Background: Neuroblastomas are characterized by hemizygous 1p deletions, suggesting that a tumor suppressor gene resides in this region. We previously mapped the smallest region of consistent deletion to a 2-Mb region of 1p36.31 that encodes 23 genes. Based on mutation analysis, expression pattern, and putative function, we identified CHD5 as the best tumor suppressor gene candidate.
Methods: We determined the methylation status of the CHD5 gene promoter in NLF and IMR5 (with 1p deletion) and SK-N-SH and SK-N-FI neuroblastoma cell lines using methylation-specific sequencing and measured CHD5 mRNA expression by reverse transcription polymerase chain reaction in cells treated with or without 5-aza-2-deoxycytidine, an inhibitor of DNA methylation. We transfected the cells with CHD5 and antisense (AS) CHD5 DNA to assess the effect of CHD5 overexpression and suppression, respectively, on colony formation in soft agar and growth of xenograft tumors in athymic mice. We also analyzed the association of CDH5 expression with outcomes of 99 neuroblastoma patients. Statistical tests were two-sided.
Results: CHD5 expression was very low or absent in neuroblastoma cell lines. The CHD5 promoter was highly methylated in NLF and IMR5 lines, and CHD5 expression increased after treatment with 5-aza-2-deoxycytidine. Clonogenicity and tumor growth were abrogated in NLF and IMR5 cells overexpressing CHD5 compared with antisense CHD5 (clonogenicity: mean no. of colonies per plate, NLF-CHD5, 43 colonies, 95% confidence interval [CI] = 35 to 51 colonies, vs NLF-CHD5-AS, 74 colonies, 95% CI = 62 to 86 colonies, P < .001; IMR5-CHD5, 11 colonies, 95% CI = 2 to 20 colonies, vs IMR5-CHD5-AS, 39 colonies, 95% CI = 17 to 60 colonies, P = .01; tumor growth, n = 10 mice per group: mean tumor size at 5 weeks, NLF-CHD5, 0.36 cm(3), 95% CI = 0.17 to 0.44 cm(3), vs NLF-CHD5-AS, 1.65 cm(3), 95% CI = 0.83 to 2.46 cm(3), P = .002; IMR5-CHD5, 0.28 cm(3), 95% CI = 0.18 to 0.38 cm(3), vs IMR5-CHD5-AS, 1.15 cm(3), 95% CI = 0.43 to 1.87 cm(3); P = .01). High CHD5 expression was strongly associated with favorable event-free and overall survival (P < .001), even after correction for MYCN amplification and 1p deletion (P = .027).
Conclusions: CHD5 is the strongest candidate tumor suppressor gene that is deleted from 1p36.31 in neuroblastomas, and inactivation of the second allele may occur by an epigenetic mechanism.