Downregulation of Notch pathway by a gamma-secretase inhibitor attenuates AKT/mammalian target of rapamycin signaling and glucose uptake in an ERBB2 transgenic breast cancer model

Notch3 deletion regulates HIV-1 gene expression and systemic inflammation to ameliorate chronic kidney disease

Antiretroviral therapy (ART) has decreased HIV-1 associated morbidity. However, despite ART, immune cells remain latently infected and slowly release viral proteins, leading to chronic inflammation and HIV-1 associated comorbidities. New strategies are needed to target viral proteins and inflammation. We found activation of Notch3 in several renal cells of the HIV-1 mouse model (HIV-Tg26) and in patients with HIV associated Nephropathy. We hypothesized that targeting Notch3 activation constitutes an effective therapy for HIV-related chronic kidney diseases (HIV-CKD). We generated HIV-Tg26 mice with Notch3 knocked out (Tg-N3KO). Compared to HIV-Tg26 mice at 3 months, HIV-Tg-N3KO mice showed a marked reduction in renal injury, skin lesions and mortality rate. Bulk RNA sequencing revealed that N3KO not only reduced renal infiltrating cells but significantly reduced the expression of HIV genes. Moreover, Notch3 activated the HIV- promoter and induction of HIV-1 resulted in increased Notch3 activation indicating a feedback mechanism. Further, bone marrow derived macrophages (BMDMs) from HIV-Tg26 mice showed activation of Notch3 indicating systemic effects. Consistent with that, systemic levels of TNF-α, MCP-1 and other inflammatory chemokines and cytokines were reduced in Tg-N3KO mice. Thus, Notch3 inhibition/deletion has a dual therapeutic effect in HIV-CKD and may extend to other HIV-related pathologies.

Notch3 as a novel therapeutic target for the treatment of ADPKD by regulating cell proliferation and renal cyst development

Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenic kidney disease. Emerging research indicates that the Notch signaling pathway plays an indispensable role in the pathogenesis of numerous kidney diseases, including ADPKD. Herein, we identified that Notch3 but not other Notch receptors was overexpressed in renal tissues from mice with ADPKD and ADPKD patients. Inhibiting Notch3 with γ-secretase inhibitors, which block a proteolytic cleavage required for Notch3 activation, or shRNA knockdown of Notch3 significantly delayed renal cyst growth in vitro and in vivo. Subsequent mechanistic study elucidated that the cleaved intracellular domain of Notch3 (N3ICD) and Hes1 could bind to the PTEN promoter, leading to transcriptional inhibition of PTEN. This further activated the downstream PI3K-AKT-mTOR pathway and promoted renal epithelial cell proliferation. Overall, Notch3 was identified as a novel contributor to renal epithelial cell proliferation and cystogenesis in ADPKD. We envision that Notch3 represents a promising target for ADPKD treatment.

Role of PGC-1α in fiber type conversion in the palatopharyngeus muscle of OSA patients

Background

Obstructive sleep apnea (OSA) has a high incidence and is harmful to health. It is characterized by repeated collapse of the upper airway. However, the mechanism underlying upper airway collapse is unclear.

Methods

Patients with OSA and chronic tonsillitis were studied. Pathological changes in palatopharyngeus muscle were detected. The expression of peroxisome proliferator‐activated receptor‐γ co‐activator‐1α (PGC‐1α) and nuclear respiratory factor‐1 (NRF‐1) in muscles was detected by PCR and Western blotting. Immunofluorescence staining was used to detect the expression of type I and type II myofibril.

Results

The structure of the palatopharyngeus muscle was changed, and the expression of PGC‐1α and NRF‐1 was decreased in the OSA group compared with that in the control group. The expression of PGC‐1α, NRF‐1, and type I myofibril in C2C12 myoblasts was decreased by intermittent hypoxia exposure. The expression of type I myofibril was decreased when knocking down PGC‐1α.

Conclusion

OSA patients exhibited pathological damage in palatopharyngeus muscle. PGC‐1α was involved in the fiber type conversion in palatopharyngeus muscle caused by intermittent hypoxia.

Notch Signalling in Breast Development and Cancer

The Notch signalling pathway is a highly conserved developmental signalling pathway, with vital roles in determining cell fate during embryonic development and tissue homeostasis. Aberrant Notch signalling has been implicated in many disease pathologies, including cancer. In this review, we will outline the mechanism and regulation of the Notch signalling pathway. We will also outline the role Notch signalling plays in normal mammary gland development and how Notch signalling is implicated in breast cancer tumorigenesis and progression. We will cover how Notch signalling controls several different hallmarks of cancer within epithelial cells with sections focussed on its roles in proliferation, apoptosis, invasion, and metastasis. We will provide evidence for Notch signalling in the breast cancer stem cell phenotype, which also has implications for therapy resistance and disease relapse in breast cancer patients. Finally, we will summarise the developments in therapeutic targeting of Notch signalling, and the pros and cons of this approach for the treatment of breast cancer.

Gamma Secretase Inhibitors in Cancer: A Current Perspective on Clinical Performance

Gamma secretase inhibitors (GSIs), initially developed as Alzheimer's therapies, have been repurposed as anticancer agents given their inhibition of Notch receptor cleavage. The success of GSIs in preclinical models has been ascribed to induction of cancer stem-like cell differentiation and apoptosis, while also impairing epithelial-to-mesenchymal transition and sensitizing cells to traditional chemoradiotherapies. The promise of these agents has yet to be realized in the clinic, however, as GSIs have failed to demonstrate clinical benefit in most solid tumors with the notable exceptions of CNS malignancies and desmoid tumors. Disappointing clinical performance to date reflects important questions that remain to be answered. For example, what is the net impact of these agents on antitumor immune responses, and will they require concurrent targeting of tumor-intrinsic compensatory pathways? Addressing these limitations in our current understanding of GSI mechanisms will undoubtedly facilitate their rational incorporation into combinatorial strategies and provide a valuable tool with which to combat Notch-dependent cancers. In the present review, we provide a current understanding of GSI mechanisms, discuss clinical performance to date, and suggest areas for future investigation that might maximize the utility of these agents. IMPLICATIONS FOR PRACTICE: The performance of gamma secretase inhibitors (GSIs) in clinical trials generally has not reflected their encouraging performance in preclinical studies. This review provides a current perspective on the clinical performance of GSIs across various solid tumor types alongside putative mechanisms of antitumor activity. Through exploration of outstanding gaps in knowledge as well as reasons for success in certain cancer types, the authors identify areas for future investigation that will likely enable incorporation of GSIs into rational combinatorial strategies for superior tumor control and patient outcomes.

Unlocking the Secrets of Cancer Stem Cells with γ-Secretase Inhibitors: A Novel Anticancer Strategy

The dysregulation of Notch signaling is associated with a wide variety of different human cancers. Notch signaling activation mostly relies on the activity of the γ-secretase enzyme that cleaves the Notch receptors and releases the active intracellular domain. It is well-documented that γ-secretase inhibitors (GSIs) block the Notch activity, mainly by inhibiting the oncogenic activity of this pathway. To date, several GSIs have been introduced clinically for the treatment of various diseases, such as Alzheimer's disease and various cancers, and their impacts on Notch inhibition have been found to be promising. Therefore, GSIs are of great interest for cancer therapy. The objective of this review is to provide a systematic review of in vitro and in vivo studies for investigating the effect of GSIs on various cancer stem cells (CSCs), mainly by modulation of the Notch signaling pathway. Various scholarly electronic databases were searched and relevant studies published in the English language were collected up to February 2020. Herein, we conclude that GSIs can be potential candidates for CSC-targeting therapy. The outcome of our study also indicates that GSIs in combination with anticancer drugs have a greater inhibitory effect on CSCs.

