The Src homology 3 domain-containing guanine nucleotide exchange factor is overexpressed in high-grade gliomas and promotes tumor necrosis factor-like weak inducer of apoptosis-fibroblast growth factor-inducible 14-induced cell migration and invasion via tumor necrosis factor receptor-associated factor 2

Intersections of Ubiquitin-Proteosome System and Autophagy in Promoting Growth of Glioblastoma Multiforme: Challenges and Opportunities

Glioblastoma multiforme (GBM) is a brain tumor notorious for its propensity to recur after the standard treatments of surgical resection, ionizing radiation (IR), and temozolomide (TMZ). Combined with the acquired resistance to standard treatments and recurrence, GBM is an especially deadly malignancy with hardly any worthwhile treatment options. The treatment resistance of GBM is influenced, in large part, by the contributions from two main degradative pathways in eukaryotic cells: ubiquitin-proteasome system (UPS) and autophagy. These two systems influence GBM cell survival by removing and recycling cellular components that have been damaged by treatments, as well as by modulating metabolism and selective degradation of components of cell survival or cell death pathways. There has recently been a large amount of interest in potential cancer therapies involving modulation of UPS or autophagy pathways. There is significant crosstalk between the two systems that pose therapeutic challenges, including utilization of ubiquitin signaling, the degradation of components of one system by the other, and compensatory activation of autophagy in the case of proteasome inhibition for GBM cell survival and proliferation. There are several important regulatory nodes which have functions affecting both systems. There are various molecular components at the intersections of UPS and autophagy pathways that pose challenges but also show some new therapeutic opportunities for GBM. This review article aims to provide an overview of the recent advancements in research regarding the intersections of UPS and autophagy with relevance to finding novel GBM treatment opportunities, especially for combating GBM treatment resistance.

Targeting fibroblast growth factor (FGF)-inducible 14 (Fn14) for tumor therapy

Fibroblast growth factor-inducible 14 (Fn14) is a member of the tumor necrosis factor (TNF) receptor superfamily (TNFRSF) and is activated by its ligand TNF-like weak inducer of apoptosis (TWEAK). The latter occurs as a homotrimeric molecule in a soluble and a membrane-bound form. Soluble TWEAK (sTWEAK) activates the weakly inflammatory alternative NF-κB pathway and sensitizes for TNF-induced cell death while membrane TWEAK (memTWEAK) triggers additionally robust activation of the classical NF-κB pathway and various MAP kinase cascades. Fn14 expression is limited in adult organisms but becomes strongly induced in non-hematopoietic cells by a variety of growth factors, cytokines and physical stressors (e.g., hypoxia, irradiation). Since all these Fn14-inducing factors are frequently also present in the tumor microenvironment, Fn14 is regularly found to be expressed by non-hematopoietic cells of the tumor microenvironment and most solid tumor cells. In general, there are three possibilities how the tumor-Fn14 linkage could be taken into consideration for tumor therapy. First, by exploitation of the cancer associated expression of Fn14 to direct cytotoxic activities (antibody-dependent cell-mediated cytotoxicity (ADCC), cytotoxic payloads, CAR T-cells) to the tumor, second by blockade of potential protumoral activities of the TWEAK/Fn14 system, and third, by stimulation of Fn14 which not only triggers proinflammtory activities but also sensitizes cells for apoptotic and necroptotic cell death. Based on a brief description of the biology of the TWEAK/Fn14 system and Fn14 signaling, we discuss the features of the most relevant Fn14-targeting biologicals and review the preclinical data obtained with these reagents. In particular, we address problems and limitations which became evident in the preclinical studies with Fn14-targeting biologicals and debate possibilities how they could be overcome.

TNF Receptor Associated Factor 2 (TRAF2) Signaling in Cancer

Simple Summary

Tumor necrosis factor (TNF) receptor associated factor-2 (TRAF2) is an intracellular adapter protein with E3 ligase activity, which interacts with a plethora of other signaling proteins, including plasma membrane receptors, kinases, phosphatases, other E3 ligases, and deubiquitinases. TRAF2 is involved in various cancer-relevant cellular processes, such as the activation of transcription factors of the NFκB family, stimulation of mitogen-activated protein (MAP) kinase cascades, endoplasmic reticulum (ER) stress signaling, autophagy, and the control of cell death programs. In a context-dependent manner, TRAF2 promotes tumor development but it can also act as a tumor suppressor. Based on a general description, how TRAF2 in concert with TRAF2-interacting proteins and other TRAF proteins act at the molecular level is discussed for its importance for tumor development and its potential usefulness as a therapeutic target in cancer therapy.

