ALK receptor tyrosine kinase promotes cell growth and neurite outgrowth

A new look at the ALK gene in cancer: copy number gain and amplification

To date, ALK-rearrangement is a molecular target in several cancers, i.e. NSCLC. The dramatic benefits of crizotinib have prompted research into identifying other possible patients carrying ALK gene alterations with possible clinical significance. The ALK gene is involved not only in several rearrangements but also in other alterations such as amplification. ALK-amplification (ALK-A) is a common genetic event in several cancers, generally associated with poor outcome and more aggressive behaviour. Here we review the role of ALK-A in cancer as a prognostic and predictive biomarker. Furthermore, several critical issues regarding ALK-A in relation to; methods of detection, acquired resistance and ALK second generation inhibitors are analyzed. We conclude that ALK-A could be an intriguing alteration in the context of targeted therapy.

Augmentor α and β (FAM150) are ligands of the receptor tyrosine kinases ALK and LTK: Hierarchy and specificity of ligand-receptor interactions

Receptor tyrosine kinases (RTKs) are a class of cell surface receptors that, upon ligand binding, stimulate a variety of critical cellular functions. The orphan receptor anaplastic lymphoma kinase (ALK) is one of very few RTKs that remain without a firmly established protein ligand. Here we present a novel cytokine, FAM150B, which we propose naming augmentor-α (AUG-α), as a ligand for ALK. AUG-α binds ALK with high affinity and activates ALK in cells with subnanomolar potency. Detailed binding experiments using cells expressing ALK or the related receptor leukocyte tyrosine kinase (LTK) demonstrate that AUG-α binds and robustly activates both ALK and LTK. We show that the previously established LTK ligand FAM150A (AUG-β) is specific for LTK and only weakly binds to ALK. Furthermore, expression of AUG-α stimulates transformation of NIH/3T3 cells expressing ALK, induces IL-3 independent growth of Ba/F3 cells expressing ALK, and is expressed in neuroblastoma, a cancer partly driven by ALK. These experiments reveal the hierarchy and specificity of two cytokines as ligands for ALK and LTK and set the stage for elucidating their roles in development and disease states.

FAM150A and FAM150B are activating ligands for anaplastic lymphoma kinase

Aberrant activation of anaplastic lymphoma kinase (ALK) has been described in a range of human cancers, including non-small cell lung cancer and neuroblastoma (Hallberg and Palmer, 2013). Vertebrate ALK has been considered to be an orphan receptor and the identity of the ALK ligand(s) is a critical issue. Here we show that FAM150A and FAM150B are potent ligands for human ALK that bind to the extracellular domain of ALK and in addition to activation of wild-type ALK are able to drive 'superactivation' of activated ALK mutants from neuroblastoma. In conclusion, our data show that ALK is robustly activated by the FAM150A/B ligands and provide an opportunity to develop ALK-targeted therapies in situations where ALK is overexpressed/activated or mutated in the context of the full length receptor.

DOI:http://dx.doi.org/10.7554/eLife.09811.001

Cells have receptor proteins on their surface that enable them to detect changes in their environment and communicate with other cells. Signal molecules bind to a segment of the receptor called the extracellular domain that faces out from the cell. This can result in the activation of another domain in the receptor that is just inside the cell, which, in turn, activates signaling pathways that relay the information around the cell.

However, these communication systems are often disrupted in cancer cells. This helps the cells to override the strict growth controls imposed upon them by other (healthy) cells in the body. The gene that encodes a receptor protein called Anaplastic Lymphoma Kinase (or ALK for short) is often mutated in some types of human cancer so that the protein is always active. However, we still do not know what signal molecules bind to the ALK protein to activate it in normal cells.

Guan, Umapathy et al. used a variety of cell biology and biochemical techniques to study the role of ALK. The experiments show that when either of two proteins called FAM150A and FAM150B are produced in rat nerve cells alongside ALK, the nerve cells rapidly respond and form outgrowths. Experiments using cancer cells derived from human nerve cells also yielded similar results. Guan, Umapathy et al. found that the extracellular domain of ALK can physically interact with FAM150A and FAM150B.

The eyes of fruit flies that had been genetically modified to produce the human ALK protein alongside either FAM150A or FAM150B grew more than normal, giving the eyes an abnormal "rough" appearance. Further experiments showed that FAM150A and FAM150B are also able to increase the level of activation of an ALK mutant protein that is already active. Therefore, in future, the development of drugs that stop FAM150A and FAM150B from binding to ALK may be useful for treating cancers that are driven by high levels of ALK activity. Many challenging questions lie ahead to better understand how FAM150A and FAM150B interact with ALK.

DOI:http://dx.doi.org/10.7554/eLife.09811.002

Ethanol activates midkine and anaplastic lymphoma kinase signaling in neuroblastoma cells and in the brain

Alcohol engages signaling pathways in the brain. Midkine (MDK) is a neurotrophic factor that is over-expressed in the prefrontal cortex of alcoholics. MDK and one of its receptors, anaplastic lymphoma kinase (ALK), also regulate behavioral responses to ethanol in mice. The goal of this study was to determine whether MDK and ALK expression and signaling are activated by ethanol. We found that ethanol treatment of neuroblastoma cells increased MDK and ALK expression. We also assessed activation of ALK by ethanol in cells and found that ALK and ALK-dependent extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription 3 (STAT3) phosphorylation increased rapidly with ethanol exposure. Similarly, treatment of cells with recombinant MDK protein increased ALK, ERK and STAT3 phosphorylation, suggesting that ethanol may utilize MDK to activate ALK signaling. In support of this, transfection of cells with MDK siRNAs attenuated ALK signaling in response to ethanol. Ethanol also activates ERK signaling in the brain. We found that inhibition of ALK or knockout of MDK attenuated ethanol-induced ERK phosphorylation in mouse amygdala. These results demonstrate that ethanol engages MDK and ALK signaling, which has important consequences for alcohol-induced neurotoxicity and the regulation of behaviors related to alcohol abuse.

Understanding the Interplay between Expression, Mutation and Activity of ALK Receptor in Rhabdomyosarcoma Cells for Clinical Application of Small-Molecule Inhibitors

BACKGROUND

Receptor tyrosine kinases (RTKs) have a central role in cancer initiation and progression, since changes in their expression and activity potentially results in cell transformation. This concept is essential from a therapeutic standpoint, as clinical evidence indicates that tumours carrying deregulated RTKs are particularly susceptible to their activity but also to their inhibition. Rhabdomyosarcoma (RMS) is an aggressive childhood cancer where emerging therapies rely on the use kinase inhibitors, and among druggable kinases ALK represents a potential therapeutic target to commit efforts against. However, the functional relevance of ALK in RMS is not known, likewise the multi-component deregulated RTK profile to which ALK belongs.

METHODS

In this study we used RMS cell lines representative of the alveolar and embrional histotype and looked at ALK intracellular localization, activity and cell signalling.

