Uracil-DNA glycosylase activity in human acute leukemia

Proteomic analysis of human acute leukemia cells: insight into their classification

PURPOSE

French-American-British (FAB) classification of acute leukemia with genetic heterogeneity is important for treatment and prognosis. However, the distinct protein profiles that contribute to the subtypes and facilitate molecular definition of acute leukemia classification are still unclear.

EXPERIMENTAL DESIGN

The proteins of leukemic cells from 61 cases of acute leukemia characterized by FAB classification were separated by two-dimensional electrophoresis, and the differentially expressed protein spots were identified by both matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) and tandem electrospray ionization MS (ESI-MS/MS).

RESULTS

The distinct protein profiles of acute leukemia FAB types or subtypes were successfully explored, including acute myeloid leukemia (AML), its subtypes (M2, M3, and M5) and acute lymphoid leukemia (ALL), which were homogeneous within substantial samples of the respective subgroups but clearly differed from all other subgroups. We found a group of proteins that were highly expressed in M2 and M3, rather than other subtypes. Among them, myeloid-related proteins 8 and 14 were first reported to mark AML differentiation and to differentiate AML from ALL. Heat shock 27 kDa protein 1 and other proteins that are highly expressed in ALL may play important roles in clinically distinguishing AML from ALL. Another set of proteins up-regulated was restricted to granulocytic lineage leukemia. High-level expression of NM23-H1 was found in all but the M3a subtype, with favorable prognosis.

CONCLUSIONS

These data have implications in delineating the pathways of aberrant gene expression underlying the pathogenesis of acute leukemia and could facilitate molecular definition of FAB classification. The extension of the present analysis to currently less well-defined acute leukemias will identify additional subgroups.

Two-dimensional electrophoresis protein profiling as an analytical tool for human acute leukemia classification

Two-dimensional electrophoresis (2-DE) was used to profile the proteins of leukemic cells from 61 cases of akute leukemia (AL) characterized by the French-American-British (FAB) classification. The differentially expressed protein spots were identified by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and electrospray ionization-tandem MS (ESI-MS/MS). The distinct protein profiles (DPPs) of AL FAB subtypes were explored successfully, including acute myeloid leukemia (AML), its subtypes (M2, M3, and M5), and acute lymphoid leukemia (ALL), which were homogeneous within different samples of the same subgroup but clearly differed from all other subgroups. We also found a group of proteins differentially expressed between AL cells and normal white blood cells. Among the DPPs of AL subtypes, some proteins have been reported, but most of them were first reported here to mark AML differentiation and to discriminate AML from ALL. These data show that 2-DE protein profiling could be used as an analytical tool for facilitating molecular definition of human AL classification and understanding the mechanism of leukemogensis, and the extension of the present analysis to the currently less well-defined AL will identify additional subgroups and may promote the identification of new targets for specific treatment approaches.

Deoxypyrimidine-induced inhibition of the cytokinetic effects of 1-beta-D-arabinofuranosyluracil

Ara-U-induced S-phase accumulation and the interaction between high concentrations of ara-U (HiCAU) and ara-C were investigated in L1210 leukemia cells in vitro. Treatment of exponentially growing L1210 murine leukemia cells with ara-U (200-1000 microM) for 48 h caused a dose-dependent accumulation of cells in the S-phase. The extent of this ara-U-induced S-phase accumulation correlated with ara-U incorporation into DNA and with increases of up to 172% and 464% in the specific activities of deoxycytidine kinase and thymidine kinase, respectively, over control values. Metabolism of 1 microM ara-C following the exposure of cells to ara-U (1 mM) resulted in 4.5 pmol araC DNA/mg protein vs 2.1 pmol/mg protein in control cells. Although 48-h exposure of cells to 200 and 400 microM ara-U is not cytotoxic, it enhances the cytotoxicity of ara-C (10-100 microM) 4- to 10-fold. Ara-U-induced S-phase accumulation is inhibited by deoxypyrimidine nucleosides but not by pyrimidine or deoxypurine nucleosides. Some of the ara-U and ara-C concentrations used in this study are achievable in clinical practice, and ara-U/ara-C interactions may explain in part the unique therapeutic utility of high-dose ara-C.

Normal uracil-DNA glycosylase activity in Bloom's syndrome cells

Cells from patients with Bloom's syndrome, a rare human disease with autosomal recessive mode of inheritance, exhibit cytological abnormalities involving DNA metabolism. Bloom's syndrome is characterized by a greatly increased cancer frequency which may reflect a specific defect in DNA repair and replication. Evidence has recently been presented of the existence in Bloom's syndrome of an abnormality of the DNA ligase involved in semiconservative DNA replication. Another abnormality, in the excision-repair pathway of Bloom's syndrome cells, is reportedly due to an aberrant immunological reactivity of the DNA-repair enzyme uracil-DNA glycosylase. In this investigation we show, however, that the catalytic activity of uracil-DNA glycosylase appears to be normal in Bloom's syndrome lymphoblastoid cells.

The DNA-repair enzyme uracil-DNA glycosylase in the human hematopoietic system

The expression of the DNA base-excision-repair enzyme uracil-DNA glycosylase in the human hematopoietic system followed a tightly regulated pattern: high enzyme activities were recorded in proliferating bone marrow progenitor cells and in peripheral blood T- and B-cells, both groups of cells requiring the integrity of their genetic information for their proper function. The blood quiescent immunocompetent cells retained their DNA-uracil exclusion capacity, even in the oldest age groups. Peripheral blood mature end cells, granulocytes, platelets and red cells had little activity, consistent with the fact that these cells are anuclear or short-lived, so that no template-primer functions of their DNA are required. Uracil-DNA glycosylase expression is high in all types of human leukemia, providing a selective advantage for survival of leukemic cells. Overall results show that a deficiency of this DNA base-excision-repair pathway is not likely to be an etiopathogenetic factor in the formation of non-random or other chromosomal abnormalities or in the leukemogenesis itself.