H3K9 methyltransferase G9a negatively regulates UHRF1 transcription during leukemia cell differentiation.

Histone H3K9 methyltransferase (HMTase) G9a-mediated transcriptional repression is a major epigenetic silencing mechanism. UHRF1 (ubiquitin-like with PHD and ring finger domains 1) binds to hemimethylated DNA and plays an essential role in the maintenance of DNA methylation. Here, we provide evidence that UHRF1 is transcriptionally downregulated by H3K9 HMTase G9a. We found that increased expression of G9a along with transcription factor YY1 specifically represses UHRF1 transcription during TPA-mediated leukemia cell differentiation. Using ChIP analysis, we found that UHRF1 was among the transcriptionally silenced genes during leukemia cell differentiation. Using a DNA methylation profiling array, we discovered that the UHRF1 promoter was hypomethylated in samples from leukemia patients, further supporting its overexpression and oncogenic activity. Finally, we showed that G9a regulates UHRF1-mediated H3K23 ubiquitination and proper DNA replication maintenance. Therefore, we propose that H3K9 HMTase G9a is a specific epigenetic regulator of UHRF1.

Differential gene expression analysis in k562 human leukemia cell line treated with benzene.

Even though exposure to benzene has been linked to a variety of cancers including leukemia, the detailed molecular mechanisms relevant to benzene-induced carcinogenesis remain to be clearly elucidated. In this study, we evaluated the effects of benzene on differential gene expression in a leukemia cell line. The K562 leukemia cell line used in this study was cultured for 3 h with 10 mM benzene and RNA was extracted. To analyze the gene expression profiles, a 41,000 human whole genome chip was employed for cDNA microarray analysis. We initially identified 6,562 genes whose expression was altered by benzene treatment. Among these, 3,395 genes were upregulated and 3,167 genes were downregulated by more than 2-fold, respectively. The results of functional classification showed that the identified genes were involved in biological pathways including transcription, cell proliferation, the cell cycle, and apoptosis. These gene expression profiles should provide us with further insights into the molecular mechanisms underlying benzene-induced carcinogenesis, including leukemia.

Transcriptional regulation of 1-cys peroxiredoxin by the proto-oncogene protein DEK.

The nuclear phosphoprotein DEK is abundantly present in cells and is implicated in diseases including leukemia and autoimmune disorders. DEK has three highly acidic amino acid domains and inhibits histone acetyltransferase activity by binding directly to histones. In a previous study, differentially regulated proteins under DEK knockdown conditions, including the up-regulated protein 1-cys peroxiredoxin (1-cys Prx), were identified by proteome analysis. Here, an in vivo reporter assay with short hairpin RNA-mediated DEK knockdown revealed that DEK negatively regulated 1-cys Prx transcription, and that the NF-κB subunit p65 had a synergistic effect on this DEK-mediated repression. Both proteins are recruited to the 1-cys Prx promoter region and regulate its transcription. Our study demonstrates that DEK modulates the transcriptional regulation of the target gene through protein interaction with other regulatory proteins.