Targeting Notch in oncology: the path forward

Notch signalling is involved in many aspects of cancer biology, including angiogenesis, tumour immunity and the maintenance of cancer stem-like cells. In addition, Notch can function as an oncogene and a tumour suppressor in different cancers and in different cell populations within the same tumour. Despite promising preclinical results and early-phase clinical trials, the goal of developing safe, effective, tumour-selective Notch-targeting agents for clinical use remains elusive. However, our continually improving understanding of Notch signalling in specific cancers, individual cancer cases and different cell populations, as well as crosstalk between pathways, is aiding the discovery and development of novel investigational Notch-targeted therapeutics.

Cancer Stem Cells, Quo Vadis? The Notch Signaling Pathway in Tumor Initiation and Progression

The Notch signaling pathway regulates cell proliferation, cytodifferentiation and cell fate decisions in both embryonic and adult life. Several aspects of stem cell maintenance are dependent from the functionality and fine tuning of the Notch pathway. In cancer, Notch is specifically involved in preserving self-renewal and amplification of cancer stem cells, supporting the formation, spread and recurrence of the tumor. As the function of Notch signaling is context dependent, we here provide an overview of its activity in a variety of tumors, focusing mostly on its role in the maintenance of the undifferentiated subset of cancer cells. Finally, we analyze the potential of molecules of the Notch pathway as diagnostic and therapeutic tools against the various cancers.

Silencing of CD133 inhibits GLUT1-mediated glucose transport through downregulation of the HER3/Akt/mTOR pathway in colon cancer

Cluster of differentiation 133 (CD133) is a transmembrane glycoprotein that has been reported as a marker of cancer stem cells or cancer-initiating cells in various cancers. However, its contribution to tumorigenesis and differentiation remains to be elucidated. To determine the role of CD133 in colon cancer, we silenced CD133 in human colon cancer cells. Silencing of CD133 results in decreased cell proliferation, survival, migration, invasion, and glucose transport. These effects are mediated by downregulation of the human epidermal growth factor receptor 3 (HER3)/Akt/mTOR signaling pathway, culminating in reduced expression of the glucose transporter GLUT1. We also confirm that the cellular phenotypes of CD133-silenced cells are mediated by GLUT1 downregulation. We conclude that CD133 is a potential tumor initiator that positively regulates GLUT1 expression through modulation of HER3/Akt/mTOR signaling.

Notch signaling in breast cancer: From pathway analysis to therapy

The Notch signaling pathway, which is highly conserved from sea urchins to humans, plays an important role in cell-differentiation, survival, proliferation, stem-cell renewal, and determining cell fate during development and morphogenesis. It is well established that signaling pathways are dysregulated in a wide-range of diseases, including human malignancies. Studies suggest that the dysregulation of the Notch pathway contributes to carcinogenesis, cancer stem cell renewal, angiogenesis, and chemo-resistance. Elevated levels of Notch receptors and ligands have been associated with cancer-progression and poor survival. Furthermore, the Notch signaling pathway regulates the transcriptional activity of key target genes through crosstalk with several other signaling pathways. Indeed, increasing evidence suggests that the Notch signaling pathway may serve as a therapeutic target for the treatment of several cancers, including breast cancer. Researchers have demonstrated the anti-tumor properties of Notch inhibitors in various cancer types. Currently, Notch inhibitors are being evaluated for anticancer efficacy in a number of clinical-trials. However, because there are multiple Notch receptors that can exhibit either oncogenic or tumor-suppressing roles in various cells, it is important that the Notch inhibitors are specific to particular receptors that are tumorigenic in nature. This review critically evaluates existing Notch inhibitory drugs and strategies and summarizes the previous discoveries, current understandings, and recent developments in support of Notch receptors as therapeutic targets in breast cancer.

LSD1 regulates Notch and PI3K/Akt/mTOR pathways through binding the promoter regions of Notch target genes in esophageal squamous cell carcinoma

Background: The aberrant activation of Lysine-specific demethylase 1(LSD1), Notch and PI3K/Akt/mTOR signaling pathways were frequently happened in many cancers, including esophageal squamous cell carcinoma (ESCC). However, the regulatory relationship between LSD1 and Notch as well as PI3K/Akt/mTOR pathways is still unclear. Purpose: This study aimed to explore the regulatory effects and mechanisms of LSD1 on Notch and PI3K/Akt/mTOR pathway in ESCC. Results: Firstly, we demonstrated that LSD1 and proteins in Notch and PI3K/Akt/mTOR pathway were expressed in ESCC cells. Secondly, inhibition of LSD1 by tranylcypromine (TCP) or shRNA could decrease the expressions of related proteins in Notch and PI3K/Akt/mTOR signaling pathways in ESCC cells. Finally, we found that LSD1 could bind to the promoter regions of Notch3, Hes1 and CR2, and the combinations between them were reduced by TCP in ESCC. Conclusion: Summarily, this study indicated that LSD1 might positively regulate Notch and PI3K/Akt/mTOR pathways through binding the promoter regions of related genes in Notch pathway in ESCC.

A novel triazole, NMK-T-057, induces autophagic cell death in breast cancer cells by inhibiting γ-secretase-mediated activation of Notch signaling

Notch signaling is reported to be deregulated in several malignancies, including breast, and the enzyme γ-secretase plays an important role in the activation and nuclear translocation of Notch intracellular domain (NICD). Hence, pharmacological inhibition of γ-secretase might lead to the subsequent inhibition of Notch signaling in cancer cells. In search of novel γ-secretase inhibitors (GSIs), we screened a series of triazole-based compounds for their potential to bind γ-secretase and observed that 3-(3'4',5'-trimethoxyphenyl)-5-(N-methyl-3'-indolyl)-1,2,4-triazole compound (also known as NMK-T-057) can bind to γ-secretase complex. Very interestingly, NMK-T-057 was found to inhibit proliferation, colony-forming ability, and motility in various breast cancer (BC) cells such as MDA-MB-231, MDA-MB-468, 4T1 (triple-negative cells), and MCF-7 (estrogen receptor (ER)/progesterone receptor (PR)-positive cell line) with negligible cytotoxicity against noncancerous cells (MCF-10A and peripheral blood mononuclear cells). Furthermore, significant induction of apoptosis and inhibition of epithelial-to-mesenchymal transition (EMT) and stemness were also observed in NMK-T-057-treated BC cells. The in silico study revealing the affinity of NMK-T-057 toward γ-secretase was further validated by a fluorescence-based γ-secretase activity assay, which confirmed inhibition of γ-secretase activity in NMK-T-057-treated BC cells. Interestingly, it was observed that NMK-T-057 induced significant autophagic responses in BC cells, which led to apoptosis. Moreover, NMK-T-057 was found to inhibit tumor progression in a 4T1-BALB/c mouse model. Hence, it may be concluded that NMK-T-057 could be a potential drug candidate against BC that can trigger autophagy-mediated cell death by inhibiting γ-secretase-mediated activation of Notch signaling.

Notch-1 Signaling Activation and Progesterone Receptor Expression in Ectopic Lesions of Women With Endometriosis

Context

Progesterone (P) resistance is a hallmark of endometriosis, but the underlying mechanism(s) for loss of P sensitivity leading to lesion establishment remains poorly understood.