RESULTS

We found that ALK was properly located at the plasma membrane of RMS cells, though in an unphosphorylated and inactive state due to intracellular tyrosine phosphatases (PTPases) activity. Indeed, increase of ALK phosphorylation was observed upon PTPase inhibition, as well as after ligand binding or protein overexpression. In these conditions, ALK signalling proceeded through the MAPK/ERK and PI3K/AKT pathways, and it was susceptible to ATP-competitive inhibitors exposure. However, drug-induced growth inhibition, cell cycle arrest and apoptosis did not correlate with ALK expression only, but relied also on the expression of other RTKs with akin drug binding affinity. Indeed, analysis of baseline and inducible RTK phosphorylation confirmed that RMS cells were susceptible to ALK kinase inhibitors even in the absence of the primary intended target, due to the presence of compensatory RTKs signalling pathways.

CONCLUSIONS

These data, hence, provided evidences of a potentially active role of ALK in RMS cells, but also suggest caution in considering ALK a major therapeutic target in this malignancy, particularly if expression and activity cannot be accurately determined.

Heparin is an activating ligand of the orphan receptor tyrosine kinase ALK

Anaplastic lymphoma kinase (ALK) is one of the few remaining "orphan" receptor tyrosine kinases (RTKs) in which the ligands are unknown. Ligand-mediated activation of RTKs is important throughout development. ALK is particularly relevant to the development of the nervous system. Increased activation of RTKs by mutation, genetic amplification, or signals from the stroma contributes to disease progression and acquired drug resistance in cancer. Aberrant activation of ALK occurs in subsets of lung adenocarcinoma, neuroblastoma, and other cancers. We found that heparin is a ligand that binds specifically to the ALK extracellular domain. Whereas heparins with short chain lengths bound to ALK in a monovalent manner and did not activate the receptor, longer heparin chains induced ALK dimerization and activation in cultured neuroblastoma cells. Heparin lacking N- and O-linked sulfate groups or other glycosaminoglycans with sulfation patterns different than heparin failed to activate ALK. Moreover, antibodies that bound to the extracellular domain of ALK interfered with heparin binding and prevented heparin-mediated activation of ALK. Thus, heparin and perhaps related glycosaminoglycans function as ligands for ALK, revealing a potential mechanism for the regulation of ALK activity in vivo and suggesting an approach for developing ALK-targeted therapies for cancer.

The Drosophila midkine/pleiotrophin homologues Miple1 and Miple2 affect adult lifespan but are dispensable for alk signaling during embryonic gut formation

Midkine (MDK) and Pleiotrophin (PTN) are small heparin-binding cytokines with closely related structures. The Drosophila genome harbours two genes encoding members of the MDK/PTN family of proteins, known as miple1 and miple2. We have investigated the role of Miple proteins in vivo, in particular with regard to their proposed role as ligands for the Alk receptor tyrosine kinase (RTK). Here we show that Miple proteins are neither required to drive Alk signaling during Drosophila embryogenesis, nor are they essential for development in the fruit fly. Additionally we show that neither MDK nor PTN can activate hALK in vivo when ectopically co-expressed in the fly. In conclusion, our data suggest that Alk is not activated by MDK/PTN related growth factors Miple1 and Miple 2 in vivo.

A spatial simulation approach to account for protein structure when identifying non-random somatic mutations

Background

Current research suggests that a small set of “driver” mutations are responsible for tumorigenesis while a larger body of “passenger” mutations occur in the tumor but do not progress the disease. Due to recent pharmacological successes in treating cancers caused by driver mutations, a variety of methodologies that attempt to identify such mutations have been developed. Based on the hypothesis that driver mutations tend to cluster in key regions of the protein, the development of cluster identification algorithms has become critical.

Results

We have developed a novel methodology, SpacePAC (Spatial Protein Amino acid Clustering), that identifies mutational clustering by considering the protein tertiary structure directly in 3D space. By combining the mutational data in the Catalogue of Somatic Mutations in Cancer (COSMIC) and the spatial information in the Protein Data Bank (PDB), SpacePAC is able to identify novel mutation clusters in many proteins such as FGFR3 and CHRM2. In addition, SpacePAC is better able to localize the most significant mutational hotspots as demonstrated in the cases of BRAF and ALK. The R package is available on Bioconductor at: http://www.bioconductor.org/packages/release/bioc/html/SpacePAC.html.

Conclusion

SpacePAC adds a valuable tool to the identification of mutational clusters while considering protein tertiary structure.

ALK-rearrangements and testing methods in non-small cell lung cancer: a review

The anaplastic lymphoma tyrosine kinase (ALK) gene was first described as a driver mutation in anaplastic non-Hodgkin's lymphoma. Dysregulated ALK expression is now an identified driver mutation in nearly twenty different human malignancies, including 4-9% of non-small cell lung cancers (NSCLC). The tyrosine kinase inhibitor crizotinib is more effective than standard chemotherapeutic agents in treating ALK positive NSCLC, making molecular diagnostic testing for dysregulated ALK expression a necessary step in identifying optimal treatment modalities. Here we review ALKmediated signal transduction pathways and compare the molecular protocols used to identify dysregulated ALK expression in NSCLC. We also discuss the use of crizotinib and second generation ALK tyrosine kinase inhibitors in the treatment of ALK positive NSCLC, and the known mechanisms of crizotinib resistance in NSCLC.

ALK gene copy number gain and its clinical significance in hepatocellular carcinoma

AIM: To examine the status and clinical significance of anaplastic lymphoma kinase (ALK) gene alterations in hepatocellular carcinoma (HCC) patients.

METHODS: A total of 213 cases of HCC were examined by fluorescent in situ hybridization using dual color break-apart ALK probes for the detection of chromosomal translocation and gene copy number gain. HCC tissue microarrays were constructed, and the correlation between the ALK status and clinicopathological variables was assessed by χ² test or Fisher’s exact test. Survival analysis was estimated using the Kaplan-Meier approach with a Log-rank test. Univariate and multivariate analyses of clinical variables were performed using the Cox proportional hazards regression model.

RESULTS: ALK gene translocation was not observed in any of the HCC cases included in the present study. ALK gene copy number gain (ALK/CNG) (≥ 4 copies/cell) was detected in 28 (13.15%) of the 213 HCC patients. The 3-year progression-free-survival (PFS) rate for ALK/CNG-positive HCC patients was significantly poorer than ALK/CNG-negative patients (27.3% vs 42.5%, P = 0.048), especially for patients with advanced stage III/IV (0% vs 33.5%, P = 0.007), and patients with grade III disease (24.8% vs 49.9%, P = 0.023). ALK/CNG-positive HCC patients had a significantly poorer prognosis than ALK/CNG-negative patients in the subgroup that was negative for serum hepatitis B virus DNA, with significantly different 3-year overall survival rates (18.2% vs 63.6%, P = 0.021) and PFS rates (18.2% vs 46.9%, P = 0.019). Multivariate Cox proportional hazards regression analysis suggested that ALK/CNG prevalence can predict death in HCC (HR = 1.596; 95%CI: 1.008-2.526, P = 0.046).

CONCLUSION: ALK/CNG, but not translocation of ALK, is present in HCC and may be an unfavorable prognostic predictor.