Abstract

Tumor necrosis factor (TNF) receptor associated factor-2 (TRAF2) has been originally identified as a protein interacting with TNF receptor 2 (TNFR2) but also binds to several other receptors of the TNF receptor superfamily (TNFRSF). TRAF2, often in concert with other members of the TRAF protein family, is involved in the activation of the classical NFκB pathway and the stimulation of various mitogen-activated protein (MAP) kinase cascades by TNFRSF receptors (TNFRs), but is also required to inhibit the alternative NFκB pathway. TRAF2 has also been implicated in endoplasmic reticulum (ER) stress signaling, the regulation of autophagy, and the control of cell death programs. TRAF2 fulfills its functions by acting as a scaffold, bringing together the E3 ligase cellular inhibitor of apoptosis-1 (cIAP1) and cIAP2 with their substrates and various regulatory proteins, e.g., deubiquitinases. Furthermore, TRAF2 can act as an E3 ligase by help of its N-terminal really interesting new gene (RING) domain. The finding that TRAF2 (but also several other members of the TRAF family) interacts with the latent membrane protein 1 (LMP1) oncogene of the Epstein–Barr virus (EBV) indicated early on that TRAF2 could play a role in the oncogenesis of B-cell malignancies and EBV-associated non-keratinizing nasopharyngeal carcinoma (NPC). TRAF2 can also act as an oncogene in solid tumors, e.g., in colon cancer by promoting Wnt/β-catenin signaling. Moreover, tumor cell-expressed TRAF2 has been identified as a major factor-limiting cancer cell killing by cytotoxic T-cells after immune checkpoint blockade. However, TRAF2 can also be context-dependent as a tumor suppressor, presumably by virtue of its inhibitory effect on the alternative NFκB pathway. For example, inactivating mutations of TRAF2 have been associated with tumor development, e.g., in multiple myeloma and mantle cell lymphoma. In this review, we summarize the various TRAF2-related signaling pathways and their relevance for the oncogenic and tumor suppressive activities of TRAF2. Particularly, we discuss currently emerging concepts to target TRAF2 for therapeutic purposes.

Anti-Fn14-Conjugated Prussian Blue Nanoparticles as a Targeted Photothermal Therapy Agent for Glioblastoma

Prussian blue nanoparticles (PBNPs) are effective photothermal therapy (PTT) agents: they absorb near-infrared radiation and reemit it as heat via phonon-phonon relaxations that, in the presence of tumors, can induce thermal and immunogenic cell death. However, in the context of central nervous system (CNS) tumors, the off-target effects of PTT have the potential to result in injury to healthy CNS tissue. Motivated by this need for targeted PTT agents for CNS tumors, we present a PBNP formulation that targets fibroblast growth factor-inducible 14 (Fn14)-expressing glioblastoma cell lines. We conjugated an antibody targeting Fn14, a receptor abundantly expressed on many glioblastomas but near absent on healthy CNS tissue, to PBNPs (aFn14-PBNPs). We measured the attachment efficiency of aFn14 onto PBNPs, the size and stability of aFn14-PBNPs, and the ability of aFn14-PBNPs to induce thermal and immunogenic cell death and target and treat glioblastoma tumor cells in vitro. aFn14 remained stably conjugated to the PBNPs for at least 21 days. Further, PTT with aFn14-PBNPs induced thermal and immunogenic cell death in glioblastoma tumor cells. However, in a targeted treatment assay, PTT was only effective in killing glioblastoma tumor cells when using aFn14-PBNPs, not when using PBNPs alone. Our methodology is novel in its targeting moiety, tumor application, and combination with PTT. To the best of our knowledge, PBNPs have not been investigated as a targeted PTT agent in glioblastoma via conjugation to aFn14. Our results demonstrate a novel and effective method for delivering targeted PTT to aFn14-expressing tumor cells via aFn14 conjugation to PBNPs.

Targeting the Ubiquitin System in Glioblastoma

Glioblastoma is the most common primary brain tumor in adults with poor overall outcome and 5-year survival of less than 5%. Treatment has not changed much in the last decade or so, with surgical resection and radio/chemotherapy being the main options. Glioblastoma is highly heterogeneous and frequently becomes treatment-resistant due to the ability of glioblastoma cells to adopt stem cell states facilitating tumor recurrence. Therefore, there is an urgent need for novel therapeutic strategies. The ubiquitin system, in particular E3 ubiquitin ligases and deubiquitinating enzymes, have emerged as a promising source of novel drug targets. In addition to conventional small molecule drug discovery approaches aimed at modulating enzyme activity, several new and exciting strategies are also being explored. Among these, PROteolysis TArgeting Chimeras (PROTACs) aim to harness the endogenous protein turnover machinery to direct therapeutically relevant targets, including previously considered "undruggable" ones, for proteasomal degradation. PROTAC and other strategies targeting the ubiquitin proteasome system offer new therapeutic avenues which will expand the drug development toolboxes for glioblastoma. This review will provide a comprehensive overview of E3 ubiquitin ligases and deubiquitinating enzymes in the context of glioblastoma and their involvement in core signaling pathways including EGFR, TGF-β, p53 and stemness-related pathways. Finally, we offer new insights into how these ubiquitin-dependent mechanisms could be exploited therapeutically for glioblastoma.

