Jelly belly protein activates the receptor tyrosine kinase Alk to specify visceral muscle pioneers

The anaplastic lymphoma kinase in the pathogenesis of cancer

Tyrosine kinases are involved in the pathogenesis of most cancers. However, few tyrosine kinases have been shown to have a well-defined pathogenetic role in lymphomas. The anaplastic lymphoma kinase (ALK) is the oncogene of most anaplastic large cell lymphomas (ALCL), driving transformation through many molecular mechanisms. In this Review, we will analyse how translocations or deregulated expression of ALK contribute to oncogenesis and how recent genetic or pharmacological tools, aimed at neutralizing its activity, can represent the basis for the design of powerful combination therapies.

Anaplastic lymphoma kinase is activated through the pleiotrophin/receptor protein-tyrosine phosphatase beta/zeta signaling pathway: an alternative mechanism of receptor tyrosine kinase activation

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) first discovered as the constitutively active nucleophosmin-ALK oncoprotein in anaplastic large cell lymphomas (ALCL). Full-length ALK has a critical role in normal development and differentiation. Activated full-length ALK also is found in different malignant cancers. Nevertheless, the ligand to activate ALK remained unknown until recently, when ALK was proposed to be the physiological receptor of the cytokine pleiotrophin (PTN, Ptn). However, earlier studies had demonstrated that receptor protein tyrosine phosphatase (RPTP) beta/zeta is a physiological PTN receptor. We now demonstrate that phosphorylation of ALK in PTN-stimulated cells is mediated through the PTN/RPTPbeta/zeta signaling pathway. ALK is phosphorylated independently of a direct interaction of PTN with ALK. The data thus support a unique model of ALK activation. In cells not stimulated by PTN, RPTPbeta/zeta dephosphorylates ALK at the site(s) in ALK that is undergoing autophosphorylation through autoactivation. In contrast, when RPTPbeta/zeta is inactivated in PTN-stimulated cells, the sites that are autophosphorylated in ALK no longer can be dephosphorylated by RPTPbeta/zeta; thus, autoactivation and tyrosine phosphorylation of ALK rapidly increase. The data indicate that the PTN/RPTPbeta/zeta signaling pathway is a critical regulator of the steady state levels of tyrosine phosphorylation and activation of ALK; the data support the conclusion that ALK phosphorylation and activation in PTN-stimulated cells are increased through a unique "alternative mechanism of RTK activation."

In contrast to agonist monoclonal antibodies, both C-terminal truncated form and full length form of Pleiotrophin failed to activate vertebrate ALK (anaplastic lymphoma kinase)?

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase essentially and transiently expressed during development in specific regions of the central and peripheral nervous system. ALK expression persists at a lower level in the adult brain. Thus, it might play an important role in both the normal development and function of the nervous system. The nature of the cognate ligand of this receptor in vertebrates is still a matter of debate. Pleiotrophin and midkine have been proposed as ligands of ALK but several independent studies do not confirm this hypothesis. Interestingly, a recent study proposed that a C-terminal truncated form of Pleiotrophin (Pleiotrophin.15) and not the full length form (Pleiotrophin.18) promotes glioblastoma proliferation in an ALK-dependent fashion. These data were obviously a strong basis to conciliate the conflicting results so far reported in the literature. In the present study, we first purified to homogeneity the two forms of Pleiotrophin secreted by HEK 293 cells. In contrast to agonist monoclonal antibodies, both Pleiotrophin.15 and Pleiotrophin.18 failed to activate ALK in neuroblastoma and glioblastoma cells expressing this receptor. Thus, for our point of view, ALK is still an orphan receptor in vertebrates.

Pathobiology of ALK+ anaplastic large-cell lymphoma

Anaplastic large-cell lymphoma (ALCL) was initially recognized on the basis of morphologic features and the consistent expression of CD30. It then became evident that the majority of these tumors are derived from lymphoid cells of T or null immunophenotype. The subsequent finding that t(2;5)(p23;q35) occurs in 40% to 60% of ALCL patients established a distinct clinicopathologic entity. This chromosomal translocation induces the formation of the chimeric protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), which possesses significant oncogenic potential resulting from the constitutive activation of the tyrosine kinase ALK. In addition to its specific pathophysiologic events, NPM-ALK-expressing lymphoma presents with consistent clinical manifestations. Only 13 years after the identification of NPM-ALK, tremendous progress has been made in our understanding of this molecule because of the relentless efforts of multiple investigators who have dissected its biologic roles using in vitro and in vivo experimental models. Several upstream modulators, cross-reacting oncogenes, and downstream effectors of NPM-ALK have been identified and characterized. Understanding these interacting oncogenic systems is expected to facilitate the design of new therapeutic strategies and agents. In this review, we briefly discuss ALCL and focus on NPM-ALK.

Hand is a direct target of the forkhead transcription factor Biniou during Drosophila visceral mesoderm differentiation

BACKGROUND

The visceral trunk mesoderm in Drosophila melanogaster develops under inductive signals from the ectoderm. This leads to the activation of the key regulators Tinman, Bagpipe and Biniou that are crucial for specification of the circular visceral muscles. How further differentiation is regulated is widely unknown, therefore it seems to be essential to identify downstream target genes of the early key regulators. In our report we focus on the analysis of the transcriptional control of the highly conserved transcription factor Hand in circular visceral muscle cells, providing evidence that the hand gene is a direct target of Biniou.