High ALK mRNA expression has a negative prognostic significance in rhabdomyosarcoma

Background:

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase aberrantly expressed in cancer, but its clinical and functional importance remain controversial. Mutation or amplification of ALK, as well as its expression levels assessed by conventional immunohistochemistry methods, has been linked to prognosis in cancer, although with potential bias because of the semi-quantitative approaches. Herein, we measured ALK mRNA expression in rhabdomyosarcoma (RMS) and determined its clinical impact on patients' stratification and outcome.

Methods:

Specimens were obtained from RMS patients and cell lines, and ALK expression was analysed by quantitative RT–PCR, western blotting, IHC, and copy number analysis.

Results:

High ALK mRNA expression was detected in the vast majority of PAX3/7-FOXO1-positive tumours, whereas PAX3/7-FOXO1-negative RMS displayed considerably lower amounts of both mRNA and protein. Notably, ALK mRNA distinguished unfavourable PAX3/7-FOXO1-positive tumours from PAX3/7-FOXO1-negative RMS (P<0.0001), and also correlated with larger tumour size (P<0.05) and advanced clinical stage (P<0.01), independently of fusion gene status. High ALK mRNA levels were of prognostic relevance by Cox univariate regression analysis and correlated with increased risk of relapse (P=0.001) and survival (P=0.01), whereas by multivariate analysis elevated ALK mRNA expression resulted a negative prognostic marker when clinical stage was not included.

Conclusion:

Quantitative assessment of ALK mRNA expression helps to improve risk stratification of RMS patients and identifies tumours with adverse biological characteristics and aggressive behaviour.

Mechanistic insight into ALK receptor tyrosine kinase in human cancer biology

The burgeoning field of anaplastic lymphoma kinase (ALK) in cancer encompasses many cancer types, from very rare cancers to the more prevalent non-small-cell lung cancer (NSCLC). The common activation of ALK has led to the use of the ALK tyrosine kinase inhibitor (TKI) crizotinib in a range of patient populations and to the rapid development of second-generation drugs targeting ALK. In this Review, we discuss our current understanding of ALK function in human cancer and the implications for tumour treatment.

New insights into the genetics of neuroblastoma

Neuroblastoma is a genetically and clinically heterogeneous tumor of childhood, arising from precursor cells of the sympathetic nervous system. It is still a challenging cancer for pediatric oncology, as some tumors will spontaneously regress, while others will become refractory to all forms of therapy. The clinical course of this disease is greatly influenced by both patient age and the genetic abnormalities that occur within the tumors. MYCN (v-myc myelocytomatosis viral related oncogene, neuroblastoma derived (avian)) amplification and loss of chromosome 11q heterozygosity have been known to be indicative of poor prognosis. In this article, we review how mutations and structural alterations in specific genes contribute to inheritable predisposition to neuroblastoma and/or to aggressive disease pathogenesis, as well as implications for diagnosis and therapy. These genes include PHOX2B (paired-like homeobox 2b), ALK (anaplastic lymphoma receptor tyrosine kinase), and ATRX (alpha thalassemia/mental retardation syndrome X-linked).

ALK amplification and protein expression predict inferior prognosis in neuroblastomas

BACKGROUND

ALK gene has been identified as a major neuroblastoma (NBL) predisposition gene. But ALK gene copy number and protein expression in ganglioneuroblastoma (GNBL) and ganglioneuroma (GN) are poorly described in the literature. Furthermore, there are controversies on the correlation between ALK protein expression and clinical outcome in NBL.

METHODS

We evaluated MYCN/ALK gene copy number by fluorescence in situ hybridization (FISH) and detected ALK protein expression by immunohistochemistry (IHC) in 188 NBL, 52 GNBL and 6 GN samples and analyzed their association with clinical outcome of the patients.

RESULTS

Although ALK gene copy number increase is a recurrent genetic aberration of neuroblastic tumors (NTs) (39.1%, 96/246), ALK amplification was only present in three NBLs (1.2%, 3/246). The frequency of ALK positivity in NBL (50.5%, 51/101) was significantly higher than in GNBL (22.6%, 7/31) and in GN (0.0%, 0/4) (P<0.05). In addition, ALK positivity also significantly correlates with MYCN/ALK gene copy number increases (P<0.05). Kaplan-Meier survival analysis indicated that MYCN/ALK amplification is correlated with decreased overall survival in NBL. A better prognosis trend was observed in patients with MYCN/ALK gain tumors compared with those with MYCN/ALK normal tumors. Furthermore, ALK positivity significantly correlated with inferior survival in NBL (P=0.044).

CONCLUSION

ALK positivity in NTs correlated with advanced tumor types and MYCN/ALK gene copy number increases. ALK positivity predicts inferior prognosis in NBL and IHC is a simplified strategy to screen ALK positivity in clinical practice.

Neuroblastoma: developmental biology, cancer genomics and immunotherapy

Neuroblastoma is a solid tumour that arises from the developing sympathetic nervous system. Over the past decade, our understanding of this disease has advanced tremendously. The future challenge is to apply the knowledge gained to developing risk-based therapies and, ultimately, improving outcome. In this Review we discuss the key discoveries in the developmental biology, molecular genetics and immunology of neuroblastoma, as well as new translational tools for bringing these promising scientific advances into the clinic.

Amplification but not translocation of anaplastic lymphoma kinase is a frequent event in oesophageal cancer

INTRODUCTION

Translocations of anaplastic lymphoma kinase (ALK) to various fusions partners and formation of oncogenic fusions proteins have been demonstrated in a variety of human malignancies. These fusion-proteins are potential pharmaceutically targets. Aim of this study was to investigate ALK gene status in a large cohort of squamous cell carcinoma (SCC) and adenocarcinoma (AC) of the oesophagus.

MATERIALS AND METHODS

117 SCCs and 136 ACs were included into this study. ALK and EML4 gene status were evaluated by fluorescence in situ hybridisation (FISH) using a triple colour break apart single fusion probe and a probe against 2p11. ALK and EML4 protein expression was determined by immunohistochemistry. Data on expression of ALK downstream effector tyrosine-705 phosphorylated STAT3 (pSTAT3) were available from a previous study.

RESULTS

FISH was performed successfully in 251 cases. All cases were negative for ALK translocations, while 14/135 (12.1%) of SCCs and 14/116 (10.4%) of ACs showed ALK amplifications. Concomitant EML4 amplifications were present in 27/28 cases with ALK amplifications. Three cases (two SCC, one with additional ALK &EML4 amplification and one AC) showed EML4 translocations not involving ALK. None of the tumours with ALK amplification showed ALK protein expression, and no correlation with clinical parameters, survival or pSTAT3 expression was observed.

CONCLUSIONS

While ALK translocations are not present in oesophageal cancer, ALK amplifications are common events with comparable rates in SCC and AC. Since ALK amplified breast cancer cells were shown to respond to ALK inhibitors, ALK amplified oesophageal cancers might be considered as possible candidates for therapies targeting ALK.

