Nerve growth factor receptor TrkA signaling in breast cancer cells involves Ku70 to prevent apoptosis

Involvement of neuronal factors in tumor angiogenesis and the shaping of the cancer microenvironment

Emerging evidence suggests that nerves within the tumor microenvironment play a crucial role in regulating angiogenesis. Neurotransmitters and neuropeptides released by nerves can interact with nearby blood vessels and tumor cells, influencing their behavior and modulating the angiogenic response. Moreover, nerve-derived signals may activate signaling pathways that enhance the production of pro-angiogenic factors within the tumor microenvironment, further supporting blood vessel growth around tumors. The intricate network of communication between neural constituents and the vascular system accentuates the potential of therapeutically targeting neural-mediated pathways as an innovative strategy to modulate tumor angiogenesis and, consequently, neoplastic proliferation. Hereby, we review studies that evaluate the precise molecular interplay and the potential clinical ramifications of manipulating neural elements for the purpose of anti-angiogenic therapeutics within the scope of cancer treatment.

Expression and Signaling Pathways of Nerve Growth Factor (NGF) and Pro-NGF in Breast Cancer: A Systematic Review

Breast cancer represents the most common type of cancer and is the leading cause of death due to cancer among women. Thus, the prevention and early diagnosis of breast cancer is of primary urgency, as well as the development of new treatments able to improve its prognosis. Nerve Growth Factor (NGF) is a neurotrophic factor involved in the regulation of neuronal functions through the binding of the Tropomyosin receptor kinase A (TrkA) and the Nerve Growth Factor receptor or Pan-Neurotrophin Receptor 75 (NGFR/p75NTR). In addition, its precursor (pro-NGF) can extert biological activity by forming a trimeric complex with NGFR/p75NTR and sortilin, or by binding to TrkA receptors with low affinity. Several examples of in vitro and in vivo evidence show that NGF is both synthesized and released by breast cancer cells, and has mitogen, antiapoptotic and angiogenic effects on these cells through the activation of different signaling cascades that involve TrkA and NGFR/p75NTR receptors. Conversely, pro-NGF signaling has been related to breast cancer invasion and metastasis. Other studies suggested that NGF and its receptors could represent a good diagnostic and prognostic tool, as well as promising therapeutic targets for breast cancer. In this paper, we comprehensively summarize and systematically review the current experimental evidence on this topic. INPLASY ID: INPLASY2022100017.

The Receptor Tyrosine Kinase TrkA Is Increased and Targetable in HER2-Positive Breast Cancer

The tyrosine kinase receptor A (NTRK1/TrkA) is increasingly regarded as a therapeutic target in oncology. In breast cancer, TrkA contributes to metastasis but the clinicopathological significance remains unclear. In this study, TrkA expression was assessed via immunohistochemistry of 158 invasive ductal carcinomas (IDC), 158 invasive lobular carcinomas (ILC) and 50 ductal carcinomas in situ (DCIS). TrkA was expressed in cancer epithelial and myoepithelial cells, with higher levels of TrkA positively associated with IDC (39% of cases) (p < 0.0001). Interestingly, TrkA was significantly increased in tumours expressing the human epidermal growth factor receptor-2 (HER2), with expression in 49% of HER2-positive compared to 25% of HER2-negative tumours (p = 0.0027). A panel of breast cancer cells were used to confirm TrkA protein expression, demonstrating higher levels of TrkA (total and phosphorylated) in HER2-positive cell lines. Functional investigations using four different HER2-positive breast cancer cell lines indicated that the Trk tyrosine kinase inhibitor GNF-5837 reduced cell viability, through decreased phospho-TrkA (Tyr490) and downstream AKT (Ser473) activation, but did not display synergy with Herceptin. Overall, these data highlight a relationship between the tyrosine kinase receptors TrkA and HER2 and suggest the potential of TrkA as a novel or adjunct target for HER2-positive breast tumours.

