Hypermethylation of the imprinted NNAT locus occurs frequently in pediatric acute leukemia

Abstract

Recent studies have demonstrated imprinting of the human neuronatin (NNAT) gene. NNAT maps to 20q11.2-q12, a region exhibiting loss of heterozygosity in acute myeloid leukemia and myelodysplastic/myeloproliferative disease. To investigate possible epigenetic dysregulation of genes in this region relevant to leukemogenesis, we analyzed methylation of the NNAT gene in normal tissues and in leukemias. We found a differential methylation pattern, typical of imprinted genes, at sites in the CpG island containing NNAT exon 1 in normal pituitary, peripheral blood cells and bone marrow-derived CD34-positive hematopoietic progenitor cells. Substantial or complete loss of the unmethylated NNAT allele was observed in leukemia cell lines and in 20 of 29 (69%) acute myeloid or lymphoid leukemia samples. While most highly expressed in brain, NNAT mRNA was also detected in normal hematopoietic progenitor cells and in leukemia cells exhibiting the normal methylation pattern, although not in hypermethylated leukemia cells. Demethylation by treatment of hypermethylated leukemia cells with 5-aza-2'-deoxycytidine resulted in reactivation of NNAT expression, concomitant with a reversion to the normal methylation pattern. The data demonstrate that hypermethylation of the NNAT locus is a frequent event in both myeloid and lymphoid acute leukemias of childhood. Aberrant hypermethylation of the NNAT locus suggests that the dysregulation of genes at 20q11.2-q12 in leukemia may be the result of epigenetic as well as genetic events.

Loss of neuronatin expression is associated with promoter hypermethylation in pituitary adenoma

“…Indeed, and in this context, decreased Nnat expression was identified in a screening study of rat cells in the progression from immortalization to transformation (Yoshioka et al 2000). Although this study did not report the functional significance of Nnat loss in this transition, other studies of different tumour types have shown that NNAT may exhibit either a tumour suppressing or in some cases a tumour promoting role (Takeuchi et al 1995, Asimakopoulos et al 1996, Usui et al 1997, Hu et al 2002, Kuerbitz et al 2002, Wood et al 2002, Becker et al 2005, Zhong et al 2006.…”

“…Genome-wide identification of genes silenced through epigenetic mechanisms, and in particular through CpG island methylation, has been investigated in multiple different tumour types (Kuerbitz et al 2002, Liang et al 2002, Suzuki et al 2002, Foltz et al 2006, Ibanez de Caceres et al 2006. These studies frequently employ pharmacological strategies to 'unmask' silent genes through inhibition of the DNA maintenance methylase enzyme, DNMT1.…”

Pharmacologic inhibition of epigenetic modifications, coupled with gene expression profiling, reveals novel targets of aberrant DNA methylation and histone deacetylation in lung cancer

“…Indeed, ectopic expression of NNAT stimulated 3T3-L1 adipocytes to differentiate into mature adipocytes by increasing intracellular calcium levels and enhancing cAMP-responsive element-binding protein (CREB) phosphorylation (Suh et al, 2005). NNAT was found to undergo LOI in 69% of leukemia samples in one study, although its effects on cell growth were not analysed (Kuerbitz et al, 2002). LOI of NNAT in 20% of the adjacent normal tissues we examined suggests that this may represent a preneoplastic alteration, as has been observed for other imprinted genes like IGF2 in colon cancer (Cui et al, 2003).…”

Methylation Silencing of Transforming Growth Factor-β Receptor Type II in Rat Prostate Cancers

“…Gas6 and Ocm have oncogenic functions (41,42). Nnat is known as an imprinting gene and its aberrant hypermethylation occurs frequently in pediatric acute leukemia (43). There is a possibility that silencing of these genes is related to the development and progression of rat prostate carcinoma.…”