Understanding cytokine and growth factor receptor activation mechanisms

Our understanding of the detailed mechanism of action of cytokine and growth factor receptors - and particularly our quantitative understanding of the link between structure, mechanism and function - lags significantly behind our knowledge of comparable functional protein classes such as enzymes, G protein-coupled receptors, and ion channels. In particular, it remains controversial whether such receptors are activated by a mechanism of ligand-induced oligomerization, versus a mechanism in which the ligand binds to a pre-associated receptor dimer or oligomer that becomes activated through subsequent conformational rearrangement. A major limitation to progress has been the relative paucity of methods for performing quantitative mechanistic experiments on unmodified receptors expressed at endogenous levels on live cells. In this article, we review the current state of knowledge on the activation mechanisms of cytokine and growth factor receptors, critically evaluate the evidence for and against the different proposed mechanisms, and highlight other key questions that remain unanswered. New approaches and techniques have led to rapid recent progress in this area, and the field is poised for major advances in the coming years which promise to revolutionize our understanding of this large and biologically and medically important class of receptors.

Crizotinib for the treatment of ALK-rearranged non-small cell lung cancer: a success story to usher in the second decade of molecular targeted therapy in oncology

Crizotinib, an ALK/MET/ROS1 inhibitor, was approved by the U.S. Food and Drug Administration for the treatment of anaplastic lymphoma kinase (ALK)-rearranged non-small cell lung cancer (NSCLC) in August 2011, merely 4 years after the first publication of ALK-rearranged NSCLC. The crizotinib approval was accompanied by the simultaneous approval of an ALK companion diagnostic fluorescent in situ hybridization assay for the detection of ALK-rearranged NSCLC. Crizotinib continued to be developed as an ALK and MET inhibitor in other tumor types driven by alteration in ALK and MET. Crizotinib has recently been shown to be an effective ROS1 inhibitor in ROS1-rearranged NSCLC, with potential future clinical applications in ROS1-rearranged tumors. Here we summarize the heterogeneity within the ALK- and ROS1-rearranged molecular subtypes of NSCLC. We review the past and future clinical development of crizotinib for ALK-rearranged NSCLC and the diagnostic assays to detect ALK-rearranged NSCLC. We highlight how the success of crizotinib has changed the paradigm of future drug development for targeted therapies by targeting a molecular-defined subtype of NSCLC despite its rarity and affected the practice of personalized medicine in oncology, emphasizing close collaboration between clinical oncologists, pathologists, and translational scientists.

NPM-ALK: The Prototypic Member of a Family of Oncogenic Fusion Tyrosine Kinases

Anaplastic lymphoma kinase (ALK) was first identified in 1994 with the discovery that the gene encoding for this kinase was involved in the t(2;5)(p23;q35) chromosomal translocation observed in a subset of anaplastic large cell lymphoma (ALCL). The NPM-ALK fusion protein generated by this translocation is a constitutively active tyrosine kinase, and much research has focused on characterizing the signalling pathways and cellular activities this oncoprotein regulates in ALCL. We now know about the existence of nearly 20 distinct ALK translocation partners, and the fusion proteins resulting from these translocations play a critical role in the pathogenesis of a variety of cancers including subsets of large B-cell lymphomas, nonsmall cell lung carcinomas, and inflammatory myofibroblastic tumours. Moreover, the inhibition of ALK has been shown to be an effective treatment strategy in some of these malignancies. In this paper we will highlight malignancies where ALK translocations have been identified and discuss why ALK fusion proteins are constitutively active tyrosine kinases. Finally, using ALCL as an example, we will examine three key signalling pathways activated by NPM-ALK that contribute to proliferation and survival in ALCL.

Internalization and down-regulation of the ALK receptor in neuroblastoma cell lines upon monoclonal antibodies treatment

Recently, activating mutations of the full length ALK receptor, with two hot spots at positions F1174 and R1275, have been characterized in sporadic cases of neuroblastoma. Here, we report similar basal patterns of ALK phosphorylation between the neuroblastoma IMR-32 cell line, which expresses only the wild-type receptor (ALK^WT), and the SH-SY5Y cell line, which exhibits a heterozygous ALK F1174L mutation and expresses both ALK^WT and ALK^F1174L receptors. We demonstrate that this lack of detectable increased phosphorylation in SH-SY5Y cells is a result of intracellular retention and proteasomal degradation of the mutated receptor. As a consequence, in SH-SY5Y cells, plasma membrane appears strongly enriched for ALK^WT whereas both ALK^WT and ALK^F1174L were present in intracellular compartments. We further explored ALK receptor trafficking by investigating the effect of agonist and antagonist mAb (monoclonal antibodies) on ALK internalization and down-regulation, either in SH-SY5Y cells or in cells expressing only ALK^WT. We observe that treatment with agonist mAbs resulted in ALK internalization and lysosomal targeting for receptor degradation. In contrast, antagonist mAb induced ALK internalization and recycling to the plasma membrane. Importantly, we correlate this differential trafficking of ALK in response to mAb with the recruitment of the ubiquitin ligase Cbl and ALK ubiquitylation only after agonist stimulation. This study provides novel insights into the mechanisms regulating ALK trafficking and degradation, showing that various ALK receptor pools are regulated by proteasome or lysosome pathways according to their intracellular localization.

Activating ALK mutations found in neuroblastoma are inhibited by Crizotinib and NVP-TAE684

Mutations in the kinase domain of ALK (anaplastic lymphoma kinase) have recently been shown to be important for the progression of the childhood tumour neuroblastoma. In the present study we investigate six of the putative reported constitutively active ALK mutations, in positions G1128A, I1171N, F1174L, R1192P, F1245C and R1275Q. Our analyses were performed in cell-culture-based systems with both mouse and human ALK mutant variants and subsequently in a Drosophila melanogaster model system. Our investigation addressed the transforming potential of the putative gain-of-function ALK mutations as well as their signalling potential and the ability of two ATP-competitive inhibitors, Crizotinib (PF-02341066) and NVP-TAE684, to abrogate the activity of ALK. The results of the present study indicate that all mutations tested are of an activating nature and thus are implicated in tumour initiation or progression of neuroblastoma. Importantly for neuroblastoma patients, all ALK mutations used in the present study can be blocked by the inhibitors, although some mutants exhibited higher levels of drug sensitivity than others.

High anaplastic lymphoma kinase immunohistochemical staining in neuroblastoma and ganglioneuroblastoma is an independent predictor of poor outcome

Anaplastic lymphoma kinase (ALK) mutations occur in 3% to 11% of neuroblastoma (NBL) cases and are associated with high ALK levels. However, high ALK levels appear to be a mutation-independent hallmark of NBL. Evidence about the prognostic relevance of ALK mutations and ALK tumor positivity in patients with NBL has been inconclusive. In this study, we investigated the prognostic relevance of ALK positivity by IHC and ALK mutation status by PCR sequencing in 71 NBL, 12 ganglioneuroblastoma (GNBL), and 20 ganglioneuroma samples in a multivariate model. ALK mutations were present in 2 of 72 NBL and 2 of 12 GNBL samples, which all contained many ALK-positive cells (>50%). In addition, half of all NBL samples showed ALK positivity in most (>50%) of tumor cells, whereas half of the GNBL showed staining in <20% of the tumor cells. In most ganglioneuroma samples, a low percentage of tumor cells stained positive for ALK, which mainly involved ganglion cells. Higher percentages of ALK-positive cells in NBL and GNBL patient samples correlated with inferior survival in univariate and multivariate analyses with established prognostic factors, such as stage, age, and MYCN status. In conclusion, ALK positivity by IHC is an independent, poor prognostic factor in patients with GNBL and NBL. ALK IHC is an easy test suitable for future risk stratification in patients with NBL and GNBL.

