Analysis of SHP-1-mediated Down-regulation of the TRK-T3 Oncoprotein Identifies Trk-fused Gene (TFG) as a Novel SHP-1-interacting Protein

Bovine ovarian follicular growth and development correlate with lysophosphatidic acid expression

The basis of successful reproduction is proper ovarian follicular growth and development. In addition to prostaglandins and vascular endothelial growth factor, a number of novel factors are suggested as important regulators of follicular growth and development: PGES, TFG, CD36, RABGAP1, DBI and BTC. This study focuses on examining the expression of these factors in granulosa and thecal cells that originate from different ovarian follicle types and their link with the expression of lysophosphatidic acid (LPA), known local regulator of reproductive functions in the cow. Ovarian follicles were divided into healthy, transitional, and atretic categories. The mRNA expression levels for PGES, TFG, CD36, RABGAP1, DBI and BTC in granulosa and thecal cells in different follicle types were measured by real-time PCR. The correlations among expression of enzymes synthesizing LPA (autotaxin, phospholipase A2), receptors for LPA and examined factors were measured. Immunolocalization of PGES, TFG, CD36, RABGAP1, DBI and BTC was examined by immunohistochemistry. We investigated follicle-type dependent mRNA expression of factors potentially involved in ovarian follicular growth and development, both in granulosa and thecal cells of bovine ovarian follicles. Strong correlations among receptors for LPA, enzymes synthesizing LPA, and the examined factors in healthy and transitional follicles were observed, with its strongest interconnection with TFG, DBI and RABGAP1 in granulosa cells, and TFG in thecal cells; whereas no correlations in atretic follicles were detected. A greater number of correlations were found in thecal cells than in granulosa cells as well as in healthy follicles than in transitional follicles. These data indicate the role of LPA in the growth, development and physiology of the bovine ovarian follicle.

Novel approaches in anaplastic thyroid cancer therapy

Anaplastic thyroid cancer (ATC), accounting for less than 2% of all thyroid cancer, is responsible for the majority of death from all thyroid malignancies and has a median survival of 6 months. The resistance of ATC to conventional thyroid cancer therapies, including radioiodine and thyroid-stimulating hormone suppression, contributes to the very poor prognosis of this malignancy. This review will cover several cellular signaling pathways and mechanisms, including RET/PTC, RAS, BRAF, Notch, p53, and histone deacetylase, which are identified to play roles in the transformation and dedifferentiation process, and therapies that target these pathways. Lastly, novel approaches and agents involving the Notch1 pathway, nuclear factor κB, Trk-fused gene, cancer stem-like cells, mitochondrial mutation, and tumor immune microenvironment are discussed. With a better understanding of the biological process and treatment modality, the hope is to improve ATC outcome in the future.

Bisem N, R. Vincent S, Tooyama I. Immunohistochemical Localization of an Isoform of TRK-Fused Gene-Like Protein in the Rat Retina

The TRK-fused gene (TFG) was originally identified in chromosome translocation events, creating a pair of oncogenes in some cancers, and was recently demonstrated as the causal gene of hereditary motor and sensory neuropathy with proximal dominant involvement. Recently, we cloned an alternative splicing variant of Tfg from a cDNA library of the rat retina, tentatively naming it retinal Tfg (rTfg). Although the common form of Tfg is ubiquitously expressed in most rat tissues, rTfg expression is localized to the central nervous system. In this study, we produced an antibody against an rTFG-specific amino acid sequence and used it to examine the localization of rTFG-like protein in the rat retina by immunohistochemistry and Western blots. Western blot analysis showed that the antibody detected a single band of 24 kDa in the rat retina. When we examined rTFG recombinant protein, the antibody detected two bands of about 42 kDa and 24 kDa. The results suggest that the 24 kDa rTFG-like protein is a fragment of rTFG. In our immunohistochemical studies of the rat retina, rTFG-like immunoreactivity was observed in all calbindin D-28K-positive horizontal cells and in some syntaxin 1-positive amacrine cells (ACs). In addition, the rTFG-like immunopositive ACs were actually glycine transporter 1-positive glycinergic or glutamate decarboxylase-positive GABAergic ACs. Our findings indicate that this novel 24 kDa rTFG-like protein may play a specific role in retinal inhibitory interneurons.

