. Epithelial cell transforming factor (epithelial cell transforming sequence 2 [ECT2]) is a member of the BRCA1 C-terminal protein family, but it is not known if ECT2 directly contributes to DNA repair. In this study, we report that ECT2 is recruited to DNA lesions in a poly (ADP-ribose) polymerase 1–dependent manner. Using co-immunoprecipitation analysis, we showed that ECT2 physically associates with KU70–KU80 and BRCA1, proteins involved in nonhomologous end joining and homologous recombination, respectively. ECT2 deficiency impairs the recruitment of KU70 and BRCA1 to DNA damage sites, resulting in defective DNA double-strand break repair, an accumulation of damaged DNA, and hypersensitivity of cells to genotoxic insults. Interestingly, we demonstrated that ECT2 promotes DNA repair and genome integrity largely independently of its canonical guanine nucleotide exchange activity. Together, these results suggest that ECT2 is directly involved in DNA double-strand break repair and is an important genome caretaker.

Protein Kinase C as a Therapeutic Target in Non-Small Cell Lung Cancer

Driver-directed therapeutics have revolutionized cancer treatment, presenting similar or better efficacy compared to traditional chemotherapy and substantially improving quality of life. Despite significant advances, targeted therapy is greatly limited by resistance acquisition, which emerges in nearly all patients receiving treatment. As a result, identifying the molecular modulators of resistance is of great interest. Recent work has implicated protein kinase C (PKC) isozymes as mediators of drug resistance in non-small cell lung cancer (NSCLC). Importantly, previous findings on PKC have implicated this family of enzymes in both tumor-promotive and tumor-suppressive biology in various tissues. Here, we review the biological role of PKC isozymes in NSCLC through extensive analysis of cell-line-based studies to better understand the rationale for PKC inhibition. PKC isoforms α, ε, η, ι, ζ upregulation has been reported in lung cancer, and overexpression correlates with worse prognosis in NSCLC patients. Most importantly, PKC isozymes have been established as mediators of resistance to tyrosine kinase inhibitors in NSCLC. Unfortunately, however, PKC-directed therapeutics have yielded unsatisfactory results, likely due to a lack of specific evaluation for PKC. To achieve satisfactory results in clinical trials, predictive biomarkers of PKC activity must be established and screened for prior to patient enrollment. Furthermore, tandem inhibition of PKC and molecular drivers may be a potential therapeutic strategy to prevent the emergence of resistance in NSCLC.

Proteogenomic insights into the biology and treatment of HPV-negative head and neck squamous cell carcinoma

We present a proteogenomic study of 108 human papilloma virus (HPV)-negative head and neck squamous cell carcinomas (HNSCCs). Proteomic analysis systematically catalogs HNSCC-associated proteins and phosphosites, prioritizes copy number drivers, and highlights an oncogenic role for RNA processing genes. Proteomic investigation of mutual exclusivity between FAT1 truncating mutations and 11q13.3 amplifications reveals dysregulated actin dynamics as a common functional consequence. Phosphoproteomics characterizes two modes of EGFR activation, suggesting a new strategy to stratify HNSCCs based on EGFR ligand abundance for effective treatment with inhibitory EGFR monoclonal antibodies. Widespread deletion of immune modulatory genes accounts for low immune infiltration in immune-cold tumors, whereas concordant upregulation of multiple immune checkpoint proteins may underlie resistance to anti-programmed cell death protein 1 monotherapy in immune-hot tumors. Multi-omic analysis identifies three molecular subtypes with high potential for treatment with CDK inhibitors, anti-EGFR antibody therapy, and immunotherapy, respectively. Altogether, proteogenomics provides a systematic framework to inform HNSCC biology and treatment.

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.

Identification of Key Phospholipids That Bind and Activate Atypical PKCs

PKCζ and PKCι/λ form the atypical protein kinase C subgroup, characterised by a lack of regulation by calcium and the neutral lipid diacylglycerol. To better understand the regulation of these kinases, we systematically explored their interactions with various purified phospholipids using the lipid overlay assays, followed by kinase activity assays to evaluate the lipid effects on their enzymatic activity. We observed that both PKCζ and PKCι interact with phosphatidic acid and phosphatidylserine. Conversely, PKCι is unique in binding also to phosphatidylinositol-monophosphates (e.g., phosphatidylinositol 3-phosphate, 4-phosphate, and 5-phosphate). Moreover, we observed that phosphatidylinositol 4-phosphate specifically activates PKCι, while both isoforms are responsive to phosphatidic acid and phosphatidylserine. Overall, our results suggest that atypical Protein kinase C (PKC) localisation and activity are regulated by membrane lipids distinct from those involved in conventional PKCs and unveil a specific regulation of PKCι by phosphatidylinositol-monophosphates.

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.

