Shinichi Fujimaki

Decreased expression of transcription factor GATA-2 in haematopoietic stem cells in patients with aplastic anaemia

Aplastic anaemia is characterized by reduced haematopoiesis resulting in pancytopenia. It has been speculated that there is an injury in haematopoietic stem cells in the bone marrow; however, the precise nature of the injury has not been elucidated. In this study, the levels of expression of mRNAs for three transcription factors, GATA‐2, SCL and AML1, which function in the early stages of haematopoiesis, were examined by quantitative polymerase chain reaction in patients with aplastic anaemia, idiopathic thrombocytopenic purpura (ITP) and normal subjects. Among these factors, expression of GATA‐2 mRNA in purified CD34‐positive cells was markedly decreased in aplastic anaemia compared with that in ITP and in normal subjects. The expression levels of SCL and AML1 mRNA in CD34‐positive cells in aplastic anaemia were not different from those in normal subjects. When the expression of GATA‐2 protein in CD34‐positive cells was examined by immunocytochemical analysis, the percentage of GATA‐2‐positive cells in aplastic anaemia was lower than that in normal subjects. These findings strongly suggest that there is an aberrant expression of transcription factors in stem cells in aplastic anaemia, which may be responsible for the development of the disease.

A quantitative reverse transcriptase polymerase chain reaction method for the detection of leukaemic cells with t(8;21) in peripheral blood.

Abstract: We evaluated the usefulness of a recently developed real‐time reverse transcriptase polymerase chain reaction (RT‐PCR) system to detect minimal residual diseases (MRD) in patients with acute myelogenous leukaemia (AML) with chromosomal translocation t(8:21). The method was simple, rapid and reproducible for the quantity of chimeric AML1‐ETO (MTG8) transcripts. The ratio of the absolute copy number of a target gene (AML1‐ETO) to a control gene (glyceraldehyde‐3‐phosphate dehydrogenase, GAPDH) was calculated by using a fluorescence curve prepared from amplicons of serially diluted standard RNA. The relative points of MRD in bone marrow (BM) of 8 patients in the acute phase of the disease was from 0.85 to 3.0, whereas those of MRD in complete remission (CR) decreased to below 6.4×10−3. This method was also applied to evaluate chimeric transcripts in peripheral blood (PB) samples. The values in patients with t(8;21) AML were from 0.97 to 2.0 in the acute phase, whereas those in CR showed less than 2.2×10−4. There was 10−5‐fold difference in AML1‐ETO mRNA expression between PB samples in the acute phase and those in CR. The results suggest that we may easily monitor MRD in patients with t(8;21) AML through quantitative analysis of AML1‐ETO transcripts in blood samples.

Increased sensitivity to cisplatin in gastric cancer by antisense inhibition of the her-2/neu (c-erbB-2) gene.

Background: The c-erbB-2 oncogene encodes a transmembrane tyrosine kinase receptor and its abnormal expression may be related to the prognosis of gastric cancer. Gastric cancer is relatively resistant to various drugs, including cisplatin. Cisplatin is widely used in cancer chemotherapy, but the mechanisms of drug resistance are not yet known. Methods: We used the human gastric cancer cell lines MKN-7 and KATO-III, which express the c-erbB-2 oncogene, as a model for relative resistance to cisplatin. We investigated whether inhibition with antisense oligonucleotides against c-erbB-2 increased the sensitivity of MKN-7 and KATO-III cells to cisplatin. Results: Antisense oligonucleotides for c-erbB-2 inhibited the expression of c-erbB-2 mRNA and protein and increased sensitivity to cisplatin, but not to other drugs, in MKN-7 and KATO-III cells. Cell growth was also inhibited by c-erbB-2 antisense oligonucleotides but not sense oligonucleotides. Conclusions: These findings indicate that c-erbB-2 expression in gastric cancer is one of the factors related to cisplatin sensitivity, and that anti-c-erbB-2 antisense oligonucleotides induced increased sensitivity to cisplatin.

