Expression of apoptosis-controlling proteins in acute leukemia cells

The expression of Bcl-2 family proteins (Bcl-2, Bcl-X, Bcl-X-L, Bcl-X-s, BAX, BAD, MCL-1) and of Interleukin-1 converting enzyme (ICE)-related proteins (ICE, CPP32, ICH-1) was analyzed in acute leukemia cells by flow cytometry, Most proteins studied were detectable in cell lines such as KG1a, HL60, K562 (myeloblastic), REH, RAJI and MOLT4 (lymphoblastic) and VAL (B-cell lymphoma), However, BCL-X-s and BAK were weakly expressed in K562, as were Bcl-X, BAD and BAK in the VAL line. In acute myeloid leukemia (66 cases studied), the proteins were expressed in most cases in a high percentage of cells, especially BAX and CPP32, without correlation with hematological characteristics. However, Bcl-2 was expressed in a higher percentage of cells in FAB M1 and M5 cases, and in CD34-positive cases, whereas Bcl-X-s was more frequently expressed in M3 cases. No differences were observed regarding fluorescence intensity. Higher percentages of Bcl-2-positive cells were associated with low remission rate, while expression of Bcl-X-s was predictive of high remission rate. In acute lymphoblastic leukemia (36 cases), all proteins studied were expressed in a majority of cases. Bcl-X-s was more frequently detected in T-cell type, and was also associated with a higher remission rate. These results suggest that apoptosis-controlling proteins may have a role in the pathogenesis and response to therapy of acute leukemia.