IRS-1 and IRS-2 are recruited by TrkA receptor and oncogenic TRK-T1

Design, synthesis, and biological evaluation of aminopyridine derivatives as novel tropomyosin receptor kinase inhibitors

Tropomyosin receptor kinase (TRK) is a successful target for the treatment of various cancers caused by NTRK gene fusions. Herein, based on a rational drug design strategy, we designed and synthesized 35 aminopyrimidine derivatives that were shown to be TRKA inhibitors in the enzyme assay, among which compounds C3, C4, and C6 showed potent inhibitory activities against TRKA with IC₅₀ values of 6.5, 5.0, and 7.0 nM, respectively. In vitro antiproliferative activity study showed that compound C3 significantly inhibited the proliferation of KM-12 cells but had weak inhibitory effect on MCF-7 cells and HUVEC cells. The preliminary druggability evaluation showed that compound C3 exhibited favorable liver microsomal and plasma stabilities and had weak or no inhibitory activity against cytochrome P450 isoforms at 10 µM. Compounds C3, C4, and C6 were also selected for ADME (absorption, distribution, metabolism, and elimination) properties prediction and molecular docking studies. Inhibition experiments showed that compound C3 was not selective for TRK subtypes. All results indicated that compound C3 was a useful candidate for the development of TRK inhibitors.

Design, synthesis and biological evaluation of pyrazolo[3,4-b]pyridine derivatives as TRK inhibitors

Tropomyosin receptor kinases (TRKs) are associated with the proliferation and differentiation of cells, and thus their continuous activation and overexpression cause cancer. Herein, based on scaffold hopping and computer-aid drug design, 38 pyrazolo[3,4-b]pyridine derivatives were synthesised. Further, we evaluated their activities to inhibit TRKA. Among them, compound C03 showed acceptable activity with an IC50 value of 56 nM and it inhibited the proliferation of the Km-12 cell line with an IC50 value of 0.304 μM together with obvious selectivity for the MCF-7 cell line and HUVEC cell line. Furthermore, compound C03 possessed good plasma stability and low inhibitory activity to a panel of cytochrome P450 isoforms except CYP2C9. Overall, C03 has potential for further exploration.

IRS1 expression in hippocampus is age-dependent and is required for mature spine maintenance and neuritogenesis

Insulin and insulin-like growth factor type I (IGF-1) play prominent roles in brain activity throughout the lifespan. Insulin/IGF1 signaling starts with the activation of the intracellular insulin receptor substrates (IRS). In this work, we performed a comparative study of IRS1 and IRS2, together with the IGF1 (IGF1R) and insulin (IR) receptor expression in the hippocampus and prefrontal cortex during development. We found that IRS1 and IRS2 expression is prominent during development and declines in the aged hippocampus, contrary to IR, which increases in adulthood and aging. In contrast, IGF1R expression is unaffected by age. Expression patterns are similar in the prefrontal cortex. Neurite development occurs postnatally in the rodent hippocampus and cortex, and it declines in the mature and aged brain and is influenced by trophic factors. In our previous work, we demonstrated that knockdown of IRS1 by shRNA impairs learning and reduces synaptic plasticity in a rat model, as measured by synaptophysin puncta in axons. In this study, we report that shIRS1 alters spine maturation in adult hilar hippocampal neurons. Lastly, to understand the role of IRS1 in neuronal neurite tree, we transfect shIRS1 into primary neuronal cultures and observed that shIRS1 reduced neurite branching and neurite length. Our results demonstrate that IRS1/2 and insulin/IGF1 receptors display different age-dependent expression profiles and that IRS1 is required for spine maturation, demonstrating a novel role for IRS1 in synaptic plasticity.

Design, synthesis, biological evaluation and pharmacophore model analysis of novel tetrahydropyrrolo[3,4-c]pyrazol derivatives as potential TRKs inhibitors

The tropomyosin receptor kinases TRKs are responsible for different tumor types which caused by NTRK gene fusion, and have been identified as a successful target for anticancer therapeutics. Herein, we report a potent and selectivity TRKs inhibitor 19m through rational drug design strategy from a micromolar potency hit 17a. Compound 19m significantly inhibits the proliferation of TRK-dependent cell lines (Km-12), while it has no inhibitory effect on TRK-independent cell lines (A549 and THLE-2). Furthermore, kinases selectivity profiling showed that in addition to TRKs, compound 19m only displayed relatively strong inhibitory activity on ALK. These data may indicate that compound 19m has a good drug safety. Partial ADME properties were evaluated in vitro and in vivo. Compound 19m exhibited a good AUC values and volume of distribution and low clearance in the pharmacokinetics experiment of rats. Finally, a pharmacophore model guided by experimental results is proposed. We hope this theoretical model can help researchers find type I TRK inhibitors more efficiently.

The oncogenic roles of NTRK fusions and methods of molecular diagnosis

The NTRK gene family is composed of NTRK1, NTRK2, and NTRK3, which encode three tropomyosin-receptor kinases, belonging to a class of tyrosine kinase receptors. These proteins are known to play roles in cell proliferation, differentiation, apoptosis, and survival. Fusions involving the NTRK genes are long known as drivers in many tumors. Although they occur in less than 5% of all malignancies, their occurrence in a great diversity of tumors has been documented. Several rare tumors including infantile fibrosarcoma, secretory breast carcinoma, and mammary analogue secretory carcinoma are accompanied by NTRK fusions in more than 90% of cases, demonstrating a diagnostic value for the NTRK fusion testing in these tumors. More recently, the development of effective targeted therapies has created a demand for their detection in all malignancies. A variety of approaches are available for testing including immunohistochemistry, fluorescence in situ hybridization (FISH), reverse transcription polymerase chain reaction (RT-PCR), and DNA- and RNA-based next-generation sequencing (NGS). This article reviews the molecular biology and tumorigenesis of NTRK fusions, their prevalence and clinical significance with a focus on available methods for fusion detection. The advantages and limitations of different technologies, the best practice algorithms for NTRK fusion detection, and the future direction of NTRK testing are also discussed.