The Role of Rho GTPases in Motility and Invasion of Glioblastoma Cells

Astrocytomas are primary malignant brain tumors that originate from astrocytes. Grade IV astrocytoma or glioblastoma is a highly invasive tumor that occur within the brain parenchyma. The Rho family of small GTPases, which includes Rac1, Cdc42, and RhoA, is an important family whose members are key regulators of the invasion and migration of glioblastoma cells. In this review, we describe the role played by the Rho family of GTPases in the regulation of the invasion and migration of glioblastoma cells. Specifically, we focus on the role played by RhoA, Rac1, RhoG, and Cdc42 in cell migration through rearrangement of actin cytoskeleton, cell adhesion, and invasion. Finally, we highlight the importance of potentially targeting Rho GTPases in the treatment of glioblastoma.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

PDZ-RhoGEF Is a Signaling Effector for TROY-Induced Glioblastoma Cell Invasion and Survival

Glioblastoma multiforme (GBM) is the most common type of malignant brain tumors in adults and has a dismal prognosis. The highly aggressive invasion of malignant cells into the normal brain parenchyma renders complete surgical resection of GBM tumors impossible, increases resistance to therapeutic treatment, and leads to near-universal tumor recurrence. We have previously demonstrated that TROY (TNFRSF19) plays an important role in glioblastoma cell invasion and therapeutic resistance. However, the potential downstream effectors of TROY signaling have not been fully characterized. Here, we identified PDZ-RhoGEF as a binding partner for TROY that potentiated TROY-induced nuclear factor kappa B activation which is necessary for both cell invasion and survival. In addition, PDZ-RhoGEF also interacts with Pyk2, indicating that PDZ-RhoGEF is a component of a signalsome that includes TROY and Pyk2. PDZ-RhoGEF is overexpressed in glioblastoma tumors and stimulates glioma cell invasion via Rho activation. Increased PDZ-RhoGEF expression enhanced TROY-induced glioma cell migration. Conversely, silencing PDZ-RhoGEF expression inhibited TROY-induced glioma cell migration, increased sensitivity to temozolomide treatment, and extended survival of orthotopic xenograft mice. Furthermore, depletion of RhoC or RhoA inhibited TROY- and PDZ-RhoGEF-induced cell migration. Mechanistically, increased TROY expression stimulated Rho activation, and depletion of PDZ-RhoGEF expression reduced this activation. Taken together, these data suggest that PDZ-RhoGEF plays an important role in TROY signaling and provides insights into a potential node of vulnerability to limit GBM cell invasion and decrease therapeutic resistance.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

Prognostic Significance of TNFR-Associated Factor 1 and 2 (TRAF1 and TRAF2) in Glioblastoma

Background

TNFR-associated factor 1 (TRAF1) and TRAF2 have been demonstrated to inhibit apoptosis and promote cell survival in glioblastoma (GBM) cells with experiments in vitro. However, their clinical and prognostic significance have not been elucidated.

Material/Methods

In our study, we for the first time investigated the expression of TRAF1 and TRAF2 in 105 GBM tissues. Furthermore, we evaluated their clinical significance, including their association with clinicopathologic factors and prognostic value. The association with clinicopathologic factors was assessed by chi-square test. The relation of TRAF1/2 expression to survival rate was assessed by Kaplan-Meier method and Cox-regression model.

Results

We demonstrated that TRAF1 expression had no significant prognostic value for GBM. On the contrary, high expression of TRAF2 can predict poorer prognosis of GBM and was identified as an independent biomarker in GBM prognosis.

Conclusions

High expression of TRAF2 was identified as an independent biomarker in GBM prognosis, indicating TRAF2 as a novel drug target in GBM treatment.

