bcl-2 proto-oncogene expression in normal and neoplastic human myeloid cells

Abstract

The present study provides immunobiochemical and molecular data on the differentiation-linked expression of the bcl-2 proto-oncogene in normal and neoplastic myeloid cells. Using a recently developed monoclonal antibody (MoAb) to the bcl-2 molecule, staining of normal bone marrow myeloblasts, promyelocytes, and myelocytes, but neither monocytes nor most polymorphonuclear cells, was demonstrated. By two-color flow cytometric analysis, bcl-2 was evidenced in CD33+ and CD33+/CD34+ myeloid cells as well as in the more primitive CD33-/CD34+ population. The leukemic cell lines HL-60, KG1, GM-1, and K562 were bcl-2 positive together with 11 of 14 acute myeloid leukemias (AML) and three of three chronic myeloid leukemias (CML) in blast crises; six of seven CML were negative. Among myelodysplastic cases, augmentation of the bcl-2 positive myeloblastic compartment was found in refractory anemia with excess of blasts (RAEB) and in transformation (RAEB-t). Western blots of myeloid leukemias and control lymphocytes extracts evidenced an anti- bcl-2 immunoreactive band of the expected size (26 Kd). Moreover, the HL-60 and KG1 cell lines, both positive for the bcl-2 protein, exhibited the appropriate size bcl-2 mRNA (7.5 Kb). These findings clearly indicate that the bcl-2 gene is operative in myeloid cells and that the anti-bcl-2 MoAb identifies its product and not a cross- reactive epitope. Induction of HL-60 differentiation toward the monocytic and granulocytic pathways was accompanied by a marked decrease in bcl-2 mRNA and protein levels; bivariate flow cytometric analysis showed that the fraction becoming bcl-2 negative was in the G1 phase of the cell cycle. These data establish that the bcl-2 proto- oncogene is expressed on myeloid cells and their progenitors and is regulated in a differentiation-linked manner.

Expression of genes involved in initiation, regulation, and execution of apoptosis in human neutrophils and during neutrophil differentiation of HL-60 cells

“…mRNA expression of bcl-2 family genes in human neutrophils and during neutrophil differentiation of HL-60 cells Apoptosis is controlled by a number of ''pro-suicide'' (bax, bcl-x s , bak, bik, bad) and ''anti-suicide'' (bcl-2, bcl-x L , bfl-1/A1, bcl-w) genes that are members of the bcl-2-related gene family [ [19][20][21][22]. Previous reports have indicated that neutrophils lack bcl-2 expression [36,39], and this could be related to their readiness to undergo spontaneous apoptosis. However, due to the redundancy in the biological actions of the bcl-2 family members, we have studied the expression of a wide panel of bcl-2 family genes in both human neutrophils and neutrophildifferentiating HL-60 cells through semiquantitative RT-PCR.…”

“…Mature neutrophils are essentially absent for bcl-2 expression [36]. HL-60 cells express bcl-2, but induction of HL-60 differentiation toward the granulocytic pathway is accompanied by a marked decrease in bcl-2 mRNA and protein levels [39][40][41]. In this report, we examine the expression of a wide number of Bcl-2 and caspase family members in mature neutrophils and during differentiation of HL-60 cells toward the neutrophil lineage.…”

All along the watchtower: on the regulation of apoptosis regulators

“…The preponderance of proapoptotic molecules may in part explain why these cells so readily undergo apoptosis in the absence of specific triggers (24,25). In addition, differentiation of myeloid leukemic cells transpires with a decrease in Bcl-2 (26). An upregulation of Bcl-2 mRNA in growth factor-dependent cells by the survival factors interleukin (IL) -2 or IL-3 has also been observed (27).…”

Viruses and cancers: possible role of hepatitis C virus

“…Specific genes could be responsible for B-cell expansion by inducing proliferation and/or death of lymphocytes. Among these, bcl-2, able to inhibit apoptosis [96], is frequently involved in both benign and malignant B-cell neoplasms [97,98]. The aberration of bcl-2 may lead to extended cell survival, which may expose the lymphocytes to another genetic aberration, such as translocation of myc oncogene; this may induce more malignant characteristics in lymphocytes as observed in highgrade lymphomas [99].…”