Mutations in the gene encoding the transcription factor CCAAT/enhancer binding protein α in myelodysplastic syndromes and acute myeloid leukemias

Abstract

The CCAAT/enhancer binding protein ␣ (C/EBP␣) protein is essential for proper lung and liver function and granulocytic and adipose tissue differentation. It was hypothesized that abnormalties in C/EBP␣ function contribute to the development of malignancies in a variety of tissues. To test this, genomic DNA from 408 patient samples and 5 cell lines representing 11 different cancers was screened for mutations in the C/EBP␣ gene. Two silent polymorphisms termed P1 and P2 were present at frequencies of 13.5% and 2.2%, respectively. Of the12 mutations detected in 10 patients, silent changes were identified in one nonsmall cell lung cancer, one prostate cancer, and one acute myelog- IntroductionThe CCAAT/enhancer binding protein ␣ (C/EBP␣) belongs to a family of proteins that possess a bipartite DNA-binding domain composed of a positively charged basic (b) region that contacts the DNA and a leucine zipper (ZIP) in the C terminus that mediates dimerization. 1 The less-conserved N terminus contains regulatory and transactivation domains. 2-5 C/EBP␣ is expressed in a number of tissues, most prominently in the highly differentiated cells of the liver, white and brown adipose, lung, and myeloid-lineage cells. [6][7][8][9] It has also been detected in the adrenal gland, skin, pancreas, prostate, differentiated enterocytes in the intestine, and, during follicular development, the ovary. [9][10][11][12] C/EBP␣ is proposed to be a regulator of energy metabolism and transcriptionally activates the promoters of energy-related genes such as GLUT4 and PEPCK in hepatocytes and adipocytes. [13][14][15] In myeloid cells, C/EBP␣ transcriptionally activates the promoters of the myeloid-specific receptors for the growth factors macrophage colony-stimulating factor, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor. [16][17][18] Studies demonstrate that C/EBP␣ is critical for the process of terminal differentiation of adipocytes. C/EBP␣ is upregulated in adipocyte differentiation, and blocking its expression halts differentiation of preadipocytes into adipocytes, while overexpression induces differentiation and inhibits proliferation. [19][20][21][22][23] Also, overexpression of C/EBP␣ induces differentiation of myeloid leukemia cell lines and inhibits the proliferation of a number of cell lines and tumor cells. [24][25][26][27] The inhibition of proliferation is partly due to the ability of C/EBP␣ to activate transcription and induce posttranscriptional stabilization of the cyclin-dependent kinase inhibitor p21 (WAF-1). 28,29 These studies suggest a central role for C/EBP␣ in the regulation of cell proliferation and differentiation.Targeted inactivation of C/EBP␣ in mice demonstrates its importance in the proper development and function of liver, adipose, lung, and hematopoietic tissues. 8,30,31 Within 8 hours after birth, the mice die of impaired glucose metabolism, and adipose metabolism is altered with a failure of adipocytes to accumulate lipids. 30,31 The lung shows hyperproliferati...

C/EBPA gene mutation and C/EBPA promoter hypermethylation in acute myeloid leukemia with normal cytogenetics

“…C/EBPA mutations were first described by Pabst et al in 2001 [9], and have subsequently been observed by many other investigators with the frequency of 5-14% in de novo AML [5][6][7][8][9]. The gene mutation is composed of base pair substitutions, deletions, and insertions and can be largely divided into two common types: First, carboxy-terminal in-frame mutations which disrupt the basic zipper region, thus affecting DNA binding as well as homodimerization and heterodimerization with other C/EBP family members.…”

“…Growing evidence indicates that the key function of C/EBPA gene can be altered by a number of mechanisms, such as gene mutation, transcriptional dysregulation, as well as epigenetic modification in leukemic cells of AML patients, and the functional inactivation of C/EBPA has become a pathophysiological signature of myeloid leukemia. The events leading to the loss of C/EBPA function facilitate leukemogenesis by blocking granulocytic differentiation in hematopoiesis of AML patients [5][6][7][8][9].…”

Characterization of CEBPA Mutations and Polymorphisms and their Prognostic Relevance in De Novo Acute Myeloid Leukemia Patients

“…Genomic DNA was isolated form Bone marrow/peripheral blood samples and four overlapping primer pairs were used to amplify the entire CEBPA coding region giving 306bp, 309bp, 366bp and 266bp for the four fragments respectively (Gombart et al, 2002). PCR-SSCP analysis was performed for mutation detection.…”

C/EBPαp30 plays transcriptional regulatory roles distinct from C/EBPαp42

“…The two C/EBPα isoforms exhibit similar biological functions; for example, both C/EBPαp42 and C/EBPαp30 can transactivate promoters of aP2 and C/EBPα [23]. However, in certain cases C/EBPαp30 acts as a dominant-negative regulator of C/EBPαp42 [26,27].…”