The TrkAIII oncoprotein inhibits mitochondrial free radical ROS-induced death of SH-SY5Y neuroblastoma cells by augmenting SOD2 expression and activity at the mitochondria, within the context of a tumour stem cell-like phenotype. PLoS One. 2014;9:e94568. [PMID: 24736663 PMCID: PMC3988074 DOI: 10.1371/journal.pone.0094568]

Molecular Characterization and Inhibition of a Novel Stress-Induced Mitochondrial Protecting Role for Misfolded TrkAIII in Human SH-SY5Y Neuroblastoma Cells

Pediatric neuroblastomas (NBs) are heterogeneous, aggressive, therapy-resistant embryonal tumors that originate from cells of neural crest origin committed to the sympathoadrenal progenitor cell lineage. Stress- and drug-resistance mechanisms drive post-therapeutic relapse and metastatic progression, the characterization and inhibition of which are major goals in improving therapeutic responses. Stress- and drug-resistance mechanisms in NBs include alternative TrkAIII splicing of the neurotrophin receptor tropomyosin-related kinase A (NTRK1/TrkA), which correlates with post-therapeutic relapse and advanced-stage metastatic disease. The TrkAIII receptor variant exerts oncogenic activity in NB models by mechanisms that include stress-induced mitochondrial importation and activation. In this study, we characterize novel targetable and non-targetable participants in this pro-survival mechanism in TrkAIII-expressing SH-SY5Y NB cells, using dithiothreitol (DTT) as an activator and a variety of inhibitors by regular and immunoprecipitation Western blotting of purified mitochondria and IncuCyte cytotoxicity assays. We report that stress-induced TrkAIII misfolding initiates this mechanism, resulting in Grp78, Ca2+-calmodulin, adenosine ribosylating factor (Arf) and Hsp90-regulated mitochondrial importation. TrkAIII imported into inner mitochondrial membranes is cleaved by Omi/high temperature requirement protein A2 (HtrA2) then activated by a mechanism dependent upon calmodulin kinase II (CaMKII), alpha serine/threonine kinase (Akt), mitochondrial Ca2+ uniporter and reactive oxygen species (ROS), involving inhibitory mitochondrial protein tyrosine phosphatase (PTPase) oxidation, resulting in phosphoinositide 3 kinase (PI3K) activation of mitochondrial Akt, which enhances stress resistance. This novel pro-survival function for misfolded TrkAIII mitigates the cytotoxicity of mitochondrial Ca2+ homeostasis disrupted during integrated stress responses, and is prevented by clinically approved Trk and Akt inhibitors and also by inhibitors of 78kDa glucose regulated protein (Grp78), heat shock protein 90 (Hsp90), Ca2+-calmodulin and PI3K. This identifies Grp78, Ca2+-calmodulin, Hsp90, PI3K and Akt as novel targetable participants in this mechanism, in addition to TrkAIII, the inhibition of which has the potential to enhance the stress-induced elimination of TrkAIII-expressing NB cells, with the potential to improve therapeutic outcomes in NBs that exhibit TrkAIII expression and activation.

The Alternative TrkAIII Splice Variant, a Targetable Oncogenic Participant in Human Cutaneous Malignant Melanoma