Neuroblastoma therapy: what is in the pipeline?

Despite the expansion of knowledge about neuroblastoma (NB) in recent years, the therapeutic outcome for children with a high-risk NB has not significantly improved. Therefore, more effective therapies are needed. This might be achieved by aiming future efforts at recently proposed but not yet developed targets for NB therapy. In this review, we discuss the recently proposed molecular targets that are in clinical trials and, in particular, those that are not yet explored in the clinic. We focus on the selection of these molecular targets for which promising in vitro and in vivo results have been obtained by silencing/inhibiting them. In addition, these selected targets are involved at least in one of the NB tumorigenic processes: proliferation, anti-apoptosis, angiogenesis and/or metastasis. In particular, we will review a recently proposed target, the microtubule-associated proteins (MAPs) encoded by doublecortin-like kinase gene (DCLK1). DCLK1-derived MAPs are crucial for proliferation and survival of neuroblasts and are highly expressed not only in NB but also in other tumours such as gliomas. Additionally, we will discuss neuropeptide Y, its Y2 receptor and cathepsin L as examples of targets to decrease angiogenesis and metastasis of NB. Furthermore, we will review the micro-RNAs that have been proposed as therapeutic targets for NB. Detailed investigation of these not yet developed targets as well as exploration of multi-target approaches might be the key to a more effective NB therapy, i.e. increasing specificity, reducing toxicity and avoiding long-term side effects.

Alk is a transcriptional target of LMO4 and ERα that promotes cocaine sensitization and reward

Previously, we showed that the mouse LIM-domain only 4 (Lmo4) gene, which encodes a protein containing two zinc-finger LIM domains that interact with various DNA-binding transcription factors, attenuates behavioral sensitivity to repeated cocaine administration. Here we show that transcription of anaplastic lymphoma kinase (Alk) is repressed by LMO4 in the striatum and that Alk promotes the development of cocaine sensitization and conditioned place preference, a measure of cocaine reward. Since LMO4 is known to interact with estrogen receptor α (ERα) at the promoters of target genes, we investigated whether Alk expression might be controlled by a similar mechanism. We found that LMO4 and ERα are associated with the Alk promoter by chromatin immunoprecipitation and that Alk is an estrogen-responsive gene in the striatum. Moreover, we show that ERα knock-out mice exhibit enhanced cocaine sensitization and conditioned place preference and an increase in Alk expression in the nucleus accumbens. These data define a novel regulatory network involved in behavioral responses to cocaine. Interestingly, sex differences in several behavioral responses to cocaine in humans and rodents have been described, and estrogen is thought to mediate some of these differences. Our data suggest that estrogen regulation of Alk may be one mechanism responsible for sexually dimorphic responses to cocaine.

Emerging importance of ALK in neuroblastoma

Since the original descriptions of gain-of function mutations in anaplastic lymphoma kinase (ALK), interest in the role of this receptor tyrosine kinase in neuroblastoma development and as a potential therapeutic target has escalated. As a group, the activating point mutations in full-length ALK, found in approximately 8% of all neuroblastoma tumors, are distributed evenly across different clinical stages. However, the most frequent somatic mutation, F1174L, is associated with amplification of the MYCN oncogene. This combination of features appears to confer a worse prognosis than MYCN amplification alone, suggesting a cooperative effect on neuroblastoma formation by these two proteins. Indeed, F1174L has shown more potent transforming activity in vivo than the second most common activating mutation, R1275Q, and is responsible for innate and acquired resistance to crizotinib, a clinically relevant ALK inhibitor that will soon be commercially available. These advances cast ALK as a bona fide oncoprotein in neuroblastoma and emphasize the need to understand ALK-mediated signaling in this tumor. This review addresses many of the current issues surrounding the role of ALK in normal development and neuroblastoma pathogenesis, and discusses the prospects for clinically effective targeted treatments based on ALK inhibition.

An evolutionary conserved role for anaplastic lymphoma kinase in behavioral responses to ethanol

Anaplastic lymphoma kinase (Alk) is a gene expressed in the nervous system that encodes a receptor tyrosine kinase commonly known for its oncogenic function in various human cancers. We have determined that Alk is associated with altered behavioral responses to ethanol in the fruit fly Drosophila melanogaster, in mice, and in humans. Mutant flies containing transposon insertions in dAlk demonstrate increased resistance to the sedating effect of ethanol. Database analyses revealed that Alk expression levels in the brains of recombinant inbred mice are negatively correlated with ethanol-induced ataxia and ethanol consumption. We therefore tested Alk gene knockout mice and found that they sedate longer in response to high doses of ethanol and consume more ethanol than wild-type mice. Finally, sequencing of human ALK led to the discovery of four polymorphisms associated with a low level of response to ethanol, an intermediate phenotype that is predictive of future alcohol use disorders (AUDs). These results suggest that Alk plays an evolutionary conserved role in ethanol-related behaviors. Moreover, ALK may be a novel candidate gene conferring risk for AUDs as well as a potential target for pharmacological intervention.

High ALK receptor tyrosine kinase expression supersedes ALK mutation as a determining factor of an unfavorable phenotype in primary neuroblastoma

PURPOSE

Genomic alterations of the anaplastic lymphoma kinase (ALK) gene have been postulated to contribute to neuroblastoma pathogenesis. This study aimed to determine the interrelation of ALK mutations, ALK expression levels, and clinical phenotype in primary neuroblastoma.

EXPERIMENTAL DESIGN

The genomic ALK status and global gene expression patterns were examined in 263 primary neuroblastomas. Allele-specific ALK expression was determined by cDNA cloning and sequencing. Associations of genomic ALK alterations and ALK expression levels with clinical phenotypes and transcriptomic profiles were compared.

RESULTS

Nonsynonymous point mutations of ALK were detected in 21 of 263 neuroblastomas (8%). Tumors with ALK mutations exhibited about 2-fold elevated median ALK mRNA levels in comparison with tumors with wild-type (WT) ALK. Unexpectedly, the WT allele was preferentially expressed in 12 of 21 mutated tumors. Whereas survival of patients with ALK mutated tumors was significantly worse as compared with the entire cohort of WT ALK patients, it was similarly poor in patients with WT ALK tumors in which ALK expression was as high as in ALK mutated neuroblastomas. Global gene expression patterns of tumors with ALK mutations or with high-level WT ALK expression were highly similar, and suggested that ALK may be involved in cellular proliferation in primary neuroblastoma.

CONCLUSIONS

Primary neuroblastomas with mutated ALK exhibit high ALK expression levels and strongly resemble neuroblastomas with elevated WT ALK expression levels in both their clinical and molecular phenotypes. These data suggest that high levels of mutated and WT ALK mediate similar molecular functions that may contribute to a malignant phenotype in primary neuroblastoma.