Targeted DNA profiling and the prevalence of NTRK aberrations in Chinese patients with head and neck cancer

OBJECTIVES

Head and neck cancers are aggressive epithelial tumours that are recognised as being particularly challenging to treat. Here, we report the targeted DNA profiling and the prevalence of neurotrophic-tropomyosin receptor tyrosine kinase gene (NTRK) aberrations in Chinese patients with head and neck cancers.

METHODS

Samples of 127 patients with head and neck cancer were retrospectively analysed. Profiling was performed by next-generation sequencing of the 1021-gene panel with tumour tissue and matched peripheral blood control samples.

RESULTS

This study was inspired by the outcome benefit of a parotid cancer patient harbouring ETV6-NTRK3 fusion, who received crizotinib treatment and achieved a 2-year progression-free survival. Genomic profiling of 127 patients with head and neck cancers indicated that TP53 is the most frequently mutated gene both in our cohort and in The Cancer Genome Atlas (TCGA) database. A higher prevalence of NTRK genetic aberrations (7.9%, 10/127), including NTRK fusion (3.1%) and mutation, was observed in our population than in TCGA. The most common fusion was the ETV6-NTRK3. Compared to the NTRK-wt group, the NTRK aberration group had more APC and PTPRD aberrations (p < 0.05). NTRK fusion was also associated with lower tumour mutation burden (TMB) (p < 0.05). TP53 and LRP1B mutations were significantly associated with higher TMB (both p < 0.01), which may be potential markers of immunotherapy.

CONCLUSIONS

This is the first study to report targeted DNA profiling of Chinese patients with head and neck cancers. As NTRK genetic aberrations are more common in this Chinese population, the efficacy of NTRK inhibitors should be studied further.

Rare cancer, rare alteration: the case of NTRK fusions in biliary tract cancers

Introduction: For patients with advanced/unresectable biliary tract cancers, cisplatin-gemcitabine combination is the standard first-line treatment. Beyond the first line, the therapeutic arsenal is limited with minimal benefit. Biliary tract cancers exhibit one of the highest frequencies of targetable molecular alterations across cancer types, and several targeted therapies are emerging as treatment options.Areas covered:We discuss neurotrophic tyrosine kinase receptor gene (NTRK) fusions in biliary tract cancers and the use of NTRK inhibitors (now approved in a 'cancer-agnostic' way), mechanisms of resistance, and emerging second-generation NTRK inhibitors.Expert opinion: Despite their rarity in biliary tract cancers, NTRK fusions are promising molecular targets because i) NTRK inhibitors have proven highly effective in NTRK-rearranged cancers and are now approved in a 'cancer-agnostic' way; ii) emerging second-generation NTRK inhibitors may overcome secondary resistance; iii) NTRK rearrangements will be readily detectable with the generalization of next-generation-sequencing in biliary tract cancers, including the detection of other frequent gene rearrangements, such as those involving the fibroblast growth factor receptor 2 gene (FGFR2). However, more data are necessary regarding the prevalence and characteristics of NTRK fusions in biliary tract cancers and the efficacy of NTRK inhibitors in these patients.

Development of small-molecule tropomyosin receptor kinase (TRK) inhibitors for NTRK fusion cancers

Tropomyosin receptor kinase A, B and C (TRKA, TRKB and TRKC), which are well-known members of the cell surface receptor tyrosine kinase (RTK) family, are encoded by the neurotrophic receptor tyrosine kinase 1, 2 and 3 (NTRK1, NTRK2 and NTRK3) genes, respectively. TRKs can regulate cell proliferation, differentiation and even apoptosis through the RAS/MAPKs, PI3K/AKT and PLCγ pathways. Gene fusions involving NTRK act as oncogenic drivers of a broad diversity of adult and pediatric tumors, and TRKs have become promising antitumor targets. Therefore, achieving a comprehensive understanding of TRKs and relevant TRK inhibitors should be urgently pursued for the further development of novel TRK inhibitors for potential clinical applications. This review focuses on summarizing the biological functions of TRKs and NTRK fusion proteins, the development of small-molecule TRK inhibitors with different chemotypes and their activity and selectivity, and the potential therapeutic applications of these inhibitors for future cancer drug discovery efforts.

Kinase gene fusions: roles and therapeutic value in progressive and refractory papillary thyroid cancer

The incidence of papillary thyroid cancer (PTC), the major type of thyroid cancer, is increasing rapidly around the world, and its pathogenesis is still unclear. There is poor prognosis for PTC involved in rapidly progressive tumors and resistance to radioiodine therapy. Kinase gene fusions have been discovered to be present in a wide variety of malignant tumors, and an increasing number of novel types have been detected in PTC, especially progressive tumors. As a tumor-driving event, kinase fusions are constitutively activated or overexpress their kinase function, conferring oncogenic potential, and their frequency is second only to BRAF^V600E mutation in PTC. Diverse forms of kinase fusions have been observed and are associated with specific pathological features of PTC (usually at an advanced stage), and clinical trials of therapeutic strategies targeting kinase gene fusions are feasible for radioiodine-resistant PTC. This review summarizes the roles of kinase gene fusions in PTC and the value of clinical therapy of targeting fusions in progressive or refractory PTC, and discusses the future perspectives and challenges related to kinase gene fusions in PTC patients.