The Specificity of EGF-Stimulated IQGAP1 Scaffold Towards the PI3K-Akt Pathway is Defined by the IQ3 motif

Epidermal growth factor receptor (EGFR) and its downstream phosphoinositide 3-kinase (PI3K) pathway are commonly deregulated in cancer. Recently, we have shown that the IQ motif-containing GTPase-activating protein 1 (IQGAP1) provides a molecular platform to scaffold all the components of the PI3K-Akt pathway and results in the sequential generation of phosphatidylinositol-3,4,5-trisphosphate (PI3,4,5P₃). In addition to the PI3K-Akt pathway, IQGAP1 also scaffolds the Ras-ERK pathway. To define the specificity of IQGAP1 for the control of PI3K signaling, we have focused on the IQ3 motif in IQGAP1 as PIPKIα and PI3K enzymes bind this region. An IQ3 deletion mutant loses interactions with the PI3K-Akt components but retains binding to ERK and EGFR. Consistently, blocking the IQ3 motif of IQGAP1 using an IQ3 motif-derived peptide mirrors the effect of IQ3 deletion mutant by reducing Akt activation but has no impact on ERK activation. Also, the peptide disrupts the binding of IQGAP1 with PI3K-Akt pathway components, while IQGAP1 interactions with ERK and EGFR are not affected. Functionally, deleting or blocking the IQ3 motif inhibits cell proliferation, invasion, and migration in a non-additive manner to a PIPKIα inhibitor, establishing the functional specificity of IQ3 motif towards the PI3K-Akt pathway. Taken together, the IQ3 motif is a specific target for suppressing activation of the PI3K-Akt but not the Ras-ERK pathway. Although EGFR stimulates the IQGAP1-PI3K and -ERK pathways, here we show that IQGAP1-PI3K controls migration, invasion, and proliferation independent of ERK. These data illustrate that the IQ3 region of IQGAP1 is a promising therapeutic target for PI3K-driven cancer.

Nerve growth factor modulates the tumor cells migration in ovarian cancer through the WNT/β-catenin pathway

Nerve growth factor (NGF)/nerve growth factor receptors (NGFRs) axis and canonical WNT/β-catenin pathway have shown to play crucial roles in tumor initiation, progression and prognosis. But little did we know the relationship between them in modulation of tumor progress. In this report, we found that NGF/NGFRs and β-catenin were coexpression in ovarian cancer cell lines, and NGF can decrease the expression level of β-catenin and affect its activities, which may be related to the NGF-induced down-regulation of B-cell CLL/lymphoma 9-like (BCL9L, BCL9-2). Furthermore, NGF can also increase or decrease the downstream target gene expression levels of WNT/β-catenin depending on the cell types. Especially, we created a novel in vitro cell growth model based on a microfluidic device to intuitively observe the effects of NGF/NGFRs on the motility behaviors of ovarian cancer cells. The results showed that the migration area and maximum distance into three dimensional (3D) matrigel were decreased in CAOV3 and OVCAR3 cells, but increased in SKOV3 cells following the stimulation with NGF. In addition, we found that the cell colony area was down-regulated in CAOV3 cells, however, it was augmented in OVCAR3 cells after treatment with NGF. The inhibitors of NGF/NGFRs, such as Ro 08-2750, K252a and LM11A-31,can all block NGF-stimulated changes of gene expression or migratory behavior on ovarian cancer cells. The different results among ovarian cancer cells illustrated the heterogeneity and complexity of ovarian cancer. Collectively, our results suggested for the first time that NGF is functionally linked to β-catenin in the migration of human ovarian cancer cells, which may be a novel therapeutic perspective to prevent the spread of ovarian carcinomas by studying the interaction between NGF/NGFRs and canonical WNT/β-catenin signaling.

Suppression of asparaginyl endopeptidase attenuates breast cancer-induced bone pain through inhibition of neurotrophin receptors

Objective Cancer-induced bone pain is a common clinical problem in breast cancer patients with bone metastasis. However, the mechanisms driving cancer-induced bone pain are poorly known. Recent studies show that a novel protease, asparaginyl endopeptidase (AEP) plays crucial roles in breast cancer metastasis and progression. We aim to determine the functions and targeted suppress of AEP in a mouse model of breast cancer-induced bone pain. Methods Breast cancer cells with AEP knocked-down or overexpression were constructed and implanted into the intramedullary space of the femur to induce pain-like behavior in mice. AEP-specific inhibitors or purified AEP proteins were further used in animal model. The histological characters of femur and pain ethological changes were measured. The expressions of AEP and neurotrophin receptors (p75NTR and TrkA) in dorsal root ganglion and spinal cord were examined. Results Femur radiographs and histological analysis revealed that cells with AEP knocked-down reduced bone destruction and pain behaviors. However, cells with AEP overexpression elevated bone damage and pain behaviors. Further, Western blot results found that the expressions of p75NTR and TrkA in dorsal root ganglions and spinal cords were reduced in mice inoculated with AEP knocked-down cells. Targeted suppression of AEP with specific small compounds significantly reduced the bone pain while purified recombinant AEP proteins increased bone pain. Conclusions AEP aggravate the development of breast cancer bone metastasis and bone pain by increasing the expression of neurotrophin receptors. AEP might be an effective target for treatment of breast cancerinduced bone pain.