FoxM1 insufficiency hyperactivates Ect2-RhoA-mDia1 signaling to drive cancer

FoxM1 activates genes that regulate S-G2-M cell-cycle progression and, when overexpressed, is associated with poor clinical outcome in multiple cancers. Here we identify FoxM1 as a tumor suppressor in mice that, through its N-terminal domain, binds to and inhibits Ect2 to limit the activity of RhoA GTPase and its effector mDia1, a catalyst of cortical actin nucleation. FoxM1 insufficiency impedes centrosome movement through excessive cortical actin polymerization, thereby causing the formation of non-perpendicular mitotic spindles that missegregate chromosomes and drive tumorigenesis in mice. Importantly, low FOXM1 expression correlates with RhoA GTPase hyperactivity in multiple human cancer types, indicating that suppression of the newly discovered Ect2-RhoAmDia1 oncogenic axis by FoxM1 is clinically relevant. Furthermore, by dissecting the domain requirements through which FoxM1 inhibits Ect2 GEF activity, we provide mechanistic insight for the development of pharmacological approaches that target protumorigenic RhoA activity.

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.

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.

Adherens junction remodelling during mitotic rounding of pseudostratified epithelial cells

Epithelial cells undergo cortical rounding at the onset of mitosis to enable spindle orientation in the plane of the epithelium. In cuboidal epithelia in culture, the adherens junction protein E-cadherin recruits Pins/LGN/GPSM2 and Mud/NuMA to orient the mitotic spindle. In the pseudostratified columnar epithelial cells of Drosophila, septate junctions recruit Mud/NuMA to orient the spindle, while Pins/LGN/GPSM2 is surprisingly dispensable. We show that these pseudostratified epithelial cells downregulate E-cadherin as they round up for mitosis. Preventing cortical rounding by inhibiting Rho-kinase-mediated actomyosin contractility blocks downregulation of E-cadherin during mitosis. Mitotic activation of Rho-kinase depends on the RhoGEF ECT2/Pebble and its binding partners RacGAP1/MgcRacGAP/CYK4/Tum and MKLP1/KIF23/ZEN4/Pav. Cell cycle control of these Rho activators is mediated by the Aurora A and B kinases, which act redundantly during mitotic rounding. Thus, in Drosophila pseudostratified epithelia, disruption of adherens junctions during mitosis necessitates planar spindle orientation by septate junctions to maintain epithelial integrity.

Targeting Rho GTPase Signaling Networks in Cancer

As key regulators of cytoskeletal dynamics, Rho GTPases coordinate a wide range of cellular processes, including cell polarity, cell migration, and cell cycle progression. The adoption of a pro-migratory phenotype enables cancer cells to invade the stroma surrounding the primary tumor and move toward and enter blood or lymphatic vessels. Targeting these early events could reduce the progression to metastatic disease, the leading cause of cancer-related deaths. Rho GTPases play a key role in the formation of dynamic actin-rich membrane protrusions and the turnover of cell-cell and cell-extracellular matrix adhesions required for efficient cancer cell invasion. Here, we discuss the roles of Rho GTPases in cancer, their validation as therapeutic targets and the challenges of developing clinically viable Rho GTPase inhibitors. We review other therapeutic targets in the wider Rho GTPase signaling network and focus on the four best characterized effector families: p21-activated kinases (PAKs), Rho-associated protein kinases (ROCKs), atypical protein kinase Cs (aPKCs), and myotonic dystrophy kinase-related Cdc42-binding kinases (MRCKs).

OTUB1-mediated deubiquitination of FOXM1 up-regulates ECT-2 to promote tumor progression in renal cell carcinoma

Background

OTUB1 (ovarian tumor domain protease domain-containing ubiquitin aldehyde-binding proteins)-mediated deubiquitination of FOXM1 (Forkhead box M1) participates in carcinogenesis of various tumors. We aim to investigate the effect and mechanism of OTUB1/FOXM1 on RCC (renal cell carcinoma) progression. Expression levels of OTUB1 in RCC tissues and cell lines were examined by qRT-PCR (quantitative real-time polymerase chain reaction) and immunohistochemistry. Cell proliferation was measured with CCK8 (Cell Counting Kit-8) and colony formation assays. Wound healing and transwell assays were used to determine cell migration and invasion, respectively. The effect of OTUB1 on FOXM1 ubiquitination was examined by Immunoprecipitation. Western blot was used to uncover the underlying mechanism. In vivo subcutaneous xenotransplanted tumor model combined with immunohistochemistry and western blot were used to examine the tumorigenic function of OTUB1.

Results

OTUB1 was up-regulated in RCC tissues and cell lines, and was associated with poor prognosis of RCC patients. Knockdown of OTUB1 inhibited cell viability and proliferation, as well as migration and invasion of RCC cells. Mechanistically, knockdown of OTUB1 down-regulated FOXM1 expression by promoting its ubiquitination. Down-regulation of FOXM1 inhibited ECT2 (epithelial cell transforming 2)-mediated Rho signaling. Moreover, the inhibition of RCC progression caused by OTUB1 knockdown was reversed by FOXM1 over-expression. In vivo subcutaneous xenotransplanted tumor model also revealed that knockdown of OTUB1 could suppress in vivo RCC growth via down-regulation of FOXM1-mediated ECT2 expression.