Pediatric hemispheric high-grade glioma: targeting the future

Pediatric high-grade gliomas (pHGGs) are a group of tumors affecting approximately 0.85 children per 100,000 annually. The general outcome for these tumors is poor with 5-year survival rates of less than 20%. It is now recognized that these tumors represent a heterogeneous group of tumors rather than one entity. Large-scale genomic analyses have led to a greater understanding of the molecular drivers of different subtypes of these tumors and have also aided in the development of subtype-specific therapies. For example, for pHGG with NTRK fusions, promising new targeted therapies are actively being explored. Herein, we review the clinico-pathologic and molecular classification of these tumors, historical treatments, current management strategies, and therapies currently under investigation.

Brain insulin resistance impairs hippocampal plasticity

Nutrient-related signals have been demonstrated to influence brain development and cognitive functions. In particular, insulin signaling has been shown to impact on molecular cascades underlying hippocampal plasticity, learning and memory. Alteration of brain insulin signaling interferes with the maintenance of neural stem cell niche and neuronal activity in the hippocampus. Brain insulin resistance is also emerging as key factor causing the cognitive impairment observed in metabolic and neurodegenerative diseases. Here, we review the molecular mechanisms involved in the insulin modulation of both adult neurogenesis and synaptic activity in the hippocampus. We also summarize the effects of altered insulin sensitivity on hippocampal plasticity. Finally, we reassume the experimental and epidemiological evidence highlighting the critical role of brain insulin resistance at the crossroad between type 2 diabetes and Alzheimer's disease.

Cancer stem cells-driven tumor growth and immune escape: the Janus face of neurotrophins

Cancer Stem Cells (CSCs) are self-renewing cancer cells responsible for expansion of the malignant mass in a dynamic process shaping the tumor microenvironment. CSCs may hijack the host immune surveillance resulting in typically aggressive tumors with poor prognosis.In this review, we focus on neurotrophic control of cellular substrates and molecular mechanisms involved in CSC-driven tumor growth as well as in host immune surveillance. Neurotrophins have been demonstrated to be key tumor promoting signaling platforms. Particularly, Nerve Growth Factor (NGF) and its specific receptor Tropomyosin related kinase A (TrkA) have been implicated in initiation and progression of many aggressive cancers. On the other hand, an active NGF pathway has been recently proven to be critical to oncogenic inflammation control and in promoting immune response against cancer, pinpointing possible pro-tumoral effects of NGF/TrkA-inhibitory therapy.A better understanding of the molecular mechanisms involved in the control of tumor growth/immunoediting is essential to identify new predictive and prognostic intervention and to design more effective therapies. Fine and timely modulation of CSCs-driven tumor growth and of peripheral lymph nodes activation by the immune system will possibly open the way to precision medicine in neurotrophic therapy and improve patient's prognosis in both TrkA- dependent and independent cancers.

NTRK fusion-positive cancers and TRK inhibitor therapy

NTRK gene fusions involving either NTRK1, NTRK2 or NTRK3 (encoding the neurotrophin receptors TRKA, TRKB and TRKC, respectively) are oncogenic drivers of various adult and paediatric tumour types. These fusions can be detected in the clinic using a variety of methods, including tumour DNA and RNA sequencing and plasma cell-free DNA profiling. The treatment of patients with NTRK fusion-positive cancers with a first-generation TRK inhibitor, such as larotrectinib or entrectinib, is associated with high response rates (>75%), regardless of tumour histology. First-generation TRK inhibitors are well tolerated by most patients, with toxicity profiles characterized by occasional off-tumour, on-target adverse events (attributable to TRK inhibition in non-malignant tissues). Despite durable disease control in many patients, advanced-stage NTRK fusion-positive cancers eventually become refractory to TRK inhibition; resistance can be mediated by the acquisition of NTRK kinase domain mutations. Fortunately, certain resistance mutations can be overcome by second-generation TRK inhibitors, including LOXO-195 and TPX-0005 that are being explored in clinical trials. In this Review, we discuss the biology of NTRK fusions, strategies to target these drivers in the treatment-naive and acquired-resistance disease settings, and the unique safety profile of TRK inhibitors.

Involvement of insulin receptor substrates in cognitive impairment and Alzheimer's disease

Type 2 diabetes—associated with impaired insulin/insulin-like growth factor-1 (IGF1) signaling (IIS)—is a risk factor for cognitive impairment and dementia including Alzheimer’s disease (AD). The insulin receptor substrate (IRS) proteins are major components of IIS, which transmit upstream signals via the insulin receptor and/or IGF1 receptor to multiple intracellular signaling pathways, including AKT/protein kinase B and extracellular-signal-regulated kinase cascades. Of the four IRS proteins in mammals, IRS1 and IRS2 play key roles in regulating growth and survival, metabolism, and aging. Meanwhile, the roles of IRS1 and IRS2 in the central nervous system with respect to cognitive abilities remain to be clarified. In contrast to IRS2 in peripheral tissues, inactivation of neural IRS2 exerts beneficial effects, resulting in the reduction of amyloid β accumulation and premature mortality in AD mouse models. On the other hand, the increased phosphorylation of IRS1 at several serine sites is observed in the brains from patients with AD and animal models of AD or cognitive impairment induced by type 2 diabetes. However, these serine sites are also activated in a mouse model of type 2 diabetes, in which the diabetes drug metformin improves memory impairment. Because IRS1 and IRS2 signaling pathways are regulated through complex mechanisms including positive and negative feedback loops, whether the elevated phosphorylation of IRS1 at specific serine sites found in AD brains is a primary response to cognitive dysfunction remains unknown. Here, we examine the associations between IRS1/IRS2-mediated signaling in the central nervous system and cognitive decline.