Src Acts as an Effector for Ku70-dependent Suppression of Apoptosis through Phosphorylation of Ku70 at Tyr-530

Src-family tyrosine kinases are widely expressed in many cell types and participate in a variety of signal transduction pathways. Despite the significance of Src in suppression of apoptosis, its mechanism remains poorly understood. Here we show that Src acts as an effector for Ku70-dependent suppression of apoptosis. Inhibition of endogenous Src activity promotes UV-induced apoptosis, which is impaired by Ku70 knockdown. Src phosphorylates Ku70 at Tyr-530, being close to the possible acetylation sites involved in promotion of apoptosis. Src-mediated phosphorylation of Ku70 at Tyr-530 decreases acetylation of Ku70, whereas Src inhibition augments acetylation of Ku70. Importantly, knockdown-rescue experiments with stable Ku70 knockdown cells show that the nonphosphorylatable Y530F mutant of Ku70 reduces the ability of Ku70 to suppress apoptosis accompanied by augmentation of Ku70 acetylation. Our results reveal that Src plays a protective role against hyperactive apoptotic cell death by reducing apoptotic susceptibility through phosphorylation of Ku70 at Tyr-530.

Nerve growth factor and proNGF simultaneously promote symmetric self-renewal, quiescence, and epithelial to mesenchymal transition to enlarge the breast cancer stem cell compartment

The discovery of cancer stem cells (CSCs) fundamentally advanced our understanding of the mechanisms governing breast cancer development. However, the stimuli that control breast CSC self-renewal and differentiation have still not been fully detailed. We previously showed that nerve growth factor (NGF) and its precursor proNGF can stimulate breast cancer cell growth and invasion in an autocrine manner. In this study, we investigated the effects of NGF and proNGF on the breast CSC compartment and found that NGF or proNGF enrich for CSCs in several breast cancer cell lines. This enrichment appeared to be achieved by increasing the number of symmetric divisions of quiescent/slow-proliferating CSCs. Interestingly, in vitro NGF pretreatment of MCF-7 luminal breast cancer cells promoted epithelial to mesenchymal transition in tumors of severe combined immunodeficient mice. Furthermore, p75(NTR), the common receptor for both neurotrophins and proneurotrophins, mediated breast CSC self-renewal by regulating the expression of pluripotency transcription factors. Our data indicate, for the first time, that the NGF/proNGF/p75(NTR) axis plays a critical role in regulating breast CSC self-renewal and plasticity.

Increasing the efficiency of homology-directed repair for CRISPR-Cas9-induced precise gene editing in mammalian cells

The insertion of precise genetic modifications by genome editing tools such as CRISPR-Cas9 is limited by the relatively low efficiency of homology-directed repair (HDR) compared with the higher efficiency of the nonhomologous end-joining (NHEJ) pathway. To enhance HDR, enabling the insertion of precise genetic modifications, we suppressed the NHEJ key molecules KU70, KU80 or DNA ligase IV by gene silencing, the ligase IV inhibitor SCR7 or the coexpression of adenovirus 4 E1B55K and E4orf6 proteins in a 'traffic light' and other reporter systems. Suppression of KU70 and DNA ligase IV promotes the efficiency of HDR 4-5-fold. When co-expressed with the Cas9 system, E1B55K and E4orf6 improved the efficiency of HDR up to eightfold and essentially abolished NHEJ activity in both human and mouse cell lines. Our findings provide useful tools to improve the frequency of precise gene modifications in mammalian cells.