Objective

To evaluate the association between Notch-1 signaling activation and P resistance in the progression of endometriosis.

Design

Case control study; archived formalin-fixed, paraffin-embedded tissues.

Setting

University hospitals (United States, Taiwan).

Patients

Women with endometriosis; human endometrial stromal cell line (HESC).

Intervention

Eutopic endometria (EU) and ectopic lesions (ECs) were collected from surgically diagnosed patients. Archived tissue sections of EU and ECs were identified. HESCs were treated with N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT) and valproic acid (VPA) to, respectively, suppress and induce Notch-1 activation.

Outcome Measures

Tissues were analyzed for Notch Intra-Cellular Domain 1 (NICD1) and progesterone receptor (PGR) protein expression by immunohistochemistry and for transcript levels of NICD1 target genes HES1, PGR, and PGR-B by quantitative reverse transcription polymerase chain reaction. DAPT- or VPA-treated HESCs with and without P cotreatment were evaluated for cell numbers and for PGR, HES1, and PGR target gene DKK1 transcript levels.

Results

Nuclear-localized stromal NICD1 protein levels were inversely associated with those of total PGR in EU and ECs. Stromal ECs displayed higher HES1 and lower total PGR and PGR-B transcript levels than EU. In HESCs, DAPT reduction of NICD1 decreased cell numbers and increased PGR transcript and nuclear PGR protein levels and, with P cotreatment, maintained P sensitivity. Conversely, VPA induction of NICD1 decreased PGR transcript levels and, with P cotreatment, abrogated P-induced DKK1 and maintained HES1 transcript levels.

Conclusions

Aberrant Notch-1 activation is associated with decreased PGR that contributes to P resistance in endometriosis.

Simultaneous blockade of interacting CK2 and EGFR pathways by tumor-targeting nanobioconjugates increases therapeutic efficacy against glioblastoma multiforme

Glioblastoma multiforme (GBM) remains the deadliest brain tumor in adults. GBM tumors are also notorious for drug and radiation resistance. To inhibit GBMs more effectively, polymalic acid-based blood-brain barrier crossing nanobioconjugates were synthesized that are delivered to the cytoplasm of cancer cells and specifically inhibit the master regulator serine/threonine protein kinase CK2 and the wild-type/mutated epidermal growth factor receptor (EGFR/EGFRvIII), which are overexpressed in gliomas according to The Cancer Genome Atlas (TCGA) GBM database. Two xenogeneic mouse models bearing intracranial human GBMs from cell lines LN229 and U87MG that expressed both CK2 and EGFR at different levels were used. Simultaneous knockdown of CK2α and EGFR/EGFRvIII suppressed their downstream prosurvival signaling. Treatment also markedly reduced the expression of programmed death-ligand 1 (PD-L1), a negative regulator of cytotoxic lymphocytes. Downregulation of CK2 and EGFR also caused deactivation of heat shock protein 90 (Hsp90) co-chaperone Cdc37, which may suppress the activity of key cellular kinases. Inhibition of either target was associated with downregulation of the other target as well, which may underlie the increased efficacy of the dual nanobioconjugate that is directed against both CK2 and EGFR. Importantly, the single nanodrugs, and especially the dual nanodrug, markedly suppressed the expression of the cancer stem cell markers c-Myc, CD133, and nestin, which could contribute to the efficacy of the treatments. In both tumor models, the nanobioconjugates significantly increased (up to 2-fold) animal survival compared with the PBS-treated control group. The versatile nanobioconjugates developed in this study, with the abilities of anti-cancer drug delivery across biobarriers and the inhibition of key tumor regulators, offer a promising nanotherapeutic approach to treat GBMs, and to potentially prevent drug resistance and retard the recurrence of brain tumors.

Identification of Keratin 19-Positive Cancer Stem Cells Associating Human Hepatocellular Carcinoma Using 18F-Fluorodeoxyglucose Positron Emission Tomography

Purpose: The current lack of tools for easy assessment of cancer stem cells (CSC) prevents the development of therapeutic strategies for hepatocellular carcinoma (HCC). We previously reported that keratin 19 (K19) is a novel HCC-CSC marker and that PET with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) is an effective method for predicting postoperative outcome in hepatocellular carcinoma. Herein, we examined whether K19⁺ HCC-CSCs can be tracked using ¹⁸F-FDG-PET.Experimental Design: K19 and glucose transporter-1 (GLUT1) expression was evaluated by IHC in 98 hepatocellular carcinoma patients who underwent ¹⁸F-FDG-PET scans before primary tumor resection. Standardized uptake values (SUV) for primary tumors and tumor-to-nontumor SUV ratios (TNR) were calculated using FDG accumulation levels, and values were compared among K19⁺/K19^- patients. Using hepatocellular carcinoma cell lines encoding with a K19 promoter-driven enhanced GFP, ¹⁸F-FDG uptake and GLUT1 expression were examined in FACS-isolated K19⁺/K19^- cells.Results: In hepatocellular carcinoma patients, K19 expression was significantly correlated with GLUT1 expression and FDG accumulation. ROC analyses revealed that among preoperative clinical factors, TNR was the most sensitive indicator of K19 expression in hepatocellular carcinoma tumors. In hepatocellular carcinoma cells, FACS-isolated K19⁺ cells displayed significantly higher ¹⁸F-FDG uptake than K19^- cells. Moreover, gain/loss-of-function experiments confirmed that K19 regulates ¹⁸F-FDG uptake through TGFβ/Smad signaling, including Sp1 and its downstream target GLUT1.Conclusions:¹⁸F-FDG-PET can be used to predict K19 expression in hepatocellular carcinoma and should thereby aid in the development of novel therapeutic strategies targeting K19⁺ HCC-CSCs. Clin Cancer Res; 23(6); 1450-60. ©2016 AACR.

Targeting Notch Signaling and Autophagy Increases Cytotoxicity in Glioblastoma Neurospheres

Glioblastomas are highly aggressive tumors that contain treatment resistant stem-like cells. Therapies targeting developmental pathways such as Notch eliminate many neoplastic glioma cells, including those with stem cell features, but their efficacy can be limited by various mechanisms. One potential avenue for chemotherapeutic resistance is the induction of autophagy, but little is known how it might modulate the response to Notch inhibitors. We used the γ-secretase inhibitor MRK003 to block Notch pathway activity in glioblastoma neurospheres and assessed its effects on autophagy. A dramatic, several fold increase of LC3B-II/LC3B-I autophagy marker was noted on western blots, along with the emergence of punctate LC3B immunostaining in cultured cells. By combining the late stage autophagy inhibitor chloroquine (CQ) with MRK003, a significant induction in apoptosis and reduction in growth was noted as compared to Notch inhibition alone. A similar beneficial effect on inhibition of cloogenicity in soft agar was seen using the combination treatment. These results demonstrated that pharmacological Notch blockade can induce protective autophagy in glioma neurospheres, resulting in chemoresistance, which can be abrogated by combination treatment with autophagy inhibitors.