Conclusions

OTUB1-mediated deubiquitination of FOXM1 up-regulates ECT-2 to promote tumor progression in RCC, providing a new potential therapeutic target for RCC treatment.

The Atypical Protein Kinase C Small Molecule Inhibitor ζ-Stat, and Its Effects on Invasion Through Decreases in PKC-ζ Protein Expression

Ovarian cancer is estimated to reach 22,530 diagnoses and cause 13,980 cancer deaths per year. The most common histology diagnosed of ovarian cancer is epithelial ovarian carcinomas (EOC). An aggressive epithelial subtype is clear cell ovarian carcinoma (CCOC) and is characterized as a non-serous ovarian cancer. Protein kinase C (PKC) is an enzymatic family of proteins that have been found to be a component in cancer progression, tissue invasion, and metastasis. The atypical PKC (aPKC) isoforms, PKC-ι and PKC-ζ, have been suggested to participate in the increased proliferation of ovarian cancers. Previous studies have indicated that novel aPKC inhibitors ICA-1S and ζ-Stat decreased the migratory behaviors of colorectal cancer cells and were selective for PKC-ι/λ and PKC-ζ, respectively. The aims of this investigation were to further determine the binding mechanisms of ζ-Stat, expand on the tissue range of these compounds, investigate the therapeutic potential of ζ-Stat in CCOC, and to illustrate the disruption of invasion via the PKC-ζ signaling cascade. The methods utilized were molecular docking and virtual target screening, Western blot analysis, end-point PCR, GST pull down, cell viability and invasion and migration assays. We discovered that the small molecule inhibitor, ζ-Stat, is a prospective drug candidate to investigate as a novel potential treatment for CCOC. We also found that the PKC-ζ/Ect2/Rac1 activation pathway was decreased by ζ-Stat, which in turn decreased invasive behavior of CCOC.

Chromosome 3q26 Gain Is an Early Event Driving Coordinated Overexpression of the PRKCI, SOX2, and ECT2 Oncogenes in Lung Squamous Cell Carcinoma

Lung squamous cell carcinoma (LSCC) is a prevalent form of lung cancer exhibiting distinctive histological and genetic characteristics. Chromosome 3q26 copy number gain (CNG) is a genetic hallmark of LSCC present in >90% of tumors. We report that 3q26 CNGs occur early in LSCC tumorigenesis, persist during tumor progression, and drive coordinate overexpression of PRKCI, SOX2, and ECT2. Overexpression of PRKCI, SOX2, and ECT2 in the context of Trp53 loss is sufficient to transform mouse lung basal stem cells into tumors with histological and genomic features of LSCC. Functionally, PRKCI and SOX2 collaborate to activate an extensive transcriptional program that enforces a lineage-restricted LSCC phenotype, whereas PRKCI and ECT2 collaborate to promote oncogenic growth. Gene signatures indicative of PKCι-SOX2 and PKCι-ECT2 signaling activity are enriched in the classical subtype of human LSCC and predict distinct therapeutic vulnerabilities. Thus, the PRKCI, SOX2, and ECT2 oncogenes represent a multigenic driver of LSCC.

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.

Oncogenic protein kinase Cι signaling mechanisms in lung cancer: Implications for improved therapeutic strategies

Protein Kinase Cι (PKCι) is a major oncogene involved in the initiation, maintenance and progression of numerous forms of human cancer. In the lung, PKCι is necessary for the maintenance of the transformed phenotype of the two major forms of non-small cell lung cancer (NSCLC), lung adenocarcinoma (LADC) and lung squamous cell carcinoma (LSCC). In addition, PKCι is necessary for both LADC and LSCC tumorigenesis by establishing and maintaining a highly aggressive stem-like, tumor-initiating cell phenotype. Interestingly however, while PKCι signaling in these two major lung cancer subtypes shares some common elements, it also drives distinct, sub-type specific pathways. Furthermore, recent analysis has revealed both PKCι-dependent and PKCι-independent pathways to LADC development. Herein, we discussion our current knowledge of oncogenic PKCι signaling in LADC and LSCC, and discuss these findings in the context of how they may inform strategies for improved therapeutic intervention in these deadly diseases.

ECT2 associated to PRICKLE1 are poor-prognosis markers in triple-negative breast cancer

Background

Triple-negative breast cancers (TNBC) are poor-prognosis tumours candidate to chemotherapy as only systemic treatment. We previously found that PRICKLE1, a prometastatic protein involved in planar cell polarity, is upregulated in TNBC. We investigated the protein complex associated with PRICKLE1 in TNBC to identify proteins possibly involved in metastatic dissemination, which might provide new prognostic and/or therapeutic targets.

Methods

We used a proteomic approach to identify protein complexes associated with PRICKLE1. The mRNA expression levels of the corresponding genes were assessed in 8982 patients with invasive primary breast cancer. We then characterised the molecular interaction between PRICKLE1 and the guanine nucleotide exchange factor ECT2. Finally, experiments in Xenopus were carried out to determine their evolutionarily conserved interaction.