RESULTS

Herein we describe the identification of a regulatory region in the hand gene essential and sufficient for the expression in the visceral mesoderm during embryogenesis. We found that hand expression in the circular visceral mesoderm is abolished in embryos mutant for the FoxF domain containing transcription factor Biniou. Furthermore we demonstrate that Biniou regulates hand expression by direct binding to a 300 bp sequence element, located within the 3rd intron of the hand gene. This regulatory element is highly conserved in different Drosophila species. In addition, we provide evidence that Hand is dispensable for the initial differentiation of the embryonic visceral mesoderm.

CONCLUSION

In the present report we show that cross species sequence comparison of non-coding sequences between orthologous genes is a powerful tool to identify conserved regulatory elements. Combining functional dissection experiments in vivo and protein/DNA binding studies we identified hand as a direct target of Biniou in the circular visceral muscles.

Surprisingly complex T-box gene complement in diploblastic metazoans

Ctenophores and cnidarians are two metazoan groups that evolved at least 600 Ma, predating the Cambrian explosion. Although both groups are commonly categorized as diploblastic animals without derivatives of the mesodermal germ layer, ctenophores possess definitive contractile "muscle" cells. T-box family transcription factors are an evolutionarily ancient gene family, arising in the common ancestor of metazoans, and have been divided into eight groups in five distinct subfamilies, many of which are involved in the specification of mesodermal as well as ectodermally and endodermally derived structures. Here, we report the cloning and expression of five T-box genes from a ctenophore, Mnemiopsis leidyi. Phylogenetic analyses demonstrated that ctenophores possess members of at least three of the five T-box subfamilies, and expression studies suggested distinct roles of each T-box genes during gastrulation and early organogenesis. Moreover, genome searches of the sea anemone, Nematostella vectensis (anthozoan cnidarian), showed at least 13 T-box genes in Nematostella, which are divided into at least six distinct groups in the same three subfamilies found in ctenophores. Our results from two diploblastic animals indicate that the common ancestor of eumetazoans had a complex set of T-box genes and that two distinct subfamilies might have appeared during triploblastic evolution.

Anterograde Jelly belly and Alk receptor tyrosine kinase signaling mediates retinal axon targeting in Drosophila

Anaplastic lymphoma kinase (Alk) has been proposed to regulate neuronal development based on its expression pattern in vertebrates and invertebrates; however, its function in vivo is unknown. We demonstrate that Alk and its ligand Jelly belly (Jeb) play a central role as an anterograde signaling pathway mediating neuronal circuit assembly in the Drosophila visual system. Alk is expressed and required in target neurons in the optic lobe, whereas Jeb is primarily generated by photoreceptor axons and functions in the eye to control target selection of R1-R6 axons in the lamina and R8 axons in the medulla. Impaired Jeb/Alk function affects layer-specific expression of three cell-adhesion molecules, Dumbfounded/Kirre, Roughest/IrreC, and Flamingo, in the medulla. Moreover, loss of flamingo in target neurons causes some R8-axon targeting errors observed in Jeb and Alk mosaic animals. Together, these findings suggest that Jeb/Alk signaling helps R-cell axons to shape their environment for target recognition.

Myoblast fusion in Drosophila melanogaster is mediated through a fusion-restricted myogenic-adhesive structure (FuRMAS)

During myogenesis in Drosophila embryos, a prominent adhesive structure is formed between precursor cells and fusion-competent myoblasts (fcms). Here, we show that Duf/Kirre and its interaction partners Rols7 (found in founder myoblasts and growing myotubes) and Sns (found in fcms) are organized in a ring-structure at the contact points of fcms with precursor cells, while cytoskeletal components like F-actin and Titin are centered in this ring in both cell types. The cytoplasmic protein Blow colocalizes with the actin plugs in fcms after cell adhesion. Furthermore, the requirement of additional as yet unidentified components was demonstrated by using mammalian C2C12 myoblasts. In this study, we propose that the fusion-restricted myogenic-adhesive structure (FuRMAS) is pivotal in linking cell adhesion as well as local F-actin assembly and dynamics to downstream events that ultimately lead to plasma membrane fusion. Moreover, we suggest that the FuRMAS may restrict the area of membrane breakdown.

