Gorica Nikoloski

Somatic mutations of the histone methyltransferase gene EZH2 in myelodysplastic syndromes

In myelodysplastic syndromes (MDS), deletions of chromosome 7 or 7q are common and correlate with a poor prognosis. The relevant genes on chromosome 7 are unknown. We report here that EZH2, located at 7q36.1, is frequently targeted in MDS. Analysis of EZH2 deletions, missense and frameshift mutations strongly suggests that EZH2 is a tumor suppressor. As EZH2 functions as a histone methyltransferase, abnormal histone modification may contribute to epigenetic deregulation in MDS.

ID1 and ID2 are retinoic acid responsive genes and induce a G0/G1 accumulation in acute promyelocytic leukemia cells.

Acute promyelocytic leukemia (APL) is uniquely sensitive to treatment with all-trans retinoic acid (ATRA), which results in the expression of genes that induce the terminal granulocytic differentiation of the leukemic blasts. Here we report the identification of two ATRA responsive genes in APL cells, ID1 and ID2. These proteins act as antagonists of basic helix–loop–helix (bHLH) transcription factors. ATRA induced a rapid increase in ID1 and ID2, both in the APL cell line NB4 as well as in primary patient cells. In addition, a strong downregulation of E2A was observed. E2A acts as a general heterodimerization partner for many bHLH proteins that are involved in differentiation control in various tissues. The simultaneous upregulation of ID1 and ID2, and the downregulation of E2A suggest a role for bHLH proteins in the induction of differentiation of APL cells following ATRA treatment. To test the relevance of this upregulation, ID1 and ID2 were overexpressed in NB4 cells. Overexpression inhibited proliferation and induced a G0/G1 accumulation. These results indicate that ID1 and ID2 are important retinoic acid responsive genes in APL, and suggest that the inhibition of specific bHLH transcription factor complexes may play a role in the therapeutic effect of ATRA in APL.

Mutations in epigenetic regulators in myelodysplastic syndromes

Until recently, the genetic aberrations that are causally linked to the pathogenesis of myelodysplastic syndromes (MDS) and myeloproliferative neoplasms were largely unknown. Using novel technologies like high-resolution SNP-array analysis and next generation sequencing, various genes have now been identified that are recurrently mutated. Strikingly, several of the newly identified genes (ASXL1, DNMT3A, EZH2, IDH1 and IDH2, and TET2) are involved in the epigenetic regulation of gene expression. Aberrant epigenetic modifications have been described in many types of cancer, including myeloid malignancies. It has been proposed that repression of genes that are crucial for the cessation of the cell cycle and induction of differentiation might contribute to the malignant transformation of normal hematopoietic cells. Several therapies that aim to re-express silenced genes are currently being tested in MDS, like histone deacetylase inhibitors and hypomethylating agents. It will be interesting to assess whether patients carrying mutations in epigenetic regulators respond differently to these novel forms of epigenetic therapies.

MPN patients harbor recurrent truncating mutations in transcription factor NF-E2

Mutations in the transcription factor NF-E2 in patients with myeloproliferative neoplasms result in a truncated protein that enhances the function of wild-type NF-E2 and causes erythrocytosis and throbocytosis in a mouse model.

Genetic defects in PRC2 components other than EZH2 are not common in myeloid malignancies

To the editor: Several genetic alterations affecting loci encoding epigenetic regulators have been discovered in myeloid malignancies in the last few years. Previously, we and others identified novel mutations in the histone methyltransferase gene EZH2 .[1][1][][2]–[3][3] EZH2 encodes the

The transcription factor nuclear factor Y regulates the proliferation of myeloid progenitor cells

The transcription factor nuclear factor Y (NF-Y) consists of three subunits; NF-YA, -B and -C, and this complex binds DNA and the basal transcription machinery through binding of TBP.[1][1] NF-Y targets include cell cycle related genes and hematopoietic (stem) cell genes such as cd34 and hoxb4 .[2][