Loss of a FYN-regulated differentiation and growth arrest pathway in advanced stage neuroblastoma.

Tumor stage, age of patient, and amplification of MYCN predict disease outcome in neuroblastoma. To gain insight into the underlying molecular pathways, we have obtained expression profiles from 94 primary neuroblastoma specimens. Advanced tumor stages show a characteristic expression profile that includes downregulation of multiple genes involved in signal transduction through Fyn and the actin cytoskeleton. High expression of Fyn and high Fyn kinase activity are restricted to low-stage tumors. In culture, expression of active Fyn kinase induces differentiation and growth arrest of neuroblastoma cells. Expression of Fyn predicts long-term survival independently of MYCN amplification. Amplification of MYCN correlates with deregulation of a distinct set of genes, many of which are target genes of Myc. Our data demonstrate a causal role for Fyn kinase in the genesis of neuroblastoma.

Allosteric Inhibition of HER2 by Moesin-Mimicking Compounds Targets HER2-Positive Cancers and Brain Metastases.

Therapies targeting the tyrosine kinase receptor HER2 have significantly improved survival of patients with HER2+ cancer. However, both de novo and acquired resistance remain a challenge, particularly in the brain metastatic setting. Here we report that, unlike other HER tyrosine kinase receptors, HER2 possesses a binding motif in its cytosolic juxtamembrane region that allows interaction with members of the Ezrin/Radixin/Moesin (ERM) family. Under physiologic conditions, this interaction controls the localization of HER2 in ERM-enriched domains and stabilizes HER2 in a catalytically repressed state. In HER2+ breast cancers, low expression of Moesin correlated with increased HER2 expression. Restoring expression of ERM proteins in HER2+ breast cancer cells was sufficient to revert HER2 activation and inhibit HER2-dependent proliferation. A high-throughput assay recapitulating the HER2-ERM interaction allowed for screening of about 1,500 approved drugs. From this screen, we found Zuclopenthixol, an antipsychotic drug that behaved as a Moesin-mimicking compound, because it directly binds the juxtamembrane region of HER2 and specifically inhibits HER2 activation in HER2+ cancers, as well as activation of oncogenic mutated and truncated forms of HER2. Zuclopenthixol efficiently inhibited HER2+ breast tumor progression in vitro and in vivo and, more importantly, showed significant activity on HER2+ brain tumor progression. Collectively, these data reveal a novel class of allosteric HER2 inhibitors, increasing the number of approaches to consider for intervention on HER2+ breast cancers and brain metastases. SIGNIFICANCE: This study demonstrates the functional role of Moesin in maintaining HER2 in a catalytically repressed state and provides novel therapeutic approaches targeting HER2+ breast cancers and brain metastasis using Moesin-mimicking compounds.

Strength of Neisseria meningitidis binding to endothelial cells requires highly-ordered CD147/ß2-adrenoceptor clusters assembled by alpha-actinin-4.

Neisseria meningitidis (meningococcus) is an invasive bacterial pathogen that colonizes human vessels, causing thrombotic lesions and meningitis. Establishment of tight interactions with endothelial cells is crucial for meningococci to resist haemodynamic forces. Two endothelial receptors, CD147 and the ß2-adrenergic receptor (ß2AR), are sequentially engaged by meningococci to adhere and promote signalling events leading to vascular colonization, but their spatiotemporal coordination is unknown. Here we report that CD147 and ß2AR form constitutive hetero-oligomeric complexes. The scaffolding protein α-actinin-4 directly binds to the cytosolic tail of CD147 and governs the assembly of CD147-ß2AR complexes in highly ordered clusters at bacterial adhesion sites. This multimolecular assembly process increases the binding strength of meningococci to endothelial cells under shear stress, and creates molecular platforms for the elongation of membrane protrusions surrounding adherent bacteria. Thus, the specific organization of cellular receptors has major impacts on host-pathogen interaction.

Reactivation of mutant p53 by a one-hybrid adaptor protein.

The most frequent genetic alteration in cancer is a mutation of p53. In most cases, this leads to a sharp increase of the p53 protein levels but abolishes p53's function as an activator of transcription. To correct this defect, wild-type p53 is being reintroduced into tumor cells through gene therapy vectors, thereby inducing cell death. However, this effect is not necessarily specific for tumor cells. Furthermore, mutant p53 in tumor cells trans-dominantly impairs the function of wild-type p53. As an approach to overcome these obstacles, we have developed an adaptor protein that reactivates mutant p53 rather than stimulating transcription on its own. The DNA binding and tetramerizing portions of the p53-homologue p73 were fused to the oligomerization domain of p53. This chimera binds to the DNA of p53-responsive promoters through the p73-derived portions, and it binds to mutant p53 by the p53-derived oligomerization domain. Through this one-hybrid system, mutant p53 is re-enabled to activate transcription. When the adaptor was expressed in tumor cells that contain mutant p53, expression of p53-responsive genes was activated, and growth was inhibited. No such effects were observed in cells that contain wild-type p53 or no p53 at all. When the adaptor was expressed through an adenovirus vector, tumor cells containing mutant p53 were specifically induced to undergo apoptosis. This strategy can turn mutant p53 into an inhibitor of tumor cell growth and might enable gene therapy to eliminate cancer cells with specificity.