Notch promotes recurrence of dormant tumor cells following HER2/neu-targeted therapy

Breast cancer mortality is principally due to recurrent tumors that arise from a reservoir of residual tumor cells that survive therapy. Remarkably, breast cancers can recur after extended periods of clinical remission, implying that at least some residual tumor cells pass through a dormant phase prior to relapse. Nevertheless, the mechanisms that contribute to breast cancer recurrence are poorly understood. Using a mouse model of recurrent mammary tumorigenesis in combination with bioinformatics analyses of breast cancer patients, we have identified a role for Notch signaling in mammary tumor dormancy and recurrence. Specifically, we found that Notch signaling is acutely upregulated in tumor cells following HER2/neu pathway inhibition, that Notch signaling remains activated in a subset of dormant residual tumor cells that persist following HER2/neu downregulation, that activation of Notch signaling accelerates tumor recurrence, and that inhibition of Notch signaling by either genetic or pharmacological approaches impairs recurrence in mice. Consistent with these findings, meta-analysis of microarray data from over 4,000 breast cancer patients revealed that elevated Notch pathway activity is independently associated with an increased rate of recurrence. Together, these results implicate Notch signaling in tumor recurrence from dormant residual tumor cells and provide evidence that dormancy is a targetable stage of breast cancer progression.

New targeted therapies for breast cancer: A focus on tumor microenvironmental signals and chemoresistant breast cancers

Breast cancer is the most frequent female malignancy worldwide. Current strategies in breast cancer therapy, including classical chemotherapy, hormone therapy, and targeted therapies, are usually associated with chemoresistance and serious adverse effects. Advances in our understanding of changes affecting the interactome in advanced and chemoresistant breast tumors have provided novel therapeutic targets, including, cyclin dependent kinases, mammalian target of rapamycin, Notch, Wnt and Shh. Inhibitors of these molecules recently entered clinical trials in mono- and combination therapy in metastatic and chemo-resistant breast cancers. Anticancer epigenetic drugs, mainly histone deacetylase inhibitors and DNA methyltransferase inhibitors, also entered clinical trials. Because of the complexity and heterogeneity of breast cancer, the future in therapy lies in the application of individualized tailored regimens. Emerging therapeutic targets and the implications for personalized-based therapy development in breast cancer are herein discussed.

Notch-EGFR/HER2 Bidirectional Crosstalk in Breast Cancer

The Notch pathway is a well-established mediator of cell-cell communication that plays a critical role in stem cell survival, self-renewal, cell fate decisions, tumorigenesis, invasion, metastasis, and drug resistance in a variety of cancers. An interesting form of crosstalk exists between the Notch receptor and the Epidermal Growth Factor Receptor Tyrosine Kinase family, which consists of HER-1, -2, -3, and -4. Overexpression of HER and/or Notch occurs in several human cancers including brain, lung, breast, ovary, and skin making them potent oncogenes capable of advancing malignant disease. Continued assessment of interplay between these two critical signaling networks uncovers new insight into mechanisms used by HER-driven cancer cells to exploit Notch as a compensatory pathway. The compensatory Notch pathway maintains HER-induced downstream signals transmitted to pathways such as Mitogen Activated Protein Kinase and Phosphatidylinositol 3-Kinase (PI3K), thereby allowing cancer cells to survive molecular targeted therapies, undergo epithelial to mesenchymal transitioning, and increase cellular invasion. Uncovering the critical crosstalk between the HER and Notch pathways can lead to improved screening for the expression of these oncogenes enabling patients to optimize their personal treatment options and predict potential treatment resistance. This review will focus on the current state of crosstalk between the HER and Notch receptors and the effectiveness of current therapies targeting HER-driven cancers.

Strong therapeutic potential of γ-secretase inhibitor MRK003 for CD44-high and CD133-low glioblastoma initiating cells

The Notch signal regulates both cell viability and apoptosis, and maintains stemness of various cancers including glioblastoma (GBM). Although Notch signal inhibition may be an effective strategy in treating GBM initiating cells (GICs), its applicability to the different subtypes of GBM remains unclear. Here, we analyzed the effectiveness of MRK003, a preclinical γ-secretase inhibitor, on GICs. Nine patient-derived GICs were treated by MRK003, and its efficacy on cell viability, apoptosis, sphere forming ability and Akt expression level which might be related to Notch downstream and be greatly important signals in GBM was evaluated. MRK003 suppressed viability and sphere-formation ability, and induced apoptosis in all GICs in varying doses of MRK003. Based on their sensitivities to MRK003, the nine GICs were divided into "relatively sensitive" and "relatively resistant" GICs. Sensitivity to MRK003 was associated with its inhibitory effect on Akt pathway. Transgenic expression of the myristoylated Akt vector in relatively sensitive GICs partially rescued the effect of MRK003, suggesting that the effect of MRK003 was, at least in part, mediated through inhibition of the Akt pathway. These GICs were differentiated by the expression of CD44 and CD133 with flow cytometric analysis. The relatively sensitive GICs are CD44-high and CD133-low. The IC50 of MRK003 in a set of GICs exhibited a negative correlation with CD44 and positive correlation with CD133. Collectively, MRK003 is partially mediated by the Akt pathway and has strong therapeutic potential for CD44-high and CD133-low GICs.

Knockdown of phosphodiesterase 4D inhibits nasopharyngeal carcinoma proliferation via the epidermal growth factor receptor signaling pathway

Phosphodiesterase 4D (PDE4D) is a subtype of metallohydrolases, and it has been reported that PDE4D functions as a proliferation promoting factor in certain types of cancer, including head and neck cancer. The present study first investigated the function of PDE4D in nasopharyngeal carcinoma (NPC). Western blot analysis was applied to detect PDE4D expression in NPC samples and cells. A lentiviral infection technique was used to stabilize the knockdown of PDE4D, which was subsequently examined in vitro and in vivo. The results showed that PDE4D was overexpressed in the NPC tissues and cells. Knockdown of PDE4D inhibited the growth of CNE2 and 5–8F, inducing cell cycle arrest in the G₀/G₁ phase in CNE2. These effects could be reversed by epidermal growth factor (EGF) stimulation. Furthermore, knockdown of PDE4D significantly inhibited the phosphorylation of epidermal growth factor receptor (EGFR) and AKT. The results were further validated in an NPC xenograft in nude mice. In conclusion, this study demonstrated that PDE4D may function as a proliferation promoting factor in NPC, by affecting the EGFR/PI3K/AKT signaling pathway. Therefore, the targeting of PDE4D may be a rational strategy in the treatment of NPC.

Signaling pathways in breast cancer: therapeutic targeting of the microenvironment

Breast cancer is the most common cancer in women worldwide. Understanding the biology of this malignant disease is a prerequisite for selecting an appropriate treatment. Cell cycle alterations are seen in many cancers, including breast cancer. Newly popular targeted agents in breast cancer include cyclin dependent kinase inhibitors (CDKIs) which are agents inhibiting the function of cyclin dependent kinases (CDKs) and agents targeting proto-oncogenic signaling pathways like Notch, Wnt, and SHH (Sonic hedgehog). CDKIs are categorized as selective and non-selective inhibitors of CDK. CDKIs have been tried as monotherapy and combination therapy. The CDKI Palbocyclib is now a promising therapeutic in breast cancer. This drug recently entered phase III trial for estrogen receptor (ER) positive breast cancer after showing encouraging results in progression free survival in a phase II trials. The tumor microenvironment is now recognized as a significant factor in cancer treatment response. The tumor microenvironment is increasingly considered as a target for combination therapy of breast cancer. Recent findings in the signaling pathways in breast cancer are herein summarized and discussed. Furthermore, the therapeutic targeting of the microenvironment in breast cancer is also considered.

The Notch pathway: a novel target for myocardial remodelling therapy?