Blown fuse regulates stretching and outgrowth but not myoblast fusion of the circular visceral muscles in Drosophila

Circular visceral muscles of Drosophila are binuclear syncytia arising from fusion of two different kinds of myoblasts: a circular visceral founder cell and one visceral fusion-competent myoblast. In contrast to fusion leading to the somatic body-wall musculature, myoblast fusion for the circular visceral muscles does not result in massive syncytia but instead in syncytia interconnected with multiple cytoplasmic bridges, which differentiate into large web-shaped muscles. Here, we show that these syncytial circular visceral muscles build a gut-enclosing network with the interwoven longitudinal visceral muscles. At the ultrastructural level, during circular visceral myoblast fusion and the first step of somatic myoblast fusion prefusion complexes and electron-dense plaques were not detectable which was surprising as these structures are characteristic for the second step of somatic myoblast fusion. Moreover, we demonstrate that Blown fuse (Blow), a cytoplasmic protein essential for the second step of somatic myoblast fusion, plays a different role in circular visceral myogenesis. Blow is known to be essential for progression beyond the prefusion complex in the somatic mesoderm; however, analysis of blow mutants established that it has a restricted role in stretching and outgrowth of the syncytia in the circular visceral muscles. Furthermore, we also found that in the visceral mesoderm, Blow is expressed in both the fusion-competent myoblasts and circular visceral founders, while expression in the somatic mesoderm is initially restricted to fusion-competent myoblasts. We also demonstrate that different enhancer elements in the first intron of blow are responsible for this distinct expression pattern. Thus, we propose a model for Blow in which this protein is involved in at least two clearly differing processes during Drosophila muscle formation, namely somatic myoblast fusion on the one hand and stretching and outgrowth of circular visceral muscles on the other.

Drosophila Anaplastic Lymphoma Kinase regulates Dpp signalling in the developing embryonic gut

The Drosophila melanogaster gene Anaplastic Lymphoma Kinase (Alk) regulates a signal transduction pathway required for founder cell specification within the visceral muscle of the developing embryonic midgut. During embryonic development, the midgut visceral muscle is lined by the endodermal cell layer. In this paper, we have investigated signalling between these two tissues. Here, we show that Alk function is required for decapentaplegic (Dpp) expression and subsequent signalling via the Mad pathway in the developing gut. We propose that not only does Alk signalling regulate founder cell specification and thus fusion in the developing visceral muscle, but that Alk also regulates Dpp signalling between the visceral muscle and the endoderm. This provides an elegant mechanism with which to temporally coordinate visceral muscle fusion and later events in midgut development.

Organization of the sex-ratio meiotic drive region in Drosophila simulans

Sex-ratio meiotic drive is the preferential transmission of the X chromosome by XY males, which occurs in several Drosophila species and results in female-biased progeny. Although the trait has long been known to exist, its molecular basis remains completely unknown. Here we report a fine-mapping experiment designed to characterize the major drive locus on a sex-ratio X chromosome of Drosophila simulans originating from the Seychelles (XSR6). This primary locus was found to contain two interacting elements at least, both of which are required for drive expression. One of them was genetically tracked to a tandem duplication containing six annotated genes (Trf2, CG32712, CG12125, CG1440, CG12123, org-1), and the other to a candidate region located approximately 110 kb away and spanning seven annotated genes. RT-PCR showed that all but two of these genes were expressed in the testis of both sex-ratio and standard males. In situ hybridization to polytene chromosomes revealed a complete association of the duplication with the sex-ratio trait in random samples of X chromosomes from Madagascar and Reunion.

The bHLH transcription factor Hand is regulated by Alk in the Drosophila embryonic gut

During embryonic development the midgut visceral muscle is formed by fusion of cells within the visceral mesoderm, a process initiated by the specification of a specialised cell type, the founder cell, within this tissue. Activation of the receptor tyrosine kinase Anaplastic lymphoma kinase (Alk) in the developing visceral muscle of Drosophila melanogaster initiates a signal transduction pathway required for muscle fusion. In this paper, we have investigated downstream components which are regulated by this novel signalling pathway. Here we show that Alk-mediated signal transduction drives the expression of the bHLH transcription factor Hand in vivo. Loss of Alk function results in a complete lack of Hand expression in this tissue, whereas Alk gain of function results in an expansion of Hand expression. Finally, we have investigated the process of muscle fusion in the gut of Hand mutant animals and can find no obvious defects in this process, suggesting that Hand is not critical for visceral muscle fusion per se.

Fusion tyrosine kinase mediated signalling pathways in the transformation of haematopoietic cells

The fusion tyrosine kinases (FTKs) are generated by chromosomal translocations creating bipartite proteins in which the kinase is hyperactivated by an adjoining oligomerization domain. Autophosphorylation of the FTK generates a 'signalosome', an ensemble of signalling proteins that transduce signals to downstream pathways. At the earliest stages of oncogenesis, FTKs can mimic mitogenic cytokine signalling pathways involving the GAB-2 adaptor protein and signal transducers and activators of transcription (STAT) factors, generating replicative stress and thereby promoting a mutator phenotype. In parallel, FTKs couple to survival pathways that upregulate prosurvival proteins such as Bcl-xL, so preventing DNA-damage-induced apoptosis. Following transformation, FTKs induce resistance to genotoxic attack by upregulating DNA repair mechanisms such as STAT5-dependent RAD51 transcription. The phenomenon of 'oncogene addiction' reflects the continued requirement of an active FTK 'signalosome' to mediate survival and mitogenic signals involving the PI 3-kinase and mitogen-activated protein stress-activated protein kinase pathways, and the nuclear factor-kappa B, activator protein 1 and STAT transcription factors. The available data so far suggest that FTKs, with some possible exceptions, induce and maintain the transformed state using similar panoplies of signals, a finding with important therapeutic implications. The FTK signalling field has matured to an exciting phase in which rapid advances are facilitating rational drug design.