The biology of IQGAP proteins: beyond the cytoskeleton

IQGAP scaffold proteins are evolutionarily conserved in eukaryotes and facilitate the formation of complexes that regulate cytoskeletal dynamics, intracellular signaling, and intercellular interactions. Fungal and mammalian IQGAPs are implicated in cytokinesis. IQGAP1, IQGAP2, and IQGAP3 have diverse roles in vertebrate physiology, operating in the kidney, nervous system, cardio-vascular system, pancreas, and lung. The functions of IQGAPs can be corrupted during oncogenesis and are usurped by microbial pathogens. Therefore, IQGAPs represent intriguing candidates for novel therapeutic agents. While modulation of the cytoskeletal architecture was initially thought to be the primary function of IQGAPs, it is now clear that they have roles beyond the cytoskeleton. This review describes contributions of IQGAPs to physiology at the organism level.

Ku70 is essential for histone deacetylase inhibitor trichostatin A-induced apoptosis

It was previously reported that the histone deacetylase inhibitor (HDACI) trichostatin A (TSA) induced B cell lymphoma 2 (Bcl-2)-associated X protein (Bax)-dependent apoptosis in colorectal cancer (CRC) cells. In addition, Ku70 has been identified as a regulator of apoptosis, the mechanism of which proceeds via interacting with Bax. The aim of the present study was to investigate the role of Ku70 in TSA-induced apoptosis in the CRC cell lines HCT116 and HT29. The results showed that TSA induced the acetylation of Ku70, which was found to be associated with increased apoptosis. In addition, TSA treatment promoted the release of Bax from its complex with Ku70. Bax was then detected to have translocated from the cytoplasm into the mitochondria, while cytochrome c was detected to have translocated from the mitochondria into the cytoplasm. Furthermore, knockdown of Ku70 using small interfering RNA decreased TSA-induced apoptosis as well as downregulated the expression of Bax. These effects were rescued through pre-treatment of cells with the proteasome inhibitor MG132. In conclusion, the results of the present study suggested that Ku70 acetylation mediated TSA-induced apoptosis in CRC cells. In addition, Ku70 was found to be indispensable in TSA-induced apoptosis due to its role in protecting Bax from proteosomal degradation.

IQGAPs choreograph cellular signaling from the membrane to the nucleus

Since its discovery in 1994, recognized cellular functions for the scaffold protein IQGAP1 have expanded immensely. Over 100 unique IQGAP1-interacting proteins have been identified, implicating IQGAP1 as a critical integrator of cellular signaling pathways. Initial research established functions for IQGAP1 in cell-cell adhesion, cell migration, and cell signaling. Recent studies have revealed additional IQGAP1 binding partners, expanding the biological roles of IQGAP1. These include crosstalk between signaling cascades, regulation of nuclear function, and Wnt pathway potentiation. Investigation of the IQGAP2 and IQGAP3 homologs demonstrates unique functions, some of which differ from those of IQGAP1. Summarized here are recent observations that enhance our understanding of IQGAP proteins in the integration of diverse signaling pathways.

NGF and ProNGF: Regulation of neuronal and neoplastic responses through receptor signaling

Nerve growth factor (NGF) and its precursor (proNGF) are primarily considered as regulators of neuronal function that induce their responses via the tyrosine kinase receptor TrkA and the pan-neurotrophin receptor p75NTR. It has been generally held that NGF exerts its effects primarily through TrkA, inducing a cascade of tyrosine kinase-initiated responses, while proNGF binds more strongly to p75NTR. When this latter entity interacts with a third receptor, sortilin, apoptotic responses are induced in contrast to the survival/differentiation associated with the other two. Recent studies have outlined portions of the downstream phosphoproteome of TrkA in the neuronal PC12 cells and have clarified the contribution of individual docking sites in the TrkA endodomain. The patterns observed showed a similarity with the profile induced by the epidermal growth factor receptor, which is extensively associated with oncogenesis. Indeed, as with other neurotrophic factors, the distribution of TrkA and p75NTR is not limited to neuronal tissue, thus providing an array of targets outside the nervous systems. One such source is breast cancer cells, in which NGF and proNGF stimulate breast cancer cell survival/growth and enhance cell invasion, respectively. This latter activity is exerted via TrkA (as opposed to p75NTR) in conjunction with sortilin. Another tissue overexpressing proNGF is prostate cancer and here the ability of cancer cells to induce neuritogenesis has been implicated in cancer progression. These studies show that the non-neuronal functions of proNGF/NGF are likely integrated with their neuronal activities and point to the clinical utility of these growth factors and their receptors as biomarkers and therapeutic targets for metastasis and cancer pain.

