Expression of L-myc and N-myc proto-oncogenes in human leukemias and leukemia cell lines

The myc proto-oncogenes encode nuclear phosphoproteins, which are believed to participate in the control of cell proliferation and differentiation. Deregulated expression of c-myc has been implicated in several human hematopoietic malignancies. We have studied the expression and mRNA processing of human L-myc, N-myc, and c-myc genes in a panel of human leukemias, leukemia cell lines, and normal hematopoietic cells. L-myc mRNA was expressed in three acute myeloid leukemias (AML) studied and in several myeloid leukemia cell lines. Only low expression levels were observed in adult bone marrow and in fetal spleen and thymus. The K562 and Dami leukemia cell lines showed a unique pattern of L-myc mRNA processing, with approximately 40% of L-myc mRNA lacking exon III and intron I. N-myc was expressed in five of six AML cases studied, in one of nine acute lymphocytic leukemia (ALL) cases, and in several leukemia cell lines, while c-myc mRNA was detected in all leukemias and leukemia cell lines studied. Coexpression of all three myc genes was observed in Dami and MOLT-4 cell lines and in two AMLs, and either L-myc or N-myc was coexpressed with c-myc in several other cases. These results show that in addition to c-myc, the L-myc and N-myc genes are expressed in some human leukemias and leukemia cell lines, and suggest a lack of mutually exclusive cross-regulation of the myc genes in human leukemia cells.     

Detection of p53 oncogene in acute-leukemia cells by immunoperoxidase technique

Expression of p53 oncogene in blast cells may have prognostic importance in acute leukemia. Simple and reliable methods which could detect enhanced p53 expression in leukemia cells would be important for follow-up studies of leukemia patients in remission. We used immunoperoxidase (IP) technique with an anti-p53 monoclonal antibody PAb421 to study the expression of p53 in leukemia cells. The expression of p53 was studied in 9 cell lines and 17 de novo acute leukemia (9 acute myeloid leukemia [AML], 8 acute lymphoblastic leukemia [ALL]) patients. The expression of p53 was demonstrated in non-T non-B cells and Burkitt's lymphoma cell lines, but neither in two myeloid leukemia cell lines nor in normal lymphoid cells after mitogenic stimulation. p53 expression was demonstrated in 7 cases (2 AML, 5 ALL) but only in ALL cases the percentage of positive of cells was over 20%. Bone marrow cells from patients were studied also after short-term culture (AML patients); in 1 case the number of PAb421-positive cells rose significantly after culture. These data suggest that IP staining with PAb421 can be used to demonstrate high p53 expression in B cell leukemias.     

Expression of TGF-beta gene in adult T cell leukemia

Peripheral mononuclear cells from adult T cell leukemia (ATL) patients were analyzed in comparison with other types of leukemia cells, for the expression of transforming growth factor-beta (TGF-beta) mRNA, for the presence of TGF-beta activity (colony stimulating activity for normal rat kidney fibroblasts [NRK]) in conditioned medium and for their susceptibility to exogenous TGF-beta. Highly elevated TGF-beta mRNA levels were observed in all five ATL cell samples tested; however, in three acute myelogenous leukemia (AML) samples, in one acute lymphatic leukemia (ALL), and one chronic myelogenous leukemia (CML), TGF-beta expression was relatively lower. In normal peripheral mononuclear cells TGF-beta mRNA was weakly detectable. Colony stimulating activity for NRK found in the conditioned medium from ATL cells as well as other leukemia cells correlated well with the levels of TGF-beta mRNA expression. In all three ATL samples tested, stimulation of 3H- thymidine uptake by purified TGF-beta from platelets was apparent. These results suggest that ATL cells are secreting active TGF-beta in a relatively high amount, as compared with other leukemia cells, and may proliferate in response to the factor via an autocrine manner. Furthermore, considering that TGF-beta stimulates bone resorption, we can speculate that the relatively high amount of TGF-beta in ATL cells contributes to the hypercalcemia frequently seen in ATL patients.     