TWEAK/Fn14 Activation Participates in Skin Inflammation

Tumor necrosis factor- (TNF-) like weak inducer of apoptosis (TWEAK) participates in multiple biological activities via binding to its sole receptor-fibroblast growth factor-inducible 14 (Fn14). The TWEAK/Fn14 signaling pathway is activated in skin inflammation and modulates the inflammatory responses of keratinocytes by activating nuclear factor-κB signals and enhancing the production of several cytokines, including interleukins, monocyte chemotactic protein-1, RANTES (regulated on activation, normal T cell expressed and secreted), and interferon gamma-induced protein 10. Mild or transient TWEAK/Fn14 activation contributes to tissular repair and regeneration while excessive or persistent TWEAK/Fn14 signals may lead to severe inflammatory infiltration and tissue damage. TWEAK also regulates cell fate of keratinocytes, involving the function of Fn14-TNF receptor-associated factor-TNF receptor axis. By recruiting inflammatory cells, promoting cytokine production, and regulating cell fate, TWEAK/Fn14 activation plays a pivotal role in the pathogenesis of various skin disorders, such as psoriasis, atopic dermatitis, cutaneous vasculitis, human papillomavirus infection and related skin tumors, and cutaneous autoimmune diseases. Therefore, the TWEAK/Fn14 pathway may be a potential target for the development of novel therapeutics for skin inflammatory diseases.

Identification of aurintricarboxylic acid as a selective inhibitor of the TWEAK-Fn14 signaling pathway in glioblastoma cells

The survival of patients diagnosed with glioblastoma (GBM), the most deadly form of brain cancer, is compromised by the proclivity for local invasion into the surrounding normal brain, which prevents complete surgical resection and contributes to therapeutic resistance. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK), a member of the tumor necrosis factor (TNF) superfamily, can stimulate glioma cell invasion and survival via binding to fibroblast growth factor-inducible 14 (Fn14) and subsequent activation of the transcription factor NF-κB. To discover small molecule inhibitors that disrupt the TWEAK-Fn14 signaling axis, we utilized a cell-based drug-screening assay using HEK293 cells engineered to express both Fn14 and a NF-κB-driven firefly luciferase reporter protein. Focusing on the LOPAC1280 library of 1280 pharmacologically active compounds, we identified aurintricarboxylic acid (ATA) as an agent that suppressed TWEAK-Fn14-NF-κB dependent signaling, but not TNFα-TNFR-NF-κB driven signaling. We demonstrated that ATA repressed TWEAK-induced glioma cell chemotactic migration and invasion via inhibition of Rac1 activation but had no effect on cell viability or Fn14 expression. In addition, ATA treatment enhanced glioma cell sensitivity to both the chemotherapeutic agent temozolomide (TMZ) and radiation-induced cell death. In summary, this work reports a repurposed use of a small molecule inhibitor that targets the TWEAK-Fn14 signaling axis, which could potentially be developed as a new therapeutic agent for treatment of GBM patients.

A RhoG-mediated signaling pathway that modulates invadopodia dynamics in breast cancer cells

One of the hallmarks of cancer is the ability of tumor cells to invade surrounding tissues and metastasize. During metastasis, cancer cells degrade the extracellular matrix, which acts as a physical barrier, by developing specialized actin-rich membrane protrusion structures called invadopodia. The formation of invadopodia is regulated by Rho GTPases, a family of proteins that regulates the actin cytoskeleton. Here, we describe a novel role for RhoG in the regulation of invadopodia disassembly in human breast cancer cells. Our results show that RhoG and Rac1 have independent and opposite roles in the regulation of invadopodia dynamics. We also show that SGEF (also known as ARHGEF26) is the exchange factor responsible for the activation of RhoG during invadopodia disassembly. When the expression of either RhoG or SGEF is silenced, invadopodia are more stable and have a longer lifetime than in control cells. Our findings also demonstrate that RhoG and SGEF modulate the phosphorylation of paxillin, which plays a key role during invadopodia disassembly. In summary, we have identified a novel signaling pathway involving SGEF, RhoG and paxillin phosphorylation, which functions in the regulation of invadopodia disassembly in breast cancer cells.

TWEAK activation of the non-canonical NF-κB signaling pathway differentially regulates melanoma and prostate cancer cell invasion

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a multifunctional cytokine that binds with high affinity to a plasma membrane-anchored receptor named Fn14. Both TWEAK and Fn14 expression has been detected in human cancer tissue, and studies have shown that TWEAK/Fn14 signaling can promote either "pro-cancer" or "anti-cancer" cellular effects in vitro, depending on the cancer cell line under investigation. In this study, we engineered murine B16 melanoma cells to secrete high levels of soluble TWEAK and examined their properties. TWEAK production by B16 cells preferentially activated the non-canonical NF-κB signaling pathway and increased the expression of several previously described TWEAK-inducible genes, including Fn14. TWEAK overexpression in B16 cells inhibited both cell growth and invasion in vitro. The TWEAK-mediated reduction in B16 cell invasive capacity was dependent on activation of the non-canonical NF-κB signaling pathway. Finally, we found that this same signaling pathway was also important for TWEAK-stimulated human DU145 prostate cancer cell invasion. Therefore, even though TWEAK:Fn14 binding activates non-canonical NF-κB signaling in both melanoma and prostate cancer cells, this shared cellular response can trigger a very different downstream outcome (inhibition or stimulation of cell invasiveness, respectively).