A Drosophila model of the rhabdomyosarcoma initiator PAX7-FKHR

Alveolar rhabdomyosarcoma (ARMS) is an aggressive myogenic-type tumor and a gain-of-function disease, caused by misexpression of the PAX3-FKHR or PAX7-FKHR fusion oncoprotein from structurally rearranged chromosomes. PAX3-FKHR misexpressed in terminally differentiating mouse myofibers can cause rhabdomyosarcoma at a low frequency, suggesting that skeletal muscle is an ARMS tissue of origin. Because patterned muscle is widely viewed as irreversibly syncytial, questions persist, however, regarding this potential pathogenetic mechanism for ARMS tumor initiation. To further explore this issue, we generated transgenic Drosophila lines that conditionally express human PAX-FKHR. Here we show that PAX7-FKHR causes nucleated cells to form and separate from syncytial myofibers, which then spread to nonmuscular tissue compartments, including the central nervous system, and that wild-type PAX3 demonstrates similar potential. We further show that Ras, which is known to interfere with the differentiation of myogenic cells, genetically interacts with PAX7-FKHR: constitutively activated Ras enhances PAX7-FKHR phenotypes, whereas loss-of-function ras alleles dominantly suppress PAX7-FKHR activity, including rescue of lethality. These results show that PAX-FKHR can drive the generation of discrete nucleated cells from differentiated myofibers in vivo, argue for syncytial muscle as an ARMS tissue of origin, and demonstrate that Drosophila provides a powerful system to screen for genetic modifiers of PAX-FKHR.

Tracing the evolution and function of the Trk superfamily of receptor tyrosine kinases

Most growth factors and their receptors have been strongly conserved during evolution. In contrast, Trks (Tropomyosin-related kinases) and related receptors in the Trk superfamily, Rors (receptor tyrosine kinase-like orphan receptors), Musks (muscle specific kinases) and Ddrs (discoidin domain receptor family), appear to be ancient, but their function has been lost in multiple lineages and the roles for the receptors have been modified over time. We will trace the evolution of the Trk superfamily and discuss possible conserved functional roles, including a unifying theme of target recognition by growing axons. We present an analogy between the evolution of G-protein-coupled receptors and receptor tyrosine kinases (RTKs), proposing that an important driving force for the divergence of receptors is the ease of divergence of their ligands.

Recruitment of insulin receptor substrate-1 and activation of NF-kappaB essential for midkine growth signaling through anaplastic lymphoma kinase

Anaplastic lymphoma kinase (ALK) is a transmembrane receptor tyrosine kinase in the insulin receptor superfamily. We recently demonstrated that the growth factors pleiotrophin (PTN) and midkine (MK) are ligands for ALK and that upon ALK activation, insulin receptor substrate-1 (IRS-1) and other substrates are phosphorylated. Here, the role of IRS-1 in ligand-mediated ALK signaling is investigated in interleukin-3 (IL-3)-dependent 32D murine myeloid cells. These cells do not express ALK and IRS family members, and do not respond to exogenously added PTN or MK. We show that expression of ALK plus IRS-1 renders these cells independent of IL-3 owing to the activation of ALK by endogenous MK. Mutational analysis reveals that this transformed phenotype of 32D cells requires kinase-active ALK as well as the interaction of ALK with IRS-1. Furthermore, 32D/IRS-1/ALK cells display an enhanced activation of mitogen-activated protein kinase and PI3-kinase pathways, and a selective transcriptional activation of nuclear factor (NF)-kappaB. Small interfering RNA-mediated knockdown of the endogenous MK or p65/NF-kappaB revealed that both these are rate limiting for the transformed phenotype induced by ALK plus IRS-1. We conclude that the recruitment of IRS-1 to activated ALK and the activation of NF-kappaB are essential for the autocrine growth and survival signaling of MK.

Expression-guided in silico evaluation of candidate cis regulatory codes for Drosophila muscle founder cells

While combinatorial models of transcriptional regulation can be inferred for metazoan systems from a priori biological knowledge, validation requires extensive and time-consuming experimental work. Thus, there is a need for computational methods that can evaluate hypothesized cis regulatory codes before the difficult task of experimental verification is undertaken. We have developed a novel computational framework (termed “CodeFinder”) that integrates transcription factor binding site and gene expression information to evaluate whether a hypothesized transcriptional regulatory model (TRM; i.e., a set of co-regulating transcription factors) is likely to target a given set of co-expressed genes. Our basic approach is to simultaneously predict cis regulatory modules (CRMs) associated with a given gene set and quantify the enrichment for combinatorial subsets of transcription factor binding site motifs comprising the hypothesized TRM within these predicted CRMs. As a model system, we have examined a TRM experimentally demonstrated to drive the expression of two genes in a sub-population of cells in the developing Drosophila mesoderm, the somatic muscle founder cells. This TRM was previously hypothesized to be a general mode of regulation for genes expressed in this cell population. In contrast, the present analyses suggest that a modified form of this cis regulatory code applies to only a subset of founder cell genes, those whose gene expression responds to specific genetic perturbations in a similar manner to the gene on which the original model was based. We have confirmed this hypothesis by experimentally discovering six (out of 12 tested) new CRMs driving expression in the embryonic mesoderm, four of which drive expression in founder cells.

