Erythropoiesis in the Rps19 disrupted mouse: Analysis of erythropoietin response and biochemical markers for Diamond-Blackfan anemia.

The human ribosomal protein S19 gene (RPS19) is mutated in approximately 20% of patients with Diamond-Blackfan anemia (DBA), a congenital disease with a specific defect in erythropoiesis. The clinical expression of DBA is highly variable, and subclinical phenotypes may be revealed by elevated erythrocyte deaminase (eADA) activity only. In mice, complete loss of Rps19 results in early embryonic lethality whereas Rps19+/- mice are viable and without major abnormalities including the hematopoietic system. We have performed a detailed analysis of the Rps19+/- mice. We estimated the Rps19 levels in hematopoietic tissues and we analyzed erythrocyte deaminase activity and globin isoforms which are used as markers for DBA. The effect of a disrupted Rps19 allele on a different genetic background was investigated as well as the response to erythropoietin (EPO). From our results, we argue that the loss of one Rps19 allele in mice is fully compensated for at the transcriptional level with preservation of erythropoiesis.

Function for p300 and not CBP in the apoptotic response to DNA damage.

The cellular response to ionizing radiation (IR) includes the induction of apoptosis. The p300/CBP proteins possess histone acetyltransferase activity and function as transcriptional coactivators of p53. We have prepared cells deficient in p300 or CBP to define the roles of these proteins in the cellular response to DNA damage. The present results demonstrate that p300, but not CBP, contributes to IR sensitivity of cells. The results also demonstrate that IR-induced apoptosis is impaired in the p300-, but not CBP-, deficient cells. These findings indicate that p300 functions in the apoptotic response to DNA damage.

Role for caspase-mediated cleavage of Rad51 in induction of apoptosis by DNA damage.

We report here that the Rad51 recombinase is cleaved in mammalian cells during the induction of apoptosis by ionizing radiation (IR) exposure. The results demonstrate that IR induces Rad51 cleavage by a caspase-dependent mechanism. Further support for involvement of caspases is provided by the finding that IR-induced proteolysis of Rad51 is inhibited by Ac-DEVD-CHO. In vitro studies show that Rad51 is cleaved by caspase 3 at a DVLD/N site. Stable expression of a Rad51 mutant in which the aspartic acid residues were mutated to alanines (AVLA/N) confirmed that the DVLD/N site is responsible for the cleavage of Rad51 in IR-induced apoptosis. The functional significance of Rad51 proteolysis is supported by the finding that, unlike intact Rad51, the N- and C-terminal cleavage products fail to exhibit recombinase activity. In cells, overexpression of the Rad51(D-A) mutant had no effect on activation of caspase 3 but did abrogate in part the apoptotic response to IR exposure. We conclude that proteolytic inactivation of Rad51 by a caspase-mediated mechanism contributes to the cell death response induced by DNA damage.

Role for p300 in stabilization of p53 in the response to DNA damage.

The nuclear p300/CBP proteins function as coactivators of gene transcription. Here, using cells deficient in p300 or CBP, we show that p300, and not CBP, is essential for ionizing radiation-induced accumulation of the p53 tumor suppressor and thereby p53-mediated growth arrest. The results demonstrate that deficiency of p300 results in increased degradation of p53. Our findings suggest that p300 contributes to the stabilization and transactivation function of p53 in the cellular response to DNA damage.

Activation of protein kinase C delta by the c-Abl tyrosine kinase in response to ionizing radiation.

The c-Abl protein tyrosine kinase is activated by ionizing radiation (IR) and certain other DNA-damaging agents. The present studies demonstrate that c-Abl associates constitutively with protein kinase C delta (PKCdelta). The results show that the SH3 domain of c-Abl interacts directly with PKCdelta. c-Abl phosphorylates and activates PKCdelta in vitro. We also show that IR treatment of cells is associated with c-Abl-dependent phosphorylation of PKCdelta and translocation of PKCdelta to the nucleus. These findings support a functional interaction between c-Abl and PKCdelta in the cellular response to genotoxic stress.