Post-therapeutic relapse, poor survival rates and increasing incidence justify the search for novel therapeutic targets and strategies in cutaneous malignant melanoma (CMM). Within this context, a potential oncogenic role for TrkA in CMM is suggested by reports of NTRK1 amplification, enhanced TrkA expression and intracellular TrkA activation associated with poor prognosis. TrkA, however, exhibits tumour-suppressing properties in melanoma cell lines and has recently been reported not to be associated with CMM progression. To better understand these contradictions, we present the first analysis of potential oncogenic alternative TrkA mRNA splicing, associated with TrkA immunoreactivity, in CMMs, and compare the behaviour of fully spliced TrkA and the alternative TrkAIII splice variant in BRAF(V600E)-mutated A375 melanoma cells. Alternative TrkA splicing in CMMs was associated with unfolded protein response (UPR) activation. Of the several alternative TrkA mRNA splice variants detected, TrkAIII was the only variant with an open reading frame and, therefore, oncogenic potential. TrkAIII expression was more frequent in metastatic CMMs, predominated over fully spliced TrkA mRNA expression in ≈50% and was invariably linked to intracellular phosphorylated TrkA immunoreactivity. Phosphorylated TrkA species resembling TrkAIII were also detected in metastatic CMM extracts. In A375 cells, reductive stress induced UPR activation and promoted TrkAIII expression and, in transient transfectants, promoted TrkAIII and Akt phosphorylation, enhancing resistance to reductive stress-induced death, which was prevented by lestaurtinib and entrectinib. In contrast, fully spliced TrkA was dysfunctional in A375 cells. The data identify fully spliced TrkA dysfunction as a novel mechanism for reducing melanoma suppression, support a causal relationship between reductive stress, UPR activation, alternative TrkAIII splicing and TrkAIII activation and characterise a targetable oncogenic pro-survival role for TrkAIII in CMM.

Doxorubicin-Induced TrkAIII Activation: A Selection Mechanism for Resistant Dormant Neuroblastoma Cells

Patients with advanced neuroblastoma (NB) receive multimodal clinical therapy, including the potent anthracycline chemotherapy drug doxorubicin (Dox). The acquisition of Dox resistance, however, is a major barrier to a sustained response and leads to a poor prognosis in advanced disease states, reinforcing the need to identify and inhibit Dox resistance mechanisms. In this context, we report on the identification and inhibition of a novel Dox resistance mechanism. This mechanism is characterized by the Dox-induced activation of the oncogenic TrkAIII alternative splice variant, resulting in increased Dox resistance, and is blocked by lestaurtinib, entrectinib, and crizotinib tyrosine kinase and LY294002 IP3-K inhibitors. Using time lapse live cell imaging, conventional and co-immunoprecipitation Western blots, RT-PCR, and inhibitor studies, we report that the Dox-induced TrkAIII activation correlates with proliferation inhibition and is CDK1- and Ca²⁺-uniporter-independent. It is mediated by ryanodine receptors; involves Ca²⁺-dependent interactions between TrkAIII, calmodulin and Hsp90; requires oxygen and oxidation; occurs within assembled ERGICs; and does not occur with fully spliced TrkA. The inhibitory effects of lestaurtinib, entrectinib, crizotinib, and LY294002 on the Dox-induced TrkAIII and Akt phosphorylation and resistance confirm roles for TrkAIII and IP3-K consistent with Dox-induced, TrkAIII-mediated pro-survival IP3K/Akt signaling. This mechanism has the potential to select resistant dormant TrkAIII-expressing NB cells, supporting the use of Trk inhibitors during Dox therapy in TrkAIII-expressing NBs.

Mechanisms involved in selecting and maintaining neuroblastoma cancer stem cell populations, and perspectives for therapeutic targeting

Pediatric neuroblastomas (NBs) are heterogeneous, aggressive, therapy-resistant embryonal tumours that originate from cells of neural crest (NC) origin and in particular neuroblasts committed to the sympathoadrenal progenitor cell lineage. Therapeutic resistance, post-therapeutic relapse and subsequent metastatic NB progression are driven primarily by cancer stem cell (CSC)-like subpopulations, which through their self-renewing capacity, intermittent and slow cell cycles, drug-resistant and reversibly adaptive plastic phenotypes, represent the most important obstacle to improving therapeutic outcomes in unfavourable NBs. In this review, dedicated to NB CSCs and the prospects for their therapeutic eradication, we initiate with brief descriptions of the unique transient vertebrate embryonic NC structure and salient molecular protagonists involved NC induction, specification, epithelial to mesenchymal transition and migratory behaviour, in order to familiarise the reader with the embryonic cellular and molecular origins and background to NB. We follow this by introducing NB and the potential NC-derived stem/progenitor cell origins of NBs, before providing a comprehensive review of the salient molecules, signalling pathways, mechanisms, tumour microenvironmental and therapeutic conditions involved in promoting, selecting and maintaining NB CSC subpopulations, and that underpin their therapy-resistant, self-renewing metastatic behaviour. Finally, we review potential therapeutic strategies and future prospects for targeting and eradication of these bastions of NB therapeutic resistance, post-therapeutic relapse and metastatic progression.

