Background: Neuroblastoma is the commonest solid tumour in early childhood. Neuroblastoma due to N-Myc oncogene amplification represents a more aggressive subtype with a worse clinical outcome. N-Myc protein is stabilized when phosphorylated at Serine 62 by extracellular signal-regulated protein kinase (ERK). The class III histone deacetylase SIRT1 induces histone deacetylation, promoter CpG island methylation, transcriptional repression, and deacetylation of tumour suppressor proteins. By blocking apoptosis and promoting cell growth, SIRT1 may play a critical role in tumour initiation and progression. Much less is known about the role of SIRT2 in cancer. Aristoforin, cambinol and tenovin-6, which are small molecule inhibitors of both SIRT1 and SIRT2, have shown promising anti-cancer effects in various animal models of cancer. We have found that N-Myc induces SIRT1 and SIRT2 over-expression in neuroblastoma cells, that SIRT1 and SIRT2 block proteasome-mediated N-Myc protein degradation, and that repression of SIRT1 or SIRT2 induces cell growth arrest. The SIRT1/SIRT2 inhibitor cambinol promotes N-Myc protein degradation and induces dose-dependant cell growth arrest. Moreover, SIRT1 and SIRT2 repress gene transcription of mitogen-activated protein kinase phosphotase 3 (MKP3), which dephosphorylates and inactivates ERK.
Aims : (1) To demonstrate that SIRT1 and SIRT2 stabilize N-Myc protein by repressing MKP3 expression and modulating N-Myc protein phosphorylation;(2) To compare the efficacy of SIRT1/SIRT2 inhibitors in promoting N-Myc protein degradation and blocking proliferation and/or survival of neuroblastoma and pre-cancer neuroblast cells;(3) To identify the SIRT1/SIRT2 inhibitor of the best choice for prevention of neuroblastoma. Research design and methods: (i) Do SIRT1 and SIRT2 block N-Myc oncoprotein degradation by blocking N-Myc oncoprotein ubiquitination? (ii) Do SIRT1 and SIRT2 stabilize N-Myc oncoprotein by repressing MKP3 gene transcription, enhancing ERK phosphorylation, and consequently inducing N-Myc protein phosphorylation at Serine 62? (iii) Do SIRT1/SIRT2 inhibitors reactivate MKP3 gene expression, dephosphorylate ERK, promote N-Myc protein degradation, and induce growth arrest and/or apoptosis in neuroblastoma cells? (iv) Do SIRT1/SIRT2 inhibitors reactivate MKP3 gene expression, dephosphorylate ERK, promote N-Myc protein degradation, and induce growth arrest and/or apoptosis in pre-cancer neuroblasts from N-Myc transgenic mice? (v) To examine and compare the efficacy of SIRT1/SIRT2 inhibitors in the prevention of neuroblastoma in N- Myc transgenic mice.
Cancer is the second commonest cause of death in children. Neuroblastoma is the commonest solid tumour in early childhood. This project aims to identify the mechanism through which SIRT1 and SIRT2 stabilize N-Myc oncoprotein, and to identify the SIRT1/SIRT2 inhibitor of the best choice for the prevention of neuroblastoma.