Expression and Localization of TRK-Fused Gene Products in the Rat Brain and Retina

The TRK-fused gene (TFG in human, Tfg in rat) was originally identified in human papillary thyroid cancer as a chimeric form of the NTRK1 gene. It has been reported that the gene product (TFG) plays a role in regulating phosphotyrosine-specific phosphatase-1 activity. However, no information regarding the localization of Tfg in rat tissues is available. In this study, we investigated the expression of Tfg mRNA in normal rat tissues using reverse transcription-polymerase chain reaction (RT-PCR). We also produced an antibody against Tfg gene products and examined the localization of TFG in the rat brain and retina. The RT-PCR experiments demonstrated that two types of Tfg mRNA were expressed in rat tissues: the conventional form of Tfg (cTfg) and a novel variant form, retinal Tfg (rTfg). RT-PCR analyses demonstrated that cTfg was ubiquitously expressed in rat tissues, while rTfg was predominantly expressed in the brain and retina. Western blot analysis demonstrated two bands with molecular weights of about 30 kDa and 50 kDa in the rat brain. Immunohistochemistry indicated that TFG proteins were predominantly expressed by neurons in the brain. In the rat retina, intense TFG-immunoreactivity was detected in the layer of rods and cones and the outer plexiform layer.

Immunohistochemical Mapping of TRK-Fused Gene Products in the Rat Brainstem

The TRK-fused gene (TFG in human, Tfg in rat) was originally identified in human papillary thyroid cancer as a chimeric form of the NTRK1 gene. It was since reported that the gene product (TFG) plays a role in regulating phosphotyrosine-specific phosphatase-1 activity. As shown in the accompanying paper, we produced an antibody to rat TFG and used it to localize TFG to selected neurons in specific regions. In the present study, we mapped the TFG-positive neurons in the brainstem, cerebellum, and spinal cord of rats. In the brainstem, neurons intensely positive for TFG were distributed in the raphe nuclei, the gigantocellular reticular nucleus, the reticulotegmental nucleus of the pons, and some cranial nerve nuclei such as the trigeminal nuclei, the vestibulocochlear nuclei, and the dorsal motor nucleus of the vagus. Purkinje cells in the cerebellum and motor neurons in the spinal anterior horn were also positive for TFG. These results provide fundamental data for studying the functions of TFG in the brain.

Mechanisms of activation and repression by the alternative splicing factors RBFOX1/2

RBFOX1 and RBFOX2 are alternative splicing factors that are predominantly expressed in the brain and skeletal muscle. They specifically bind the RNA element UGCAUG, and regulate alternative splicing positively or negatively in a position-dependent manner. The molecular basis for the position dependence of these and other splicing factors on alternative splicing of their targets is not known. We explored the mechanisms of RBFOX splicing activation and repression using an MS2-tethering assay. We found that the Ala/Tyr/Gly-rich C-terminal domain is sufficient for exon activation when tethered to the downstream intron, whereas both the C-terminal domain and the central RRM are required for exon repression when tethered to the upstream intron. Using immunoprecipitation and mass spectrometry, we identified hnRNP H1, RALY, and TFG as proteins that specifically interact with the C-terminal domain of RBFOX1 and RBFOX2. RNA interference experiments showed that hnRNP H1 and TFG modulate the splicing activity of RBFOX1/2, whereas RALY had no effect. However, TFG is localized in the cytoplasm, and likely modulates alternative splicing indirectly.

Rearrangements of NTRK1 gene in papillary thyroid carcinoma

TRK oncogenes are observed in a consistent fraction of papillary thyroid carcinoma (PTC); they arise from the fusion of the 3' terminal sequences of the NTRK1/NGF receptor gene with 5' terminal sequences of various activating genes, such as TPM3, TPR and TFG. TRK oncoproteins display constitutive tyrosine-kinase activity, leading to in vitro and in vivo transformation. In this review studies performed during the last 20 years will be summarized. The following topics will be illustrated: (a) frequency of TRK oncogenes and correlation with radiation and tumor histopathological features; (b) molecular mechanisms underlying NTRK1 oncogenic rearrangements; (c) molecular and biochemical characterization of TRK oncoproteins, and their mechanism of action; (d) role of activating sequences in the activation of TRK oncoproteins.

