The phosphoinositide 3-kinase signaling pathway as a therapeutic target in grade IV brain tumors

Brain tumors comprise a wide variety of neoplasia classified according to their cellular origin and their morphological and histological characteristics. The transformed phenotype of brain tumor cells has been extensively studied in the past years, achieving a significant progress in our understanding of the molecular pathways leading to tumorigenesis. It has been reported that the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway is frequently altered in grade IV brain tumors resulting in uncontrolled cell growth, survival, proliferation, angiogenesis, and migration. This aberrant activation can be explained by oncogenic mutations in key components of the pathway or through abnormalities in its regulation. These alterations include overexpression and mutations of receptor tyrosine kinases (RTKs), mutations and deletions of the phosphatase and tensin homologue deleted on chromosome 10 (PTEN) tumor suppressor gene, encoding a lipid kinase that directly antagonized PI3K activity, and alterations in Ras signaling. Due to promising results of preclinical studies investigating the PI3K/AKT pathway in grade IV brain tumors like glioblastoma and medulloblastoma, the components of this pathway have emerged as promising therapeutic targets to treat these malignant brain tumors. Although an arsenal of small molecule inhibitors that target specific components of this signaling pathway is being developed, its successful application in the clinics remains a challenge. In this article we will review the molecular basis of the PI3K/AKT signaling pathway in malignant brain tumors, mainly focusing on glioblastoma and medulloblastoma, and we will further discuss the current status and potential of molecular targeted therapies.

Disruption of SIRPα signaling in macrophages eliminates human acute myeloid leukemia stem cells in xenografts

Although tumor surveillance by T and B lymphocytes is well studied, the role of innate immune cells, in particular macrophages, is less clear. Moreover, the existence of subclonal genetic and functional diversity in some human cancers such as leukemia underscores the importance of defining tumor surveillance mechanisms that effectively target the disease-sustaining cancer stem cells in addition to bulk cells. In this study, we report that leukemia stem cell function in xenotransplant models of acute myeloid leukemia (AML) depends on SIRPα-mediated inhibition of macrophages through engagement with its ligand CD47. We generated mice expressing SIRPα variants with differential ability to bind human CD47 and demonstrated that macrophage-mediated phagocytosis and clearance of AML stem cells depend on absent SIRPα signaling. We obtained independent confirmation of the genetic restriction observed in our mouse models by using SIRPα-Fc fusion protein to disrupt SIRPα-CD47 engagement. Treatment with SIRPα-Fc enhanced phagocytosis of AML cells by both mouse and human macrophages and impaired leukemic engraftment in mice. Importantly, SIRPα-Fc treatment did not significantly enhance phagocytosis of normal hematopoietic targets. These findings support the development of therapeutics that antagonize SIRPα signaling to enhance macrophage-mediated elimination of AML.

Cardiac tissue-restricted deletion of plakoglobin results in progressive cardiomyopathy and activation of {beta}-catenin signaling

Mutations in the plakoglobin (JUP) gene have been identified in arrhythmogenic right ventricular cardiomyopathy (ARVC) patients. However, the mechanisms underlying plakoglobin dysfunction involved in the pathogenesis of ARVC remain poorly understood. Plakoglobin is a component of both desmosomes and adherens junctions located at the intercalated disc (ICD) of cardiomyocytes, where it functions to link cadherins to the cytoskeleton. In addition, plakoglobin functions as a signaling protein via its ability to modulate the Wnt/beta-catenin signaling pathway. To investigate the role of plakoglobin in ARVC, we generated an inducible cardiorestricted knockout (CKO) of the plakoglobin gene in mice. Plakoglobin CKO mice exhibited progressive loss of cardiac myocytes, extensive inflammatory infiltration, fibrous tissue replacement, and cardiac dysfunction similar to those of ARVC patients. Desmosomal proteins from the ICD were decreased, consistent with altered desmosome ultrastructure in plakoglobin CKO hearts. Despite gap junction remodeling, plakoglobin CKO hearts were refractory to induced arrhythmias. Ablation of plakoglobin caused increase beta-catenin stabilization associated with activated AKT and inhibition of glycogen synthase kinase 3beta. Finally, beta-catenin/TCF transcriptional activity may contribute to the cardiac hypertrophy response in plakoglobin CKO mice. This novel model of ARVC demonstrates for the first time how plakoglobin affects beta-catenin activity in the heart and its implications for disease pathogenesis.

Lymphotoxin β receptor signaling promotes development of autoimmune pancreatitis

Little is known about the pathogenic mechanisms of autoimmune pancreatitis (AIP), an increasingly recognized, immune-mediated form of chronic pancreatitis. Current treatment options are limited and disease relapse is frequent. We investigated factors that contribute to the development of AIP and new therapeutic strategies.