Results

Among the PRICKLE1 proteins network, we identified several small G-protein regulators. Combined analysis of the expression of PRICKLE1 and small G-protein regulators had a strong prognostic value in TNBC. Notably, the combined expression of ECT2 and PRICKLE1 provided a worst prognosis than PRICKLE1 expression alone in TNBC. PRICKLE1 regulated ECT2 activity and this interaction was evolutionary conserved.

Conclusions

This work supports the idea that an evolutionarily conserved signalling pathway required for embryogenesis and activated in cancer may represent a suitable therapeutic target.

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.

aPKCι promotes gallbladder cancer tumorigenesis and gemcitabine resistance by competing with Nrf2 for binding to Keap1

Gallbladder cancer (GBC) is a highly malignant bile duct cancer with poor prognosis characterized by its insensitivity to chemotherapy. Emerging evidence indicates that cytoprotective antioxidation is involved in drug resistance of various cancers; however, the underlying molecular mechanisms remain obscure. Here, we demonstrated that atypical protein kinase Cι (aPKCι) mediated reactive oxygen species (ROS) inhibition in a kinase-independent manner, which played a crucial role in tumorigenesis and chemoresistance. Mechanistically, we found that aPKCι facilitated nuclear factor erythroid 2-related factor 2 (Nrf2) accumulation, nuclear translocation and activated its target genes by competing with Nrf2 for binding to Kelch-like ECH-associated protein 1 (Keap1) through a highly conserved DLL motif. In addition, the aPKCι-Keap1 interaction was required for antioxidant effect, cell growth and gemcitabine resistance in GBC. Importantly, we further confirmed that aPKCι was frequently upregulated and correlated with poor prognosis in patients with GBC. Collectively, our findings suggested that aPKCι positively modulated the Keap1-Nrf2 pathway to enhance GBC growth and gemcitabine resistance, implying that the aPKCι-Keap1-Nrf2 axis may be a potential approach to overcome the drug resistance for the treatment of GBC.

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aPKCι inhibits ROS in a kinase-independent manner.

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aPKCι competes with Nrf2 for binding to Keap1 via a DLL motif.

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The aPKCι-Keap1 interaction promotes cell growth and gemcitabine resistance.

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Upregulation of aPKCι was linked to poor prognosis in patients with GBC.

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aPKCι-Keap1-Nrf2 axis may be a potential therapeutic target for GBC.

Polymerase-δ-interacting protein 2 activates the RhoGEF epithelial cell transforming sequence 2 in vascular smooth muscle cells

Polymerase-δ-interacting protein 2 (Poldip2) controls a wide variety of cellular functions and vascular pathologies. To mediate these effects, Poldip2 interacts with numerous proteins and generates reactive oxygen species via the enzyme NADPH oxidase 4 (Nox4). We have previously shown that Poldip2 can activate the Rho family GTPase RhoA, another signaling node within the cell. In this study, we aimed to better understand how Poldip2 activates Rho family GTPases and the functions of the involved proteins in vascular smooth muscle cells (VSMCs). RhoA is activated by guanine nucleotide exchange factors. Using nucleotide-free RhoA (isolated from bacteria) to pulldown active RhoGEFs, we found that the RhoGEF epithelial cell transforming sequence 2 (Ect2) is activated by Poldip2. Ect2 is a critical RhoGEF for Poldip2-mediated RhoA activation, because siRNA against Ect2 prevented Poldip2-mediated RhoA activity (measured by rhotekin pulldowns). Surprisingly, we were unable to detect a direct interaction between Poldip2 and Ect2, as they did not coimmunoprecipitate. Nox4 is not required for Poldip2-driven Ect2 activation, as Poldip2 overexpression induced Ect2 activation in Nox4 knockout VSMCs similar to wild-type cells. However, antioxidant treatment blocked Poldip2-induced Ect2 activation. This indicates a novel reactive oxygen species-driven mechanism by which Poldip2 regulates Rho family GTPases. Finally, we examined the function of these proteins in VSMCs, using siRNA against Poldip2 or Ect2 and determined that Poldip2 and Ect2 are both essential for vascular smooth muscle cell cytokinesis and proliferation.

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.

Protein kinase Cι: A versatile oncogene in the lung

We have recently demonstrated that protein kinase Cι (PKCι) promotes a stem-like, tumor-initiating cell phenotype in KRAS-driven lung adenocarcinoma by activating a novel ELF3-NOTCH3 signaling axis.¹ Combined PKCι and NOTCH inhibition was identified as a novel strategy for the treatment of KRAS-driven lung adenocarcinoma.