Anaplastic lymphoma kinase (ALK) inhibitor response in neuroblastoma is highly correlated with ALK mutation status, ALK mRNA and protein levels

BACKGROUND

In pediatric neuroblastoma (NBL), high anaplastic lymphoma kinase (ALK) levels appear to be correlated with an unfavorable prognosis, regardless of ALK mutation status. This suggests a therapeutic role for ALK inhibitors in NBL patients. We examined the correlation between levels of ALK, phosphorylated ALK (pALK) and downstream signaling proteins and response to ALK inhibition in a large panel of both ALK mutated and wild type (WT) NBL cell lines.

METHODS

We measured protein levels by western blot and ALK inhibitor sensitivity (TAE684) by viability assays in 19 NBL cell lines of which 6 had a point mutation and 4 an amplification of the ALK gene.

RESULTS

ALK 220 kDa (p = 0.01) and ALK 140 kDa (p = 0.03) protein levels were higher in ALK mutant than WT cell lines. Response to ALK inhibition was significantly correlated with ALK protein levels (p < 0.01). ALK mutant cell lines (n = 4) were 14,9 fold (p < 0,01) more sensitive to ALK inhibition than eight WT cell lines.

CONCLUSION

NBL cell lines often express ALK at high levels and are responsive to ALK inhibitors. Mutated cell lines express ALK at higher levels, which may define their superior response to ALK inhibition.

Identification of novel prognostic markers in relapsing localized resectable neuroblastoma

Patients with localized resectable neuroblastoma (NB) generally have an excellent prognosis and can be treated by surgery alone, but approximately 10% of them develop local recurrences or metastatic progression. The known predictive risk factors are important for the identification of localized resectable NB patients at risk of relapse and/or progression, who may benefit from early and aggressive treatment. These factors, however, identify only a subset of patients at risk, and the search for novel prognostic markers is warranted. This review focuses on the recent advances in the identification of new prognostic markers. Recently we addressed the search of novel genetic prognostic markers in a selected cohort of patients with stroma-poor localized resectable NB who underwent disease relapse or progression (group 1) or complete remission (group 2). High-resolution array-comparative genomic hybridization (CGH) DNA copy-number analysis technology was used. Chromosome 1p36.22p36.32 loss and 1q22qter gain, detected almost exclusively in group 1 patients, were significantly associated with poor event-free survival (EFS). Increasing evidence points to anaplastic lymphoma kinase (ALK) as a fundamental oncogene associated with NB. The immunohistochemical analysis of sporadic NB localized resectable primary tumors (stage 1-2) showed a correlation between aberrant ALK level of expression and tumor progression and clinical outcome. Moreover, other factors that might influence the clinical behavior of these tumors will be reviewed.

The connections between neural crest development and neuroblastoma

Neuroblastoma (NB), the most common extracranial solid tumor in childhood, is an extremely heterogeneous disease both biologically and clinically. Although significant progress has been made in identifying molecular and genetic markers for NB, this disease remains an enigmatic challenge. Since NB is thought to be an embryonal tumor that is derived from precursor cells of the peripheral (sympathetic) nervous system, understanding the development of normal sympathetic nervous system may highlight abnormal events that contribute to NB initiation. Therefore, this review focuses on the development of the peripheral trunk neural crest, the current understanding of how developmental factors may contribute to NB and on recent advances in the identification of important genetic lesions and signaling pathways involved in NB tumorigenesis and metastasis. Finally, we discuss how future advances in identification of molecular alterations in NB may lead to more effective, less toxic therapies, and improve the prognosis for NB patients.

Appearance of the novel activating F1174S ALK mutation in neuroblastoma correlates with aggressive tumor progression and unresponsiveness to therapy

Mutations in the kinase domain of the ALK kinase have emerged recently as important players in the genetics of the childhood tumor neuroblastoma. Here, we report the appearance of a novel ALK mutation in neuroblastoma, correlating with aggressive tumor behavior. Analyses of genomic DNA from biopsy samples initially showed ALK sequence to be wild type. However, during disease progression, mutation of amino acid F1174 to a serine within the ALK kinase domain was observed, which correlated with aggressive neuroblastoma progression in the patient. We show that mutation of F1174 to serine generates a potent gain-of-function mutant, as observed in 2 independent systems. First, PC12 cell lines expressing ALK(F1174S) display ligand-independent activation of ALK and further downstream signaling activation. Second, analysis of ALK(F1174S) in Drosophila models confirms that the mutation mediates a strong, rough eye phenotype upon expression in the developing eye. Thus, we report a novel ALK(F1174S) mutation that displays ligand-independent activity in vivo, correlating with rapid and treatment-resistant tumor growth. The study also shows that initial screening in the first tumor biopsy of a patient may not be sufficient and that further molecular analysis, in particular in tumor progression and/or tumor relapse, is warranted for better understanding of the treatment of neuroblastoma patients.

Nef and cell signaling transduction: a possible involvement in the pathogenesis of human immunodeficiency virus-associated dementia

Although the introduction of highly active antiretroviral therapy (HAART) has resulted in a significant decrease of acquired immunodeficiency syndrome (AIDS) morbidity and mortality, the prevalence of human immunodeficiency virus (HIV)-associated dementia (HAD) has actually risen, due to the increasing life expectancy of the infected subjects. To date, several aspects of the HAD pathogenesis remain to be dissected. In particular, the viral-cellular protein interplay is still under investigation. Given their specific features, two viral proteins, Tat and Nef, have been mainly hypothesized to play a role in HIV neuropathology. Here we show that HIV-1 Nef has an effect on the transcriptional levels of a cellular protein, anaplastic lymphoma kinase (ALK), that is preferentially expressed in the central and peripheral nervous system at late embryonic stages. By its overexpression along with Nef, the authors demonstrate ALK ability to influence, at least in the U87MG astrocytic glioma cells, the mytogen-activated protein kinase (MAP-K)-dependent pathway. Moreover, although in the absence of a physical direct interaction, Nef and ALK activate matrix metalloproteinases (MMPs), which are likely to contribute to blood-brain barrier (BBB) damage in HAD. Finally, in the in vitro model of glioblastoma cells adopted, Nef and ALK show similar effects by increasing different cytochines/chemokines that may be relevant for HAD pathogenesis. If confirmed in vivo, these data may indicate that, thanks to its ability to interfere with specific cellular pathways involved in BBB damage and in central nervous system (CNS) integrity, Nef, along with specific cellular counterparts, could be one of the viral players implicated in HAD development.

The beta isotypes of tubulin in neuronal differentiation

The differences among the vertebrate beta isotypes of tubulin are highly conserved in evolution, suggesting that they have functional significance. To address this, we have used differentiating neuroblastoma cells as a model system. These cells express the betaI, betaII, and betaIII isotypes. Although there is no difference prior to differentiation, a striking difference is seen after differentiation. Both betaI and betaIII occur in cell bodies and neurites, while betaII occurs mostly in neurites. Knocking down betaI causes a large decrease in cell viability while silencing betaII and betaIII does not. Knocking down betaII causes a large decrease in neurite outgrowth without affecting viability. Knocking down betaIII has little effect on neurite outgrowth and only decreases viability if cells are treated with glutamate and glycine, a combination known to generate free radicals and reactive oxygen species. It appears, therefore, that betaI is required for cell viability, betaII for neurite outgrowth and betaIII for protection against free radicals and reactive oxygen species.