RNA interference screening identifies a novel role for autocrine fibroblast growth factor signaling in neuroblastoma chemoresistance

Chemotherapeutic drug resistance is one of the major causes for treatment failure in high-risk neuroblastoma (NB), the most common extra cranial solid tumor in children. Poor prognosis is typically associated with MYCN amplification. Here, we utilized a loss-of-function kinome-wide RNA interference screen to identify genes that cause cisplatin sensitization. We identified fibroblast growth factor receptor 2 (FGFR2) as an important determinant of cisplatin resistance. Pharmacological inhibition of FGFR2 confirmed the importance of this kinase in NB chemoresistance. Silencing of FGFR2 sensitized NB cells to cisplatin-induced apoptosis, which was regulated by the downregulation of the anti-apoptotic proteins BCL2 and BCLX(L). Mechanistically, FGFR2 was shown to activate protein kinase C-δ to induce BCL2 expression. FGFR2, as well as the ligand fibroblast growth factor-2, were consistently expressed in primary NB and NB cell lines, indicating the presence of an autocrine loop. Expression analysis revealed that FGFR2 correlates with MYCN amplification and with advanced stage disease, demonstrating the clinical relevance of FGFR2 in NB. These findings suggest a novel role for FGFR2 in chemoresistance and provide a rational to combine pharmacological inhibitors against FGFR2 with chemotherapeutic agents for the treatment of NB.Oncogene advance online publication, 1 October 2012; doi:10.1038/onc.2012.416.

Molecular analysis of HER2 signaling in human breast cancer by functional protein pathway activation mapping

Targeting of the HER2 protein in human breast cancer represents a major advance in oncology but relies on measurements of total HER2 protein and not HER2 signaling network activation. We used reverse-phase protein microarrays (RPMA) to measure total and phosphorylated HER2 in the context of HER family signaling to understand correlations between phosphorylated and total levels of HER2 and downstream signaling activity.

Modulating CD27 signaling to treat cancer

CD27 signaling can either improve T-cell function or lead to T-cell dysfunction, depending on the duration and conditions of receptor ligation. Recent studies have shown that modulating the CD70-CD27 interaction is an attractive strategy to treat solid tumors and also to directly target leukemia stem cells.

CD27 signaling increases the frequency of regulatory T cells and promotes tumor growth

Signaling of the TNF receptor superfamily member CD27 activates costimulatory pathways to elicit T- and B-cell responses. CD27 signaling is regulated by the expression of its ligand CD70 on subsets of dendritic cells and lymphocytes. Here, we analyzed the role of the CD27-CD70 interaction in the immunologic control of solid tumors in Cd27-deficient mice. In tumor-bearing wild-type mice, the CD27-CD70 interaction increased the frequency of regulatory T cells (Tregs), reduced tumor-specific T-cell responses, increased angiogenesis, and promoted tumor growth. CD27 signaling reduced apoptosis of Tregs in vivo and induced CD4(+) effector T cells (Teffs) to produce interleukin-2, a key survival factor for Tregs. Consequently, the frequency of Tregs and growth of solid tumors were reduced in Cd27-deficient mice or in wild-type mice treated with monoclonal antibody to block CD27 signaling. Our findings, therefore, provide a novel mechanism by which the adaptive immune system enhances tumor growth and may offer an attractive strategy to treat solid tumors.

The ubiquitin ligase XIAP recruits LUBAC for NOD2 signaling in inflammation and innate immunity

Nucleotide-binding and oligomerization domain (NOD)-like receptors constitute a first line of defense against invading bacteria. X-linked Inhibitor of Apoptosis (XIAP) is implicated in the control of bacterial infections, and mutations in XIAP are causally linked to immunodeficiency in X-linked lymphoproliferative syndrome type-2 (XLP-2). Here, we demonstrate that the RING domain of XIAP is essential for NOD2 signaling and that XIAP contributes to exacerbation of inflammation-induced hepatitis in experimental mice. We find that XIAP ubiquitylates RIPK2 and recruits the linear ubiquitin chain assembly complex (LUBAC) to NOD2. We further show that LUBAC activity is required for efficient NF-κB activation and secretion of proinflammatory cytokines after NOD2 stimulation. Remarkably, XLP-2-derived XIAP variants have impaired ubiquitin ligase activity, fail to ubiquitylate RIPK2, and cannot facilitate NOD2 signaling. We conclude that XIAP and LUBAC constitute essential ubiquitin ligases in NOD2-mediated inflammatory signaling and propose that deregulation of NOD2 signaling contributes to XLP-2 pathogenesis.