PerPAS: Topology-Based Single Sample Pathway Analysis Method

Identification of intracellular pathways that play key roles in cancer progression and drug resistance is a prerequisite for developing targeted cancer treatments. The era of personalized medicine calls for computational methods that can function with one sample or a very small set of samples. Developing such methods is challenging because standard statistical approaches pose several limiting assumptions, such as number of samples, that prevent their application when approaches to one. We have developed a novel pathway analysis method called PerPAS to estimate pathway activity at a single sample level by integrating pathway topology and transcriptomics data. In addition, PerPAS is able to identify altered pathways between cancer and control samples as well as to identify key nodes that contribute to the pathway activity. In our case study using breast cancer data, we show that PerPAS can identify highly altered pathways that are associated with patient survival. PerPAS identified four pathways that were associated with patient survival and were successfully validated in three independent breast cancer cohorts. In comparison to two other pathway analysis methods that function at a single sample level, PerPAS had superior performance in both synthetic and breast cancer expression datasets. PerPAS is a free R package (http://csbi.ltdk.helsinki.fi/pub/czliu/perpas/).

Roles of partitioning-defective protein 6 (Par6) and its complexes in the proliferation, migration and invasion of cancer cells

A pivotal regulator of cell polarity and homeostasis, partitioning-defective protein 6 (Par6) forms multicomponent complexes that not only regulate cell polarity and stabilize cell morphology, but have also been demonstrated to participate in the proliferation, migration and invasion of cancer cells. The transforming growth factor (TGF)-β and extracellular signal-regulated kinase (Erk) 1/2 pathways are the most thoroughly studied pathways involving Par6 in many cancers. Aurothiomalate has been used to disrupt the interaction between Par6 and atypical protein kinase C within the multicomponent complexes, and has been shown to effectively block transformed growth and metastasis in vitro and/or in vivo in a variety of cancers, including pancreatic, prostate and lung cancers, as well as alveolar rhabdomyosarcoma. It is likely that with further revelations regarding the critical roles of Par6 in cancer initiation, progression and metastasis, targeted therapies against Par6 will be discovered and prove effective preclinically, and hopefully clinically, in cancer treatment.

The Scribble Cell Polarity Module in the Regulation of Cell Signaling in Tissue Development and Tumorigenesis

The Scribble cell polarity module, comprising Scribbled (Scrib), Discs-large (Dlg) and Lethal-2-giant larvae (Lgl), has a tumor suppressive role in mammalian epithelial cancers. The Scribble module proteins play key functions in the establishment and maintenance of different modes of cell polarity, as well as in the control of tissue growth, differentiation and directed cell migration, and therefore are major regulators of tissue development and homeostasis. Whilst molecular details are known regarding the roles of Scribble module proteins in cell polarity regulation, their precise mode of action in the regulation of other key cellular processes remains enigmatic. An accumulating body of evidence indicates that Scribble module proteins play scaffolding roles in the control of various signaling pathways, which are linked to the control of tissue growth, differentiation and cell migration. Multiple Scrib, Dlg and Lgl interacting proteins have been discovered, which are involved in diverse processes, however many function in the regulation of cellular signaling. Herein, we review the components of the Scrib, Dlg and Lgl protein interactomes, and focus on the mechanism by which they regulate cellular signaling pathways in metazoans, and how their disruption leads to cancer.

High ECT2 expression is an independent prognostic factor for poor overall survival and recurrence-free survival in non-small cell lung adenocarcinoma

Different subtypes of non-small cell lung cancer (NSCLC) have distinct sites of origin, histologies, genetic and epigenetic changes. In this study, we explored the mechanisms of ECT2 dysregulation and compared its prognostic value in lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC). In addition, we also investigated the enrichment of ECT2 co-expressed genes in KEGG pathways in LUAD and LUSC. Bioinformatic analysis was performed based on data from the Cancer Genome Atlas (TCGA)-LUAD and TCGA-LUSC. Results showed that ECT2 expression was significantly upregulated in both LUAD and LUSC compared with normal lung tissues. ECT2 expression was considerably higher in LUSC than in LUAD. The level of ECT2 DNA methylation was significantly lower in LUSC than in LUAD. ECT2 mutation was observed in 5% of LUAD and in 51% of LUSC cases. Amplification was the predominant alteration. LUAD patients with ECT2 amplification had significantly worse disease-free survival (p = 0.022). High ECT2 expression was associated with unfavorable overall survival (OS) (p<0.0001) and recurrence-free survival (RFS) (p = 0.001) in LUAD patients. Nevertheless, these associations were not observed in patients with LUSC. The following univariate and multivariate analysis showed that the high ECT2 expression was an independent prognostic factor for poor OS (HR: 2.039, 95%CI: 1.457–2.852, p<0.001) and RFS (HR: 1.715, 95%CI: 1.210–2.432, p = 0.002) in LUAD patients, but not in LUSC patients. Among 518 genes co-expressed with ECT2 in LUAD and 386 genes co-expressed with ECT2 in LUSC, there were only 98 genes in the overlapping cluster. Some of the genes related KEGG pathways in LUAD were not observed in LUSC. These differences might help to explain the different prognostic value of ECT2 in LUAD and LUSC, which are also worthy of further studies.