The tyrosine 343 residue of nucleophosmin (NPM)-anaplastic lymphoma kinase (ALK) is important for its interaction with SHP1, a cytoplasmic tyrosine phosphatase with tumor suppressor functions

The cytoplasmic tyrosine phosphatase SHP1 has been shown to inhibit the oncogenic fusion protein nucleophosmin (NPM)-anaplastic lymphoma kinase (ALK), and loss of SHP1 contributes to NPM-ALK-mediated tumorigenesis. In this study, we aimed to further understand how SHP1 interacts and regulates NPM-ALK. We employed an in vitro model in which GP293 cells were transfected with various combinations of NPM-ALK (or mutants) and SHP1 (or mutants) expression vectors. We found that SHP1 co-immunoprecipitated with NPM-ALK, but not the enzymatically inactive NPM-ALK(K210R) mutant, or the mutant in which all three functionally important tyrosine residues (namely, Tyr(338), Tyr(342), and Tyr(343)) in the kinase activation loop (KAL) of ALK were mutated. Interestingly, whereas mutation of Tyr(338) or Tyr(342) did not result in any substantial change in the NPM-ALK/SHP1 binding (assessed by co-immunoprecipitation), mutation of Tyr(343) abrogated this interaction. Furthermore, the NPM-ALK/SHP1 binding was readily detectable when each of the remaining 8 tyrosine residues known to be phosphorylated were mutated. Although the expression of SHP1 effectively reduced the level of tyrosine phosphorylation of NPM-ALK, it did not affect that of the NPM-ALK(Y343F) mutant. In soft agar clonogenic assay, SHP1 expression significantly reduced the tumorigenicity of NPM-ALK but not that of NPM-ALK(Y343F). In conclusion, we identified Tyr(343) of NPM-ALK as the crucial site for mediating the NPM-ALK/SHP1 interaction. Our results also support the notion that the tumor suppressor effects of SHP1 on NPM-ALK are dependent on its ability to bind to this oncogenic protein.

Role of STAT3 in in vitro transformation triggered by TRK oncogenes

TRK oncoproteins are chimeric versions of the NTRK1/NGF receptor and display constitutive tyrosine kinase activity leading to transformation of NIH3T3 cells and neuronal differentiation of PC12 cells. Signal Transducer and Activator of Transcription (STAT) 3 is activated in response to cytokines and growth factors and it has been recently identified as a novel signal transducer for TrkA, mediating the functions of NGF in nervous system. In this paper we have investigated STAT3 involvement in signalling induced by TRK oncogenes. We showed that TRK oncogenes trigger STAT3 phosphorylation both on Y705 and S727 residues and STAT3 transcriptional activity. MAPK pathway was involved in the induction of STAT3 phosphorylation. Interestingly, we have shown reduced STAT3 protein level in NIH3T3 transformed foci expressing TRK oncogenes. Overall, we have unveiled a dual role for STAT3 in TRK oncogenes-induced NIH3T3 transformation: i) decreased STAT3 protein levels, driven by TRK oncoproteins activity, are associated to morphological transformation; ii) residual STAT3 transcriptional activity is required for cell growth.

Repression of SHP-1 expression by p53 leads to trkA tyrosine phosphorylation and suppression of breast cancer cell proliferation

The nerve growth factor (NGF) receptor, trkA, the tumour suppressor p53 and the phosphatase SHP-1 are critical in cell proliferation and differentiation. SHP-1 is a trkA phosphatase that dephosphorylates trkA at tyrosines (Y) 674 and 675. p53 can induce trkA activation and tyrosine phosphorylation in the absence of NGF stimulation. In breast cancer tumours trkA expression is associated with increased patient survival. TrkA protein expression is higher in breast-cancer cell lines than in normal breast epithelia. In cell lines (but not in normal breast epithelia) trkA is functional and can be NGF-stimulated to promote cell proliferation. This study investigates the functional relationship between trkA, p53 and SHP-1 in breast-cancer, and reveals that in wild-type (wt) trkA expressing breast-cancer cells both endogenous wtp53, activated by therapeutic agents, and transfected wtp53 repress expression of SHP-1 through the proximal CCAAT sequence of the SHP-1-P1-promoter and the transcription factor NF-Y. In these cells trkA-Y674/Y675 phosphorylation is detected when SHP-1 protein levels decrease in a wtp53-dependent manner. Proliferation and cell-cycle assays, with cells expressing endogenous or transfected wt-trkA and a temperature-sensitive p53 grown at 32 degrees C (when p53 is in the wt configuration), show suppressed cell proliferation. Suppression is not detected when grown at 37 degrees C (when p53 is in the mutant configuration). A release from suppression is observed when these cells are transiently transfected with wt-SHP-1 and grown at 32 degrees C. Suppression is also detected when, as control, wt-trkA-expressing cells are transiently transfected with SHP-1-siRNA, but not when a dominant-negative (DN) mutant trkA is used to abolish wt-trkA activity. Importantly, suppression is not seen with control trkA-negative breast-cancer cells (expressing wtp53, wt-SHP-1 and undetectable trkA), transfected with Y674F/Y675F mutant-trkA. BrdU-incorporation experiments reveal lack of incorporation in cells expressing wt-trkA and wtp53, or wt-trkA and SHP-1-siRNA. However, BrdU is incorporated in the presence of Y674F/Y675F mutant trkA or DN mutant trkA. These results indicate that p53 repression of SHP-1 expression leads to trkA-Y674/Y675 phosphorylation and trkA-dependent suppression of breast-cancer cell proliferation. These data provide an explanation as to why high trkA levels are associated with favourable prognosis.

