Identification of Brain-Derived Neurotrophic Factor as a Novel Functional Protein in Hepatocellular Carcinoma

Neurotrophic factors stimulate the activation of hepatic stellate cells in liver fibrosis

BACKGROUND AND AIMS

Patients with liver fibrosis who have pain in the liver region may have changed nerve factors. The expression of neurokines and hepatic nerves in liver fibrosis, however, was little understood. In order to better understand how liver fibrosis develops, we plan to look into the hepatic nerve and neurokine changes and how they relate to hepatic stellate cells (HSCs).

METHODS

The expression of neurokines in liver samples from 55 chronic hepatitis B patients and the carbon tetrachloride (CCl₄) animal model were studied. The co-staining of Nissl and α-SMA allowed us to investigate the neurons and their interaction with α-SMA in fibrotic livers, as well as the expression of the glial cell marker glial fibrillary acidic protein (GFAP) and its relationship with α-SMA, a marker of HSCs. SH-SY5Y cells were treated with a fibrotic serum to imitate the hepatic microenvironment on neuronal cells. We also used brain-derived neurotrophic factor (BDNF) to stimulate mouse primary HSCs and LX2.

RESULTS

The levels of mRNA for neurokines such as BDNF, GFAP, and growth-associated protein (GAP43) are significantly increased in both human and animal liver fibrosis. As liver fibrosis advances, we found that Nissl bodies and α-SMA may co-localize, suggesting a connection between hepatic nerves and HSCs. Human fibrotic serum may increase neurkines, notably BDNF, in SH-SY5Y cells. We also found that BDNF increased pro-inflammatory cytokines and fibrogenic markers in hHSCs.

CONCLUSIONS

Patients with hepatic fibrosis had significantly higher levels of BDNF, GFAP, GAP43, and nerve fibers. HSC and nerve fibers interact, and nerves also create neurogenic substances that promote liver fibrosis and HSC activation.

Brain-derived neurotrophic factor-TrkB signaling in the medial prefrontal cortex plays a role in the anhedonia-like phenotype after spared nerve injury

Although depressive symptoms including anhedonia (i.e., loss of pleasure) frequently accompany pain, little is known about the risk factors contributing to individual differences in pain-induced anhedonia. In this study, we examined if signaling of brain-derived neurotrophic factor (BDNF) and its receptor tropomyosin-receptor-kinase B (TrkB) contribute to individual differences in the development of neuropathic pain-induced anhedonia. Rats were randomly subjected to spared nerved ligation (SNI) or sham surgery. The SNI rats were divided into two groups based on the results of a sucrose preference test. Rats with anhedonia-like phenotype displayed lower tissue levels of BDNF in the medial prefrontal cortex (mPFC) compared with rats without anhedonia-like phenotype and sham-operated rats. In contrast, tissue levels of BDNF in the nucleus accumbens (NAc) of rats with an anhedonia-like phenotype were higher compared with those of rats without anhedonia-like phenotype and sham-operated rats. Furthermore, tissue levels of BDNF in the hippocampus, L2-5 spinal cord, muscle, and liver from both rats with or without anhedonia-like phenotype were lower compared with those of sham-operated rats. A single injection of 7,8-dihydroxyflavone (10 mg/kg; TrkB agonist), but not ANA-12 (0.5 mg/kg; TrkB antagonist), ameliorated reduced sucrose preference and reduced BDNF-TrkB signaling in the mPFC in the rats with anhedonia-like phenotype. These findings suggest that reduced BDNF-TrkB signaling in the mPFC might contribute to neuropathic pain-induced anhedonia, and that TrkB agonists could be potential therapeutic drugs for pain-induced anhedonia.