The Medial Septum Is Insulin Resistant in the AD Presymptomatic Phase: Rescue by Nerve Growth Factor-Driven IRS1 Activation

Basal forebrain cholinergic neurons (BFCN) are key modulators of learning and memory and are high energy-demanding neurons. Impaired neuronal metabolism and reduced insulin signaling, known as insulin resistance, has been reported in the early phase of Alzheimer's disease (AD), which has been suggested to be "Type 3 Diabetes." We hypothesized that BFCN may develop insulin resistance and their consequent failure represents one of the earliest event in AD. We found that a condition reminiscent of insulin resistance occurs in the medial septum of 3 months old 3×Tg-AD mice, reported to develop typical AD histopathology and cognitive deficits in adulthood. Further, we obtained insulin resistant BFCN by culturing them with high insulin concentrations. By means of these paradigms, we observed that nerve growth factor (NGF) reduces insulin resistance in vitro and in vivo. NGF activates the insulin receptor substrate 1 (IRS1) and rescues c-Fos expression and glucose metabolism. This effect involves binding of activated IRS1 to the NGF receptor TrkA, and is lost in presence of the specific IRS inhibitor NT157. Overall, our findings indicate that, in a well-established animal model of AD, the medial septum develops insulin resistance several months before it is detectable in the neocortex and hippocampus. Remarkably, NGF counteracts molecular alterations downstream of insulin-resistant receptor and its nasal administration restores insulin signaling in 3×Tg-AD mice by TrkA/IRS1 activation. The cross-talk between NGF and insulin pathways downstream the insulin receptor suggests novel potential therapeutic targets to slow cognitive decline in AD and diabetes-related brain insulin resistance.

Insights into Current Tropomyosin Receptor Kinase (TRK) Inhibitors: Development and Clinical Application

The use of kinase-directed precision medicine has been heavily pursued since the discovery and development of imatinib. Annually, it is estimated that around ∼20 000 new cases of tropomyosin receptor kinase (TRK) cancers are diagnosed, with the majority of cases exhibiting a TRK genomic rearrangement. In this Perspective, we discuss current development and clinical applications for TRK precision medicine by providing the following: (1) the biological background and significance of the TRK kinase family, (2) a compilation of known TRK inhibitors and analysis of their cocrystal structures, (3) an overview of TRK clinical trials, and (4) future perspectives for drug discovery and development of TRK inhibitors.

The Novel Functions of High-Molecular-Mass Complexes Containing Insulin Receptor Substrates in Mediation and Modulation of Insulin-Like Activities: Emerging Concept of Diverse Functions by IRS-Associated Proteins

Insulin-like peptides, such as insulin-like growth factors (IGFs) and insulin, induce a variety of bioactivities, such as growth, differentiation, survival, increased anabolism, and decreased catabolism in many cell types and in vivo. In general, IGFs or insulin bind to IGF-I receptor (IGF-IR) or insulin receptor (IR), activating the receptor tyrosine kinase. Insulin receptor substrates (IRSs) are known to be major substrates of receptor kinases, mediating IGF/insulin signals to direct bioactivities. Recently, we discovered that IRSs form high-molecular-mass complexes (referred to here as IRSomes) even without IGF/insulin stimulation. These complexes contain proteins (referred to here as IRSAPs; IRS-associated proteins), which modulate tyrosine phosphorylation of IRSs by receptor kinases, control IRS stability, and determine intracellular localization of IRSs. In addition, in these complexes, we found not only proteins that are involved in RNA metabolism but also RNAs themselves. Thus, IRSAPs possibly contribute to modulation of IGF/insulin bioactivities. Since it is established that disorder of modulation of insulin-like activities causes various age-related diseases including cancer, we could propose that the IRSome is an important target for treatment of these diseases.

TRKing down an old oncogene in a new era of targeted therapy

The use of high-throughput next-generation sequencing techniques in multiple tumor types during the last few years has identified NTRK1, 2, and 3 gene rearrangements encoding novel oncogenic fusions in 19 different tumor types to date. These recent developments have led us to revisit an old oncogene, Trk (originally identified as OncD), which encodes the TPM3-NTRK1 gene fusion and was one of the first transforming chromosomal rearrangements identified 32 years ago. However, no drug has yet been approved by the FDA for cancers harboring this oncogene. This review will discuss the biology of the TRK family of receptors, their role in human cancer, the types of oncogenic alterations, and drugs that are currently in development for this family of oncogene targets.

SIGNIFICANCE

Precision oncology approaches have accelerated recently due to advancements in our ability to detect oncogenic mutations in tumor samples. Oncogenic alterations, most commonly gene fusions, have now been detected for the genes encoding the TRKA, TRKB, and TRKC receptor tyrosine kinases across multiple tumor types. The scientific rationale for the targeting of the TRK oncogene family will be discussed here.