Hypoxia-induced alternative splicing: the 11th Hallmark of Cancer

Hypoxia-induced alternative splicing is a potent driving force in tumour pathogenesis and progression. In this review, we update currents concepts of hypoxia-induced alternative splicing and how it influences tumour biology. Following brief descriptions of tumour-associated hypoxia and the pre-mRNA splicing process, we review the many ways hypoxia regulates alternative splicing and how hypoxia-induced alternative splicing impacts each individual hallmark of cancer. Hypoxia-induced alternative splicing integrates chemical and cellular tumour microenvironments, underpins continuous adaptation of the tumour cellular microenvironment responsible for metastatic progression and plays clear roles in oncogene activation and autonomous tumour growth, tumor suppressor inactivation, tumour cell immortalization, angiogenesis, tumour cell evasion of programmed cell death and the anti-tumour immune response, a tumour-promoting inflammatory response, adaptive metabolic re-programming, epithelial to mesenchymal transition, invasion and genetic instability, all of which combine to promote metastatic disease. The impressive number of hypoxia-induced alternative spliced protein isoforms that characterize tumour progression, classifies hypoxia-induced alternative splicing as the 11th hallmark of cancer, and offers a fertile source of potential diagnostic/prognostic markers and therapeutic targets.

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.

Discovery, characterization and potential roles of a novel NF-YAx splice variant in human neuroblastoma

BACKGROUND

Identification of novel cancer-associated splice variants is of potential diagnostic, prognostic and therapeutic importance. NF-Y transcription factor is comprised of NF-YA, NF-YB and NF-YC subunits, binds inverted CCAAT-boxes in ≈70% of gene promoters, regulates > 1000 cancer-associated genes and proteins involved in proliferation, staminality, differentiation, apoptosis, metabolism and is subject to component alternative splicing. RT-PCR evaluation of alternative NF-YA splicing in primary human neuroblastomas (NBs), led to discovery of a novel NF-YAx splice variant, also expressed during mouse embryo development and induced by doxorubicin in NB cells. Here, we report the discovery and characterisation of NF-YAx and discus its potential roles in NB.

METHODS

NF-YAx cDNA was RT-PCR-cloned from a stage 3 NB (provided by the Italian Association of Haematology and Paediatric Oncology, Genova, IT), sequenced and expressed as a protein using standard methods and compared to known fully-spliced NF-YAl and exon B-skipped NF-YAs isoforms in: EMSAs for capacity to form NF-Y complexes; by co-transfection, co-immunoprecipitation and Western blotting for capacity to bind Sp1; by IF for localisation; in AO/EtBr cell-death and colony formation assays for relative cytotoxicity, and by siRNA knockdown, use of inhibitors and Western blotting for potential mechanisms of action. Stable SH-SY5Y transfectants of all three NF-YA isoforms were also propagated and compared by RT-PCR and Western blotting for differences in cell-death and stem cell (SC)-associated gene expression, in cell-death assays for sensitivity to doxorubicin and in in vitro proliferation, substrate-independent growth and in vivo tumour xenograft assays for differences in growth and tumourigenic capacity.

RESULTS

NF-YAx was characterized as a novel variant with NF-YA exons B, D and partial F skipping, detected in 20% of NF-YA positive NBs, was the exclusive isoform in a stage 3 NB, expressed in mouse stage E11.5-14 embryos and induced by doxorubicin in SH-SY5Y NB cells. The NF-YAx protein exhibited nuclear localisation, competed with other isoforms in CCAAT box-binding NF-Y complexes but, in contrast to other isoforms, did not bind Sp1. NF-YAx expression in neural-related progenitor and NB cells repressed Bmi1 expression, induced KIF1Bβ expression and promoted KIF1Bβ-dependent necroptosis but in NB cells also selected tumourigenic, doxorubicin-resistant, CSC-like sub-populations, resistant to NF-YAx cytotoxicity.