MicroRNA‑584 prohibits hepatocellular carcinoma cell proliferation and invasion by directly targeting BDNF

In recent decades, an increasing number of studies have demonstrated that numerous microRNAs (miRNAs) are dysregulated in hepatocellular carcinoma (HCC); these aberrantly expressed miRNAs are contributing regulators of HCC formation and progression. Thus, revealing the biological roles of miRNAs in HCC may provide novel information on the identification of effective therapeutic targets and valuable diagnosis methods. Herein, reverse transcription‑quantitative PCR was performed to determine the expression profile of miRNA‑584 (miR‑584) in HCC tissues and cell lines. Cell Counting Kit‑8 and cell invasion assays were utilized to evaluate the influence of mIR‑584 overexpression on HCC cell proliferation and invasion, respectively. The present study demonstrated that miR‑584 expression was reduced in HCC tissues and cell lines compared with normal controls. Clinical analysis indicated that decreased miR‑584 expression was significantly associated with tumor size, TNM stage and lymph node metastasis of patients with HCC. Additionally, resumption of miR‑584 expression inhibited proliferation and invasion of HCC cells. Mechanistically, it was demonstrated that miR‑584 can directly interact with the 3'‑untranslated regions of brain‑derived neurotrophic factor (BDNF) mRNA, and reduce its mRNA and protein levels in HCC cells. Furthermore, BDNF was upregulated in HCC tissues, and its level was inversely correlated with miR‑584 expression. Notably, restored BDNF expression antagonized the inhibitory effects of miR‑584 overexpression on HCC cells. In conclusion, miR‑584 may serve tumor‑suppressive roles in HCC by directly targeting BDNF, thus suggesting that miR‑584 may serve as a potential candidate for treatment of patients with this disease.

CA10 and CA11 negatively regulate neuronal activity-dependent growth of gliomas

Recent studies have revealed that neurons can promote glioma growth through activity‐dependent secretion of neurotrophins, especially neuroligin‐3. It has therefore been suggested that blocking neuron‐derived neurotrophins may serve as a therapeutic intervention for gliomas. Carbonic anhydrase‐related proteins 11 and 10 (CA11 and CA10) are secreted synaptic proteins which function as neurexin ligands, and the gene‐encoding CA11 is part of a gene signature associated with radiotherapy and prognosis in gliomas. We therefore hypothesized that CA11/CA10 might participate in the neuronal activity‐dependent regulation of glioma growth. In this study, we report that CA11 secreted by depolarized cultured neurons within conditioned medium (CM) inhibited the growth of glioma cell lines. CM from depolarized neurons inhibited CA11 expression in glioma cell lines via the Akt signaling pathway. Consistently, CA11 expression was also reduced in clinical glioma samples and negatively associated with high histological grade. Low CA11 expression of gliomas was associated with short survival in four independent datasets [repository of brain neoplasia data (REMBRANDT), The Cancer Genome Atlas (TCGA) lower grade glioma (LGG), GSE4271, and GSE42669]. CA11 knockdown promoted cell growth, clone formation, and migration; inhibited apoptosis; and increased tumor size in xenografted nude mice. Similarly, CA10 and CA10 secreted by depolarized cultured neurons also inhibited the growth of glioma cell lines. Low CA10 expression was associated with short survival in REMBRANDT, TCGA LGG, and GEO GSE4271 datasets. Our results suggest that CA11 and CA10 negatively regulate neuronal activity‐dependent glioma growth and inhibit glioma aggression. Thus, CA11/CA10 may represent a potential therapeutic target for the treatment of gliomas.

P2X4R silence suppresses glioma cell growth through BDNF/TrkB/ATF4 signaling pathway

Purinergic receptor P2X 4 (P2X4R), a member of purinergic channels family and a subtype of ionotropic adenosine triphosphate receptors, plays a critical role in tumorigenesis. Evidence suggested that P2X4R is expressed in rat C6 glioma model, however, its role and the underlying mechanism of action are still unclear in human glioblastoma multiforme (GBM). In the current study, our aim is to examine the function and the molecular basis of P2X4R in GBM. We first observed that GBM cells, U251, T98, U87, U373, and A172 were all high expressed P2X4R, when compared with the normal human astrocytes (NHA) cells. To gain the function of P2X4R, P2X4R silence cells were constructed by transfection with P2X4R small interfering RNA (siRNA). We found that P2X4R deletion impeded T98 and U87 cell viability and proliferation, and further studies indicated that cell apoptosis and caspase-3 activity was increased in T98 and U87 cell transfected with P2X4R siRNA. Subsequently, we confirmed that P2X4R silence suppressed brain-derived neurotrophic factor (BDNF), Trk receptor tyrosine kinases (TrkB), and activating transcription factor 4 (ATF4) expression in T98 and U87 cells. And P2X4R siRNA-induced ATF4-expression inhibition dependent on BDNF/TrkB signaling pathway. The impact of P2X4R silence on T98 and U87 cell growth and apoptosis was reversed by ATF4 overexpression. In summary, this study provides the first evidence that P2X4R plays important roles in GBM cell growth and apoptosis.