Repair Injured Heart by Regulating Cardiac Regenerative Signals

Cardiac regeneration is a homeostatic cardiogenic process by which the sections of malfunctioning adult cardiovascular tissues are repaired and renewed employing a combination of both cardiomyogenesis and angiogenesis. Unfortunately, while high-quality regeneration can be performed in amphibians and zebrafish hearts, mammalian hearts do not respond in kind. Indeed, a long-term loss of proliferative capacity in mammalian adult cardiomyocytes in combination with dysregulated induction of tissue fibrosis impairs mammalian endogenous heart regenerative capacity, leading to deleterious cardiac remodeling at the end stage of heart failure. Interestingly, several studies have demonstrated that cardiomyocyte proliferation capacity is retained in mammals very soon after birth, and cardiac regeneration potential is correspondingly preserved in some preadolescent vertebrates after myocardial infarction. There is therefore great interest in uncovering the molecular mechanisms that may allow heart regeneration during adult stages. This review will summarize recent findings on cardiac regenerative regulatory mechanisms, especially with respect to extracellular signals and intracellular pathways that may provide novel therapeutics for heart diseases. Particularly, both in vitro and in vivo experimental evidences will be presented to highlight the functional role of these signaling cascades in regulating cardiomyocyte proliferation, cardiomyocyte growth, and maturation, with special emphasis on their responses to heart tissue injury.

Tyrosine Phosphorylation of SGEF Regulates RhoG Activity and Cell Migration

SGEF and Ephexin4 are members of the Ephexin subfamily of RhoGEFs that specifically activate the small GTPase RhoG. It is reported that Ephexin1 and Ephexin5, two well-characterized Ephexin subfamily RhoGEFs, are tyrosine-phosphorylated by Src, and that their phosphorylation affect their activities and functions. In this study, we show that SGEF, but not Ephexin4, is tyrosine-phosphorylated by Src. Tyrosine phosphorylation of SGEF suppresses its interaction with RhoG, the elevation of RhoG activity, and SGEF-mediated promotion of cell migration. We identified tyrosine 530 (Y530), which is located within the Dbl homology domain, as a major phosphorylation site of SGEF by Src, and Y530F mutation blocked the inhibitory effect of Src on SGEF. Taken together, these results suggest that the activity of SGEF is negatively regulated by tyrosine phosphorylation of the DH domain.

SGEF Is Regulated via TWEAK/Fn14/NF-κB Signaling and Promotes Survival by Modulation of the DNA Repair Response to Temozolomide

Glioblastoma (GB) is the highest grade and most common form of primary adult brain tumors. Despite surgical removal followed by concomitant radiation and chemotherapy with the alkylating agent temozolomide, GB tumors develop treatment resistance and ultimately recur. Impaired response to treatment occurs rapidly, conferring a median survival of just fifteen months. Thus, it is necessary to identify the genetic and signaling mechanisms that promote tumor resistance to develop targeted therapies to combat this refractory disease. Previous observations indicated that SGEF (ARHGEF26), a RhoG-specific guanine nucleotide exchange factor (GEF), is overexpressed in GB tumors and plays a role in promoting TWEAK-Fn14-mediated glioma invasion. Here, further investigation revealed an important role for SGEF in glioma cell survival. SGEF expression is upregulated by TWEAK-Fn14 signaling via NF-κB activity while shRNA-mediated reduction of SGEF expression sensitizes glioma cells to temozolomide-induced apoptosis and suppresses colony formation following temozolomide treatment. Nuclear SGEF is activated following temozolomide exposure and complexes with the DNA damage repair (DDR) protein BRCA1. Moreover, BRCA1 phosphorylation in response to temozolomide treatment is hindered by SGEF knockdown. The role of SGEF in promoting chemotherapeutic resistance highlights a heretofore unappreciated driver, and suggests its candidacy for development of novel targeted therapeutics for temozolomide-refractory, invasive GB cells.

IMPLICATION

SGEF, as a dual process modulator of cell survival and invasion, represents a novel target for treatment refractory glioblastoma.