CONCLUSIONS

The discovery of NF-YAx in NBs, its expression in mouse embryos and induction by doxorubicin in NB cells, unveils a novel NF-YA splice mechanism and variant, regulated by and involved in development, genotoxic-stress and NB. NF-YAx substitution of other isoforms in NF-Y complexes and loss of capacity to bind Sp1, characterises this novel isoform as a functional modifier of NF-Y and its promotion of KIF1Bβ-dependent neural-lineage progenitor and NB cell necroptosis, association with doxorubicin-induced necroptosis and expression in mouse embryos coinciding with KIF1Bβ-dependent sympathetic neuroblast-culling, confirm a cytotoxic function and potential role in suppressing NB initiation. On the other hand, the in vitro selection of CSC-like NB subpopulations resistant to NF-YAx cytotoxicity not only helps to explain high-level exclusive NF-YAx expression in a stage 3 NB but also supports a role for NF-YAx in disease progression and identifies a potential doxorubicin-inducible mechanism for post-therapeutic relapse.

A pilot study of alternative TrkAIII splicing in Merkel cell carcinoma: a potential oncogenic mechanism and novel therapeutic target

BACKGROUND

Merkel cell carcinomas (MCCs) are rare, aggressive, therapeutically-challenging skin tumours that are increasing in incidence and have poor survival rates. The majority are caused by genomic Merkel cell polyomavirus (MCPyV) integration and MCPyV T-antigen expression. Recently, a potential oncogenic role for the tropomyosin-related tyrosine kinase A receptor (TrkA) has been proposed in MCC. Alternative TrkAIII splicing is a TrkA oncogenic activation mechanism that can be promoted by SV40 large T-antigen, an analogue of MCPyV large T-antigen. In this pilot study, therefore, we have evaluated TrkAIII splicing as a novel potential oncogenic mechanism and therapeutic target in MCPyV positive MCC.

METHODS

Formalin-fixed paraffin-embedded MCC tissues, consisting of 10 stage IV, 1 stage IIIB, 1 stage IIB, 4 stage IIA and 2 stage I tumours, from patients diagnosed and treated from September 2006 to March, 2019, at the University of L'Aquila, L'Aquila, Italy, were compared to 3 primary basal cell carcinomas (BCCs), 3 primary squamous cell carcinomas (SCCs) and 2 normal skin samples by RT-PCR for MCPyV large T-antigen, small T-antigen, VP-1 expression and alternative TrkAIII splicing and by indirect IF for evidence of intracellular TrkA isoform expression and activation.

RESULTS

9 of 10 Recurrent stage IV MCCs were from patients (P.1-3) treated with surgery plus loco-regional Melphalan chemotherapy and remaining MMCs, including 1 stage IV tumour, were from patients treated with surgery alone (P. 4-11). All MCPyV positive MCCs exhibiting MCPyV large T-antigen expression (17 of 18MCCs, 90%) exhibited alternative TrkAIII mRNA splicing (100%), which was exclusive in a significant number and predominant (> 50%) in all stage IV MCCs and the majority of stage 1-III MCCs. MCCs with higher TrkAIII to 18S rRNA expression ratios also exhibited strong or intermediate immunoreactivity to anti-TrkA antibodies, consistent with cytoplasmic TrkAIII expression and activation. In contrast, the MCPyV negative MCC, BCCs, SCCs and normal skin tissues all exhibited exclusive fully-spliced TrkA mRNA expression, associated with variable immunoreactivity for non-phosphorylated but not phosphorylated TrkA.

CONCLUSIONS

MCPyV positive MCCs but not MCPyV negative MCC, BCCs and SCCs exhibit predominant alternative TrkAIII splicing, with evidence of intracellular TrkAIII activation. This establishes a new potential MCC subset, unveils a novel potential MCPyV oncogenic mechanism and identifies TrkAIII as a novel potential therapeutic target in MCPyV positive MCC.

