BAX and PKC alpha modulate the prognostic impact of BCL2 expression in acute myelogenous leukemia

Previously, we demonstrated that the level of BCL2 expression is prognostic in acute myelogenous leukemia (AML). High levels of BCL2 correlate with an adverse outcome when associated with favorable and intermediate prognosis cytogenetics (FIPC), whereas low levels portend an adverse outcome when ass ociated with unfavorable cytogenetics (UC). Because BCL2 function can be mo dulated by dimerization with family members, like BAX, or by phosphorylatio n by protein kinase C alpha (PKC alpha), we hypothesize that the relative e xpression of these proteins in primary leukemic cells might alter the progn ostic impact of BCL2 expression. We therefore measured BAX and PKC alpha pr otein levels in peripheral blood mononuclear cell lysates from 165 newly di agnosed AML patients and correlated the expression of these proteins with B CL2 expression, patient survival, and remission induction success. Expressi on levels of BAX and PKC alpha were normalized against a control cell Line, K562. BAX and PKC alpha expression levels were heterogeneous and did not c orrelate with the percentage of blasts in the sample (R-2 = 0.01 and <0.01) . The median expression of both was similar across FAB groups but the range was greater for M4. A similar distribution of expression was observed in a ll cytogenetic groups, except that patients with inversion 16 demonstrated lower levels of BAX. Individually, neither PKC alpha nor BAX expression was prognostic of response to induction therapy or survival. A similar outcome was obtained when patients were stratified by cytogenetics into FIPC and U C groups. However, the ratio of either BCL2:BAX (B2:BX) or PKC alpha*B2:BX (PK*B2:BX) was highly prognostic. Patients with FIPC and a lower ratio (les s than median) of either B2:BX or PK*B2:BX had a significantly higher remis sion induction rate (89 versus 69%, P = 0.04) and longer survival (median: 141 versus 80.5 weeks, P = 0.007) compared with those with ratios more than median. For patients with UC, values of either B2:BX or PK*B2:BX below the median had an inferior response rate to induction therapy (35 versus 78%, P = 0.0006) and inferior survival outcomes (median survival: 11 versus 53 w eeks, P = 0.00002). Interestingly, FIPC and UC patients with antiapoptotic ratios (defined as B2:BX or PK*B2:BX more than median) had identical respon se rates and survival outcomes. In multivariate analyses, the compound vari ables of cytogenetics and B2:BX, or PK*B2:BX were independent predictors of survival. These results suggest that expression levels of proteins that af fect the functional status of BCL2 modify the prognostic impact of BCL2 and suggest that the role of apoptosis in different cases of AML varies indepe ndently in the different cytogenetic subgroups.