Gene expression profiling of bovine preovulatory follicles: gonadotropin surge and prostanoid-dependent up-regulation of genes potentially linked to the ovulatory process

The molecular mechanisms of ovulation and luteinization have not been well established, partially due to lack of a comprehensive understanding of functionally significant genes up-regulated in response to an ovulatory stimulus and the signaling pathways involved. In the present study, transcripts increased in bovine preovulatory follicles following a GnRH-induced LH surge were identified using microarray technology. Increased expression of 368 and 878 genes was detected at 12 (368 genes) and 20 h (878 genes) following GnRH injection. The temporal, cell specific and prostanoid-dependent regulation of selected genes (ADAM10, DBI, CD36, MTSS1, TFG, and RABGAP1) identified from microarray studies and related genes (ADAM17 and AREG) of potential significance were also investigated. Expression of mRNA for DBI and CD36 was simultaneously up-regulated in theca and granulosa cells (GC) following the LH surge, whereas temporal regulation of ADAM10, MTSS1, TFG, and RABGAP1 was distinct in the two cell compartments and increased granulosa TFG and RABGAP1 mRNA were prostanoid dependent. AREG mRNA was increased in theca and GCs at 12 and 24 h following GnRH injection. ADAM17 mRNA was increased in theca, but reduced in GCs 24 h following GnRH injection. The increased ADAM17 and AREG mRNA were prostanoid dependent. ADAM10 and ADAM17 protein were increased specifically in the apex but not the base of preovulatory follicles and the increase in ADAM17 was prostanoid dependent. Results reveal novel information on the regulation of preovulatory gene expression and suggest a potential functional role for ADAM10 and ADAM17 proteins in the region of follicle rupture.

ced-4 and proto-oncogene tfg-1 antagonistically regulate cell size and apoptosis in C. elegans

BACKGROUND

Cell-size-control systems, coupled with apoptotic- and cell-proliferation-regulatory mechanisms, determine the overall dimensions of organs and organisms, and their dysregulation can lead to tumor formation. The interrelationship between cell-growth-regulatory mechanisms and apoptosis during normal development and cancer is not understood. The TRK-fused gene (TFG) promotes tumorigenesis when present in chromosomal rearrangements from various human-cancer types by unknown mechanisms. Apaf1/CED-4 is essential for apoptosis but has not been shown to function in cell-growth control.

RESULTS

We found that loss of TFG-1, the TFG ortholog in Caenorhabditis elegans, results in supernumerary apoptotic corpses, whereas its overexpression is sufficient to inhibit developmentally programmed cell death. TFG-1 is also required for cells and nuclei to grow to normal size. Furthermore, we found that CED-4 is required for cell-growth inhibition in animals lacking TFG-1. However, caspases, the downstream effectors of CED-4-mediated apoptosis, are not required in TFG-1- or CED-4-regulated cell-size control. CED-4 acts to inhibit cell growth by antagonizing the effects of other conserved cell-size-regulating proteins, including cAMP response element binding (CREB) protein, translation-initiation factor eIF2B, and the nucleolar p53-interacting protein nucleostemin.

CONCLUSIONS

These findings show that TFG-1 suppresses apoptosis and is essential for normal cell-size control, suggesting that abnormalities in the cell-growth-promoting and apoptosis-inhibiting functions of TFG might be responsible for its action in tumorigenesis. Also, they reveal that CED-4 plays a pivotal role in activating apoptosis and restricting cell and nuclear size, thereby determining the appropriate overall size of an animal. Thus, these findings reveal links between the control mechanisms for apoptosis and cell growth.

