Christina Schönherr

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.

Appearance of the novel activating F1174S ALK mutation in neuroblastoma correlates with aggressive tumour 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.

Anaplastic Lymphoma Kinase (ALK) regulates initiation of transcription of MYCN in neuroblastoma cells

Neuroblastoma is a neural crest-derived embryonal tumour of the postganglionic sympathetic nervous system and a disease with several different chromosomal gains and losses, which include MYCN-amplified neuroblastoma on chromosome 2, deletions of parts of the chromosomes 1p and 11q, gain of parts of 17q and triploidy. Recently, activating mutations of the ALK (Anaplastic Lymphoma Kinase) RTK (Receptor Tyrosine Kinase) gene have been described in neuroblastoma. A meta-analysis of neuroblastoma cases revealed that ALK mutations (49 of 709 cases) in relation to genomic subtype were most frequently observed in MYCN amplified tumours (8.9%), correlating with a poor clinical outcome. MYCN proteins target proliferation and apoptotic pathways, and have an important role in the progression of neuroblastoma. Here, we show that both wild-type and gain-of-function mutants in ALK are able to stimulate transcription at the MYCN promoter and initiate mRNA transcription of the MYCN gene in both neuronal and neuroblastoma cell lines. Further, this stimulation of MYCN gene transcription and de novo MYCN protein expression is abrogated by specific ALK inhibitors, such as crizotinib (PF-2341066), NVP-TAE684, and by small interfering RNA to ALK resulting in a decrease in proliferation rate. Finally, co-transfection of ALK gain-of-function mutations together with MYCN leads to an increase in transformation potential. Taken together, our results indicate that ALK signalling regulates initiation of transcription of the MYCN gene providing a possible explanation for the poor clinical outcome observed when MYCN is amplified together with activated ALK.

Cell culture and Drosophila model systems define three classes of anaplastic lymphoma kinase mutations in neuroblastoma

SUMMARY Neuroblastoma is a childhood extracranial solid tumour that is associated with a number of genetic changes. Included in these genetic alterations are mutations in the kinase domain of the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase (RTK), which have been found in both somatic and familial neuroblastoma. In order to treat patients accordingly requires characterisation of these mutations in terms of their response to ALK tyrosine kinase inhibitors (TKIs). Here, we report the identification and characterisation of two novel neuroblastoma ALK mutations (A1099T and R1464STOP), which we have investigated together with several previously reported but uncharacterised ALK mutations (T1087I, D1091N, T1151M, M1166R, F1174I and A1234T). In order to understand the potential role of these ALK mutations in neuroblastoma progression, we have employed cell culture-based systems together with the model organism Drosophila as a readout for ligand-independent activity. Mutation of ALK at position 1174 (F1174I) generates a gain-of-function receptor capable of activating intracellular targets such as ERK (extracellular signal regulated kinase) and STAT3 (signal transducer and activator of transcription 3) in a ligand-independent manner. Analysis of these previously uncharacterised ALK mutants and comparison with ALKF1174 mutants suggests that ALK mutations observed in neuroblastoma fall into three classes. These classes are: (i) gain-of-function ligand-independent mutations such as ALKF1174l, (ii) kinase-dead ALK mutants, e.g. ALKI1250T (Schönherr et al., 2011a) and (iii) ALK mutations that are ligand-dependent in nature. Irrespective of the nature of the observed ALK mutants, in every case the activity of the mutant ALK receptors could be abrogated by the ALK inhibitor crizotinib (Xalkori/PF-02341066), albeit with differing levels of sensitivity.

The kinase ALK stimulates the kinase ERK5 to promote the expression of the oncogene MYCN in neuroblastoma

Targeting the kinase ERK5 may disrupt the activation of an oncogenic transcription factor in a subset of neuroblastoma patients. A New Target in Neuroblastoma Neuroblastoma is a common and aggressive pediatric cancer caused by various molecular abnormalites. Similar to other cancers, poor prognosis correlates with increased abundance or activation of the cell surface receptor tyrosine kinase ALK or increased abundance of the transcription factor MYCN. An ALK inhibitor used in the clinic is not wholly effective, and there are no therapies to directly target MYCN. Umapathy et al. found that ALK stimulated the expression of the gene encoding MYCN through a pathway involving several kinases in patient tumor cells. Targeting one of these kinases, ERK5, decreased the abundance of MYCN and suppressed proliferation in ALK-positive neuroblastoma cells in culture. Combined inhibition of ALK and ERK5 was more effective than the ALK inhibitor alone in limiting tumor growth in a mouse model. Thus, ERK5 represents a new target for treating ALK-driven cancers. Anaplastic lymphoma kinase (ALK) is an important molecular target in neuroblastoma. Although tyrosine kinase inhibitors abrogating ALK activity are currently in clinical use for the treatment of ALK-positive (ALK+) disease, monotherapy with ALK tyrosine kinase inhibitors may not be an adequate solution for ALK+ neuroblastoma patients. Increased expression of the gene encoding the transcription factor MYCN is common in neuroblastomas and correlates with poor prognosis. We found that the kinase ERK5 [also known as big mitogen-activated protein kinase (MAPK) 1 (BMK1)] is activated by ALK through a pathway mediated by phosphoinositide 3-kinase (PI3K), AKT, MAPK kinase kinase 3 (MEKK3), and MAPK kinase 5 (MEK5). ALK-induced transcription of MYCN and stimulation of cell proliferation required ERK5. Pharmacological or RNA interference–mediated inhibition of ERK5 suppressed the proliferation of neuroblastoma cells in culture and enhanced the antitumor efficacy of the ALK inhibitor crizotinib in both cells and xenograft models. Together, our results indicate that ERK5 mediates ALK-induced transcription of MYCN and proliferation of neuroblastoma, suggesting that targeting both ERK5 and ALK may be beneficial in neuroblastoma patients.

