Abstract 1258: Bin1 enhances anoikis via p38 MAPK: A potential inhibitory role in neuroblastoma metastasis

Abstract

Abstract Neuroblastoma (NB) is the most common extracranial solid tumor in children and approximately half of all children with NB are designated as high-risk patients. Most high-risk children experience metastatic recurrence despite aggressive treatment and nearly all children who relapse eventually die from disease progression. Clearly, there is a great demand for novel specific therapeutics against NB and the metastasis in particular. This relies on our understanding of the molecular mechanism that leads to metastasis. Unfortunately, this area is still largely unexplored. Based on the modern biological view of metastasis, cancer cells undergo multiple steps, including survival in circulation, to spread to distant organs. We have reported that Bin1 expression is frequently reduced in NB cell lines and forced Bin1 overexpression by transfer of an ectopic Bin1 gene into a NB cell line (SA-N-AS), designated SK-N-AS(pBin1), enhances cell death in suspension culture. This result implies that tumor cells with Bin1 loss may gain a survival advantage in blood or lymphatic system, thus allowing for distant metastasis. We therefore hypothesized that Bin1 can suppress NB metastasis via enhancing cancer cell apoptosis in circulation. Apoptosis induced by loss of cell adhesion to the extracellular matrix (ECM) is termed anoikis. The molecular mechanism by which Bin1 enhances cell death in suspension was investigated in this study. Flow cytometric analysis of floating SK-N-AS(pBin1) cells revealed that the nature of Bin1-enhanced cell death is anoikis. The anoikis was found to be mediated by a mitogen-activated protein kinase (MAPK), p38. By use of an antibody specific for p38 phosphorylated at threonine180 and tyrosine182, we show that p38 was phosphorylated (activated) in floating SK-N-AS(pBin1) cells but not in the vector control SK-N-AS(pcDNA3). Phosphorylation of p38 at these sites was undetectable in both cell lines under an adherent condition. These results indicate that (a) p38 acts as a stress kinase in NB cells; (b) Bin1 does not stimulate p38 phosphorylation without a stress induction; and (c) Bin1 enhances anoikis, at least partly, via the p38 MAPK pathway. We also show that the MEK-ERK MAPK survival pathway was inhibited by ECM-detachment, and the inhibition is, at least in part, mediated by p38 activation because pharmacological inhibition of p38 activity in floating SK-N-AS(pBin1) reactivated this pathway. Additionally, the MEK-ERK pathway was inhibited by a specific MEK inhibitor, which provides a potentially useful therapeutic target against metastasis. In conclusion, these results identify a novel link between Bin1 and MAPK pathways in NB anoikis and provide an insight into the molecular mechanism of metastasis. Further defining the involved pathways could offer multiple novel molecular targets that can be manipulated to control NB metastasis and improve the survival for this deadly disease in young children. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1258.