Conventional karyotype showed no signs of del(5)(q22q35) MDS, however bone marrow next-generation sequencing (NGS) demonstrated the accrual of a nonsense mutation (c.211del pL71*) in exon 3 of EZH2.
Higher PLA2G4A expression is associated with mutations in NRAS (P < .001), RUNX1 (P = .012), ASXL1 (P = .007), and EZH2 (P = .038), all of which are known to contribute to MDS development.
Newer genomic technologies, such as single-nucleotide polymorphism array and next-generation sequencing, revealed the heterozygous deletions resulting in haploinsufficient gene expression (e.g., CSNK1A1, DDX41 on chromosome 5, CUX1, LUC7L2, EZH2 on chromosome 7) involved in the pathogenesis of MDS.
In myelodysplastic syndromes (MDS), loss of function of EZH2 is known to contribute to pathogenesis, however the pattern of EZH2 mRNA and protein expression in MDS has not been extensively characterized.
To further characterize molecular alterations of EZH2, and their potential prognostic impact in MDS, we assessed EZH2 RNA expression in primary bone marrow CD34+ cells from 78 patients.
As an example, missplicing of the enhancer of zeste homolog 2 histone methyltransferase premRNA in response to hot spot mutation of the splicing factor SRSF2 was found to participate to the pathogenesis of myelodysplastic syndrome.
Patients with U2AF1, SRSF2, and EZH2 mutations more commonly had high-risk than low-risk subtypes, while SF3B1 mutations were frequently confirmed in MDS subtypes with increased ring sideroblasts.
Recent studies are shedding light on the molecular basis of myelodysplasia and how mutations and epimutations can induce and promote this neoplastic process through aberrant transcription factor function (RUNX1, ETV6, TP53), kinase signalling (FLT3, NRAS, KIT, CBL) and epigenetic deregulation (TET2, IDH1/2, DNMT3A, EZH2, ASXL1, SF3B1, U2AF1, SRSF2, ZRSR2).
These findings provide a comprehensive picture of how Ezh2 loss collaborates with RUNX1 mutants in the pathogenesis of MDS in both cell autonomous and non-autonomous manners.
Let-7b levels were significantly higher, and KDM2B and EZH2 expression was lower in primary CD34+ MDS marrow cells (n = 44) than in healthy controls (n = 21; p<0.013, and p<0.0001, respectively).
Another significant advance in MDS pathogenesis research is the recent identification of mutations in genes encoding transcription factors implicated in hematopoiesis and proteins involved in splicing (SF3B1), methylation (DNMT3A), regulation of methylation (TET2 and IDH), DNA conformation (EZH2 and ASXL1) and differentiation (N- and K-RAS).
Over the past few years, large-scale genomic studies of patients with myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML) have unveiled recurrent somatic mutations in genes involved in epigenetic regulation (DNMT3A, IDH1/2, TET2, ASXL1, EZH2 and MLL) and the spliceosomal machinery (SF3B1, U2AF1, SRSF2, ZRSR2, SF3A1, PRPF40B, U2AF2, and SF1).
Aberrant differentiation in MDS can often be traced to abnormal DNA methylation (both gains and losses of DNA methylation genome wide and at specific loci) as well as mutations in genes that regulate epigenetic programs (TET2 and DNMT3a, both involved in DNA methylation control; EZH2 and ASXL1, both involved in histone methylation control).
These data suggest ASXL1 mutations might results in dominance of the mutant clone in Chinese with MDS whereas EZH2 mutations might predict an increased risk of transformation to AML.
Furthermore, concurrent depletion of Ezh2 and Tet2 established more advanced myelodysplasia and markedly accelerated the development of myelodysplastic disorders including both MDS and MDS/MPN.
A wave of novel mutations have recently been reported in MDS and other myeloid disorders, several of which regulate endogenous methylation networks within cells (including TET2, DNMT3A, IDH and EZH2).
Overexpression of the EZH2, RING1 and BMI1 genes is common in myelodysplastic syndromes: relation to adverse epigenetic alteration and poor prognostic scoring.