NGF signaling in PC12 cells: the cooperation of p75(NTR) with TrkA is needed for the activation of both mTORC2 and the PI3K signalling cascade

PC12-27, a PC12 clone characterized by high levels of the transcription repressor REST and by very low mTORC2 activity, had been shown to be unresponsive to NGF, possibly because of its lack of the specific TrkA receptor. The neurotrophin receptor repressed by high REST in PC12-27 cells, however, is shown now to be not TrkA, which is normal, but p75(NTR), whose expression is inhibited at the transcriptional level. When treated with NGF, the PC12-27 cells lacking p75(NTR) exhibited a defective TrkA autophosphorylation restricted, however, to the TrkA(Y490) site, and an impairment of the PI3K signaling cascade. This defect was sustained in part by a mTORC1-dependent feed-back inhibition that in wtPC12 cells appeared marginal. Transfection of p75(NTR) to a level and surface distribution analogous to wtPC12 did not modify various high REST-dependent properties of PC12-27 cells such as high β-catenin, low TSC2 and high proliferation rate. In contrast, the defective PI3K signaling cascade and its associated mTORC2 activity were largely rescued together with the NGF-induced neurite outgrowth response. These changes were not due to p75(NTR) alone but required its cooperation with TrkA. Our results demonstrate that, in PC12, high REST induces alterations of NGF signaling which, however, are indirect, dependent on the repression of p75(NTR); and that the well-known potentiation by p75(NTR) of the TrkA signaling does not concern all the effects induced by NGF but primarily the PI3K cascade and its associated mTORC2, a complex known to play an important role in neural cell differentiation.

Nerve growth factor receptor TrkA, a new receptor in insulin signaling pathway in PC12 cells

TrkA is a cell surface transmembrane receptor tyrosine kinase for nerve growth factor (NGF). TrkA has an NPXY motif and kinase regulatory loop similar to insulin receptor (INSR) suggesting that NGF→TrkA signaling might overlap with insulin→INSR signaling. During insulin or NGF stimulation TrkA, insulin receptor substrate-1 (IRS-1), INSR (and presumably other proteins) forms a complex in PC12 cells. In PC12 cells, tyrosine phosphorylation of INSR and IRS-1 is dependent upon the functional TrkA kinase domain. Moreover, expression of TrkA kinase-inactive mutant blocked the activation of Akt and Erk5 in response to insulin or NGF. Based on these data, we propose that TrkA participates in insulin signaling pathway in PC12 cells.

IRS2 signalling is required for the development of a subset of sensory spinal neurons

Insulin and insulin-like growth factor-I play important roles in the development and maintenance of neurons and glial cells of the nervous system. Both factors activate tyrosine kinase receptors, which signal through adapter proteins of the insulin receptor substrate (IRS) family. Although insulin and insulin-like growth factor-I receptors are expressed in dorsal root ganglia (DRG), the function of IRS-mediated signalling in these structures has not been studied. Here we address the role of IRS2-mediated signalling in murine DRG. Studies in cultured DRG neurons from different embryonic stages indicated that a subset of nerve growth factor-responsive neurons is also dependent on insulin for survival at very early time points. Consistent with this, increased apoptosis during gangliogenesis resulted in a partial loss of trkA-positive neurons in DRG of Irs2 mutant embryos. Analyses in adult Irs2(-/-) mice revealed that unmyelinated fibre afferents, which express calcitonin gene-related peptide/substance P and isolectin B4, as well as some myelinated afferents to the skin were affected by the mutation. The diminished innervation of glabrous skin in adult Irs2(-/-) mice correlated with longer paw withdrawal latencies in the hot-plate assay. Collectively, these findings indicate that IRS2 signalling is required for the proper development of spinal sensory neurons involved in the perception of pain.

Downstream of tyrosine kinase/docking protein 6, as a novel substrate of tropomyosin-related kinase C receptor, is involved in neurotrophin 3-mediated neurite outgrowth in mouse cortex neurons

BACKGROUND

The downstream of tyrosine kinase/docking protein (Dok) adaptor protein family has seven members, Dok1 to Dok7, that act as substrates of multiple receptor tyrosine kinase and non-receptor tyrosine kinase. The tropomyosin-related kinase (Trk) receptor family, which has three members (TrkA, TrkB and TrkC), are receptor tyrosine kinases that play pivotal roles in many stages of nervous system development, such as differentiation, migration, axon and dendrite projection and neuron patterning. Upon related neurotrophin growth factor stimulation, dimerisation and autophosphorylation of Trk receptors can occur, recruiting adaptor proteins to mediate signal transduction.

RESULTS

In this report, by using yeast two-hybrid assays, glutathione S-transferase (GST) precipitation assays and coimmunoprecipitation (Co-IP) experiments, we demonstrate that Dok6 selectively binds to the NPQY motif of TrkC through its phosphotyrosine-binding (PTB) domain in a kinase activity-dependent manner. We further confirmed their interaction by coimmunoprecipitation and colocalisation in E18.5 mouse cortex neurons, which provided more in vivo evidence. Next, we demonstrated that Dok6 is involved in neurite outgrowth in mouse cortex neurons via the RNAi method. Knockdown of Dok6 decreased neurite outgrowth in cortical neurons upon neurotrophin 3 (NT-3) stimulation.