Cancer Stem Cells in Neuroblastoma: Expanding the Therapeutic Frontier

Neuroblastoma (NB) is the most common extracranial solid tumor often diagnosed in childhood. Despite intense efforts to develop a successful treatment, current available therapies are still challenged by high rates of resistance, recurrence and progression, most notably in advanced cases and highly malignant tumors. Emerging evidence proposes that this might be due to a subpopulation of cancer stem cells (CSCs) or tumor-initiating cells (TICs) found in the bulk of the tumor. Therefore, the development of more targeted therapy is highly dependent on the identification of the molecular signatures and genetic aberrations characteristic to this subpopulation of cells. This review aims at providing an overview of the key molecular players involved in NB CSCs and focuses on the experimental evidence from NB cell lines, patient-derived xenografts and primary tumors. It also provides some novel approaches of targeting multiple drivers governing the stemness of CSCs to achieve better anti-tumor effects than the currently used therapeutic agents.

The oncogenic neurotrophin receptor tropomyosin-related kinase variant, TrkAIII

Oncogenes derived from the neurotrophin receptor tropomyosin-related kinase TrkA act as drivers in sub-populations of a wide-range of human cancers. This, combined with a recent report that both adult and childhood cancers driven by novel oncogenic TrkA chimeric-fusions exhibit profound, long-lived therapeutic responses to the Trk inhibitor Larotrectinib, highlights the need to improve clinical detection of TrkA oncogene-driven cancers in order to maximise this novel therapeutic potential. Cancers potentially driven by TrkA oncogenes include a proportion of paediatric neuroblastomas (NBs) that express the alternative TrkA splice variant TrkAIII, which exhibits exon 6, 7 and 9 skipping and oncogenic-activity that depends upon deletion of the extracellular D4 Ig-like domain. In contrast to fully spliced TrkA, which exhibits tumour suppressor activity in NB and associates with good prognosis, TrkAIII associates with advanced stage metastatic disease, post therapeutic relapse and worse prognosis, induces malignant transformation of NIH-3T3 cells and exhibits oncogenic activity in NB models. TrkAIII induction in NB cells is stress-regulated by conditions that mimic hypoxia or perturbate the ER with potential to change TrkA tumour-suppressing signals into oncogenic TrkAIII signals within the stressful tumour microenvironment. In contrast to cell surface TrkA, TrkAIII re-localises to intracellular pre-Golgi membranes, centrosomes and mitochondria, within which it exhibits spontaneous ligand-independent activation, triggering a variety of mechanisms that promote tumorigenicity and malignant behaviour, which impact the majority of cancer hallmarks. In this review, we present updates on TrkAIII detection and association with human malignancies, the multiple ways TrkAIII exerts oncogenic activity and potential therapeutic approaches for TrkAIII expressing cancers, with particular reference to NB.

TRAIL induces pro-apoptotic crosstalk between the TRAIL-receptor signaling pathway and TrkAIII in SH-SY5Y cells, unveiling a potential therapeutic "Achilles heel" for the TrkAIII oncoprotein in neuroblastoma

TrkAIII expression in neuroblastoma (NB) associates with advanced stage disease, worse prognosis, post therapeutic relapse, and in NB models TrkAIII exhibits oncogenic activity and promotes chemotherapeutic-resistance. Here, we report a potential therapeutic “Achilles heel” for the TrkAIII oncoprotein in a SH-SY5Y NB model that is characterised by one-way TRAIL-induced, pro-apoptotic crosstalk between the TRAIL receptor signaling pathway and TrkAIII that results in the delayed induction of apoptosis. In TrkAIII SH-SY5Y cells, blocked in the intrinsic apoptosis pathway by elevated constitutive Bcl-2, Bcl-xL and Mcl-1 expression, TRAIL induced delayed caspase-dependent apoptosis via the extrinsic pathway and completely abrogated tumourigenic capacity in vitro. This effect was initiated by TRAIL-induced SHP-dependent c-Src activation, the induction of TrkAIII/SHP-1/c-Src complexing leading to SHP-mediated TrkAIII de-phosphorylation, subsequent induction of complexing between de-phosphorylated TrkAIII and cFLIP associated with a time-dependent increase the caspase-8 to cFLIP ratio at activated death receptors, resulting in delayed caspase cleavage and caspase-dependent apoptosis. We also confirm rate-limiting roles for c-FLIP and Mcl-1 in regulating the sensitivity of TrkAIII SH-SY5Y cells to TRAIL-induced apoptosis via the extrinsic and intrinsic pathways, respectively. Our study unveils a novel mechanism for the TRAIL-induced apoptosis of TrkAIII expressing NB cells that depends upon SHP/Src-mediated crosstalk between the TRAIL-receptor signaling pathway and TrkAIII, and supports a novel potential pro-apoptotic therapeutic use for TRAIL in TrkAIII expressing NB.

