CEBPA protein is specifically suppressed in AML-M4 patients with CBFB-SMMHC. (A) Ninety-two patients with AML of all subtypes were analyzed for CEBPA mRNA expression by quantitative RT-PCR. Differences among subtypes were not significant (P = .327). Mean values and standard deviation (error bars) are depicted. (B) Subgroup analysis using quantitative RT-PCR analysis of CEBPA mRNA levels from AML-M4Eo with CBFB-SMMHC (n = 12) and AML-M4 with a normal karyotype (n = 6). The n-fold expression levels were calculated. Mean values and SDs are shown. The difference between AML-M4Eo and normal karyotype AML-M4 was not significant (P = .478). In addition, AML-M2 patients with the AML1-ETO rearrangement were compared to AML-M2 patients with a normal karyotype. This difference was significant (P = .012). (C) Whole-cell lysates of 12 AML-M4Eo CBFB-SMMHC patient samples (lanes 1-8 and 9-12) and of 2 AML-M4 patients with a normal karyotype (first lane in left and right panels) were subjected to Western blotting with a CEBPA antibody (top blots). None of the samples from the AML-M4 patients with inv(16) had detectable CEBPA protein. Eleven patients with AML-M4 and normal karyotypes were tested, with 6 having high expression as shown in the first lane of the 2 panels, 3 having weak CEBPA expression, and 2 having no detectable CEBPA protein. The same membrane was subsequently incubated with an antibody against β-actin for control of loading and integrity (bottom blots). (D) CEBPA-binding activity was measured using the Transam assay. Mean values and SDs are shown. OD indicates spectophotometric result at 450 nm wavelength.