Phosphatidylinositol 3-kinase regulation of gastrin-releasing peptide-induced cell cycle progression in neuroblastoma cells

Department of Surgery, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 07/2007; 1770(6):927-32. DOI: 10.1016/j.bbagen.2007.02.002
Source: PubMed

ABSTRACT Gastrin-releasing peptide (GRP), the mammalian equivalent of bombesin (BBS), is an autocrine growth factor for neuroblastoma; its receptor is up-regulated in undifferentiated neuroblastomas. Phosphatidylinositol 3-kinase (PI3K) is a critical cell survival pathway; it is negatively regulated by the PTEN tumor suppressor gene. We have recently found that poorly differentiated neuroblastomas express decreased PTEN protein levels. Moreover, overexpression of the GRP receptor, a member of the G-protein coupled receptor family, down-regulates PTEN expression, resulting in increased neuroblastoma cell growth. Therefore, we sought to determine whether GRP or BBS activates PI3K in neuroblastoma cells (BE(2)-C, LAN-1, SK-N-SH). GRP or BBS treatment rapidly increased phosphorylation of Akt and GSK-3beta in neuroblastoma cells. Inhibition of GRP receptor, with antagonist GRP-H2756 or siRNA, attenuated BBS-induced phosphorylation of Akt. LY294002, a PI3K inhibitor, also abrogated BBS-stimulated phospho-Akt as well as its cell cycle targets. GRP increased G1/S phase progression in SK-N-SH cells. BBS-mediated BrdU incorporation was blocked by LY294002. Our findings identify PI3K as an important signaling pathway for GRP-mediated neuroblastoma cell growth. A novel therapy targeted at GRP/GRP receptor may prove to be an effective treatment option to inhibit PI3K in neuroblastomas.