Propentofylline inhibits glioblastoma cell invasion and survival by targeting the TROY signaling pathway

Glioblastoma (GBM) is the most common primary tumor of the CNS and carries a dismal prognosis. The aggressive invasion of GBM cells into the surrounding normal brain makes complete resection impossible, significantly increases resistance to the standard therapy regimen, and virtually assures tumor recurrence. Median survival for newly diagnosed GBM is 14.6 months and declines to 8 months for patients with recurrent GBM. New therapeutic strategies that target the molecular drivers of invasion are required for improved clinical outcome. We have demonstrated that TROY (TNFRSF19), a member of the TNFR super-family, plays an important role in GBM invasion and resistance. Knockdown of TROY expression inhibits GBM cell invasion, increases sensitivity to temozolomide, and prolongs survival in an intracranial xenograft model. Propentofylline (PPF), an atypical synthetic methylxanthine compound, has been extensively studied in Phase II and Phase III clinical trials for Alzheimer's disease and vascular dementia where it has demonstrated blood-brain permeability and minimal adverse side effects. Here we showed that PPF decreased GBM cell expression of TROY, inhibited glioma cell invasion, and sensitized GBM cells to TMZ. Mechanistically, PPF decreased glioma cell invasion by modulating TROY expression and downstream signaling, including AKT, NF-κB, and Rac1 activation. Thus, PPF may provide a pharmacologic approach to target TROY, inhibit cell invasion, and reduce therapeutic resistance in GBM.

Expression, correlation, and prognostic value of TRAF2 and TRAF4 expression in malignant plural effusion cells in human breast cancer

BACKGROUND

TRAF2 and TRAF4, members of the tumor necrosis factor receptor- associated factor family of intracellular signal transduction proteins, are associated with breast cancer progression and metastasis.

METHODS

We collected malignant serous effusion cells from the patients with breast cancer (n = 46). Cell blocks prepared from plural effusions (n = 46) and primary breast cancer (n = 50), lymph node metastases (n = 50), and normal breast tissue specimens (n = 30). The immunohistochemistry was performed for the detection of TRAF2 and TRAF4 expression with the correlation of their expression with clinicopathological parameters and survival rate analyzed.

RESULTS

Compared with normal breast tissues, TRAF2 expression was upregulated, and nuclear TRAF4 expression was downregulated in malignant pleural effusion cells, primary tumors, and lymph node metastases (P < 0.05). Multivariate analysis revealed TRAF2 expression in pleural effusions was associated with the molecular/pathological type, venous invasion, and lymph node metastasis, while nuclear TRAF4 expression was associated with age, tumor size, venous invasion, and lymph node metastasis, clinical staging, molecular/pathological subtype and p53 status (P < 0.05). There was a significant positive correlation between TRAF2 and TRAF4 expression levels in malignant pleural effusion cells (r = 0.937; P < 0.01). Kaplan-Meire analysis demonstrated a close correlation of TRAF2 and TRAF4 expression in malignant pleural effusion cells with cumulative overall survival (P < 0.05).

CONCLUSION

TRAF2 and nuclear TRAF4 expression in malignant pleural effusion cells may represent potential prognostic factors and biomarkers of invasion and metastasis in breast cancer.

The TWEAK receptor Fn14 is a potential cell surface portal for targeted delivery of glioblastoma therapeutics

Fibroblast growth factor-inducible 14 (Fn14; TNFRSF12A) is the cell surface receptor for the tumor necrosis factor (TNF) family member TNF-like weak inducer of apoptosis (TWEAK). The Fn14 gene is normally expressed at low levels in healthy tissues but expression is significantly increased after tissue injury and in many solid tumor types, including glioblastoma (GB; formerly referred to as 'GB multiforme'). GB is the most common and aggressive primary malignant brain tumor and the current standard-of-care therapeutic regimen has a relatively small impact on patient survival, primarily because glioma cells have an inherent propensity to invade into normal brain parenchyma, which invariably leads to tumor recurrence and patient death. Despite major, concerted efforts to find new treatments, a new GB therapeutic that improves survival has not been introduced since 2005. In this review article, we summarize studies indicating that (i) Fn14 gene expression is low in normal brain tissue but is upregulated in advanced brain cancers and, in particular, in GB tumors exhibiting the mesenchymal molecular subtype; (ii) Fn14 expression can be detected in glioma cells residing in both the tumor core and invasive rim regions, with the maximal levels found in the invading glioma cells located within normal brain tissue; and (iii)

TWEAK

Fn14 engagement as well as Fn14 overexpression can stimulate glioma cell migration, invasion and resistance to chemotherapeutic agents in vitro. We also discuss two new therapeutic platforms that are currently in development that leverage Fn14 overexpression in GB tumors as a way to deliver cytotoxic agents to the glioma cells remaining after surgical resection while sparing normal healthy brain cells.

