Assessment of Ecotropic Viral Integration Site 2b (Evi2b) Gene in Juvenile Myelomonocytic Leukemia and Neurofibromatosis Type 1 Nf1 Tumors

Abstract

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease that affects the development and growth of various tissues. NF1 is a major risk factor for the development of malignancies, particularly malignant peripheral nerve sheath tumors, optic gliomas, and leukemia. NF1 encodes a neurofibromin. Three genes, EVI2A, EVI2B, and OMGP, are embedded within intron 27b of NF1. However, the function of these genes remains unclear. EVI2A and EVI2B encode for putative transmembrane proteins. Mouse homologs are associated with viral insertions involved in leukemia in mice. Mouse Evi2b has been identified as a direct target gene of C/EBP & alpha;, a transcription factor critical for myeloid differentiation. Also possible is that these genes are related to the leukemia observed in patients with NF1. These genes might act as modifiers of NF1 phenotypic variations. Therefore, we investigated the EVI2B gene in leukemia and NF1 tumors. We analyzed DNA from 10, 20, and 3 patients with NF1, leukemia, and NF1-leukemia, respectively, and six NF1 tumor tissues. DNA sequencing analysis was used to identify the viral integration sequence, and the protein amounts and EVI2B gene expression were analyzed by flow cytometry and quantitative real-time PCR techniques. The EVI2B gene expression was increased in cutaneous neurofibroma compared with the control both at the level of protein and mRNA. However, its expression in plexiform neurofibroma was decreased significantly at protein level and increased at mRNA level compare to control. Moreover, integration of 455 bases near the 3 & PRIME; end of the exon was detected. When this integrated sequence was blasted into the NCBI retroviral genome database, an 87% match with the HIV-1 virus envelope gene was obtained. These preliminary results show that EVI2B might be important in NF1 tumorigenesis and leukemia.