Differing patterns of proto-oncogene expression in immature and mature myeloid cells.

Comparisons of the level of proto-oncogene expression in neoplastic cells and in normal cells are being made to determine the role of these genes in neoplastic development. Recent papers have reported that leukemic cells differ from normal cells in having higher c-myc RNA levels. One problem in interpreting these data is that leukemic and normal cell populations differ in the proportion of immature cells present in each. The studies described here, using chronic phase chronic myelogenous leukemia (CML) cells, compared the level of proto-oncogene expression in immature and mature myeloid cells. Substantial differences in the level and pattern of expression were found with the immature cells containing higher c-myc RNA levels and the mature cells containing higher histone H3 RNA levels. c-fos RNA levels parallel the distribution of monocytes. While the c-myc RNA level in the CML cell population as a whole is similar to that in normal marrow cell populations and less than that in the bone marrow cells of patients with acute myelogenous leukemia (AML), c-myc RNA levels in subpopulations of immature chronic phase CML myeloid cells approximate that found in AML cells. Additionally, the studies described here suggest that the presence of high c-myc and c-fos RNA levels in light density immature cells may be a unique characteristic of acute myeloid leukemic cells.