TrkAIII signals endoplasmic reticulum stress to the mitochondria in neuroblastoma cells, resulting in glycolytic metabolic adaptation

Alternative TrkAIII splicing characterises advanced stage metastatic disease and post-therapeutic relapse in neuroblastoma (NB), and in NB models TrkAIII exhibits oncogenic activity. In this study, we report a novel role for TrkAIII in signaling ER stress to the mitochondria in SH-SY5Y NB cells that results in glycolytic metabolic adaptation. The ER stress-inducing agents DTT, A23187 and thapsigargin activated the ER stress-response in control pcDNA SH-SY5Y and TrkAIII expressing SH-SY5Y cells and in TrkAIII SH-SY5Y cells increased TrkAIII targeting to mitochondria and internalisation into inner-mitochondrial membranes. Within inner-mitochondrial membranes, TrkAIII was subjected to Omi/HtrA2-dependent cleavage to tyrosine phosphorylated 45–48kDa carboxyl terminal active fragments, localised predominantly in tyrosine kinase-domain mitochondrial matrix orientation. This stress-induced activation of mitochondrial TrkAIII was associated with increased ROS production, prevented by the ROS scavenger Resveratrol and underpinned by changes in Ca2+ movement, implicating ROS/Ca2+ interplay in overcoming the mitochondrial TrkAIII activation threshold. Stress-induced, cleavage-activation of mitochondrial TrkAIII resulted in mitochondrial PDHK1 tyrosine phosphorylation, leading to glycolytic metabolic adaptation. This novel mitochondrial role for TrkAIII provides a potential self-perpetuating, drug reversible way through which tumour microenvironmental stress may maintain the metastasis promoting “Warburg effect” in TrkAIII expressing NBs.

TrkA is a binding partner of NPM-ALK that promotes the survival of ALK+ T-cell lymphoma

Nucleophosmin‐anaplastic lymphoma kinase‐expressing (NPM‐ALK⁺) T‐cell lymphoma is an aggressive neoplasm that is more commonly seen in children and young adults. The pathogenesis of NPM‐ALK⁺ T‐cell lymphoma is not completely understood. Wild‐type ALK is a receptor tyrosine kinase that is physiologically expressed in neural tissues during early stages of human development, which suggests that ALK may interact with neurotrophic factors. The aberrant expression of NPM‐ALK results from a translocation between the ALK gene on chromosome 2p23 and the NPM gene on chromosome 5q35. The nerve growth factor (NGF) is the first neurotrophic factor attributed to non‐neural functions including cancer cell survival, proliferation, and metastasis. These functions are primarily mediated through the tropomyosin receptor kinase A (TrkA). The expression and role of NGF/TrkA in NPM‐ALK⁺ T‐cell lymphoma are not known. In this study, we tested the hypothesis that TrkA signaling is upregulated and sustains the survival of this lymphoma. Our data illustrate that TrkA and NGF are expressed in five NPM‐ALK⁺ T‐cell lymphoma cell lines and TrkA is expressed in 11 of 13 primary lymphoma tumors from patients. In addition, we found evidence to support that NPM‐ALK and TrkA functionally interact. A selective TrkA inhibitor induced apoptosis and decreased cell viability, proliferation, and colony formation of NPM‐ALK⁺ T‐cell lymphoma cell lines. These effects were associated with downregulation of cell survival regulatory proteins. Similar results were also observed using specific knockdown of TrkA in NPM‐ALK⁺ T‐cell lymphoma cells by siRNA. Importantly, the inhibition of TrkA signaling was associated with antitumor effects in vivo, because tumor xenografts in mice regressed and the mice exhibited improved survival. In conclusion, TrkA plays an important role in the pathogenesis of NPM‐ALK⁺ T‐cell lymphoma, and therefore, targeting TrkA signaling may represent a novel approach to eradicate this aggressive neoplasm.

