J Anastasi

Myelodysplasia and acute leukemia following high-dose chemotherapy and autologous bone marrow or peripheral blood stem cell transplantation.

Therapy-related myelodysplastic syndrome (t-MDS)/ acute myeloid leukemia (t-AML) has been reported after autologous bone marrow or peripheral blood stem cell transplantation (ABMT/PBSCT) for various malignancies. We retrospectively reviewed all adult ABMT/PBSCT cases performed at the University of Chicago Medical Center from 1985 to 1997 in order to determine the incidence of therapy-related leukemia. Among 649 patients, seven (1.1%) developed therapy-related acute lymphoblastic leukemia (one patient) or t-MDS/t-AML (six patients). Of these seven, primary malignancies included one case of breast carcinoma, five cases of Hodgkin’s disease (HD) and one case of non-Hodgkin’s lymphoma (NHL). Disease-specific incidences for therapy-related leukemia occurring after ABMT/PBSCT were one in 354 (0.3%) for breast carcinoma, five in 79 (6.3%) for HD and one in 103 (1%) for NHL. The median latency periods for the development of therapy-related leukemia from the time of initial diagnosis and of ABMT/PBSCT were 5.5 and 1.5 years, respectively, for the combined HD and NHL group of patients and 4.4 and 2.8 years, respectively, for the one breast carcinoma patient. All seven patients had clonal cytogenetic abnormalities, and five had recurring abnormalities typical of myeloid disorders. Given the similar latency period observed in patients treated with conventional chemotherapy alone, our findings support the hypothesis that therapy-related leukemia after ABMT/PBSCT likely results from pre-transplant therapy. Early detection of therapy-related leukemia is therefore critical to exclude these patients from undergoing ABMT/PBSCT.

DNMT3B7, a truncated DNMT3B isoform expressed in human tumors, disrupts embryonic development and accelerates lymphomagenesis

Epigenetic changes are among the most common alterations observed in cancer cells, yet the mechanism by which cancer cells acquire and maintain abnormal DNA methylation patterns is not understood. Cancer cells have an altered distribution of DNA methylation and express aberrant DNA methyltransferase 3B transcripts, which encode truncated proteins, some of which lack the COOH-terminal catalytic domain. To test if a truncated DNMT3B isoform disrupts DNA methylation in vivo, we constructed two lines of transgenic mice expressing DNMT3B7, a truncated DNMT3B isoform commonly found in cancer cells. DNMT3B7 transgenic mice exhibit altered embryonic development, including lymphopenia, craniofacial abnormalities, and cardiac defects, similar to Dnmt3b-deficient animals, but rarely develop cancer. However, when DNMT3B7 transgenic mice are bred with Emicro-Myc transgenic mice, which model aggressive B-cell lymphoma, DNMT3B7 expression increases the frequency of mediastinal lymphomas in Emicro-Myc animals. Emicro-Myc/DNMT3B7 mediastinal lymphomas have more chromosomal rearrangements, increased global DNA methylation levels, and more locus-specific perturbations in DNA methylation patterns compared with Emicro-Myc lymphomas. These data represent the first in vivo modeling of cancer-associated DNA methylation changes and suggest that truncated DNMT3B isoforms contribute to the redistribution of DNA methylation characterizing virtually every human tumor.

Hemoglobin S-mediated membrane oxidant injury: Protection from malaria and pathology in sickle cell disease

It is suggested here that a Hemoglobin S (HbS)-mediated membrane oxidant injury is responsible for both the protection from malaria infection in the heterozygous sickle cell state, and for a critical pathologic process in homozygous sickle cell disease. This suggestion is arrived at by applying to the HbS condition the oxidant stress model for malaria resistance. Such a model had been developed to explain the protection from malaria in thalassemia and in glucose-6-phosphate dehydrogenase (G6PD) deficiency (9).

Genome-wide profiling reveals epigenetic inactivation of the PU.1 pathway by histone H3 lysine 27 trimethylation in cytogenetically normal myelodysplastic syndrome

Cytogenetically normal myelodysplastic syndrome (CN-MDS) can pose diagnostic challenges and its pathogenetic mechanism remains elusive. By focusing on cytogenetically normal refractory cytopenia with multilineage dysplasia (CN-RCMD), a subtype of MDS, our genome-wide profiling showed ∼4600 annotated gene promoters with increased Histone H3 lysine 27 trimethylation (H3K27me3) in CN-RCMD, when compared with normal controls. Computational analysis revealed a statistically significant enrichment of the PU.1-binding DNA motif (PU-box) in the regions with increased H3K27me3. An inverse relationship between the levels of H3K27me3 and the levels of PU.1 binding and its downstream myeloid gene expressions was observed. Whole-exome sequencing analysis and Sanger sequencing analysis revealed some recurrent mutations, but no mutations in the PU.1 regulatory regions or in the EZH1/2, H3K27 methytransferase encoding genes. Using an MDS-derived erythroid/myeloid line and primary MDS bone marrow cells, we demonstrated that H3K27me3 inhibitors can increase the expression of PU.1 and its downstream genes and also promote cell differentiation via reducing H3K27me3 at the PU.1 gene locus. Finally, ectopic expression of PU.1 significantly inhibited proliferation of the MDS-derived cell line. Based on these data, we propose a hypothetical model of epigenetic inactivation of the PU.1 pathway due to increased H3K27me3 in some cases of CN-RCMD.

The Clathrin-Binding Domain of CALM-AF10 Alters the Phenotype of Myeloid Neoplasms in Mice

The PICALM (CALM) gene, whose product is involved in clathrin-mediated endocytosis, has been identified in two recurring chromosomal translocations, involving either MLL or MLLT10 (AF10). We developed a mouse model of CALM-AF10+ leukemia to examine the hypothesis that disruption of endocytosis contributes to leukemogenesis. Exclusion of the C-terminal portion of CALM from the fusion protein, which is required for optimal binding to clathrin, resulted in the development of a myeloproliferative disease, whereas inclusion of this domain led to the development of acute myeloid leukemia and changes in gene expression of several cancer-related genes, notably Pim1 and Crebbp. Nonetheless, the development of leukemia could not be attributed directly to interference with endocytosis or consequential changes in proliferation and signaling. In leukemia cells, full-length CALM-AF10 localized to the nucleus with no consistent effect on growth factor endocyctosis, and suppressed histone H3 lysine 79 methylation regardless of the presence of clathrin. Using fluorescence resonance energy transfer analysis, we show that CALM-AF10 has a propensity to homo-oligomerize, raising the possibility that the function of endocytic proteins involved in chimeric fusions may be to provide dimerization properties, a recognized mechanism for unleashing oncogenic properties of chimeric transcription factors, rather than disrupting the internalization of growth factor receptors.