Calreticulin expression and activity are induced following conditional expression of CBFB-SMMHC in leukemic U937 cells and in CBFB-SMMHC AML-M4Eo patient samples. (A) Calreticulin (CRT) mRNA levels following induction of CBFB-SMMHC in U937 cells are determined by quantitative RT-PCR. Mean values and SDs (error bars) are shown. (B) Calreticulin mRNA levels are assessed by RT-PCR after withdrawal of tetracycline in the parental U937 T cells. (C) Calreticulin mRNA levels were determined in AML-M4 patients with CBFB-SMMHC compared to AML-M4 patients with a normal karyotype. (D) Calreticulin protein was analyzed by Western blot analysis in U937 cells following induction of CBFB-SMMHC by withdrawal of tetracycline. Quantification as calreticulin/β-actin ratio is indicated below. (E) Calreticulin protein was analyzed in AML-M4 patient samples with CBFB-SMMHC (lanes 1-8 and 9-12) and in representative AML-M4 patients with a normal karyotype (lanes 1 and 10). (F) Calreticulin activity of U937-CBFB-SMMHC cells following withdrawal of tetracycline was assessed by UV cross-linking to directly visualize the physical interaction between calreticulin protein and CEBPA mRNA.