Download full-text


Available from: Jingbo Qiao, Sep 29, 2015
8 Reads
  • Source
    • "Among them, gastrin-releasing peptide (GRP), the mammalian equivalent of bombesin (BBS), has been shown to play a key role in the mitogenic potential of neuroblastoma cells [4]. We have reported that GRP stimulates neuroblastoma cell proliferation [4] and promotes PI3K/AKT-mediated cell survival [5]. We also showed that BBS/GRP increases angiogenesis and primary neuroblastoma growth in vivo [6]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We have previously demonstrated the role of gastrin-releasing peptide (GRP) as an autocrine growth factor for neuroblastoma. Here, we report that GRP silencing regulates cell signaling involved in the invasion-metastasis cascade. Using a doxycycline inducible system, we demonstrate that GRP silencing decreased anchorage-independent growth, inhibited migration and neuroblastoma cell-mediated angiogenesis in vitro, and suppressed metastasis in vivo. Targeted inhibition of GRP decreased the mRNA levels of oncogenes responsible for neuroblastoma progression. We also identified PTEN/AKT signaling as a key mediator of the tumorigenic properties of GRP in neuroblastoma cells. Interestingly, PTEN overexpression decreased GRP-mediated migration and angiogenesis; a novel role for this, otherwise, understated tumor suppressor in neuroblastoma. Furthermore, activation of AKT (pAKT) positively correlated with neuroblastoma progression in an in vivo tumor-metastasis model. PTEN expression was slightly decreased in metastatic lesions. A similar phenomenon was observed in human neuroblastoma sections, where, early-stage localized tumors had a higher PTEN expression relative to pAKT; however, an inverse expression pattern was observed in liver lesions. Taken together, our results argue for a dual purpose of targeting GRP in neuroblastoma -1) decreasing expression of critical oncogenes involved in tumor progression, and 2) enhancing activation of tumor suppressor genes to treat aggressive, advanced-stage disease.
    PLoS ONE 09/2013; 8(9):e72570. DOI:10.1371/journal.pone.0072570 · 3.23 Impact Factor
  • Source
    • "β-catenin, in particular, has been shown to modulate the cell cycle regulators myc and cyclin D1.33,34 Furthermore, regulation of cell cycle progression involves the PI3K/Akt/GSK-3β pathway. Thus, PI3K/Akt-mediated phosphorylation of GSK-3β leads to nuclear accumulation of cyclinD1, promoting cell cycle progression, and enhances degradation of cyclin-dependent kinase inhibitor p27, a negative regulator of the cell cycle.22,35 During the G1/S phase, Rb phosphorylation releases the E2F transcription factor from an inhibitory Rb complex, which then activates genes required for cell cycle progression.36 "
    [Show abstract] [Hide abstract]
    ABSTRACT: Bupleuri Radix (BR) is a major component of several Oriental herbal medicines used to treat stress and mental illness. There are evidences that antidepressant drugs modulate oxidative damage implicated in the pathophysiology of neuropsychiatric disorder, including depression. The aim of the present study was to investigate antioxidant and proliferative effects of BR against oxidative stress induced by serum deprivation in SH-SY5Y cells. We examined the antioxidant effects of BR on a number of measures, including cell viability, formation of reactive oxygen species (ROS), superoxide dismutase (SOD) activity and levels of both Bcl-2 and Bax. We also investigated the effects of BR on cell proliferation using the bromodeoxyuridine (BrdU) assay, and used Western blot analysis to measure changes in expression of the cell cycle phase regulators. 1) Serum deprivation significantly induced the loss of cell viability, the formation of ROS, the reduction of SOD activity, down-regulation of Bcl-2 expression and up-regulation of Bax expression. However, BR extract reversed these effects in dose-dependent manner. 2) Serum deprivation significantly reduced cell proliferation. Western blot analysis revealed that serum deprivation significantly decreased cyclinD1 and phosphorylated retinoblastoma (pRb) expression, and increased p27 expression. On the other hand, BR dose dependently reversed these effects. This study suggests that aqueous extract of BR may exert potent antioxidant effects and also play an important role in regulating cell cycle progression during neurogenesis. These effects of BR may be a potentially important mechanism of antidepressant underlying the observed antioxidant and proliferative effects.
    Psychiatry investigation 03/2013; 10(1):81-88. DOI:10.4306/pi.2013.10.1.81 · 1.28 Impact Factor
  • Source
    • "In spite of recent advances in understanding the role of GRP/GRP-R in tumor progression [3]–[5], signal transduction pathways regulated by GRP and its receptor are not completely understood. We have previously reported that the PI3K/AKT pathway, in part, mediates GRP-induced G1-S phase cell cycle progression and that bombesin, an amphibian equivalent of GRP, induces vascularization of neuroblastoma xenografts by upregulation of vascular endothelial growth factor (VEGF) [3], [4]. Correspondingly, we also reported that GRP-R overexpressing neuroblastoma cells induce AKT activation, and the ratio of AKT to PTEN, an endogenous negative regulator of PI3K, is increased in neuroblastoma patients [5]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Activation of PI3K/AKT pathway correlates with poor prognosis in patients with neuroblastoma. Our previous studies have demonstrated that PI3K/AKT signaling is critical for the oncogenic transformations induced by gastrin-releasing peptide (GRP) and its receptor, GRP-R, in neuroblastoma. Moreover, PI3K/AKT-dependent oncogenic transformations require N-myc, an extensively studied oncogene in neuroblastoma. Whether AKT directly regulates the expression of N-myc oncogene is yet to be determined. Here, we report a novel finding that of the three AKT isoforms, AKT2 specifically regulated N-myc expression in neuroblastoma cells. We also confirmed that GRP-R is upstream of AKT2 and in turn, regulated N-myc expression via AKT2 in neuroblastoma cells. Functional assays demonstrated that attenuation of AKT2 impaired cell proliferation and anchorage-independent cell growth, and decreased the secretion of angiogenic factor VEGF . Furthermore, silencing AKT2 inhibited migration and invasion of neuroblastoma cells . Xenografts established by injecting AKT2 silenced human neuroblastoma cells into murine spleen expressed decreased levels of AKT2 and resulted in fewer liver metastases compared to controls . Hence, our study highlights the potential molecular mechanism(s) mediating the oncogenic role of GRP/GRP-R and demonstrates a novel role for AKT2 in neuroblastoma tumorigenesis, indicating that targeting the GRP/GRP-R/AKT2 axis may be important for developing novel therapeutics in the treatment of clinically aggressive neuroblastoma.
    PLoS ONE 02/2013; 8(2):e56382. DOI:10.1371/journal.pone.0056382 · 3.23 Impact Factor
Show more