miR-128 and miR-149 enhance the chemosensitivity of temozolomide by Rap1B-mediated cytoskeletal remodeling in glioblastoma

Glioblastoma multiforme (GBM) is one of the most deadly diseases affecting humans, and is often characterized by poor survival and by high resistance to chemotherapy and radiotherapy. Temozolomide (TMZ) is an oral alkylating agent which is widely used in the treatment of GBM following surgery. Although TMZ may restrain GBM growth, TMZ resistance is also common and accounts for numerous cases of treatment failure. Studies indicate that aberrant miRNA expression is associated with hallmark malignant properties of GBM. Thus, miRNA-based anticancer therapeutic approaches have been exploited, either alone or in combination with standard targeted therapies to enhance the efficacy of chemotherapy agents. In the present study, we demonstrated that the expression of miR-128 and miR-149 was downregulated in glioblastoma, and their overexpression inhibited the invasion of glioblastoma cells by targeting Rap1B-mediated cytoskeletal and related molecular alterations. Moreover, miR-128 and miR-149 enhanced the chemosensitivity of glioblastoma cells to TMZ.

FN14 expression correlates with MET in NSCLC and promotes MET-driven cell invasion

The five-year survival rate in advanced non-small cell lung cancer (NSCLC) remains below ten percent. The invasive and metastatic nature of NSCLC tumor cells contributes to the high mortality rate, and as such the mechanisms that govern NSCLC metastasis is an active area of investigation. Two surface receptors that influence NSCLC invasion and metastasis are the hepatocyte growth factor receptor (HGFR/MET) and fibroblast growth factor-inducible 14 (FN14). MET protein is over-expressed in NSCLC tumors and associated with poor clinical outcome and metastasis. FN14 protein is also elevated in NSCLC tumors and positively correlates with tumor cell migration and invasion. In this report, we show that MET and FN14 protein expressions are significantly correlated in human primary NSCLC tumors, and the protein levels of MET and FN14 are elevated in metastatic lesions relative to patient-matched primary tumors. In vitro, HGF/MET activation significantly enhances FN14 mRNA and protein expression. Importantly, depletion of FN14 is sufficient to inhibit MET-driven NSCLC tumor cell migration and invasion in vitro. This work suggests that MET and FN14 protein expressions are associated with the invasive and metastatic potential of NSCLC. Receptor-targeted therapeutics for both MET and FN14 are in clinical development, the use of which may mitigate the metastatic potential of NSCLC.

TNF Receptor-Associated Factor 1 is a Major Target of Soluble TWEAK

Soluble tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), in contrast to membrane TWEAK and TNF, is only a weak activator of the classical NFκB pathway. We observed that soluble TWEAK was regularly more potent than TNF with respect to the induction of TNF receptor-associated factor 1 (TRAF1), a NFκB-controlled signaling protein involved in the regulation of inflammatory signaling pathways. TNF-induced TRAF1 expression was efficiently blocked by inhibition of the classical NFκB pathway using the IKK2 inhibitor, TPCA1. In contrast, in some cell lines, TWEAK-induced TRAF1 production was only partly inhibited by TPCA1. The NEDD8-activating enzyme inhibitor MLN4924, however, which inhibits classical and alternative NFκB signaling, blocked TNF- and TWEAK-induced TRAF1 expression. This suggests that TRAF1 induction by soluble TWEAK is based on the cooperative activity of the two NFκB signaling pathways. We have previously shown that oligomerization of soluble TWEAK results in ligand complexes with membrane TWEAK-like activity. Oligomerization of soluble TWEAK showed no effect on the dose response of TRAF1 induction, but potentiated the ability of soluble TWEAK to trigger production of the classical NFκB-regulated cytokine IL8. Transfectants expressing soluble TWEAK and membrane TWEAK showed similar induction of TRAF1 while only the membrane TWEAK expressing cells robustly stimulated IL8 production. These data indicate that soluble TWEAK may efficiently induce a distinct subset of the membrane TWEAK-targeted genes and argue again for a crucial role of classical NFκB pathway-independent signaling in TWEAK-induced TRAF1 expression. Other TWEAK targets, which can be equally well induced by soluble and membrane TWEAK, remain to be identified and the relevance of the ability of soluble TWEAK to induce such a distinct subset of membrane TWEAK-targeted genes for TWEAK biology will have to be clarified in future studies.