Pathological ventricle remodelling, which follows a cardiac insult, causes heart failure. Despite the existence of multiple pharmaceutical approaches, heart failure is one of the leading causes of death worldwide and there is an urgent need to explore new therapeutic avenues. The Notch pathway is an evolutionary conserved fundamental pathway that regulates cell fate during development as well as throughout postnatal life in self-renewing tissues. In the myocardium, Notch signalling is involved in the modulation of cardiomyocytes survival, cardiac stem cells differentiation, and angiogenesis which are factors known to determine the extent of pathological cardiac remodelling. Modulation of the Notch pathway could become a tool to limit ventricle remodelling and the associated inexorable deterioration of cardiac performance.

Notch signaling regulates the phosphorylation of Akt and survival of lipopolysaccharide-activated macrophages via regulator of G protein signaling 19 (RGS19)

Macrophages play critical roles in innate immune defense by sensing microbes using pattern-recognition receptors. Lipopolysaccharide (LPS) stimulates macrophages via TLR, which leads to activation of downstream signaling cascades. In this study, we investigated the roles of a conserved signaling pathway, Notch signaling, in regulating the downstream signaling cascades of the LPS/TLR4 pathways in macrophages. Using a phospho-proteomic approach and a gamma-secretase inhibitor (GSI) to suppress the processing and activation of Notch signaling, we identified regulator of G protein signaling 19 (RGS19) as a target protein whose phosphorylation was affected by GSI treatment. RGS19 is a guanosine triphosphatase (GTPase)-activating protein that functions to negatively regulate G protein-coupled receptors via Gαi/Gαq-linked signaling. Stimulation of RAW264.7 cells with LPS increased the level of the phosphorylated form of RGS19, while LPS stimulation in the presence of GSI decreased its level. GSI treatment did not alter the mRNA level of rgs19. Treatment with GSI or silencing of rgs19 in macrophages impaired the phosphorylation of Akt Thr(308) upon LPS stimulation. Furthermore, targeted deletion of a DNA-binding protein and binding partner of the Notch receptor, RBP-Jκ/CSL, in macrophages resulted in delayed and decreased Akt phosphorylation. Because the PI3K/Akt pathway regulates cell survival in various cell types, the cell cycle and cell death were assayed upon GSI treatment, phosphatidylinositol 3 kinase (PI3K) inhibitor treatment or silencing of rgs19. GSI treatment resulted in decreased cell populations in the G1 and S phases, while it increased the cell population of cell death. Similarly, silencing of rgs19 resulted in a decreased cell population in the G1 phase and an increased cell population in the subG1 phase. Inhibition of Akt phosphorylation by PI3K inhibitor in LPS-stimulated macrophages increased cell population in G1 phase, suggesting a possible cell cycle arrest. Taken together, these results indicate that Notch signaling positively regulates phosphorylation of Akt, possibly via phosphorylation of RGS19, and inhibition of both molecules affects the cell survival and cell cycle of macrophages upon LPS stimulation.

The matricellular protein CCN3 regulates NOTCH1 signalling in chronic myeloid leukaemia

Deregulated NOTCH1 has been reported in lymphoid leukaemia, although its role in chronic myeloid leukaemia (CML) is not well established. We previously reported BCR-ABL down-regulation of a novel haematopoietic regulator, CCN3, in CML; CCN3 is a non-canonical NOTCH1 ligand. This study characterizes the NOTCH1–CCN3 signalling axis in CML. In K562 cells, BCR-ABL silencing reduced full-length NOTCH1 (NOTCH1-FL) and inhibited the cleavage of NOTCH1 intracellular domain (NOTCH1-ICD), resulting in decreased expression of the NOTCH1 targets c-MYC and HES1. K562 cells stably overexpressing CCN3 (K562/CCN3) or treated with recombinant CCN3 (rCCN3) showed a significant reduction in NOTCH1 signalling (> 50% reduction in NOTCH1-ICD, p < 0.05). Gamma secretase inhibitor (GSI), which blocks NOTCH1 signalling, reduced K562/CCN3 colony formation but increased that of K562/control cells. GSI combined with either rCCN3 or imatinib reduced K562 colony formation with enhanced reduction of NOTCH1 signalling observed with combination treatments. We demonstrate an oncogenic role for NOTCH1 in CML and suggest that BCR-ABL disruption of NOTCH1–CCN3 signalling contributes to the pathogenesis of CML.

Rheb GTPase regulates β-secretase levels and amyloid β generation

The β-site amyloid precursor protein (APP)-cleaving enzyme 1 (β-secretase, BACE1) initiates amyloidogenic processing of APP to generate amyloid β (Aβ), which is a hallmark of Alzheimer disease (AD) pathology. Cerebral levels of BACE1 are elevated in individuals with AD, but the molecular mechanisms are not completely understood. We demonstrate that Rheb GTPase (Ras homolog enriched in brain), which induces mammalian target of rapamycin (mTOR) activity, is a physiological regulator of BACE1 stability and activity. Rheb overexpression depletes BACE1 protein levels and reduces Aβ generation, whereas the RNAi knockdown of endogenous Rheb promotes BACE1 accumulation, and this effect by Rheb is independent of its mTOR signaling. Moreover, GTP-bound Rheb interacts with BACE1 and degrades it through proteasomal and lysosomal pathways. Finally, we demonstrate that Rheb levels are down-regulated in the AD brain, which is consistent with an increased BACE1 expression. Altogether, our study defines Rheb as a novel physiological regulator of BACE1 levels and Aβ generation, and the Rheb-BACE1 circuitry may have a role in brain biology and disease.

Pharmacologic inhibition of vacuolar H+ ATPase reduces physiologic and oncogenic Notch signaling

Notch signaling in prominently involved in growth regulation in metazoan tissues. Because of this, Notch is often upregulated in cancer and current efforts point to developing drugs that block its activation. Notch receptor endocytosis towards acidic compartments is a recently appreciated determinant of signaling activation. Vacuolar H+ ATPase (V‐ATPase) is responsible for acidification of endocytic organelles and mutants in V‐ATPase subunit encoding genes in model organisms have been recently shown to display loss of Notch signaling. Here, we show that administration of BafilomycinA1 (BafA1), a highly specific V‐ATPase inhibitor decreases Notch signaling during Drosophila and Zebrafish development, and in human cells in culture. In normal breast cells, we find that BafA1 treatment leads to accumulation of Notch in the endo‐lysosomal system, and reduces its processing and signaling activity. In Notch‐addicted breast cancer cells, BafA1 treatment reduces growth in cells expressing membrane tethered forms of Notch, while sparing cells expressing cytoplasmic forms. In contrast, we find that V‐ATPase inhibition reduces growth of leukemia cells, without affecting Notch activatory cleavage. However, consistent with the emerging roles of V‐ATPase in controlling multiple signaling pathways, in these cells Akt activation is reduced, as it is also the case in BafA1‐treated breast cancer cells. Our data support V‐ATPase inhibition as a novel therapeutic approach to counteract tumor growth via signaling pathways regulated at the endo‐lysosomal level.

V‐ATPase inhibition decreases Notch signaling during fly and fish development.

V‐ATPase inhibition reduces Notch signaling in normal and breast cancer cells.

V‐ATPase inhibition blocks degradation of membrane‐bound Notch forms.

V‐ATPase inhibition prevents Notch cleavage and nuclear translocation.

V‐ATPase inhibition reduces Akt signaling in breast cancer and T‐ALL cells.