Nervous system and primary liver cancer

Recent advances have found irregular activities of the nervous system-associated factors in the development and progression of primary liver cancer. These factors contributed in the regulation of migration, proliferation, and apoptosis of cancer cells, and took a role in modulating invasion, metastasis, and recurrence after curative treatment. In clinical researches, neural-related factors were found to be significant prognostic factors, suggesting that the interactions between nervous system and primary liver cancer are indispensable in understanding underlying biological mechanisms. Herein, we reviewed up-to-date achievements in this area and the future perspectives of the interactions between the nervous system and primary liver cancer.

Stress hormones concentrations in the normal microenvironment predict risk for chemically induced cancer in rats

Evidence show that stress hormones can influence cancer progression, but its role in carcinogenesis is poorly understood. In this study, we used a new method based on oral carcinogenesis model in rats to test the hypothesis that physiological levels of stress hormones in the normal tissue microenvironment would have significant predictive value for chemically induced cancer occurrence. Male Wistar rats were submitted to a tongue biopsy for measuring not-stress induced levels of norepinephrine, corticosterone, adrenocorticotropic hormone (ACTH) and brain-derived neurotrophic factor (BDNF) in the tissue before carcinogenic induction. Rats were treated with the 4-nitroquinoline-1-oxide (4NQO) chemical carcinogen for twenty weeks and then euthanized for microscopic evaluation of the tongue lesions. Increased pre-carcinogen norepinephrine concentrations and reduced basal corticosterone levels in the normal tissue microenvironment were predictive for oral squamous cell carcinoma (OSCC) occurrence. Likewise, increased pre-carcinogen norepinephrine levels in the normal microenvironment were associated a lower expression of pCDKN2a-p16 in OSCCs. Post-carcinogen levels of corticosterone and BDNF in oral leukoplakia tissues (precursor lesion of OSCC) and post-carcinogen corticosterone concentrations in OSCCs were higher than basal levels in the normal mucosa. Increased norepinephrine concentrations in OSCCs were associated to a greater tumor volume and thickness. Furthermore, higher levels of norepinephrine, ACTH and BDNF in OSCCs were associated to a lesser intensity of the lymphoplasmocytic infiltrate. This study shows that pre-carcinogen stress hormones levels in the normal microenvironment may be predictive for chemically induced cancer in rats. Moreover, chemical carcinogenesis can promote stressor-like effects with hormonal changes in the tissue microenvironment, which may be associated to tumor progression.

MicroRNA-103 suppresses glioma cell proliferation and invasion by targeting the brain-derived neurotrophic factor

Glioma is the most common and aggressive of malignant brain tumours. MicroRNAs (miRNAs/miRs) are involved in tumour development of various human cancers, including glioma. Therefore, miRNAs may have potential tumour diagnostic, prognostic and therapeutic values in human glioma. miR‑103 is abnormally expressed in various human cancer types. However, the detailed expression pattern, biological functions and underlying molecular mechanism of miR‑103 in glioma remain unclear. Therefore, the present study aimed to investigate the expression, biological roles and underlying mechanisms of miR‑103 in glioma. Results of the present study demonstrated that miR‑103 was significantly down‑regulated in glioma tissues and cell lines. Functional experiments demonstrated that miR‑103 overexpression inhibited the proliferation and invasion of glioma cells in vitro. Additionally, brain‑derived neurotrophic factor (BDNF) was identified as a direct functional target of miR‑103 in glioma. Furthermore, mRNA and protein expression levels of BDNF were highly upregulated in glioma tissues compared with normal brain tissues. Spearman's correlation analysis indicated a negative association between miR‑103 and BDNF mRNA expression levels in glioma tissues. Furthermore, rescue experiments demonstrated that BDNF up‑regulation reversed the suppressive effects of miR‑103 on glioma cell proliferation and invasion. Therefore, the authors of the present study hypothesized that the interaction between miR‑103 and BDNF serves a role in glioma progression and, in the future, may serve as a therapeutic target for glioma treatment.