Cytokine-regulated expression of survivin in myeloid leukemia

Survivin, a member of the inhibitors-of-apoptosis gene family, is expressed in a cell-cycle-dependent manner in all the most common cancers but not in normal differentiated adult tissues. Survivin expression and regulation were examined in acute myeloid leukemia (AML). Survivin was detected by Western blot analysis in all myeloid leukemia cell lines and in 16 of 18 primary AML samples tested. In contrast, normal CD34(+) cells and normal peripheral blood mononuclear cells expressed no or very low levels of survivin. Cytokine stimulation increased survivin expression in leukemic cell lines and in primary AML samples. In cultured primary samples, single-cytokine stimulation substantially increased survivin expression in comparison with control cells, and the combination of G-CSF, GM-CSF, and SCF increased survivin levels even further. Conversely, all-trans retinoic acid significantly decreased survivin protein levels in HL-60, OCI-AML3, and NB-4 cells within 96 hours, parallel to the induction of myelomonocytic differentiation. Using selective pharmacologic inhibitors, the differential involvement of mitogen-activated protein kinase kinase (MEK) and phosphatidylinositol-3 kinase (PI3K) pathways were demonstrated in the regulation of survivin expression. The MEK inhibitor PD98059 down-regulated survivin expression in both resting and GM-CSF-stimulated OCI-AML3 cells, whereas the PI3K inhibitor LY294002 inhibited survivin expression only on GM-CSF stimulation. In conclusion, these results demonstrate that survivin is highly expressed and cytokine-regulated in myeloid leukemias and suggest that hematopoietic cytokines exert their antiapoptotic and mitogenic effects, at least in part, by increasing survivin levels.     

Survivin is highly expressed in CD34(+)38(-) leukemic stem/progenitor cells and predicts poor clinical outcomes in AML

Survivin, a member of the inhibitors of apoptosis protein family, plays important roles in cell proliferation and survival and is highly expressed in various malignancies, including leukemias. To better understand its role in acute myeloid leukemia (AML), we profiled survivin expression in samples obtained from 511 newly diagnosed AML patients and in CD34(+)38(-) AML stem/progenitor cells using a validated reverse-phase protein array; we correlated its levels with clinical outcomes and with levels of other proteins in the same sample set. We found that survivin levels were higher in bone marrow than in paired peripheral blood leukemic cells (n = 140, P = .0001) and that higher survivin levels significantly predicted shorter overall (P = .016) and event-free (P = .023) survival in multivariate Cox model analysis. Importantly, survivin levels were significantly higher in CD34(+)38(-) AML stem/progenitor cells than in bulk blasts and total CD34(+) AML cells (P < .05). Survivin expression correlated with the expressions of multiple proteins involved with cell proliferation and survival. Particularly, its expression strongly correlated with HIF1α in the stem/progenitor cell compartment. These results suggest that survivin is a prognostic biomarker in AML and that survivin, which is overexpressed in AML stem/progenitor cells, remains a potentially important target for leukemia therapy.     

MicroRNA expression signatures accurately discriminate acute lymphoblastic leukemia from acute myeloid leukemia

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer, whereas acute myeloid leukemia (AML) is the most common acute leukemia in adults. In general, ALL has a better prognosis than AML. To understand the distinct mechanisms in leukemogenesis between ALL and AML and to identify markers for diagnosis and treatment, we performed a large-scale genome-wide microRNA (miRNA, miR) expression profiling assay and identified 27 miRNAs that are differentially expressed between ALL and AML. Among them, miR-128a and -128b are significantly overexpressed, whereas let-7b and miR-223 are significantly down-regulated in ALL compared with AML. They are the most discriminatory miRNAs between ALL and AML. Using the expression signatures of a minimum of two of these miRNAs resulted in an accuracy rate of >95% in the diagnosis of ALL and AML. The differential expression patterns of these four miRNAs were validated further through large-scale real-time PCR on 98 acute leukemia samples covering most of the common cytogenetic subtypes, along with 10 normal control samples. Furthermore, we found that overexpression of miR-128 in ALL was at least partly associated with promoter hypomethylation and not with an amplification of its genomic locus. Taken together, we showed that expression signatures of as few as two miRNAs could accurately discriminate ALL from AML, and that epigenetic regulation might play an important role in the regulation of expression of miRNAs in acute leukemias.     

Expression of IAP-family proteins in adult acute mixed lineage leukemia (AMLL)

Inhibitor of apoptosis protein (IAP)-family proteins suppress apoptotic signaling in normal/neoplastic cells in various settings. To determine the apoptosis-resistant mechanism in adult acute mixed lineage leukemia (AMLL) with biphenotypic blasts responsible for resistance against chemotherapy, the expression levels of IAP-family proteins in AMLL bone marrow cells were analyzed by quantitative RT-PCR. The overall expression levels of IAPs were higher than those in control, AML, and ALL cells. A significant difference for the expression of survivin was observed between AMLL and AML (P <0.05), and differences between AMLL and ALL were significant for the expression of survivin (P <0.05), NAIP (P <0.05), and XIAP (P <0.05). These findings suggest that higher expression of various IAPs is associated with the chemotherapy-resistant nature of this specific type of leukemia.     