Expression of antagonists of WNT and BMP signaling after non-rigid fixation of osteotomies

Delayed fracture healing and non-unions represent rare but severe complications in orthopedic surgery. Further knowledge on the mechanisms of the bone repair process and of the development of a pseudoarthrosis is essential to predict and prevent impaired healing of fractures. The present study aimed at elucidating differences in gene expression during the repair of rigidly and non-rigidly fixed osteotomies. For this purpose, the MouseFix™ and the FlexiPlate™ systems (AO Development Institute, Davos, CH), allowing the creation of well defined osteotomies in mouse femora, were employed. A time course following the healing process of the osteotomy was performed and bones and periimplant tissues were analyzed by high-resolution X-ray, MicroCT and by histology. For the assessment of gene expression, Low Density Arrays (LDA) were done. In animals with rigid fixation, X-ray and MicroCT revealed healing of the osteotomy within 3 weeks. Using the FlexiPlate™ system, the osteotomy was still visible by X-ray after 3 weeks and a stabilizing cartilaginous callus was formed. After 4.5 weeks, the callus was remodeled and the osteotomy was, on a histological level, healed. Gene expression studies revealed levels of transcripts encoding proteins associated with inflammatory processes not to be altered in tissues from bones with rigid and non-rigid fixation, respectively. Levels of transcripts encoding proteins of the extracellular matrix and essential for bone cell functions were not increased in the rigidly fixed group when compared to controls without osteotomy. In the FlexiPlate™ group, levels of transcripts encoding the same set of genes were significantly increased 3 weeks after surgery. Expression of transcripts encoding BMPs and BMP antagonists was increased after 3 weeks in repair tissues from bones fixed with FlexiPlate™, as were inhibitors of the WNT signaling pathways. Little changes only were detected in transcript levels of tissues from rigidly fixed bones. The data of the present study suggest that rigid fixation enables accelerated healing of an experimental osteotomy as compared to non-rigid fixation. The changes in the healing process after non-rigid fixation are accompanied by an increase in the levels of transcripts encoding inhibitors of osteogenic pathways and, probably as a consequence, by temporal changes in bone matrix synthesis.

The multifaceted roles of Eph/ephrin signaling in breast cancer

http://www.ncbi.nlm.nih.gov/pubmed/22568950

Interleukin-17 signaling in inflammatory, Kupffer cells, and hepatic stellate cells exacerbates liver fibrosis in mice

Interleukin (IL)-17 signaling has been implicated in lung and skin fibrosis. We examined the role of IL-17 signaling in the pathogenesis of liver fibrosis in mice.

Modulation of L-α-lysophosphatidylinositol/GPR55 mitogen-activated protein kinase (MAPK) signaling by cannabinoids

GPR55 is activated by l-α-lysophosphatidylinositol (LPI) but also by certain cannabinoids. In this study, we investigated the GPR55 pharmacology of various cannabinoids, including analogues of the CB1 receptor antagonist Rimonabant®, CB2 receptor agonists, and Cannabis sativa constituents. To test ERK1/2 phosphorylation, a primary downstream signaling pathway that conveys LPI-induced activation of GPR55, a high throughput system, was established using the AlphaScreen® SureFire® assay. Here, we show that CB1 receptor antagonists can act both as agonists alone and as inhibitors of LPI signaling under the same assay conditions. This study clarifies the controversy surrounding the GPR55-mediated actions of SR141716A; some reports indicate the compound to be an agonist and some report antagonism. In contrast, we report that the CB2 ligand GW405833 behaves as a partial agonist of GPR55 alone and enhances LPI signaling. GPR55 has been implicated in pain transmission, and thus our results suggest that this receptor may be responsible for some of the antinociceptive actions of certain CB2 receptor ligands. The phytocannabinoids Δ9-tetrahydrocannabivarin, cannabidivarin, and cannabigerovarin are also potent inhibitors of LPI. These Cannabis sativa constituents may represent novel therapeutics targeting GPR55.

Role of FGFRL1 and other FGF signaling proteins in early kidney development

The mammalian kidney develops from the ureteric bud and the metanephric mesenchyme. In mice, the ureteric bud invades the metanephric mesenchyme at day E10.5 and begins to branch. The tips of the ureteric bud induce the metanephric mesenchyme to condense and form the cap mesenchyme. Some cells of this cap mesenchyme undergo a mesenchymal-to-epithelial transition and differentiate into renal vesicles, which further develop into nephrons. The developing kidney expresses Fibroblast growth factor (Fgf)1, 7, 8, 9, 10, 12 and 20 and Fgf receptors Fgfr1 and Fgfr2. Fgf7 and Fgf10, mainly secreted by the metanephric mesenchyme, bind to Fgfr2b of the ureteric bud and induce branching. Fgfr1 and Fgfr2c are required for formation of the metanephric mesenchyme, however the two receptors can substitute for one another. Fgf8, secreted by renal vesicles, binds to Fgfr1 and supports survival of cells in the nascent nephrons. Fgf9 and Fgf20, expressed in the metanephric mesenchyme, are necessary to maintain survival of progenitor cells in the cortical region of the kidney. FgfrL1 is a novel member of the Fgfr family that lacks the intracellular tyrosine kinase domain. It is expressed in the ureteric bud and all nephrogenic structures. Targeted deletion of FgfrL1 leads to severe kidney dysgenesis due to the lack of renal vesicles. FgfrL1 is known to interact mainly with Fgf8. It is therefore conceivable that FgfrL1 restricts signaling of Fgf8 to the precise location of the nascent nephrons. It might also promote tight adhesion of cells in the condensed metanephric mesenchyme as required for the mesenchymal-to-epithelial transition.