Brain-derived neurotrophic factor/tropomyosin-related kinase B signaling pathway contributes to the aggressive behavior of lung squamous cell carcinoma

The tropomyosin-related kinase (Trk) family consists of TrkA, TrkB, and TrkC, which play essential roles in tumor progression and/or suppression in various cancers. Little is known about the biological significance of the Trk family in human lung squamous cell carcinoma (SCC). Here we investigated the clinical significance of the protein expression of Trk family members in samples from 99 SCC patients, and we explored the relationship between invasion/proliferation activities and Trk expression using lung SCC cell lines to clarify the biological significance of the Trk family in lung SCC. Immunohistochemical high expression of TrkB was significantly correlated with vascular invasion (P=0.004), lymph node metastasis (P<0.001), and advanced stage (P=0.0015). The overall survival of the patients with TrkB-high expression was significantly shorter than those with TrkB-low expression (P=0.0110). TrkA/TrkC expressions were not predictors of poor prognosis. An in vitro assay demonstrated that the inhibition of brain-derived neurotrophic factor (BDNF) (a TrkB ligand) and TrkB by K252a (a Trk inhibitor) or siRNA (BDNF-siRNA, TrkB-siRNA) suppressed the invasion, migration, and proliferative activities of lung SCC cells. The administration of recombinant human BDNF (rhBDNF) enhanced the invasion, migration, and proliferation activities, which were abrogated by K252a. TrkB-siRNA transfection increased the protein expression of E-cadherin and decreased vimentin expressions in lung SCC cells. Matrix metalloproteinase-2 (MMP-2)-mediated gelatin degradations were decreased in lung SCC cells transfected with TrkB-siRNA. Thus, TrkB-high expression is an indicator of poor prognosis in lung SCC, probably due to invasion/proliferation activities promoted by the BDNF/TrkB signaling pathway, which could become a therapeutic target for lung SCC.

PI3K and MAPK pathways mediate the BDNF/TrkB-increased metastasis in neuroblastoma

Brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor TrkB have been reported to be associated with poor prognosis in neuroblastoma (NB) patients. Our previous studies indicated that BDNF activation of TrkB induces chemo-resistance through activation of phosphoinositide-3-kinase (PI3K)/Akt pathway. In this study, we investigated the role of BDNF/TrkB on metastasis in NB. A tetracycline-regulated TrkB-expressing NB cell line (TB3) was used. Scratch wound healing assay, Boyden chamber migration, and invasion assays were performed to study the migration and invasion of TB3 cells. A tumor xenograft model using SCID-Beige mice was utilized to detect the metastasis of NB tumors in vivo. Inhibitors of PI3K, MAPK, Akt, and mTOR were used. Western blotting was performed to study the expressions of P-Akt, P-Erk, and P-mTOR. Our results showed that in TrkB-expressing NB cells, BDNF treatment significantly increased gap closing (P < 0.01) in scratch wound healing assay, also significantly enhanced the numbers of migrating cells (P < 0.01) and invading cells (P < 0.01) in the Boyden chamber migration and invasion assays. In vivo, NB distant metastases were significantly increased in mice with TrkB-expressing xenograft tumors compared to those with non-TrkB-expressing tumors (P < 0.05). Pre-treatment with any of the inhibitors for PI3K (LY294002), MAPK (PD98059), Akt (perifosine), or mTOR (rapamycin) blocked the BDNF/TrkB-induced increases of cell migration and invasion in TB3 cells, and also blocked the BDNF/TrkB-induced expressions of P-Akt, P-Erk, and P-mTOR. These data indicated that BDNF/TrkB increased metastasis in NB via PI3K/Akt/mTOR and MAPK pathways, and BDNF/TrkB and the downstream targets may be potential targets for the treatment of NB metastasis.

Autocrine activity of BDNF induced by the STAT3 signaling pathway causes prolonged TrkB activation and promotes human non-small-cell lung cancer proliferation

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin superfamily, which has been implicated in the pathophysiology of the nervous system. Recently, several studies have suggested that BDNF and/or its receptor, tropomyosin related kinase B (TrkB), are involved in tumor growth and metastasis in several cancers, including prostate cancer, neuroblastoma, pancreatic ductal carcinoma, hepatocellular carcinoma, and lung cancer. Despite the increasing emphasis on BDNF/TrkB signaling in human tumors, how it participates in primary tumors has not yet been determined. Additionally, little is known about the molecular mechanisms that elicit signaling downstream of TrkB in the progression of non-small-cell lung cancer (NSCLC). In this study, we report the significant expression of BDNF in NSCLC samples and show that BDNF stimulation increases the synthesis of BDNF itself through activation of STAT3 in lung cancer cells. The release of BDNF can in turn activate TrkB signaling. The activation of both TrkB and STAT3 contribute to downstream signaling and promote human non-small-cell lung cancer proliferation.