Guanine nucleotide exchange factor Dock7 mediates HGF-induced glioblastoma cell invasion via Rac activation

Background:

Glioblastoma multiforme (GBM), a highly invasive primary brain tumour, remains an incurable disease. Rho GTPases and their activators, guanine nucleotide exchange factors (GEFs), have central roles in GBM invasion. Anti-angiogenic therapies may stimulate GBM invasion via HGF/c-Met signalling. We aim to identify mediators of HGF-induced GBM invasion that may represent targets in a combination anti-angiogenic/anti-invasion therapeutic paradigm.

Methods:

Guanine nucleotide exchange factor expression was measured by microarray analysis and western blotting. Specific depletion of proteins was accomplished using siRNA. Cell invasion was determined using matrigel and brain slice assays. Cell proliferation and survival were monitored using sulforhodamine B and colony formation assays. Guanine nucleotide exchange factor and GTPase activities were determined using specific affinity precipitation assays.

Results:

We found that expression of Dock7, a GEF, is elevated in human GBM tissue in comparison with non-neoplastic brain. We showed that Dock7 mediates serum- and HGF-induced glioblastoma cell invasion. We also showed that Dock7 co-immunoprecipitates with c-Met and that this interaction is enhanced upon HGF stimulation in a manner that is dependent on the adaptor protein Gab1. Dock7 and Gab1 also co-immunoprecipitate in an HGF-dependent manner. Furthermore, Gab1 is required for HGF-induced Dock7 and Rac1 activation and glioblastoma cell invasion.

Conclusions:

Dock7 mediates HGF-induced GBM invasion. Targeting Dock7 in GBM may inhibit c-MET-mediated invasion in tumours treated with anti-angiogenic regimens.

Mcl-1 mediates TWEAK/Fn14-induced non-small cell lung cancer survival and therapeutic response

Insensitivity to standard clinical interventions, including chemotherapy, radiotherapy, and tyrosine kinase inhibitor (TKI) treatment, remains a substantial hindrance towards improving the prognosis of patients with non-small cell lung cancer (NSCLC). The molecular mechanism of therapeutic resistance remains poorly understood. The TNF-like weak inducer of apoptosis (TWEAK)-FGF-inducible 14 (TNFRSF12A/Fn14) signaling axis is known to promote cancer cell survival via NF-κB activation and the upregulation of prosurvival Bcl-2 family members. Here, a role was determined for TWEAK-Fn14 prosurvival signaling in NSCLC through the upregulation of myeloid cell leukemia sequence 1 (MCL1/Mcl-1). Mcl-1 expression significantly correlated with Fn14 expression, advanced NSCLC tumor stage, and poor patient prognosis in human primary NSCLC tumors. TWEAK stimulation of NSCLC cells induced NF-κB-dependent Mcl-1 protein expression and conferred Mcl-1-dependent chemo- and radioresistance. Depletion of Mcl-1 via siRNA or pharmacologic inhibition of Mcl-1, using EU-5148, sensitized TWEAK-treated NSCLC cells to cisplatin- or radiation-mediated inhibition of cell survival. Moreover, EU-5148 inhibited cell survival across a panel of NSCLC cell lines. In contrast, inhibition of Bcl-2/Bcl-xL function had minimal effect on suppressing TWEAK-induced cell survival. Collectively, these results position TWEAK-Fn14 signaling through Mcl-1 as a significant mechanism for NSCLC tumor cell survival and open new therapeutic avenues to abrogate the high mortality rate seen in NSCLC.

IMPLICATIONS

The TWEAK-Fn14 signaling axis enhances lung cancer cell survival and therapeutic resistance through Mcl-1, positioning both TWEAK-Fn14 and Mcl-1 as therapeutic opportunities in lung cancer.

Implications of Rho GTPase Signaling in Glioma Cell Invasion and Tumor Progression

Glioblastoma (GB) is the most malignant of primary adult brain tumors, characterized by a highly locally invasive cell population, as well as abundant proliferative cells, neoangiogenesis, and necrosis. Clinical intervention with chemotherapy or radiation may either promote or establish an environment for manifestation of invasive behavior. Understanding the molecular drivers of invasion in the context of glioma progression may be insightful in directing new treatments for patients with GB. Here, we review current knowledge on Rho family GTPases, their aberrant regulation in GB, and their effect on GB cell invasion and tumor progression. Rho GTPases are modulators of cell migration through effects on actin cytoskeleton rearrangement; in non-neoplastic tissue, expression and activation of Rho GTPases are normally under tight regulation. In GB, Rho GTPases are deregulated, often via hyperactivity or overexpression of their activators, Rho GEFs. Downstream effectors of Rho GTPases have been shown to promote invasiveness and, importantly, glioma cell survival. The study of aberrant Rho GTPase signaling in GB is thus an important investigation of cell invasion as well as treatment resistance and disease progression.