Retrograde TrkAIII transport from ERGIC to ER: a re-localisation mechanism for oncogenic activity

In human SH-SY5Y neuroblastoma (NB) cells, nascent immature N-glycosylated 110kDa TrkA moves rapidly from the endoplasmic reticulum (ER) to the Golgi Network (GN), where it matures into the 140kDa receptor prior to being transported to the cell surface, creating GN and cell surface pools of inactive receptor maintained below the spontaneous activation threshold by a full compliment of inhibitory domains and endogenous PTPases. In contrast, the oncogenic alternative TrkAIII splice variant is not expressed at the cell surface but re-localises to intracellular membranes, within which it exhibits spontaneous ERGIC/COPI-associated activation and oncogenic Akt signalling. In this study, we characterise the mechanism responsible for TrkAIII re-localisation. Spontaneous TrkAIII activation, facilitated by D4 IG-like domain and N-glycosylation site omission, increases spontaneous activation potential by altering intracellular trafficking, inhibiting cell surface expression and eliminating an important inhibitory domain. TrkAIII, spontaneously activated within the permissive ERGIC/COPI compartment, rather than moving in an anterograde direction to the GN exhibits retrograde transport back to the ER, where it is inactivated. This sets-up self-perpetuating TrkAIII re-cycling between the ERGIC and ER, that ensures continual accumulation above the spontaneous activation threshold of the ERGIC/COPI compartment. This is reversed by TrkA tyrosine kinase inhibitors, which promote anterograde transport of inactivated TrkAIII to the GN, resulting in GN-associated TrkAIII maturation to a 120kDa species that is degraded at the proteasome.

Mitochondrial aerobic respiration is activated during hair follicle stem cell differentiation, and its dysfunction retards hair regeneration

Background. Emerging research revealed the essential role of mitochondria in regulating stem/progenitor cell differentiation of neural progenitor cells, mesenchymal stem cells and other stem cells through reactive oxygen species (ROS), Notch or other signaling pathway. Inhibition of mitochondrial protein synthesis results in hair loss upon injury. However, alteration of mitochondrial morphology and metabolic function during hair follicle stem cells (HFSCs) differentiation and how they affect hair regeneration has not been elaborated upon.

Methods. We compared the difference in mitochondrial morphology and activity between telogen bulge cells and anagen matrix cells. Expression levels of mitochondrial ROS and superoxide dismutase 2 (SOD2) were measured to evaluate redox balance. In addition, the level of pyruvate dehydrogenase kinase (PDK) and pyruvate dehydrogenase (PDH) were estimated to present the change in energetic metabolism during differentiation. To explore the effect of the mitochondrial metabolism on regulating hair regeneration, hair growth was observed after application of a mitochondrial respiratory inhibitor upon hair plucking.

Results. During HFSCs differentiation, mitochondria became elongated with more abundant organized cristae and showed higher activity in differentiated cells. SOD2 was enhanced for redox balance with relatively stable ROS levels in differentiated cells. PDK increased in HFSCs while differentiated cells showed enhanced PDH, indicating that respiration switched from glycolysis to oxidative phosphorylation during differentiation. Inhibiting mitochondrial respiration in differentiated hair follicle cells upon hair plucking repressed hair regeneration in vivo.

Conclusions. Upon HFSCs differentiation, mitochondria are elongated with more abundant cristae and show higher activity, accompanying with activated aerobic respiration in differentiated cells for higher energy supply. Also, dysfunction of mitochondrial respiration delays hair regeneration upon injury.