Monoclonal antiglycophorin as a probe for erythroleukemias

A monoclonal antibody (LICR.LON.R10) specific for the major sialoglycoprotein of the erythroid cell membrane, glycophorin A (alpha), has been used to test the possibility that "cryptic" erythroleukemia may be diagnosed as acute lymphoblastic leukemia (ALL) or acute myeloblastic leukemia (AML). In addition to 27 overt erythroleukemias, 724 leukemias, including 329 ALL (103 in relapse), 205 AML, and 109 blast crises of Ph1-positive chronic myeloid leukemia, were analyzed. Twenty cases with a significant proportion of glycophorin-A-positive (gA+) cells were found; 8 of these (5 AML and 3 blast crises of chronic myeloid leukemia, CML) had an obvious erythroid component, but 12 others were diagnosed as AML (2), AMML (1), CML in myeloid blast crisis (4) or megakaryoblastic blast crisis (1), acute megakaryoblastic leukemia (2), or acute lymphoblastic leukemia (2). The latter two patients had no immunologic evidence supporting a diagnosis of ALL and were resistant to chemotherapy. We conclude that AML and ALL only very rarely express gA, and these are probably genuine "cryptic" erythroleukemias. Other gA+ leukemias (megakaryoblastic and CML blast crises) may arise from bi- or pluripotent stem cells and contain distinct and separable blast cell populations.     

Sensitive detection technique of myeloperoxidase precursor protein by flow cytometry with monoclonal antibodies

This report describes the analysis of culture cells and blast cells separated from the heparinized bone marrow and whole blood of patients with acute leukemias by means of a density-gradient technique (Ficoll-sodium metrizoate d = 1.077 g/cm³). Cell-surface antigens were analyzed by a fluorescence-activated cell sorter using a panel of monoclonal antibodies (MAbs). The blast cells and culture cells were fixed by 3% paraformaldehyde in phosphate-buffered saline. A low level of expression of MPO precursor protein was found in THP−1. K-562 and HEL, MEG-01, erythro-megakaryocytic leukemia cell lines, Jurkat, MOLT-3, MOLT-4, RPMI8402, ATL-5, T-cell leukemia cell lines, Raji, Daudi. BALL-1, B-cell leukemia cell lines, and AGNK1 showed negative reaction. The de novo MPO-negative acute leukemias, middle level of expression of MPO precursor protein, was found in the blasts of MPO-negative AML (AML, M0), which coexpressed CD13, CD33, CD34, and CD38. A high level of expression of MPO protein was found in all cases of AML, M1, and M2. The MPO expression was not found in all cases of acute lymphoblastic leukemia. The highest level of MPO expression was found in cases of AML, M3, and AML, M3v, suggesting the diagnostic value for this type of leukemia. The detection of MPO precursor protein by flow cytometric analysis with monoclonal antibodies is essential for the determination of lineage and precise diagnosis of acute unclassifiable leukemia, and should contribute substantially to the development of an effective form of therapy and cure. Am. J. Hematol. 58:241–243, 1998. © 1998 Wiley-Liss, Inc.     

Expression of the Fas antigen on primary human leukemia cells

Summary The antigen defined by the monoclonal antibody anti-Fas can mediate apoptosis, is associated with the receptor for tumor necrosis factor, and is expressed on a limited number of human tissues. In this study we analyzed the expression of Fas on primary human leukemic cells and on mononuclear cells from other hematologic disorders. A total of 95 samples of blood or bone marrow were studied by indirect immunofluorescence. These samples included the normal controls, 47 cases of acute myelogenous leukemia (AML), 11 cases of acute lymphoblastic leukemia (ALL), 21 cases of leukemic lymphoma, seven cases of chronic myelogenous leukemia (CML), five cases of plasma cell leukemia or multiple myeloma, and five cases of myelodysplastic or myeloproliferative syndromes. Normal controls were negative without exception. Among AML, 13/47 cases (28%) were positive; among ALL, 1/11 cases (9%) was positive; among leukemic lymphomas, 3/21 cases (14%) were positive. In a case of plasma cell leukemia which strongly expressed the Fas antigen, we demonstrated that the antibody mediates cell lysis, which was synergistically enhanced by the addition of rabbit complement. In patients with AML, Fas positivity had no obvious clinical relevance. Taken together, our results show that approximately 30% of cases of AML and occasionally other leukemias express the Fas antigens, whereas normal controls are negative in our test system. These findings may be useful in the treatment of refractory leukemias or may permit the purging of autologous transplants.Presented in part at the 34th annual meeting of the American Society of Hematology, Anaheim, CA, December 1992     