CONCLUSIONS

We conclude that Dok6 interacts with the NPQY motif of the TrkC receptor through its PTB domain in a kinase activity-dependent manner, and works as a novel substrate of the TrkC receptor involved in NT-3-mediated neurite outgrowth in mouse cortex neurons.

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.

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.

Antineoplastic effect of rapamycin is potentiated by inhibition of IRS-1 signaling in prostate cancer cells xenografts

Proper activation of phosphoinositide 3-kinase-Akt pathway is critical for the prevention of tumorigenesis. Recent data have characterized a negative feedback loop, wherein mammalian target of rapamycin (mTOR) blocks additional activation of the Akt/mTOR pathway through inhibition insulin receptor substrate 1 (IRS-1) function. However, the potential of IRS-1 inhibition during rapamycin treatment has not been examined. Herein, we show that IRS-1 antisense oligonucleotide and rapamycin synergistically antagonize the activation of mTOR in vivo and induced tumor suppression, through inhibition of proliferation and induction of apoptosis, in prostate cancer cell xenografts. These data demonstrate that the addition of agents that blocks IRS-1 potentiate the effect of mTOR inhibition in the growth of prostate cancer cell xenografts.

Variants in ARHGEF11, a candidate gene for the linkage to type 2 diabetes on chromosome 1q, are nominally associated with insulin resistance and type 2 diabetes in Pima Indians

A prior genome-wide linkage scan in Pima Indians indicated a young-onset (aged <45 years) type 2 diabetes susceptibility locus on chromosome 1q21-q23. ARHGEF11, which encodes the Rho guanine nucleotide exchange factor 11, was analyzed as a positional candidate gene for this linkage because this protein may stimulate Rho-dependent signals, such as the insulin signaling cascade. The ARHGEF11 gene, and two adjacent genes NTRK1 and INSRR, were sequenced in 24 Pima Indians who were not first-degree relatives. Sequencing of the coding regions, 5' and 3' untranslated regions and putative promoter regions of these genes, identified 28 variants in ARHGEF11, 11 variants in NTRK1, and 8 variants in INSSR. These 47 variants, as well as 84 additional public database variants within/between these genes, were genotyped for association analysis in the same group of Pima Indians who had participated in the linkage study (n = 1,228). An R1467H in ARHGEF11, and several additional noncoding variants that were in high linkage disequilibrium with this variant, were nominally associated with young-onset type 2 diabetes (P = 0.01; odds ratio 3.39) after adjusting for sex, family membership, and Pima heritage. The risk allele H had a frequency of 0.10. In a subgroup of 262 nondiabetic, full-heritage Pima Indians who had undergone detailed metabolic testing, the risk allele H also was associated with a lower mean insulin-mediated glucose disposal rate and a lower mean nonoxidative glucose storage rate after adjusting for age, sex, nuclear family membership, and percentage of body fat (P < or = 0.01). These findings suggest that variation within ARHGEF11 nominally increases risk of type 2 diabetes, possibly as a result of increased insulin resistance.

Tuberin: a stimulus-regulated tumor suppressor protein controlled by a diverse array of receptor tyrosine kinases and G protein-coupled receptors

Tuberin, a tumor suppressor protein, is involved in various cellular functions including survival, proliferation, and growth. It has emerged as an important effector regulated by receptor tyrosine kinases (RTKs) and G protein-coupled receptors (GPCRs). Regulation of tuberin by RTKs and GPCRs is highly complex and dependent on the type of receptors and their associated signaling molecules. Apart from Akt, the first kinase recognized to phosphorylate and inactivate tuberin upon growth factor stimulation, an increasing number of kinases upstream of tuberin have been identified. Furthermore, recruitment of different scaffolding adaptor components to the activated receptors appears to play an important role in the regulation of tuberin activity. More recently, the differential regulation of tuberin by various G protein family members have also been intensively studied, it appears that G proteins can both facilitate (e.g., G(i/o)) as well as inhibit (e.g., G(q)) tuberin phosphorylation. In the present review, we attempt to summarize our emerging understandings of the roles of RTKs, GPCRs, and their cross-talk on the regulation of tuberin.

Dok5 is substrate of TrkB and TrkC receptors and involved in neurotrophin induced MAPK activation

Tropomyosin-related kinase (Trk) family receptors are a group of high affinity receptors for neurotrophin growth factors, which have pivotal functions in many physiological processes of nervous system. Trk receptors can dimerize and autophosphorylate upon neurotrophin stimulation, then recruit multiple adaptor proteins to transduct signal. In this report, we identified Dok5, a member of Dok family, as a new substrate of TrkB/C receptors. In yeast two-hybrid assay, Dok5 can interact with intracellular domain of TrkB and TrkC receptor through its PTB domain, but not with that of TrkA receptor. The interaction was then confirmed by GST pull-down assay and Co-IP experiment. Dok5 co-localized with TrkB and TrkC in differentiated PC12 cells, providing another evidence for their interaction. By using mutational analysis, we characterized that Dok5 PTB domain bound to Trk receptor NPQY motif in a kinase-activity-dependent manner. Furthermore, competition experiment indicated that Dok5 competed with N-shc for binding to the receptors at the same site. Finally, we showed that Dok5 was involved in the activation of MAPK pathway induced by neurotrophin stimulation. Taken together, these results suggest that Dok5 acts as substrate of TrkB/C receptors and is involved in neurotrophin induced MAPK signal pathway activation.