Anaplastic lymphoma kinase activates the small GTPase Rap1 via the Rap1-specific GEF C3G in both neuroblastoma and PC12 cells

Many different types of cancer originate from aberrant signaling from the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase (RTK), arising through different translocation events and overexpression. Further, activating point mutations in the ALK domain have been recently reported in neuroblastoma. To characterize signaling in the context of the full-length receptor, we have examined whether ALK is able to activate Rap1 and contribute to differentiation/proliferation processes. We show that ALK activates Rap1 via the Rap1-specific guanine-nucleotide exchange factor C3G, which binds in a constitutive complex with CrkL to activated ALK. The activation of the C3G/Rap1 pathway results in neurite outgrowth of PC12 cells, which is inhibited by either overexpression of Rap1GAP or siRNA-mediated knockdown of Rap1 itself or the guanine nucleotide exchange factor C3G. Significantly, this pathway also appears to function in the regulation of proliferation of neuroblastoma cells such as SK-N-SH and SH-SY5Y, because abrogation of Rap1 activity by Rap1-specific siRNA or overexpression of Rap1GAP reduces cellular growth. These results suggest that ALK activation of Rap1 may contribute to cell proliferation and oncogenesis of neuroblastoma driven by gain-of-function mutant ALK receptors.

The PTB domain of ShcA couples receptor activation to the cytoskeletal regulator IQGAP1

Adaptor proteins respond to stimuli and recruit downstream complexes using interactions conferred by associated protein domains and linear motifs. The ShcA adaptor contains two phosphotyrosine recognition modules responsible for binding activated receptors, resulting in the subsequent recruitment of Grb2 and activation of Ras/MAPK. However, there is evidence that Grb2-independent signalling from ShcA has an important role in development. Using mass spectrometry, we identified the multidomain scaffold IQGAP1 as a ShcA-interacting protein. IQGAP1 and ShcA co-precipitate and are co-recruited to membrane ruffles induced by activated receptors of the ErbB family, and a reduction in ShcA protein levels inhibits the formation of lamellipodia. We used NMR to characterize a direct, non-canonical ShcA PTB domain interaction with a helical fragment from the IQGAP1 N-terminal region that is pTyr-independent. This interaction is mutually exclusive with binding to a more conventional PTB domain peptide ligand from PTP-PEST. ShcA-mediated recruitment of IQGAP1 may have an important role in cytoskeletal reorganization downstream of activated receptors at the cell surface.

Pleiotrophin induces neurite outgrowth and up-regulates growth-associated protein (GAP)-43 mRNA through the ALK/GSK3beta/beta-catenin signaling in developing mouse neurons

Pleiotrophin (PTN) is highly expressed in the nervous system during embryogenesis; however, little is known about its functional role in neural development. By using whole mount in situ hybridization, we observed that the expression pattern of PTN was similar to that of Wnt3a; PTN mRNA was abundant in the nervous tissue along the dorsal midline and in the forelimb and hindlimb buds of embryonic mice (E8.5-E12.5). Treatment with recombinant PTN (100ng/ml) induced phosphorylation of glycogen synthase kinase 3beta (GSK3beta), nuclear localization of beta-catenin and up-regulation of growth-associated protein (GAP)-43 mRNA in cultured embryonic mouse (E14.5) neurons. Furthermore, recombinant PTN enhanced neurite outgrowth from cortical explants embedded in Matrigel. These PTN-induced biochemical changes and neurite outgrowth were attenuated by the co-treatment with anti-anaplastic lymphoma kinase (ALK) antibodies, but not with anti-protein tyrosine phosphatase (PTP)zeta antibodies. These findings imply that ALK is involved in the PTN signaling on neural development.

Mutation-independent anaplastic lymphoma kinase overexpression in poor prognosis neuroblastoma patients

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase predominantly expressed in the developing nervous system. Recently, mutated ALK has been identified as a major oncogene associated with familial and sporadic neuroblastomas (NBL). Yet, a direct correlation between endogenous expression level of the ALK protein, oncogenic potential, and clinical outcome has not been established. We investigated ALK genetic mutations, protein expression/phosphorylation, and functional inhibition both in NBL-derived cell lines and in 34 localized and 48 advanced/metastatic NBL patients. ALK constitutive phosphorylation/activation was observed in high-ALK expressing cells, harboring either a mutated or a wild-type receptor. No activation was found in cell lines with low expression of wild-type ALK. After 72 hours of treatments, small molecule ALK inhibitor CEP-14083 (60 nmol/L) induced growth arrest and cell death in NBL cells overexpressing wild-type (viability: ALK(high) 12.8%, ALK(low) 73%, P = 0.0035; cell death: ALK(high) 56.4%, ALK(low) 16.2%, P = 0.0001) or mutated ALK. ALK protein expression was significantly up-regulated in advanced/metastatic compared with localized NBLs (ALK overexpressing patients: stage 1-2, 23.5%; stage 3-4, 77%; P < 0.0001). Interestingly, protein levels did not always correlate with ALK genetic alterations and/or mRNA abundance. Both mutated and wild-type ALK receptor can exert oncogenic activity in NBL cells. However, wild-type ALK receptor requires a critical threshold of expression to achieve oncogenic activation. Overexpression of either mutated or wild-type ALK defines poor prognosis patients. Alternative mechanisms other than direct mutations and/or gene amplification regulate the ALK level of expression in NBL cells. Wild-type ALK is a potential therapeutic target for advanced/metastatic NBLs.

ALK (Anaplastic Lymphoma Kinase) expression in DRG neurons and its involvement in neuron-Schwann cells interaction

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) transiently expressed in specific regions of the central and peripheral nervous systems. In this study, we focused on the rat developing dorsal root ganglion (DRG). This ganglion is composed of heterogeneous sensory neurons characterized by the expression of RTK for neurotrophic factors, such as the nerve growth factor receptor TrkA or the glial-derived neurotrophic factor family receptor Ret, which are specifically detected in nociceptive neurons. In DRG, ALK expression reached a maximum around birth. We showed that ALK is specifically present in a subtype of neurons during DRG development, and that the majority of these neurons co-expressed TrkA and Ret. Interestingly, we identified only one form (220 kDa) of ALK in DRG neurons both in vivo and in vitro. On the opposite, in transfected cells as well as in brain extracts, ALK was identified as two forms (220 and 140 kDa). The DRG is composed of neurons and glial cells, principally satellite Schwann cells. Thus, we hypothesized that the presence of satellite Schwann cells was involved in the absence of truncated ALK. Using two different cell types, HEK293 cells stably expressing ALK, and MSC80 cells, a previously described Schwann cell line, we showed that a factor secreted by the Schwann cells is likely involved in the absence of ALK cleavage. All these data hence open new perspectives concerning the role of ALK in the specification of nociceptive DRG neurons and in the neurons-Schwann cells interaction.

