PU.1 expression in primary APL cells: inverse correlation with PML-RARA at diagnosis, and induction of expression following treatment with ATRA in vivo. (A) Correlation of PU.1 and OCT-1 mRNA expression and inverse correlation between PML-RARA vs. PU.1 and OCT-1 transcripts in bone marrow cells at diagnosis of 9 patients with newly diagnosed t(15;17) AML-M3 as assessed by quantitative real-time PCR. The median value was determined as 100% for PML-RARA, OCT-1, and PU.1, respectively. The percentage of blasts was more than 90% in all patients. The correlation coefficient PML-RARA versus OCT-1 was r = -0.887, for PML-RARA versus PU.1 it was r = -0.912, and for OCT-1 versus PU.1 it was r = 0.907. (Different symbols indicate different patients.) (B) RNA expression was determined by quantitative RT-PCR of CEBPA, PU.1, CEBPB, OCT-1, and CEBPE in primary cells from a patient with newly diagnosed APL treated with orally given ATRA (45 mg/m²). No additional chemotherapy was given. The cells analyzed on a daily basis were obtained from peripheral blood (Table S1). Error bars depict the standard deviation as the result of triplicate mRNA determinations.