Myelodysplastic syndrome (MDS) with erythroid aplasia is a very rare disorder that has not been clearly defined. We experienced a case of pure red cell aplasia (PRCA), which evolved to MDS with erythroid aplasia. A 59-year-old male with transfusion-dependent PRCA was referred to our hospital for an evaluation of newly developed thrombocytopenia. Two years ago, PRCA was diagnosed by the laboratory findings and a bone marrow examination, which showed no evidence of any myelodysplastic features and thymoma. Upon admission, the bone marrow findings showed marked hypercellularity. with numerous dysplastic features in the three lineages including erythroid hypoplasia. These findings were compatible with a diagnosis of MDS with red cell aplasia. It is very interesting that the PRCA evolved to MDS with red cell aplasia, which strongly suggests an autoimmune mechanism for the development of MDS.
Erythroid Progenitor Cells/*pathology ; Humans ; Male ; Middle Aged ; Myelodysplastic Syndromes/*complications/pathology ; Red-Cell Aplasia, Pure/*complications/pathology

The chronic myelogenous leukemic K562 cell line carrying Bcr-Abl tyrosine kinase is considered as pluripotent hematopoietic progenitor cells expressing markers for erythroid, granulocytic, monocytic, and megakaryocytic lineages. Here we investigated the signaling modulations required for induction of erythroid differentiation of K562 cells. When the K562 cells were treated with herbimycin A (an inhibitor of protein tyrosine kinase), ras antisense oligonucleotide, and PD98059 (a specific inhibitor of MEK), inhibition of ERK/MAPK activity and cell growth, and induction of erythroid differentiation were observed. The ras mutant, pZIPRas61leu-transfected cells, K562-Ras61leu, have shown a markedly decreased cell proliferation rate with approximately 2-fold doubling time, compared with the parental K562 cells, and about 60% of these cells have shown the phenotype of erythroid differentiation. In addition, herbimycin A inhibited the growth rate and increased the erythroid differentiation, but did not affect the elevated activity of ERK/MAPK in the K562-Ras61leu cells. On the other hand, effects of PD98059 on the growth and differentiation of K562-Ras61leu cells were biphasic. At low concentration of PD98059, which inhibited the elevated activity of ERK/MAPK to the level of parental cells, the growth rate increased and the erythroid differentiation decreased slightly, and at high concentration of PD98059, which inhibited the elevated activity of ERK/MAPK below that of the parental cells, the growth rate turned down and the erythroid differentiation was restored to the untreated control level. Taken together, these results suggest that an appropriate activity of ERK/MAPK is required to maintain the rapid growth and transformed phenotype of K562 cells.
Androstadienes/pharmacology ; Ca(2+)-Calmodulin Dependent Protein Kinase ; Cell Differentiation/drug effects ; Enzyme Inhibitors/pharmacology ; Erythroid Progenitor Cells/physiology* ; Erythroid Progenitor Cells/cytology ; Erythropoiesis* ; Flavones/pharmacology ; Human ; K562 Cells ; Leukemia, Myeloid/pathology ; Oligonucleotides, Antisense/pharmacology ; Quinones/pharmacology ; ras Proteins/metabolism*

BACKGROUND AND OBJECTIVELeukemic microenvironment has a major role in the progression of leukemia. Leukemic cells can induce reversible changes in microenvironmental components, especially the stromal function which results in improved growth conditions for maintaining the malignant leukemic cells. This study aimed to investigate the survival advantage of leukemic cells over normal hematopoietic cells in stromal microenvironment in long term.

METHODSThe mice were injected intraperitoneally with N-N' ethylnitrosourea (ENU) to induce leukemia; the mice received injection of normal saline were used as control. At 180 days after ENU induction, the mice were killed and the bone marrows were cultured for 19 days. Colony-forming assays were used to analyze the formation of various cell colonies. The expression of Sca-1, CD146, VEGFR2, CD95, pStat3, pStat5, and Bcl-xL in marrow cells were detected by flow cytometry.

RESULTSLong-term leukemic bone marrow culture showed abnormal elongated stromal fibroblasts with almost absence of normal hematopoietic cells. Adherent cell colonies were increased, but CFU-F and other hematopoietic cell colonies were significantly decreased in leukemia group (P<0.001). Primitive progenitor-specific Sca-1 receptor expression was decreased with subsequent increased expression of CD146 and VEGFR-2 in leukemic bone marrow cells. Decreased Fas antigen expression with increased intracellular pStat3, pStat5 and Bcl-xL proteins were observed in leukemic bone marrow cells.

CONCLUSIONSStromal microenvironment shows altered morphology and decreased maturation in leukemia. Effective progenitor cells are decreased in leukemia with increased leukemia-specific cell population. Leukemic microenvironment plays a role in promoting and maintaining the leukemic cell proliferation and survivability in long term.

Animals ; Antigens, Ly ; metabolism ; Bone Marrow Cells ; metabolism ; pathology ; CD146 Antigen ; metabolism ; Cell Count ; Cells, Cultured ; Colony-Forming Units Assay ; Erythroid Precursor Cells ; metabolism ; pathology ; Ethylnitrosourea ; Female ; Fibroblasts ; metabolism ; pathology ; Granulocyte-Macrophage Progenitor Cells ; metabolism ; pathology ; Granulocytes ; metabolism ; pathology ; Hematopoiesis ; Hematopoietic Stem Cells ; metabolism ; pathology ; Leukemia ; chemically induced ; metabolism ; pathology ; Male ; Membrane Proteins ; metabolism ; Mice ; Myeloid Progenitor Cells ; metabolism ; pathology ; Phenotype ; STAT3 Transcription Factor ; metabolism ; STAT5 Transcription Factor ; metabolism ; Tumor Microenvironment ; physiology ; Vascular Endothelial Growth Factor Receptor-2 ; metabolism ; bcl-X Protein ; metabolism ; fas Receptor ; metabolism