Mutations of Myeloid Transcription Factors AML1, CEBPα and PU.1 in Patients with De Novo Myelodysplastic Syndrome: An Analysis of Paired Bone Marrow Samples at Diagnosis and at AML Transformation.

Abstract

Transcription factors AML1, PU.1 and CEBPα are essential for normal hematopoiesis. Recently, somatic mutations of genes encoding these transcription factors have been described in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). The role of mutations of these transcription factors in the progression of MDS into AML remained to be determined, as no matched paired samples of both phases have been analyzed in the previous studies. We analyzed mutations of AML1, CEBPα and PU.1 on paired bone marrow samples at initial diagnosis of de novo MDS (8 RCMD, 12 RAEB-1, and 17 RAEB-2) and at AML transformation. Mutation analysis was performed by direct sequencing of all RT-PCR or DNA PCR products using different primer pairs which cover the entire coding sequences of AML1, PU.1 and CEBPα genes. Eight of 37 patients (21.6%) had AML1 mutations and one of them had 2 mutations; 3 mutations were located in Runt homology domain (RHD) (exons 3–5), whereas 6 mutations were located in the C-terminal region (exons 6–8) at initial presentation of MDS. Another 2 acquired C-terminal mutations at AML transformation. The 11 AML1 mutations detected in 10 patients during their disease course, included 4 missense mutations, 3 nonsense mutations, 1 silent mutation, and 3 frameshift mutations. Taken together, 30% (3/10) of AML1 mutations detected in MDS patients were located in RHD and were exclusively missense compared with 70% at C-terminal region with frequent nonsense or frameshift mutations (86%) (P=0.033). Patients with AML1 mutations were older than those without mutations (P=0.019). No differences were observed between patients with and without AML1 mutations with respect to sex, blood counts, percentage of blasts in bone marrow or peripheral blood, morphologic subtype, and cytogenetic risk group. There was no difference in the time to AML transformation and overall survival with respect to the status of AML1 mutation. Only one out of 34 MDS patients had CEBPα mutation at initial diagnosis, she lost the mutation after chemotherapy and no mutation was detected at AML transformation. Another one did not have CEBPα mutation at diagnosis but acquired CEBPα mutation at AML transformation, the patient also had AML1 mutation at both phases. PU.1 mutation was not detected in 32 patients examined at both MDS and AML phases. The present study showed that AML1 mutations were common in patients with MDS, especially at C-terminal region and frequently with frameshift or nonsense mutations, and might be acquired during AML transformation; whereas CEBPα mutations were infrequent and PU.1 mutation was absent.