Regulation of Rad51 function by c-Abl in response to DNA damage.

The Rad51 protein, a homolog of bacterial RecA, functions in DNA double-strand break repair and genetic recombination. Whereas Rad51 catalyzes ATP-dependent pairing and strand exchange between homologous DNA molecules, regulation of this function is unknown. The c-Abl tyrosine kinase is activated by ionizing radiation and certain other DNA-damaging agents. Here we demonstrate that c-Abl interacts constitutively with Rad51. We show that c-Abl phosphorylates Rad51 on Tyr-54 in vitro. The results also show that treatment of cells with ionizing radiation induces c-Abl-dependent phosphorylation of Rad51. Phosphorylation of Rad51 by c-Abl inhibits the binding of Rad51 to DNA and the function of Rad51 in ATP-dependent DNA strand exchange reactions. These findings represent the first demonstration that Rad51 is regulated by phosphorylation and support a functional role for c-Abl in regulating Rad51-dependent recombination in the response to DNA damage.

Pro-apoptotic effect of the c-Abl tyrosine kinase in the cellular response to 1-beta-D-arabinofuranosylcytosine.

Treatment of cells with the antimetabolite 1-beta-D-arabinofuranosylcytosine (ara-C) and other genotoxic agents is associated with activation of the c-Abl protein tyrosine kinase. The functional role of c-Abl in the response to DNA damage, however, remains unclear. The present studies demonstrate that cells expressing a dominant negative, kinase-inactive c-Abl (K-R) are resistant to killing by ara-C. The expression of c-Abl (K-R) blocked ara-C-induced apoptosis by a mechanism that is at least in part independent of the p53 tumor suppressor. Cells null for c-Abl also exhibited resistance to induction of apoptosis. These findings provide support for a pro-apoptotic function of c-Abl in the response to certain genotoxic drugs.

Inhibition of phosphatidylinositol 3-kinase by c-Abl in the genotoxic stress response.

Activation of phosphatidylinositol (PI) 3-kinase by growth factors results in phosphorylation of phosphatidylinositol lipids at the D3 position. Although PI 3-kinase is essential to cell survival, little is known about mechanisms that negatively regulate this activity. Here we show that the c-Abl tyrosine kinase interacts directly with the p85 subunit of PI 3-kinase. Activation of c-Abl by ionizing radiation exposure is associated with c-Abl-dependent phosphorylation of PI 3-kinase. We also show that phosphorylation of p85 by c-Abl inhibits PI 3-kinase activity in vitro and in irradiated cells. These findings indicate that c-Abl negatively regulates PI 3-kinase in the stress response to DNA damage.

Role for E2F in DNA damage-induced entry of cells into S phase.

Mammalian cells respond to ionizing radiation (IR) with transient cell cycle arrest and induction of apoptosis. Here we show that IR increases the expression of the E2F-1 transcription factor and the entry of cells into S phase. E2F-1 transactivation function is inhibited by cyclin A-kinase to ensure orderly progression through S phase. However, in contrast to proliferating cells, IR treatment results in down-regulation of cyclin A-kinase. Expression of a dominant negative form of the E2F heterodimeric partner DP-1 confirmed the involvement of E2F in IR-induced S-phase entry. These findings also support opposing signals involving the induction of E2F and the down-regulation of cyclin A-kinase in the IR response.

[Early establishment of bone marrow hypoplasia by antileukemic chemotherapy with concurrent rhG-CSF in a case of acute myelogenous leukemia complicated with intestinal perforation].