Expression of the insulin receptor-related receptor is induced by the preovulatory surge of luteinizing hormone in thecal-interstitial cells of the rat ovary

The insulin receptor-related receptor (IRR) is a member of the insulin receptor family that, on its own, recognizes neither insulin nor any of the identified insulin-related peptides. In both the nervous system and peripheral tissues, IRR mRNA is detected in cells that also express trkA, the nerve growth factor tyrosine kinase receptor. In the ovary, the trkA gene is transiently activated in thecal-interstitial cells of large antral follicles at the time of the preovulatory surge of gonadotropins. The present study shows that the IRR gene is expressed in the same ovarian compartment, that IRR mRNA content increases strikingly in these cells in the afternoon of the first proestrus, and that--as in the case of trkA mRNA--the increase is caused by gonadotropins. The IRR mRNA species primarily affected is that encoding the full-length receptor; its increased abundance was accompanied by a corresponding change in IRR protein content. An extensive molecular search using several approaches, including the screening of cDNA libraries and PCR amplification with degenerate primers, did not yield an IRR ligand. Phylogenetic analysis of 20 insulin-related sequences and 15 relaxin family peptides from selected vertebrates indicated that the mammalian genome is unlikely to contain an additional ligand expressed from a distinct gene that is closely related to the insulin family. Although the functional nature of the relationship between IRR and trkA receptors is unknown, the remarkable temporal and spatial specificities of their coordinated expression in the ovary before ovulation suggests that they target a functionally related set of downstream events associated with the ovulatory process.

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.

ETV6–NTRK3: a chimeric protein tyrosine kinase with transformation activity in multiple cell lineages

The ETV6-NTRK3 (TEL-TRKC) gene fusion was discovered by breakpoint analysis of the t(12;15)(p13;q25) translocation associated with congenital fibrosarcoma, a pediatric soft tissue malignancy. ETV6-NTRK3 (EN) encodes the sterile alpha motif oligomerization domain of the ETV6 (TEL) transcription factor linked to the protein tyrosine kinase domain of the neurotrophin-3 receptor NTRK3 (TRKC). The EN chimeric oncoprotein links to multiple signaling cascades including Ras-MAP kinase and PI3K-AKT through the IRS-1 adapter protein. Recent evidence indicates that a functional insulin-like growth factor 1 receptor axis and higher order polymer formation are essential for EN oncogenesis. EN has been detected in other malignancies, including secretory breast carcinoma. This chimeric oncoprotein is therefore unique in being expressed in tumors derived from multiple cell lineages.

A highly conserved NTRK3 C-terminal sequence in the ETV6-NTRK3 oncoprotein binds the phosphotyrosine binding domain of insulin receptor substrate-1: an essential interaction for transformation

Receptor tyrosine kinases are integral components of cellular signaling pathways and are frequently deregulated in malignancies. The NTRK family of neurotrophin receptors mediate neuronal cell survival and differentiation, but altered NTRK signaling has also been implicated in oncogenesis. The ETV6-NTRK3 (EN) gene fusion occurs in human pediatric spindle cell sarcomas and secretory breast carcinoma, and encodes the oligomerization domain of the ETV6 transcription factor fused to the protein-tyrosine kinase domain of NTRK3. The EN protein functions as a constitutively active protein-tyrosine kinase with potent transforming activity in multiple cell lineages, and EN constitutively activates both the Ras-MAPK and phosphatidylinositol 3-kinase-Akt pathways. EN transformation is associated with constitutive tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1). Further, IRS-1 functions as the adaptor protein linking EN to downstream signaling pathways. However, the exact nature of the EN-IRS-1 interaction remains unknown. We now demonstrate that EN specifically binds the phosphotyrosine binding domain of IRS-1 via an interaction at the C terminus of EN. An EN mutant lacking the C-terminal 19 amino acids does not bind IRS-1 and lacks transforming ability. Moreover, expression of an IRS-1 polypeptide containing the phosphotyrosine binding domain acts in a dominant negative manner to inhibit EN transformation, and overexpression of IRS-1 potentiates EN transforming activity. These findings indicate that EN.IRS-1 complex formation through the NTRK3 C terminus is essential for EN transformation.

Role of TFG sequences outside the coiled-coil domain in TRK-T3 oncogenic activation

The TRK-T3 oncoprotein, isolated from a human papillary thyroid tumor, arises from the fusion between the N-terminal domain of the TFG gene and the tyrosine kinase domain of the NTRK1 receptor. The 68 kDa TRK-T3 oncoprotein displays a constitutive tyrosine kinase activity resulting in its capability to transform NIH3T3 cells. The TFG portion of TRK-T3 contains a coiled-coil domain, which mediates protein oligomerization essential for the oncogene constitutive activation, and several consensus sites for protein interaction. In this study, we investigate the role of TFG sequences outside the coiled-coil domain on TRK-T3 activation, We constructed four mutants carrying different deletions of TFG sequences and expressed them in mammalian cells. By performing biochemical and biological assays we demonstrated that all the deleted regions are required for TRK-T3 activation, as they are involved in different mechanisms such as protein processing, formation of stable and/or functional complexes, and possible interaction with other proteins. By constructing site-specific mutants, we demonstrated a crucial role for a PB1 domain and a considerable contribution of an SH2-binding motif in TRK-T3 oncogenic activation. This work establishes an important role for TFG sequences outside the coiled-coil domain in the activation of the thyroid TRK-T3 oncogene.

