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Oncogenic transcription factor MYCN modulates gene transcription and induces neuroblastoma initiation. Recruitment of histone deacetylase (HDAC) to DNA-bound transcription factors results in removal of acetyl groups from nucleosomal histones, tightening of nucleosomal integrity, and suppression of transcription, particularly of tumor suppressor genes. Reversely, dissociation of HDAC from transcription factors inactivates HDAC enzyme. We have carried out experiments to investigate whether MYCN interacts with HDAC to exert transcriptional regulation. cDNA microarray indicated that MYCN over-expression suppressed tissue transglutaminase (TGM2) gene expression by 40 folds in SHEP S1 MYCN stable transfectants, compared with SHEP EV empty vector control. This transcriptional regulation was further confirmed in tetracycline withdrawal-inducible MYCN-expressing SHEP cells (SHEP TET-OFF). The down-regulation of TGM2 and promotion of cell proliferation by MYCN in SHEP S1 cells was reversed by intervention with TSA, a specific inhibitor of HDAC. Small interfering RNA (siRNA) targeting TGM2 knocked out TGM2 gene expression, and promoted proliferation of SHEP EV, SHEP TET-OFF, but not SHEP S1 cells without TSA treatment. TGM2 siRNA also partly blocked TSA-induced SHEP S1 cell growth inhibition. HDAC enzymatic assay indicated that MYCN up-regulation correlated with increased HDAC enzymatic activity in the cells. Furthermore, competitive RT-PCR revealed that down-regulation of TGM2 correlated with advanced tumor stages, and Kaplan-Meiers analysis demonstrated that down-regulation of TGM2 predicted poor clinical prognosis in 31 neuroblastoma tissue samples from patients. In conclusion, MYCN interacts with HDAC to modulate target gene transcription, and to promote cell proliferation through down-regulation of TGM2.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]