Interplay between the Notch and PI3K/Akt pathways in high glucose-induced podocyte apoptosis

Podocyte apoptosis contributes to the pathogenesis of diabetic nephropathy (DN). However, the mechanisms that mediate high glucose (HG)-induced podocyte apoptosis remain poorly understood. Conditionally immortalized mouse podocytes were cultured in HG medium. A chemical inhibitor or a specific short-hairpin RNA (shRNA) vector was used to inhibit the activation of the Notch pathway and the PI3K/Akt pathway in HG-treated podocytes. Western blotting and real-time PCR were used to evaluate the levels of Notch, PI3K/Akt, and apoptotic pathway signaling. The apoptosis rate of HG-treated podocytes was assessed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling and annexin V/propidium iodide staining. In HG-treated podocytes, PI3K/Akt pathway activation prevented podocyte apoptosis in the early stage of HG stimulation and Notch pathway-induced podocyte apoptosis in the late stage of HG stimulation. The inhibition of the Notch pathway or the activation of the PI3K/Akt pathway prevented cell apoptosis in HG-treated podocytes. These findings suggest that the Notch and PI3K/Akt pathways may mediate HG-induced podocyte apoptosis.

Γ-secretase components as predictors of breast cancer outcome

γ-secretase is a large ubiquitously expressed protease complex composed of four core subunits: presenilin, Aph1, PEN-2, and nicastrin. The function of γ-secretase in the cells is to proteolytically cleave various proteins within their transmembrane domains. Presenilin and Aph1 occur as alternative variants belonging to mutually exclusive γ-secretase complexes and providing the complexes with heterogeneous biochemical and physiological properties. γ-secretase is proposed to have a role in the development and progression of cancer and γ-secretase inhibitors are intensively studied for their probable anti-tumor effects in various types of cancer models. Here, we for the first time determined mRNA expression levels of presenilin-1, presenilin-2, Aph1a, Aph1b, PEN-2, and nicastrin in a set of breast cancer tissue samples (N = 55) by quantitative real-time PCR in order to clarify the clinical significance of the expression of different γ-secretase complex components in breast cancer. We found a high positive correlation between the subunit expression levels implying a common regulation of transcription. Our univariate Kaplan-Meier survival analyses established low expression level of γ-secretase complex as a risk factor for breast cancer specific mortality. The tumors expressing low levels of γ-secretase complex were characterized by high histopathological tumor grade, low or no expression of estrogen and progesterone receptors and consequently high probability to fall into the class of triple negative breast cancer tumors. These results may provide novel tools to further categorize breast cancer tumors, especially the highly aggressive and poorly treatable breast cancer type of triple negative cases, and suggest a significant role for γ-secretase in breast cancer.

Regulation of angiogenesis via Notch signaling in breast cancer and cancer stem cells

Breast cancer angiogenesis is elicited and regulated by a number of factors including the Notch signaling. Notch receptors and ligands are expressed in breast cancer cells as well as in the stromal compartment and have been implicated in carcinogenesis. Signals exchanged between neighboring cells through the Notch pathway can amplify and consolidate molecular differences, which eventually dictate cell fates. Notch signaling and its crosstalk with many signaling pathways play an important role in breast cancer cell growth, migration, invasion, metastasis and angiogenesis, as well as cancer stem cell (CSC) self-renewal. Therefore, significant attention has been paid in recent years toward the development of clinically useful antagonists of Notch signaling. Better understanding of the structure, function and regulation of Notch intracellular signaling pathways, as well as its complex crosstalk with other oncogenic signals in breast cancer cells will be essential to ensure rational design and application of new combinatory therapeutic strategies. Novel opportunities have emerged from the discovery of Notch crosstalk with inflammatory and angiogenic cytokines and their links to CSCs. Combinatory treatments with drugs designed to prevent Notch oncogenic signal crosstalk may be advantageous over λ secretase inhibitors (GSIs) alone. In this review, we focus on the more recent advancements in our knowledge of aberrant Notch signaling contributing to breast cancer angiogenesis, as well as its crosstalk with other factors contributing to angiogenesis and CSCs.

Solute carriers (SLCs) in cancer

During tumor progression cells acquire an altered metabolism, either as a cause or as a consequence of an increased need of energy and nutrients. All four major classes of macromolecules are affected: carbohydrates, proteins, lipids and nucleic acids. As a result of the changed needs, solute carriers (SLCs) which are the major transporters of these molecules are differently expressed. This renders them important targets in the treatment of cancer. Blocking or activating SLCs is one possible therapeutic strategy. For example, some SLCs are upregulated in tumor cells due to the increased demand for energy and nutritional needs. Thus, blocking them and turning off the delivery of fuel or nutrients could be one way to interfere with tumor progression. Specific drug delivery to cancer cells via transporters is another approach. Some SLCs are also interesting as chemosensitizing targets because blocking or activating them may result in an altered response to chemotherapy. In this review we summarize the roles of SLCs in cancer therapy and specifically their potential as direct or indirect targets, as drug carriers or as chemosensitizing targets.

DAPT protects brain against cerebral ischemia by down-regulating the expression of Notch 1 and nuclear factor κB in rats

Gamma-secretase inhibitor, N-[N-(3,5-difluorophenacetyl)-1-alanyl]-S-phenylglycine t-butyl ester (DAPT) suppresses the activation of Notch 1 signaling, which is recognized as the cell fate signaling and may participate in inflammatory processes together with NF-κB pathway that contributes to the brain damage after stroke. DAPT has important pharmacological roles in many diseases. However, little is known about the effect of DAPT on NF-κB during cerebral ischemia. This study investigated the time course expression of Notch 1 and the effects of DAPT on Notch 1 and NF-jB after MCAO. The results showed that Notch 1 signaling was up-regulated at the early stage after MCAO, DAPT down-regulated the expression of Notch 1 and NF-κB and protected brain from damage caused by MCAO. These results may indicate that the downregulation of Notch 1–NF-κB pathway after ischemia by administration of DAPT is a potential mechanism for its protection.

Inhibition of Notch uncouples Akt activation from hepatic lipid accumulation by decreasing mTorc1 stability

Increased hepatic lipid content is an early correlate of insulin resistance, and can be caused by nutrient-induced mTor activation. The latter increases basal Akt activity, leading to a self-perpetuating lipogenic cycle. We have previously shown that the developmental Notch pathway has metabolic functions in adult liver. Acute or chronic inhibition of Notch dampens hepatic glucose production and increases Akt tone, and might therefore be predicted to increase hepatic lipid content. Surprisingly, we show that constitutive liver-specific ablation of Notch signaling, or its acute inhibition with a decoy Notch1 receptor, prevents hepatosteatosis by blocking mTorc1. Conversely, Notch gain-of-function causes fatty liver through constitutive activation of mTorc1, an effect reversible by rapamycin treatment. We demonstrate that Notch signaling increases mTorc1 complex stability, augmenting mTorc1 function and Srebp1c-mediated lipogenesis. The data identify Notch as a therapeutically actionable branch point of metabolic signaling, where hepatic Akt activation can be uncoupled from steatosis.

Prolonged inhibition of glioblastoma xenograft initiation and clonogenic growth following in vivo Notch blockade

PURPOSE

To examine the effects of clinically relevant pharmacologic Notch inhibition on glioblastoma xenografts.

EXPERIMENTAL DESIGN

Murine orthotopic xenografts generated from temozolomide-sensitive and -resistant glioblastoma neurosphere lines were treated with the γ-secretase inhibitor MRK003. Tumor growth was tracked by weekly imaging, and the effects on animal survival and tumor proliferation were assessed, along with the expression of Notch targets, stem cell, and differentiation markers, and the biology of neurospheres isolated from previously treated xenografts and controls.