We report a case of 53-year-old man with acute myelogenous leukemia (M2) showing a karyotype of t(7;11) (p15;p15), del(10) (q11;q12), who was complicated with perforation of a duodenal ulcer during the antileukemic chemotherapy using behenoyl ara-C, daunorubicin, 6-mercaptopurine and prednisolone. As his bone marrow still showed high cell density and leukemic proliferation at the time of intestinal perforation, the therapeutic regimen was changed to a combination of behenoyl are-C and mitoxantrone, and daily rhG-CSF was concurrently administered for the purpose of early establishment of bone marrow hypoplasia. On the 8th day after the therapeutic regimen had been changed, his bone marrow became nearly aplastic, and complete remission was obtained on the 24th day. This case may indicate that the concurrent administration of cell-cycle specific antileukemic drugs and rhG-CSF is available for AML patients with emergent need of leukemic cell reduction.

A combination chemotherapy with low doses of cytarabine and etoposide for high risk myelodysplastic syndromes and their leukemic stage. A pilot study.

BACKGROUND: Even now, no definitely effective therapy is inducted to high risk myelodysplastic syndromes (MDS) and their leukemic stage (MDS-AML) except bone marrow transplantation. METHODS: Ten patients with high risk MDS and 6 with MDS-AML were treated with daily low doses of cytarabine (10 mg/m2/12h, infused over 2h) etoposide (50 mg/m2/day, infused over 2h). RESULTS: Fourteen of these patients were finally evaluated among whom 6 with high risk MDS and 3 with MDS-AML (64.3%) had complete remission, and 2 with high risk MDS (14.3%) achieved partial remission after this chemotherapy for 9 to 21 days. Three of 11 responders were resistant to the prior chemotherapies with single and low dose cytotoxic agents including cytarabine, etoposide, or aclarubicin. Although all of the patients who could be assessed developed severe marrow hypoplasia after chemotherapy, the nonhematologic side effects were mild enough to be tolerated. CONCLUSIONS: This combination chemotherapy must be effective and useful in high risk MDS and MDS-AML not only without prior chemotherapy but in cases which have been resistant to single and low dose oncostatic agent.

[Interleukin-3 therapy in patients with aplastic anemia refractory to prior therapies].

A therapeutic trial of interleukin-3 (IL-3) was carried out in four patients with aplastic anemia refractory to the prior therapies. Daily subcutaneous doses of 2.5, 5.0 or 7.5 micrograms/kg was given for 7 or 14 days. In a patient who had co- and immediate boost-administration of granulocyte colony-stimulating factor (G-CSF) and/or erythropoietin (Epo) and another who had sequential administration of G-CSF and Epo two weeks after IL-3, definite hematological response was obtained during the course after IL-3. In one patient, moderate to severe side effects consisting of facial edema, conjunctival bleeding, chills and fever, were observed after two days' administration of IL-3. Co- or sequential administration of other hemopoietic factor(s) may be essential in IL-3 therapy for aplastic anemia.

[Hematological stability under ubenimex monotherapy in a patient with acute myelogenous leukemia developing marrow karyotypic changes during the course].

We encountered a 71-year-old female with acute myelogenous leukemia (AML, M1), who maintained a steady hematological state for 22 months under ubenimex monotherapy. At the first medical examination in our hospital, the marrow cellularity was approximately 40% containing leukemic myeloblasts of 41.4% in the total nucleated cells, and the marrow cytogenetic study revealed 47, XX, + 8 in 13 of 20 cells analyzed. Nineteen months later, the bone marrow showed definite hypoplasia with leukemic blasts of 39.8% and chromosome finding of 46, XX, ins (10;?) (q11;?) in all cells analyzed. During the course, the patient has been doing well without transfusion of red blood cells or platelets.

[Morphological observation of a process of bone marrow hypoplastic formation in a case of aplastic anemia].