The Rac GTPase in Cancer: From Old Concepts to New Paradigms

Rho family GTPases are critical regulators of cellular functions that play important roles in cancer progression. Aberrant activity of Rho small G-proteins, particularly Rac1 and their regulators, is a hallmark of cancer and contributes to the tumorigenic and metastatic phenotypes of cancer cells. This review examines the multiple mechanisms leading to Rac1 hyperactivation, particularly focusing on emerging paradigms that involve gain-of-function mutations in Rac and guanine nucleotide exchange factors, defects in Rac1 degradation, and mislocalization of Rac signaling components. The unexpected pro-oncogenic functions of Rac GTPase-activating proteins also challenged the dogma that these negative Rac regulators solely act as tumor suppressors. The potential contribution of Rac hyperactivation to resistance to anticancer agents, including targeted therapies, as well as to the suppression of antitumor immune response, highlights the critical need to develop therapeutic strategies to target the Rac pathway in a clinical setting. Cancer Res; 77(20); 5445-51. ©2017 AACR.

Plk1 regulates contraction of postmitotic smooth muscle cells and is required for vascular homeostasis

Polo-like kinase 1 (PLK1), an essential regulator of cell division, is currently undergoing clinical evaluation as a target for cancer therapy. We report an unexpected function of Plk1 in sustaining cardiovascular homeostasis. Plk1 haploinsufficiency in mice did not induce obvious cell proliferation defects but did result in arterial structural alterations, which frequently led to aortic rupture and death. Specific ablation of Plk1 in vascular smooth muscle cells (VSMCs) led to reduced arterial elasticity, hypotension, and an impaired arterial response to angiotensin II in vivo. Mechanistically, we found that Plk1 regulated angiotensin II-dependent activation of RhoA and actomyosin dynamics in VSMCs in a mitosis-independent manner. This regulation depended on Plk1 kinase activity, and the administration of small-molecule Plk1 inhibitors to angiotensin II-treated mice led to reduced arterial fitness and an elevated risk of aneurysm and aortic rupture. We thus conclude that a partial reduction of Plk1 activity that does not block cell division can nevertheless impair aortic homeostasis. Our findings have potentially important implications for current approaches aimed at PLK1 inhibition for cancer therapy.

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.

P53 and Protein Phosphorylation Regulate the Oncogenic Role of Epithelial Cell Transforming 2 (ECT2)

BACKGROUND Gastric cancer (GC) is the second leading cause of cancer-related death worldwide, but little progress has been achieved in the treatment of advanced or metastatic GC. GC is highly heterogeneous and more studies are needed to elucidate the metastatic mechanisms. Epithelial cell transforming 2 (ECT2) has been reported to be up-regulated in GC tissues, but its signaling mechanisms remain unclear. MATERIAL AND METHODS In this study, we used Western blot analysis to compare the expression level of ECT2 in 2 GC cell lines: MKN1 and MKN45. Mutagenesis and transfections were conducted to investigate the oncogenic mechanisms of ECT2 in GC cells. RESULTS ECT2 was expressed at higher levels in MKN1 than in MKN45. Immunoblotting results showed that MKN1 expression was suppressed by p53-WT but was enhanced by p53-mutant. In addition, in vitro experiments showed that ECT2 positively regulated the proliferation and invasion of GC cells. To better explore the mechanisms of ECT2 in promoting GC progression, we introduced site-directed mutants of ECT2, and found that the phosphor-mimic mutant T359D enhanced its oncogenic activity. In contrast, activation of RhoA was inhibited in cells transfected with ECT2 phosphor-deficient mutant T359A. We found that the epithelial cell biomarker E-cadherin was down-regulated by ECT2-T359D, highlighting the role of phosphorylation in regulating epithelial-mesenchymal transition. CONCLUSIONS Our results identified p53 as a novel up-stream signaling molecule of ECT2 in GC cells, and the post-translational modifications of ECT2 play important roles in regulating cancer development and progression.

Nuclear PKCι-ECT2-Rac1 and Ribosome Biogenesis: A Novel Axis in Lung Tumorigenesis

The RhoGEF Ect2 controls cell division and exerts oncogenic functions in multiple cancers. In this issue of Cancer Cell, Justilien et al. report that Ect2 is required for lung tumorigenesis and identified a role for this GEF in ribosomal RNA (rRNA) synthesis that is mediated by Rac1 and PKCι-dependent phosphorylation.

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.