The kringle 1 domain of hepatocyte growth factor has antiangiogenic and antitumor cell effects on hepatocellular carcinoma

The kringle 1 domain of human hepatocyte growth factor (HGFK1) was previously shown to inhibit bovine aortic endothelial cell proliferation, suggesting that it might be an antiangiogenic molecule. Here, we evaluated the in vivo efficacy of a recombinant adenoassociated virus carrying HGFK1 (rAAV-HGFK1) for the treatment of hepatocellular carcinoma (HCC) in a rat orthotopic HCC model and explored its molecular mechanisms in vitro in both endothelial and tumor cells. We first showed that rAAV-HGFK1 treatment significantly prolonged the survival time of rats transplanted with tumor cells. Treatment with rAAV-HGFK1 inhibited tumor growth, decreased tumor microvessel density, and completely prevented intrahepatic, lung, and peritoneal metastasis in this in vivo model. In vitro, rAAV-HGFK1 exhibited both antiangiogenic and antitumor cell effects, inhibiting the proliferation of both murine microvascular endothelial cells (MEC) and tumor cells, and inducing apoptosis and G(0)-G(1) phase arrest in these cells. To our surprise, rAAV-HGFK1 did not act through the hepatocyte growth factor/hepatocyte growth factor receptor pathway. Instead, it worked mainly through epidermal growth factor (EGF)/epidermal growth factor receptor (EGFR) signaling, with more minor contributions from vascular endothelial growth factor/vascular endothelial growth factor receptor and beta fibroblast growth factor (bFGF)/beta fibroblast growth factor receptor (bFGFR) signaling. In both MECs and tumor cells, rAAV-HGFK1 acted through two pathways downstream of EGFR, namely inhibition of extracellular signal-regulated kinase activation and stimulation of p38 mitogen-activated protein kinase/c-Jun-NH(2)-kinase activation. These results suggest for the first time that HGFK1 exerts both antiangiogenic and antitumor cell activities mainly through EGF/EGFR signaling, and may thus be considered as a novel therapeutic strategy for the treatment of HCC.

Brain-derived neurotrophic factor activation of TrkB induces vascular endothelial growth factor expression via hypoxia-inducible factor-1alpha in neuroblastoma cells

The extent of angiogenesis and/or vascular endothelial growth factor (VEGF) expression in neuroblastoma tumors correlates with metastases, N-myc amplification, and poor clinical outcome. Recently, we have shown that insulin-like growth factor-I and serum-derived growth factors stimulate VEGF expression in neuroblastoma cells via induction of hypoxia-inducible factor-1alpha (HIF-1alpha). Because another marker of poor prognosis in neuroblastoma tumors is high expression of brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor, TrkB, we sought to evaluate the involvement of BDNF and TrkB in the regulation of VEGF expression. VEGF mRNA levels in neuroblastoma cells cultured in serum-free media increased after 8 to 16 hours in BDNF. BDNF induced increases in VEGF and HIF-1alpha protein, whereas HIF-1beta levels were unaffected. BDNF induced a 2- to 4-fold increase in VEGF promoter activity, which could be abrogated if the hypoxia response element in the VEGF promoter was mutated. Transfection of HIF-1alpha small interfering RNA blocked BDNF-stimulated increases in VEGF promoter activity and VEGF protein expression. The BDNF-stimulated increases in HIF-1alpha and VEGF expression required TrkB tyrosine kinase activity and were completely blocked by inhibitors of phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) pathways. These data indicate that BDNF plays a role in regulating VEGF levels in neuroblastoma cells and that targeted therapies to BDNF/TrkB, PI3K, mTOR signal transduction pathways, and/or HIF-1alpha have the potential to inhibit VEGF expression and limit neuroblastoma tumor growth.