In vitro leukemia cell models of Ara-C resistance

Cells of the human leukemia line K562 were continuously exposed to cytosine arabinoside (Ara-C) at increasing concentrations for 3 months. The resulting cell line, termed K562/AC, showed 48-fold resistance to Ara-C, compared with the parental K562 cells. The sensitivities of K562/AC to adriamycin (ADR), vincristine (VCR) and etoposide (VP16) were similar to those of parental K562. Gene analysis revealed that this cell line lacked expression of the deoxycytidine kinase (dCK) gene, which was evident in Ara-C-sensitive cells. As in K562 cells, multidrug resistance (MDR-1) and multidrug resistance protein (MRP) genes were not expressed in K562/AC. We also established an in vitro model of Ara-C resistance using phosphorothioate antisense oligonucleotides to dCK (dCK-AS). Treatment of K562 with dCK-AS caused decreased dCK expression and 6- to 10-fold increases in resistance to Ara-C, compared with that in cells treated with sense oligonucleotides to dCK (dCK-S) or in non-transfected cells. The cells described here may contribute to the study of a novel mechanism associated with Ara-C resistance, in which reduced dCK activity may play an important role.

Gene Expression Profiling Identifies HOXB4 as a Direct Downstream Target of GATA-2 in Human CD34+ Hematopoietic Cells

Aplastic anemia is characterized by a reduced hematopoietic stem cell number. Although GATA-2 expression was reported to be decreased in CD34-positive cells in aplastic anemia, many questions remain regarding the intrinsic characteristics of hematopoietic stem cells in this disease. In this study, we identified HOXB4 as a downstream target of GATA-2 based on expression profiling with human cord blood-derived CD34-positive cells infected with control or GATA-2 lentiviral shRNA. To confirm the functional link between GATA-2 and HOXB4, we conducted GATA-2 gain-of-function and loss-of-function experiments, and HOXB4 promoter analysis, including luciferase assay, in vitro DNA binding analysis and quantitative ChIP analysis, using K562 and CD34-positive cells. The analyses suggested that GATA-2 directly regulates HOXB4 expression through the GATA sequence in the promoter region. Furthermore, we assessed GATA-2 and HOXB4 expression in CD34-positive cells from patients with aplastic anemia (n = 10) and idiopathic thrombocytopenic purpura (n = 13), and demonstrated that the expression levels of HOXB4 and GATA-2 were correlated in these populations (r = 0.6573, p<0.01). Our results suggested that GATA-2 directly regulates HOXB4 expression in hematopoietic stem cells, which may play an important role in the development and/or progression of aplastic anemia.

Increased sensitivity to cytosine arabinoside in human leukemia by c-raf-1 antisense oligonucleotides.

c-raf-1, a cytoplasmic serine/threonine protein kinase, plays an important role in mitogen- and damage-responsive cellular signal transduction pathways. Expression of c-raf-1 modifies cell growth, proliferation and survival. Although expression of c-raf-1 has been studied in several tumors, the role of c-raf-1 in leukemia is so far unclear. We examined the expression of c-raf-1 in the human leukemia cell lines U937 and K562, and in a cytosine arabinoside (Ara-C)-resistant cell line (K562AC) derived from K562. Expression of c-raf-1 was increased in U937 and in Ara-C-resistant K562AC cells compared with the parental cells. We then investigated whether inhibition of c-raf-1 expression by antisense oligonucleotides increases the sensitivity to Ara-C in U937 and K562AC cells. Antisense oligonucleotides for c-raf-1 inhibited expression of c-raf-1 mRNA, but did not affect cell growth and increased sensitivity to Ara-C but not to other drugs such as adriamycin, VP-16 or vincristine. These results suggest that c-raf-1 is one of the factors involved in Ara-C resistance in leukemia and lend weight to the case for development of anti-cancer therapeutics involving oncogene-targeted antisense oligonucleotides.