Biological activity of the thyroid TRK-T3 oncogene requires signalling through Shc

The thyroid TRK-T3 oncogene, produced by a chromosomal translocation, is a chimeric, constitutively activated version of the NTRK1/NGF receptor and it is able to transform NIH3T3 cells and differentiate PC12 cells. TRK-T3 oncoprotein triggers multiple signal transduction pathways. Among others, TRK-T3 binds and phosphorylates the Shc and SNT1/FRS2 adaptor proteins both involved in coupling the receptor tyrosine kinase to the mitogen-activated protein kinase pathway by recruiting Grb2/SOS. We were interested in defining the role of Shc in the oncogenesis by TRK-T3. The mutation of TRK-T3 tyrosine 291, docking site for both Shc and FRS2, abrogates the oncogene biological activity. To directly explore the role of Shc we used the ShcY317F mutant, which carries the mutation of a tyrosine residue involved in Grb2 recruitment. We demonstrated that the ShcY317F mutant exerts an inhibitory effect on TRK-T3 transforming activity. Such effect can be modulated by the amount of ShcY317F protein and affects the viability of cells expressing TRK-T3 by means of a mechanism involving apoptosis. Our results indicate a definitive role of the adaptor protein Shc in TRK-T3 transforming activity.

ETV6-NTRK3 transformation requires insulin-like growth factor 1 receptor signaling and is associated with constitutive IRS-1 tyrosine phosphorylation

Congenital fibrosarcoma (CFS) and cellular mesoblastic nephroma (CMN) are pediatric spindle cell malignancies that share two specific cytogenetic abnormalities: trisomy of chromosome 11 and a t(12;15)(p13;q25) translocation. The t(12;15) rearrangement creates a transcriptionally active fusion gene that encodes a chimeric oncoprotein, ETV6-NTRK3 (EN). EN transforms NIH3T3 fibroblasts through constitutive activation of both the Ras-mitogen-activated protein kinase (MAPK) pathway and the phosphatidylinositol-3'kinase (PI3K)-Akt pathway. However, the role of trisomy 11 in CFS and CMN remains unknown. In this study we demonstrate elevated expression of the chromosome 11p15.5 insulin-like growth factor 2 gene (IGF2) in CFS and CMN tumors. Moreover, we present evidence that an intact IGF signaling axis is essential for in vitro EN-mediated transformation. EN only very weakly transformed so-called R-murine fibroblasts derived from mice with a targeted disruption of the IGF1 receptor gene (IGFRI), but transformation activity was fully restored in R- cells engineered to re-express IGFRI (R+ cells). We also observed that the major IGFRI substrate, insulin-receptor substrate-1 (IRS-1), was constitutively tyrosine phosphorylated and could be co-immunoprecipitated with EN in either R- or R+ cells expressing the EN oncoprotein. IRS-1 association with Grb2 and PI3K p85, which link IGFRI to the Ras-MAPK and PI3K-Akt pathways, respectively, was enhanced in both cell types in the presence of EN. However, activation of the Ras-MAPK and PI3K-Akt pathways was markedly attenuated in EN-expressing R- cells compared to EN-transformed R+ cells. This suggests that IRS-1 may be functioning as an adaptor in EN signal transduction, but that a link to EN transformation pathways requires the presence of IGFRI. Our findings indicate that an intact IGF signaling axis is essential for EN transformation, and are consistent with a role for trisomy 11 in augmenting this pathway in EN expressing tumors.

Insulin receptor substrate-2 phosphorylation is necessary for protein kinase C zeta activation by insulin in L6hIR cells

We have investigated glycogen synthase (GS) activation in L6hIR cells expressing a peptide corresponding to the kinase regulatory loop binding domain of insulin receptor substrate-2 (IRS-2) (KRLB). In several clones of these cells (B2, F4), insulin-dependent binding of the KRLB to insulin receptors was accompanied by a block of IRS-2, but not IRS-1, phosphorylation, and insulin receptor binding. GS activation by insulin was also inhibited by >70% in these cells (p < 0.001). The impairment of GS activation was paralleled by a similarly sized inhibition of glycogen synthase kinase 3 alpha (GSK3 alpha) and GSK3 beta inactivation by insulin with no change in protein phosphatase 1 activity. PDK1 (a phosphatidylinositol trisphosphate-dependent kinase) and Akt/protein kinase B (PKB) activation by insulin showed no difference in B2, F4, and in control L6hIR cells. At variance, insulin did not activate PKC zeta in B2 and F4 cells. In L6hIR, inhibition of PKC zeta activity by either a PKC zeta antisense or a dominant negative mutant also reduced by 75% insulin inactivation of GSK3 alpha and -beta (p < 0.001) and insulin stimulation of GS (p < 0.002), similar to Akt/PKB inhibition. In L6hIR, insulin induced protein kinase C zeta (PKC zeta) co-precipitation with GSK3 alpha and beta. PKC zeta also phosphorylated GSK3 alpha and -beta. Alone, these events did not significantly affect GSK3 alpha and -beta activities. Inhibition of PKC zeta activity, however, reduced Akt/PKB phosphorylation of the key serine sites on GSK3 alpha and -beta by >80% (p < 0.001) and prevented full GSK3 inactivation by insulin. Thus, IRS-2, not IRS-1, signals insulin activation of GS in the L6hIR skeletal muscle cells. In these cells, insulin inhibition of GSK3 alpha and -beta requires dual phosphorylation by both Akt/PKB and PKC zeta.