Although genome sequences and much gene expression data are readily available, the determination of sets of transcription factors regulating particular gene expression patterns remains a problem of fundamental importance. Tissue-specific gene expression in developing animals is regulated through the combinatorial interactions of transcription factors with DNA regulatory elements termed cis regulatory modules (CRMs). Although genetic and biochemical experiments allow the identification of transcription factors and CRMs, those experiments are laborious and time-consuming. Philippakis et al. introduce a new approach (termed “CodeFinder”) for quantifying the enrichment for particular combinations of transcription factor binding site motifs within predicted CRMs associated with a given gene set of interest, identified from gene expression data. The authors' analyses allowed them to discover a specific combination of transcription factor binding site motifs that constitute a core cis regulatory code for expression of a particular subset of genes in muscle founder cells, an embryonic cell population in the developing fruit fly (Drosophila melanogaster) mesoderm, and also led them to the discovery and subsequent experimental validation of novel, tissue-specific CRMs. Importantly, the CodeFinder approach is generally applicable, and thus could be used to support, refute, or refine a known or hypothesized cis regulatory code for any biological system or genome of interest.

Anaplastic lymphoma kinase is dynamically expressed on subsets of motor neurons and in the peripheral nervous system

During embryonic development, complex events, such as cellular proliferation, differentiation, survival, and guidance of axons, are orchestrated and regulated by a variety of extracellular signals. Receptor tyrosine kinases mediate many of these events, with several playing critical roles in neuronal survival and axonal guidance. It is evident that not all the receptor tyrosine kinases that play key roles in regulating neuronal development have been identified. In this study, we have characterized the spatial-temporal expression profile of a recently identified receptor tyrosine kinase, anaplastic lymphoma kinase (ALK), in embryonic chick by means of whole-mount in situ hybridization in conjunction with immunohistochemistry. Our findings reveal that Alk is expressed in sympathetic and dorsal root ganglia as early as stage 19. In addition, mRNA is expressed from stage 23/24 (E4) to stage 39 (E13) in discrete motor neuron subsets of chick spinal cord along with a select group of muscles that are innervated by one of these particular motor neuron clusters. Expression within the spinal cord is coincident with the onset and duration of motor neuron programmed cell death and during the period of musculature innervation and synapse formation. Hence, the data presented here identify ALK as a novel candidate receptor for regulating critical events in the development of neurons in both the central and the peripheral nervous systems.

Drosophila Rolling pebbles colocalises and putatively interacts with alpha-Actinin and the Sls isoform Zormin in the Z-discs of the sarcomere and with Dumbfounded/Kirre, alpha-Actinin and Zormin in the terminal Z-discs

The rolling pebbles gene of Drosophila encodes two proteins, one of which, Rols7, is essential for myoblast fusion. In addition, Rols 7 is expressed during myofibrillogenesis and in the mature muscles. Here it overlaps with alpha-Actinin (alpha-Actn) and the N-terminus of D-Titin/Kettin/Zormin in the Z-line of the sarcomeres. In the attachment sites of the somatic muscles, Rols7 and the immunoglobulin superfamily protein Dumbfounded/Kin of irreC (Duf/Kirre) colocalise. As Duf/Kirre is detectable only transiently, it may be involved in establishing the first contact of the outgrowing muscle fiber to the epidermal attachment site. We propose that Rols7 and Duf/Kirre link the terminal Z-disc to the cell membrane by direct interaction. This is supported by the fact that in yeast two hybrid assays the tetratricopeptide repeat E (TPR E) of Rols7 shows interaction with the intracellular domain of Duf/Kirre. The colocalisation of Rols7 with alpha-Actn and with D-Titin/Kettin/Zormin in the Z-dics is reflected in interactions with different domains of Rols7 in this assay. In summary, these data show that besides the role in myoblast fusion, Rols7 is a scaffold protein during myofibrillogenesis and in the Z-line of the sarcomere as well as in the terminal Z-disc linking the muscle to the epidermal attachment sites.

Characterization of the expression of the ALK receptor tyrosine kinase in mice

Anaplastic Lymphoma Kinase (ALK), a receptor tyrosine kinase, was first described as the fusion product causing a subtype of non-Hodgkin's lymphoma. To date Alk has been reported to be mainly expressed in CNS and other parts of the brain. Here we describe an extensive characterization of the mRNA and protein expression of ALK during mouse development. We show that mRNA and ALK protein show overlapping expressing patterns in specific regions of the central and the peripheral nervous systems. Furthermore, ALK is also expressed in the eye, nasal epithelium, olfactory nerve, tongue, skin, tissue surrounding the esophagus, stomach and midgut but not the hindgut. Expression of ALK is also found in testis and ovary.