RESULTS

Weekly MRK003 therapy resulted in significant reductions in growth as measured by imaging, as well as prolongation of survival. Microscopic examination confirmed a statistically significant reduction in cross-sectional tumor area and mitotic index in a MRK003-treated cohort as compared with controls. Expression of multiple Notch targets was reduced in the xenografts, along with neural stem/progenitor cell markers, whereas glial differentiation was induced. Neurospheres derived from MRK003-treated xenografts exhibited reduced clonogenicity and formed less aggressive secondary xenografts. Neurospheres isolated from treated xenografts remained sensitive to MRK003, suggesting that therapeutic resistance does not rapidly arise during in vivo Notch blockade.

CONCLUSIONS

Weekly oral delivery of MRK003 results in significant in vivo inhibition of Notch pathway activity, tumor growth, stem cell marker expression, and clonogenicity, providing preclinical support for the use of such compounds in patients with malignant brain tumors. Some of these effects can persist for some time after in vivo therapy is complete.

Genome-wide reprogramming of the chromatin landscape underlies endocrine therapy resistance in breast cancer

The estrogen receptor (ER)α drives growth in two-thirds of all breast cancers. Several targeted therapies, collectively termed endocrine therapy, impinge on estrogen-induced ERα activation to block tumor growth. However, half of ERα-positive breast cancers are tolerant or acquire resistance to endocrine therapy. We demonstrate that genome-wide reprogramming of the chromatin landscape, defined by epigenomic maps for regulatory elements or transcriptional activation and chromatin openness, underlies resistance to endocrine therapy. This annotation reveals endocrine therapy-response specific regulatory networks where NOTCH pathway is overactivated in resistant breast cancer cells, whereas classical ERα signaling is epigenetically disengaged. Blocking NOTCH signaling abrogates growth of resistant breast cancer cells. Its activation state in primary breast tumors is a prognostic factor of resistance in endocrine treated patients. Overall, our work demonstrates that chromatin landscape reprogramming underlies changes in regulatory networks driving endocrine therapy resistance in breast cancer.

Inhibition of Notch pathway attenuates the progression of human immunodeficiency virus-associated nephropathy

The Notch pathway is an evolutionarily conserved signaling cascade that is critical in kidney development and has also been shown to play a pathogenetic role in a variety of kidney diseases. We have previously shown that the Notch signaling pathway is activated in human immunodeficiency virus-associated nephropathy (HIVAN) as well as in a rat model of the disease. In this study, we examined Notch signaling in the well established Tg26 mouse model of HIVAN. Notch signaling components were distinctly upregulated in the kidneys of these mice as well as in immortalized podocytes derived from these mice. Notch1 and Notch4 were upregulated in the Tg26 glomeruli, and Notch4 was also expressed in tubules. Notch ligands Jagged1, Jagged2, Delta-like1, and Delta-like 4 were all upregulated in the tubules of Tg26 mice, but glomeruli showed minimal expression of Notch ligands. To examine a potential pathogenetic role for Notch in HIVAN, Tg26 mice were treated with GSIXX, a gamma secretase inhibitor that blocks Notch signaling. Strikingly, GSIXX treatment resulted in significant improvement in both histological kidney injury scores and renal function. GSIXX-treated Tg26 mice also showed diminished podocyte proliferation and dedifferentiation, cellular hallmarks of the disease. Moreover, GSIXX blocked podocyte proliferation in vitro induced by HIV proteins Nef and Tat. These studies suggest that Notch signaling can promote HIVAN progression and that Notch inhibition may be a viable treatment strategy for HIVAN.

Molecular dissection of AKT activation in lung cancer cell lines

AKT is a critical signaling node downstream of phosphoinositide 3-kinase (PI3K), which is often activated in cancer. We analyzed the state of activation of AKT in 80 human non-small cell lung carcinoma cell lines under serum starvation conditions. We identified 13 lines, which showed persistent AKT activation in the absence of serum. In 12 of 13 lines, AKT activation could be attributed to loss of PTEN, activating mutation in EGF receptor (EGFR) or PIK3CA, or amplification of ERBB2. HCC2429 was the only cell line that had no alterations in those genes, but had high phospho-AKT(Ser473) levels under serum starvation conditions. However, the activation of AKT in HCC2429 was PI3K- and mTOR complex 2 (mTORC2)-dependent based upon use of specific inhibitors. Kinome tyrosine phosphorylation profiling showed that both Notch and SRC were highly activated in this cell line. Despite the activation of Notch, AKT activation and cell survival were not affected by Notch inhibitors DAPT or compound E. In contrast, SRC inhibitors PP2 and dasatinib both significantly decreased pAKT(Ser473) levels and reduced cell survival by inducing apoptosis. Furthermore, a combination of SRC and mTOR inhibition synergistically blocked activation of AKT and induced apoptosis. Overexpression of SRC has been identified previously in human lung cancers, and these results suggest that a combination of SRC and mTOR inhibitors may have unique therapeutic benefit for a subset of lung cancers with these molecular features.

Evidence of mTOR Activation by an AKT-Independent Mechanism Provides Support for the Combined Treatment of PTEN-Deficient Prostate Tumors with mTOR and AKT Inhibitors

Activation of the phosphoinositide 3-kinase pathway is commonly observed in human prostate cancer. Loss of function of phosphatase and tensin homolog (PTEN) is associated with the activation of AKT and mammalian target of rapamycin (mTOR) in many cancer cell lines as well as in other model systems. However, activation of mTOR is also dependent of kinases other than AKT. Here, we show that activation of mTOR is not dependent on AKT in a prostate-specific PTEN-deficient mouse model of prostate cancer. Pathway bifurcation of AKT and mTOR was noted in both mouse and human prostate tumors. We demonstrated for the first time that cotargeting mTOR and AKT with ridaforolimus/MK-8669 and M1K-2206, respectively, delivers additive antitumor effects in vivo when compared to single agents. Our preclinical data suggest that the combination of AKT and mTOR inhibitors might be more effective in treating prostate cancer patients than current treatment regimens or either treatment alone.

Notch-mediated suppression of TSC2 expression regulates cell differentiation in the Drosophila intestinal stem cell lineage

Epithelial homeostasis in the posterior midgut of Drosophila is maintained by multipotent intestinal stem cells (ISCs). ISCs self-renew and produce enteroblasts (EBs) that differentiate into either enterocytes (ECs) or enteroendocrine cells (EEs) in response to differential Notch (N) activation. Various environmental and growth signals dynamically regulate ISC activity, but their integration with differentiation cues in the ISC lineage remains unclear. Here we identify Notch-mediated repression of Tuberous Sclerosis Complex 2 (TSC2) in EBs as a required step in the commitment of EBs into the EC fate. The TSC1/2 complex inhibits TOR signaling, acting as a tumor suppressor in vertebrates and regulating cell growth. We find that TSC2 is expressed highly in ISCs, where it maintains stem cell identity, and that N-mediated repression of TSC2 in EBs is required and sufficient to promote EC differentiation. Regulation of TSC/TOR activity by N signaling thus emerges as critical for maintenance and differentiation in somatic stem cell lineages.