Bone marrow morphological change was consecutively analyzed form the disease onset to the formation of bone marrow aplasia in a patient with post-hepatitic aplastic anemia. In this case, the mean bone marrow cellularity and absolute numbers of erythroids and megakaryocytes were continuously higher than those in normal subjects for 3 weeks after the appearance of peripheral pancytopenia. During this stage, administration of recombinant human granulocyte colony-stimulating factor (G-CSF) improved marrow myeloid hypoplasia and peripheral neutropenia. During the period in which the marrow cellularity transformed from hyperplasia to hypoplasia, the bone marrow showed a mixture of hyper-, normo- and hypocellular portions, and the decrease in the megakaryocytes was the faster than myeloid and erythroid cells. These findings indicate that (1) ineffective hematopoiesis might be present in the early stage of the disease, (2) G-CSF responsive granulocytic precursors remained during the early stage of the disease, and (3) the marrow aplasia progressed in the manner of aplastic nest formation during the period in which the marrow cellularity declined to hypoplasia. We experienced another case of aplastic anemia showing the same progress of bone marrow findings and speculated that this might be one of the ways of the progression of bone marrow hypoplastic formation in aplastic anemia.

[Initiation of hematopoietic recovery by recombinant human granulocyte-macrophage colony-stimulating factor in a case of severe aplastic anemia induced by gold salt].

A 65-year-old female with severe aplastic anemia induced by gold salt, whose hematopoietic recovery was initiated by rhGM-CSF therapy, was reported. The patient has been given a total of 500 mg of gold-sodium thiomalate for treatment of her rheumatoid arthritis. Two months after the final administration of it, she was admitted to our hospital with complaints of palpitation and shortness of breath. The hemogulobin was 5.9 g/dl, the platelet count was 0.5 x 10(4)/microliter, and the leukocyte count was 800/microliters with 19% neutrophils. Her bone marrow showed aplasia, and both of Ham and sugar-water tests were positive. Three times of bolus-methylprednisolone treatment, with or without methenolone acetate, resulted in no definite improvement of peripheral pancytopenia and marrow aplasia. Subsequent subcutaneous rhGM-CSF, 300 micrograms daily for 28 days with oral prednisolone 5 mg and methenolone acetate 40 mg daily, initiated hematopoietic recovery of all three cell lineages in both peripheral blood and bone marrow. The same doses of prednisolone and methenolone acetate were continued after rhGM-CSF administration, and three months later peripheral cytopenia and positive Ham and sugar-water tests disappeared completely.

[Indications of G-CSF in patients with drug-induced agranulocytosis].

Bone marrow findings at the onset of disease were analyzed in five patients with drug-induced agranulocytosis to detect simple indices for a determination of the indications G-CSF therapy. Two patients showed severe marrow hypoplasia, extremely low ME ratio and complete absence of myelocytes or more mature neutrophils in their bone marrow. In these cases, the periods for recovery to 500 or more peripheral neutrophils per microliter were 5 and 9 days in a G-CSF-treated patient and a non-treated patient, respectively. On the other hand, the bone marrow of other three patients revealed normal or slightly high cellularity, moderately low ME ratio and appearance of myelocytes and more mature neutrophils. In the latter cases, the periods for recovery to 500 or more peripheral neutrophils were 3 days in all cases, regardless of whether G-CSF was administered or not. These findings suggest that G-CSF should be administered to drug-induced agranulocytic patients with severe marrow hypoplasia, extremely low ME ratio and absence of marrow neutrophilic cells.

[Long-term maintenance of platelets by IFN alpha-2b in a case of chronic idiopathic thrombocytopenic purpura refractory to prednisolone therapy].

A 63-year-old female with chronic idiopathic thrombocytopenic purpura refractory to prednisolone therapy was treated with interferon alpha-2b (IFN alpha-2b). Initially, the patient received 2 courses of short-course therapy in which 1.5 million IU and IFN alpha-2b was subcutaneously injected 3 times a week every other day for 4 weeks. During the first course, the platelet count rose from 1.0 x 10(4)/microliters to 12.4 x 10(4)/microliters 3 weeks after the beginning of the therapy, but the effect was transient. In the second course the platelet-increasing effect was lower than that in the first course. Then, intermittent injections of 3 million IU of IFN alpha-2b once a week were subsequently begun. Consequently, the patient's platelet count has been maintained at 5 to 9 x 10(4)/microliters for more than 19 months since the beginning of intermittent IFN alpha-2b therapy.