Role of the subcellular localization of ALK tyrosine kinase domain in neuronal differentiation of PC12 cells

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase essentially and transiently expressed in specific areas of the developing central and peripheral nervous systems. We previously demonstrated that a membrane-bound and constitutively active form of the ALK protein tyrosine kinase (PTK) domain induced the neuron-like differentiation of PC12 cells through specific activation of the mitogen-activated protein kinase (MAP kinase) pathway. Its PTK domain had been originally identified in a nucleo-cytosolic and constitutively active transforming protein, NPM-ALK. Downstream targets involved in oncogenic proliferation and survival processes have been proposed to include phospholipase Cgamma (PLCgamma), phosphoinositide 3-kinase (PI 3-kinase)/AKT, STAT 3/5 and Src. We therefore postulated that activation of specific signaling pathways leading to differentiation or proliferation can be differently controlled depending on the subcellular localization of ALK PTK domain. To increase knowledge of its physiological role in the nervous system, we focused in the present study on the influence of its subcellular localization on neuronal differentiation. To achieve this goal, we characterized biological responses and transduction pathways in PC12 cells elicited by various constructs encoding membrane-bound (through transmembrane or myristyl sequences) or cytosolic ALK-derived proteins. In order to control the activation of their PTK domain, we used an inducible dimerization system. Here, we demonstrate that membrane attachment of the ALK PTK domain, in PC12 cells, is crucial for initiation of neurite outgrowth and proliferation arrest through a decrease of DNA synthesis. Furthermore, we show that this differentiation process relies on specific and sustained activation of ERK 1/2 proteins. By contrast, activation of the cytosolic form of this domain fails to induce MAP kinase activation and cell differentiation but promotes a PI 3-kinase/AKT-dependent PC12 cell proliferation. These data indicate that subcellular localization of the ALK PTK domain was a determinant for the control and specificity of downstream transduction cascades and was crucial for deciding the fate to which the neuronal cell will be committed.

Neuronal substrates of complex behaviors in C. elegans

A current challenge in neuroscience is to bridge the gaps between genes, proteins, neurons, neural circuits, and behavior in a single animal model. The nematode Caenorhabditis elegans has unique features that facilitate this synthesis. Its nervous system includes exactly 302 neurons, and their pattern of synaptic connectivity is known. With only five olfactory neurons, C. elegans can dynamically respond to dozens of attractive and repellent odors. Thermosensory neurons enable the nematode to remember its cultivation temperature and to track narrow isotherms. Polymodal sensory neurons detect a wide range of nociceptive cues and signal robust escape responses. Pairing of sensory stimuli leads to long-lived changes in behavior consistent with associative learning. Worms exhibit social behaviors and complex ultradian rhythms driven by Ca(2+) oscillators with clock-like properties. Genetic analysis has identified gene products required for nervous system function and elucidated the molecular and neural bases of behaviors.

Ablation of oncogenic ALK is a viable therapeutic approach for anaplastic large-cell lymphomas

Anaplastic large-cell lymphomas (ALCLs) carry chromosome translocations in which the anaplastic lymphoma kinase (ALK) gene is fused to several partners, most frequently, the NPM1 gene. We have demonstrated that the constitutive activation of ALK fusion proteins results in cellular transformation and lymphoid neoplasia. Herein, we specifically down-regulated ALK protein expression by using small hairpin RNA (shRNA) targeting a sequence coding for the catalytic domain of ALK. The ablation of ALK leads to the down-modulation of known ALK downstream effectors, cell growth arrest, and reversion of the transformed phenotype of ALK(+) mouse embryonic fibroblasts in vitro and in vivo. In human ALCL cells lentiviral-mediated ALK knock-down leads to G(1) cell-cycle arrest and apoptosis in vitro and tumor growth inhibition and regression in vivo. Using a specific approach we have demonstrated that the survival and growth of ALK(+) ALCLs are strictly dependent on ALK activation and signaling. Therefore, ALK is a viable target for therapeutic intervention and its inactivation might represent a pivotal approach for the treatment of ALK lymphomas and other ALK-dependent human tumors.

What have we learnt from mouse models of NPM-ALK-induced lymphomagenesis?

The nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) is generated as a t(2;5) chromosomal breakpoint product, typically in CD30(+) anaplastic large cell lymphomas. Activation of the NPM-ALK tyrosine kinase by NPM dimerisation causes autophosphorylation at multiple tyrosine residues and the consequent recruitment of a 'signalosome' that couples the fusion protein to pathways regulating mitogenesis and apoptosis. This review focuses on recent advances in our understanding of the transforming signals induced by this fusion protein in mouse models.