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.

Phosphoproteomic analysis of anaplastic lymphoma kinase (ALK) downstream signaling pathways identifies signal transducer and activator of transcription 3 as a functional target of activated ALK in neuroblastoma cells

Activation of the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase is a key oncogenic mechanism in a growing number of tumor types. In the majority of cases, ALK is activated by fusion with a dimerizing partner protein as a result of chromosomal translocation events, most studied in the case of the nucleophosmin–ALK and echinoderm microtubule‐associated protein‐like 4–ALK oncoproteins. It is now also appreciated that the full‐length ALK receptor can be activated by point mutations and by deletions within the extracellular domain, such as those observed in neuroblastoma. Several studies have employed phosphoproteomics approaches to find substrates of ALK fusion proteins. In this study, we used MS‐based phosphotyrosine profiling to characterize phosphotyrosine signaling events associated with the full‐length ALK receptor. A number of previously identified and novel targets were identified. One of these, signal transducer and activator of transcription 3 (STAT3), has previously been observed to be activated in response to oncogenic ALK signaling, but the significance of this in signaling from the full‐length ALK receptor has not been explored further. We show here that activated ALK robustly activates STAT3 on Tyr705 in a number of independent neuroblastoma cell lines. Furthermore, knockdown of STAT3 by RNA interference resulted in a reduction in myelocytomatosis neuroblastom (MYCN) protein levels downstream of ALK signaling. These observations, together with a decreased level of MYCN and inhibition of neuroblastoma cell growth in the presence of STAT3 inhibitors, suggest that activation of STAT3 is important for ALK signaling activity in neuroblastoma.

Goliath family E3 ligases regulate the recycling endosome pathway via VAMP3 ubiquitylation

Diverse cellular processes depend on endocytosis, intracellular vesicle trafficking, sorting and exocytosis, processes regulated post‐transcriptionally by modifications such as phosphorylation and ubiquitylation. In addition to sorting to the lysosome, cargo is recycled to the plasma membrane via recycling endosomes. Here, we describe a role of the goliath gene family of protease‐associated (PA) domain E3 ligases in regulating recycling endosome trafficking. The two Drosophila members of this family—Goliath and GodzillaCG10277—are located on endosomes, and both ectopic expression and loss‐of‐function lead to the accumulation of Rab5‐positive giant endosomes. Furthermore, the human homologue RNF167 exhibits similar behaviour. We show that the soluble N‐ethylmaleimide‐sensitive fusion attachment protein receptor (SNARE) protein VAMP3 is a target of these ubiquitin ligases, and that recycling endosome trafficking is abrogated in response to their activity. Furthermore, mutation of the Godzilla ubiquitylation target lysines on VAMP3 abrogates the formation of enlarged endosomes induced by either Godzilla or RNF167. Thus, Goliath ubiquitin ligases play a novel role in regulating recycling endosome trafficking via ubiquitylation of the VAMP3 SNARE protein.

Jeb/Alk signalling regulates the Lame duck GLI family transcription factor in the Drosophila visceral mesoderm

The Jelly belly (Jeb)/Anaplastic Lymphoma Kinase (Alk) signalling pathway regulates myoblast fusion in the circular visceral mesoderm (VM) of Drosophila embryos via specification of founder cells. However, only a limited number of target molecules for this pathway are described. We have investigated the role of the Lame Duck (Lmd) transcription factor in VM development in relationship to Jeb/Alk signal transduction. We show that Alk signalling negatively regulates Lmd activity post-transcriptionally through the MEK/MAPK (ERK) cascade resulting in a relocalisation of Lmd protein from the nucleus to cytoplasm. It has previously been shown that downregulation of Lmd protein is necessary for the correct specification of founder cells. In the visceral mesoderm of lmd mutant embryos, fusion-competent myoblasts seem to be converted to ‘founder-like’ cells that are still able to build a gut musculature even in the absence of fusion. The ability of Alk signalling to downregulate Lmd protein requires the N-terminal 140 amino acids, as a Lmd141-866 mutant remains nuclear in the presence of active ALK and is able to drive robust expression of the Lmd downstream target Vrp1 in the developing VM. Our results suggest that Lmd is a target of Jeb/Alk signalling in the VM of Drosophila embryos.