RARβ2 is a candidate tumor suppressor gene in myelofibrosis with myeloid metaplasia

Abstract

Myelofibrosis with myeloid metaplasia (MMM) is a clonal stem-cell disorder that leads to ineffective hematopoiesis, bone marrow fibrosis, and extramedullary hematopoiesis. The molecular mechanisms underlying the development of this myeloproliferative syndrome are currently unknown. In order to identify tumor suppressor genes that may be involved in the disease process, we performed an analysis for loss of heterozygosity (LOH) in CD34 þ cells from 29 patients with MMM. We observed a frequency of allelic loss on chromosomal arm 3p in 24% of cases. Detailed mapping of 3p revealed a distinct region of deletion at 3p24. Among the genes known to map within this region is the retinoic acid receptor-b (RARb2) gene. To determine whether RARb2 gene activity is diminished in this disease, we analysed its expression in CD34 þ cells from 17 patients with MMM using quantitative PCR. Our results indicate that expression of RARb2 is significantly decreased in 100% of patient samples compared to that in CD34 þ cells from 10 normal individuals. Since allelic loss at 3p24 occurs in o25% of patients, we investigated the contribution of epigenetic modifications to RARb2 inactivity. Using methylationspecific PCR, we found hypermethylation of RARb2 in 16 of 18 patients (89%), while the methylated form of the gene was absent in CD34 þ cells from nine normal individuals. Our results suggest that RARb2 acts as a tumor suppressor gene in MMM and that epigenetic changes are the most significant determinants of RARb2 gene activity in these patients.

Effects of Chromatin-Modifying Agents on CD34+ Cells from Patients with Idiopathic Myelofibrosis

“…A substantial amount of evidence has been generated which indicates that these somatic mutations play a significant role in the pathobiology of the MPDs. In addition to these genetic mechanisms, a growing number of investigators have provided data which indicate that epigenetic mechanisms silence genes that impede cellular proliferation or movement in IM (19)(20)(21). Rossi et al (39) have reported aberrant methylation of a variety of negative regulators of JAK2 activation/phosphorylation, including SHP-1, SOCS-1, and SOCS-3, which have been observed in patients with both JAK2V617F-positive or JAK2V617F-negative IM.…”

“…We have previously reported that CXCR4 expression was down-regulated in the CD34 + cells of patients with IM; this abnormality was thought to contribute to the constitutive mobilization of hematopoietic stem and progenitor cells that occurs in patients with IM (14,18). The malignant phenotype in IM likely results from a combination of genetic abnormalities and epigenetic modifications leading to the dysregulation of critical genes that contribute to cell proliferation, differentiation, and cell death (2)(3)(4)(5)(6)(7)(19)(20)(21). Methylation of cytosine residues in the promoter region as well transcriptional inhibitory complexes including histone deacetylases (HDAC) play a role in the transcriptional silencing of genes in a variety of human cancers (22)(23)(24).…”

Methylation of the suppressor of cytokine signaling 3 gene (SOCS3) in myeloproliferative disorders

“…CpG island methylation has been infrequently assessed in patients with a MPD. Jones et al 44 detected methylation of the retinoic acid receptor-β gene (RARB) in 89% (16/18) of IMF patients and also showed reduced expression in CD34 + cells. However, Jost et al 45 failed to detect methylation of RARB in any of 23 MF patients.…”

Sequential treatment of CD34+ cells from patients with primary myelofibrosis with chromatin-modifying agents eliminate JAK2V617F-positive NOD/SCID marrow repopulating cells

“…7 Epigenetic modifications leading to the dysregulation of critical genes that contribute to cell proliferation, differentiation, cell death, and trafficking have also been thought to play a role in the origins of PMF. [8][9] Mutations in TET2, for instance, might contribute to the origins of PMF by altering chromatin structure. TET1 affects the conversion of 5-methylcytosine to 5-hydroxymethylcytosine and therefore influences epigenetic regulation of transcription.…”