p130Cas mediates the transforming properties of the anaplastic lymphoma kinase

Translocations of the anaplastic lymphoma kinase (ALK) gene have been described in anaplastic large-cell lymphomas (ALCLs) and in stromal tumors. The most frequent translocation, t(2;5), generates the fusion protein nucleophosmin (NPM)-ALK with intrinsic tyrosine kinase activity. Along with transformation, NPM-ALK induces morphologic changes in fibroblasts and lymphoid cells, suggesting a direct role of ALK in cell shaping. In this study, we used a mass-spectrometry-based proteomic approach to search for proteins involved in cytoskeleton remodeling and identified p130Cas (p130 Crk-associated substrate) as a novel interactor of NPM-ALK. In 293 cells and in fibroblasts as well as in human ALK-positive lymphoma cell lines, NPM-ALK was able to bind p130Cas and to induce its phosphorylation. Both of the effects were dependent on ALK kinase activity and on the adaptor protein growth factor receptor-bound protein 2 (Grb2), since no binding or phosphorylation was found with the kinase-dead mutant NPM-ALK(K210R) or in the presence of a Grb2 dominant-negative protein. Phosphorylation of p130Cas by NPM-ALK was partially independent from Src (tyrosine kinase pp60c-src) kinase activity, as it was still detectable in Syf-/- cells. Finally, p130Cas-/- (also known as Bcar1-/-) fibroblasts expressing NPM-ALK showed impaired actin filament depolymerization and were no longer transformed compared with wild-type cells, indicating an essential role of p130Cas activation in ALK-mediated transformation.

Activation and inhibition of anaplastic lymphoma kinase receptor tyrosine kinase by monoclonal antibodies and absence of agonist activity of pleiotrophin

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase that is transiently expressed in specific regions of the central and peripheral nervous systems, suggesting a role in its normal development and function. The nature of the cognate ligands of ALK in vertebrate is still a matter of debate. We produced a panel of monoclonal antibodies (mAbs) directed against the extracellular domain of the human receptor. Two major species of ALK (220 and 140 kDa) were identified in transfected cells, and the use of our mAbs established that the 140-kDa species results from a cleavage of the 220-kDa form. Two mAbs, in the nm range, induced the differentiation of PC12 cells transiently transfected with ALK. In human embryonic kidney 293 cells stably expressing ALK, these two mAbs strongly activated the receptor and subsequently the mitogen-activated protein kinase pathway. We further showed for the first time that activation of ALK also resulted in a specific activation of STAT3. In contrast, other mAbs presented the characteristics of blocking antibodies. Finally, in these cell systems, a mitogenic form of pleiotrophin, a proposed ligand of ALK, failed to activate this receptor. Thus, in the absence of clearly established ligand(s) in vertebrates, the availability of mAbs allowing the activation or the inhibition of the receptor will be essential for a better understanding of the biological roles of ALK.

Nuclear integration of positive Dpp signals, antagonistic Wg inputs and mesodermal competence factors during Drosophila visceral mesoderm induction

Tissue induction during embryonic development relies to a significant degree on the integration of combinatorial regulatory inputs at the enhancer level of target genes. During mesodermal tissue induction in Drosophila, various combinations of inductive signals and mesoderm-intrinsic transcription factors cooperate to induce the progenitors of different types of muscle and heart precursors at precisely defined positions within the mesoderm layer. Dpp signals are required in cooperation with the mesoderm-specific NK homeodomain transcription factor Tinman (Tin) to induce all dorsal mesodermal tissue derivatives, which include dorsal somatic muscles, the dorsal vessel and visceral muscles of the midgut. Wingless (Wg) signals modulate the responses to Dpp/Tin along anteroposterior positions by cooperating with Dpp/Tin during dorsal vessel and somatic muscle induction while antagonizing Dpp/Tin during visceral mesoderm induction. As a result, dorsal muscle and cardiac progenitors form in a pattern that is reciprocal to that of visceral muscle precursors along the anteroposterior axis. Our present study addresses how positive Dpp signals and antagonistic Wg inputs are integrated at the enhancer level of bagpipe (bap), a NK homeobox gene that serves as an early regulator of visceral mesoderm development. We show that an evolutionarily conserved bap enhancer element requires combinatorial binding sites for Tin and Dpp-activated Smad proteins for its activity. Adjacent binding sites for the FoxG transcription factors encoded by the Sloppy paired genes (slp1 and slp2), which are direct targets of the Wg signaling cascade, serve to block the synergistic activity of Tin and activated Smads during bap induction. In addition, we show that binding sites for yet unknown repressors are essential to prevent the induction of the bap enhancer by Dpp in the dorsal ectoderm. Our data illustrate how the same signal combinations can have opposite effects on different targets in the same cells during tissue induction.

The relative role of the T-domain and flanking sequences for developmental control and transcriptional regulation in protein chimeras of Drosophila OMB and ORG-1

optomotor-blind (omb) and optomotor-blind related-1 (org-1) encode T-domain DNA binding proteins in Drosophila. Members of this family of transcription factors play widely varying roles during early development and organogenesis in both vertebrates and invertebrates. Functional specificity differs in spite of similar DNA binding preferences of all family members. Using a series of domain swap chimeras, in which different parts of OMB and ORG-1 were mutually exchanged, we investigated the relevance of individual domains in vitro and in vivo. In cell culture transfection assays, ORG-1 was a strong transcriptional activator, whereas OMB appeared neutral. The main transcriptional activation function was identified in the C-terminal part of ORG-1. Also in vivo, OMB and ORG-1 showed qualitative differences when the proteins were ectopically expressed during development. Gain-of-function expression of OMB is known to counteract eye formation and resulted in the loss of the arista, whereas ORG-1 had little effect on eye development but caused antenna-to-leg transformations and shortened legs in the corresponding gain-of-function situations. The functional properties of OMB/ORG-1 chimeras in several developmental contexts was dominated by the origin of the C-terminal region, suggesting that the transcriptional activation potential can be one major determinant of developmental specificity. In late eye development, we observed, however, a strong influence of the T-domain on ommatidial differentiation. The specificity of chimeric omb/org-1transgenes, thus, depended on the cellular context in which they were expressed. This suggests that both transcriptional activation/repression properties as well as intrinsic DNA binding specificity can contribute to the functional characteristics of T-domain factors.