PKCι regulates nuclear YAP1 localization and ovarian cancer tumorigenesis

Atypical protein kinase Cι (PKCι) is an oncogene in lung and ovarian cancer. The PKCι gene PRKCI is targeted for frequent tumor-specific copy number gain (CNG) in both lung squamous cell carcinoma (LSCC) and ovarian serous carcinoma (OSC). We recently demonstrated that in LSCC cells PRKCI CNG functions to drive transformed growth and tumorigenicity by activating PKCι-dependent cell autonomous Hedgehog (Hh) signaling. Here, we assessed whether OSC cells harboring PRKCI CNG exhibit similar PKCι-dependent Hh signaling. Surprisingly, we find that whereas PKCι is required for the transformed growth of OSC cells harboring PRKCI CNG, these cells do not exhibit PKCι-dependent Hh signaling or Hh-dependent proliferation. Rather, transformed growth of OSC cells is regulated by PKCι-dependent nuclear localization of the oncogenic transcription factor, YAP1. Lentiviral shRNA-mediated knockdown (KD) of PKCι leads to decreased nuclear YAP1 and increased YAP1 binding to angiomotin (AMOT), which sequesters YAP1 in the cytoplasm. Biochemical analysis reveals that PKCι directly phosphorylates AMOT at a unique site, Thr750, whose phosphorylation inhibits YAP1 binding. Pharmacologic inhibition of PKCι decreases YAP1 nuclear localization and blocks OSC tumor growth in vitro and in vivo. Immunohistochemical analysis reveals a strong positive correlation between tumor PKCι expression and nuclear YAP1 in primary OSC tumor samples, indicating the clinical relevance of PKCι-YAP1 signaling. Our results uncover a novel PKCι-AMOT-YAP1 signaling axis that promotes OSC tumor growth, and provide a rationale for therapeutic targeting of this pathway for treatment of OSC.

Oncogenic role of epithelial cell transforming sequence 2 in lung adenocarcinoma cells

Lung adenocarcinoma, which is the most common non-small cell lung cancer, is the leading cause of death from cancer worldwide. Epithelial cell transforming sequence 2 (ECT2) is frequently upregulated and acts as an oncogene in various human cancers. In addition, ECT2 was reported to be upregulated in early stage lung adenocarcinoma. However, the detailed role of ECT2 in mediating the malignant phenotypes of lung adenocarcinoma cells has not previously been elucidated. Reverse transcription-quantitative polymerase chain reaction and western blot analysis were used to examine ECT2 mRNA and protein expression levels, respectively. MTT, wound healing and Transwell assays were conducted to determine cell proliferation, migration and invasion abilities, respectively. In the present study, ECT2 was significantly upregulated in lung adenocarcinoma cell lines (H650, EKVX, HCC4006, HCC827, HCC2935, Hop62 and A549), as compared with a normal lung epithelial cell line (BEAS-2B). Moreover, knockdown of ECT2, induced by transfection with ECT2 siRNA, significantly inhibited the proliferation of lung adenocarcinoma A549 cells, whereas overexpression of ECT2 enhanced A549 cell proliferation. Furthermore, knockdown of ECT2 expression suppressed the migration and invasion of A549 cells, whereas overexpression of ECT2 enhanced the migration and invasion abilities of A549 cells. Notably, inhibition of ECT2 also suppressed the expression levels of N-cadherin and vimentin, whereas it enhanced the expression level of E-cadherin, indicating that ECT2 is associated with the epithelial-mesenchymal transition in A549 cells. On the contrary, overexpression of ECT2 enhanced the expression levels of N-cadherin and vimentin, whereas it reduced the expression level of E-cadherin in A549 cells. In conclusion, the results of the present study suggest that ECT2 has an oncogenic role in lung adenocarcinoma cells. Therefore, ECT2 may be a potential novel target for the treatment of lung adenocarcinoma.

Regulating Rho GTPases and their regulators

Rho GTPases regulate cytoskeletal and cell adhesion dynamics and thereby coordinate a wide range of cellular processes, including cell migration, cell polarity and cell cycle progression. Most Rho GTPases cycle between a GTP-bound active conformation and a GDP-bound inactive conformation to regulate their ability to activate effector proteins and to elicit cellular responses. However, it has become apparent that Rho GTPases are regulated by post-translational modifications and the formation of specific protein complexes, in addition to GTP-GDP cycling. The canonical regulators of Rho GTPases - guanine nucleotide exchange factors, GTPase-activating proteins and guanine nucleotide dissociation inhibitors - are regulated similarly, creating a complex network of interactions to determine the precise spatiotemporal activation of Rho GTPases.

PKCι regulates nuclear YAP1 localization and ovarian cancer tumorigenesis

Atypical protein kinase Cι (PKCι) is an oncogene in lung and ovarian cancer. The PKCι gene PRKCI is targeted for frequent tumor-specific copy number gain (CNG) in both lung squamous cell carcinoma (LSCC) and ovarian serous carcinoma (OSC). We recently demonstrated that in LSCC cells PRKCI CNG functions to drive transformed growth and tumorigenicity by activating PKCι-dependent cell autonomous Hedgehog (Hh) signaling. Here, we assessed whether OSC cells harboring PRKCI CNG exhibit similar PKCι-dependent Hh signaling. Surprisingly, we find that whereas PKCι is required for the transformed growth for OSC cells harboring PRKCI CNG, these cells do not exhibit PKCι-dependent Hh signaling or Hh-dependent proliferation. Rather, transformed growth of OSC cells is regulated by PKCι-dependent nuclear localization of the oncogenic transcription factor, YAP1. Lentiviral shRNA-mediated knock down (KD) of PKCι leads to decreased nuclear YAP1 and increased YAP1 binding to angiomotin (AMOT), which sequesters YAP1 in the cytoplasm. Biochemical analysis reveals that PKCι directly phosphorylates AMOT at a unique site, Thr750, whose phosphorylation inhibits YAP1 binding. Pharmacologic inhibition of PKCι decreases YAP1 nuclear localization and blocks OSC tumor growth in vitro and in vivo. Immunohistochemical analysis reveals a strong positive correlation between tumor PKCι expression and nuclear YAP1 in primary OSC tumor samples, indicating the clinical relevance of PKCι-YAP1 signaling. Our results uncover a novel PKCι-AMOT-YAP1 signaling axis that promotes OSC tumor growth, and provide a rationale for therapeutic targeting of this pathway for treatment of OSC.