Characterization of Thy-1 (CDw90) expression in CD34+ acute leukemia

Thy-1 (CDw90) is a phosphatidylinositol-anchored cell surface molecule which, when coexpressed with CD34 in normal human bone marrow, identifies a population of immature cells that includes putative hematopoietic stem cells. To date, the characterization of Thy-1 expression has been confined largely to normal tissues and cell lines. In this study, we evaluated the frequency and intensity of Thy-1 expression as defined by reactivity with the anti-Thy-1 antibody 5E10 in 38 cases of CD34+ acute leukemia (21 acute myelogenous leukemia [AML], 8 chronic myelogenous leukemia [CML] in blast crisis, and 9 acute lymphoblastic leukemia [ALL]). In 34 of 38 cases (89%) the CD34+ cells lacked expression of the Thy-1 antigen. High-density Thy-1 expression was found in 1 case of CML in lymphoid blast crisis, and low- density Thy-1 expression was identified on a portion of the leukemic cells in 2 cases of AML with myelodysplastic features, and 1 case of CML in myeloid blast crisis, suggesting a possible correlation between Thy-1 expression and certain instances of stem cell disorders such as CML and AML with dysplastic features. In contrast, the dissociation of Thy-1 and CD34 expression in the majority of acute leukemias studied suggests that the development of these leukemias occurs at a later stage than the hematopoietic stem cell. Characterization of Thy-1 expression in acute leukemia may eventually provide insights into the origin of the disease. In addition, separation of leukemic blasts from normal stem cells based on Thy-1 expression may prove useful in assessing residual disease, as well as in excluding leukemic blasts from stem cell preparations destined for autologous bone marrow or peripheral stem cell transplantation.     

Gene Expression Profiling in Childhood Acute Leukemia: Progress and Perspectives

Recent advances in treatment have transformed childhood acute leukemias into curable diseases. However, 20% to 40% of acute leukemia patients still experience a relapse. Microarrays typically contain thousands of oligonucleotides or complementary DNAs and are rapidly becoming important research tools for the identification of novel classifications of leukemias and lymphomas. Microarray-based identification of several translocations has been performed in acute lymphoblastic leukemia (ALL), leading to the discovery of t(1;19), t(12;21), and 11q23 translocations, and in acute myeloid leukemia (AML), finding t(8;21), inv(16), and t(15;17). Correlations between gene expression profiles and clinical features have been reported in ALL and AML. Recently, it was reported that gene expression profiling can be used to predict the prognosis of childhood acute leukemia. In this report, the recent progress in microarray analysis of childhood acute leukemia is reviewed. Gene expression profiling provides new insights into the biological mechanisms of leukemogenesis and the prognosis of childhood acute leukemia.     

Expression of the intestinal T-lymphocyte-associated-molecule recognized by the HML-1 antibody on mononuclear cells from HTLV-I-infected subjects

We investigated the expression of a monoclonal antibody (HML-1) defined antigen that appears on human intestinal T-lymphocytes in HTLV-I-related disease. We studied 25 ATL, and 24 healthy HTLV-I carriers. Patients with acute ATL showed a variety of the expression of the HML-1 antigen (range 0.4–74.8%). HML-1 expression on mononuclear cells (MNCs) in blood from patients with chronic ATL ranged from 1.7–43.6% (mean 13.5%). This level of expression was less than that of patients with acute ATL, but not significantly. In patients with smoldering ATL, the degree of patients with acute ATL, but not significantly. In patients with smoldering ATL, the degree of expression ranged from 1.6–13.3% (mean 8.0%). In contrast to patients wtih acute ATL, MNCs from patients with acute myelogenous leukemia (AML), acute lymphocytic leukemia (ALL), and B-cell type chronic lymphocytic leukemia (B-CLL) did not express the HML-1 antigen, except for the 2 patients with ALL. Healthy HTLV-I carriers and healthy controls also were negative for HML-1 reactivity. In acute ATL, patients with gastrointestinal tract infiltration tended to have high expression of the HML-1 epitope. After stimulation with phytohemagglutinin (PHA), healthy HTLV-I carriers showed significantly increased expression of the HML-1 epitope (P < 0.05). Recently, the β7 integrin family has been found to play a specific role in mucosal localization or adhesion, and HML-1 protein was found to match the deduced β7 N-terminal sequence. We propose that the cellular gene responsible for HML-1 epitope expression may, like IL-2, IL-2R, etc., be transactivated by infection with HTLV-I, and that HML-1 antigen gene expression by HTLV-I infection may lead to infiltration of ATL cells with highly expressed HML-1 epitope into the gut mucosa.     