Identification of pyrazine-based TrkA inhibitors: design, synthesis, evaluation, and computational modeling studies

Trk receptors play a key role in the development and maintenance of neuronal networks. Recent evidence suggests that the Trk family, specifically TrkA, is an important driver for tumour growth, inflammatory and neuropathic pain, and chemoresistance. Through a computational screen, a novel Trk active pharmacophore was identified and a series of pyrazine-based inhibitors were developed, which potently inhibited TrkA. Inhibitors displayed the highest activity on TrkA when screened against a small, tyrosine kinase panel and also exhibited a non-linear SAR. Predicted binding modes of the inhibitors were examined, which identified exploitable regions for future development of more advanced inhibitors.

Repair of chromosomal double-strand breaks by precise ligation in human cells

Double-strand breaks (DSBs), a common type of DNA lesion, occur daily in human cells as a result of both endogenous and exogenous damaging agents. DSBs are repaired in two general ways: by the homology-dependent, error-free pathways of homologous recombination (HR) and by the homology-independent, error-prone pathways of nonhomologous end-joining (NHEJ), with NHEJ predominating in most cells. DSBs with compatible ends can be re-joined in vitro with DNA ligase alone, which raises the question of whether such DSBs require the more elaborate machinery of NHEJ to be repaired in cells. Here we report that chromosomal DSBs with compatible ends introduced by the rare-cutting endonuclease, ISceI, are repaired by precise ligation nearly 100% of the time in human cells. Precise ligation depends on the classical NHEJ components Ku70, XRCC4, and DNA ligase IV, since siRNA knockdowns of these factors significantly reduced the efficiency of precise ligation. Interestingly, knockdown of the tumor suppressors p53 or BRCA1 showed similar effects as the knockdowns of NHEJ factors. In contrast, knockdown of components involved in alternative NHEJ, mismatch repair, nucleotide excision repair, and single-strand break repair did not reduce precise ligation. In summary, our results demonstrate that DSBs in human cells are efficiently repaired by precise ligation, which requires classical NHEJ components and is enhanced by p53 and BRCA1.

Proliferation enhanced by NGF-NTRK1 signaling makes pancreatic cancer cells more sensitive to 2DG-induced apoptosis

Rapidly proliferating cancer cells rely on increased glucose consumption for survival. The glucose analog 2-deoxy-D-glucose (2DG) cannot complete glycolysis and inhibits the growth of many types of cancers. It is unknown whether reduced glycolysis inhibits the growth of pancreatic cancer. Activation of nerve growth factor (NGF)-neurotrophic tyrosine kinase receptor type 1 (NTRK1) signaling leads to enhanced proliferation of these cells. We investigated the effect of 2DG treatment on the viability of NTRK1-transfected pancreatic cancer cells. After treatment with 2DG, the viability of pancreatic cancer cells was evaluated by MTT assay. SB203580 (a specific inhibitor of the p38-MAPK pathway) and PD98059 (an MAP2K1 [mitogen-activated protein kinase kinase 1, previously, MEK1] inhibitor) were used to inhibit p38-MAPK and ERKs, respectively. The percentage of apoptotic cells was determined by flow cytometry. Overexpression of NTRK1 in pancreatic cancer cells resulted in increased cell proliferation, which was reduced by PD98059-mediated inhibition of ERKs but not by suppression of p38-MAPK with SB203580. After treatment with 2DG, the percentage of apoptotic cells was greater in those with high expression of NTRK1 than in cells with low NTRK1 expression. Blocking the p38-MAPK pathway with SB203580 effectively abolished the apoptosis induced by 2DG. We conclude that pancreatic cancer cells with a high expression of NTRK1 are more sensitive to 2DG-induced apoptosis, through the p38-MAPK pathway.

IQGAP1 and its binding proteins control diverse biological functions

IQGAP proteins have been identified in a wide spectrum of organisms, ranging from yeast to humans. The most extensively studied family member is the ubiquitously expressed scaffold protein IQGAP1, which participates in multiple essential aspects of mammalian biology. IQGAP1 mediates these effects by binding to and regulating the function of numerous interacting proteins. Over ninety proteins have been reported to associate with IQGAP1, either directly or as part of a larger complex. In this review, we summarise those IQGAP1 binding partners that have been identified in the last five years. The molecular mechanisms by which these interactions contribute to the functions of receptors and their signalling cascades, small GTPase function, cytoskeletal dynamics, neuronal regulation and intracellular trafficking are evaluated. The evidence that has accumulated recently validates the role of IQGAP1 as a scaffold protein and expands the repertoire of cellular activities in which it participates.