An SCF-like ubiquitin ligase complex that controls presynaptic differentiation

During synapse formation, specialized subcellular structures develop at synaptic junctions in a tightly regulated fashion. Cross-signalling initiated by ephrins, Wnts and transforming growth factor-beta family members between presynaptic and postsynaptic termini are proposed to govern synapse formation. It is not well understood how multiple signals are integrated and regulated by developing synaptic termini to control synaptic differentiation. Here we report the identification of FSN-1, a novel F-box protein that is required in presynaptic neurons for the restriction and/or maturation of synapses in Caenorhabditis elegans. Many F-box proteins are target recognition subunits of SCF (Skp, Cullin, F-box) ubiquitin-ligase complexes. fsn-1 functions in the same pathway as rpm-1, a gene encoding a large protein with RING finger domains. FSN-1 physically associates with RPM-1 and the C. elegans homologues of SKP1 and Cullin to form a new type of SCF complex at presynaptic periactive zones. We provide evidence that T10H9.2, which encodes the C. elegans receptor tyrosine kinase ALK (anaplastic lymphoma kinase), may be a target or a downstream effector through which FSN-1 stabilizes synapse formation. This neuron-specific, SCF-like complex therefore provides a localized signal to attenuate presynaptic differentiation.

Anaplastic lymphoma kinase proteins in growth control and cancer

The normal functions of full-length anaplastic lymphoma kinase (ALK) remain to be completely elucidated. Although considered to be important in neural development, recent studies in Drosophila also highlight a role for ALK in gut muscle differentiation. Indeed, the Drosophila model offers a future arena for the study of ALK, its ligands and signalling cascades. The discovery of activated fusion forms of the ALK tyrosine kinase in anaplastic large cell lymphoma (ALCL) has dramatically improved our understanding of the pathogenesis of these lymphomas and enhanced the pathological diagnosis of this subtype of non-Hodgkin's lymphoma (NHL). Likewise, the realisation that a high percentage of inflammatory myofibroblastic tumours express activated-ALK fusion proteins has clarified the causation of these mesenchymal neoplasms and provided for their easier discrimination from other mesenchymal-derived inflammatory myofibroblastic tumour (IMT) mimics. Recent reports of ALK expression in a range of carcinoma-derived cell lines together with its apparent role as a receptor for PTN and MK, both of which have been implicated in tumourigenesis, raise the possibility that ALK-mediated signalling could play a role in the development and/or progression of a number of common solid tumours. The therapeutic targeting of ALK may prove to have efficacy in the treatment of many of these neoplasms.

Tbx1 has a dual role in the morphogenesis of the cardiac outflow tract

Dysmorphogenesis of the cardiac outflow tract (OFT) causes many congenital heart defects, including those associated with DiGeorge syndrome. Genetic manipulation in the mouse and mutational analysis in patients have shown that Tbx1, a T-box transcription factor, has a key role in the pathogenesis of this syndrome. Here, we have dissected Tbx1 function during OFT development using genetically modified mice and tissue-specific deletion, and have defined a dual role for this protein in OFT morphogenesis. We show that Tbx1 regulates cell contribution to the OFT by supporting cell proliferation in the secondary heart field, a source of cells fated to the OFT. This process might be regulated in part by Fgf10, which we show for the first time to be a direct target of Tbx1 in vitro. We also show that Tbx1 expression is required in cells expressing Nkx2.5 for the formation of the aorto-pulmonary septum, which divides the aorta from the main pulmonary artery. These results explain why aortic arch patterning defects and OFT defects can occur independently in individuals with DiGeorge syndrome. Furthermore, our data link, for the first time, the function of the secondary heart field to congenital heart disease.

T-box genes and heart development: Putting the ?T? in heart

Members of the T-box gene family (Tbx) are essential for normal heart development, and mutations in human TBX genes cause congenital cardiovascular malformations. T-box genes have been implicated in early cardiac lineage determination, chamber specification, valvuloseptal development, and diversification of the specialized conduction system in vertebrate embryos. These genes include Tbx1, Tbx2, Tbx3, Tbx5, Tbx18, and Tbx20, all of which exhibit complex temporal spatial regulation in developing cardiac structures. Less is known about T-box genes in invertebrate heart development, but multiple T-box genes are expressed in Drosophila cardiac lineages. The molecular hierarchies and developmental processes controlled by T-box genes in the heart are the focus of this review.