Neurotrophin signaling in cancer stem cells

Cancer stem cells (CSCs), are thought to be at the origin of tumor development and resistance to therapies. Thus, a better understanding of the molecular mechanisms involved in the control of CSC stemness is essential to the design of more effective therapies for cancer patients. Cancer cell stemness and the subsequent expansion of CSCs are regulated by micro-environmental signals including neurotrophins. Over the years, the roles of neurotrophins in tumor development have been well established and regularly reviewed. Especially, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are reported to stimulate tumor cell proliferation, survival, migration and/or invasion, and favors tumor angiogenesis. More recently, neurotrophins have been reported to regulate CSCs. This review briefly presents neurotrophins and their receptors, summarizes their roles in different cancers, and discusses the emerging evidence of neurotrophins-induced enrichment of CSCs as well as the involved signaling pathways.

Enhancement of SOX-2 expression and ROS accumulation by culture of A172 glioblastoma cells under non-adherent culture conditions

More efficient isolation and identification of cancer stem cells (CSCs) would help in determining their fundamental roles in tumor biology. The classical tool for this purpose is anchorage-independent tumorsphere culture. We compared the effects of differently textured culture plates and serum deprivation on the acquisition of CSC properties of A172 glioblastoma cells. Cells were cultured on standard polystyrene-treated plates, ultra-low attachment, poly (2-hydroxyethyl methacrylate)-coated plates, and 1% agar-coated plates with 10% serum or in serum-free glioblastoma sphere medium (GBM). Based on mitochondrial reductase activity and subG1 proportions, non-adherent conditions had a greater impact on A172 cell viability than serum deprivation. Among the stemness-related genes, SOX-2 expression was significantly upregulated by serum deprivation under non-adherent conditions, while several epithelial-to-mesenchymal transition (EMT)-related genes were less dependent on serum. In addition, reactive oxygen species (ROS) accumulation in A172 cells was significantly increased in GBM under non-adherent conditions. Despite the correlation between SOX-2 induction and ROS accumulation, treatment with the ROS scavenger N-acetyl-l-cysteine did not prevent SOX-2 expression, suggesting that ROS accumulation is not an essential requirement for induction of SOX-2. Our results suggested that cultivation of cancer cells under conditions of serum deprivation in an anchorage-independent manner may enrich SOX-2-expressing CSC-like cells in vitro.

Induction of neurite outgrowth in PC12 cells treated with temperature-controlled repeated thermal stimulation

To promote the functional restoration of the nervous system following injury, it is necessary to provide optimal extracellular signals that can induce neuronal regenerative activities, particularly neurite formation. This study aimed to examine the regulation of neuritogenesis by temperature-controlled repeated thermal stimulation (TRTS) in rat PC12 pheochromocytoma cells, which can be induced by neurotrophic factors to differentiate into neuron-like cells with elongated neurites. A heating plate was used to apply thermal stimulation, and the correlation of culture medium temperature with varying surface temperature of the heating plate was monitored. Plated PC12 cells were exposed to TRTS at two different temperatures via heating plate (preset surface temperature of the heating plate, 39.5°C or 42°C) in growth or differentiating medium for up to 18 h per day. We then measured the extent of growth, neuritogenesis, or acetylcholine esterase (AChE) activity (a neuronal marker). To analyze the mechanisms underlying the effects of TRTS on these cells, we examined changes in intracellular signaling using the following: tropomyosin-related kinase A inhibitor GW441756; p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580; and MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor U0126 with its inactive analog, U0124, as a control. While a TRTS of 39.5°C did not decrease the growth rate of cells in the cell growth assay, it did increase the number of neurite-bearing PC12 cells and AChE activity without the addition of other neuritogenesis inducers. Furthermore, U0126, and SB203580, but not U0124 and GW441756, considerably inhibited TRTS-induced neuritogenesis. These results suggest that TRTS can induce neuritogenesis and that participation of both the ERK1/2 and p38 MAPK signaling pathways is required for TRTS-dependent neuritogenesis in PC12 cells. Thus, TRTS may be an effective technique for regenerative neuromedicine.