Targeting oncogenic protein kinase Cι for treatment of mutant KRAS LADC

Lung cancer is the leading cause of cancer death in the US with ∼124,000 new cases annually, and a 5 y survival rate of ∼16%. Mutant KRAS-driven lung adenocarcinoma (KRAS LADC) is a particularly prevalent and deadly form of lung cancer. Protein kinase Cι (PKCι) is an oncogenic effector of KRAS that activates multiple signaling pathways that stimulate transformed growth and invasion, and maintain a KRAS LADC tumor-initiating cell (TIC) phenotype. PKCι inhibitors used alone and in strategic combination show promise as new therapeutic approaches to treatment of KRAS LADC. These novel drug combinations may improve clinical management of KRAS LADC.

The dynamic behavior of Ect2 in response to DNA damage

Ect2 is a BRCT-containing guanidine exchange factor for Rho GTPases. It is essential for cytokinesis and is also involved in tumorigenesis. Since most BRCT-containing proteins are involved in DNA damage response and/or DNA repair, we tested whether Ect2 plays similar roles. We report that in primary mouse embryonic fibroblasts (MEFs), DNA damage quickly led to Ect2 relocalization to the chromatin and DNA damage foci-like structures. Ect2 knockdown did not affect foci localization of γH2AX, TopBP1, or Brca1, or activation of Atm, yet it impeded p53 Ser15 phosphorylation and activation, and resulted in defects in apoptosis and activation of S and G2/M checkpoints in response to DNA damage. These results suggest that Ect2 plays a role in DNA damage response. Interestingly, Ect2 is down-regulated at late stages of DNA damage response. Although p53 and E2F1 have been shown to regulate Ect2 transcription, DNA damage-induced Ect2 down-regulation occurred in p53-/- or Atm-/- MEFs and E2F1 knockdown cells. Instead, DNA damage-induced Ect2 down-regulation is mainly attributable to decreased protein stability. Like Ect2 knockdown, Ect2 destabilization may help the cell to recover from DNA damage response. These results suggest that Ect2 plays roles in multiple aspects of DNA damage response.

Protein Kinase Cι Drives a NOTCH3-dependent Stem-like Phenotype in Mutant KRAS Lung Adenocarcinoma

We report that the protein kinase Cι (PKCι) oncogene controls expression of NOTCH3, a key driver of stemness, in KRAS-mediated lung adenocarcinoma (LADC). PKCι activates NOTCH3 expression by phosphorylating the ELF3 transcription factor and driving ELF3 occupancy on the NOTCH3 promoter. PKCι-ELF3-NOTCH3 signaling controls the tumor-initiating cell phenotype by regulating asymmetric cell division, a process necessary for tumor initiation and maintenance. Primary LADC tumors exhibit PKCι-ELF3-NOTCH3 signaling, and combined pharmacologic blockade of PKCι and NOTCH synergistically inhibits tumorigenic behavior in vitro and LADC growth in vivo demonstrating the therapeutic potential of PKCι-ELF3-NOTCH3 signal inhibition to more effectively treat KRAS LADC.

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.

Discovery of MINC1, a GTPase-activating protein small molecule inhibitor, targeting MgcRacGAP

The Rho family of Ras superfamily small GTPases regulates a broad range of biological processes such as migration, differentiation, cell growth and cell survival. Therefore, the availability of small molecule modulators as tool compounds could greatly enhance research on these proteins and their biological function. To this end, we designed a biochemical, high throughput screening assay with complementary follow-up assays to identify small molecule compounds inhibiting MgcRacGAP, a Rho family GTPase activating protein involved in cytokinesis and transcriptionally upregulated in many cancers. We first performed an in-house screen of 20,480 compounds, and later we tested the assay against 342,046 compounds from the NIH Molecular Libraries Small Molecule Repository. Primary screening hit rates were about 1% with the majority of those affecting the primary readout, an enzyme-coupled GDP detection assay. After orthogonal and counter screens, we identified two hits with high selectivity towards MgcRacGAP, compared with other RhoGAPs, and potencies in the low micromolar range. The most promising hit, termed MINC1, was then examined with cell-based testing where it was observed to induce an increased rate of cytokinetic failure and multinucleation in addition to other cell division defects, suggesting that it may act as an MgcRacGAP inhibitor also in cells.