Activation of proto-oncogenes in human leukemias

Review of clinical, cytogenetic, and molecular aspects of Ph-negative CML

Between 1985 and 1989, many cases of Philadelphia (Ph) chromosome negative chronic myelogenous leukemia (CML) were reported. For this review, the following selection criteria were used: the original articles on Ph-negative cases should provide clinical, hematologic, cytogenetic as well as molecular data. In addition, eight unpublished cases of Ph-negative CML are included that were studied in our institute during the last two years. Our purpose was to correlate presence or absence of the Ph rearrangement with the clinical features in an attempt to test whether the entity "Ph-negative CML" really exists and to identify the pathologic characteristics, frequency of occurrence, prognosis for survival, and underlying molecular mechanisms. Data on Ph-negative CML patients were compared with data on Ph-positive CML, atypical CML (aCML), and chronic myelomonocytic leukemia (CMMoL), reported in the same papers as the Ph negative patients. Essential for comparison of data from the different investigators appeared to be a clear description of criteria they used to establish the diagnosis CML, or alternatively a complete presentation of data for all patients reported in the articles. In most cases, Ph-negative CML was distinguishable from CMMoL and aCML, using simple criteria, e.g., differential count of peripheral blood and absence of dysplasia in the bone marrow. Cytogenetic analysis showed normal karyotype in most cases of Ph-negative CML. Interestingly, in cases with abnormal karyotype, chromosome 9 band q34 was relatively frequently involved in translocations with other chromosomes than chromosome 22, suggesting a variant Ph translocation not visible by cytogenetic techniques. This assumption was confirmed by molecular analysis, demonstrating bcr-abl rearrangement in 9 out of 10 of the latter cases. Results of cytogenetic and molecular investigations in 136 cases of Ph-negative CML reviewed in this article clearly indicated that molecular techniques are valuable tools for identification of bcr-abl rearrangements, indicative for the Ph translocation. The different mechanisms responsible for bcr-abl rearrangement in Ph-negative CML patients are discussed. The question remains whether all Ph-negative CML patients will have bcr-abl rearrangements, or whether alternative mechanisms will be identified that are responsible for this disease.

Population analysis of karyotypic heterogeneity of the Raji Burkitt lymphoma cell line. Analysis of 100 karyotypes

A constant lymphoblastoid line Raji (Burkitt lymphoma) has been used as a model for population cytogenetic studies. In analyzing 100 G-banded metaphase plates, four karyotypically distinct clones of cells with 48 chromosomes have been recognized, forming a modal class. In tracing the origin of marker chromosomes (in all 15), the presence of material specific for Burkitt chromosome markers 14q+ and 8q- has been shown. The application of the method of karyotype reconstruction has shown a uniformity in the overall chromosome material of all four groups of cells despite a different set of normal and marker chromosomes. The presence of 40% of cells with unique structural rearrangements (USR) demonstrated, to a significant extent, the structural instability of chromosomes in Raji cells. The nonrandom nature of distribution of "hot spots" along the chromosomes in the process of formation of both markers and USR has been shown. A preferential involvement of chromosomes #6, #7, and #8, as well as of separate regions 1p32, 6q15, 11q13, and 21p13 has been recorded. This report discusses aspects of karyotypic heterogeneity of cell populations in vitro and structural instability of regions of chromosomes #1 and #11, that coincide with the localization of the oncogene L-MYC or sequence BLYM-1 and the oncogene BCL-1.