IQGAP1 protein binds human epidermal growth factor receptor 2 (HER2) and modulates trastuzumab resistance

Human epidermal growth factor receptor 2 (HER2) is overexpressed in 20-25% of breast cancers. Increased HER2 expression is an adverse prognostic factor and correlates with decreased patient survival. HER2-positive (HER2(+)) breast cancer is treated with trastuzumab. Unfortunately, some patients are intrinsically refractory to therapy, and many who do respond initially become resistant within 1 year. Understanding the molecular mechanisms underlying HER2 signaling and trastuzumab resistance is essential to reduce breast cancer mortality. IQGAP1 is a ubiquitously expressed scaffold protein that contains multiple protein interaction domains. By regulating its binding partners IQGAP1 integrates signaling pathways, several of which contribute to breast tumorigenesis. We show here that IQGAP1 is overexpressed in HER2(+) breast cancer tissue and binds directly to HER2. Knockdown of IQGAP1 decreases HER2 expression, phosphorylation, signaling, and HER2-stimulated cell proliferation, effects that are all reversed by reconstituting cells with IQGAP1. Reducing IQGAP1 up-regulates p27, and blocking this increase attenuates the growth inhibitory effects of IQGAP1 knockdown. Importantly, IQGAP1 is overexpressed in trastuzumab-resistant breast epithelial cells, and reducing IQGAP1 both augments the inhibitory effects of trastuzumab and restores trastuzumab sensitivity to trastuzumab-resistant SkBR3 cells. These data suggest that inhibiting IQGAP1 function may represent a rational strategy for treating HER2(+) breast carcinoma.

Necdin and neurotrophin receptors: interactors of relevance for neuronal resistance to oxidant stress

Necdin is a protein known to interact with the neurotrophin receptors, neurotrophic tyrosine kinase receptor type 1 (TrkA) and 75 kD low-affinity neurotrophin receptor (p75NTR). TrkA and p75NTR play roles in development and disease of the nervous system and chemoresistance of nervous system tumors. Necdin deletion is associated with Prader-Willi syndrome. The present studies demonstrate that the effects of necdin on the susceptibility of neuroblastoma cells to oxidant stress are dependent on the ratio of p75NTR to TrkA in the cell. In low p75NTR:TrkA ratio cells, necdin down-regulation decreases sensitivity to oxidant stress and expression of and signaling through TrkA. In high p75NTR:TrkA cells, necdin down-regulation is without effect. The effects of necdin deletion on the developing nervous system may depend on the relative expression of p75NTR and TrkA in the cells of particular regions of the nervous system.

Nerve growth factor in cancer cell death and survival

One of the major challenges for cancer therapeutics is the resistance of many tumor cells to induction of cell death due to pro-survival signaling in the cancer cells. Here we review the growing literature which shows that neurotrophins contribute to pro-survival signaling in many different types of cancer. In particular, nerve growth factor, the archetypal neurotrophin, has been shown to play a role in tumorigenesis over the past decade. Nerve growth factor mediates its effects through its two cognate receptors, TrkA, a receptor tyrosine kinase and p75NTR, a member of the death receptor superfamily. Depending on the tumor origin, pro-survival signaling can be mediated by TrkA receptors or by p75NTR. For example, in breast cancer the aberrant expression of nerve growth factor stimulates proliferative signaling through TrkA and pro-survival signaling through p75NTR. This latter signaling through p75NTR promotes increased resistance to the induction of cell death by chemotherapeutic treatments. In contrast, in prostate cells the p75NTR mediates cell death and prevents metastasis. In prostate cancer, expression of this receptor is lost, which contributes to tumor progression by allowing cells to survive, proliferate and metastasize. This review focuses on our current knowledge of neurotrophin signaling in cancer, with a particular emphasis on nerve growth factor regulation of cell death and survival in cancer.

Ku86 is important for TrkA overexpression-induced breast cancer cell invasion

PURPOSE

We have recently shown that breast tumors express high levels of TrkA compared with normal breast tissues, with TrkA overexpression enhancing breast cancer cell invasion in vitro and metastasis in animal models. In this study, we tried to identify molecules involved in TrkA overexpression-mediated biological effects in breast cancer cells.