Stem cells maintain tissue homeostasis in metazoans. A productive model to study the regulation of stem cell function is the Drosophila posterior midgut. Notch (N) signaling controls intestinal stem cell (ISC) differentiation in this tissue, while ISC proliferation is regulated by growth factor signaling pathways, including Insulin/IGF signaling (IIS). In this study, we explore the interaction between growth signals and N signaling in the control of ISC proliferation and differentiation. We show that TOR signaling, which promotes growth and can be activated by the IIS pathway, is maintained in ISCs in an inactive state by high expression of the TOR inhibitor TSC2. TSC2 expression shelters ISCs from nutritional cues, ensuring their long-term maintenance. In response to N pathway activation in enteroblasts (EB), the ISC daughter cells, TSC2 is transcriptionally repressed and TOR is activated. We demonstrate that this negative interaction between N and TSC2 is required and sufficient for differentiation of EBs into enterocytes (ECs), the absorptive cells of the epithelium. Our findings establish a critical role for TSC in ISC maintenance and provide a mechanism by which N promotes differentiation into the EC fate. The human homologue of TSC2 is an important tumor suppressor, and our study provides new insight into how its regulation controls regenerative processes.

Prioritising risk pathways of complex human diseases based on functional profiling

Analysis of the biological pathways involved in complex human diseases is an important step in elucidating the pathogenesis and mechanism of diseases. Most pathway analysis approaches identify disease-related biological pathways using overlapping genes between pathways and diseases. However, these approaches ignore the functional biological association between pathways and diseases. In this paper, we designed a novel computational framework for prioritising disease-risk pathways based on functional profiling. The disease gene set and biological pathways were translated into functional profiles in the context of GO annotations. We then implemented a semantic similarity measurement for calculating the concordance score between a functional profile of disease genes and a functional profile of pathways (FPP); the concordance score was then used to prioritise and infer disease-risk pathways. A freely accessible web toolkit, 'Functional Profiling-based Pathway Prioritisation' (FPPP), was developed (http://bioinfo.hrbmu.edu.cn/FPPP). During validation, our method successfully identified known disease-pathway pairs with area under the ROC curve (AUC) values of 96.73 and 95.02% in tests using both pathway randomisation and disease randomisation. A robustness analysis showed that FPPP is reliable even when using data containing noise. A case study based on a dilated cardiomyopathy data set indicated that the high-ranking pathways from FPPP are well known to be linked with this disease. Furthermore, we predicted the risk pathways of 413 diseases by using FPPP to build a disease similarity landscape that systematically reveals the global modular organisation of disease associations.

Arsenic trioxide inhibits cell growth and induces apoptosis through inactivation of notch signaling pathway in breast cancer

Arsenic trioxide has been reported to inhibit cell growth and induce apoptotic cell death in many human cancer cells including breast cancer. However, the precise molecular mechanisms underlying the anti-tumor activity of arsenic trioxide are still largely unknown. In the present study, we assessed the effects of arsenic trioxide on cell viability and apoptosis in breast cancer cells. For mechanistic studies, we used multiple cellular and molecular approaches such as MTT assay, apoptosis ELISA assay, gene transfection, RT-PCR, Western blotting, and invasion assays. For the first time, we found a significant reduction in cell viability in arsenic trioxide-treated cells in a dose-dependent manner, which was consistent with induction of apoptosis and also associated with down-regulation of Notch-1 and its target genes. Taken together, our findings provide evidence showing that the down-regulation of Notch-1 by arsenic trioxide could be an effective approach, to cause down-regulation of Bcl-2, and NF-κB, resulting in the inhibition of cell growth and invasion as well as induction of apoptosis. These results suggest that the anti-tumor activity of arsenic trioxide is in part mediated through a novel mechanism involving inactivation of Notch-1 and its target genes. We also suggest that arsenic trioxide could be further developed as a potential therapeutic agent for the treatment of breast cancer.

Targeting γ-secretase in breast cancer

γ-secretase complexes are multisubunit protease complexes that perform the intramembrane cleavage of more than 60 type-I transmembrane proteins, including Notch receptors. Since dysregulated Notch signaling has been implicated in the tumorigenesis and progression of breast cancer, small molecule γ-secretase inhibitors (GSIs) are being tested for their therapeutic potential in breast cancer treatment in several clinical trials. Here, the structure of γ-secretase complex and the development of GSIs are briefly reviewed, the roles of Notch and several other γ-secretase substrates in breast cancer are discussed, and the difference between γ-secretase inhibition and Notch inhibition, as well as the side effects associated with GSIs, are described. A better understanding of molecular mechanisms that affect the responsiveness of breast cancer to GSI might help to develop strategies to enhance the antitumor activity and, at the same time, alleviate the side effects of GSI.

γ-Secretase inhibitor enhances antitumour effect of radiation in Notch-expressing lung cancer

Background:

Notch receptor has an important role in both development and cancer. We previously reported that inhibition of the Notch3 by γ-secretase inhibitor (GSI) induces apoptosis and suppresses tumour proliferation in non-small-cell lung cancer. Although radiation is reported to induce Notch activation, little is known about the relationship between radiation and Notch pathway.

Methods:

We examined the effect of combining GSI and radiation at different dosing in three Notch expressing lung cancer cell lines. The cytotoxic effect of GSI and radiation was evaluated using MTT assay and clonogenic assay in vitro and xenograft models. Expressions of Notch pathway, mitogen-activated protein kinase (MAPK) pathway and Bcl-2 family proteins were investigated using western blot analysis.

Results:

We discovered that the antitumour effect of combining GSI and radiation was dependent on treatment schedule. γ-Secretase inhibitor administration after radiation had the greatest growth inhibition of lung cancer in vitro and in vivo. We showed that the combination induced apoptosis of lung cancer cell lines through the regulation of MAPK and Bcl-2 family proteins. Furthermore, activation of Notch after radiation was ameliorated by GSI administration, suggesting that treatment with GSI prevents Notch-induced radiation resistance.

Conclusion:

Notch has an important role in lung cancer. Treatment with GSI after radiation can significantly enhance radiation-mediated tumour cytotoxicity.

The BRAF V600E mutation in papillary thyroid carcinoma is associated with glucose transporter 1 overexpression

BACKGROUND

The glucose transporter 1 (GLUT1) is a key protein that facilitates the extensive glucose uptake of cancer cells, and its overexpression is associated with more aggressive tumor phenotypes. In cases of BRAF mutations, GLUT1 seems to be a target of the constitutive activation of the RAF/MEK/ERK pathway. In this study, we hypothesized that the common BRAF V600E mutation was associated with GLUT1 overexpression and proliferation in papillary thyroid carcinomas (PTCs).

METHODS

A total of 57 cases of paraffin-embedded PTC (31 BRAF V600E, 26 wild-type BRAF) were investigated using immunohistochemistry with antibodies against GLUT1 and Ki-67 (MK167) protein. The BRAF V600E mutations were detected using direct sequencing of genomic DNA that was isolated from formalin-fixed paraffin-embedded tumor tissues. GLUT1 expression was assessed using the Remmele immunoreactive score and subdivided into three groups (I=negative, II=weakly positive, and III=positive). The Ki-67 labeling index (Ki-67 LI) was determined by counting Ki-67-positive nuclei.

RESULTS

GLUT1 expression was found in 39/57 (68.4%) samples of PTC. The occurrence of the BRAF V600E genetic variant was significantly correlated with GLUT1 overexpression (p=0.007) and showed a trend toward higher proliferation, which was indicated by Ki-67 LI (p=0.06). Moreover, GLUT1 overexpression was positively associated with Ki-67 labeling (p=0.023).

CONCLUSIONS

The V600E BRAF mutation in PTC may contribute to the initiation of the glycolytic phenotype and confers growth advantages in cancer cells. Better understanding of the molecular mechanisms of cancer cell energy metabolism may lead to the implementation of targeted treatment modalities, which regulate cancer glucose uptake.