Gastrin-releasing peptide receptor silencing suppresses the tumorigenesis and metastatic potential of neuroblastoma

Abstract

Neuroblastoma accounts for nearly 15% of all pediatric cancerrelated deaths. We have previously shown that gastrin-releasing peptide (GRP) stimulates neuroblastoma growth, and that its cell surface receptor, GRP-R, is overexpressed in advanced-stage human neuroblastomas; however, the effects of GRP/GRP-R on tumorigenesis and metastasis in vivo are not clearly elucidated. In the present study, we found that GRP-R knockdown in the aggressive cell line BE(2)-C induced cell morphology changes, reduced cell size, decreased cell proliferation, and inhibited DNA synthesis, corresponding to cell cycle arrest at G 2/M phase. Activated Akt, a crucial regulator of cell survival and metastasis, was down-regulated by GRP-R silencing. In addition, expression of p-p70S6K and its downstream target molecule S6, key regulators of protein synthesis and cell metabolism, were also significantly decreased by GRP-R silencing. GRP-R knockdown also up-regulated the expression of tumor suppressor PTEN, the inhibitor of the PI3K/Akt pathway. Furthermore, silencing GRP-R as well as GRP in BE(2)-C cells suppressed anchorage-independent growth in vitro. Conversely, overexpression of GRP-R in less aggressive SK-N-SH neuroblastoma cells resulted in soft agar colony formation, which was inhibited by a GRP-blocking antibody. Moreover, GRP-R deficiency significantly delayed tumor growth and diminished liver metastases in vivo. Our findings demonstrate that GRP and GRP-R have important oncogenic properties beyond their established mitogenic functions. Therefore, GRP-R may be an ideal therapeutic target for the treatment of aggressive neuroblastomas.Akt ͉ RNAi ͉ anchorage independence ͉ metastasis

Silencing of HIF-1α suppresses tumorigenicity of renal cell carcinoma through induction of apoptosis

“…In RCC cell lines, we found that HIF-1a silencing downregulated the phosphorylation of Akt, which is a common mediator of cell survival signals, has been shown to inhibit apoptosis by attenuating activity of proapoptotic factors Bad and caspase-9, and enhance survival by increasing the phosphorylation of IKKb, which led to activation of nuclear factor-kB. 31,32 In addition, previous study reported that Akt could inhibit apoptosis of tumor through negative regulating of FKHR, a member of the forkhead family of transcription factors, which could promote apoptosis by inducing the expression of Bim and FasL. 33 Further study showed that HIF-1a silencing appears to reduce Akt activation indirectly through inhibition of PDK1, which activates Akt.…”

Gastrin-releasing peptide promotes the growth of HepG2 cells via EGFR-independent ERK1/2 activation

“…At present, several GRP analogues and GRPR antagonists are in preclinical trials for tumor imaging and anticancer therapy (8)(9)(10)(11)(12)(13)(14). Although it has been reported that GRP played a role in hepatocarcinogenesis in rat (19), no data are currently available confirming the contribution of GRP to human HCC.…”

“…In particular, GRP serves as a potent mitogen for various types of tumor including small cell lung, pancreatic, prostate, renal, breast and colon cancers (1)(2)(3)(4)(5)(6)(7). Furthermore, treatment with GRP antibody was found to lead to significant anti-proliferative effects, indicating that GRP is an autocrine growth factor and GRPR may be a drug target for tumor imaging and anti-tumor therapy (8)(9)(10)(11)(12)(13)(14).…”

Silencing Gastrin-Releasing Peptide Receptor Suppresses Key Regulators of Aerobic Glycolysis in Neuroblastoma Cells

“…Several known regulators of glucose metabolism include the family of hypoxia inducible factors (HIFs), the c-Myc oncogene, members of the AKT family and the tumor suppressor, p53 (23)(24)(25). Given previous work from our laboratory demonstrating a critical role of GRP-R signaling in neuroblastoma development and malignant potential (12,26), we hypothesized that GRP-R may also be critical in regulating tumor glucose metabolism.…”