SH2B1beta adaptor is a key enhancer of RET tyrosine kinase signaling

The RET gene encodes two main isoforms of a receptor tyrosine kinase (RTK) implicated in various human diseases. Activating germ-line point mutations are responsible for multiple endocrine neoplasia type 2-associated medullary thyroid carcinomas, inactivating germ-line mutations for Hirschsprung's disease, while somatic rearrangements (RET/PTCs) are specific to papillary thyroid carcinomas. SH2B1beta, a member of the SH2B adaptors family, and binding partner for several RTKs, has been recently described to interact with proto-RET. Here, we show that both RET isoforms and its oncogenic derivatives bind to SH2B1beta through the SRC homology 2 (SH2) domain and a kinase activity-dependent mechanism. As a result, RET phosphorylates SH2B1beta, which in turn enhances its autophosphorylation, kinase activity, and downstream signaling. RET tyrosine residues 905 and 981 are important determinants for functional binding of the adaptor, as removal of both autophosphorylation sites displaces its recruitment. Binding of SH2B1beta appears to protect RET from dephosphorylation by protein tyrosine phosphatases, and might represent a likely mechanism contributing to its upregulation. Thus, overexpression of SH2B1beta, by enhancing phosphorylation/activation of RET transducers, potentiates the cellular differentiation and the neoplastic transformation thereby induced, and counteracts the action of RET inhibitors. Overall, our results identify SH2B1beta as a key enhancer of RET physiologic and pathologic activities.

A novel model to identify interaction partners of the PTEN tumor suppressor gene in human bladder cancer

Phosphatase and tensin homolog (PTEN), deleted on chromosome 10, is a potent tumor suppressor. PTEN expression is reduced in advanced bladder cancer and reduction correlates with disease stage. To gain insights into the function of PTEN in human bladder cancer by identifying its binding partners, we developed a novel IPTG inducible PTEN expression system and evaluated this system in the PTEN null UMUC-3 human bladder cancer xenograft model. In this model, induction of PTEN in vivo resulted in reduced tumor growth. We used mass spectrometry to identify PTEN interaction partners in these cells, which identified known interaction partners major vault protein (MVP) and paxillin as well as a novel interaction partner, TRK fused gene (TFG). In conclusion, using a biologically relevant model system to dissect PTEN tumor suppressor function in human bladder cancer, we identified three molecules important for many cellular functions in complex with PTEN.

The TFG protein, involved in oncogenic rearrangements, interacts with TANK and NEMO, two proteins involved in the NF-κB pathway

TRK-fused gene (TFG) was first identified as a partner of NTRK1 in generating the thyroid TRK-T3 oncogene, and is also involved in oncogenic rearrangements with ALK in anaplastic lymphoma and NOR1 in mixoid chondrosarcoma. The TFG physiological role is still unknown, but the presence of a number of motifs involved in protein interactions suggests that it may function by associating with other proteins. We have recently demonstrated that TFG associates and regulates the activity of the tyrosine phosphatase SHP-1. In this study by yeast two-hybrid screening we identified NEMO and TANK, two proteins modulating the NF-kappaB pathway, as novel TFG-interacting proteins. These interactions were further characterized in vitro and in vivo. We provide evidence that TFG and NEMO may be part of the same high molecular weight complex. TFG enhances the effect of TNF-alpha, TANK, TNF receptor-associated factor (TRAF)2, and TRAF6 in inducing NF-kappaB activity. We suggest that TFG is a novel member of the NF-kappaB pathway.

Oncogenic rearrangements of the NTRK1/NGF receptor

The NTRK1 gene encodes the high affinity receptor for Nerve Growth Factor, and its action regulates neural development and differentiation. Deregulation of NTRK1 activity is associated with several human disorders. Loss of function mutations causes the genetic disease congenital insensitivity to pain with anhidrosis (CIPA). Constitutive activation of NTRK1 has been detected in several tumor types. An autocrine loop involving NTRK1 and NGF is associated with tumor progression in prostate carcinoma and in breast cancer. A novel alternative splicing variant with constitutive oncogenic potential has been recently described in neuroblastoma. Somatic rearrangements of NTRK1, producing chimeric oncogenes with constitutive tyrosine kinase activity, have been detected in a consistent fraction of papillary thyroid tumors. The topic of this review is a detailed analysis of the thyroid TRK oncogenes. The modalities of their activation, their mechanism of action, the contribution of activating sequences, and the molecular mechanisms underlying their generation will be discussed.