Anaplastic lymphoma kinase: signalling in development and disease

RTKs (receptor tyrosine kinases) play important roles in cellular proliferation and differentiation. In addition, RTKs reveal oncogenic potential when their kinase activities are constitutively enhanced by point mutation, amplification or rearrangement of the corresponding genes. The ALK (anaplastic lymphoma kinase) RTK was originally identified as a member of the insulin receptor subfamily of RTKs that acquires transforming capability when truncated and fused to NPM (nucleophosmin) in the t(2;5) chromosomal rearrangement associated with ALCL (anaplastic large cell lymphoma). To date, many chromosomal rearrangements leading to enhanced ALK activity have been described and are implicated in a number of cancer types. Recent reports of the EML4 (echinoderm microtubule-associated protein like 4)–ALK oncoprotein in NSCLC (non-small cell lung cancer), together with the identification of activating point mutations in neuroblastoma, have highlighted ALK as a significant player and target for drug development in cancer. In the present review we address the role of ALK in development and disease and discuss implications for the future.

Fbxo45 forms a novel ubiquitin ligase complex and is required for neuronal development

Fbxo45 is an F-box protein that is restricted to the nervous system. Unlike other F-box proteins, Fbxo45 was found not to form an SCF complex as a result of an amino acid substitution in the consensus sequence for Cul1 binding. Proteomics analysis revealed that Fbxo45 specifically associates with PAM (protein associated with Myc), a RING finger-type ubiquitin ligase. Mice deficient in Fbxo45 were generated and found to die soon after birth as a result of respiratory distress. Fbxo45(-)(/)(-) embryos show abnormal innervation of the diaphragm, impaired synapse formation at neuromuscular junctions, and aberrant development of axon fiber tracts in the brain. Similar defects are also observed in mice lacking Phr1 (mouse ortholog of PAM), suggesting that Fbxo45 and Phr1 function in the same pathway. In addition, neuronal migration was impaired in Fbxo45(-)(/)(-) mice. These results suggest that Fbxo45 forms a novel Fbxo45-PAM ubiquitin ligase complex that plays an important role in neural development.

Identification of ALK as a major familial neuroblastoma predisposition gene

Neuroblastoma is a childhood cancer that can be inherited, but the genetic aetiology is largely unknown. Here we show that germline mutations in the anaplastic lymphoma kinase (ALK) gene explain most hereditary neuroblastomas, and that activating mutations can also be somatically acquired. We first identified a significant linkage signal at chromosome bands 2p23-24 using a whole-genome scan in neuroblastoma pedigrees. Resequencing of regional candidate genes identified three separate germline missense mutations in the tyrosine kinase domain of ALK that segregated with the disease in eight separate families. Resequencing in 194 high-risk neuroblastoma samples showed somatically acquired mutations in the tyrosine kinase domain in 12.4% of samples. Nine of the ten mutations map to critical regions of the kinase domain and were predicted, with high probability, to be oncogenic drivers. Mutations resulted in constitutive phosphorylation, and targeted knockdown of ALK messenger RNA resulted in profound inhibition of growth in all cell lines harbouring mutant or amplified ALK, as well as in two out of six wild-type cell lines for ALK. Our results demonstrate that heritable mutations of ALK are the main cause of familial neuroblastoma, and that germline or acquired activation of this cell-surface kinase is a tractable therapeutic target for this lethal paediatric malignancy.

Myosin II regulates the shape of three-dimensional intestinal epithelial cysts

The development of luminal organs begins with the formation of spherical cysts composed of a single layer of epithelial cells. Using a model three-dimensional cell culture, this study examines the role of a cytoskeletal motor, myosin II, in cyst formation. Caco-2 and SK-CO15 intestinal epithelial cells were embedded into Matrigel, and myosin II was inhibited by blebbistatin or siRNA-mediated knockdown. Whereas control cells formed spherical cysts with a smooth surface, inhibition of myosin II induced the outgrowth of F-actin-rich surface protrusions. The development of these protrusions was abrogated after inhibition of F-actin polymerization or of phospholipase C (PLC) activity, as well as after overexpression of a dominant-negative ADF/cofilin. Surface protrusions were enriched in microtubules and their formation was prevented by microtubule depolymerization. Myosin II inhibition caused a loss of peripheral F-actin bundles and a submembranous extension of cortical microtubules. Our findings suggest that inhibition of myosin II eliminates the cortical F-actin barrier, allowing microtubules to reach and activate PLC at the plasma membrane. PLC-dependent stimulation of ADF/cofilin creates actin-filament barbed ends and promotes the outgrowth of F-actin-rich protrusions. We conclude that myosin II regulates the spherical shape of epithelial cysts by controlling actin polymerization at the cyst surface.

Anti-neuroblastoma activity of Helminthosporium carbonum (HC)-toxin is superior to that of other differentiating compounds in vitro

Treatment of high-risk neuroblastoma (NB) is difficult. Novel therapeutics improving survival rates are urgently required. We have previously shown that the histone deacetylase inhibitor (HDACI) Helminthosporium carbonum (HC)-toxin induces differentiation of neuroblastoma (NB) cells. Here, we show that HC-toxin inhibits the growth of both established NB cell lines and primary cultures with and without amplified MYCN stronger than retinoids (RAs) and other HDACIs (MS-275, n-butyric acid, suberoylanilide hydroxamic acid, trichostatin A, valproic acid). Nanomolar dosages suppress E2F-1, N-myc, Skp2, Mad2 and survivin proteins, found at high levels in high-risk NBs, more efficiently than both RAs and other HDACIs. The level of hypophosphorylated active retinoblastoma (RB) tumor suppressor protein is increased most effectively. HC-toxin's epoxy group is essential for inhibiting HDACs and promoting anti-NB activity. Without this functional group, those cellular effects are not observed. In conclusion, the anti-NB activity of HC-toxin is superior to that of RAs and that of all other HDACIs tested.

The ligand Jelly Belly (Jeb) activates the Drosophila Alk RTK to drive PC12 cell differentiation, but is unable to activate the mouse ALK RTK

The Drosophila Alk receptor tyrosine kinase (RTK) drives founder cell specification in the developing visceral mesoderm and is crucial for the formation of the fly gut. Activation of Alk occurs in response to the secreted ligand Jelly Belly. No homologues of Jelly Belly are described in vertebrates, therefore we have approached the question of the evolutionary conservation of the Jeb-Alk interaction by asking whether vertebrate ALK is able to function in Drosophila. Here we show that the mouse ALK RTK is unable to rescue a Drosophila Alk mutant, indicating that mouse ALK is unable to recognise and respond to the Drosophila Jeb molecule. Furthermore, the overexpression of a dominant-negative Drosophila Alk transgene is able to block the visceral muscle fusion event, which an identically designed dominant-negative construct for the mouse ALK is not. Using PC12 cells as a model for neurite outgrowth, we show here for the first time that activation of dAlk by Jeb results in neurite extension. However, the mouse Alk receptor is unable to respond in any way to the Drosophila Jeb protein in the PC12 system. In conclusion, we find that the mammalian ALK receptor is unable to respond to the Jeb ligand in vivo or in vitro. These results suggest that either (i) mouse ALK and "mouse Jeb" have co-evolved to the extent that mALK can no longer recognise the Drosophila Jeb ligand or (ii) that the mALK RTK has evolved such that it is no longer activated by a Jeb-like molecule in vertebrates.