Pathogenic Neisseria meningitidis utilizes CD147 for vascular colonization.

Neisseria meningitidis is a cause of meningitis epidemics worldwide and of rapidly progressing fatal septic shock. A crucial step in the pathogenesis of invasive meningococcal infections is the adhesion of bloodborne meningococci to both peripheral and brain endothelia, leading to major vascular dysfunction. Initial adhesion of pathogenic strains to endothelial cells relies on meningococcal type IV pili, but the endothelial receptor for bacterial adhesion remains unknown. Here, we report that the immunoglobulin superfamily member CD147 (also called extracellular matrix metalloproteinase inducer (EMMPRIN) or Basigin) is a critical host receptor for the meningococcal pilus components PilE and PilV. Interfering with this interaction potently inhibited the primary attachment of meningococci to human endothelial cells in vitro and prevented colonization of vessels in human brain tissue explants ex vivo and in humanized mice in vivo. These findings establish the molecular events by which meningococci target human endothelia, and they open new perspectives for treatment and prevention of meningococcus-induced vascular dysfunctions.

C-myc activation impairs the NF-kappaB and the interferon response: implications for the pathogenesis of Burkitt's lymphoma.

Deregulation of the proto-oncogene c-myc is a key event in the pathogenesis of many tumors. A paradigm is the activation of the c-myc gene by chromosomal translocations in Burkitt lymphoma (BL). Despite expression of a restricted set of Epstein-Barr viral (EBV) antigens, BL cells are not recognized by antigen-specific cytotoxic T cells (CTLs) because of their inability to process and present HLA class I-restricted antigens. In contrast, cells of EBV-driven posttransplant lymphoproliferative disease (PTLD) are recognized and rejected by EBV-specific CTLs. It is not known whether the poor immunogenicity of BL cells is due to nonexpression of viral antigens, overexpression of c-myc, or both. To understand the basis for immune recognition and escape, we have compared the mRNA expression profiles of BL and EBV-immortalized cells (as PTLD model). Among the genes expressed at low level in BL cells, we have identified many genes involved in the NF-kappaB and interferon response that play a pivotal role in antigen presentation and immune recognition. Using a cell line in which EBNA2 and c-myc can be regulated at will, we show that c-MYC negatively regulates STAT1, the central player linking the Type-I and Type-II interferon response. Switching off c-myc expression leads to STAT1 induction through a direct and indirect mechanism involving induction of Type-I interferons. c-MYC thus masks an interferon-inducing activity in these cells. Our findings imply that immune escape of tumor cells is not only a matter of in vivo selection but may be additionally promoted by activation of a cellular oncogene.

Control of cell proliferation and growth by Myc proteins.

Myc proteins act as signal transducers that alter cell proliferation in dependence on signals from the extracellular environment. In normal cells, the expression of MYC genes is therefore under tight control by growth factor dependent signals. The enormous interest in the function of these proteins is motivated by the observation that the close control of MYC expression is disrupted in a large percentage of human tumors, leading to deregulated expression of Myc proteins. A large body of evidence shows that this deregulation is a major driving force of human tumorigenesis; in cells with deregulated Myc, proliferation often takes place in the complete absence of external stimuli. We will discuss current models to understand Myc function and also potential avenues to selectively interfere with the proliferation of Myc-transformed cells.

The ubiquitin ligase HectH9 regulates transcriptional activation by Myc and is essential for tumor cell proliferation.

The Myc oncoprotein forms a binary activating complex with its partner protein, Max, and a ternary repressive complex that, in addition to Max, contains the zinc finger protein Miz1. Here we show that the E3 ubiquitin ligase HectH9 ubiquitinates Myc in vivo and in vitro, forming a lysine 63-linked polyubiquitin chain. Miz1 inhibits this ubiquitination. HectH9-mediated ubiquitination of Myc is required for transactivation of multiple target genes, recruitment of the coactivator p300, and induction of cell proliferation by Myc. HectH9 is overexpressed in multiple human tumors and is essential for proliferation of a subset of tumor cells. Our results suggest that site-specific ubiquitination regulates the switch between an activating and a repressive state of the Myc protein, and they suggest a strategy to interfere with Myc function in vivo.