Expression levels of ASNS in mesenchymal stromal cells in childhood acute lymphoblastic leukemia

Increased levels of asparagine synthetase (ASNS), an enzyme producing intracellular asparagine, have been implicated in the development of asparaginase resistance. The aim of this study was to assess ASNS mRNA and protein expression in bone marrow cell populations of children with acute lymphoblastic leukemia (ALL). Bone marrow mononuclear cells at diagnosis, day 33 of treatment, and after completion of chemotherapy were isolated and studied. ASNS mRNA expression was assessed by real-time PCR, and protein levels by Western blot. Our results indicate that MSC ASNS mRNA expression is upregulated in ALL samples compared to controls. ASNS expression of mesenchymal stromal cells (MSC) was found to be 2.3 times higher than that of blasts at diagnosis of ALL. We also observed that the values of the ASNS mRNA of MSC seem to reach a peak at diagnosis, and tend to decline with treatment. No correlation was found between the ASNS mRNA and protein levels. Chemotherapy does not exert any effect on the protein expression. Variability of asparaginase-induced effect may be attributable to factors involved in the interaction of hematopoietic cells with their microenvironment.     

RNAi screening of the kinome with cytarabine in leukemias

To identify rational therapeutic combinations with cytarabine (Ara-C), we developed a high-throughput, small-interference RNA (siRNA) platform for myeloid leukemia cells. Of 572 kinases individually silenced in combination with Ara-C, silencing of 10 (1.7%) and 8 (1.4%) kinases strongly increased Ara-C activity in TF-1 and THP-1 cells, respectively. The strongest molecular concepts emerged around kinases involved in cell-cycle checkpoints and DNA-damage repair. In confirmatory siRNA assays, inhibition of WEE1 resulted in more potent and universal sensitization across myeloid cell lines than siRNA inhibition of PKMYT1, CHEK1, or ATR. Treatment of 8 acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML) cell lines with commercial and the first-in-class clinical WEE1 kinase inhibitor MK1775 confirmed sensitization to Ara-C up to 97-fold. Ex vivo, adding MK1775 substantially reduced viability in 13 of 14 AML, CML, and myelodysplastic syndrome patient samples compared with Ara-C alone. Maximum sensitization occurred at lower to moderate concentrations of both drugs. Induction of apoptosis was increased using a combination of Ara-C and MK1775 compared with using either drug alone. WEE1 is expressed in primary AML, ALL, and CML specimens. Data from this first siRNA-kinome sensitizer screen suggests that inhibiting WEE1 in combination with Ara-C is a rational combination for the treatment of myeloid and lymphoid leukemias.     

RNAi-mediated silencing of TEL/AML1 reveals a heat-shock protein- and survivin-dependent mechanism for survival

The TEL/AML1 fusion gene results from the most frequent t(12;21)(p13;q22) translocation in childhood acute lymphoblastic leukemia (ALL). Its contribution to transformation is largely unknown, in particular with respect to survival and apoptosis. We therefore silenced TEL/AML1 expression in leukemic REH cells by RNA inhibition, which eventually led to programmed cell death. Microarray and 2D gel electrophoresis data demonstrated a differential regulation of heat-shock proteins (HSPs), among them HSP90, as well as of its client, survivin. Consistent with these findings, ectopic expression of TEL/AML1 in Ba/F3 cells increased protein levels of HSP90 and survivin and conferred resistance to apoptotic stimuli. Our data suggest that TEL/AML1 not only contributes to leukemogenesis by affecting an antiapoptotic network but also seems to be indispensable for maintaining the malignant phenotype. The functional relationship between TEL/AML1, HSP90, and survivin provides the rational for targeted therapy, be it the fusion gene or the latter 2 proteins.