EXPERIMENTAL DESIGN

We used a proteomic-based approach to identify proteins involved in TrkA overexpression-stimulated invasion of MDA-MB-231 breast cancer cells. Proteins from control and TrkA overexpressing cells were separated using a cup-loading two-dimensional electrophoresis system before MALDI and LC-MS/MS mass spectrometry analysis.

RESULTS

Among several putative regulated proteins, Ku86 was found increased in TrkA overexpressing cells. Moreover, Ku86 was co-immunoprecipitated with TrkA, suggesting the interaction of these two proteins in TrkA overexpressing cells. Interestingly, inhibition with small-interfering RNA and neutralizing antibodies showed that Ku86 was required for TrkA-stimulated cell invasion.

CONCLUSIONS AND CLINICAL RELEVANCE

These data allowed the identification of Ku86 as a new player involved in metastasis in breast cancer cells. Our findings suggest that TrkA and its down stream signaling pathways should be regarded as potential new targets for the development of future breast cancer therapy.

Bone marrow cells produce nerve growth factor and promote angiogenesis around transplanted islets

AIM: To clarify the mechanism by which bone marrow cells promote angiogenesis around transplanted islets.

METHODS: Streptozotocin induced diabetic BALB/c mice were transplanted syngeneically under the kidney capsule with the following: (1) 200 islets (islet group: n = 12), (2) 1-5 × 10⁶ bone marrow cells (bone marrow group: n = 11), (3) 200 islets and 1-5 × 10⁶ bone marrow cells (islet + bone marrow group: n = 13), or (4) no cells (sham group: n = 5). All mice were evaluated for blood glucose, serum insulin, serum nerve growth factor (NGF) and glucose tolerance (GTT) up to postoperative day (POD) 14. Histological assessment for insulin, von Willebrand factor (vWF) and NGF was performed at POD 3, 7 and 14.

RESULTS: Blood glucose level was lowest and serum insulin was highest in the islet + bone marrow group. Serum NGF increased in islet, bone marrow, and islet + bone marrow groups after transplantation, and there was a significant difference (P = 0.0496, ANOVA) between the bone marrow and sham groups. The number of vessels within the graft area was significantly increased in both the bone marrow and islet + bone marrow groups at POD 14 as compared to the islet alone group (21.2 ± 3.6 in bone marrow, P = 0.01, vs islet group, 22.6 ± 1.9 in islet + bone marrow, P = 0.0003, vs islet group, 5.3 ± 1.6 in islet-alone transplants). NGF was more strongly expressed in bone marrow cells compared with islets.

CONCLUSION: Bone marrow cells produce NGF and promote angiogenesis. Islet co-transplantation with bone marrow is associated with improvement of islet graft function.

Necdin and TrkA contribute to modulation by p75NTR of resistance to oxidant stress

The neurotrophin receptor p75NTR provides protection from oxidant stress induced by 6-hydroxydopamine (6-OHDA) and resultant cell death. In the absence of p75NTR, TrkA is upregulated and its signaling pathway effectors are increasingly activated. Necdin, a MAGE protein and known interactor of p75NTR and TrkA, is a potential mediator of this phenomenon. Decreased expression of necdin protein in p75NTR-deficient PC12 cells decreased TrkA expression and increased PC12 cell resistance to 6-OHDA. Inhibition of JNK phosphorylation by SP600125 also resulted in increased resistance to 6-OHDA, suggesting that TrkA signaling underlies the susceptibility of these cells to oxidant stress.

Proteomics of membrane receptors and signaling

Receptors represent an abundant class of integral membrane proteins that transmit information on various types of signals within the cell. Assemblages of receptors and their interacting proteins (receptor complexes) have emerged as important units of signal transduction for various types of receptors including G protein coupled, ligand-gated ion channel, and receptor tyrosine kinase. This review aims to summarize the major approaches and findings of receptor proteomics. Isolation and characterization of receptor complexes from cells has become common using the methods of immunoaffinity-, ligand-, and tag-based chromatography followed by MS for the analysis of enriched receptor preparations. In addition, tools such as stable isotope labeling have contributed to understanding quantitative properties and PTMs to receptors and their interacting proteins. As data from studies on receptor-protein interactions considerably expands, complementary approaches such as bioinformatics and computational biology will undoubtedly play a significant role in defining cellular and network functions for various types of receptor complexes. Findings from receptor proteomics may also shed light on the mechanism of action for pharmacological drugs and can be of value in understanding molecular pathologies of disease states.